1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Generic ring buffer
4  *
5  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
6  */
7 #include <linux/trace_recursion.h>
8 #include <linux/trace_events.h>
9 #include <linux/ring_buffer.h>
10 #include <linux/trace_clock.h>
11 #include <linux/sched/clock.h>
12 #include <linux/trace_seq.h>
13 #include <linux/spinlock.h>
14 #include <linux/irq_work.h>
15 #include <linux/security.h>
16 #include <linux/uaccess.h>
17 #include <linux/hardirq.h>
18 #include <linux/kthread.h>	/* for self test */
19 #include <linux/module.h>
20 #include <linux/percpu.h>
21 #include <linux/mutex.h>
22 #include <linux/delay.h>
23 #include <linux/slab.h>
24 #include <linux/init.h>
25 #include <linux/hash.h>
26 #include <linux/list.h>
27 #include <linux/cpu.h>
28 #include <linux/oom.h>
29 
30 #include <asm/local.h>
31 
32 /*
33  * The "absolute" timestamp in the buffer is only 59 bits.
34  * If a clock has the 5 MSBs set, it needs to be saved and
35  * reinserted.
36  */
37 #define TS_MSB		(0xf8ULL << 56)
38 #define ABS_TS_MASK	(~TS_MSB)
39 
40 static void update_pages_handler(struct work_struct *work);
41 
42 /*
43  * The ring buffer header is special. We must manually up keep it.
44  */
ring_buffer_print_entry_header(struct trace_seq * s)45 int ring_buffer_print_entry_header(struct trace_seq *s)
46 {
47 	trace_seq_puts(s, "# compressed entry header\n");
48 	trace_seq_puts(s, "\ttype_len    :    5 bits\n");
49 	trace_seq_puts(s, "\ttime_delta  :   27 bits\n");
50 	trace_seq_puts(s, "\tarray       :   32 bits\n");
51 	trace_seq_putc(s, '\n');
52 	trace_seq_printf(s, "\tpadding     : type == %d\n",
53 			 RINGBUF_TYPE_PADDING);
54 	trace_seq_printf(s, "\ttime_extend : type == %d\n",
55 			 RINGBUF_TYPE_TIME_EXTEND);
56 	trace_seq_printf(s, "\ttime_stamp : type == %d\n",
57 			 RINGBUF_TYPE_TIME_STAMP);
58 	trace_seq_printf(s, "\tdata max type_len  == %d\n",
59 			 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
60 
61 	return !trace_seq_has_overflowed(s);
62 }
63 
64 /*
65  * The ring buffer is made up of a list of pages. A separate list of pages is
66  * allocated for each CPU. A writer may only write to a buffer that is
67  * associated with the CPU it is currently executing on.  A reader may read
68  * from any per cpu buffer.
69  *
70  * The reader is special. For each per cpu buffer, the reader has its own
71  * reader page. When a reader has read the entire reader page, this reader
72  * page is swapped with another page in the ring buffer.
73  *
74  * Now, as long as the writer is off the reader page, the reader can do what
75  * ever it wants with that page. The writer will never write to that page
76  * again (as long as it is out of the ring buffer).
77  *
78  * Here's some silly ASCII art.
79  *
80  *   +------+
81  *   |reader|          RING BUFFER
82  *   |page  |
83  *   +------+        +---+   +---+   +---+
84  *                   |   |-->|   |-->|   |
85  *                   +---+   +---+   +---+
86  *                     ^               |
87  *                     |               |
88  *                     +---------------+
89  *
90  *
91  *   +------+
92  *   |reader|          RING BUFFER
93  *   |page  |------------------v
94  *   +------+        +---+   +---+   +---+
95  *                   |   |-->|   |-->|   |
96  *                   +---+   +---+   +---+
97  *                     ^               |
98  *                     |               |
99  *                     +---------------+
100  *
101  *
102  *   +------+
103  *   |reader|          RING BUFFER
104  *   |page  |------------------v
105  *   +------+        +---+   +---+   +---+
106  *      ^            |   |-->|   |-->|   |
107  *      |            +---+   +---+   +---+
108  *      |                              |
109  *      |                              |
110  *      +------------------------------+
111  *
112  *
113  *   +------+
114  *   |buffer|          RING BUFFER
115  *   |page  |------------------v
116  *   +------+        +---+   +---+   +---+
117  *      ^            |   |   |   |-->|   |
118  *      |   New      +---+   +---+   +---+
119  *      |  Reader------^               |
120  *      |   page                       |
121  *      +------------------------------+
122  *
123  *
124  * After we make this swap, the reader can hand this page off to the splice
125  * code and be done with it. It can even allocate a new page if it needs to
126  * and swap that into the ring buffer.
127  *
128  * We will be using cmpxchg soon to make all this lockless.
129  *
130  */
131 
132 /* Used for individual buffers (after the counter) */
133 #define RB_BUFFER_OFF		(1 << 20)
134 
135 #define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
136 
137 #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
138 #define RB_ALIGNMENT		4U
139 #define RB_MAX_SMALL_DATA	(RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
140 #define RB_EVNT_MIN_SIZE	8U	/* two 32bit words */
141 
142 #ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
143 # define RB_FORCE_8BYTE_ALIGNMENT	0
144 # define RB_ARCH_ALIGNMENT		RB_ALIGNMENT
145 #else
146 # define RB_FORCE_8BYTE_ALIGNMENT	1
147 # define RB_ARCH_ALIGNMENT		8U
148 #endif
149 
150 #define RB_ALIGN_DATA		__aligned(RB_ARCH_ALIGNMENT)
151 
152 /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
153 #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
154 
155 enum {
156 	RB_LEN_TIME_EXTEND = 8,
157 	RB_LEN_TIME_STAMP =  8,
158 };
159 
160 #define skip_time_extend(event) \
161 	((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
162 
163 #define extended_time(event) \
164 	(event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
165 
rb_null_event(struct ring_buffer_event * event)166 static inline int rb_null_event(struct ring_buffer_event *event)
167 {
168 	return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
169 }
170 
rb_event_set_padding(struct ring_buffer_event * event)171 static void rb_event_set_padding(struct ring_buffer_event *event)
172 {
173 	/* padding has a NULL time_delta */
174 	event->type_len = RINGBUF_TYPE_PADDING;
175 	event->time_delta = 0;
176 }
177 
178 static unsigned
rb_event_data_length(struct ring_buffer_event * event)179 rb_event_data_length(struct ring_buffer_event *event)
180 {
181 	unsigned length;
182 
183 	if (event->type_len)
184 		length = event->type_len * RB_ALIGNMENT;
185 	else
186 		length = event->array[0];
187 	return length + RB_EVNT_HDR_SIZE;
188 }
189 
190 /*
191  * Return the length of the given event. Will return
192  * the length of the time extend if the event is a
193  * time extend.
194  */
195 static inline unsigned
rb_event_length(struct ring_buffer_event * event)196 rb_event_length(struct ring_buffer_event *event)
197 {
198 	switch (event->type_len) {
199 	case RINGBUF_TYPE_PADDING:
200 		if (rb_null_event(event))
201 			/* undefined */
202 			return -1;
203 		return  event->array[0] + RB_EVNT_HDR_SIZE;
204 
205 	case RINGBUF_TYPE_TIME_EXTEND:
206 		return RB_LEN_TIME_EXTEND;
207 
208 	case RINGBUF_TYPE_TIME_STAMP:
209 		return RB_LEN_TIME_STAMP;
210 
211 	case RINGBUF_TYPE_DATA:
212 		return rb_event_data_length(event);
213 	default:
214 		WARN_ON_ONCE(1);
215 	}
216 	/* not hit */
217 	return 0;
218 }
219 
220 /*
221  * Return total length of time extend and data,
222  *   or just the event length for all other events.
223  */
224 static inline unsigned
rb_event_ts_length(struct ring_buffer_event * event)225 rb_event_ts_length(struct ring_buffer_event *event)
226 {
227 	unsigned len = 0;
228 
229 	if (extended_time(event)) {
230 		/* time extends include the data event after it */
231 		len = RB_LEN_TIME_EXTEND;
232 		event = skip_time_extend(event);
233 	}
234 	return len + rb_event_length(event);
235 }
236 
237 /**
238  * ring_buffer_event_length - return the length of the event
239  * @event: the event to get the length of
240  *
241  * Returns the size of the data load of a data event.
242  * If the event is something other than a data event, it
243  * returns the size of the event itself. With the exception
244  * of a TIME EXTEND, where it still returns the size of the
245  * data load of the data event after it.
246  */
ring_buffer_event_length(struct ring_buffer_event * event)247 unsigned ring_buffer_event_length(struct ring_buffer_event *event)
248 {
249 	unsigned length;
250 
251 	if (extended_time(event))
252 		event = skip_time_extend(event);
253 
254 	length = rb_event_length(event);
255 	if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
256 		return length;
257 	length -= RB_EVNT_HDR_SIZE;
258 	if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
259                 length -= sizeof(event->array[0]);
260 	return length;
261 }
262 EXPORT_SYMBOL_GPL(ring_buffer_event_length);
263 
264 /* inline for ring buffer fast paths */
265 static __always_inline void *
rb_event_data(struct ring_buffer_event * event)266 rb_event_data(struct ring_buffer_event *event)
267 {
268 	if (extended_time(event))
269 		event = skip_time_extend(event);
270 	WARN_ON_ONCE(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
271 	/* If length is in len field, then array[0] has the data */
272 	if (event->type_len)
273 		return (void *)&event->array[0];
274 	/* Otherwise length is in array[0] and array[1] has the data */
275 	return (void *)&event->array[1];
276 }
277 
278 /**
279  * ring_buffer_event_data - return the data of the event
280  * @event: the event to get the data from
281  */
ring_buffer_event_data(struct ring_buffer_event * event)282 void *ring_buffer_event_data(struct ring_buffer_event *event)
283 {
284 	return rb_event_data(event);
285 }
286 EXPORT_SYMBOL_GPL(ring_buffer_event_data);
287 
288 #define for_each_buffer_cpu(buffer, cpu)		\
289 	for_each_cpu(cpu, buffer->cpumask)
290 
291 #define for_each_online_buffer_cpu(buffer, cpu)		\
292 	for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
293 
294 #define TS_SHIFT	27
295 #define TS_MASK		((1ULL << TS_SHIFT) - 1)
296 #define TS_DELTA_TEST	(~TS_MASK)
297 
rb_event_time_stamp(struct ring_buffer_event * event)298 static u64 rb_event_time_stamp(struct ring_buffer_event *event)
299 {
300 	u64 ts;
301 
302 	ts = event->array[0];
303 	ts <<= TS_SHIFT;
304 	ts += event->time_delta;
305 
306 	return ts;
307 }
308 
309 /* Flag when events were overwritten */
310 #define RB_MISSED_EVENTS	(1 << 31)
311 /* Missed count stored at end */
312 #define RB_MISSED_STORED	(1 << 30)
313 
314 struct buffer_data_page {
315 	u64		 time_stamp;	/* page time stamp */
316 	local_t		 commit;	/* write committed index */
317 	unsigned char	 data[] RB_ALIGN_DATA;	/* data of buffer page */
318 };
319 
320 /*
321  * Note, the buffer_page list must be first. The buffer pages
322  * are allocated in cache lines, which means that each buffer
323  * page will be at the beginning of a cache line, and thus
324  * the least significant bits will be zero. We use this to
325  * add flags in the list struct pointers, to make the ring buffer
326  * lockless.
327  */
328 struct buffer_page {
329 	struct list_head list;		/* list of buffer pages */
330 	local_t		 write;		/* index for next write */
331 	unsigned	 read;		/* index for next read */
332 	local_t		 entries;	/* entries on this page */
333 	unsigned long	 real_end;	/* real end of data */
334 	struct buffer_data_page *page;	/* Actual data page */
335 };
336 
337 /*
338  * The buffer page counters, write and entries, must be reset
339  * atomically when crossing page boundaries. To synchronize this
340  * update, two counters are inserted into the number. One is
341  * the actual counter for the write position or count on the page.
342  *
343  * The other is a counter of updaters. Before an update happens
344  * the update partition of the counter is incremented. This will
345  * allow the updater to update the counter atomically.
346  *
347  * The counter is 20 bits, and the state data is 12.
348  */
349 #define RB_WRITE_MASK		0xfffff
350 #define RB_WRITE_INTCNT		(1 << 20)
351 
rb_init_page(struct buffer_data_page * bpage)352 static void rb_init_page(struct buffer_data_page *bpage)
353 {
354 	local_set(&bpage->commit, 0);
355 }
356 
357 /*
358  * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
359  * this issue out.
360  */
free_buffer_page(struct buffer_page * bpage)361 static void free_buffer_page(struct buffer_page *bpage)
362 {
363 	free_page((unsigned long)bpage->page);
364 	kfree(bpage);
365 }
366 
367 /*
368  * We need to fit the time_stamp delta into 27 bits.
369  */
test_time_stamp(u64 delta)370 static inline int test_time_stamp(u64 delta)
371 {
372 	if (delta & TS_DELTA_TEST)
373 		return 1;
374 	return 0;
375 }
376 
377 #define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
378 
379 /* Max payload is BUF_PAGE_SIZE - header (8bytes) */
380 #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
381 
ring_buffer_print_page_header(struct trace_seq * s)382 int ring_buffer_print_page_header(struct trace_seq *s)
383 {
384 	struct buffer_data_page field;
385 
386 	trace_seq_printf(s, "\tfield: u64 timestamp;\t"
387 			 "offset:0;\tsize:%u;\tsigned:%u;\n",
388 			 (unsigned int)sizeof(field.time_stamp),
389 			 (unsigned int)is_signed_type(u64));
390 
391 	trace_seq_printf(s, "\tfield: local_t commit;\t"
392 			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
393 			 (unsigned int)offsetof(typeof(field), commit),
394 			 (unsigned int)sizeof(field.commit),
395 			 (unsigned int)is_signed_type(long));
396 
397 	trace_seq_printf(s, "\tfield: int overwrite;\t"
398 			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
399 			 (unsigned int)offsetof(typeof(field), commit),
400 			 1,
401 			 (unsigned int)is_signed_type(long));
402 
403 	trace_seq_printf(s, "\tfield: char data;\t"
404 			 "offset:%u;\tsize:%u;\tsigned:%u;\n",
405 			 (unsigned int)offsetof(typeof(field), data),
406 			 (unsigned int)BUF_PAGE_SIZE,
407 			 (unsigned int)is_signed_type(char));
408 
409 	return !trace_seq_has_overflowed(s);
410 }
411 
412 struct rb_irq_work {
413 	struct irq_work			work;
414 	wait_queue_head_t		waiters;
415 	wait_queue_head_t		full_waiters;
416 	long				wait_index;
417 	bool				waiters_pending;
418 	bool				full_waiters_pending;
419 	bool				wakeup_full;
420 };
421 
422 /*
423  * Structure to hold event state and handle nested events.
424  */
425 struct rb_event_info {
426 	u64			ts;
427 	u64			delta;
428 	u64			before;
429 	u64			after;
430 	unsigned long		length;
431 	struct buffer_page	*tail_page;
432 	int			add_timestamp;
433 };
434 
435 /*
436  * Used for the add_timestamp
437  *  NONE
438  *  EXTEND - wants a time extend
439  *  ABSOLUTE - the buffer requests all events to have absolute time stamps
440  *  FORCE - force a full time stamp.
441  */
442 enum {
443 	RB_ADD_STAMP_NONE		= 0,
444 	RB_ADD_STAMP_EXTEND		= BIT(1),
445 	RB_ADD_STAMP_ABSOLUTE		= BIT(2),
446 	RB_ADD_STAMP_FORCE		= BIT(3)
447 };
448 /*
449  * Used for which event context the event is in.
450  *  TRANSITION = 0
451  *  NMI     = 1
452  *  IRQ     = 2
453  *  SOFTIRQ = 3
454  *  NORMAL  = 4
455  *
456  * See trace_recursive_lock() comment below for more details.
457  */
458 enum {
459 	RB_CTX_TRANSITION,
460 	RB_CTX_NMI,
461 	RB_CTX_IRQ,
462 	RB_CTX_SOFTIRQ,
463 	RB_CTX_NORMAL,
464 	RB_CTX_MAX
465 };
466 
467 #if BITS_PER_LONG == 32
468 #define RB_TIME_32
469 #endif
470 
471 /* To test on 64 bit machines */
472 //#define RB_TIME_32
473 
474 #ifdef RB_TIME_32
475 
476 struct rb_time_struct {
477 	local_t		cnt;
478 	local_t		top;
479 	local_t		bottom;
480 	local_t		msb;
481 };
482 #else
483 #include <asm/local64.h>
484 struct rb_time_struct {
485 	local64_t	time;
486 };
487 #endif
488 typedef struct rb_time_struct rb_time_t;
489 
490 #define MAX_NEST	5
491 
492 /*
493  * head_page == tail_page && head == tail then buffer is empty.
494  */
495 struct ring_buffer_per_cpu {
496 	int				cpu;
497 	atomic_t			record_disabled;
498 	atomic_t			resize_disabled;
499 	struct trace_buffer	*buffer;
500 	raw_spinlock_t			reader_lock;	/* serialize readers */
501 	arch_spinlock_t			lock;
502 	struct lock_class_key		lock_key;
503 	struct buffer_data_page		*free_page;
504 	unsigned long			nr_pages;
505 	unsigned int			current_context;
506 	struct list_head		*pages;
507 	struct buffer_page		*head_page;	/* read from head */
508 	struct buffer_page		*tail_page;	/* write to tail */
509 	struct buffer_page		*commit_page;	/* committed pages */
510 	struct buffer_page		*reader_page;
511 	unsigned long			lost_events;
512 	unsigned long			last_overrun;
513 	unsigned long			nest;
514 	local_t				entries_bytes;
515 	local_t				entries;
516 	local_t				overrun;
517 	local_t				commit_overrun;
518 	local_t				dropped_events;
519 	local_t				committing;
520 	local_t				commits;
521 	local_t				pages_touched;
522 	local_t				pages_lost;
523 	local_t				pages_read;
524 	long				last_pages_touch;
525 	size_t				shortest_full;
526 	unsigned long			read;
527 	unsigned long			read_bytes;
528 	rb_time_t			write_stamp;
529 	rb_time_t			before_stamp;
530 	u64				event_stamp[MAX_NEST];
531 	u64				read_stamp;
532 	/* ring buffer pages to update, > 0 to add, < 0 to remove */
533 	long				nr_pages_to_update;
534 	struct list_head		new_pages; /* new pages to add */
535 	struct work_struct		update_pages_work;
536 	struct completion		update_done;
537 
538 	struct rb_irq_work		irq_work;
539 };
540 
541 struct trace_buffer {
542 	unsigned			flags;
543 	int				cpus;
544 	atomic_t			record_disabled;
545 	cpumask_var_t			cpumask;
546 
547 	struct lock_class_key		*reader_lock_key;
548 
549 	struct mutex			mutex;
550 
551 	struct ring_buffer_per_cpu	**buffers;
552 
553 	struct hlist_node		node;
554 	u64				(*clock)(void);
555 
556 	struct rb_irq_work		irq_work;
557 	bool				time_stamp_abs;
558 };
559 
560 struct ring_buffer_iter {
561 	struct ring_buffer_per_cpu	*cpu_buffer;
562 	unsigned long			head;
563 	unsigned long			next_event;
564 	struct buffer_page		*head_page;
565 	struct buffer_page		*cache_reader_page;
566 	unsigned long			cache_read;
567 	u64				read_stamp;
568 	u64				page_stamp;
569 	struct ring_buffer_event	*event;
570 	int				missed_events;
571 };
572 
573 #ifdef RB_TIME_32
574 
575 /*
576  * On 32 bit machines, local64_t is very expensive. As the ring
577  * buffer doesn't need all the features of a true 64 bit atomic,
578  * on 32 bit, it uses these functions (64 still uses local64_t).
579  *
580  * For the ring buffer, 64 bit required operations for the time is
581  * the following:
582  *
583  *  - Reads may fail if it interrupted a modification of the time stamp.
584  *      It will succeed if it did not interrupt another write even if
585  *      the read itself is interrupted by a write.
586  *      It returns whether it was successful or not.
587  *
588  *  - Writes always succeed and will overwrite other writes and writes
589  *      that were done by events interrupting the current write.
590  *
591  *  - A write followed by a read of the same time stamp will always succeed,
592  *      but may not contain the same value.
593  *
594  *  - A cmpxchg will fail if it interrupted another write or cmpxchg.
595  *      Other than that, it acts like a normal cmpxchg.
596  *
597  * The 60 bit time stamp is broken up by 30 bits in a top and bottom half
598  *  (bottom being the least significant 30 bits of the 60 bit time stamp).
599  *
600  * The two most significant bits of each half holds a 2 bit counter (0-3).
601  * Each update will increment this counter by one.
602  * When reading the top and bottom, if the two counter bits match then the
603  *  top and bottom together make a valid 60 bit number.
604  */
605 #define RB_TIME_SHIFT	30
606 #define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
607 #define RB_TIME_MSB_SHIFT	 60
608 
rb_time_cnt(unsigned long val)609 static inline int rb_time_cnt(unsigned long val)
610 {
611 	return (val >> RB_TIME_SHIFT) & 3;
612 }
613 
rb_time_val(unsigned long top,unsigned long bottom)614 static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
615 {
616 	u64 val;
617 
618 	val = top & RB_TIME_VAL_MASK;
619 	val <<= RB_TIME_SHIFT;
620 	val |= bottom & RB_TIME_VAL_MASK;
621 
622 	return val;
623 }
624 
__rb_time_read(rb_time_t * t,u64 * ret,unsigned long * cnt)625 static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
626 {
627 	unsigned long top, bottom, msb;
628 	unsigned long c;
629 
630 	/*
631 	 * If the read is interrupted by a write, then the cnt will
632 	 * be different. Loop until both top and bottom have been read
633 	 * without interruption.
634 	 */
635 	do {
636 		c = local_read(&t->cnt);
637 		top = local_read(&t->top);
638 		bottom = local_read(&t->bottom);
639 		msb = local_read(&t->msb);
640 	} while (c != local_read(&t->cnt));
641 
642 	*cnt = rb_time_cnt(top);
643 
644 	/* If top and bottom counts don't match, this interrupted a write */
645 	if (*cnt != rb_time_cnt(bottom))
646 		return false;
647 
648 	/* The shift to msb will lose its cnt bits */
649 	*ret = rb_time_val(top, bottom) | ((u64)msb << RB_TIME_MSB_SHIFT);
650 	return true;
651 }
652 
rb_time_read(rb_time_t * t,u64 * ret)653 static bool rb_time_read(rb_time_t *t, u64 *ret)
654 {
655 	unsigned long cnt;
656 
657 	return __rb_time_read(t, ret, &cnt);
658 }
659 
rb_time_val_cnt(unsigned long val,unsigned long cnt)660 static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
661 {
662 	return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
663 }
664 
rb_time_split(u64 val,unsigned long * top,unsigned long * bottom,unsigned long * msb)665 static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom,
666 				 unsigned long *msb)
667 {
668 	*top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
669 	*bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
670 	*msb = (unsigned long)(val >> RB_TIME_MSB_SHIFT);
671 }
672 
rb_time_val_set(local_t * t,unsigned long val,unsigned long cnt)673 static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
674 {
675 	val = rb_time_val_cnt(val, cnt);
676 	local_set(t, val);
677 }
678 
rb_time_set(rb_time_t * t,u64 val)679 static void rb_time_set(rb_time_t *t, u64 val)
680 {
681 	unsigned long cnt, top, bottom, msb;
682 
683 	rb_time_split(val, &top, &bottom, &msb);
684 
685 	/* Writes always succeed with a valid number even if it gets interrupted. */
686 	do {
687 		cnt = local_inc_return(&t->cnt);
688 		rb_time_val_set(&t->top, top, cnt);
689 		rb_time_val_set(&t->bottom, bottom, cnt);
690 		rb_time_val_set(&t->msb, val >> RB_TIME_MSB_SHIFT, cnt);
691 	} while (cnt != local_read(&t->cnt));
692 }
693 
694 static inline bool
rb_time_read_cmpxchg(local_t * l,unsigned long expect,unsigned long set)695 rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
696 {
697 	unsigned long ret;
698 
699 	ret = local_cmpxchg(l, expect, set);
700 	return ret == expect;
701 }
702 
rb_time_cmpxchg(rb_time_t * t,u64 expect,u64 set)703 static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
704 {
705 	unsigned long cnt, top, bottom, msb;
706 	unsigned long cnt2, top2, bottom2, msb2;
707 	u64 val;
708 
709 	/* The cmpxchg always fails if it interrupted an update */
710 	 if (!__rb_time_read(t, &val, &cnt2))
711 		 return false;
712 
713 	 if (val != expect)
714 		 return false;
715 
716 	 cnt = local_read(&t->cnt);
717 	 if ((cnt & 3) != cnt2)
718 		 return false;
719 
720 	 cnt2 = cnt + 1;
721 
722 	 rb_time_split(val, &top, &bottom, &msb);
723 	 top = rb_time_val_cnt(top, cnt);
724 	 bottom = rb_time_val_cnt(bottom, cnt);
725 
726 	 rb_time_split(set, &top2, &bottom2, &msb2);
727 	 top2 = rb_time_val_cnt(top2, cnt2);
728 	 bottom2 = rb_time_val_cnt(bottom2, cnt2);
729 
730 	if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2))
731 		return false;
732 	if (!rb_time_read_cmpxchg(&t->msb, msb, msb2))
733 		return false;
734 	if (!rb_time_read_cmpxchg(&t->top, top, top2))
735 		return false;
736 	if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2))
737 		return false;
738 	return true;
739 }
740 
741 #else /* 64 bits */
742 
743 /* local64_t always succeeds */
744 
rb_time_read(rb_time_t * t,u64 * ret)745 static inline bool rb_time_read(rb_time_t *t, u64 *ret)
746 {
747 	*ret = local64_read(&t->time);
748 	return true;
749 }
rb_time_set(rb_time_t * t,u64 val)750 static void rb_time_set(rb_time_t *t, u64 val)
751 {
752 	local64_set(&t->time, val);
753 }
754 
rb_time_cmpxchg(rb_time_t * t,u64 expect,u64 set)755 static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
756 {
757 	u64 val;
758 	val = local64_cmpxchg(&t->time, expect, set);
759 	return val == expect;
760 }
761 #endif
762 
763 /*
764  * Enable this to make sure that the event passed to
765  * ring_buffer_event_time_stamp() is not committed and also
766  * is on the buffer that it passed in.
767  */
768 //#define RB_VERIFY_EVENT
769 #ifdef RB_VERIFY_EVENT
770 static struct list_head *rb_list_head(struct list_head *list);
verify_event(struct ring_buffer_per_cpu * cpu_buffer,void * event)771 static void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
772 			 void *event)
773 {
774 	struct buffer_page *page = cpu_buffer->commit_page;
775 	struct buffer_page *tail_page = READ_ONCE(cpu_buffer->tail_page);
776 	struct list_head *next;
777 	long commit, write;
778 	unsigned long addr = (unsigned long)event;
779 	bool done = false;
780 	int stop = 0;
781 
782 	/* Make sure the event exists and is not committed yet */
783 	do {
784 		if (page == tail_page || WARN_ON_ONCE(stop++ > 100))
785 			done = true;
786 		commit = local_read(&page->page->commit);
787 		write = local_read(&page->write);
788 		if (addr >= (unsigned long)&page->page->data[commit] &&
789 		    addr < (unsigned long)&page->page->data[write])
790 			return;
791 
792 		next = rb_list_head(page->list.next);
793 		page = list_entry(next, struct buffer_page, list);
794 	} while (!done);
795 	WARN_ON_ONCE(1);
796 }
797 #else
verify_event(struct ring_buffer_per_cpu * cpu_buffer,void * event)798 static inline void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
799 			 void *event)
800 {
801 }
802 #endif
803 
804 /*
805  * The absolute time stamp drops the 5 MSBs and some clocks may
806  * require them. The rb_fix_abs_ts() will take a previous full
807  * time stamp, and add the 5 MSB of that time stamp on to the
808  * saved absolute time stamp. Then they are compared in case of
809  * the unlikely event that the latest time stamp incremented
810  * the 5 MSB.
811  */
rb_fix_abs_ts(u64 abs,u64 save_ts)812 static inline u64 rb_fix_abs_ts(u64 abs, u64 save_ts)
813 {
814 	if (save_ts & TS_MSB) {
815 		abs |= save_ts & TS_MSB;
816 		/* Check for overflow */
817 		if (unlikely(abs < save_ts))
818 			abs += 1ULL << 59;
819 	}
820 	return abs;
821 }
822 
823 static inline u64 rb_time_stamp(struct trace_buffer *buffer);
824 
825 /**
826  * ring_buffer_event_time_stamp - return the event's current time stamp
827  * @buffer: The buffer that the event is on
828  * @event: the event to get the time stamp of
829  *
830  * Note, this must be called after @event is reserved, and before it is
831  * committed to the ring buffer. And must be called from the same
832  * context where the event was reserved (normal, softirq, irq, etc).
833  *
834  * Returns the time stamp associated with the current event.
835  * If the event has an extended time stamp, then that is used as
836  * the time stamp to return.
837  * In the highly unlikely case that the event was nested more than
838  * the max nesting, then the write_stamp of the buffer is returned,
839  * otherwise  current time is returned, but that really neither of
840  * the last two cases should ever happen.
841  */
ring_buffer_event_time_stamp(struct trace_buffer * buffer,struct ring_buffer_event * event)842 u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
843 				 struct ring_buffer_event *event)
844 {
845 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[smp_processor_id()];
846 	unsigned int nest;
847 	u64 ts;
848 
849 	/* If the event includes an absolute time, then just use that */
850 	if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
851 		ts = rb_event_time_stamp(event);
852 		return rb_fix_abs_ts(ts, cpu_buffer->tail_page->page->time_stamp);
853 	}
854 
855 	nest = local_read(&cpu_buffer->committing);
856 	verify_event(cpu_buffer, event);
857 	if (WARN_ON_ONCE(!nest))
858 		goto fail;
859 
860 	/* Read the current saved nesting level time stamp */
861 	if (likely(--nest < MAX_NEST))
862 		return cpu_buffer->event_stamp[nest];
863 
864 	/* Shouldn't happen, warn if it does */
865 	WARN_ONCE(1, "nest (%d) greater than max", nest);
866 
867  fail:
868 	/* Can only fail on 32 bit */
869 	if (!rb_time_read(&cpu_buffer->write_stamp, &ts))
870 		/* Screw it, just read the current time */
871 		ts = rb_time_stamp(cpu_buffer->buffer);
872 
873 	return ts;
874 }
875 
876 /**
877  * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
878  * @buffer: The ring_buffer to get the number of pages from
879  * @cpu: The cpu of the ring_buffer to get the number of pages from
880  *
881  * Returns the number of pages used by a per_cpu buffer of the ring buffer.
882  */
ring_buffer_nr_pages(struct trace_buffer * buffer,int cpu)883 size_t ring_buffer_nr_pages(struct trace_buffer *buffer, int cpu)
884 {
885 	return buffer->buffers[cpu]->nr_pages;
886 }
887 
888 /**
889  * ring_buffer_nr_dirty_pages - get the number of used pages in the ring buffer
890  * @buffer: The ring_buffer to get the number of pages from
891  * @cpu: The cpu of the ring_buffer to get the number of pages from
892  *
893  * Returns the number of pages that have content in the ring buffer.
894  */
ring_buffer_nr_dirty_pages(struct trace_buffer * buffer,int cpu)895 size_t ring_buffer_nr_dirty_pages(struct trace_buffer *buffer, int cpu)
896 {
897 	size_t read;
898 	size_t lost;
899 	size_t cnt;
900 
901 	read = local_read(&buffer->buffers[cpu]->pages_read);
902 	lost = local_read(&buffer->buffers[cpu]->pages_lost);
903 	cnt = local_read(&buffer->buffers[cpu]->pages_touched);
904 
905 	if (WARN_ON_ONCE(cnt < lost))
906 		return 0;
907 
908 	cnt -= lost;
909 
910 	/* The reader can read an empty page, but not more than that */
911 	if (cnt < read) {
912 		WARN_ON_ONCE(read > cnt + 1);
913 		return 0;
914 	}
915 
916 	return cnt - read;
917 }
918 
full_hit(struct trace_buffer * buffer,int cpu,int full)919 static __always_inline bool full_hit(struct trace_buffer *buffer, int cpu, int full)
920 {
921 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
922 	size_t nr_pages;
923 	size_t dirty;
924 
925 	nr_pages = cpu_buffer->nr_pages;
926 	if (!nr_pages || !full)
927 		return true;
928 
929 	dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
930 
931 	return (dirty * 100) > (full * nr_pages);
932 }
933 
934 /*
935  * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
936  *
937  * Schedules a delayed work to wake up any task that is blocked on the
938  * ring buffer waiters queue.
939  */
rb_wake_up_waiters(struct irq_work * work)940 static void rb_wake_up_waiters(struct irq_work *work)
941 {
942 	struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
943 
944 	wake_up_all(&rbwork->waiters);
945 	if (rbwork->full_waiters_pending || rbwork->wakeup_full) {
946 		rbwork->wakeup_full = false;
947 		rbwork->full_waiters_pending = false;
948 		wake_up_all(&rbwork->full_waiters);
949 	}
950 }
951 
952 /**
953  * ring_buffer_wake_waiters - wake up any waiters on this ring buffer
954  * @buffer: The ring buffer to wake waiters on
955  *
956  * In the case of a file that represents a ring buffer is closing,
957  * it is prudent to wake up any waiters that are on this.
958  */
ring_buffer_wake_waiters(struct trace_buffer * buffer,int cpu)959 void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu)
960 {
961 	struct ring_buffer_per_cpu *cpu_buffer;
962 	struct rb_irq_work *rbwork;
963 
964 	if (!buffer)
965 		return;
966 
967 	if (cpu == RING_BUFFER_ALL_CPUS) {
968 
969 		/* Wake up individual ones too. One level recursion */
970 		for_each_buffer_cpu(buffer, cpu)
971 			ring_buffer_wake_waiters(buffer, cpu);
972 
973 		rbwork = &buffer->irq_work;
974 	} else {
975 		if (WARN_ON_ONCE(!buffer->buffers))
976 			return;
977 		if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
978 			return;
979 
980 		cpu_buffer = buffer->buffers[cpu];
981 		/* The CPU buffer may not have been initialized yet */
982 		if (!cpu_buffer)
983 			return;
984 		rbwork = &cpu_buffer->irq_work;
985 	}
986 
987 	rbwork->wait_index++;
988 	/* make sure the waiters see the new index */
989 	smp_wmb();
990 
991 	rb_wake_up_waiters(&rbwork->work);
992 }
993 
994 /**
995  * ring_buffer_wait - wait for input to the ring buffer
996  * @buffer: buffer to wait on
997  * @cpu: the cpu buffer to wait on
998  * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
999  *
1000  * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
1001  * as data is added to any of the @buffer's cpu buffers. Otherwise
1002  * it will wait for data to be added to a specific cpu buffer.
1003  */
ring_buffer_wait(struct trace_buffer * buffer,int cpu,int full)1004 int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
1005 {
1006 	struct ring_buffer_per_cpu *cpu_buffer;
1007 	DEFINE_WAIT(wait);
1008 	struct rb_irq_work *work;
1009 	long wait_index;
1010 	int ret = 0;
1011 
1012 	/*
1013 	 * Depending on what the caller is waiting for, either any
1014 	 * data in any cpu buffer, or a specific buffer, put the
1015 	 * caller on the appropriate wait queue.
1016 	 */
1017 	if (cpu == RING_BUFFER_ALL_CPUS) {
1018 		work = &buffer->irq_work;
1019 		/* Full only makes sense on per cpu reads */
1020 		full = 0;
1021 	} else {
1022 		if (!cpumask_test_cpu(cpu, buffer->cpumask))
1023 			return -ENODEV;
1024 		cpu_buffer = buffer->buffers[cpu];
1025 		work = &cpu_buffer->irq_work;
1026 	}
1027 
1028 	wait_index = READ_ONCE(work->wait_index);
1029 
1030 	while (true) {
1031 		if (full)
1032 			prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
1033 		else
1034 			prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
1035 
1036 		/*
1037 		 * The events can happen in critical sections where
1038 		 * checking a work queue can cause deadlocks.
1039 		 * After adding a task to the queue, this flag is set
1040 		 * only to notify events to try to wake up the queue
1041 		 * using irq_work.
1042 		 *
1043 		 * We don't clear it even if the buffer is no longer
1044 		 * empty. The flag only causes the next event to run
1045 		 * irq_work to do the work queue wake up. The worse
1046 		 * that can happen if we race with !trace_empty() is that
1047 		 * an event will cause an irq_work to try to wake up
1048 		 * an empty queue.
1049 		 *
1050 		 * There's no reason to protect this flag either, as
1051 		 * the work queue and irq_work logic will do the necessary
1052 		 * synchronization for the wake ups. The only thing
1053 		 * that is necessary is that the wake up happens after
1054 		 * a task has been queued. It's OK for spurious wake ups.
1055 		 */
1056 		if (full)
1057 			work->full_waiters_pending = true;
1058 		else
1059 			work->waiters_pending = true;
1060 
1061 		if (signal_pending(current)) {
1062 			ret = -EINTR;
1063 			break;
1064 		}
1065 
1066 		if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
1067 			break;
1068 
1069 		if (cpu != RING_BUFFER_ALL_CPUS &&
1070 		    !ring_buffer_empty_cpu(buffer, cpu)) {
1071 			unsigned long flags;
1072 			bool pagebusy;
1073 			bool done;
1074 
1075 			if (!full)
1076 				break;
1077 
1078 			raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
1079 			pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
1080 			done = !pagebusy && full_hit(buffer, cpu, full);
1081 
1082 			if (!cpu_buffer->shortest_full ||
1083 			    cpu_buffer->shortest_full > full)
1084 				cpu_buffer->shortest_full = full;
1085 			raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
1086 			if (done)
1087 				break;
1088 		}
1089 
1090 		schedule();
1091 
1092 		/* Make sure to see the new wait index */
1093 		smp_rmb();
1094 		if (wait_index != work->wait_index)
1095 			break;
1096 	}
1097 
1098 	if (full)
1099 		finish_wait(&work->full_waiters, &wait);
1100 	else
1101 		finish_wait(&work->waiters, &wait);
1102 
1103 	return ret;
1104 }
1105 
1106 /**
1107  * ring_buffer_poll_wait - poll on buffer input
1108  * @buffer: buffer to wait on
1109  * @cpu: the cpu buffer to wait on
1110  * @filp: the file descriptor
1111  * @poll_table: The poll descriptor
1112  * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
1113  *
1114  * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
1115  * as data is added to any of the @buffer's cpu buffers. Otherwise
1116  * it will wait for data to be added to a specific cpu buffer.
1117  *
1118  * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
1119  * zero otherwise.
1120  */
ring_buffer_poll_wait(struct trace_buffer * buffer,int cpu,struct file * filp,poll_table * poll_table,int full)1121 __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
1122 			  struct file *filp, poll_table *poll_table, int full)
1123 {
1124 	struct ring_buffer_per_cpu *cpu_buffer;
1125 	struct rb_irq_work *work;
1126 
1127 	if (cpu == RING_BUFFER_ALL_CPUS) {
1128 		work = &buffer->irq_work;
1129 		full = 0;
1130 	} else {
1131 		if (!cpumask_test_cpu(cpu, buffer->cpumask))
1132 			return -EINVAL;
1133 
1134 		cpu_buffer = buffer->buffers[cpu];
1135 		work = &cpu_buffer->irq_work;
1136 	}
1137 
1138 	if (full) {
1139 		poll_wait(filp, &work->full_waiters, poll_table);
1140 		work->full_waiters_pending = true;
1141 	} else {
1142 		poll_wait(filp, &work->waiters, poll_table);
1143 		work->waiters_pending = true;
1144 	}
1145 
1146 	/*
1147 	 * There's a tight race between setting the waiters_pending and
1148 	 * checking if the ring buffer is empty.  Once the waiters_pending bit
1149 	 * is set, the next event will wake the task up, but we can get stuck
1150 	 * if there's only a single event in.
1151 	 *
1152 	 * FIXME: Ideally, we need a memory barrier on the writer side as well,
1153 	 * but adding a memory barrier to all events will cause too much of a
1154 	 * performance hit in the fast path.  We only need a memory barrier when
1155 	 * the buffer goes from empty to having content.  But as this race is
1156 	 * extremely small, and it's not a problem if another event comes in, we
1157 	 * will fix it later.
1158 	 */
1159 	smp_mb();
1160 
1161 	if (full)
1162 		return full_hit(buffer, cpu, full) ? EPOLLIN | EPOLLRDNORM : 0;
1163 
1164 	if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
1165 	    (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
1166 		return EPOLLIN | EPOLLRDNORM;
1167 	return 0;
1168 }
1169 
1170 /* buffer may be either ring_buffer or ring_buffer_per_cpu */
1171 #define RB_WARN_ON(b, cond)						\
1172 	({								\
1173 		int _____ret = unlikely(cond);				\
1174 		if (_____ret) {						\
1175 			if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
1176 				struct ring_buffer_per_cpu *__b =	\
1177 					(void *)b;			\
1178 				atomic_inc(&__b->buffer->record_disabled); \
1179 			} else						\
1180 				atomic_inc(&b->record_disabled);	\
1181 			WARN_ON(1);					\
1182 		}							\
1183 		_____ret;						\
1184 	})
1185 
1186 /* Up this if you want to test the TIME_EXTENTS and normalization */
1187 #define DEBUG_SHIFT 0
1188 
rb_time_stamp(struct trace_buffer * buffer)1189 static inline u64 rb_time_stamp(struct trace_buffer *buffer)
1190 {
1191 	u64 ts;
1192 
1193 	/* Skip retpolines :-( */
1194 	if (IS_ENABLED(CONFIG_RETPOLINE) && likely(buffer->clock == trace_clock_local))
1195 		ts = trace_clock_local();
1196 	else
1197 		ts = buffer->clock();
1198 
1199 	/* shift to debug/test normalization and TIME_EXTENTS */
1200 	return ts << DEBUG_SHIFT;
1201 }
1202 
ring_buffer_time_stamp(struct trace_buffer * buffer)1203 u64 ring_buffer_time_stamp(struct trace_buffer *buffer)
1204 {
1205 	u64 time;
1206 
1207 	preempt_disable_notrace();
1208 	time = rb_time_stamp(buffer);
1209 	preempt_enable_notrace();
1210 
1211 	return time;
1212 }
1213 EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
1214 
ring_buffer_normalize_time_stamp(struct trace_buffer * buffer,int cpu,u64 * ts)1215 void ring_buffer_normalize_time_stamp(struct trace_buffer *buffer,
1216 				      int cpu, u64 *ts)
1217 {
1218 	/* Just stupid testing the normalize function and deltas */
1219 	*ts >>= DEBUG_SHIFT;
1220 }
1221 EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
1222 
1223 /*
1224  * Making the ring buffer lockless makes things tricky.
1225  * Although writes only happen on the CPU that they are on,
1226  * and they only need to worry about interrupts. Reads can
1227  * happen on any CPU.
1228  *
1229  * The reader page is always off the ring buffer, but when the
1230  * reader finishes with a page, it needs to swap its page with
1231  * a new one from the buffer. The reader needs to take from
1232  * the head (writes go to the tail). But if a writer is in overwrite
1233  * mode and wraps, it must push the head page forward.
1234  *
1235  * Here lies the problem.
1236  *
1237  * The reader must be careful to replace only the head page, and
1238  * not another one. As described at the top of the file in the
1239  * ASCII art, the reader sets its old page to point to the next
1240  * page after head. It then sets the page after head to point to
1241  * the old reader page. But if the writer moves the head page
1242  * during this operation, the reader could end up with the tail.
1243  *
1244  * We use cmpxchg to help prevent this race. We also do something
1245  * special with the page before head. We set the LSB to 1.
1246  *
1247  * When the writer must push the page forward, it will clear the
1248  * bit that points to the head page, move the head, and then set
1249  * the bit that points to the new head page.
1250  *
1251  * We also don't want an interrupt coming in and moving the head
1252  * page on another writer. Thus we use the second LSB to catch
1253  * that too. Thus:
1254  *
1255  * head->list->prev->next        bit 1          bit 0
1256  *                              -------        -------
1257  * Normal page                     0              0
1258  * Points to head page             0              1
1259  * New head page                   1              0
1260  *
1261  * Note we can not trust the prev pointer of the head page, because:
1262  *
1263  * +----+       +-----+        +-----+
1264  * |    |------>|  T  |---X--->|  N  |
1265  * |    |<------|     |        |     |
1266  * +----+       +-----+        +-----+
1267  *   ^                           ^ |
1268  *   |          +-----+          | |
1269  *   +----------|  R  |----------+ |
1270  *              |     |<-----------+
1271  *              +-----+
1272  *
1273  * Key:  ---X-->  HEAD flag set in pointer
1274  *         T      Tail page
1275  *         R      Reader page
1276  *         N      Next page
1277  *
1278  * (see __rb_reserve_next() to see where this happens)
1279  *
1280  *  What the above shows is that the reader just swapped out
1281  *  the reader page with a page in the buffer, but before it
1282  *  could make the new header point back to the new page added
1283  *  it was preempted by a writer. The writer moved forward onto
1284  *  the new page added by the reader and is about to move forward
1285  *  again.
1286  *
1287  *  You can see, it is legitimate for the previous pointer of
1288  *  the head (or any page) not to point back to itself. But only
1289  *  temporarily.
1290  */
1291 
1292 #define RB_PAGE_NORMAL		0UL
1293 #define RB_PAGE_HEAD		1UL
1294 #define RB_PAGE_UPDATE		2UL
1295 
1296 
1297 #define RB_FLAG_MASK		3UL
1298 
1299 /* PAGE_MOVED is not part of the mask */
1300 #define RB_PAGE_MOVED		4UL
1301 
1302 /*
1303  * rb_list_head - remove any bit
1304  */
rb_list_head(struct list_head * list)1305 static struct list_head *rb_list_head(struct list_head *list)
1306 {
1307 	unsigned long val = (unsigned long)list;
1308 
1309 	return (struct list_head *)(val & ~RB_FLAG_MASK);
1310 }
1311 
1312 /*
1313  * rb_is_head_page - test if the given page is the head page
1314  *
1315  * Because the reader may move the head_page pointer, we can
1316  * not trust what the head page is (it may be pointing to
1317  * the reader page). But if the next page is a header page,
1318  * its flags will be non zero.
1319  */
1320 static inline int
rb_is_head_page(struct buffer_page * page,struct list_head * list)1321 rb_is_head_page(struct buffer_page *page, struct list_head *list)
1322 {
1323 	unsigned long val;
1324 
1325 	val = (unsigned long)list->next;
1326 
1327 	if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
1328 		return RB_PAGE_MOVED;
1329 
1330 	return val & RB_FLAG_MASK;
1331 }
1332 
1333 /*
1334  * rb_is_reader_page
1335  *
1336  * The unique thing about the reader page, is that, if the
1337  * writer is ever on it, the previous pointer never points
1338  * back to the reader page.
1339  */
rb_is_reader_page(struct buffer_page * page)1340 static bool rb_is_reader_page(struct buffer_page *page)
1341 {
1342 	struct list_head *list = page->list.prev;
1343 
1344 	return rb_list_head(list->next) != &page->list;
1345 }
1346 
1347 /*
1348  * rb_set_list_to_head - set a list_head to be pointing to head.
1349  */
rb_set_list_to_head(struct list_head * list)1350 static void rb_set_list_to_head(struct list_head *list)
1351 {
1352 	unsigned long *ptr;
1353 
1354 	ptr = (unsigned long *)&list->next;
1355 	*ptr |= RB_PAGE_HEAD;
1356 	*ptr &= ~RB_PAGE_UPDATE;
1357 }
1358 
1359 /*
1360  * rb_head_page_activate - sets up head page
1361  */
rb_head_page_activate(struct ring_buffer_per_cpu * cpu_buffer)1362 static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
1363 {
1364 	struct buffer_page *head;
1365 
1366 	head = cpu_buffer->head_page;
1367 	if (!head)
1368 		return;
1369 
1370 	/*
1371 	 * Set the previous list pointer to have the HEAD flag.
1372 	 */
1373 	rb_set_list_to_head(head->list.prev);
1374 }
1375 
rb_list_head_clear(struct list_head * list)1376 static void rb_list_head_clear(struct list_head *list)
1377 {
1378 	unsigned long *ptr = (unsigned long *)&list->next;
1379 
1380 	*ptr &= ~RB_FLAG_MASK;
1381 }
1382 
1383 /*
1384  * rb_head_page_deactivate - clears head page ptr (for free list)
1385  */
1386 static void
rb_head_page_deactivate(struct ring_buffer_per_cpu * cpu_buffer)1387 rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
1388 {
1389 	struct list_head *hd;
1390 
1391 	/* Go through the whole list and clear any pointers found. */
1392 	rb_list_head_clear(cpu_buffer->pages);
1393 
1394 	list_for_each(hd, cpu_buffer->pages)
1395 		rb_list_head_clear(hd);
1396 }
1397 
rb_head_page_set(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * head,struct buffer_page * prev,int old_flag,int new_flag)1398 static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
1399 			    struct buffer_page *head,
1400 			    struct buffer_page *prev,
1401 			    int old_flag, int new_flag)
1402 {
1403 	struct list_head *list;
1404 	unsigned long val = (unsigned long)&head->list;
1405 	unsigned long ret;
1406 
1407 	list = &prev->list;
1408 
1409 	val &= ~RB_FLAG_MASK;
1410 
1411 	ret = cmpxchg((unsigned long *)&list->next,
1412 		      val | old_flag, val | new_flag);
1413 
1414 	/* check if the reader took the page */
1415 	if ((ret & ~RB_FLAG_MASK) != val)
1416 		return RB_PAGE_MOVED;
1417 
1418 	return ret & RB_FLAG_MASK;
1419 }
1420 
rb_head_page_set_update(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * head,struct buffer_page * prev,int old_flag)1421 static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
1422 				   struct buffer_page *head,
1423 				   struct buffer_page *prev,
1424 				   int old_flag)
1425 {
1426 	return rb_head_page_set(cpu_buffer, head, prev,
1427 				old_flag, RB_PAGE_UPDATE);
1428 }
1429 
rb_head_page_set_head(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * head,struct buffer_page * prev,int old_flag)1430 static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
1431 				 struct buffer_page *head,
1432 				 struct buffer_page *prev,
1433 				 int old_flag)
1434 {
1435 	return rb_head_page_set(cpu_buffer, head, prev,
1436 				old_flag, RB_PAGE_HEAD);
1437 }
1438 
rb_head_page_set_normal(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * head,struct buffer_page * prev,int old_flag)1439 static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
1440 				   struct buffer_page *head,
1441 				   struct buffer_page *prev,
1442 				   int old_flag)
1443 {
1444 	return rb_head_page_set(cpu_buffer, head, prev,
1445 				old_flag, RB_PAGE_NORMAL);
1446 }
1447 
rb_inc_page(struct buffer_page ** bpage)1448 static inline void rb_inc_page(struct buffer_page **bpage)
1449 {
1450 	struct list_head *p = rb_list_head((*bpage)->list.next);
1451 
1452 	*bpage = list_entry(p, struct buffer_page, list);
1453 }
1454 
1455 static struct buffer_page *
rb_set_head_page(struct ring_buffer_per_cpu * cpu_buffer)1456 rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
1457 {
1458 	struct buffer_page *head;
1459 	struct buffer_page *page;
1460 	struct list_head *list;
1461 	int i;
1462 
1463 	if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
1464 		return NULL;
1465 
1466 	/* sanity check */
1467 	list = cpu_buffer->pages;
1468 	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
1469 		return NULL;
1470 
1471 	page = head = cpu_buffer->head_page;
1472 	/*
1473 	 * It is possible that the writer moves the header behind
1474 	 * where we started, and we miss in one loop.
1475 	 * A second loop should grab the header, but we'll do
1476 	 * three loops just because I'm paranoid.
1477 	 */
1478 	for (i = 0; i < 3; i++) {
1479 		do {
1480 			if (rb_is_head_page(page, page->list.prev)) {
1481 				cpu_buffer->head_page = page;
1482 				return page;
1483 			}
1484 			rb_inc_page(&page);
1485 		} while (page != head);
1486 	}
1487 
1488 	RB_WARN_ON(cpu_buffer, 1);
1489 
1490 	return NULL;
1491 }
1492 
rb_head_page_replace(struct buffer_page * old,struct buffer_page * new)1493 static int rb_head_page_replace(struct buffer_page *old,
1494 				struct buffer_page *new)
1495 {
1496 	unsigned long *ptr = (unsigned long *)&old->list.prev->next;
1497 	unsigned long val;
1498 	unsigned long ret;
1499 
1500 	val = *ptr & ~RB_FLAG_MASK;
1501 	val |= RB_PAGE_HEAD;
1502 
1503 	ret = cmpxchg(ptr, val, (unsigned long)&new->list);
1504 
1505 	return ret == val;
1506 }
1507 
1508 /*
1509  * rb_tail_page_update - move the tail page forward
1510  */
rb_tail_page_update(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * tail_page,struct buffer_page * next_page)1511 static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1512 			       struct buffer_page *tail_page,
1513 			       struct buffer_page *next_page)
1514 {
1515 	unsigned long old_entries;
1516 	unsigned long old_write;
1517 
1518 	/*
1519 	 * The tail page now needs to be moved forward.
1520 	 *
1521 	 * We need to reset the tail page, but without messing
1522 	 * with possible erasing of data brought in by interrupts
1523 	 * that have moved the tail page and are currently on it.
1524 	 *
1525 	 * We add a counter to the write field to denote this.
1526 	 */
1527 	old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1528 	old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1529 
1530 	local_inc(&cpu_buffer->pages_touched);
1531 	/*
1532 	 * Just make sure we have seen our old_write and synchronize
1533 	 * with any interrupts that come in.
1534 	 */
1535 	barrier();
1536 
1537 	/*
1538 	 * If the tail page is still the same as what we think
1539 	 * it is, then it is up to us to update the tail
1540 	 * pointer.
1541 	 */
1542 	if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1543 		/* Zero the write counter */
1544 		unsigned long val = old_write & ~RB_WRITE_MASK;
1545 		unsigned long eval = old_entries & ~RB_WRITE_MASK;
1546 
1547 		/*
1548 		 * This will only succeed if an interrupt did
1549 		 * not come in and change it. In which case, we
1550 		 * do not want to modify it.
1551 		 *
1552 		 * We add (void) to let the compiler know that we do not care
1553 		 * about the return value of these functions. We use the
1554 		 * cmpxchg to only update if an interrupt did not already
1555 		 * do it for us. If the cmpxchg fails, we don't care.
1556 		 */
1557 		(void)local_cmpxchg(&next_page->write, old_write, val);
1558 		(void)local_cmpxchg(&next_page->entries, old_entries, eval);
1559 
1560 		/*
1561 		 * No need to worry about races with clearing out the commit.
1562 		 * it only can increment when a commit takes place. But that
1563 		 * only happens in the outer most nested commit.
1564 		 */
1565 		local_set(&next_page->page->commit, 0);
1566 
1567 		/* Again, either we update tail_page or an interrupt does */
1568 		(void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1569 	}
1570 }
1571 
rb_check_bpage(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * bpage)1572 static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1573 			  struct buffer_page *bpage)
1574 {
1575 	unsigned long val = (unsigned long)bpage;
1576 
1577 	if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1578 		return 1;
1579 
1580 	return 0;
1581 }
1582 
1583 /**
1584  * rb_check_list - make sure a pointer to a list has the last bits zero
1585  */
rb_check_list(struct ring_buffer_per_cpu * cpu_buffer,struct list_head * list)1586 static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1587 			 struct list_head *list)
1588 {
1589 	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1590 		return 1;
1591 	if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1592 		return 1;
1593 	return 0;
1594 }
1595 
1596 /**
1597  * rb_check_pages - integrity check of buffer pages
1598  * @cpu_buffer: CPU buffer with pages to test
1599  *
1600  * As a safety measure we check to make sure the data pages have not
1601  * been corrupted.
1602  */
rb_check_pages(struct ring_buffer_per_cpu * cpu_buffer)1603 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1604 {
1605 	struct list_head *head = cpu_buffer->pages;
1606 	struct buffer_page *bpage, *tmp;
1607 
1608 	/* Reset the head page if it exists */
1609 	if (cpu_buffer->head_page)
1610 		rb_set_head_page(cpu_buffer);
1611 
1612 	rb_head_page_deactivate(cpu_buffer);
1613 
1614 	if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1615 		return -1;
1616 	if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1617 		return -1;
1618 
1619 	if (rb_check_list(cpu_buffer, head))
1620 		return -1;
1621 
1622 	list_for_each_entry_safe(bpage, tmp, head, list) {
1623 		if (RB_WARN_ON(cpu_buffer,
1624 			       bpage->list.next->prev != &bpage->list))
1625 			return -1;
1626 		if (RB_WARN_ON(cpu_buffer,
1627 			       bpage->list.prev->next != &bpage->list))
1628 			return -1;
1629 		if (rb_check_list(cpu_buffer, &bpage->list))
1630 			return -1;
1631 	}
1632 
1633 	rb_head_page_activate(cpu_buffer);
1634 
1635 	return 0;
1636 }
1637 
__rb_allocate_pages(struct ring_buffer_per_cpu * cpu_buffer,long nr_pages,struct list_head * pages)1638 static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1639 		long nr_pages, struct list_head *pages)
1640 {
1641 	struct buffer_page *bpage, *tmp;
1642 	bool user_thread = current->mm != NULL;
1643 	gfp_t mflags;
1644 	long i;
1645 
1646 	/*
1647 	 * Check if the available memory is there first.
1648 	 * Note, si_mem_available() only gives us a rough estimate of available
1649 	 * memory. It may not be accurate. But we don't care, we just want
1650 	 * to prevent doing any allocation when it is obvious that it is
1651 	 * not going to succeed.
1652 	 */
1653 	i = si_mem_available();
1654 	if (i < nr_pages)
1655 		return -ENOMEM;
1656 
1657 	/*
1658 	 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
1659 	 * gracefully without invoking oom-killer and the system is not
1660 	 * destabilized.
1661 	 */
1662 	mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
1663 
1664 	/*
1665 	 * If a user thread allocates too much, and si_mem_available()
1666 	 * reports there's enough memory, even though there is not.
1667 	 * Make sure the OOM killer kills this thread. This can happen
1668 	 * even with RETRY_MAYFAIL because another task may be doing
1669 	 * an allocation after this task has taken all memory.
1670 	 * This is the task the OOM killer needs to take out during this
1671 	 * loop, even if it was triggered by an allocation somewhere else.
1672 	 */
1673 	if (user_thread)
1674 		set_current_oom_origin();
1675 	for (i = 0; i < nr_pages; i++) {
1676 		struct page *page;
1677 
1678 		bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1679 				    mflags, cpu_to_node(cpu_buffer->cpu));
1680 		if (!bpage)
1681 			goto free_pages;
1682 
1683 		rb_check_bpage(cpu_buffer, bpage);
1684 
1685 		list_add(&bpage->list, pages);
1686 
1687 		page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags, 0);
1688 		if (!page)
1689 			goto free_pages;
1690 		bpage->page = page_address(page);
1691 		rb_init_page(bpage->page);
1692 
1693 		if (user_thread && fatal_signal_pending(current))
1694 			goto free_pages;
1695 	}
1696 	if (user_thread)
1697 		clear_current_oom_origin();
1698 
1699 	return 0;
1700 
1701 free_pages:
1702 	list_for_each_entry_safe(bpage, tmp, pages, list) {
1703 		list_del_init(&bpage->list);
1704 		free_buffer_page(bpage);
1705 	}
1706 	if (user_thread)
1707 		clear_current_oom_origin();
1708 
1709 	return -ENOMEM;
1710 }
1711 
rb_allocate_pages(struct ring_buffer_per_cpu * cpu_buffer,unsigned long nr_pages)1712 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1713 			     unsigned long nr_pages)
1714 {
1715 	LIST_HEAD(pages);
1716 
1717 	WARN_ON(!nr_pages);
1718 
1719 	if (__rb_allocate_pages(cpu_buffer, nr_pages, &pages))
1720 		return -ENOMEM;
1721 
1722 	/*
1723 	 * The ring buffer page list is a circular list that does not
1724 	 * start and end with a list head. All page list items point to
1725 	 * other pages.
1726 	 */
1727 	cpu_buffer->pages = pages.next;
1728 	list_del(&pages);
1729 
1730 	cpu_buffer->nr_pages = nr_pages;
1731 
1732 	rb_check_pages(cpu_buffer);
1733 
1734 	return 0;
1735 }
1736 
1737 static struct ring_buffer_per_cpu *
rb_allocate_cpu_buffer(struct trace_buffer * buffer,long nr_pages,int cpu)1738 rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
1739 {
1740 	struct ring_buffer_per_cpu *cpu_buffer;
1741 	struct buffer_page *bpage;
1742 	struct page *page;
1743 	int ret;
1744 
1745 	cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1746 				  GFP_KERNEL, cpu_to_node(cpu));
1747 	if (!cpu_buffer)
1748 		return NULL;
1749 
1750 	cpu_buffer->cpu = cpu;
1751 	cpu_buffer->buffer = buffer;
1752 	raw_spin_lock_init(&cpu_buffer->reader_lock);
1753 	lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1754 	cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1755 	INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1756 	init_completion(&cpu_buffer->update_done);
1757 	init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1758 	init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1759 	init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1760 
1761 	bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1762 			    GFP_KERNEL, cpu_to_node(cpu));
1763 	if (!bpage)
1764 		goto fail_free_buffer;
1765 
1766 	rb_check_bpage(cpu_buffer, bpage);
1767 
1768 	cpu_buffer->reader_page = bpage;
1769 	page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1770 	if (!page)
1771 		goto fail_free_reader;
1772 	bpage->page = page_address(page);
1773 	rb_init_page(bpage->page);
1774 
1775 	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1776 	INIT_LIST_HEAD(&cpu_buffer->new_pages);
1777 
1778 	ret = rb_allocate_pages(cpu_buffer, nr_pages);
1779 	if (ret < 0)
1780 		goto fail_free_reader;
1781 
1782 	cpu_buffer->head_page
1783 		= list_entry(cpu_buffer->pages, struct buffer_page, list);
1784 	cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1785 
1786 	rb_head_page_activate(cpu_buffer);
1787 
1788 	return cpu_buffer;
1789 
1790  fail_free_reader:
1791 	free_buffer_page(cpu_buffer->reader_page);
1792 
1793  fail_free_buffer:
1794 	kfree(cpu_buffer);
1795 	return NULL;
1796 }
1797 
rb_free_cpu_buffer(struct ring_buffer_per_cpu * cpu_buffer)1798 static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1799 {
1800 	struct list_head *head = cpu_buffer->pages;
1801 	struct buffer_page *bpage, *tmp;
1802 
1803 	free_buffer_page(cpu_buffer->reader_page);
1804 
1805 	if (head) {
1806 		rb_head_page_deactivate(cpu_buffer);
1807 
1808 		list_for_each_entry_safe(bpage, tmp, head, list) {
1809 			list_del_init(&bpage->list);
1810 			free_buffer_page(bpage);
1811 		}
1812 		bpage = list_entry(head, struct buffer_page, list);
1813 		free_buffer_page(bpage);
1814 	}
1815 
1816 	kfree(cpu_buffer);
1817 }
1818 
1819 /**
1820  * __ring_buffer_alloc - allocate a new ring_buffer
1821  * @size: the size in bytes per cpu that is needed.
1822  * @flags: attributes to set for the ring buffer.
1823  * @key: ring buffer reader_lock_key.
1824  *
1825  * Currently the only flag that is available is the RB_FL_OVERWRITE
1826  * flag. This flag means that the buffer will overwrite old data
1827  * when the buffer wraps. If this flag is not set, the buffer will
1828  * drop data when the tail hits the head.
1829  */
__ring_buffer_alloc(unsigned long size,unsigned flags,struct lock_class_key * key)1830 struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1831 					struct lock_class_key *key)
1832 {
1833 	struct trace_buffer *buffer;
1834 	long nr_pages;
1835 	int bsize;
1836 	int cpu;
1837 	int ret;
1838 
1839 	/* keep it in its own cache line */
1840 	buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1841 			 GFP_KERNEL);
1842 	if (!buffer)
1843 		return NULL;
1844 
1845 	if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1846 		goto fail_free_buffer;
1847 
1848 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1849 	buffer->flags = flags;
1850 	buffer->clock = trace_clock_local;
1851 	buffer->reader_lock_key = key;
1852 
1853 	init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1854 	init_waitqueue_head(&buffer->irq_work.waiters);
1855 
1856 	/* need at least two pages */
1857 	if (nr_pages < 2)
1858 		nr_pages = 2;
1859 
1860 	buffer->cpus = nr_cpu_ids;
1861 
1862 	bsize = sizeof(void *) * nr_cpu_ids;
1863 	buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1864 				  GFP_KERNEL);
1865 	if (!buffer->buffers)
1866 		goto fail_free_cpumask;
1867 
1868 	cpu = raw_smp_processor_id();
1869 	cpumask_set_cpu(cpu, buffer->cpumask);
1870 	buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1871 	if (!buffer->buffers[cpu])
1872 		goto fail_free_buffers;
1873 
1874 	ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1875 	if (ret < 0)
1876 		goto fail_free_buffers;
1877 
1878 	mutex_init(&buffer->mutex);
1879 
1880 	return buffer;
1881 
1882  fail_free_buffers:
1883 	for_each_buffer_cpu(buffer, cpu) {
1884 		if (buffer->buffers[cpu])
1885 			rb_free_cpu_buffer(buffer->buffers[cpu]);
1886 	}
1887 	kfree(buffer->buffers);
1888 
1889  fail_free_cpumask:
1890 	free_cpumask_var(buffer->cpumask);
1891 
1892  fail_free_buffer:
1893 	kfree(buffer);
1894 	return NULL;
1895 }
1896 EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1897 
1898 /**
1899  * ring_buffer_free - free a ring buffer.
1900  * @buffer: the buffer to free.
1901  */
1902 void
ring_buffer_free(struct trace_buffer * buffer)1903 ring_buffer_free(struct trace_buffer *buffer)
1904 {
1905 	int cpu;
1906 
1907 	cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1908 
1909 	for_each_buffer_cpu(buffer, cpu)
1910 		rb_free_cpu_buffer(buffer->buffers[cpu]);
1911 
1912 	kfree(buffer->buffers);
1913 	free_cpumask_var(buffer->cpumask);
1914 
1915 	kfree(buffer);
1916 }
1917 EXPORT_SYMBOL_GPL(ring_buffer_free);
1918 
ring_buffer_set_clock(struct trace_buffer * buffer,u64 (* clock)(void))1919 void ring_buffer_set_clock(struct trace_buffer *buffer,
1920 			   u64 (*clock)(void))
1921 {
1922 	buffer->clock = clock;
1923 }
1924 
ring_buffer_set_time_stamp_abs(struct trace_buffer * buffer,bool abs)1925 void ring_buffer_set_time_stamp_abs(struct trace_buffer *buffer, bool abs)
1926 {
1927 	buffer->time_stamp_abs = abs;
1928 }
1929 
ring_buffer_time_stamp_abs(struct trace_buffer * buffer)1930 bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
1931 {
1932 	return buffer->time_stamp_abs;
1933 }
1934 
1935 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1936 
rb_page_entries(struct buffer_page * bpage)1937 static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1938 {
1939 	return local_read(&bpage->entries) & RB_WRITE_MASK;
1940 }
1941 
rb_page_write(struct buffer_page * bpage)1942 static inline unsigned long rb_page_write(struct buffer_page *bpage)
1943 {
1944 	return local_read(&bpage->write) & RB_WRITE_MASK;
1945 }
1946 
1947 static int
rb_remove_pages(struct ring_buffer_per_cpu * cpu_buffer,unsigned long nr_pages)1948 rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1949 {
1950 	struct list_head *tail_page, *to_remove, *next_page;
1951 	struct buffer_page *to_remove_page, *tmp_iter_page;
1952 	struct buffer_page *last_page, *first_page;
1953 	unsigned long nr_removed;
1954 	unsigned long head_bit;
1955 	int page_entries;
1956 
1957 	head_bit = 0;
1958 
1959 	raw_spin_lock_irq(&cpu_buffer->reader_lock);
1960 	atomic_inc(&cpu_buffer->record_disabled);
1961 	/*
1962 	 * We don't race with the readers since we have acquired the reader
1963 	 * lock. We also don't race with writers after disabling recording.
1964 	 * This makes it easy to figure out the first and the last page to be
1965 	 * removed from the list. We unlink all the pages in between including
1966 	 * the first and last pages. This is done in a busy loop so that we
1967 	 * lose the least number of traces.
1968 	 * The pages are freed after we restart recording and unlock readers.
1969 	 */
1970 	tail_page = &cpu_buffer->tail_page->list;
1971 
1972 	/*
1973 	 * tail page might be on reader page, we remove the next page
1974 	 * from the ring buffer
1975 	 */
1976 	if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1977 		tail_page = rb_list_head(tail_page->next);
1978 	to_remove = tail_page;
1979 
1980 	/* start of pages to remove */
1981 	first_page = list_entry(rb_list_head(to_remove->next),
1982 				struct buffer_page, list);
1983 
1984 	for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1985 		to_remove = rb_list_head(to_remove)->next;
1986 		head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1987 	}
1988 
1989 	next_page = rb_list_head(to_remove)->next;
1990 
1991 	/*
1992 	 * Now we remove all pages between tail_page and next_page.
1993 	 * Make sure that we have head_bit value preserved for the
1994 	 * next page
1995 	 */
1996 	tail_page->next = (struct list_head *)((unsigned long)next_page |
1997 						head_bit);
1998 	next_page = rb_list_head(next_page);
1999 	next_page->prev = tail_page;
2000 
2001 	/* make sure pages points to a valid page in the ring buffer */
2002 	cpu_buffer->pages = next_page;
2003 
2004 	/* update head page */
2005 	if (head_bit)
2006 		cpu_buffer->head_page = list_entry(next_page,
2007 						struct buffer_page, list);
2008 
2009 	/*
2010 	 * change read pointer to make sure any read iterators reset
2011 	 * themselves
2012 	 */
2013 	cpu_buffer->read = 0;
2014 
2015 	/* pages are removed, resume tracing and then free the pages */
2016 	atomic_dec(&cpu_buffer->record_disabled);
2017 	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
2018 
2019 	RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
2020 
2021 	/* last buffer page to remove */
2022 	last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
2023 				list);
2024 	tmp_iter_page = first_page;
2025 
2026 	do {
2027 		cond_resched();
2028 
2029 		to_remove_page = tmp_iter_page;
2030 		rb_inc_page(&tmp_iter_page);
2031 
2032 		/* update the counters */
2033 		page_entries = rb_page_entries(to_remove_page);
2034 		if (page_entries) {
2035 			/*
2036 			 * If something was added to this page, it was full
2037 			 * since it is not the tail page. So we deduct the
2038 			 * bytes consumed in ring buffer from here.
2039 			 * Increment overrun to account for the lost events.
2040 			 */
2041 			local_add(page_entries, &cpu_buffer->overrun);
2042 			local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2043 			local_inc(&cpu_buffer->pages_lost);
2044 		}
2045 
2046 		/*
2047 		 * We have already removed references to this list item, just
2048 		 * free up the buffer_page and its page
2049 		 */
2050 		free_buffer_page(to_remove_page);
2051 		nr_removed--;
2052 
2053 	} while (to_remove_page != last_page);
2054 
2055 	RB_WARN_ON(cpu_buffer, nr_removed);
2056 
2057 	return nr_removed == 0;
2058 }
2059 
2060 static int
rb_insert_pages(struct ring_buffer_per_cpu * cpu_buffer)2061 rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
2062 {
2063 	struct list_head *pages = &cpu_buffer->new_pages;
2064 	int retries, success;
2065 
2066 	raw_spin_lock_irq(&cpu_buffer->reader_lock);
2067 	/*
2068 	 * We are holding the reader lock, so the reader page won't be swapped
2069 	 * in the ring buffer. Now we are racing with the writer trying to
2070 	 * move head page and the tail page.
2071 	 * We are going to adapt the reader page update process where:
2072 	 * 1. We first splice the start and end of list of new pages between
2073 	 *    the head page and its previous page.
2074 	 * 2. We cmpxchg the prev_page->next to point from head page to the
2075 	 *    start of new pages list.
2076 	 * 3. Finally, we update the head->prev to the end of new list.
2077 	 *
2078 	 * We will try this process 10 times, to make sure that we don't keep
2079 	 * spinning.
2080 	 */
2081 	retries = 10;
2082 	success = 0;
2083 	while (retries--) {
2084 		struct list_head *head_page, *prev_page, *r;
2085 		struct list_head *last_page, *first_page;
2086 		struct list_head *head_page_with_bit;
2087 
2088 		head_page = &rb_set_head_page(cpu_buffer)->list;
2089 		if (!head_page)
2090 			break;
2091 		prev_page = head_page->prev;
2092 
2093 		first_page = pages->next;
2094 		last_page  = pages->prev;
2095 
2096 		head_page_with_bit = (struct list_head *)
2097 				     ((unsigned long)head_page | RB_PAGE_HEAD);
2098 
2099 		last_page->next = head_page_with_bit;
2100 		first_page->prev = prev_page;
2101 
2102 		r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
2103 
2104 		if (r == head_page_with_bit) {
2105 			/*
2106 			 * yay, we replaced the page pointer to our new list,
2107 			 * now, we just have to update to head page's prev
2108 			 * pointer to point to end of list
2109 			 */
2110 			head_page->prev = last_page;
2111 			success = 1;
2112 			break;
2113 		}
2114 	}
2115 
2116 	if (success)
2117 		INIT_LIST_HEAD(pages);
2118 	/*
2119 	 * If we weren't successful in adding in new pages, warn and stop
2120 	 * tracing
2121 	 */
2122 	RB_WARN_ON(cpu_buffer, !success);
2123 	raw_spin_unlock_irq(&cpu_buffer->reader_lock);
2124 
2125 	/* free pages if they weren't inserted */
2126 	if (!success) {
2127 		struct buffer_page *bpage, *tmp;
2128 		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
2129 					 list) {
2130 			list_del_init(&bpage->list);
2131 			free_buffer_page(bpage);
2132 		}
2133 	}
2134 	return success;
2135 }
2136 
rb_update_pages(struct ring_buffer_per_cpu * cpu_buffer)2137 static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
2138 {
2139 	int success;
2140 
2141 	if (cpu_buffer->nr_pages_to_update > 0)
2142 		success = rb_insert_pages(cpu_buffer);
2143 	else
2144 		success = rb_remove_pages(cpu_buffer,
2145 					-cpu_buffer->nr_pages_to_update);
2146 
2147 	if (success)
2148 		cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
2149 }
2150 
update_pages_handler(struct work_struct * work)2151 static void update_pages_handler(struct work_struct *work)
2152 {
2153 	struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
2154 			struct ring_buffer_per_cpu, update_pages_work);
2155 	rb_update_pages(cpu_buffer);
2156 	complete(&cpu_buffer->update_done);
2157 }
2158 
2159 /**
2160  * ring_buffer_resize - resize the ring buffer
2161  * @buffer: the buffer to resize.
2162  * @size: the new size.
2163  * @cpu_id: the cpu buffer to resize
2164  *
2165  * Minimum size is 2 * BUF_PAGE_SIZE.
2166  *
2167  * Returns 0 on success and < 0 on failure.
2168  */
ring_buffer_resize(struct trace_buffer * buffer,unsigned long size,int cpu_id)2169 int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
2170 			int cpu_id)
2171 {
2172 	struct ring_buffer_per_cpu *cpu_buffer;
2173 	unsigned long nr_pages;
2174 	int cpu, err;
2175 
2176 	/*
2177 	 * Always succeed at resizing a non-existent buffer:
2178 	 */
2179 	if (!buffer)
2180 		return 0;
2181 
2182 	/* Make sure the requested buffer exists */
2183 	if (cpu_id != RING_BUFFER_ALL_CPUS &&
2184 	    !cpumask_test_cpu(cpu_id, buffer->cpumask))
2185 		return 0;
2186 
2187 	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
2188 
2189 	/* we need a minimum of two pages */
2190 	if (nr_pages < 2)
2191 		nr_pages = 2;
2192 
2193 	/* prevent another thread from changing buffer sizes */
2194 	mutex_lock(&buffer->mutex);
2195 
2196 
2197 	if (cpu_id == RING_BUFFER_ALL_CPUS) {
2198 		/*
2199 		 * Don't succeed if resizing is disabled, as a reader might be
2200 		 * manipulating the ring buffer and is expecting a sane state while
2201 		 * this is true.
2202 		 */
2203 		for_each_buffer_cpu(buffer, cpu) {
2204 			cpu_buffer = buffer->buffers[cpu];
2205 			if (atomic_read(&cpu_buffer->resize_disabled)) {
2206 				err = -EBUSY;
2207 				goto out_err_unlock;
2208 			}
2209 		}
2210 
2211 		/* calculate the pages to update */
2212 		for_each_buffer_cpu(buffer, cpu) {
2213 			cpu_buffer = buffer->buffers[cpu];
2214 
2215 			cpu_buffer->nr_pages_to_update = nr_pages -
2216 							cpu_buffer->nr_pages;
2217 			/*
2218 			 * nothing more to do for removing pages or no update
2219 			 */
2220 			if (cpu_buffer->nr_pages_to_update <= 0)
2221 				continue;
2222 			/*
2223 			 * to add pages, make sure all new pages can be
2224 			 * allocated without receiving ENOMEM
2225 			 */
2226 			INIT_LIST_HEAD(&cpu_buffer->new_pages);
2227 			if (__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
2228 						&cpu_buffer->new_pages)) {
2229 				/* not enough memory for new pages */
2230 				err = -ENOMEM;
2231 				goto out_err;
2232 			}
2233 		}
2234 
2235 		cpus_read_lock();
2236 		/*
2237 		 * Fire off all the required work handlers
2238 		 * We can't schedule on offline CPUs, but it's not necessary
2239 		 * since we can change their buffer sizes without any race.
2240 		 */
2241 		for_each_buffer_cpu(buffer, cpu) {
2242 			cpu_buffer = buffer->buffers[cpu];
2243 			if (!cpu_buffer->nr_pages_to_update)
2244 				continue;
2245 
2246 			/* Can't run something on an offline CPU. */
2247 			if (!cpu_online(cpu)) {
2248 				rb_update_pages(cpu_buffer);
2249 				cpu_buffer->nr_pages_to_update = 0;
2250 			} else {
2251 				schedule_work_on(cpu,
2252 						&cpu_buffer->update_pages_work);
2253 			}
2254 		}
2255 
2256 		/* wait for all the updates to complete */
2257 		for_each_buffer_cpu(buffer, cpu) {
2258 			cpu_buffer = buffer->buffers[cpu];
2259 			if (!cpu_buffer->nr_pages_to_update)
2260 				continue;
2261 
2262 			if (cpu_online(cpu))
2263 				wait_for_completion(&cpu_buffer->update_done);
2264 			cpu_buffer->nr_pages_to_update = 0;
2265 		}
2266 
2267 		cpus_read_unlock();
2268 	} else {
2269 		cpu_buffer = buffer->buffers[cpu_id];
2270 
2271 		if (nr_pages == cpu_buffer->nr_pages)
2272 			goto out;
2273 
2274 		/*
2275 		 * Don't succeed if resizing is disabled, as a reader might be
2276 		 * manipulating the ring buffer and is expecting a sane state while
2277 		 * this is true.
2278 		 */
2279 		if (atomic_read(&cpu_buffer->resize_disabled)) {
2280 			err = -EBUSY;
2281 			goto out_err_unlock;
2282 		}
2283 
2284 		cpu_buffer->nr_pages_to_update = nr_pages -
2285 						cpu_buffer->nr_pages;
2286 
2287 		INIT_LIST_HEAD(&cpu_buffer->new_pages);
2288 		if (cpu_buffer->nr_pages_to_update > 0 &&
2289 			__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
2290 					    &cpu_buffer->new_pages)) {
2291 			err = -ENOMEM;
2292 			goto out_err;
2293 		}
2294 
2295 		cpus_read_lock();
2296 
2297 		/* Can't run something on an offline CPU. */
2298 		if (!cpu_online(cpu_id))
2299 			rb_update_pages(cpu_buffer);
2300 		else {
2301 			schedule_work_on(cpu_id,
2302 					 &cpu_buffer->update_pages_work);
2303 			wait_for_completion(&cpu_buffer->update_done);
2304 		}
2305 
2306 		cpu_buffer->nr_pages_to_update = 0;
2307 		cpus_read_unlock();
2308 	}
2309 
2310  out:
2311 	/*
2312 	 * The ring buffer resize can happen with the ring buffer
2313 	 * enabled, so that the update disturbs the tracing as little
2314 	 * as possible. But if the buffer is disabled, we do not need
2315 	 * to worry about that, and we can take the time to verify
2316 	 * that the buffer is not corrupt.
2317 	 */
2318 	if (atomic_read(&buffer->record_disabled)) {
2319 		atomic_inc(&buffer->record_disabled);
2320 		/*
2321 		 * Even though the buffer was disabled, we must make sure
2322 		 * that it is truly disabled before calling rb_check_pages.
2323 		 * There could have been a race between checking
2324 		 * record_disable and incrementing it.
2325 		 */
2326 		synchronize_rcu();
2327 		for_each_buffer_cpu(buffer, cpu) {
2328 			cpu_buffer = buffer->buffers[cpu];
2329 			rb_check_pages(cpu_buffer);
2330 		}
2331 		atomic_dec(&buffer->record_disabled);
2332 	}
2333 
2334 	mutex_unlock(&buffer->mutex);
2335 	return 0;
2336 
2337  out_err:
2338 	for_each_buffer_cpu(buffer, cpu) {
2339 		struct buffer_page *bpage, *tmp;
2340 
2341 		cpu_buffer = buffer->buffers[cpu];
2342 		cpu_buffer->nr_pages_to_update = 0;
2343 
2344 		if (list_empty(&cpu_buffer->new_pages))
2345 			continue;
2346 
2347 		list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
2348 					list) {
2349 			list_del_init(&bpage->list);
2350 			free_buffer_page(bpage);
2351 		}
2352 	}
2353  out_err_unlock:
2354 	mutex_unlock(&buffer->mutex);
2355 	return err;
2356 }
2357 EXPORT_SYMBOL_GPL(ring_buffer_resize);
2358 
ring_buffer_change_overwrite(struct trace_buffer * buffer,int val)2359 void ring_buffer_change_overwrite(struct trace_buffer *buffer, int val)
2360 {
2361 	mutex_lock(&buffer->mutex);
2362 	if (val)
2363 		buffer->flags |= RB_FL_OVERWRITE;
2364 	else
2365 		buffer->flags &= ~RB_FL_OVERWRITE;
2366 	mutex_unlock(&buffer->mutex);
2367 }
2368 EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
2369 
__rb_page_index(struct buffer_page * bpage,unsigned index)2370 static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
2371 {
2372 	return bpage->page->data + index;
2373 }
2374 
2375 static __always_inline struct ring_buffer_event *
rb_reader_event(struct ring_buffer_per_cpu * cpu_buffer)2376 rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
2377 {
2378 	return __rb_page_index(cpu_buffer->reader_page,
2379 			       cpu_buffer->reader_page->read);
2380 }
2381 
rb_page_commit(struct buffer_page * bpage)2382 static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
2383 {
2384 	return local_read(&bpage->page->commit);
2385 }
2386 
2387 static struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter * iter)2388 rb_iter_head_event(struct ring_buffer_iter *iter)
2389 {
2390 	struct ring_buffer_event *event;
2391 	struct buffer_page *iter_head_page = iter->head_page;
2392 	unsigned long commit;
2393 	unsigned length;
2394 
2395 	if (iter->head != iter->next_event)
2396 		return iter->event;
2397 
2398 	/*
2399 	 * When the writer goes across pages, it issues a cmpxchg which
2400 	 * is a mb(), which will synchronize with the rmb here.
2401 	 * (see rb_tail_page_update() and __rb_reserve_next())
2402 	 */
2403 	commit = rb_page_commit(iter_head_page);
2404 	smp_rmb();
2405 	event = __rb_page_index(iter_head_page, iter->head);
2406 	length = rb_event_length(event);
2407 
2408 	/*
2409 	 * READ_ONCE() doesn't work on functions and we don't want the
2410 	 * compiler doing any crazy optimizations with length.
2411 	 */
2412 	barrier();
2413 
2414 	if ((iter->head + length) > commit || length > BUF_MAX_DATA_SIZE)
2415 		/* Writer corrupted the read? */
2416 		goto reset;
2417 
2418 	memcpy(iter->event, event, length);
2419 	/*
2420 	 * If the page stamp is still the same after this rmb() then the
2421 	 * event was safely copied without the writer entering the page.
2422 	 */
2423 	smp_rmb();
2424 
2425 	/* Make sure the page didn't change since we read this */
2426 	if (iter->page_stamp != iter_head_page->page->time_stamp ||
2427 	    commit > rb_page_commit(iter_head_page))
2428 		goto reset;
2429 
2430 	iter->next_event = iter->head + length;
2431 	return iter->event;
2432  reset:
2433 	/* Reset to the beginning */
2434 	iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
2435 	iter->head = 0;
2436 	iter->next_event = 0;
2437 	iter->missed_events = 1;
2438 	return NULL;
2439 }
2440 
2441 /* Size is determined by what has been committed */
rb_page_size(struct buffer_page * bpage)2442 static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
2443 {
2444 	return rb_page_commit(bpage);
2445 }
2446 
2447 static __always_inline unsigned
rb_commit_index(struct ring_buffer_per_cpu * cpu_buffer)2448 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
2449 {
2450 	return rb_page_commit(cpu_buffer->commit_page);
2451 }
2452 
2453 static __always_inline unsigned
rb_event_index(struct ring_buffer_event * event)2454 rb_event_index(struct ring_buffer_event *event)
2455 {
2456 	unsigned long addr = (unsigned long)event;
2457 
2458 	return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
2459 }
2460 
rb_inc_iter(struct ring_buffer_iter * iter)2461 static void rb_inc_iter(struct ring_buffer_iter *iter)
2462 {
2463 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
2464 
2465 	/*
2466 	 * The iterator could be on the reader page (it starts there).
2467 	 * But the head could have moved, since the reader was
2468 	 * found. Check for this case and assign the iterator
2469 	 * to the head page instead of next.
2470 	 */
2471 	if (iter->head_page == cpu_buffer->reader_page)
2472 		iter->head_page = rb_set_head_page(cpu_buffer);
2473 	else
2474 		rb_inc_page(&iter->head_page);
2475 
2476 	iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
2477 	iter->head = 0;
2478 	iter->next_event = 0;
2479 }
2480 
2481 /*
2482  * rb_handle_head_page - writer hit the head page
2483  *
2484  * Returns: +1 to retry page
2485  *           0 to continue
2486  *          -1 on error
2487  */
2488 static int
rb_handle_head_page(struct ring_buffer_per_cpu * cpu_buffer,struct buffer_page * tail_page,struct buffer_page * next_page)2489 rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
2490 		    struct buffer_page *tail_page,
2491 		    struct buffer_page *next_page)
2492 {
2493 	struct buffer_page *new_head;
2494 	int entries;
2495 	int type;
2496 	int ret;
2497 
2498 	entries = rb_page_entries(next_page);
2499 
2500 	/*
2501 	 * The hard part is here. We need to move the head
2502 	 * forward, and protect against both readers on
2503 	 * other CPUs and writers coming in via interrupts.
2504 	 */
2505 	type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
2506 				       RB_PAGE_HEAD);
2507 
2508 	/*
2509 	 * type can be one of four:
2510 	 *  NORMAL - an interrupt already moved it for us
2511 	 *  HEAD   - we are the first to get here.
2512 	 *  UPDATE - we are the interrupt interrupting
2513 	 *           a current move.
2514 	 *  MOVED  - a reader on another CPU moved the next
2515 	 *           pointer to its reader page. Give up
2516 	 *           and try again.
2517 	 */
2518 
2519 	switch (type) {
2520 	case RB_PAGE_HEAD:
2521 		/*
2522 		 * We changed the head to UPDATE, thus
2523 		 * it is our responsibility to update
2524 		 * the counters.
2525 		 */
2526 		local_add(entries, &cpu_buffer->overrun);
2527 		local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2528 		local_inc(&cpu_buffer->pages_lost);
2529 
2530 		/*
2531 		 * The entries will be zeroed out when we move the
2532 		 * tail page.
2533 		 */
2534 
2535 		/* still more to do */
2536 		break;
2537 
2538 	case RB_PAGE_UPDATE:
2539 		/*
2540 		 * This is an interrupt that interrupt the
2541 		 * previous update. Still more to do.
2542 		 */
2543 		break;
2544 	case RB_PAGE_NORMAL:
2545 		/*
2546 		 * An interrupt came in before the update
2547 		 * and processed this for us.
2548 		 * Nothing left to do.
2549 		 */
2550 		return 1;
2551 	case RB_PAGE_MOVED:
2552 		/*
2553 		 * The reader is on another CPU and just did
2554 		 * a swap with our next_page.
2555 		 * Try again.
2556 		 */
2557 		return 1;
2558 	default:
2559 		RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2560 		return -1;
2561 	}
2562 
2563 	/*
2564 	 * Now that we are here, the old head pointer is
2565 	 * set to UPDATE. This will keep the reader from
2566 	 * swapping the head page with the reader page.
2567 	 * The reader (on another CPU) will spin till
2568 	 * we are finished.
2569 	 *
2570 	 * We just need to protect against interrupts
2571 	 * doing the job. We will set the next pointer
2572 	 * to HEAD. After that, we set the old pointer
2573 	 * to NORMAL, but only if it was HEAD before.
2574 	 * otherwise we are an interrupt, and only
2575 	 * want the outer most commit to reset it.
2576 	 */
2577 	new_head = next_page;
2578 	rb_inc_page(&new_head);
2579 
2580 	ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2581 				    RB_PAGE_NORMAL);
2582 
2583 	/*
2584 	 * Valid returns are:
2585 	 *  HEAD   - an interrupt came in and already set it.
2586 	 *  NORMAL - One of two things:
2587 	 *            1) We really set it.
2588 	 *            2) A bunch of interrupts came in and moved
2589 	 *               the page forward again.
2590 	 */
2591 	switch (ret) {
2592 	case RB_PAGE_HEAD:
2593 	case RB_PAGE_NORMAL:
2594 		/* OK */
2595 		break;
2596 	default:
2597 		RB_WARN_ON(cpu_buffer, 1);
2598 		return -1;
2599 	}
2600 
2601 	/*
2602 	 * It is possible that an interrupt came in,
2603 	 * set the head up, then more interrupts came in
2604 	 * and moved it again. When we get back here,
2605 	 * the page would have been set to NORMAL but we
2606 	 * just set it back to HEAD.
2607 	 *
2608 	 * How do you detect this? Well, if that happened
2609 	 * the tail page would have moved.
2610 	 */
2611 	if (ret == RB_PAGE_NORMAL) {
2612 		struct buffer_page *buffer_tail_page;
2613 
2614 		buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2615 		/*
2616 		 * If the tail had moved passed next, then we need
2617 		 * to reset the pointer.
2618 		 */
2619 		if (buffer_tail_page != tail_page &&
2620 		    buffer_tail_page != next_page)
2621 			rb_head_page_set_normal(cpu_buffer, new_head,
2622 						next_page,
2623 						RB_PAGE_HEAD);
2624 	}
2625 
2626 	/*
2627 	 * If this was the outer most commit (the one that
2628 	 * changed the original pointer from HEAD to UPDATE),
2629 	 * then it is up to us to reset it to NORMAL.
2630 	 */
2631 	if (type == RB_PAGE_HEAD) {
2632 		ret = rb_head_page_set_normal(cpu_buffer, next_page,
2633 					      tail_page,
2634 					      RB_PAGE_UPDATE);
2635 		if (RB_WARN_ON(cpu_buffer,
2636 			       ret != RB_PAGE_UPDATE))
2637 			return -1;
2638 	}
2639 
2640 	return 0;
2641 }
2642 
2643 static inline void
rb_reset_tail(struct ring_buffer_per_cpu * cpu_buffer,unsigned long tail,struct rb_event_info * info)2644 rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2645 	      unsigned long tail, struct rb_event_info *info)
2646 {
2647 	struct buffer_page *tail_page = info->tail_page;
2648 	struct ring_buffer_event *event;
2649 	unsigned long length = info->length;
2650 
2651 	/*
2652 	 * Only the event that crossed the page boundary
2653 	 * must fill the old tail_page with padding.
2654 	 */
2655 	if (tail >= BUF_PAGE_SIZE) {
2656 		/*
2657 		 * If the page was filled, then we still need
2658 		 * to update the real_end. Reset it to zero
2659 		 * and the reader will ignore it.
2660 		 */
2661 		if (tail == BUF_PAGE_SIZE)
2662 			tail_page->real_end = 0;
2663 
2664 		local_sub(length, &tail_page->write);
2665 		return;
2666 	}
2667 
2668 	event = __rb_page_index(tail_page, tail);
2669 
2670 	/* account for padding bytes */
2671 	local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2672 
2673 	/*
2674 	 * Save the original length to the meta data.
2675 	 * This will be used by the reader to add lost event
2676 	 * counter.
2677 	 */
2678 	tail_page->real_end = tail;
2679 
2680 	/*
2681 	 * If this event is bigger than the minimum size, then
2682 	 * we need to be careful that we don't subtract the
2683 	 * write counter enough to allow another writer to slip
2684 	 * in on this page.
2685 	 * We put in a discarded commit instead, to make sure
2686 	 * that this space is not used again.
2687 	 *
2688 	 * If we are less than the minimum size, we don't need to
2689 	 * worry about it.
2690 	 */
2691 	if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2692 		/* No room for any events */
2693 
2694 		/* Mark the rest of the page with padding */
2695 		rb_event_set_padding(event);
2696 
2697 		/* Make sure the padding is visible before the write update */
2698 		smp_wmb();
2699 
2700 		/* Set the write back to the previous setting */
2701 		local_sub(length, &tail_page->write);
2702 		return;
2703 	}
2704 
2705 	/* Put in a discarded event */
2706 	event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2707 	event->type_len = RINGBUF_TYPE_PADDING;
2708 	/* time delta must be non zero */
2709 	event->time_delta = 1;
2710 
2711 	/* Make sure the padding is visible before the tail_page->write update */
2712 	smp_wmb();
2713 
2714 	/* Set write to end of buffer */
2715 	length = (tail + length) - BUF_PAGE_SIZE;
2716 	local_sub(length, &tail_page->write);
2717 }
2718 
2719 static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2720 
2721 /*
2722  * This is the slow path, force gcc not to inline it.
2723  */
2724 static noinline struct ring_buffer_event *
rb_move_tail(struct ring_buffer_per_cpu * cpu_buffer,unsigned long tail,struct rb_event_info * info)2725 rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2726 	     unsigned long tail, struct rb_event_info *info)
2727 {
2728 	struct buffer_page *tail_page = info->tail_page;
2729 	struct buffer_page *commit_page = cpu_buffer->commit_page;
2730 	struct trace_buffer *buffer = cpu_buffer->buffer;
2731 	struct buffer_page *next_page;
2732 	int ret;
2733 
2734 	next_page = tail_page;
2735 
2736 	rb_inc_page(&next_page);
2737 
2738 	/*
2739 	 * If for some reason, we had an interrupt storm that made
2740 	 * it all the way around the buffer, bail, and warn
2741 	 * about it.
2742 	 */
2743 	if (unlikely(next_page == commit_page)) {
2744 		local_inc(&cpu_buffer->commit_overrun);
2745 		goto out_reset;
2746 	}
2747 
2748 	/*
2749 	 * This is where the fun begins!
2750 	 *
2751 	 * We are fighting against races between a reader that
2752 	 * could be on another CPU trying to swap its reader
2753 	 * page with the buffer head.
2754 	 *
2755 	 * We are also fighting against interrupts coming in and
2756 	 * moving the head or tail on us as well.
2757 	 *
2758 	 * If the next page is the head page then we have filled
2759 	 * the buffer, unless the commit page is still on the
2760 	 * reader page.
2761 	 */
2762 	if (rb_is_head_page(next_page, &tail_page->list)) {
2763 
2764 		/*
2765 		 * If the commit is not on the reader page, then
2766 		 * move the header page.
2767 		 */
2768 		if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2769 			/*
2770 			 * If we are not in overwrite mode,
2771 			 * this is easy, just stop here.
2772 			 */
2773 			if (!(buffer->flags & RB_FL_OVERWRITE)) {
2774 				local_inc(&cpu_buffer->dropped_events);
2775 				goto out_reset;
2776 			}
2777 
2778 			ret = rb_handle_head_page(cpu_buffer,
2779 						  tail_page,
2780 						  next_page);
2781 			if (ret < 0)
2782 				goto out_reset;
2783 			if (ret)
2784 				goto out_again;
2785 		} else {
2786 			/*
2787 			 * We need to be careful here too. The
2788 			 * commit page could still be on the reader
2789 			 * page. We could have a small buffer, and
2790 			 * have filled up the buffer with events
2791 			 * from interrupts and such, and wrapped.
2792 			 *
2793 			 * Note, if the tail page is also on the
2794 			 * reader_page, we let it move out.
2795 			 */
2796 			if (unlikely((cpu_buffer->commit_page !=
2797 				      cpu_buffer->tail_page) &&
2798 				     (cpu_buffer->commit_page ==
2799 				      cpu_buffer->reader_page))) {
2800 				local_inc(&cpu_buffer->commit_overrun);
2801 				goto out_reset;
2802 			}
2803 		}
2804 	}
2805 
2806 	rb_tail_page_update(cpu_buffer, tail_page, next_page);
2807 
2808  out_again:
2809 
2810 	rb_reset_tail(cpu_buffer, tail, info);
2811 
2812 	/* Commit what we have for now. */
2813 	rb_end_commit(cpu_buffer);
2814 	/* rb_end_commit() decs committing */
2815 	local_inc(&cpu_buffer->committing);
2816 
2817 	/* fail and let the caller try again */
2818 	return ERR_PTR(-EAGAIN);
2819 
2820  out_reset:
2821 	/* reset write */
2822 	rb_reset_tail(cpu_buffer, tail, info);
2823 
2824 	return NULL;
2825 }
2826 
2827 /* Slow path */
2828 static struct ring_buffer_event *
rb_add_time_stamp(struct ring_buffer_event * event,u64 delta,bool abs)2829 rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
2830 {
2831 	if (abs)
2832 		event->type_len = RINGBUF_TYPE_TIME_STAMP;
2833 	else
2834 		event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2835 
2836 	/* Not the first event on the page, or not delta? */
2837 	if (abs || rb_event_index(event)) {
2838 		event->time_delta = delta & TS_MASK;
2839 		event->array[0] = delta >> TS_SHIFT;
2840 	} else {
2841 		/* nope, just zero it */
2842 		event->time_delta = 0;
2843 		event->array[0] = 0;
2844 	}
2845 
2846 	return skip_time_extend(event);
2847 }
2848 
2849 #ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
sched_clock_stable(void)2850 static inline bool sched_clock_stable(void)
2851 {
2852 	return true;
2853 }
2854 #endif
2855 
2856 static void
rb_check_timestamp(struct ring_buffer_per_cpu * cpu_buffer,struct rb_event_info * info)2857 rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2858 		   struct rb_event_info *info)
2859 {
2860 	u64 write_stamp;
2861 
2862 	WARN_ONCE(1, "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
2863 		  (unsigned long long)info->delta,
2864 		  (unsigned long long)info->ts,
2865 		  (unsigned long long)info->before,
2866 		  (unsigned long long)info->after,
2867 		  (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
2868 		  sched_clock_stable() ? "" :
2869 		  "If you just came from a suspend/resume,\n"
2870 		  "please switch to the trace global clock:\n"
2871 		  "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
2872 		  "or add trace_clock=global to the kernel command line\n");
2873 }
2874 
rb_add_timestamp(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event ** event,struct rb_event_info * info,u64 * delta,unsigned int * length)2875 static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2876 				      struct ring_buffer_event **event,
2877 				      struct rb_event_info *info,
2878 				      u64 *delta,
2879 				      unsigned int *length)
2880 {
2881 	bool abs = info->add_timestamp &
2882 		(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
2883 
2884 	if (unlikely(info->delta > (1ULL << 59))) {
2885 		/*
2886 		 * Some timers can use more than 59 bits, and when a timestamp
2887 		 * is added to the buffer, it will lose those bits.
2888 		 */
2889 		if (abs && (info->ts & TS_MSB)) {
2890 			info->delta &= ABS_TS_MASK;
2891 
2892 		/* did the clock go backwards */
2893 		} else if (info->before == info->after && info->before > info->ts) {
2894 			/* not interrupted */
2895 			static int once;
2896 
2897 			/*
2898 			 * This is possible with a recalibrating of the TSC.
2899 			 * Do not produce a call stack, but just report it.
2900 			 */
2901 			if (!once) {
2902 				once++;
2903 				pr_warn("Ring buffer clock went backwards: %llu -> %llu\n",
2904 					info->before, info->ts);
2905 			}
2906 		} else
2907 			rb_check_timestamp(cpu_buffer, info);
2908 		if (!abs)
2909 			info->delta = 0;
2910 	}
2911 	*event = rb_add_time_stamp(*event, info->delta, abs);
2912 	*length -= RB_LEN_TIME_EXTEND;
2913 	*delta = 0;
2914 }
2915 
2916 /**
2917  * rb_update_event - update event type and data
2918  * @cpu_buffer: The per cpu buffer of the @event
2919  * @event: the event to update
2920  * @info: The info to update the @event with (contains length and delta)
2921  *
2922  * Update the type and data fields of the @event. The length
2923  * is the actual size that is written to the ring buffer,
2924  * and with this, we can determine what to place into the
2925  * data field.
2926  */
2927 static void
rb_update_event(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event * event,struct rb_event_info * info)2928 rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2929 		struct ring_buffer_event *event,
2930 		struct rb_event_info *info)
2931 {
2932 	unsigned length = info->length;
2933 	u64 delta = info->delta;
2934 	unsigned int nest = local_read(&cpu_buffer->committing) - 1;
2935 
2936 	if (!WARN_ON_ONCE(nest >= MAX_NEST))
2937 		cpu_buffer->event_stamp[nest] = info->ts;
2938 
2939 	/*
2940 	 * If we need to add a timestamp, then we
2941 	 * add it to the start of the reserved space.
2942 	 */
2943 	if (unlikely(info->add_timestamp))
2944 		rb_add_timestamp(cpu_buffer, &event, info, &delta, &length);
2945 
2946 	event->time_delta = delta;
2947 	length -= RB_EVNT_HDR_SIZE;
2948 	if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2949 		event->type_len = 0;
2950 		event->array[0] = length;
2951 	} else
2952 		event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2953 }
2954 
rb_calculate_event_length(unsigned length)2955 static unsigned rb_calculate_event_length(unsigned length)
2956 {
2957 	struct ring_buffer_event event; /* Used only for sizeof array */
2958 
2959 	/* zero length can cause confusions */
2960 	if (!length)
2961 		length++;
2962 
2963 	if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2964 		length += sizeof(event.array[0]);
2965 
2966 	length += RB_EVNT_HDR_SIZE;
2967 	length = ALIGN(length, RB_ARCH_ALIGNMENT);
2968 
2969 	/*
2970 	 * In case the time delta is larger than the 27 bits for it
2971 	 * in the header, we need to add a timestamp. If another
2972 	 * event comes in when trying to discard this one to increase
2973 	 * the length, then the timestamp will be added in the allocated
2974 	 * space of this event. If length is bigger than the size needed
2975 	 * for the TIME_EXTEND, then padding has to be used. The events
2976 	 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2977 	 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2978 	 * As length is a multiple of 4, we only need to worry if it
2979 	 * is 12 (RB_LEN_TIME_EXTEND + 4).
2980 	 */
2981 	if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2982 		length += RB_ALIGNMENT;
2983 
2984 	return length;
2985 }
2986 
rb_time_delta(struct ring_buffer_event * event)2987 static u64 rb_time_delta(struct ring_buffer_event *event)
2988 {
2989 	switch (event->type_len) {
2990 	case RINGBUF_TYPE_PADDING:
2991 		return 0;
2992 
2993 	case RINGBUF_TYPE_TIME_EXTEND:
2994 		return rb_event_time_stamp(event);
2995 
2996 	case RINGBUF_TYPE_TIME_STAMP:
2997 		return 0;
2998 
2999 	case RINGBUF_TYPE_DATA:
3000 		return event->time_delta;
3001 	default:
3002 		return 0;
3003 	}
3004 }
3005 
3006 static inline int
rb_try_to_discard(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event * event)3007 rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
3008 		  struct ring_buffer_event *event)
3009 {
3010 	unsigned long new_index, old_index;
3011 	struct buffer_page *bpage;
3012 	unsigned long index;
3013 	unsigned long addr;
3014 	u64 write_stamp;
3015 	u64 delta;
3016 
3017 	new_index = rb_event_index(event);
3018 	old_index = new_index + rb_event_ts_length(event);
3019 	addr = (unsigned long)event;
3020 	addr &= PAGE_MASK;
3021 
3022 	bpage = READ_ONCE(cpu_buffer->tail_page);
3023 
3024 	delta = rb_time_delta(event);
3025 
3026 	if (!rb_time_read(&cpu_buffer->write_stamp, &write_stamp))
3027 		return 0;
3028 
3029 	/* Make sure the write stamp is read before testing the location */
3030 	barrier();
3031 
3032 	if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
3033 		unsigned long write_mask =
3034 			local_read(&bpage->write) & ~RB_WRITE_MASK;
3035 		unsigned long event_length = rb_event_length(event);
3036 
3037 		/* Something came in, can't discard */
3038 		if (!rb_time_cmpxchg(&cpu_buffer->write_stamp,
3039 				       write_stamp, write_stamp - delta))
3040 			return 0;
3041 
3042 		/*
3043 		 * It's possible that the event time delta is zero
3044 		 * (has the same time stamp as the previous event)
3045 		 * in which case write_stamp and before_stamp could
3046 		 * be the same. In such a case, force before_stamp
3047 		 * to be different than write_stamp. It doesn't
3048 		 * matter what it is, as long as its different.
3049 		 */
3050 		if (!delta)
3051 			rb_time_set(&cpu_buffer->before_stamp, 0);
3052 
3053 		/*
3054 		 * If an event were to come in now, it would see that the
3055 		 * write_stamp and the before_stamp are different, and assume
3056 		 * that this event just added itself before updating
3057 		 * the write stamp. The interrupting event will fix the
3058 		 * write stamp for us, and use the before stamp as its delta.
3059 		 */
3060 
3061 		/*
3062 		 * This is on the tail page. It is possible that
3063 		 * a write could come in and move the tail page
3064 		 * and write to the next page. That is fine
3065 		 * because we just shorten what is on this page.
3066 		 */
3067 		old_index += write_mask;
3068 		new_index += write_mask;
3069 		index = local_cmpxchg(&bpage->write, old_index, new_index);
3070 		if (index == old_index) {
3071 			/* update counters */
3072 			local_sub(event_length, &cpu_buffer->entries_bytes);
3073 			return 1;
3074 		}
3075 	}
3076 
3077 	/* could not discard */
3078 	return 0;
3079 }
3080 
rb_start_commit(struct ring_buffer_per_cpu * cpu_buffer)3081 static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
3082 {
3083 	local_inc(&cpu_buffer->committing);
3084 	local_inc(&cpu_buffer->commits);
3085 }
3086 
3087 static __always_inline void
rb_set_commit_to_write(struct ring_buffer_per_cpu * cpu_buffer)3088 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
3089 {
3090 	unsigned long max_count;
3091 
3092 	/*
3093 	 * We only race with interrupts and NMIs on this CPU.
3094 	 * If we own the commit event, then we can commit
3095 	 * all others that interrupted us, since the interruptions
3096 	 * are in stack format (they finish before they come
3097 	 * back to us). This allows us to do a simple loop to
3098 	 * assign the commit to the tail.
3099 	 */
3100  again:
3101 	max_count = cpu_buffer->nr_pages * 100;
3102 
3103 	while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
3104 		if (RB_WARN_ON(cpu_buffer, !(--max_count)))
3105 			return;
3106 		if (RB_WARN_ON(cpu_buffer,
3107 			       rb_is_reader_page(cpu_buffer->tail_page)))
3108 			return;
3109 		local_set(&cpu_buffer->commit_page->page->commit,
3110 			  rb_page_write(cpu_buffer->commit_page));
3111 		rb_inc_page(&cpu_buffer->commit_page);
3112 		/* add barrier to keep gcc from optimizing too much */
3113 		barrier();
3114 	}
3115 	while (rb_commit_index(cpu_buffer) !=
3116 	       rb_page_write(cpu_buffer->commit_page)) {
3117 
3118 		local_set(&cpu_buffer->commit_page->page->commit,
3119 			  rb_page_write(cpu_buffer->commit_page));
3120 		RB_WARN_ON(cpu_buffer,
3121 			   local_read(&cpu_buffer->commit_page->page->commit) &
3122 			   ~RB_WRITE_MASK);
3123 		barrier();
3124 	}
3125 
3126 	/* again, keep gcc from optimizing */
3127 	barrier();
3128 
3129 	/*
3130 	 * If an interrupt came in just after the first while loop
3131 	 * and pushed the tail page forward, we will be left with
3132 	 * a dangling commit that will never go forward.
3133 	 */
3134 	if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
3135 		goto again;
3136 }
3137 
rb_end_commit(struct ring_buffer_per_cpu * cpu_buffer)3138 static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
3139 {
3140 	unsigned long commits;
3141 
3142 	if (RB_WARN_ON(cpu_buffer,
3143 		       !local_read(&cpu_buffer->committing)))
3144 		return;
3145 
3146  again:
3147 	commits = local_read(&cpu_buffer->commits);
3148 	/* synchronize with interrupts */
3149 	barrier();
3150 	if (local_read(&cpu_buffer->committing) == 1)
3151 		rb_set_commit_to_write(cpu_buffer);
3152 
3153 	local_dec(&cpu_buffer->committing);
3154 
3155 	/* synchronize with interrupts */
3156 	barrier();
3157 
3158 	/*
3159 	 * Need to account for interrupts coming in between the
3160 	 * updating of the commit page and the clearing of the
3161 	 * committing counter.
3162 	 */
3163 	if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
3164 	    !local_read(&cpu_buffer->committing)) {
3165 		local_inc(&cpu_buffer->committing);
3166 		goto again;
3167 	}
3168 }
3169 
rb_event_discard(struct ring_buffer_event * event)3170 static inline void rb_event_discard(struct ring_buffer_event *event)
3171 {
3172 	if (extended_time(event))
3173 		event = skip_time_extend(event);
3174 
3175 	/* array[0] holds the actual length for the discarded event */
3176 	event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
3177 	event->type_len = RINGBUF_TYPE_PADDING;
3178 	/* time delta must be non zero */
3179 	if (!event->time_delta)
3180 		event->time_delta = 1;
3181 }
3182 
rb_commit(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event * event)3183 static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
3184 		      struct ring_buffer_event *event)
3185 {
3186 	local_inc(&cpu_buffer->entries);
3187 	rb_end_commit(cpu_buffer);
3188 }
3189 
3190 static __always_inline void
rb_wakeups(struct trace_buffer * buffer,struct ring_buffer_per_cpu * cpu_buffer)3191 rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
3192 {
3193 	if (buffer->irq_work.waiters_pending) {
3194 		buffer->irq_work.waiters_pending = false;
3195 		/* irq_work_queue() supplies it's own memory barriers */
3196 		irq_work_queue(&buffer->irq_work.work);
3197 	}
3198 
3199 	if (cpu_buffer->irq_work.waiters_pending) {
3200 		cpu_buffer->irq_work.waiters_pending = false;
3201 		/* irq_work_queue() supplies it's own memory barriers */
3202 		irq_work_queue(&cpu_buffer->irq_work.work);
3203 	}
3204 
3205 	if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
3206 		return;
3207 
3208 	if (cpu_buffer->reader_page == cpu_buffer->commit_page)
3209 		return;
3210 
3211 	if (!cpu_buffer->irq_work.full_waiters_pending)
3212 		return;
3213 
3214 	cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
3215 
3216 	if (!full_hit(buffer, cpu_buffer->cpu, cpu_buffer->shortest_full))
3217 		return;
3218 
3219 	cpu_buffer->irq_work.wakeup_full = true;
3220 	cpu_buffer->irq_work.full_waiters_pending = false;
3221 	/* irq_work_queue() supplies it's own memory barriers */
3222 	irq_work_queue(&cpu_buffer->irq_work.work);
3223 }
3224 
3225 #ifdef CONFIG_RING_BUFFER_RECORD_RECURSION
3226 # define do_ring_buffer_record_recursion()	\
3227 	do_ftrace_record_recursion(_THIS_IP_, _RET_IP_)
3228 #else
3229 # define do_ring_buffer_record_recursion() do { } while (0)
3230 #endif
3231 
3232 /*
3233  * The lock and unlock are done within a preempt disable section.
3234  * The current_context per_cpu variable can only be modified
3235  * by the current task between lock and unlock. But it can
3236  * be modified more than once via an interrupt. To pass this
3237  * information from the lock to the unlock without having to
3238  * access the 'in_interrupt()' functions again (which do show
3239  * a bit of overhead in something as critical as function tracing,
3240  * we use a bitmask trick.
3241  *
3242  *  bit 1 =  NMI context
3243  *  bit 2 =  IRQ context
3244  *  bit 3 =  SoftIRQ context
3245  *  bit 4 =  normal context.
3246  *
3247  * This works because this is the order of contexts that can
3248  * preempt other contexts. A SoftIRQ never preempts an IRQ
3249  * context.
3250  *
3251  * When the context is determined, the corresponding bit is
3252  * checked and set (if it was set, then a recursion of that context
3253  * happened).
3254  *
3255  * On unlock, we need to clear this bit. To do so, just subtract
3256  * 1 from the current_context and AND it to itself.
3257  *
3258  * (binary)
3259  *  101 - 1 = 100
3260  *  101 & 100 = 100 (clearing bit zero)
3261  *
3262  *  1010 - 1 = 1001
3263  *  1010 & 1001 = 1000 (clearing bit 1)
3264  *
3265  * The least significant bit can be cleared this way, and it
3266  * just so happens that it is the same bit corresponding to
3267  * the current context.
3268  *
3269  * Now the TRANSITION bit breaks the above slightly. The TRANSITION bit
3270  * is set when a recursion is detected at the current context, and if
3271  * the TRANSITION bit is already set, it will fail the recursion.
3272  * This is needed because there's a lag between the changing of
3273  * interrupt context and updating the preempt count. In this case,
3274  * a false positive will be found. To handle this, one extra recursion
3275  * is allowed, and this is done by the TRANSITION bit. If the TRANSITION
3276  * bit is already set, then it is considered a recursion and the function
3277  * ends. Otherwise, the TRANSITION bit is set, and that bit is returned.
3278  *
3279  * On the trace_recursive_unlock(), the TRANSITION bit will be the first
3280  * to be cleared. Even if it wasn't the context that set it. That is,
3281  * if an interrupt comes in while NORMAL bit is set and the ring buffer
3282  * is called before preempt_count() is updated, since the check will
3283  * be on the NORMAL bit, the TRANSITION bit will then be set. If an
3284  * NMI then comes in, it will set the NMI bit, but when the NMI code
3285  * does the trace_recursive_unlock() it will clear the TRANSITION bit
3286  * and leave the NMI bit set. But this is fine, because the interrupt
3287  * code that set the TRANSITION bit will then clear the NMI bit when it
3288  * calls trace_recursive_unlock(). If another NMI comes in, it will
3289  * set the TRANSITION bit and continue.
3290  *
3291  * Note: The TRANSITION bit only handles a single transition between context.
3292  */
3293 
3294 static __always_inline int
trace_recursive_lock(struct ring_buffer_per_cpu * cpu_buffer)3295 trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
3296 {
3297 	unsigned int val = cpu_buffer->current_context;
3298 	int bit = interrupt_context_level();
3299 
3300 	bit = RB_CTX_NORMAL - bit;
3301 
3302 	if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {
3303 		/*
3304 		 * It is possible that this was called by transitioning
3305 		 * between interrupt context, and preempt_count() has not
3306 		 * been updated yet. In this case, use the TRANSITION bit.
3307 		 */
3308 		bit = RB_CTX_TRANSITION;
3309 		if (val & (1 << (bit + cpu_buffer->nest))) {
3310 			do_ring_buffer_record_recursion();
3311 			return 1;
3312 		}
3313 	}
3314 
3315 	val |= (1 << (bit + cpu_buffer->nest));
3316 	cpu_buffer->current_context = val;
3317 
3318 	return 0;
3319 }
3320 
3321 static __always_inline void
trace_recursive_unlock(struct ring_buffer_per_cpu * cpu_buffer)3322 trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
3323 {
3324 	cpu_buffer->current_context &=
3325 		cpu_buffer->current_context - (1 << cpu_buffer->nest);
3326 }
3327 
3328 /* The recursive locking above uses 5 bits */
3329 #define NESTED_BITS 5
3330 
3331 /**
3332  * ring_buffer_nest_start - Allow to trace while nested
3333  * @buffer: The ring buffer to modify
3334  *
3335  * The ring buffer has a safety mechanism to prevent recursion.
3336  * But there may be a case where a trace needs to be done while
3337  * tracing something else. In this case, calling this function
3338  * will allow this function to nest within a currently active
3339  * ring_buffer_lock_reserve().
3340  *
3341  * Call this function before calling another ring_buffer_lock_reserve() and
3342  * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
3343  */
ring_buffer_nest_start(struct trace_buffer * buffer)3344 void ring_buffer_nest_start(struct trace_buffer *buffer)
3345 {
3346 	struct ring_buffer_per_cpu *cpu_buffer;
3347 	int cpu;
3348 
3349 	/* Enabled by ring_buffer_nest_end() */
3350 	preempt_disable_notrace();
3351 	cpu = raw_smp_processor_id();
3352 	cpu_buffer = buffer->buffers[cpu];
3353 	/* This is the shift value for the above recursive locking */
3354 	cpu_buffer->nest += NESTED_BITS;
3355 }
3356 
3357 /**
3358  * ring_buffer_nest_end - Allow to trace while nested
3359  * @buffer: The ring buffer to modify
3360  *
3361  * Must be called after ring_buffer_nest_start() and after the
3362  * ring_buffer_unlock_commit().
3363  */
ring_buffer_nest_end(struct trace_buffer * buffer)3364 void ring_buffer_nest_end(struct trace_buffer *buffer)
3365 {
3366 	struct ring_buffer_per_cpu *cpu_buffer;
3367 	int cpu;
3368 
3369 	/* disabled by ring_buffer_nest_start() */
3370 	cpu = raw_smp_processor_id();
3371 	cpu_buffer = buffer->buffers[cpu];
3372 	/* This is the shift value for the above recursive locking */
3373 	cpu_buffer->nest -= NESTED_BITS;
3374 	preempt_enable_notrace();
3375 }
3376 
3377 /**
3378  * ring_buffer_unlock_commit - commit a reserved
3379  * @buffer: The buffer to commit to
3380  * @event: The event pointer to commit.
3381  *
3382  * This commits the data to the ring buffer, and releases any locks held.
3383  *
3384  * Must be paired with ring_buffer_lock_reserve.
3385  */
ring_buffer_unlock_commit(struct trace_buffer * buffer,struct ring_buffer_event * event)3386 int ring_buffer_unlock_commit(struct trace_buffer *buffer,
3387 			      struct ring_buffer_event *event)
3388 {
3389 	struct ring_buffer_per_cpu *cpu_buffer;
3390 	int cpu = raw_smp_processor_id();
3391 
3392 	cpu_buffer = buffer->buffers[cpu];
3393 
3394 	rb_commit(cpu_buffer, event);
3395 
3396 	rb_wakeups(buffer, cpu_buffer);
3397 
3398 	trace_recursive_unlock(cpu_buffer);
3399 
3400 	preempt_enable_notrace();
3401 
3402 	return 0;
3403 }
3404 EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
3405 
3406 /* Special value to validate all deltas on a page. */
3407 #define CHECK_FULL_PAGE		1L
3408 
3409 #ifdef CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS
dump_buffer_page(struct buffer_data_page * bpage,struct rb_event_info * info,unsigned long tail)3410 static void dump_buffer_page(struct buffer_data_page *bpage,
3411 			     struct rb_event_info *info,
3412 			     unsigned long tail)
3413 {
3414 	struct ring_buffer_event *event;
3415 	u64 ts, delta;
3416 	int e;
3417 
3418 	ts = bpage->time_stamp;
3419 	pr_warn("  [%lld] PAGE TIME STAMP\n", ts);
3420 
3421 	for (e = 0; e < tail; e += rb_event_length(event)) {
3422 
3423 		event = (struct ring_buffer_event *)(bpage->data + e);
3424 
3425 		switch (event->type_len) {
3426 
3427 		case RINGBUF_TYPE_TIME_EXTEND:
3428 			delta = rb_event_time_stamp(event);
3429 			ts += delta;
3430 			pr_warn("  [%lld] delta:%lld TIME EXTEND\n", ts, delta);
3431 			break;
3432 
3433 		case RINGBUF_TYPE_TIME_STAMP:
3434 			delta = rb_event_time_stamp(event);
3435 			ts = rb_fix_abs_ts(delta, ts);
3436 			pr_warn("  [%lld] absolute:%lld TIME STAMP\n", ts, delta);
3437 			break;
3438 
3439 		case RINGBUF_TYPE_PADDING:
3440 			ts += event->time_delta;
3441 			pr_warn("  [%lld] delta:%d PADDING\n", ts, event->time_delta);
3442 			break;
3443 
3444 		case RINGBUF_TYPE_DATA:
3445 			ts += event->time_delta;
3446 			pr_warn("  [%lld] delta:%d\n", ts, event->time_delta);
3447 			break;
3448 
3449 		default:
3450 			break;
3451 		}
3452 	}
3453 }
3454 
3455 static DEFINE_PER_CPU(atomic_t, checking);
3456 static atomic_t ts_dump;
3457 
3458 /*
3459  * Check if the current event time stamp matches the deltas on
3460  * the buffer page.
3461  */
check_buffer(struct ring_buffer_per_cpu * cpu_buffer,struct rb_event_info * info,unsigned long tail)3462 static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
3463 			 struct rb_event_info *info,
3464 			 unsigned long tail)
3465 {
3466 	struct ring_buffer_event *event;
3467 	struct buffer_data_page *bpage;
3468 	u64 ts, delta;
3469 	bool full = false;
3470 	int e;
3471 
3472 	bpage = info->tail_page->page;
3473 
3474 	if (tail == CHECK_FULL_PAGE) {
3475 		full = true;
3476 		tail = local_read(&bpage->commit);
3477 	} else if (info->add_timestamp &
3478 		   (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
3479 		/* Ignore events with absolute time stamps */
3480 		return;
3481 	}
3482 
3483 	/*
3484 	 * Do not check the first event (skip possible extends too).
3485 	 * Also do not check if previous events have not been committed.
3486 	 */
3487 	if (tail <= 8 || tail > local_read(&bpage->commit))
3488 		return;
3489 
3490 	/*
3491 	 * If this interrupted another event,
3492 	 */
3493 	if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
3494 		goto out;
3495 
3496 	ts = bpage->time_stamp;
3497 
3498 	for (e = 0; e < tail; e += rb_event_length(event)) {
3499 
3500 		event = (struct ring_buffer_event *)(bpage->data + e);
3501 
3502 		switch (event->type_len) {
3503 
3504 		case RINGBUF_TYPE_TIME_EXTEND:
3505 			delta = rb_event_time_stamp(event);
3506 			ts += delta;
3507 			break;
3508 
3509 		case RINGBUF_TYPE_TIME_STAMP:
3510 			delta = rb_event_time_stamp(event);
3511 			ts = rb_fix_abs_ts(delta, ts);
3512 			break;
3513 
3514 		case RINGBUF_TYPE_PADDING:
3515 			if (event->time_delta == 1)
3516 				break;
3517 			fallthrough;
3518 		case RINGBUF_TYPE_DATA:
3519 			ts += event->time_delta;
3520 			break;
3521 
3522 		default:
3523 			RB_WARN_ON(cpu_buffer, 1);
3524 		}
3525 	}
3526 	if ((full && ts > info->ts) ||
3527 	    (!full && ts + info->delta != info->ts)) {
3528 		/* If another report is happening, ignore this one */
3529 		if (atomic_inc_return(&ts_dump) != 1) {
3530 			atomic_dec(&ts_dump);
3531 			goto out;
3532 		}
3533 		atomic_inc(&cpu_buffer->record_disabled);
3534 		/* There's some cases in boot up that this can happen */
3535 		WARN_ON_ONCE(system_state != SYSTEM_BOOTING);
3536 		pr_warn("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s\n",
3537 			cpu_buffer->cpu,
3538 			ts + info->delta, info->ts, info->delta,
3539 			info->before, info->after,
3540 			full ? " (full)" : "");
3541 		dump_buffer_page(bpage, info, tail);
3542 		atomic_dec(&ts_dump);
3543 		/* Do not re-enable checking */
3544 		return;
3545 	}
3546 out:
3547 	atomic_dec(this_cpu_ptr(&checking));
3548 }
3549 #else
check_buffer(struct ring_buffer_per_cpu * cpu_buffer,struct rb_event_info * info,unsigned long tail)3550 static inline void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
3551 			 struct rb_event_info *info,
3552 			 unsigned long tail)
3553 {
3554 }
3555 #endif /* CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS */
3556 
3557 static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu * cpu_buffer,struct rb_event_info * info)3558 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
3559 		  struct rb_event_info *info)
3560 {
3561 	struct ring_buffer_event *event;
3562 	struct buffer_page *tail_page;
3563 	unsigned long tail, write, w;
3564 	bool a_ok;
3565 	bool b_ok;
3566 
3567 	/* Don't let the compiler play games with cpu_buffer->tail_page */
3568 	tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
3569 
3570  /*A*/	w = local_read(&tail_page->write) & RB_WRITE_MASK;
3571 	barrier();
3572 	b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
3573 	a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3574 	barrier();
3575 	info->ts = rb_time_stamp(cpu_buffer->buffer);
3576 
3577 	if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
3578 		info->delta = info->ts;
3579 	} else {
3580 		/*
3581 		 * If interrupting an event time update, we may need an
3582 		 * absolute timestamp.
3583 		 * Don't bother if this is the start of a new page (w == 0).
3584 		 */
3585 		if (unlikely(!a_ok || !b_ok || (info->before != info->after && w))) {
3586 			info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
3587 			info->length += RB_LEN_TIME_EXTEND;
3588 		} else {
3589 			info->delta = info->ts - info->after;
3590 			if (unlikely(test_time_stamp(info->delta))) {
3591 				info->add_timestamp |= RB_ADD_STAMP_EXTEND;
3592 				info->length += RB_LEN_TIME_EXTEND;
3593 			}
3594 		}
3595 	}
3596 
3597  /*B*/	rb_time_set(&cpu_buffer->before_stamp, info->ts);
3598 
3599  /*C*/	write = local_add_return(info->length, &tail_page->write);
3600 
3601 	/* set write to only the index of the write */
3602 	write &= RB_WRITE_MASK;
3603 
3604 	tail = write - info->length;
3605 
3606 	/* See if we shot pass the end of this buffer page */
3607 	if (unlikely(write > BUF_PAGE_SIZE)) {
3608 		/* before and after may now different, fix it up*/
3609 		b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
3610 		a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3611 		if (a_ok && b_ok && info->before != info->after)
3612 			(void)rb_time_cmpxchg(&cpu_buffer->before_stamp,
3613 					      info->before, info->after);
3614 		if (a_ok && b_ok)
3615 			check_buffer(cpu_buffer, info, CHECK_FULL_PAGE);
3616 		return rb_move_tail(cpu_buffer, tail, info);
3617 	}
3618 
3619 	if (likely(tail == w)) {
3620 		u64 save_before;
3621 		bool s_ok;
3622 
3623 		/* Nothing interrupted us between A and C */
3624  /*D*/		rb_time_set(&cpu_buffer->write_stamp, info->ts);
3625 		barrier();
3626  /*E*/		s_ok = rb_time_read(&cpu_buffer->before_stamp, &save_before);
3627 		RB_WARN_ON(cpu_buffer, !s_ok);
3628 		if (likely(!(info->add_timestamp &
3629 			     (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
3630 			/* This did not interrupt any time update */
3631 			info->delta = info->ts - info->after;
3632 		else
3633 			/* Just use full timestamp for interrupting event */
3634 			info->delta = info->ts;
3635 		barrier();
3636 		check_buffer(cpu_buffer, info, tail);
3637 		if (unlikely(info->ts != save_before)) {
3638 			/* SLOW PATH - Interrupted between C and E */
3639 
3640 			a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3641 			RB_WARN_ON(cpu_buffer, !a_ok);
3642 
3643 			/* Write stamp must only go forward */
3644 			if (save_before > info->after) {
3645 				/*
3646 				 * We do not care about the result, only that
3647 				 * it gets updated atomically.
3648 				 */
3649 				(void)rb_time_cmpxchg(&cpu_buffer->write_stamp,
3650 						      info->after, save_before);
3651 			}
3652 		}
3653 	} else {
3654 		u64 ts;
3655 		/* SLOW PATH - Interrupted between A and C */
3656 		a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3657 		/* Was interrupted before here, write_stamp must be valid */
3658 		RB_WARN_ON(cpu_buffer, !a_ok);
3659 		ts = rb_time_stamp(cpu_buffer->buffer);
3660 		barrier();
3661  /*E*/		if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
3662 		    info->after < ts &&
3663 		    rb_time_cmpxchg(&cpu_buffer->write_stamp,
3664 				    info->after, ts)) {
3665 			/* Nothing came after this event between C and E */
3666 			info->delta = ts - info->after;
3667 		} else {
3668 			/*
3669 			 * Interrupted between C and E:
3670 			 * Lost the previous events time stamp. Just set the
3671 			 * delta to zero, and this will be the same time as
3672 			 * the event this event interrupted. And the events that
3673 			 * came after this will still be correct (as they would
3674 			 * have built their delta on the previous event.
3675 			 */
3676 			info->delta = 0;
3677 		}
3678 		info->ts = ts;
3679 		info->add_timestamp &= ~RB_ADD_STAMP_FORCE;
3680 	}
3681 
3682 	/*
3683 	 * If this is the first commit on the page, then it has the same
3684 	 * timestamp as the page itself.
3685 	 */
3686 	if (unlikely(!tail && !(info->add_timestamp &
3687 				(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
3688 		info->delta = 0;
3689 
3690 	/* We reserved something on the buffer */
3691 
3692 	event = __rb_page_index(tail_page, tail);
3693 	rb_update_event(cpu_buffer, event, info);
3694 
3695 	local_inc(&tail_page->entries);
3696 
3697 	/*
3698 	 * If this is the first commit on the page, then update
3699 	 * its timestamp.
3700 	 */
3701 	if (unlikely(!tail))
3702 		tail_page->page->time_stamp = info->ts;
3703 
3704 	/* account for these added bytes */
3705 	local_add(info->length, &cpu_buffer->entries_bytes);
3706 
3707 	return event;
3708 }
3709 
3710 static __always_inline struct ring_buffer_event *
rb_reserve_next_event(struct trace_buffer * buffer,struct ring_buffer_per_cpu * cpu_buffer,unsigned long length)3711 rb_reserve_next_event(struct trace_buffer *buffer,
3712 		      struct ring_buffer_per_cpu *cpu_buffer,
3713 		      unsigned long length)
3714 {
3715 	struct ring_buffer_event *event;
3716 	struct rb_event_info info;
3717 	int nr_loops = 0;
3718 	int add_ts_default;
3719 
3720 	rb_start_commit(cpu_buffer);
3721 	/* The commit page can not change after this */
3722 
3723 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
3724 	/*
3725 	 * Due to the ability to swap a cpu buffer from a buffer
3726 	 * it is possible it was swapped before we committed.
3727 	 * (committing stops a swap). We check for it here and
3728 	 * if it happened, we have to fail the write.
3729 	 */
3730 	barrier();
3731 	if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
3732 		local_dec(&cpu_buffer->committing);
3733 		local_dec(&cpu_buffer->commits);
3734 		return NULL;
3735 	}
3736 #endif
3737 
3738 	info.length = rb_calculate_event_length(length);
3739 
3740 	if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
3741 		add_ts_default = RB_ADD_STAMP_ABSOLUTE;
3742 		info.length += RB_LEN_TIME_EXTEND;
3743 	} else {
3744 		add_ts_default = RB_ADD_STAMP_NONE;
3745 	}
3746 
3747  again:
3748 	info.add_timestamp = add_ts_default;
3749 	info.delta = 0;
3750 
3751 	/*
3752 	 * We allow for interrupts to reenter here and do a trace.
3753 	 * If one does, it will cause this original code to loop
3754 	 * back here. Even with heavy interrupts happening, this
3755 	 * should only happen a few times in a row. If this happens
3756 	 * 1000 times in a row, there must be either an interrupt
3757 	 * storm or we have something buggy.
3758 	 * Bail!
3759 	 */
3760 	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
3761 		goto out_fail;
3762 
3763 	event = __rb_reserve_next(cpu_buffer, &info);
3764 
3765 	if (unlikely(PTR_ERR(event) == -EAGAIN)) {
3766 		if (info.add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND))
3767 			info.length -= RB_LEN_TIME_EXTEND;
3768 		goto again;
3769 	}
3770 
3771 	if (likely(event))
3772 		return event;
3773  out_fail:
3774 	rb_end_commit(cpu_buffer);
3775 	return NULL;
3776 }
3777 
3778 /**
3779  * ring_buffer_lock_reserve - reserve a part of the buffer
3780  * @buffer: the ring buffer to reserve from
3781  * @length: the length of the data to reserve (excluding event header)
3782  *
3783  * Returns a reserved event on the ring buffer to copy directly to.
3784  * The user of this interface will need to get the body to write into
3785  * and can use the ring_buffer_event_data() interface.
3786  *
3787  * The length is the length of the data needed, not the event length
3788  * which also includes the event header.
3789  *
3790  * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
3791  * If NULL is returned, then nothing has been allocated or locked.
3792  */
3793 struct ring_buffer_event *
ring_buffer_lock_reserve(struct trace_buffer * buffer,unsigned long length)3794 ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length)
3795 {
3796 	struct ring_buffer_per_cpu *cpu_buffer;
3797 	struct ring_buffer_event *event;
3798 	int cpu;
3799 
3800 	/* If we are tracing schedule, we don't want to recurse */
3801 	preempt_disable_notrace();
3802 
3803 	if (unlikely(atomic_read(&buffer->record_disabled)))
3804 		goto out;
3805 
3806 	cpu = raw_smp_processor_id();
3807 
3808 	if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
3809 		goto out;
3810 
3811 	cpu_buffer = buffer->buffers[cpu];
3812 
3813 	if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
3814 		goto out;
3815 
3816 	if (unlikely(length > BUF_MAX_DATA_SIZE))
3817 		goto out;
3818 
3819 	if (unlikely(trace_recursive_lock(cpu_buffer)))
3820 		goto out;
3821 
3822 	event = rb_reserve_next_event(buffer, cpu_buffer, length);
3823 	if (!event)
3824 		goto out_unlock;
3825 
3826 	return event;
3827 
3828  out_unlock:
3829 	trace_recursive_unlock(cpu_buffer);
3830  out:
3831 	preempt_enable_notrace();
3832 	return NULL;
3833 }
3834 EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
3835 
3836 /*
3837  * Decrement the entries to the page that an event is on.
3838  * The event does not even need to exist, only the pointer
3839  * to the page it is on. This may only be called before the commit
3840  * takes place.
3841  */
3842 static inline void
rb_decrement_entry(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event * event)3843 rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
3844 		   struct ring_buffer_event *event)
3845 {
3846 	unsigned long addr = (unsigned long)event;
3847 	struct buffer_page *bpage = cpu_buffer->commit_page;
3848 	struct buffer_page *start;
3849 
3850 	addr &= PAGE_MASK;
3851 
3852 	/* Do the likely case first */
3853 	if (likely(bpage->page == (void *)addr)) {
3854 		local_dec(&bpage->entries);
3855 		return;
3856 	}
3857 
3858 	/*
3859 	 * Because the commit page may be on the reader page we
3860 	 * start with the next page and check the end loop there.
3861 	 */
3862 	rb_inc_page(&bpage);
3863 	start = bpage;
3864 	do {
3865 		if (bpage->page == (void *)addr) {
3866 			local_dec(&bpage->entries);
3867 			return;
3868 		}
3869 		rb_inc_page(&bpage);
3870 	} while (bpage != start);
3871 
3872 	/* commit not part of this buffer?? */
3873 	RB_WARN_ON(cpu_buffer, 1);
3874 }
3875 
3876 /**
3877  * ring_buffer_discard_commit - discard an event that has not been committed
3878  * @buffer: the ring buffer
3879  * @event: non committed event to discard
3880  *
3881  * Sometimes an event that is in the ring buffer needs to be ignored.
3882  * This function lets the user discard an event in the ring buffer
3883  * and then that event will not be read later.
3884  *
3885  * This function only works if it is called before the item has been
3886  * committed. It will try to free the event from the ring buffer
3887  * if another event has not been added behind it.
3888  *
3889  * If another event has been added behind it, it will set the event
3890  * up as discarded, and perform the commit.
3891  *
3892  * If this function is called, do not call ring_buffer_unlock_commit on
3893  * the event.
3894  */
ring_buffer_discard_commit(struct trace_buffer * buffer,struct ring_buffer_event * event)3895 void ring_buffer_discard_commit(struct trace_buffer *buffer,
3896 				struct ring_buffer_event *event)
3897 {
3898 	struct ring_buffer_per_cpu *cpu_buffer;
3899 	int cpu;
3900 
3901 	/* The event is discarded regardless */
3902 	rb_event_discard(event);
3903 
3904 	cpu = smp_processor_id();
3905 	cpu_buffer = buffer->buffers[cpu];
3906 
3907 	/*
3908 	 * This must only be called if the event has not been
3909 	 * committed yet. Thus we can assume that preemption
3910 	 * is still disabled.
3911 	 */
3912 	RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
3913 
3914 	rb_decrement_entry(cpu_buffer, event);
3915 	if (rb_try_to_discard(cpu_buffer, event))
3916 		goto out;
3917 
3918  out:
3919 	rb_end_commit(cpu_buffer);
3920 
3921 	trace_recursive_unlock(cpu_buffer);
3922 
3923 	preempt_enable_notrace();
3924 
3925 }
3926 EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
3927 
3928 /**
3929  * ring_buffer_write - write data to the buffer without reserving
3930  * @buffer: The ring buffer to write to.
3931  * @length: The length of the data being written (excluding the event header)
3932  * @data: The data to write to the buffer.
3933  *
3934  * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
3935  * one function. If you already have the data to write to the buffer, it
3936  * may be easier to simply call this function.
3937  *
3938  * Note, like ring_buffer_lock_reserve, the length is the length of the data
3939  * and not the length of the event which would hold the header.
3940  */
ring_buffer_write(struct trace_buffer * buffer,unsigned long length,void * data)3941 int ring_buffer_write(struct trace_buffer *buffer,
3942 		      unsigned long length,
3943 		      void *data)
3944 {
3945 	struct ring_buffer_per_cpu *cpu_buffer;
3946 	struct ring_buffer_event *event;
3947 	void *body;
3948 	int ret = -EBUSY;
3949 	int cpu;
3950 
3951 	preempt_disable_notrace();
3952 
3953 	if (atomic_read(&buffer->record_disabled))
3954 		goto out;
3955 
3956 	cpu = raw_smp_processor_id();
3957 
3958 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
3959 		goto out;
3960 
3961 	cpu_buffer = buffer->buffers[cpu];
3962 
3963 	if (atomic_read(&cpu_buffer->record_disabled))
3964 		goto out;
3965 
3966 	if (length > BUF_MAX_DATA_SIZE)
3967 		goto out;
3968 
3969 	if (unlikely(trace_recursive_lock(cpu_buffer)))
3970 		goto out;
3971 
3972 	event = rb_reserve_next_event(buffer, cpu_buffer, length);
3973 	if (!event)
3974 		goto out_unlock;
3975 
3976 	body = rb_event_data(event);
3977 
3978 	memcpy(body, data, length);
3979 
3980 	rb_commit(cpu_buffer, event);
3981 
3982 	rb_wakeups(buffer, cpu_buffer);
3983 
3984 	ret = 0;
3985 
3986  out_unlock:
3987 	trace_recursive_unlock(cpu_buffer);
3988 
3989  out:
3990 	preempt_enable_notrace();
3991 
3992 	return ret;
3993 }
3994 EXPORT_SYMBOL_GPL(ring_buffer_write);
3995 
rb_per_cpu_empty(struct ring_buffer_per_cpu * cpu_buffer)3996 static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3997 {
3998 	struct buffer_page *reader = cpu_buffer->reader_page;
3999 	struct buffer_page *head = rb_set_head_page(cpu_buffer);
4000 	struct buffer_page *commit = cpu_buffer->commit_page;
4001 
4002 	/* In case of error, head will be NULL */
4003 	if (unlikely(!head))
4004 		return true;
4005 
4006 	/* Reader should exhaust content in reader page */
4007 	if (reader->read != rb_page_commit(reader))
4008 		return false;
4009 
4010 	/*
4011 	 * If writers are committing on the reader page, knowing all
4012 	 * committed content has been read, the ring buffer is empty.
4013 	 */
4014 	if (commit == reader)
4015 		return true;
4016 
4017 	/*
4018 	 * If writers are committing on a page other than reader page
4019 	 * and head page, there should always be content to read.
4020 	 */
4021 	if (commit != head)
4022 		return false;
4023 
4024 	/*
4025 	 * Writers are committing on the head page, we just need
4026 	 * to care about there're committed data, and the reader will
4027 	 * swap reader page with head page when it is to read data.
4028 	 */
4029 	return rb_page_commit(commit) == 0;
4030 }
4031 
4032 /**
4033  * ring_buffer_record_disable - stop all writes into the buffer
4034  * @buffer: The ring buffer to stop writes to.
4035  *
4036  * This prevents all writes to the buffer. Any attempt to write
4037  * to the buffer after this will fail and return NULL.
4038  *
4039  * The caller should call synchronize_rcu() after this.
4040  */
ring_buffer_record_disable(struct trace_buffer * buffer)4041 void ring_buffer_record_disable(struct trace_buffer *buffer)
4042 {
4043 	atomic_inc(&buffer->record_disabled);
4044 }
4045 EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
4046 
4047 /**
4048  * ring_buffer_record_enable - enable writes to the buffer
4049  * @buffer: The ring buffer to enable writes
4050  *
4051  * Note, multiple disables will need the same number of enables
4052  * to truly enable the writing (much like preempt_disable).
4053  */
ring_buffer_record_enable(struct trace_buffer * buffer)4054 void ring_buffer_record_enable(struct trace_buffer *buffer)
4055 {
4056 	atomic_dec(&buffer->record_disabled);
4057 }
4058 EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
4059 
4060 /**
4061  * ring_buffer_record_off - stop all writes into the buffer
4062  * @buffer: The ring buffer to stop writes to.
4063  *
4064  * This prevents all writes to the buffer. Any attempt to write
4065  * to the buffer after this will fail and return NULL.
4066  *
4067  * This is different than ring_buffer_record_disable() as
4068  * it works like an on/off switch, where as the disable() version
4069  * must be paired with a enable().
4070  */
ring_buffer_record_off(struct trace_buffer * buffer)4071 void ring_buffer_record_off(struct trace_buffer *buffer)
4072 {
4073 	unsigned int rd;
4074 	unsigned int new_rd;
4075 
4076 	do {
4077 		rd = atomic_read(&buffer->record_disabled);
4078 		new_rd = rd | RB_BUFFER_OFF;
4079 	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
4080 }
4081 EXPORT_SYMBOL_GPL(ring_buffer_record_off);
4082 
4083 /**
4084  * ring_buffer_record_on - restart writes into the buffer
4085  * @buffer: The ring buffer to start writes to.
4086  *
4087  * This enables all writes to the buffer that was disabled by
4088  * ring_buffer_record_off().
4089  *
4090  * This is different than ring_buffer_record_enable() as
4091  * it works like an on/off switch, where as the enable() version
4092  * must be paired with a disable().
4093  */
ring_buffer_record_on(struct trace_buffer * buffer)4094 void ring_buffer_record_on(struct trace_buffer *buffer)
4095 {
4096 	unsigned int rd;
4097 	unsigned int new_rd;
4098 
4099 	do {
4100 		rd = atomic_read(&buffer->record_disabled);
4101 		new_rd = rd & ~RB_BUFFER_OFF;
4102 	} while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
4103 }
4104 EXPORT_SYMBOL_GPL(ring_buffer_record_on);
4105 
4106 /**
4107  * ring_buffer_record_is_on - return true if the ring buffer can write
4108  * @buffer: The ring buffer to see if write is enabled
4109  *
4110  * Returns true if the ring buffer is in a state that it accepts writes.
4111  */
ring_buffer_record_is_on(struct trace_buffer * buffer)4112 bool ring_buffer_record_is_on(struct trace_buffer *buffer)
4113 {
4114 	return !atomic_read(&buffer->record_disabled);
4115 }
4116 
4117 /**
4118  * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
4119  * @buffer: The ring buffer to see if write is set enabled
4120  *
4121  * Returns true if the ring buffer is set writable by ring_buffer_record_on().
4122  * Note that this does NOT mean it is in a writable state.
4123  *
4124  * It may return true when the ring buffer has been disabled by
4125  * ring_buffer_record_disable(), as that is a temporary disabling of
4126  * the ring buffer.
4127  */
ring_buffer_record_is_set_on(struct trace_buffer * buffer)4128 bool ring_buffer_record_is_set_on(struct trace_buffer *buffer)
4129 {
4130 	return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
4131 }
4132 
4133 /**
4134  * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
4135  * @buffer: The ring buffer to stop writes to.
4136  * @cpu: The CPU buffer to stop
4137  *
4138  * This prevents all writes to the buffer. Any attempt to write
4139  * to the buffer after this will fail and return NULL.
4140  *
4141  * The caller should call synchronize_rcu() after this.
4142  */
ring_buffer_record_disable_cpu(struct trace_buffer * buffer,int cpu)4143 void ring_buffer_record_disable_cpu(struct trace_buffer *buffer, int cpu)
4144 {
4145 	struct ring_buffer_per_cpu *cpu_buffer;
4146 
4147 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4148 		return;
4149 
4150 	cpu_buffer = buffer->buffers[cpu];
4151 	atomic_inc(&cpu_buffer->record_disabled);
4152 }
4153 EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
4154 
4155 /**
4156  * ring_buffer_record_enable_cpu - enable writes to the buffer
4157  * @buffer: The ring buffer to enable writes
4158  * @cpu: The CPU to enable.
4159  *
4160  * Note, multiple disables will need the same number of enables
4161  * to truly enable the writing (much like preempt_disable).
4162  */
ring_buffer_record_enable_cpu(struct trace_buffer * buffer,int cpu)4163 void ring_buffer_record_enable_cpu(struct trace_buffer *buffer, int cpu)
4164 {
4165 	struct ring_buffer_per_cpu *cpu_buffer;
4166 
4167 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4168 		return;
4169 
4170 	cpu_buffer = buffer->buffers[cpu];
4171 	atomic_dec(&cpu_buffer->record_disabled);
4172 }
4173 EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
4174 
4175 /*
4176  * The total entries in the ring buffer is the running counter
4177  * of entries entered into the ring buffer, minus the sum of
4178  * the entries read from the ring buffer and the number of
4179  * entries that were overwritten.
4180  */
4181 static inline unsigned long
rb_num_of_entries(struct ring_buffer_per_cpu * cpu_buffer)4182 rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
4183 {
4184 	return local_read(&cpu_buffer->entries) -
4185 		(local_read(&cpu_buffer->overrun) + cpu_buffer->read);
4186 }
4187 
4188 /**
4189  * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
4190  * @buffer: The ring buffer
4191  * @cpu: The per CPU buffer to read from.
4192  */
ring_buffer_oldest_event_ts(struct trace_buffer * buffer,int cpu)4193 u64 ring_buffer_oldest_event_ts(struct trace_buffer *buffer, int cpu)
4194 {
4195 	unsigned long flags;
4196 	struct ring_buffer_per_cpu *cpu_buffer;
4197 	struct buffer_page *bpage;
4198 	u64 ret = 0;
4199 
4200 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4201 		return 0;
4202 
4203 	cpu_buffer = buffer->buffers[cpu];
4204 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4205 	/*
4206 	 * if the tail is on reader_page, oldest time stamp is on the reader
4207 	 * page
4208 	 */
4209 	if (cpu_buffer->tail_page == cpu_buffer->reader_page)
4210 		bpage = cpu_buffer->reader_page;
4211 	else
4212 		bpage = rb_set_head_page(cpu_buffer);
4213 	if (bpage)
4214 		ret = bpage->page->time_stamp;
4215 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4216 
4217 	return ret;
4218 }
4219 EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
4220 
4221 /**
4222  * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
4223  * @buffer: The ring buffer
4224  * @cpu: The per CPU buffer to read from.
4225  */
ring_buffer_bytes_cpu(struct trace_buffer * buffer,int cpu)4226 unsigned long ring_buffer_bytes_cpu(struct trace_buffer *buffer, int cpu)
4227 {
4228 	struct ring_buffer_per_cpu *cpu_buffer;
4229 	unsigned long ret;
4230 
4231 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4232 		return 0;
4233 
4234 	cpu_buffer = buffer->buffers[cpu];
4235 	ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
4236 
4237 	return ret;
4238 }
4239 EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
4240 
4241 /**
4242  * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
4243  * @buffer: The ring buffer
4244  * @cpu: The per CPU buffer to get the entries from.
4245  */
ring_buffer_entries_cpu(struct trace_buffer * buffer,int cpu)4246 unsigned long ring_buffer_entries_cpu(struct trace_buffer *buffer, int cpu)
4247 {
4248 	struct ring_buffer_per_cpu *cpu_buffer;
4249 
4250 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4251 		return 0;
4252 
4253 	cpu_buffer = buffer->buffers[cpu];
4254 
4255 	return rb_num_of_entries(cpu_buffer);
4256 }
4257 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
4258 
4259 /**
4260  * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
4261  * buffer wrapping around (only if RB_FL_OVERWRITE is on).
4262  * @buffer: The ring buffer
4263  * @cpu: The per CPU buffer to get the number of overruns from
4264  */
ring_buffer_overrun_cpu(struct trace_buffer * buffer,int cpu)4265 unsigned long ring_buffer_overrun_cpu(struct trace_buffer *buffer, int cpu)
4266 {
4267 	struct ring_buffer_per_cpu *cpu_buffer;
4268 	unsigned long ret;
4269 
4270 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4271 		return 0;
4272 
4273 	cpu_buffer = buffer->buffers[cpu];
4274 	ret = local_read(&cpu_buffer->overrun);
4275 
4276 	return ret;
4277 }
4278 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
4279 
4280 /**
4281  * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
4282  * commits failing due to the buffer wrapping around while there are uncommitted
4283  * events, such as during an interrupt storm.
4284  * @buffer: The ring buffer
4285  * @cpu: The per CPU buffer to get the number of overruns from
4286  */
4287 unsigned long
ring_buffer_commit_overrun_cpu(struct trace_buffer * buffer,int cpu)4288 ring_buffer_commit_overrun_cpu(struct trace_buffer *buffer, int cpu)
4289 {
4290 	struct ring_buffer_per_cpu *cpu_buffer;
4291 	unsigned long ret;
4292 
4293 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4294 		return 0;
4295 
4296 	cpu_buffer = buffer->buffers[cpu];
4297 	ret = local_read(&cpu_buffer->commit_overrun);
4298 
4299 	return ret;
4300 }
4301 EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
4302 
4303 /**
4304  * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
4305  * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
4306  * @buffer: The ring buffer
4307  * @cpu: The per CPU buffer to get the number of overruns from
4308  */
4309 unsigned long
ring_buffer_dropped_events_cpu(struct trace_buffer * buffer,int cpu)4310 ring_buffer_dropped_events_cpu(struct trace_buffer *buffer, int cpu)
4311 {
4312 	struct ring_buffer_per_cpu *cpu_buffer;
4313 	unsigned long ret;
4314 
4315 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4316 		return 0;
4317 
4318 	cpu_buffer = buffer->buffers[cpu];
4319 	ret = local_read(&cpu_buffer->dropped_events);
4320 
4321 	return ret;
4322 }
4323 EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
4324 
4325 /**
4326  * ring_buffer_read_events_cpu - get the number of events successfully read
4327  * @buffer: The ring buffer
4328  * @cpu: The per CPU buffer to get the number of events read
4329  */
4330 unsigned long
ring_buffer_read_events_cpu(struct trace_buffer * buffer,int cpu)4331 ring_buffer_read_events_cpu(struct trace_buffer *buffer, int cpu)
4332 {
4333 	struct ring_buffer_per_cpu *cpu_buffer;
4334 
4335 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4336 		return 0;
4337 
4338 	cpu_buffer = buffer->buffers[cpu];
4339 	return cpu_buffer->read;
4340 }
4341 EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
4342 
4343 /**
4344  * ring_buffer_entries - get the number of entries in a buffer
4345  * @buffer: The ring buffer
4346  *
4347  * Returns the total number of entries in the ring buffer
4348  * (all CPU entries)
4349  */
ring_buffer_entries(struct trace_buffer * buffer)4350 unsigned long ring_buffer_entries(struct trace_buffer *buffer)
4351 {
4352 	struct ring_buffer_per_cpu *cpu_buffer;
4353 	unsigned long entries = 0;
4354 	int cpu;
4355 
4356 	/* if you care about this being correct, lock the buffer */
4357 	for_each_buffer_cpu(buffer, cpu) {
4358 		cpu_buffer = buffer->buffers[cpu];
4359 		entries += rb_num_of_entries(cpu_buffer);
4360 	}
4361 
4362 	return entries;
4363 }
4364 EXPORT_SYMBOL_GPL(ring_buffer_entries);
4365 
4366 /**
4367  * ring_buffer_overruns - get the number of overruns in buffer
4368  * @buffer: The ring buffer
4369  *
4370  * Returns the total number of overruns in the ring buffer
4371  * (all CPU entries)
4372  */
ring_buffer_overruns(struct trace_buffer * buffer)4373 unsigned long ring_buffer_overruns(struct trace_buffer *buffer)
4374 {
4375 	struct ring_buffer_per_cpu *cpu_buffer;
4376 	unsigned long overruns = 0;
4377 	int cpu;
4378 
4379 	/* if you care about this being correct, lock the buffer */
4380 	for_each_buffer_cpu(buffer, cpu) {
4381 		cpu_buffer = buffer->buffers[cpu];
4382 		overruns += local_read(&cpu_buffer->overrun);
4383 	}
4384 
4385 	return overruns;
4386 }
4387 EXPORT_SYMBOL_GPL(ring_buffer_overruns);
4388 
rb_iter_reset(struct ring_buffer_iter * iter)4389 static void rb_iter_reset(struct ring_buffer_iter *iter)
4390 {
4391 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4392 
4393 	/* Iterator usage is expected to have record disabled */
4394 	iter->head_page = cpu_buffer->reader_page;
4395 	iter->head = cpu_buffer->reader_page->read;
4396 	iter->next_event = iter->head;
4397 
4398 	iter->cache_reader_page = iter->head_page;
4399 	iter->cache_read = cpu_buffer->read;
4400 
4401 	if (iter->head) {
4402 		iter->read_stamp = cpu_buffer->read_stamp;
4403 		iter->page_stamp = cpu_buffer->reader_page->page->time_stamp;
4404 	} else {
4405 		iter->read_stamp = iter->head_page->page->time_stamp;
4406 		iter->page_stamp = iter->read_stamp;
4407 	}
4408 }
4409 
4410 /**
4411  * ring_buffer_iter_reset - reset an iterator
4412  * @iter: The iterator to reset
4413  *
4414  * Resets the iterator, so that it will start from the beginning
4415  * again.
4416  */
ring_buffer_iter_reset(struct ring_buffer_iter * iter)4417 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
4418 {
4419 	struct ring_buffer_per_cpu *cpu_buffer;
4420 	unsigned long flags;
4421 
4422 	if (!iter)
4423 		return;
4424 
4425 	cpu_buffer = iter->cpu_buffer;
4426 
4427 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4428 	rb_iter_reset(iter);
4429 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4430 }
4431 EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
4432 
4433 /**
4434  * ring_buffer_iter_empty - check if an iterator has no more to read
4435  * @iter: The iterator to check
4436  */
ring_buffer_iter_empty(struct ring_buffer_iter * iter)4437 int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
4438 {
4439 	struct ring_buffer_per_cpu *cpu_buffer;
4440 	struct buffer_page *reader;
4441 	struct buffer_page *head_page;
4442 	struct buffer_page *commit_page;
4443 	struct buffer_page *curr_commit_page;
4444 	unsigned commit;
4445 	u64 curr_commit_ts;
4446 	u64 commit_ts;
4447 
4448 	cpu_buffer = iter->cpu_buffer;
4449 	reader = cpu_buffer->reader_page;
4450 	head_page = cpu_buffer->head_page;
4451 	commit_page = cpu_buffer->commit_page;
4452 	commit_ts = commit_page->page->time_stamp;
4453 
4454 	/*
4455 	 * When the writer goes across pages, it issues a cmpxchg which
4456 	 * is a mb(), which will synchronize with the rmb here.
4457 	 * (see rb_tail_page_update())
4458 	 */
4459 	smp_rmb();
4460 	commit = rb_page_commit(commit_page);
4461 	/* We want to make sure that the commit page doesn't change */
4462 	smp_rmb();
4463 
4464 	/* Make sure commit page didn't change */
4465 	curr_commit_page = READ_ONCE(cpu_buffer->commit_page);
4466 	curr_commit_ts = READ_ONCE(curr_commit_page->page->time_stamp);
4467 
4468 	/* If the commit page changed, then there's more data */
4469 	if (curr_commit_page != commit_page ||
4470 	    curr_commit_ts != commit_ts)
4471 		return 0;
4472 
4473 	/* Still racy, as it may return a false positive, but that's OK */
4474 	return ((iter->head_page == commit_page && iter->head >= commit) ||
4475 		(iter->head_page == reader && commit_page == head_page &&
4476 		 head_page->read == commit &&
4477 		 iter->head == rb_page_commit(cpu_buffer->reader_page)));
4478 }
4479 EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
4480 
4481 static void
rb_update_read_stamp(struct ring_buffer_per_cpu * cpu_buffer,struct ring_buffer_event * event)4482 rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
4483 		     struct ring_buffer_event *event)
4484 {
4485 	u64 delta;
4486 
4487 	switch (event->type_len) {
4488 	case RINGBUF_TYPE_PADDING:
4489 		return;
4490 
4491 	case RINGBUF_TYPE_TIME_EXTEND:
4492 		delta = rb_event_time_stamp(event);
4493 		cpu_buffer->read_stamp += delta;
4494 		return;
4495 
4496 	case RINGBUF_TYPE_TIME_STAMP:
4497 		delta = rb_event_time_stamp(event);
4498 		delta = rb_fix_abs_ts(delta, cpu_buffer->read_stamp);
4499 		cpu_buffer->read_stamp = delta;
4500 		return;
4501 
4502 	case RINGBUF_TYPE_DATA:
4503 		cpu_buffer->read_stamp += event->time_delta;
4504 		return;
4505 
4506 	default:
4507 		RB_WARN_ON(cpu_buffer, 1);
4508 	}
4509 	return;
4510 }
4511 
4512 static void
rb_update_iter_read_stamp(struct ring_buffer_iter * iter,struct ring_buffer_event * event)4513 rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
4514 			  struct ring_buffer_event *event)
4515 {
4516 	u64 delta;
4517 
4518 	switch (event->type_len) {
4519 	case RINGBUF_TYPE_PADDING:
4520 		return;
4521 
4522 	case RINGBUF_TYPE_TIME_EXTEND:
4523 		delta = rb_event_time_stamp(event);
4524 		iter->read_stamp += delta;
4525 		return;
4526 
4527 	case RINGBUF_TYPE_TIME_STAMP:
4528 		delta = rb_event_time_stamp(event);
4529 		delta = rb_fix_abs_ts(delta, iter->read_stamp);
4530 		iter->read_stamp = delta;
4531 		return;
4532 
4533 	case RINGBUF_TYPE_DATA:
4534 		iter->read_stamp += event->time_delta;
4535 		return;
4536 
4537 	default:
4538 		RB_WARN_ON(iter->cpu_buffer, 1);
4539 	}
4540 	return;
4541 }
4542 
4543 static struct buffer_page *
rb_get_reader_page(struct ring_buffer_per_cpu * cpu_buffer)4544 rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
4545 {
4546 	struct buffer_page *reader = NULL;
4547 	unsigned long overwrite;
4548 	unsigned long flags;
4549 	int nr_loops = 0;
4550 	int ret;
4551 
4552 	local_irq_save(flags);
4553 	arch_spin_lock(&cpu_buffer->lock);
4554 
4555  again:
4556 	/*
4557 	 * This should normally only loop twice. But because the
4558 	 * start of the reader inserts an empty page, it causes
4559 	 * a case where we will loop three times. There should be no
4560 	 * reason to loop four times (that I know of).
4561 	 */
4562 	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
4563 		reader = NULL;
4564 		goto out;
4565 	}
4566 
4567 	reader = cpu_buffer->reader_page;
4568 
4569 	/* If there's more to read, return this page */
4570 	if (cpu_buffer->reader_page->read < rb_page_size(reader))
4571 		goto out;
4572 
4573 	/* Never should we have an index greater than the size */
4574 	if (RB_WARN_ON(cpu_buffer,
4575 		       cpu_buffer->reader_page->read > rb_page_size(reader)))
4576 		goto out;
4577 
4578 	/* check if we caught up to the tail */
4579 	reader = NULL;
4580 	if (cpu_buffer->commit_page == cpu_buffer->reader_page)
4581 		goto out;
4582 
4583 	/* Don't bother swapping if the ring buffer is empty */
4584 	if (rb_num_of_entries(cpu_buffer) == 0)
4585 		goto out;
4586 
4587 	/*
4588 	 * Reset the reader page to size zero.
4589 	 */
4590 	local_set(&cpu_buffer->reader_page->write, 0);
4591 	local_set(&cpu_buffer->reader_page->entries, 0);
4592 	local_set(&cpu_buffer->reader_page->page->commit, 0);
4593 	cpu_buffer->reader_page->real_end = 0;
4594 
4595  spin:
4596 	/*
4597 	 * Splice the empty reader page into the list around the head.
4598 	 */
4599 	reader = rb_set_head_page(cpu_buffer);
4600 	if (!reader)
4601 		goto out;
4602 	cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
4603 	cpu_buffer->reader_page->list.prev = reader->list.prev;
4604 
4605 	/*
4606 	 * cpu_buffer->pages just needs to point to the buffer, it
4607 	 *  has no specific buffer page to point to. Lets move it out
4608 	 *  of our way so we don't accidentally swap it.
4609 	 */
4610 	cpu_buffer->pages = reader->list.prev;
4611 
4612 	/* The reader page will be pointing to the new head */
4613 	rb_set_list_to_head(&cpu_buffer->reader_page->list);
4614 
4615 	/*
4616 	 * We want to make sure we read the overruns after we set up our
4617 	 * pointers to the next object. The writer side does a
4618 	 * cmpxchg to cross pages which acts as the mb on the writer
4619 	 * side. Note, the reader will constantly fail the swap
4620 	 * while the writer is updating the pointers, so this
4621 	 * guarantees that the overwrite recorded here is the one we
4622 	 * want to compare with the last_overrun.
4623 	 */
4624 	smp_mb();
4625 	overwrite = local_read(&(cpu_buffer->overrun));
4626 
4627 	/*
4628 	 * Here's the tricky part.
4629 	 *
4630 	 * We need to move the pointer past the header page.
4631 	 * But we can only do that if a writer is not currently
4632 	 * moving it. The page before the header page has the
4633 	 * flag bit '1' set if it is pointing to the page we want.
4634 	 * but if the writer is in the process of moving it
4635 	 * than it will be '2' or already moved '0'.
4636 	 */
4637 
4638 	ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
4639 
4640 	/*
4641 	 * If we did not convert it, then we must try again.
4642 	 */
4643 	if (!ret)
4644 		goto spin;
4645 
4646 	/*
4647 	 * Yay! We succeeded in replacing the page.
4648 	 *
4649 	 * Now make the new head point back to the reader page.
4650 	 */
4651 	rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
4652 	rb_inc_page(&cpu_buffer->head_page);
4653 
4654 	local_inc(&cpu_buffer->pages_read);
4655 
4656 	/* Finally update the reader page to the new head */
4657 	cpu_buffer->reader_page = reader;
4658 	cpu_buffer->reader_page->read = 0;
4659 
4660 	if (overwrite != cpu_buffer->last_overrun) {
4661 		cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
4662 		cpu_buffer->last_overrun = overwrite;
4663 	}
4664 
4665 	goto again;
4666 
4667  out:
4668 	/* Update the read_stamp on the first event */
4669 	if (reader && reader->read == 0)
4670 		cpu_buffer->read_stamp = reader->page->time_stamp;
4671 
4672 	arch_spin_unlock(&cpu_buffer->lock);
4673 	local_irq_restore(flags);
4674 
4675 	/*
4676 	 * The writer has preempt disable, wait for it. But not forever
4677 	 * Although, 1 second is pretty much "forever"
4678 	 */
4679 #define USECS_WAIT	1000000
4680         for (nr_loops = 0; nr_loops < USECS_WAIT; nr_loops++) {
4681 		/* If the write is past the end of page, a writer is still updating it */
4682 		if (likely(!reader || rb_page_write(reader) <= BUF_PAGE_SIZE))
4683 			break;
4684 
4685 		udelay(1);
4686 
4687 		/* Get the latest version of the reader write value */
4688 		smp_rmb();
4689 	}
4690 
4691 	/* The writer is not moving forward? Something is wrong */
4692 	if (RB_WARN_ON(cpu_buffer, nr_loops == USECS_WAIT))
4693 		reader = NULL;
4694 
4695 	/*
4696 	 * Make sure we see any padding after the write update
4697 	 * (see rb_reset_tail())
4698 	 */
4699 	smp_rmb();
4700 
4701 
4702 	return reader;
4703 }
4704 
rb_advance_reader(struct ring_buffer_per_cpu * cpu_buffer)4705 static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
4706 {
4707 	struct ring_buffer_event *event;
4708 	struct buffer_page *reader;
4709 	unsigned length;
4710 
4711 	reader = rb_get_reader_page(cpu_buffer);
4712 
4713 	/* This function should not be called when buffer is empty */
4714 	if (RB_WARN_ON(cpu_buffer, !reader))
4715 		return;
4716 
4717 	event = rb_reader_event(cpu_buffer);
4718 
4719 	if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
4720 		cpu_buffer->read++;
4721 
4722 	rb_update_read_stamp(cpu_buffer, event);
4723 
4724 	length = rb_event_length(event);
4725 	cpu_buffer->reader_page->read += length;
4726 }
4727 
rb_advance_iter(struct ring_buffer_iter * iter)4728 static void rb_advance_iter(struct ring_buffer_iter *iter)
4729 {
4730 	struct ring_buffer_per_cpu *cpu_buffer;
4731 
4732 	cpu_buffer = iter->cpu_buffer;
4733 
4734 	/* If head == next_event then we need to jump to the next event */
4735 	if (iter->head == iter->next_event) {
4736 		/* If the event gets overwritten again, there's nothing to do */
4737 		if (rb_iter_head_event(iter) == NULL)
4738 			return;
4739 	}
4740 
4741 	iter->head = iter->next_event;
4742 
4743 	/*
4744 	 * Check if we are at the end of the buffer.
4745 	 */
4746 	if (iter->next_event >= rb_page_size(iter->head_page)) {
4747 		/* discarded commits can make the page empty */
4748 		if (iter->head_page == cpu_buffer->commit_page)
4749 			return;
4750 		rb_inc_iter(iter);
4751 		return;
4752 	}
4753 
4754 	rb_update_iter_read_stamp(iter, iter->event);
4755 }
4756 
rb_lost_events(struct ring_buffer_per_cpu * cpu_buffer)4757 static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
4758 {
4759 	return cpu_buffer->lost_events;
4760 }
4761 
4762 static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer_per_cpu * cpu_buffer,u64 * ts,unsigned long * lost_events)4763 rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
4764 	       unsigned long *lost_events)
4765 {
4766 	struct ring_buffer_event *event;
4767 	struct buffer_page *reader;
4768 	int nr_loops = 0;
4769 
4770 	if (ts)
4771 		*ts = 0;
4772  again:
4773 	/*
4774 	 * We repeat when a time extend is encountered.
4775 	 * Since the time extend is always attached to a data event,
4776 	 * we should never loop more than once.
4777 	 * (We never hit the following condition more than twice).
4778 	 */
4779 	if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
4780 		return NULL;
4781 
4782 	reader = rb_get_reader_page(cpu_buffer);
4783 	if (!reader)
4784 		return NULL;
4785 
4786 	event = rb_reader_event(cpu_buffer);
4787 
4788 	switch (event->type_len) {
4789 	case RINGBUF_TYPE_PADDING:
4790 		if (rb_null_event(event))
4791 			RB_WARN_ON(cpu_buffer, 1);
4792 		/*
4793 		 * Because the writer could be discarding every
4794 		 * event it creates (which would probably be bad)
4795 		 * if we were to go back to "again" then we may never
4796 		 * catch up, and will trigger the warn on, or lock
4797 		 * the box. Return the padding, and we will release
4798 		 * the current locks, and try again.
4799 		 */
4800 		return event;
4801 
4802 	case RINGBUF_TYPE_TIME_EXTEND:
4803 		/* Internal data, OK to advance */
4804 		rb_advance_reader(cpu_buffer);
4805 		goto again;
4806 
4807 	case RINGBUF_TYPE_TIME_STAMP:
4808 		if (ts) {
4809 			*ts = rb_event_time_stamp(event);
4810 			*ts = rb_fix_abs_ts(*ts, reader->page->time_stamp);
4811 			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4812 							 cpu_buffer->cpu, ts);
4813 		}
4814 		/* Internal data, OK to advance */
4815 		rb_advance_reader(cpu_buffer);
4816 		goto again;
4817 
4818 	case RINGBUF_TYPE_DATA:
4819 		if (ts && !(*ts)) {
4820 			*ts = cpu_buffer->read_stamp + event->time_delta;
4821 			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4822 							 cpu_buffer->cpu, ts);
4823 		}
4824 		if (lost_events)
4825 			*lost_events = rb_lost_events(cpu_buffer);
4826 		return event;
4827 
4828 	default:
4829 		RB_WARN_ON(cpu_buffer, 1);
4830 	}
4831 
4832 	return NULL;
4833 }
4834 EXPORT_SYMBOL_GPL(ring_buffer_peek);
4835 
4836 static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter * iter,u64 * ts)4837 rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
4838 {
4839 	struct trace_buffer *buffer;
4840 	struct ring_buffer_per_cpu *cpu_buffer;
4841 	struct ring_buffer_event *event;
4842 	int nr_loops = 0;
4843 
4844 	if (ts)
4845 		*ts = 0;
4846 
4847 	cpu_buffer = iter->cpu_buffer;
4848 	buffer = cpu_buffer->buffer;
4849 
4850 	/*
4851 	 * Check if someone performed a consuming read to
4852 	 * the buffer. A consuming read invalidates the iterator
4853 	 * and we need to reset the iterator in this case.
4854 	 */
4855 	if (unlikely(iter->cache_read != cpu_buffer->read ||
4856 		     iter->cache_reader_page != cpu_buffer->reader_page))
4857 		rb_iter_reset(iter);
4858 
4859  again:
4860 	if (ring_buffer_iter_empty(iter))
4861 		return NULL;
4862 
4863 	/*
4864 	 * As the writer can mess with what the iterator is trying
4865 	 * to read, just give up if we fail to get an event after
4866 	 * three tries. The iterator is not as reliable when reading
4867 	 * the ring buffer with an active write as the consumer is.
4868 	 * Do not warn if the three failures is reached.
4869 	 */
4870 	if (++nr_loops > 3)
4871 		return NULL;
4872 
4873 	if (rb_per_cpu_empty(cpu_buffer))
4874 		return NULL;
4875 
4876 	if (iter->head >= rb_page_size(iter->head_page)) {
4877 		rb_inc_iter(iter);
4878 		goto again;
4879 	}
4880 
4881 	event = rb_iter_head_event(iter);
4882 	if (!event)
4883 		goto again;
4884 
4885 	switch (event->type_len) {
4886 	case RINGBUF_TYPE_PADDING:
4887 		if (rb_null_event(event)) {
4888 			rb_inc_iter(iter);
4889 			goto again;
4890 		}
4891 		rb_advance_iter(iter);
4892 		return event;
4893 
4894 	case RINGBUF_TYPE_TIME_EXTEND:
4895 		/* Internal data, OK to advance */
4896 		rb_advance_iter(iter);
4897 		goto again;
4898 
4899 	case RINGBUF_TYPE_TIME_STAMP:
4900 		if (ts) {
4901 			*ts = rb_event_time_stamp(event);
4902 			*ts = rb_fix_abs_ts(*ts, iter->head_page->page->time_stamp);
4903 			ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4904 							 cpu_buffer->cpu, ts);
4905 		}
4906 		/* Internal data, OK to advance */
4907 		rb_advance_iter(iter);
4908 		goto again;
4909 
4910 	case RINGBUF_TYPE_DATA:
4911 		if (ts && !(*ts)) {
4912 			*ts = iter->read_stamp + event->time_delta;
4913 			ring_buffer_normalize_time_stamp(buffer,
4914 							 cpu_buffer->cpu, ts);
4915 		}
4916 		return event;
4917 
4918 	default:
4919 		RB_WARN_ON(cpu_buffer, 1);
4920 	}
4921 
4922 	return NULL;
4923 }
4924 EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
4925 
rb_reader_lock(struct ring_buffer_per_cpu * cpu_buffer)4926 static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
4927 {
4928 	if (likely(!in_nmi())) {
4929 		raw_spin_lock(&cpu_buffer->reader_lock);
4930 		return true;
4931 	}
4932 
4933 	/*
4934 	 * If an NMI die dumps out the content of the ring buffer
4935 	 * trylock must be used to prevent a deadlock if the NMI
4936 	 * preempted a task that holds the ring buffer locks. If
4937 	 * we get the lock then all is fine, if not, then continue
4938 	 * to do the read, but this can corrupt the ring buffer,
4939 	 * so it must be permanently disabled from future writes.
4940 	 * Reading from NMI is a oneshot deal.
4941 	 */
4942 	if (raw_spin_trylock(&cpu_buffer->reader_lock))
4943 		return true;
4944 
4945 	/* Continue without locking, but disable the ring buffer */
4946 	atomic_inc(&cpu_buffer->record_disabled);
4947 	return false;
4948 }
4949 
4950 static inline void
rb_reader_unlock(struct ring_buffer_per_cpu * cpu_buffer,bool locked)4951 rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
4952 {
4953 	if (likely(locked))
4954 		raw_spin_unlock(&cpu_buffer->reader_lock);
4955 	return;
4956 }
4957 
4958 /**
4959  * ring_buffer_peek - peek at the next event to be read
4960  * @buffer: The ring buffer to read
4961  * @cpu: The cpu to peak at
4962  * @ts: The timestamp counter of this event.
4963  * @lost_events: a variable to store if events were lost (may be NULL)
4964  *
4965  * This will return the event that will be read next, but does
4966  * not consume the data.
4967  */
4968 struct ring_buffer_event *
ring_buffer_peek(struct trace_buffer * buffer,int cpu,u64 * ts,unsigned long * lost_events)4969 ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
4970 		 unsigned long *lost_events)
4971 {
4972 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4973 	struct ring_buffer_event *event;
4974 	unsigned long flags;
4975 	bool dolock;
4976 
4977 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
4978 		return NULL;
4979 
4980  again:
4981 	local_irq_save(flags);
4982 	dolock = rb_reader_lock(cpu_buffer);
4983 	event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4984 	if (event && event->type_len == RINGBUF_TYPE_PADDING)
4985 		rb_advance_reader(cpu_buffer);
4986 	rb_reader_unlock(cpu_buffer, dolock);
4987 	local_irq_restore(flags);
4988 
4989 	if (event && event->type_len == RINGBUF_TYPE_PADDING)
4990 		goto again;
4991 
4992 	return event;
4993 }
4994 
4995 /** ring_buffer_iter_dropped - report if there are dropped events
4996  * @iter: The ring buffer iterator
4997  *
4998  * Returns true if there was dropped events since the last peek.
4999  */
ring_buffer_iter_dropped(struct ring_buffer_iter * iter)5000 bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
5001 {
5002 	bool ret = iter->missed_events != 0;
5003 
5004 	iter->missed_events = 0;
5005 	return ret;
5006 }
5007 EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
5008 
5009 /**
5010  * ring_buffer_iter_peek - peek at the next event to be read
5011  * @iter: The ring buffer iterator
5012  * @ts: The timestamp counter of this event.
5013  *
5014  * This will return the event that will be read next, but does
5015  * not increment the iterator.
5016  */
5017 struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter * iter,u64 * ts)5018 ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
5019 {
5020 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
5021 	struct ring_buffer_event *event;
5022 	unsigned long flags;
5023 
5024  again:
5025 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5026 	event = rb_iter_peek(iter, ts);
5027 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5028 
5029 	if (event && event->type_len == RINGBUF_TYPE_PADDING)
5030 		goto again;
5031 
5032 	return event;
5033 }
5034 
5035 /**
5036  * ring_buffer_consume - return an event and consume it
5037  * @buffer: The ring buffer to get the next event from
5038  * @cpu: the cpu to read the buffer from
5039  * @ts: a variable to store the timestamp (may be NULL)
5040  * @lost_events: a variable to store if events were lost (may be NULL)
5041  *
5042  * Returns the next event in the ring buffer, and that event is consumed.
5043  * Meaning, that sequential reads will keep returning a different event,
5044  * and eventually empty the ring buffer if the producer is slower.
5045  */
5046 struct ring_buffer_event *
ring_buffer_consume(struct trace_buffer * buffer,int cpu,u64 * ts,unsigned long * lost_events)5047 ring_buffer_consume(struct trace_buffer *buffer, int cpu, u64 *ts,
5048 		    unsigned long *lost_events)
5049 {
5050 	struct ring_buffer_per_cpu *cpu_buffer;
5051 	struct ring_buffer_event *event = NULL;
5052 	unsigned long flags;
5053 	bool dolock;
5054 
5055  again:
5056 	/* might be called in atomic */
5057 	preempt_disable();
5058 
5059 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5060 		goto out;
5061 
5062 	cpu_buffer = buffer->buffers[cpu];
5063 	local_irq_save(flags);
5064 	dolock = rb_reader_lock(cpu_buffer);
5065 
5066 	event = rb_buffer_peek(cpu_buffer, ts, lost_events);
5067 	if (event) {
5068 		cpu_buffer->lost_events = 0;
5069 		rb_advance_reader(cpu_buffer);
5070 	}
5071 
5072 	rb_reader_unlock(cpu_buffer, dolock);
5073 	local_irq_restore(flags);
5074 
5075  out:
5076 	preempt_enable();
5077 
5078 	if (event && event->type_len == RINGBUF_TYPE_PADDING)
5079 		goto again;
5080 
5081 	return event;
5082 }
5083 EXPORT_SYMBOL_GPL(ring_buffer_consume);
5084 
5085 /**
5086  * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
5087  * @buffer: The ring buffer to read from
5088  * @cpu: The cpu buffer to iterate over
5089  * @flags: gfp flags to use for memory allocation
5090  *
5091  * This performs the initial preparations necessary to iterate
5092  * through the buffer.  Memory is allocated, buffer recording
5093  * is disabled, and the iterator pointer is returned to the caller.
5094  *
5095  * Disabling buffer recording prevents the reading from being
5096  * corrupted. This is not a consuming read, so a producer is not
5097  * expected.
5098  *
5099  * After a sequence of ring_buffer_read_prepare calls, the user is
5100  * expected to make at least one call to ring_buffer_read_prepare_sync.
5101  * Afterwards, ring_buffer_read_start is invoked to get things going
5102  * for real.
5103  *
5104  * This overall must be paired with ring_buffer_read_finish.
5105  */
5106 struct ring_buffer_iter *
ring_buffer_read_prepare(struct trace_buffer * buffer,int cpu,gfp_t flags)5107 ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags)
5108 {
5109 	struct ring_buffer_per_cpu *cpu_buffer;
5110 	struct ring_buffer_iter *iter;
5111 
5112 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5113 		return NULL;
5114 
5115 	iter = kzalloc(sizeof(*iter), flags);
5116 	if (!iter)
5117 		return NULL;
5118 
5119 	iter->event = kmalloc(BUF_MAX_DATA_SIZE, flags);
5120 	if (!iter->event) {
5121 		kfree(iter);
5122 		return NULL;
5123 	}
5124 
5125 	cpu_buffer = buffer->buffers[cpu];
5126 
5127 	iter->cpu_buffer = cpu_buffer;
5128 
5129 	atomic_inc(&cpu_buffer->resize_disabled);
5130 
5131 	return iter;
5132 }
5133 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
5134 
5135 /**
5136  * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
5137  *
5138  * All previously invoked ring_buffer_read_prepare calls to prepare
5139  * iterators will be synchronized.  Afterwards, read_buffer_read_start
5140  * calls on those iterators are allowed.
5141  */
5142 void
ring_buffer_read_prepare_sync(void)5143 ring_buffer_read_prepare_sync(void)
5144 {
5145 	synchronize_rcu();
5146 }
5147 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
5148 
5149 /**
5150  * ring_buffer_read_start - start a non consuming read of the buffer
5151  * @iter: The iterator returned by ring_buffer_read_prepare
5152  *
5153  * This finalizes the startup of an iteration through the buffer.
5154  * The iterator comes from a call to ring_buffer_read_prepare and
5155  * an intervening ring_buffer_read_prepare_sync must have been
5156  * performed.
5157  *
5158  * Must be paired with ring_buffer_read_finish.
5159  */
5160 void
ring_buffer_read_start(struct ring_buffer_iter * iter)5161 ring_buffer_read_start(struct ring_buffer_iter *iter)
5162 {
5163 	struct ring_buffer_per_cpu *cpu_buffer;
5164 	unsigned long flags;
5165 
5166 	if (!iter)
5167 		return;
5168 
5169 	cpu_buffer = iter->cpu_buffer;
5170 
5171 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5172 	arch_spin_lock(&cpu_buffer->lock);
5173 	rb_iter_reset(iter);
5174 	arch_spin_unlock(&cpu_buffer->lock);
5175 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5176 }
5177 EXPORT_SYMBOL_GPL(ring_buffer_read_start);
5178 
5179 /**
5180  * ring_buffer_read_finish - finish reading the iterator of the buffer
5181  * @iter: The iterator retrieved by ring_buffer_start
5182  *
5183  * This re-enables the recording to the buffer, and frees the
5184  * iterator.
5185  */
5186 void
ring_buffer_read_finish(struct ring_buffer_iter * iter)5187 ring_buffer_read_finish(struct ring_buffer_iter *iter)
5188 {
5189 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
5190 	unsigned long flags;
5191 
5192 	/*
5193 	 * Ring buffer is disabled from recording, here's a good place
5194 	 * to check the integrity of the ring buffer.
5195 	 * Must prevent readers from trying to read, as the check
5196 	 * clears the HEAD page and readers require it.
5197 	 */
5198 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5199 	rb_check_pages(cpu_buffer);
5200 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5201 
5202 	atomic_dec(&cpu_buffer->resize_disabled);
5203 	kfree(iter->event);
5204 	kfree(iter);
5205 }
5206 EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
5207 
5208 /**
5209  * ring_buffer_iter_advance - advance the iterator to the next location
5210  * @iter: The ring buffer iterator
5211  *
5212  * Move the location of the iterator such that the next read will
5213  * be the next location of the iterator.
5214  */
ring_buffer_iter_advance(struct ring_buffer_iter * iter)5215 void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
5216 {
5217 	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
5218 	unsigned long flags;
5219 
5220 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5221 
5222 	rb_advance_iter(iter);
5223 
5224 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5225 }
5226 EXPORT_SYMBOL_GPL(ring_buffer_iter_advance);
5227 
5228 /**
5229  * ring_buffer_size - return the size of the ring buffer (in bytes)
5230  * @buffer: The ring buffer.
5231  * @cpu: The CPU to get ring buffer size from.
5232  */
ring_buffer_size(struct trace_buffer * buffer,int cpu)5233 unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
5234 {
5235 	/*
5236 	 * Earlier, this method returned
5237 	 *	BUF_PAGE_SIZE * buffer->nr_pages
5238 	 * Since the nr_pages field is now removed, we have converted this to
5239 	 * return the per cpu buffer value.
5240 	 */
5241 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5242 		return 0;
5243 
5244 	return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
5245 }
5246 EXPORT_SYMBOL_GPL(ring_buffer_size);
5247 
5248 static void
rb_reset_cpu(struct ring_buffer_per_cpu * cpu_buffer)5249 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
5250 {
5251 	rb_head_page_deactivate(cpu_buffer);
5252 
5253 	cpu_buffer->head_page
5254 		= list_entry(cpu_buffer->pages, struct buffer_page, list);
5255 	local_set(&cpu_buffer->head_page->write, 0);
5256 	local_set(&cpu_buffer->head_page->entries, 0);
5257 	local_set(&cpu_buffer->head_page->page->commit, 0);
5258 
5259 	cpu_buffer->head_page->read = 0;
5260 
5261 	cpu_buffer->tail_page = cpu_buffer->head_page;
5262 	cpu_buffer->commit_page = cpu_buffer->head_page;
5263 
5264 	INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
5265 	INIT_LIST_HEAD(&cpu_buffer->new_pages);
5266 	local_set(&cpu_buffer->reader_page->write, 0);
5267 	local_set(&cpu_buffer->reader_page->entries, 0);
5268 	local_set(&cpu_buffer->reader_page->page->commit, 0);
5269 	cpu_buffer->reader_page->read = 0;
5270 
5271 	local_set(&cpu_buffer->entries_bytes, 0);
5272 	local_set(&cpu_buffer->overrun, 0);
5273 	local_set(&cpu_buffer->commit_overrun, 0);
5274 	local_set(&cpu_buffer->dropped_events, 0);
5275 	local_set(&cpu_buffer->entries, 0);
5276 	local_set(&cpu_buffer->committing, 0);
5277 	local_set(&cpu_buffer->commits, 0);
5278 	local_set(&cpu_buffer->pages_touched, 0);
5279 	local_set(&cpu_buffer->pages_lost, 0);
5280 	local_set(&cpu_buffer->pages_read, 0);
5281 	cpu_buffer->last_pages_touch = 0;
5282 	cpu_buffer->shortest_full = 0;
5283 	cpu_buffer->read = 0;
5284 	cpu_buffer->read_bytes = 0;
5285 
5286 	rb_time_set(&cpu_buffer->write_stamp, 0);
5287 	rb_time_set(&cpu_buffer->before_stamp, 0);
5288 
5289 	memset(cpu_buffer->event_stamp, 0, sizeof(cpu_buffer->event_stamp));
5290 
5291 	cpu_buffer->lost_events = 0;
5292 	cpu_buffer->last_overrun = 0;
5293 
5294 	rb_head_page_activate(cpu_buffer);
5295 }
5296 
5297 /* Must have disabled the cpu buffer then done a synchronize_rcu */
reset_disabled_cpu_buffer(struct ring_buffer_per_cpu * cpu_buffer)5298 static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
5299 {
5300 	unsigned long flags;
5301 
5302 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5303 
5304 	if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
5305 		goto out;
5306 
5307 	arch_spin_lock(&cpu_buffer->lock);
5308 
5309 	rb_reset_cpu(cpu_buffer);
5310 
5311 	arch_spin_unlock(&cpu_buffer->lock);
5312 
5313  out:
5314 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5315 }
5316 
5317 /**
5318  * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
5319  * @buffer: The ring buffer to reset a per cpu buffer of
5320  * @cpu: The CPU buffer to be reset
5321  */
ring_buffer_reset_cpu(struct trace_buffer * buffer,int cpu)5322 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
5323 {
5324 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5325 
5326 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5327 		return;
5328 
5329 	/* prevent another thread from changing buffer sizes */
5330 	mutex_lock(&buffer->mutex);
5331 
5332 	atomic_inc(&cpu_buffer->resize_disabled);
5333 	atomic_inc(&cpu_buffer->record_disabled);
5334 
5335 	/* Make sure all commits have finished */
5336 	synchronize_rcu();
5337 
5338 	reset_disabled_cpu_buffer(cpu_buffer);
5339 
5340 	atomic_dec(&cpu_buffer->record_disabled);
5341 	atomic_dec(&cpu_buffer->resize_disabled);
5342 
5343 	mutex_unlock(&buffer->mutex);
5344 }
5345 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
5346 
5347 /**
5348  * ring_buffer_reset_online_cpus - reset a ring buffer per CPU buffer
5349  * @buffer: The ring buffer to reset a per cpu buffer of
5350  * @cpu: The CPU buffer to be reset
5351  */
ring_buffer_reset_online_cpus(struct trace_buffer * buffer)5352 void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
5353 {
5354 	struct ring_buffer_per_cpu *cpu_buffer;
5355 	int cpu;
5356 
5357 	/* prevent another thread from changing buffer sizes */
5358 	mutex_lock(&buffer->mutex);
5359 
5360 	for_each_online_buffer_cpu(buffer, cpu) {
5361 		cpu_buffer = buffer->buffers[cpu];
5362 
5363 		atomic_inc(&cpu_buffer->resize_disabled);
5364 		atomic_inc(&cpu_buffer->record_disabled);
5365 	}
5366 
5367 	/* Make sure all commits have finished */
5368 	synchronize_rcu();
5369 
5370 	for_each_online_buffer_cpu(buffer, cpu) {
5371 		cpu_buffer = buffer->buffers[cpu];
5372 
5373 		reset_disabled_cpu_buffer(cpu_buffer);
5374 
5375 		atomic_dec(&cpu_buffer->record_disabled);
5376 		atomic_dec(&cpu_buffer->resize_disabled);
5377 	}
5378 
5379 	mutex_unlock(&buffer->mutex);
5380 }
5381 
5382 /**
5383  * ring_buffer_reset - reset a ring buffer
5384  * @buffer: The ring buffer to reset all cpu buffers
5385  */
ring_buffer_reset(struct trace_buffer * buffer)5386 void ring_buffer_reset(struct trace_buffer *buffer)
5387 {
5388 	struct ring_buffer_per_cpu *cpu_buffer;
5389 	int cpu;
5390 
5391 	/* prevent another thread from changing buffer sizes */
5392 	mutex_lock(&buffer->mutex);
5393 
5394 	for_each_buffer_cpu(buffer, cpu) {
5395 		cpu_buffer = buffer->buffers[cpu];
5396 
5397 		atomic_inc(&cpu_buffer->resize_disabled);
5398 		atomic_inc(&cpu_buffer->record_disabled);
5399 	}
5400 
5401 	/* Make sure all commits have finished */
5402 	synchronize_rcu();
5403 
5404 	for_each_buffer_cpu(buffer, cpu) {
5405 		cpu_buffer = buffer->buffers[cpu];
5406 
5407 		reset_disabled_cpu_buffer(cpu_buffer);
5408 
5409 		atomic_dec(&cpu_buffer->record_disabled);
5410 		atomic_dec(&cpu_buffer->resize_disabled);
5411 	}
5412 
5413 	mutex_unlock(&buffer->mutex);
5414 }
5415 EXPORT_SYMBOL_GPL(ring_buffer_reset);
5416 
5417 /**
5418  * ring_buffer_empty - is the ring buffer empty?
5419  * @buffer: The ring buffer to test
5420  */
ring_buffer_empty(struct trace_buffer * buffer)5421 bool ring_buffer_empty(struct trace_buffer *buffer)
5422 {
5423 	struct ring_buffer_per_cpu *cpu_buffer;
5424 	unsigned long flags;
5425 	bool dolock;
5426 	int cpu;
5427 	int ret;
5428 
5429 	/* yes this is racy, but if you don't like the race, lock the buffer */
5430 	for_each_buffer_cpu(buffer, cpu) {
5431 		cpu_buffer = buffer->buffers[cpu];
5432 		local_irq_save(flags);
5433 		dolock = rb_reader_lock(cpu_buffer);
5434 		ret = rb_per_cpu_empty(cpu_buffer);
5435 		rb_reader_unlock(cpu_buffer, dolock);
5436 		local_irq_restore(flags);
5437 
5438 		if (!ret)
5439 			return false;
5440 	}
5441 
5442 	return true;
5443 }
5444 EXPORT_SYMBOL_GPL(ring_buffer_empty);
5445 
5446 /**
5447  * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
5448  * @buffer: The ring buffer
5449  * @cpu: The CPU buffer to test
5450  */
ring_buffer_empty_cpu(struct trace_buffer * buffer,int cpu)5451 bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
5452 {
5453 	struct ring_buffer_per_cpu *cpu_buffer;
5454 	unsigned long flags;
5455 	bool dolock;
5456 	int ret;
5457 
5458 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5459 		return true;
5460 
5461 	cpu_buffer = buffer->buffers[cpu];
5462 	local_irq_save(flags);
5463 	dolock = rb_reader_lock(cpu_buffer);
5464 	ret = rb_per_cpu_empty(cpu_buffer);
5465 	rb_reader_unlock(cpu_buffer, dolock);
5466 	local_irq_restore(flags);
5467 
5468 	return ret;
5469 }
5470 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
5471 
5472 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
5473 /**
5474  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
5475  * @buffer_a: One buffer to swap with
5476  * @buffer_b: The other buffer to swap with
5477  * @cpu: the CPU of the buffers to swap
5478  *
5479  * This function is useful for tracers that want to take a "snapshot"
5480  * of a CPU buffer and has another back up buffer lying around.
5481  * it is expected that the tracer handles the cpu buffer not being
5482  * used at the moment.
5483  */
ring_buffer_swap_cpu(struct trace_buffer * buffer_a,struct trace_buffer * buffer_b,int cpu)5484 int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
5485 			 struct trace_buffer *buffer_b, int cpu)
5486 {
5487 	struct ring_buffer_per_cpu *cpu_buffer_a;
5488 	struct ring_buffer_per_cpu *cpu_buffer_b;
5489 	int ret = -EINVAL;
5490 
5491 	if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
5492 	    !cpumask_test_cpu(cpu, buffer_b->cpumask))
5493 		goto out;
5494 
5495 	cpu_buffer_a = buffer_a->buffers[cpu];
5496 	cpu_buffer_b = buffer_b->buffers[cpu];
5497 
5498 	/* At least make sure the two buffers are somewhat the same */
5499 	if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
5500 		goto out;
5501 
5502 	ret = -EAGAIN;
5503 
5504 	if (atomic_read(&buffer_a->record_disabled))
5505 		goto out;
5506 
5507 	if (atomic_read(&buffer_b->record_disabled))
5508 		goto out;
5509 
5510 	if (atomic_read(&cpu_buffer_a->record_disabled))
5511 		goto out;
5512 
5513 	if (atomic_read(&cpu_buffer_b->record_disabled))
5514 		goto out;
5515 
5516 	/*
5517 	 * We can't do a synchronize_rcu here because this
5518 	 * function can be called in atomic context.
5519 	 * Normally this will be called from the same CPU as cpu.
5520 	 * If not it's up to the caller to protect this.
5521 	 */
5522 	atomic_inc(&cpu_buffer_a->record_disabled);
5523 	atomic_inc(&cpu_buffer_b->record_disabled);
5524 
5525 	ret = -EBUSY;
5526 	if (local_read(&cpu_buffer_a->committing))
5527 		goto out_dec;
5528 	if (local_read(&cpu_buffer_b->committing))
5529 		goto out_dec;
5530 
5531 	buffer_a->buffers[cpu] = cpu_buffer_b;
5532 	buffer_b->buffers[cpu] = cpu_buffer_a;
5533 
5534 	cpu_buffer_b->buffer = buffer_a;
5535 	cpu_buffer_a->buffer = buffer_b;
5536 
5537 	ret = 0;
5538 
5539 out_dec:
5540 	atomic_dec(&cpu_buffer_a->record_disabled);
5541 	atomic_dec(&cpu_buffer_b->record_disabled);
5542 out:
5543 	return ret;
5544 }
5545 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
5546 #endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
5547 
5548 /**
5549  * ring_buffer_alloc_read_page - allocate a page to read from buffer
5550  * @buffer: the buffer to allocate for.
5551  * @cpu: the cpu buffer to allocate.
5552  *
5553  * This function is used in conjunction with ring_buffer_read_page.
5554  * When reading a full page from the ring buffer, these functions
5555  * can be used to speed up the process. The calling function should
5556  * allocate a few pages first with this function. Then when it
5557  * needs to get pages from the ring buffer, it passes the result
5558  * of this function into ring_buffer_read_page, which will swap
5559  * the page that was allocated, with the read page of the buffer.
5560  *
5561  * Returns:
5562  *  The page allocated, or ERR_PTR
5563  */
ring_buffer_alloc_read_page(struct trace_buffer * buffer,int cpu)5564 void *ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
5565 {
5566 	struct ring_buffer_per_cpu *cpu_buffer;
5567 	struct buffer_data_page *bpage = NULL;
5568 	unsigned long flags;
5569 	struct page *page;
5570 
5571 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5572 		return ERR_PTR(-ENODEV);
5573 
5574 	cpu_buffer = buffer->buffers[cpu];
5575 	local_irq_save(flags);
5576 	arch_spin_lock(&cpu_buffer->lock);
5577 
5578 	if (cpu_buffer->free_page) {
5579 		bpage = cpu_buffer->free_page;
5580 		cpu_buffer->free_page = NULL;
5581 	}
5582 
5583 	arch_spin_unlock(&cpu_buffer->lock);
5584 	local_irq_restore(flags);
5585 
5586 	if (bpage)
5587 		goto out;
5588 
5589 	page = alloc_pages_node(cpu_to_node(cpu),
5590 				GFP_KERNEL | __GFP_NORETRY, 0);
5591 	if (!page)
5592 		return ERR_PTR(-ENOMEM);
5593 
5594 	bpage = page_address(page);
5595 
5596  out:
5597 	rb_init_page(bpage);
5598 
5599 	return bpage;
5600 }
5601 EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
5602 
5603 /**
5604  * ring_buffer_free_read_page - free an allocated read page
5605  * @buffer: the buffer the page was allocate for
5606  * @cpu: the cpu buffer the page came from
5607  * @data: the page to free
5608  *
5609  * Free a page allocated from ring_buffer_alloc_read_page.
5610  */
ring_buffer_free_read_page(struct trace_buffer * buffer,int cpu,void * data)5611 void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu, void *data)
5612 {
5613 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5614 	struct buffer_data_page *bpage = data;
5615 	struct page *page = virt_to_page(bpage);
5616 	unsigned long flags;
5617 
5618 	/* If the page is still in use someplace else, we can't reuse it */
5619 	if (page_ref_count(page) > 1)
5620 		goto out;
5621 
5622 	local_irq_save(flags);
5623 	arch_spin_lock(&cpu_buffer->lock);
5624 
5625 	if (!cpu_buffer->free_page) {
5626 		cpu_buffer->free_page = bpage;
5627 		bpage = NULL;
5628 	}
5629 
5630 	arch_spin_unlock(&cpu_buffer->lock);
5631 	local_irq_restore(flags);
5632 
5633  out:
5634 	free_page((unsigned long)bpage);
5635 }
5636 EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
5637 
5638 /**
5639  * ring_buffer_read_page - extract a page from the ring buffer
5640  * @buffer: buffer to extract from
5641  * @data_page: the page to use allocated from ring_buffer_alloc_read_page
5642  * @len: amount to extract
5643  * @cpu: the cpu of the buffer to extract
5644  * @full: should the extraction only happen when the page is full.
5645  *
5646  * This function will pull out a page from the ring buffer and consume it.
5647  * @data_page must be the address of the variable that was returned
5648  * from ring_buffer_alloc_read_page. This is because the page might be used
5649  * to swap with a page in the ring buffer.
5650  *
5651  * for example:
5652  *	rpage = ring_buffer_alloc_read_page(buffer, cpu);
5653  *	if (IS_ERR(rpage))
5654  *		return PTR_ERR(rpage);
5655  *	ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
5656  *	if (ret >= 0)
5657  *		process_page(rpage, ret);
5658  *
5659  * When @full is set, the function will not return true unless
5660  * the writer is off the reader page.
5661  *
5662  * Note: it is up to the calling functions to handle sleeps and wakeups.
5663  *  The ring buffer can be used anywhere in the kernel and can not
5664  *  blindly call wake_up. The layer that uses the ring buffer must be
5665  *  responsible for that.
5666  *
5667  * Returns:
5668  *  >=0 if data has been transferred, returns the offset of consumed data.
5669  *  <0 if no data has been transferred.
5670  */
ring_buffer_read_page(struct trace_buffer * buffer,void ** data_page,size_t len,int cpu,int full)5671 int ring_buffer_read_page(struct trace_buffer *buffer,
5672 			  void **data_page, size_t len, int cpu, int full)
5673 {
5674 	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5675 	struct ring_buffer_event *event;
5676 	struct buffer_data_page *bpage;
5677 	struct buffer_page *reader;
5678 	unsigned long missed_events;
5679 	unsigned long flags;
5680 	unsigned int commit;
5681 	unsigned int read;
5682 	u64 save_timestamp;
5683 	int ret = -1;
5684 
5685 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
5686 		goto out;
5687 
5688 	/*
5689 	 * If len is not big enough to hold the page header, then
5690 	 * we can not copy anything.
5691 	 */
5692 	if (len <= BUF_PAGE_HDR_SIZE)
5693 		goto out;
5694 
5695 	len -= BUF_PAGE_HDR_SIZE;
5696 
5697 	if (!data_page)
5698 		goto out;
5699 
5700 	bpage = *data_page;
5701 	if (!bpage)
5702 		goto out;
5703 
5704 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5705 
5706 	reader = rb_get_reader_page(cpu_buffer);
5707 	if (!reader)
5708 		goto out_unlock;
5709 
5710 	event = rb_reader_event(cpu_buffer);
5711 
5712 	read = reader->read;
5713 	commit = rb_page_commit(reader);
5714 
5715 	/* Check if any events were dropped */
5716 	missed_events = cpu_buffer->lost_events;
5717 
5718 	/*
5719 	 * If this page has been partially read or
5720 	 * if len is not big enough to read the rest of the page or
5721 	 * a writer is still on the page, then
5722 	 * we must copy the data from the page to the buffer.
5723 	 * Otherwise, we can simply swap the page with the one passed in.
5724 	 */
5725 	if (read || (len < (commit - read)) ||
5726 	    cpu_buffer->reader_page == cpu_buffer->commit_page) {
5727 		struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
5728 		unsigned int rpos = read;
5729 		unsigned int pos = 0;
5730 		unsigned int size;
5731 
5732 		/*
5733 		 * If a full page is expected, this can still be returned
5734 		 * if there's been a previous partial read and the
5735 		 * rest of the page can be read and the commit page is off
5736 		 * the reader page.
5737 		 */
5738 		if (full &&
5739 		    (!read || (len < (commit - read)) ||
5740 		     cpu_buffer->reader_page == cpu_buffer->commit_page))
5741 			goto out_unlock;
5742 
5743 		if (len > (commit - read))
5744 			len = (commit - read);
5745 
5746 		/* Always keep the time extend and data together */
5747 		size = rb_event_ts_length(event);
5748 
5749 		if (len < size)
5750 			goto out_unlock;
5751 
5752 		/* save the current timestamp, since the user will need it */
5753 		save_timestamp = cpu_buffer->read_stamp;
5754 
5755 		/* Need to copy one event at a time */
5756 		do {
5757 			/* We need the size of one event, because
5758 			 * rb_advance_reader only advances by one event,
5759 			 * whereas rb_event_ts_length may include the size of
5760 			 * one or two events.
5761 			 * We have already ensured there's enough space if this
5762 			 * is a time extend. */
5763 			size = rb_event_length(event);
5764 			memcpy(bpage->data + pos, rpage->data + rpos, size);
5765 
5766 			len -= size;
5767 
5768 			rb_advance_reader(cpu_buffer);
5769 			rpos = reader->read;
5770 			pos += size;
5771 
5772 			if (rpos >= commit)
5773 				break;
5774 
5775 			event = rb_reader_event(cpu_buffer);
5776 			/* Always keep the time extend and data together */
5777 			size = rb_event_ts_length(event);
5778 		} while (len >= size);
5779 
5780 		/* update bpage */
5781 		local_set(&bpage->commit, pos);
5782 		bpage->time_stamp = save_timestamp;
5783 
5784 		/* we copied everything to the beginning */
5785 		read = 0;
5786 	} else {
5787 		/* update the entry counter */
5788 		cpu_buffer->read += rb_page_entries(reader);
5789 		cpu_buffer->read_bytes += BUF_PAGE_SIZE;
5790 
5791 		/* swap the pages */
5792 		rb_init_page(bpage);
5793 		bpage = reader->page;
5794 		reader->page = *data_page;
5795 		local_set(&reader->write, 0);
5796 		local_set(&reader->entries, 0);
5797 		reader->read = 0;
5798 		*data_page = bpage;
5799 
5800 		/*
5801 		 * Use the real_end for the data size,
5802 		 * This gives us a chance to store the lost events
5803 		 * on the page.
5804 		 */
5805 		if (reader->real_end)
5806 			local_set(&bpage->commit, reader->real_end);
5807 	}
5808 	ret = read;
5809 
5810 	cpu_buffer->lost_events = 0;
5811 
5812 	commit = local_read(&bpage->commit);
5813 	/*
5814 	 * Set a flag in the commit field if we lost events
5815 	 */
5816 	if (missed_events) {
5817 		/* If there is room at the end of the page to save the
5818 		 * missed events, then record it there.
5819 		 */
5820 		if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
5821 			memcpy(&bpage->data[commit], &missed_events,
5822 			       sizeof(missed_events));
5823 			local_add(RB_MISSED_STORED, &bpage->commit);
5824 			commit += sizeof(missed_events);
5825 		}
5826 		local_add(RB_MISSED_EVENTS, &bpage->commit);
5827 	}
5828 
5829 	/*
5830 	 * This page may be off to user land. Zero it out here.
5831 	 */
5832 	if (commit < BUF_PAGE_SIZE)
5833 		memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
5834 
5835  out_unlock:
5836 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5837 
5838  out:
5839 	return ret;
5840 }
5841 EXPORT_SYMBOL_GPL(ring_buffer_read_page);
5842 
5843 /*
5844  * We only allocate new buffers, never free them if the CPU goes down.
5845  * If we were to free the buffer, then the user would lose any trace that was in
5846  * the buffer.
5847  */
trace_rb_cpu_prepare(unsigned int cpu,struct hlist_node * node)5848 int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
5849 {
5850 	struct trace_buffer *buffer;
5851 	long nr_pages_same;
5852 	int cpu_i;
5853 	unsigned long nr_pages;
5854 
5855 	buffer = container_of(node, struct trace_buffer, node);
5856 	if (cpumask_test_cpu(cpu, buffer->cpumask))
5857 		return 0;
5858 
5859 	nr_pages = 0;
5860 	nr_pages_same = 1;
5861 	/* check if all cpu sizes are same */
5862 	for_each_buffer_cpu(buffer, cpu_i) {
5863 		/* fill in the size from first enabled cpu */
5864 		if (nr_pages == 0)
5865 			nr_pages = buffer->buffers[cpu_i]->nr_pages;
5866 		if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
5867 			nr_pages_same = 0;
5868 			break;
5869 		}
5870 	}
5871 	/* allocate minimum pages, user can later expand it */
5872 	if (!nr_pages_same)
5873 		nr_pages = 2;
5874 	buffer->buffers[cpu] =
5875 		rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
5876 	if (!buffer->buffers[cpu]) {
5877 		WARN(1, "failed to allocate ring buffer on CPU %u\n",
5878 		     cpu);
5879 		return -ENOMEM;
5880 	}
5881 	smp_wmb();
5882 	cpumask_set_cpu(cpu, buffer->cpumask);
5883 	return 0;
5884 }
5885 
5886 #ifdef CONFIG_RING_BUFFER_STARTUP_TEST
5887 /*
5888  * This is a basic integrity check of the ring buffer.
5889  * Late in the boot cycle this test will run when configured in.
5890  * It will kick off a thread per CPU that will go into a loop
5891  * writing to the per cpu ring buffer various sizes of data.
5892  * Some of the data will be large items, some small.
5893  *
5894  * Another thread is created that goes into a spin, sending out
5895  * IPIs to the other CPUs to also write into the ring buffer.
5896  * this is to test the nesting ability of the buffer.
5897  *
5898  * Basic stats are recorded and reported. If something in the
5899  * ring buffer should happen that's not expected, a big warning
5900  * is displayed and all ring buffers are disabled.
5901  */
5902 static struct task_struct *rb_threads[NR_CPUS] __initdata;
5903 
5904 struct rb_test_data {
5905 	struct trace_buffer *buffer;
5906 	unsigned long		events;
5907 	unsigned long		bytes_written;
5908 	unsigned long		bytes_alloc;
5909 	unsigned long		bytes_dropped;
5910 	unsigned long		events_nested;
5911 	unsigned long		bytes_written_nested;
5912 	unsigned long		bytes_alloc_nested;
5913 	unsigned long		bytes_dropped_nested;
5914 	int			min_size_nested;
5915 	int			max_size_nested;
5916 	int			max_size;
5917 	int			min_size;
5918 	int			cpu;
5919 	int			cnt;
5920 };
5921 
5922 static struct rb_test_data rb_data[NR_CPUS] __initdata;
5923 
5924 /* 1 meg per cpu */
5925 #define RB_TEST_BUFFER_SIZE	1048576
5926 
5927 static char rb_string[] __initdata =
5928 	"abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
5929 	"?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
5930 	"!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
5931 
5932 static bool rb_test_started __initdata;
5933 
5934 struct rb_item {
5935 	int size;
5936 	char str[];
5937 };
5938 
rb_write_something(struct rb_test_data * data,bool nested)5939 static __init int rb_write_something(struct rb_test_data *data, bool nested)
5940 {
5941 	struct ring_buffer_event *event;
5942 	struct rb_item *item;
5943 	bool started;
5944 	int event_len;
5945 	int size;
5946 	int len;
5947 	int cnt;
5948 
5949 	/* Have nested writes different that what is written */
5950 	cnt = data->cnt + (nested ? 27 : 0);
5951 
5952 	/* Multiply cnt by ~e, to make some unique increment */
5953 	size = (cnt * 68 / 25) % (sizeof(rb_string) - 1);
5954 
5955 	len = size + sizeof(struct rb_item);
5956 
5957 	started = rb_test_started;
5958 	/* read rb_test_started before checking buffer enabled */
5959 	smp_rmb();
5960 
5961 	event = ring_buffer_lock_reserve(data->buffer, len);
5962 	if (!event) {
5963 		/* Ignore dropped events before test starts. */
5964 		if (started) {
5965 			if (nested)
5966 				data->bytes_dropped += len;
5967 			else
5968 				data->bytes_dropped_nested += len;
5969 		}
5970 		return len;
5971 	}
5972 
5973 	event_len = ring_buffer_event_length(event);
5974 
5975 	if (RB_WARN_ON(data->buffer, event_len < len))
5976 		goto out;
5977 
5978 	item = ring_buffer_event_data(event);
5979 	item->size = size;
5980 	memcpy(item->str, rb_string, size);
5981 
5982 	if (nested) {
5983 		data->bytes_alloc_nested += event_len;
5984 		data->bytes_written_nested += len;
5985 		data->events_nested++;
5986 		if (!data->min_size_nested || len < data->min_size_nested)
5987 			data->min_size_nested = len;
5988 		if (len > data->max_size_nested)
5989 			data->max_size_nested = len;
5990 	} else {
5991 		data->bytes_alloc += event_len;
5992 		data->bytes_written += len;
5993 		data->events++;
5994 		if (!data->min_size || len < data->min_size)
5995 			data->max_size = len;
5996 		if (len > data->max_size)
5997 			data->max_size = len;
5998 	}
5999 
6000  out:
6001 	ring_buffer_unlock_commit(data->buffer, event);
6002 
6003 	return 0;
6004 }
6005 
rb_test(void * arg)6006 static __init int rb_test(void *arg)
6007 {
6008 	struct rb_test_data *data = arg;
6009 
6010 	while (!kthread_should_stop()) {
6011 		rb_write_something(data, false);
6012 		data->cnt++;
6013 
6014 		set_current_state(TASK_INTERRUPTIBLE);
6015 		/* Now sleep between a min of 100-300us and a max of 1ms */
6016 		usleep_range(((data->cnt % 3) + 1) * 100, 1000);
6017 	}
6018 
6019 	return 0;
6020 }
6021 
rb_ipi(void * ignore)6022 static __init void rb_ipi(void *ignore)
6023 {
6024 	struct rb_test_data *data;
6025 	int cpu = smp_processor_id();
6026 
6027 	data = &rb_data[cpu];
6028 	rb_write_something(data, true);
6029 }
6030 
rb_hammer_test(void * arg)6031 static __init int rb_hammer_test(void *arg)
6032 {
6033 	while (!kthread_should_stop()) {
6034 
6035 		/* Send an IPI to all cpus to write data! */
6036 		smp_call_function(rb_ipi, NULL, 1);
6037 		/* No sleep, but for non preempt, let others run */
6038 		schedule();
6039 	}
6040 
6041 	return 0;
6042 }
6043 
test_ringbuffer(void)6044 static __init int test_ringbuffer(void)
6045 {
6046 	struct task_struct *rb_hammer;
6047 	struct trace_buffer *buffer;
6048 	int cpu;
6049 	int ret = 0;
6050 
6051 	if (security_locked_down(LOCKDOWN_TRACEFS)) {
6052 		pr_warn("Lockdown is enabled, skipping ring buffer tests\n");
6053 		return 0;
6054 	}
6055 
6056 	pr_info("Running ring buffer tests...\n");
6057 
6058 	buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
6059 	if (WARN_ON(!buffer))
6060 		return 0;
6061 
6062 	/* Disable buffer so that threads can't write to it yet */
6063 	ring_buffer_record_off(buffer);
6064 
6065 	for_each_online_cpu(cpu) {
6066 		rb_data[cpu].buffer = buffer;
6067 		rb_data[cpu].cpu = cpu;
6068 		rb_data[cpu].cnt = cpu;
6069 		rb_threads[cpu] = kthread_run_on_cpu(rb_test, &rb_data[cpu],
6070 						     cpu, "rbtester/%u");
6071 		if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
6072 			pr_cont("FAILED\n");
6073 			ret = PTR_ERR(rb_threads[cpu]);
6074 			goto out_free;
6075 		}
6076 	}
6077 
6078 	/* Now create the rb hammer! */
6079 	rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
6080 	if (WARN_ON(IS_ERR(rb_hammer))) {
6081 		pr_cont("FAILED\n");
6082 		ret = PTR_ERR(rb_hammer);
6083 		goto out_free;
6084 	}
6085 
6086 	ring_buffer_record_on(buffer);
6087 	/*
6088 	 * Show buffer is enabled before setting rb_test_started.
6089 	 * Yes there's a small race window where events could be
6090 	 * dropped and the thread wont catch it. But when a ring
6091 	 * buffer gets enabled, there will always be some kind of
6092 	 * delay before other CPUs see it. Thus, we don't care about
6093 	 * those dropped events. We care about events dropped after
6094 	 * the threads see that the buffer is active.
6095 	 */
6096 	smp_wmb();
6097 	rb_test_started = true;
6098 
6099 	set_current_state(TASK_INTERRUPTIBLE);
6100 	/* Just run for 10 seconds */;
6101 	schedule_timeout(10 * HZ);
6102 
6103 	kthread_stop(rb_hammer);
6104 
6105  out_free:
6106 	for_each_online_cpu(cpu) {
6107 		if (!rb_threads[cpu])
6108 			break;
6109 		kthread_stop(rb_threads[cpu]);
6110 	}
6111 	if (ret) {
6112 		ring_buffer_free(buffer);
6113 		return ret;
6114 	}
6115 
6116 	/* Report! */
6117 	pr_info("finished\n");
6118 	for_each_online_cpu(cpu) {
6119 		struct ring_buffer_event *event;
6120 		struct rb_test_data *data = &rb_data[cpu];
6121 		struct rb_item *item;
6122 		unsigned long total_events;
6123 		unsigned long total_dropped;
6124 		unsigned long total_written;
6125 		unsigned long total_alloc;
6126 		unsigned long total_read = 0;
6127 		unsigned long total_size = 0;
6128 		unsigned long total_len = 0;
6129 		unsigned long total_lost = 0;
6130 		unsigned long lost;
6131 		int big_event_size;
6132 		int small_event_size;
6133 
6134 		ret = -1;
6135 
6136 		total_events = data->events + data->events_nested;
6137 		total_written = data->bytes_written + data->bytes_written_nested;
6138 		total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
6139 		total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
6140 
6141 		big_event_size = data->max_size + data->max_size_nested;
6142 		small_event_size = data->min_size + data->min_size_nested;
6143 
6144 		pr_info("CPU %d:\n", cpu);
6145 		pr_info("              events:    %ld\n", total_events);
6146 		pr_info("       dropped bytes:    %ld\n", total_dropped);
6147 		pr_info("       alloced bytes:    %ld\n", total_alloc);
6148 		pr_info("       written bytes:    %ld\n", total_written);
6149 		pr_info("       biggest event:    %d\n", big_event_size);
6150 		pr_info("      smallest event:    %d\n", small_event_size);
6151 
6152 		if (RB_WARN_ON(buffer, total_dropped))
6153 			break;
6154 
6155 		ret = 0;
6156 
6157 		while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
6158 			total_lost += lost;
6159 			item = ring_buffer_event_data(event);
6160 			total_len += ring_buffer_event_length(event);
6161 			total_size += item->size + sizeof(struct rb_item);
6162 			if (memcmp(&item->str[0], rb_string, item->size) != 0) {
6163 				pr_info("FAILED!\n");
6164 				pr_info("buffer had: %.*s\n", item->size, item->str);
6165 				pr_info("expected:   %.*s\n", item->size, rb_string);
6166 				RB_WARN_ON(buffer, 1);
6167 				ret = -1;
6168 				break;
6169 			}
6170 			total_read++;
6171 		}
6172 		if (ret)
6173 			break;
6174 
6175 		ret = -1;
6176 
6177 		pr_info("         read events:   %ld\n", total_read);
6178 		pr_info("         lost events:   %ld\n", total_lost);
6179 		pr_info("        total events:   %ld\n", total_lost + total_read);
6180 		pr_info("  recorded len bytes:   %ld\n", total_len);
6181 		pr_info(" recorded size bytes:   %ld\n", total_size);
6182 		if (total_lost) {
6183 			pr_info(" With dropped events, record len and size may not match\n"
6184 				" alloced and written from above\n");
6185 		} else {
6186 			if (RB_WARN_ON(buffer, total_len != total_alloc ||
6187 				       total_size != total_written))
6188 				break;
6189 		}
6190 		if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
6191 			break;
6192 
6193 		ret = 0;
6194 	}
6195 	if (!ret)
6196 		pr_info("Ring buffer PASSED!\n");
6197 
6198 	ring_buffer_free(buffer);
6199 	return 0;
6200 }
6201 
6202 late_initcall(test_ringbuffer);
6203 #endif /* CONFIG_RING_BUFFER_STARTUP_TEST */
6204