1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  linux/kernel/printk.c
4  *
5  *  Copyright (C) 1991, 1992  Linus Torvalds
6  *
7  * Modified to make sys_syslog() more flexible: added commands to
8  * return the last 4k of kernel messages, regardless of whether
9  * they've been read or not.  Added option to suppress kernel printk's
10  * to the console.  Added hook for sending the console messages
11  * elsewhere, in preparation for a serial line console (someday).
12  * Ted Ts'o, 2/11/93.
13  * Modified for sysctl support, 1/8/97, Chris Horn.
14  * Fixed SMP synchronization, 08/08/99, Manfred Spraul
15  *     manfred@colorfullife.com
16  * Rewrote bits to get rid of console_lock
17  *	01Mar01 Andrew Morton
18  */
19 
20 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
21 
22 #include <linux/kernel.h>
23 #include <linux/mm.h>
24 #include <linux/tty.h>
25 #include <linux/tty_driver.h>
26 #include <linux/console.h>
27 #include <linux/init.h>
28 #include <linux/jiffies.h>
29 #include <linux/nmi.h>
30 #include <linux/module.h>
31 #include <linux/moduleparam.h>
32 #include <linux/delay.h>
33 #include <linux/smp.h>
34 #include <linux/security.h>
35 #include <linux/memblock.h>
36 #include <linux/syscalls.h>
37 #include <linux/crash_core.h>
38 #include <linux/ratelimit.h>
39 #include <linux/kmsg_dump.h>
40 #include <linux/syslog.h>
41 #include <linux/cpu.h>
42 #include <linux/rculist.h>
43 #include <linux/poll.h>
44 #include <linux/irq_work.h>
45 #include <linux/ctype.h>
46 #include <linux/uio.h>
47 #include <linux/sched/clock.h>
48 #include <linux/sched/debug.h>
49 #include <linux/sched/task_stack.h>
50 
51 #include <linux/uaccess.h>
52 #include <asm/sections.h>
53 
54 #include <trace/events/initcall.h>
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/printk.h>
57 
58 #include "printk_ringbuffer.h"
59 #include "console_cmdline.h"
60 #include "braille.h"
61 #include "internal.h"
62 
63 int console_printk[4] = {
64 	CONSOLE_LOGLEVEL_DEFAULT,	/* console_loglevel */
65 	MESSAGE_LOGLEVEL_DEFAULT,	/* default_message_loglevel */
66 	CONSOLE_LOGLEVEL_MIN,		/* minimum_console_loglevel */
67 	CONSOLE_LOGLEVEL_DEFAULT,	/* default_console_loglevel */
68 };
69 EXPORT_SYMBOL_GPL(console_printk);
70 
71 atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
72 EXPORT_SYMBOL(ignore_console_lock_warning);
73 
74 /*
75  * Low level drivers may need that to know if they can schedule in
76  * their unblank() callback or not. So let's export it.
77  */
78 int oops_in_progress;
79 EXPORT_SYMBOL(oops_in_progress);
80 
81 /*
82  * console_sem protects the console_drivers list, and also
83  * provides serialisation for access to the entire console
84  * driver system.
85  */
86 static DEFINE_SEMAPHORE(console_sem);
87 struct console *console_drivers;
88 EXPORT_SYMBOL_GPL(console_drivers);
89 
90 /*
91  * System may need to suppress printk message under certain
92  * circumstances, like after kernel panic happens.
93  */
94 int __read_mostly suppress_printk;
95 
96 /*
97  * During panic, heavy printk by other CPUs can delay the
98  * panic and risk deadlock on console resources.
99  */
100 static int __read_mostly suppress_panic_printk;
101 
102 #ifdef CONFIG_LOCKDEP
103 static struct lockdep_map console_lock_dep_map = {
104 	.name = "console_lock"
105 };
106 #endif
107 
108 enum devkmsg_log_bits {
109 	__DEVKMSG_LOG_BIT_ON = 0,
110 	__DEVKMSG_LOG_BIT_OFF,
111 	__DEVKMSG_LOG_BIT_LOCK,
112 };
113 
114 enum devkmsg_log_masks {
115 	DEVKMSG_LOG_MASK_ON             = BIT(__DEVKMSG_LOG_BIT_ON),
116 	DEVKMSG_LOG_MASK_OFF            = BIT(__DEVKMSG_LOG_BIT_OFF),
117 	DEVKMSG_LOG_MASK_LOCK           = BIT(__DEVKMSG_LOG_BIT_LOCK),
118 };
119 
120 /* Keep both the 'on' and 'off' bits clear, i.e. ratelimit by default: */
121 #define DEVKMSG_LOG_MASK_DEFAULT	0
122 
123 static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
124 
__control_devkmsg(char * str)125 static int __control_devkmsg(char *str)
126 {
127 	size_t len;
128 
129 	if (!str)
130 		return -EINVAL;
131 
132 	len = str_has_prefix(str, "on");
133 	if (len) {
134 		devkmsg_log = DEVKMSG_LOG_MASK_ON;
135 		return len;
136 	}
137 
138 	len = str_has_prefix(str, "off");
139 	if (len) {
140 		devkmsg_log = DEVKMSG_LOG_MASK_OFF;
141 		return len;
142 	}
143 
144 	len = str_has_prefix(str, "ratelimit");
145 	if (len) {
146 		devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT;
147 		return len;
148 	}
149 
150 	return -EINVAL;
151 }
152 
control_devkmsg(char * str)153 static int __init control_devkmsg(char *str)
154 {
155 	if (__control_devkmsg(str) < 0) {
156 		pr_warn("printk.devkmsg: bad option string '%s'\n", str);
157 		return 1;
158 	}
159 
160 	/*
161 	 * Set sysctl string accordingly:
162 	 */
163 	if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
164 		strcpy(devkmsg_log_str, "on");
165 	else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
166 		strcpy(devkmsg_log_str, "off");
167 	/* else "ratelimit" which is set by default. */
168 
169 	/*
170 	 * Sysctl cannot change it anymore. The kernel command line setting of
171 	 * this parameter is to force the setting to be permanent throughout the
172 	 * runtime of the system. This is a precation measure against userspace
173 	 * trying to be a smarta** and attempting to change it up on us.
174 	 */
175 	devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
176 
177 	return 1;
178 }
179 __setup("printk.devkmsg=", control_devkmsg);
180 
181 char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
182 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
devkmsg_sysctl_set_loglvl(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)183 int devkmsg_sysctl_set_loglvl(struct ctl_table *table, int write,
184 			      void *buffer, size_t *lenp, loff_t *ppos)
185 {
186 	char old_str[DEVKMSG_STR_MAX_SIZE];
187 	unsigned int old;
188 	int err;
189 
190 	if (write) {
191 		if (devkmsg_log & DEVKMSG_LOG_MASK_LOCK)
192 			return -EINVAL;
193 
194 		old = devkmsg_log;
195 		strncpy(old_str, devkmsg_log_str, DEVKMSG_STR_MAX_SIZE);
196 	}
197 
198 	err = proc_dostring(table, write, buffer, lenp, ppos);
199 	if (err)
200 		return err;
201 
202 	if (write) {
203 		err = __control_devkmsg(devkmsg_log_str);
204 
205 		/*
206 		 * Do not accept an unknown string OR a known string with
207 		 * trailing crap...
208 		 */
209 		if (err < 0 || (err + 1 != *lenp)) {
210 
211 			/* ... and restore old setting. */
212 			devkmsg_log = old;
213 			strncpy(devkmsg_log_str, old_str, DEVKMSG_STR_MAX_SIZE);
214 
215 			return -EINVAL;
216 		}
217 	}
218 
219 	return 0;
220 }
221 #endif /* CONFIG_PRINTK && CONFIG_SYSCTL */
222 
223 /* Number of registered extended console drivers. */
224 static int nr_ext_console_drivers;
225 
226 /*
227  * Helper macros to handle lockdep when locking/unlocking console_sem. We use
228  * macros instead of functions so that _RET_IP_ contains useful information.
229  */
230 #define down_console_sem() do { \
231 	down(&console_sem);\
232 	mutex_acquire(&console_lock_dep_map, 0, 0, _RET_IP_);\
233 } while (0)
234 
__down_trylock_console_sem(unsigned long ip)235 static int __down_trylock_console_sem(unsigned long ip)
236 {
237 	int lock_failed;
238 	unsigned long flags;
239 
240 	/*
241 	 * Here and in __up_console_sem() we need to be in safe mode,
242 	 * because spindump/WARN/etc from under console ->lock will
243 	 * deadlock in printk()->down_trylock_console_sem() otherwise.
244 	 */
245 	printk_safe_enter_irqsave(flags);
246 	lock_failed = down_trylock(&console_sem);
247 	printk_safe_exit_irqrestore(flags);
248 
249 	if (lock_failed)
250 		return 1;
251 	mutex_acquire(&console_lock_dep_map, 0, 1, ip);
252 	return 0;
253 }
254 #define down_trylock_console_sem() __down_trylock_console_sem(_RET_IP_)
255 
__up_console_sem(unsigned long ip)256 static void __up_console_sem(unsigned long ip)
257 {
258 	unsigned long flags;
259 
260 	mutex_release(&console_lock_dep_map, ip);
261 
262 	printk_safe_enter_irqsave(flags);
263 	up(&console_sem);
264 	printk_safe_exit_irqrestore(flags);
265 }
266 #define up_console_sem() __up_console_sem(_RET_IP_)
267 
panic_in_progress(void)268 static bool panic_in_progress(void)
269 {
270 	return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
271 }
272 
273 /*
274  * This is used for debugging the mess that is the VT code by
275  * keeping track if we have the console semaphore held. It's
276  * definitely not the perfect debug tool (we don't know if _WE_
277  * hold it and are racing, but it helps tracking those weird code
278  * paths in the console code where we end up in places I want
279  * locked without the console semaphore held).
280  */
281 static int console_locked, console_suspended;
282 
283 /*
284  *	Array of consoles built from command line options (console=)
285  */
286 
287 #define MAX_CMDLINECONSOLES 8
288 
289 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
290 
291 static int preferred_console = -1;
292 int console_set_on_cmdline;
293 EXPORT_SYMBOL(console_set_on_cmdline);
294 
295 /* Flag: console code may call schedule() */
296 static int console_may_schedule;
297 
298 enum con_msg_format_flags {
299 	MSG_FORMAT_DEFAULT	= 0,
300 	MSG_FORMAT_SYSLOG	= (1 << 0),
301 };
302 
303 static int console_msg_format = MSG_FORMAT_DEFAULT;
304 
305 /*
306  * The printk log buffer consists of a sequenced collection of records, each
307  * containing variable length message text. Every record also contains its
308  * own meta-data (@info).
309  *
310  * Every record meta-data carries the timestamp in microseconds, as well as
311  * the standard userspace syslog level and syslog facility. The usual kernel
312  * messages use LOG_KERN; userspace-injected messages always carry a matching
313  * syslog facility, by default LOG_USER. The origin of every message can be
314  * reliably determined that way.
315  *
316  * The human readable log message of a record is available in @text, the
317  * length of the message text in @text_len. The stored message is not
318  * terminated.
319  *
320  * Optionally, a record can carry a dictionary of properties (key/value
321  * pairs), to provide userspace with a machine-readable message context.
322  *
323  * Examples for well-defined, commonly used property names are:
324  *   DEVICE=b12:8               device identifier
325  *                                b12:8         block dev_t
326  *                                c127:3        char dev_t
327  *                                n8            netdev ifindex
328  *                                +sound:card0  subsystem:devname
329  *   SUBSYSTEM=pci              driver-core subsystem name
330  *
331  * Valid characters in property names are [a-zA-Z0-9.-_]. Property names
332  * and values are terminated by a '\0' character.
333  *
334  * Example of record values:
335  *   record.text_buf                = "it's a line" (unterminated)
336  *   record.info.seq                = 56
337  *   record.info.ts_nsec            = 36863
338  *   record.info.text_len           = 11
339  *   record.info.facility           = 0 (LOG_KERN)
340  *   record.info.flags              = 0
341  *   record.info.level              = 3 (LOG_ERR)
342  *   record.info.caller_id          = 299 (task 299)
343  *   record.info.dev_info.subsystem = "pci" (terminated)
344  *   record.info.dev_info.device    = "+pci:0000:00:01.0" (terminated)
345  *
346  * The 'struct printk_info' buffer must never be directly exported to
347  * userspace, it is a kernel-private implementation detail that might
348  * need to be changed in the future, when the requirements change.
349  *
350  * /dev/kmsg exports the structured data in the following line format:
351  *   "<level>,<sequnum>,<timestamp>,<contflag>[,additional_values, ... ];<message text>\n"
352  *
353  * Users of the export format should ignore possible additional values
354  * separated by ',', and find the message after the ';' character.
355  *
356  * The optional key/value pairs are attached as continuation lines starting
357  * with a space character and terminated by a newline. All possible
358  * non-prinatable characters are escaped in the "\xff" notation.
359  */
360 
361 /* syslog_lock protects syslog_* variables and write access to clear_seq. */
362 static DEFINE_MUTEX(syslog_lock);
363 
364 #ifdef CONFIG_PRINTK
365 DECLARE_WAIT_QUEUE_HEAD(log_wait);
366 /* All 3 protected by @syslog_lock. */
367 /* the next printk record to read by syslog(READ) or /proc/kmsg */
368 static u64 syslog_seq;
369 static size_t syslog_partial;
370 static bool syslog_time;
371 
372 struct latched_seq {
373 	seqcount_latch_t	latch;
374 	u64			val[2];
375 };
376 
377 /*
378  * The next printk record to read after the last 'clear' command. There are
379  * two copies (updated with seqcount_latch) so that reads can locklessly
380  * access a valid value. Writers are synchronized by @syslog_lock.
381  */
382 static struct latched_seq clear_seq = {
383 	.latch		= SEQCNT_LATCH_ZERO(clear_seq.latch),
384 	.val[0]		= 0,
385 	.val[1]		= 0,
386 };
387 
388 #ifdef CONFIG_PRINTK_CALLER
389 #define PREFIX_MAX		48
390 #else
391 #define PREFIX_MAX		32
392 #endif
393 
394 /* the maximum size of a formatted record (i.e. with prefix added per line) */
395 #define CONSOLE_LOG_MAX		1024
396 
397 /* the maximum size for a dropped text message */
398 #define DROPPED_TEXT_MAX	64
399 
400 /* the maximum size allowed to be reserved for a record */
401 #define LOG_LINE_MAX		(CONSOLE_LOG_MAX - PREFIX_MAX)
402 
403 #define LOG_LEVEL(v)		((v) & 0x07)
404 #define LOG_FACILITY(v)		((v) >> 3 & 0xff)
405 
406 /* record buffer */
407 #define LOG_ALIGN __alignof__(unsigned long)
408 #define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
409 #define LOG_BUF_LEN_MAX (u32)(1 << 31)
410 static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
411 static char *log_buf = __log_buf;
412 static u32 log_buf_len = __LOG_BUF_LEN;
413 
414 /*
415  * Define the average message size. This only affects the number of
416  * descriptors that will be available. Underestimating is better than
417  * overestimating (too many available descriptors is better than not enough).
418  */
419 #define PRB_AVGBITS 5	/* 32 character average length */
420 
421 #if CONFIG_LOG_BUF_SHIFT <= PRB_AVGBITS
422 #error CONFIG_LOG_BUF_SHIFT value too small.
423 #endif
424 _DEFINE_PRINTKRB(printk_rb_static, CONFIG_LOG_BUF_SHIFT - PRB_AVGBITS,
425 		 PRB_AVGBITS, &__log_buf[0]);
426 
427 static struct printk_ringbuffer printk_rb_dynamic;
428 
429 static struct printk_ringbuffer *prb = &printk_rb_static;
430 
431 /*
432  * We cannot access per-CPU data (e.g. per-CPU flush irq_work) before
433  * per_cpu_areas are initialised. This variable is set to true when
434  * it's safe to access per-CPU data.
435  */
436 static bool __printk_percpu_data_ready __read_mostly;
437 
printk_percpu_data_ready(void)438 bool printk_percpu_data_ready(void)
439 {
440 	return __printk_percpu_data_ready;
441 }
442 
443 /* Must be called under syslog_lock. */
latched_seq_write(struct latched_seq * ls,u64 val)444 static void latched_seq_write(struct latched_seq *ls, u64 val)
445 {
446 	raw_write_seqcount_latch(&ls->latch);
447 	ls->val[0] = val;
448 	raw_write_seqcount_latch(&ls->latch);
449 	ls->val[1] = val;
450 }
451 
452 /* Can be called from any context. */
latched_seq_read_nolock(struct latched_seq * ls)453 static u64 latched_seq_read_nolock(struct latched_seq *ls)
454 {
455 	unsigned int seq;
456 	unsigned int idx;
457 	u64 val;
458 
459 	do {
460 		seq = raw_read_seqcount_latch(&ls->latch);
461 		idx = seq & 0x1;
462 		val = ls->val[idx];
463 	} while (read_seqcount_latch_retry(&ls->latch, seq));
464 
465 	return val;
466 }
467 
468 /* Return log buffer address */
log_buf_addr_get(void)469 char *log_buf_addr_get(void)
470 {
471 	return log_buf;
472 }
473 
474 /* Return log buffer size */
log_buf_len_get(void)475 u32 log_buf_len_get(void)
476 {
477 	return log_buf_len;
478 }
479 
480 /*
481  * Define how much of the log buffer we could take at maximum. The value
482  * must be greater than two. Note that only half of the buffer is available
483  * when the index points to the middle.
484  */
485 #define MAX_LOG_TAKE_PART 4
486 static const char trunc_msg[] = "<truncated>";
487 
truncate_msg(u16 * text_len,u16 * trunc_msg_len)488 static void truncate_msg(u16 *text_len, u16 *trunc_msg_len)
489 {
490 	/*
491 	 * The message should not take the whole buffer. Otherwise, it might
492 	 * get removed too soon.
493 	 */
494 	u32 max_text_len = log_buf_len / MAX_LOG_TAKE_PART;
495 
496 	if (*text_len > max_text_len)
497 		*text_len = max_text_len;
498 
499 	/* enable the warning message (if there is room) */
500 	*trunc_msg_len = strlen(trunc_msg);
501 	if (*text_len >= *trunc_msg_len)
502 		*text_len -= *trunc_msg_len;
503 	else
504 		*trunc_msg_len = 0;
505 }
506 
507 int dmesg_restrict = IS_ENABLED(CONFIG_SECURITY_DMESG_RESTRICT);
508 
syslog_action_restricted(int type)509 static int syslog_action_restricted(int type)
510 {
511 	if (dmesg_restrict)
512 		return 1;
513 	/*
514 	 * Unless restricted, we allow "read all" and "get buffer size"
515 	 * for everybody.
516 	 */
517 	return type != SYSLOG_ACTION_READ_ALL &&
518 	       type != SYSLOG_ACTION_SIZE_BUFFER;
519 }
520 
check_syslog_permissions(int type,int source)521 static int check_syslog_permissions(int type, int source)
522 {
523 	/*
524 	 * If this is from /proc/kmsg and we've already opened it, then we've
525 	 * already done the capabilities checks at open time.
526 	 */
527 	if (source == SYSLOG_FROM_PROC && type != SYSLOG_ACTION_OPEN)
528 		goto ok;
529 
530 	if (syslog_action_restricted(type)) {
531 		if (capable(CAP_SYSLOG))
532 			goto ok;
533 		/*
534 		 * For historical reasons, accept CAP_SYS_ADMIN too, with
535 		 * a warning.
536 		 */
537 		if (capable(CAP_SYS_ADMIN)) {
538 			pr_warn_once("%s (%d): Attempt to access syslog with "
539 				     "CAP_SYS_ADMIN but no CAP_SYSLOG "
540 				     "(deprecated).\n",
541 				 current->comm, task_pid_nr(current));
542 			goto ok;
543 		}
544 		return -EPERM;
545 	}
546 ok:
547 	return security_syslog(type);
548 }
549 
append_char(char ** pp,char * e,char c)550 static void append_char(char **pp, char *e, char c)
551 {
552 	if (*pp < e)
553 		*(*pp)++ = c;
554 }
555 
info_print_ext_header(char * buf,size_t size,struct printk_info * info)556 static ssize_t info_print_ext_header(char *buf, size_t size,
557 				     struct printk_info *info)
558 {
559 	u64 ts_usec = info->ts_nsec;
560 	char caller[20];
561 #ifdef CONFIG_PRINTK_CALLER
562 	u32 id = info->caller_id;
563 
564 	snprintf(caller, sizeof(caller), ",caller=%c%u",
565 		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
566 #else
567 	caller[0] = '\0';
568 #endif
569 
570 	do_div(ts_usec, 1000);
571 
572 	return scnprintf(buf, size, "%u,%llu,%llu,%c%s;",
573 			 (info->facility << 3) | info->level, info->seq,
574 			 ts_usec, info->flags & LOG_CONT ? 'c' : '-', caller);
575 }
576 
msg_add_ext_text(char * buf,size_t size,const char * text,size_t text_len,unsigned char endc)577 static ssize_t msg_add_ext_text(char *buf, size_t size,
578 				const char *text, size_t text_len,
579 				unsigned char endc)
580 {
581 	char *p = buf, *e = buf + size;
582 	size_t i;
583 
584 	/* escape non-printable characters */
585 	for (i = 0; i < text_len; i++) {
586 		unsigned char c = text[i];
587 
588 		if (c < ' ' || c >= 127 || c == '\\')
589 			p += scnprintf(p, e - p, "\\x%02x", c);
590 		else
591 			append_char(&p, e, c);
592 	}
593 	append_char(&p, e, endc);
594 
595 	return p - buf;
596 }
597 
msg_add_dict_text(char * buf,size_t size,const char * key,const char * val)598 static ssize_t msg_add_dict_text(char *buf, size_t size,
599 				 const char *key, const char *val)
600 {
601 	size_t val_len = strlen(val);
602 	ssize_t len;
603 
604 	if (!val_len)
605 		return 0;
606 
607 	len = msg_add_ext_text(buf, size, "", 0, ' ');	/* dict prefix */
608 	len += msg_add_ext_text(buf + len, size - len, key, strlen(key), '=');
609 	len += msg_add_ext_text(buf + len, size - len, val, val_len, '\n');
610 
611 	return len;
612 }
613 
msg_print_ext_body(char * buf,size_t size,char * text,size_t text_len,struct dev_printk_info * dev_info)614 static ssize_t msg_print_ext_body(char *buf, size_t size,
615 				  char *text, size_t text_len,
616 				  struct dev_printk_info *dev_info)
617 {
618 	ssize_t len;
619 
620 	len = msg_add_ext_text(buf, size, text, text_len, '\n');
621 
622 	if (!dev_info)
623 		goto out;
624 
625 	len += msg_add_dict_text(buf + len, size - len, "SUBSYSTEM",
626 				 dev_info->subsystem);
627 	len += msg_add_dict_text(buf + len, size - len, "DEVICE",
628 				 dev_info->device);
629 out:
630 	return len;
631 }
632 
633 /* /dev/kmsg - userspace message inject/listen interface */
634 struct devkmsg_user {
635 	atomic64_t seq;
636 	struct ratelimit_state rs;
637 	struct mutex lock;
638 	char buf[CONSOLE_EXT_LOG_MAX];
639 
640 	struct printk_info info;
641 	char text_buf[CONSOLE_EXT_LOG_MAX];
642 	struct printk_record record;
643 };
644 
645 static __printf(3, 4) __cold
devkmsg_emit(int facility,int level,const char * fmt,...)646 int devkmsg_emit(int facility, int level, const char *fmt, ...)
647 {
648 	va_list args;
649 	int r;
650 
651 	va_start(args, fmt);
652 	r = vprintk_emit(facility, level, NULL, fmt, args);
653 	va_end(args);
654 
655 	return r;
656 }
657 
devkmsg_write(struct kiocb * iocb,struct iov_iter * from)658 static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
659 {
660 	char *buf, *line;
661 	int level = default_message_loglevel;
662 	int facility = 1;	/* LOG_USER */
663 	struct file *file = iocb->ki_filp;
664 	struct devkmsg_user *user = file->private_data;
665 	size_t len = iov_iter_count(from);
666 	ssize_t ret = len;
667 
668 	if (!user || len > LOG_LINE_MAX)
669 		return -EINVAL;
670 
671 	/* Ignore when user logging is disabled. */
672 	if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
673 		return len;
674 
675 	/* Ratelimit when not explicitly enabled. */
676 	if (!(devkmsg_log & DEVKMSG_LOG_MASK_ON)) {
677 		if (!___ratelimit(&user->rs, current->comm))
678 			return ret;
679 	}
680 
681 	buf = kmalloc(len+1, GFP_KERNEL);
682 	if (buf == NULL)
683 		return -ENOMEM;
684 
685 	buf[len] = '\0';
686 	if (!copy_from_iter_full(buf, len, from)) {
687 		kfree(buf);
688 		return -EFAULT;
689 	}
690 
691 	/*
692 	 * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
693 	 * the decimal value represents 32bit, the lower 3 bit are the log
694 	 * level, the rest are the log facility.
695 	 *
696 	 * If no prefix or no userspace facility is specified, we
697 	 * enforce LOG_USER, to be able to reliably distinguish
698 	 * kernel-generated messages from userspace-injected ones.
699 	 */
700 	line = buf;
701 	if (line[0] == '<') {
702 		char *endp = NULL;
703 		unsigned int u;
704 
705 		u = simple_strtoul(line + 1, &endp, 10);
706 		if (endp && endp[0] == '>') {
707 			level = LOG_LEVEL(u);
708 			if (LOG_FACILITY(u) != 0)
709 				facility = LOG_FACILITY(u);
710 			endp++;
711 			line = endp;
712 		}
713 	}
714 
715 	devkmsg_emit(facility, level, "%s", line);
716 	kfree(buf);
717 	return ret;
718 }
719 
devkmsg_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)720 static ssize_t devkmsg_read(struct file *file, char __user *buf,
721 			    size_t count, loff_t *ppos)
722 {
723 	struct devkmsg_user *user = file->private_data;
724 	struct printk_record *r = &user->record;
725 	size_t len;
726 	ssize_t ret;
727 
728 	if (!user)
729 		return -EBADF;
730 
731 	ret = mutex_lock_interruptible(&user->lock);
732 	if (ret)
733 		return ret;
734 
735 	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
736 		if (file->f_flags & O_NONBLOCK) {
737 			ret = -EAGAIN;
738 			goto out;
739 		}
740 
741 		/*
742 		 * Guarantee this task is visible on the waitqueue before
743 		 * checking the wake condition.
744 		 *
745 		 * The full memory barrier within set_current_state() of
746 		 * prepare_to_wait_event() pairs with the full memory barrier
747 		 * within wq_has_sleeper().
748 		 *
749 		 * This pairs with __wake_up_klogd:A.
750 		 */
751 		ret = wait_event_interruptible(log_wait,
752 				prb_read_valid(prb,
753 					atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
754 		if (ret)
755 			goto out;
756 	}
757 
758 	if (r->info->seq != atomic64_read(&user->seq)) {
759 		/* our last seen message is gone, return error and reset */
760 		atomic64_set(&user->seq, r->info->seq);
761 		ret = -EPIPE;
762 		goto out;
763 	}
764 
765 	len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
766 	len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
767 				  &r->text_buf[0], r->info->text_len,
768 				  &r->info->dev_info);
769 
770 	atomic64_set(&user->seq, r->info->seq + 1);
771 
772 	if (len > count) {
773 		ret = -EINVAL;
774 		goto out;
775 	}
776 
777 	if (copy_to_user(buf, user->buf, len)) {
778 		ret = -EFAULT;
779 		goto out;
780 	}
781 	ret = len;
782 out:
783 	mutex_unlock(&user->lock);
784 	return ret;
785 }
786 
787 /*
788  * Be careful when modifying this function!!!
789  *
790  * Only few operations are supported because the device works only with the
791  * entire variable length messages (records). Non-standard values are
792  * returned in the other cases and has been this way for quite some time.
793  * User space applications might depend on this behavior.
794  */
devkmsg_llseek(struct file * file,loff_t offset,int whence)795 static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
796 {
797 	struct devkmsg_user *user = file->private_data;
798 	loff_t ret = 0;
799 
800 	if (!user)
801 		return -EBADF;
802 	if (offset)
803 		return -ESPIPE;
804 
805 	switch (whence) {
806 	case SEEK_SET:
807 		/* the first record */
808 		atomic64_set(&user->seq, prb_first_valid_seq(prb));
809 		break;
810 	case SEEK_DATA:
811 		/*
812 		 * The first record after the last SYSLOG_ACTION_CLEAR,
813 		 * like issued by 'dmesg -c'. Reading /dev/kmsg itself
814 		 * changes no global state, and does not clear anything.
815 		 */
816 		atomic64_set(&user->seq, latched_seq_read_nolock(&clear_seq));
817 		break;
818 	case SEEK_END:
819 		/* after the last record */
820 		atomic64_set(&user->seq, prb_next_seq(prb));
821 		break;
822 	default:
823 		ret = -EINVAL;
824 	}
825 	return ret;
826 }
827 
devkmsg_poll(struct file * file,poll_table * wait)828 static __poll_t devkmsg_poll(struct file *file, poll_table *wait)
829 {
830 	struct devkmsg_user *user = file->private_data;
831 	struct printk_info info;
832 	__poll_t ret = 0;
833 
834 	if (!user)
835 		return EPOLLERR|EPOLLNVAL;
836 
837 	poll_wait(file, &log_wait, wait);
838 
839 	if (prb_read_valid_info(prb, atomic64_read(&user->seq), &info, NULL)) {
840 		/* return error when data has vanished underneath us */
841 		if (info.seq != atomic64_read(&user->seq))
842 			ret = EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
843 		else
844 			ret = EPOLLIN|EPOLLRDNORM;
845 	}
846 
847 	return ret;
848 }
849 
devkmsg_open(struct inode * inode,struct file * file)850 static int devkmsg_open(struct inode *inode, struct file *file)
851 {
852 	struct devkmsg_user *user;
853 	int err;
854 
855 	if (devkmsg_log & DEVKMSG_LOG_MASK_OFF)
856 		return -EPERM;
857 
858 	/* write-only does not need any file context */
859 	if ((file->f_flags & O_ACCMODE) != O_WRONLY) {
860 		err = check_syslog_permissions(SYSLOG_ACTION_READ_ALL,
861 					       SYSLOG_FROM_READER);
862 		if (err)
863 			return err;
864 	}
865 
866 	user = kvmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
867 	if (!user)
868 		return -ENOMEM;
869 
870 	ratelimit_default_init(&user->rs);
871 	ratelimit_set_flags(&user->rs, RATELIMIT_MSG_ON_RELEASE);
872 
873 	mutex_init(&user->lock);
874 
875 	prb_rec_init_rd(&user->record, &user->info,
876 			&user->text_buf[0], sizeof(user->text_buf));
877 
878 	atomic64_set(&user->seq, prb_first_valid_seq(prb));
879 
880 	file->private_data = user;
881 	return 0;
882 }
883 
devkmsg_release(struct inode * inode,struct file * file)884 static int devkmsg_release(struct inode *inode, struct file *file)
885 {
886 	struct devkmsg_user *user = file->private_data;
887 
888 	if (!user)
889 		return 0;
890 
891 	ratelimit_state_exit(&user->rs);
892 
893 	mutex_destroy(&user->lock);
894 	kvfree(user);
895 	return 0;
896 }
897 
898 const struct file_operations kmsg_fops = {
899 	.open = devkmsg_open,
900 	.read = devkmsg_read,
901 	.write_iter = devkmsg_write,
902 	.llseek = devkmsg_llseek,
903 	.poll = devkmsg_poll,
904 	.release = devkmsg_release,
905 };
906 
907 #ifdef CONFIG_CRASH_CORE
908 /*
909  * This appends the listed symbols to /proc/vmcore
910  *
911  * /proc/vmcore is used by various utilities, like crash and makedumpfile to
912  * obtain access to symbols that are otherwise very difficult to locate.  These
913  * symbols are specifically used so that utilities can access and extract the
914  * dmesg log from a vmcore file after a crash.
915  */
log_buf_vmcoreinfo_setup(void)916 void log_buf_vmcoreinfo_setup(void)
917 {
918 	struct dev_printk_info *dev_info = NULL;
919 
920 	VMCOREINFO_SYMBOL(prb);
921 	VMCOREINFO_SYMBOL(printk_rb_static);
922 	VMCOREINFO_SYMBOL(clear_seq);
923 
924 	/*
925 	 * Export struct size and field offsets. User space tools can
926 	 * parse it and detect any changes to structure down the line.
927 	 */
928 
929 	VMCOREINFO_STRUCT_SIZE(printk_ringbuffer);
930 	VMCOREINFO_OFFSET(printk_ringbuffer, desc_ring);
931 	VMCOREINFO_OFFSET(printk_ringbuffer, text_data_ring);
932 	VMCOREINFO_OFFSET(printk_ringbuffer, fail);
933 
934 	VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
935 	VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
936 	VMCOREINFO_OFFSET(prb_desc_ring, descs);
937 	VMCOREINFO_OFFSET(prb_desc_ring, infos);
938 	VMCOREINFO_OFFSET(prb_desc_ring, head_id);
939 	VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
940 
941 	VMCOREINFO_STRUCT_SIZE(prb_desc);
942 	VMCOREINFO_OFFSET(prb_desc, state_var);
943 	VMCOREINFO_OFFSET(prb_desc, text_blk_lpos);
944 
945 	VMCOREINFO_STRUCT_SIZE(prb_data_blk_lpos);
946 	VMCOREINFO_OFFSET(prb_data_blk_lpos, begin);
947 	VMCOREINFO_OFFSET(prb_data_blk_lpos, next);
948 
949 	VMCOREINFO_STRUCT_SIZE(printk_info);
950 	VMCOREINFO_OFFSET(printk_info, seq);
951 	VMCOREINFO_OFFSET(printk_info, ts_nsec);
952 	VMCOREINFO_OFFSET(printk_info, text_len);
953 	VMCOREINFO_OFFSET(printk_info, caller_id);
954 	VMCOREINFO_OFFSET(printk_info, dev_info);
955 
956 	VMCOREINFO_STRUCT_SIZE(dev_printk_info);
957 	VMCOREINFO_OFFSET(dev_printk_info, subsystem);
958 	VMCOREINFO_LENGTH(printk_info_subsystem, sizeof(dev_info->subsystem));
959 	VMCOREINFO_OFFSET(dev_printk_info, device);
960 	VMCOREINFO_LENGTH(printk_info_device, sizeof(dev_info->device));
961 
962 	VMCOREINFO_STRUCT_SIZE(prb_data_ring);
963 	VMCOREINFO_OFFSET(prb_data_ring, size_bits);
964 	VMCOREINFO_OFFSET(prb_data_ring, data);
965 	VMCOREINFO_OFFSET(prb_data_ring, head_lpos);
966 	VMCOREINFO_OFFSET(prb_data_ring, tail_lpos);
967 
968 	VMCOREINFO_SIZE(atomic_long_t);
969 	VMCOREINFO_TYPE_OFFSET(atomic_long_t, counter);
970 
971 	VMCOREINFO_STRUCT_SIZE(latched_seq);
972 	VMCOREINFO_OFFSET(latched_seq, val);
973 }
974 #endif
975 
976 /* requested log_buf_len from kernel cmdline */
977 static unsigned long __initdata new_log_buf_len;
978 
979 /* we practice scaling the ring buffer by powers of 2 */
log_buf_len_update(u64 size)980 static void __init log_buf_len_update(u64 size)
981 {
982 	if (size > (u64)LOG_BUF_LEN_MAX) {
983 		size = (u64)LOG_BUF_LEN_MAX;
984 		pr_err("log_buf over 2G is not supported.\n");
985 	}
986 
987 	if (size)
988 		size = roundup_pow_of_two(size);
989 	if (size > log_buf_len)
990 		new_log_buf_len = (unsigned long)size;
991 }
992 
993 /* save requested log_buf_len since it's too early to process it */
log_buf_len_setup(char * str)994 static int __init log_buf_len_setup(char *str)
995 {
996 	u64 size;
997 
998 	if (!str)
999 		return -EINVAL;
1000 
1001 	size = memparse(str, &str);
1002 
1003 	log_buf_len_update(size);
1004 
1005 	return 0;
1006 }
1007 early_param("log_buf_len", log_buf_len_setup);
1008 
1009 #ifdef CONFIG_SMP
1010 #define __LOG_CPU_MAX_BUF_LEN (1 << CONFIG_LOG_CPU_MAX_BUF_SHIFT)
1011 
log_buf_add_cpu(void)1012 static void __init log_buf_add_cpu(void)
1013 {
1014 	unsigned int cpu_extra;
1015 
1016 	/*
1017 	 * archs should set up cpu_possible_bits properly with
1018 	 * set_cpu_possible() after setup_arch() but just in
1019 	 * case lets ensure this is valid.
1020 	 */
1021 	if (num_possible_cpus() == 1)
1022 		return;
1023 
1024 	cpu_extra = (num_possible_cpus() - 1) * __LOG_CPU_MAX_BUF_LEN;
1025 
1026 	/* by default this will only continue through for large > 64 CPUs */
1027 	if (cpu_extra <= __LOG_BUF_LEN / 2)
1028 		return;
1029 
1030 	pr_info("log_buf_len individual max cpu contribution: %d bytes\n",
1031 		__LOG_CPU_MAX_BUF_LEN);
1032 	pr_info("log_buf_len total cpu_extra contributions: %d bytes\n",
1033 		cpu_extra);
1034 	pr_info("log_buf_len min size: %d bytes\n", __LOG_BUF_LEN);
1035 
1036 	log_buf_len_update(cpu_extra + __LOG_BUF_LEN);
1037 }
1038 #else /* !CONFIG_SMP */
log_buf_add_cpu(void)1039 static inline void log_buf_add_cpu(void) {}
1040 #endif /* CONFIG_SMP */
1041 
set_percpu_data_ready(void)1042 static void __init set_percpu_data_ready(void)
1043 {
1044 	__printk_percpu_data_ready = true;
1045 }
1046 
add_to_rb(struct printk_ringbuffer * rb,struct printk_record * r)1047 static unsigned int __init add_to_rb(struct printk_ringbuffer *rb,
1048 				     struct printk_record *r)
1049 {
1050 	struct prb_reserved_entry e;
1051 	struct printk_record dest_r;
1052 
1053 	prb_rec_init_wr(&dest_r, r->info->text_len);
1054 
1055 	if (!prb_reserve(&e, rb, &dest_r))
1056 		return 0;
1057 
1058 	memcpy(&dest_r.text_buf[0], &r->text_buf[0], r->info->text_len);
1059 	dest_r.info->text_len = r->info->text_len;
1060 	dest_r.info->facility = r->info->facility;
1061 	dest_r.info->level = r->info->level;
1062 	dest_r.info->flags = r->info->flags;
1063 	dest_r.info->ts_nsec = r->info->ts_nsec;
1064 	dest_r.info->caller_id = r->info->caller_id;
1065 	memcpy(&dest_r.info->dev_info, &r->info->dev_info, sizeof(dest_r.info->dev_info));
1066 
1067 	prb_final_commit(&e);
1068 
1069 	return prb_record_text_space(&e);
1070 }
1071 
1072 static char setup_text_buf[LOG_LINE_MAX] __initdata;
1073 
setup_log_buf(int early)1074 void __init setup_log_buf(int early)
1075 {
1076 	struct printk_info *new_infos;
1077 	unsigned int new_descs_count;
1078 	struct prb_desc *new_descs;
1079 	struct printk_info info;
1080 	struct printk_record r;
1081 	unsigned int text_size;
1082 	size_t new_descs_size;
1083 	size_t new_infos_size;
1084 	unsigned long flags;
1085 	char *new_log_buf;
1086 	unsigned int free;
1087 	u64 seq;
1088 
1089 	/*
1090 	 * Some archs call setup_log_buf() multiple times - first is very
1091 	 * early, e.g. from setup_arch(), and second - when percpu_areas
1092 	 * are initialised.
1093 	 */
1094 	if (!early)
1095 		set_percpu_data_ready();
1096 
1097 	if (log_buf != __log_buf)
1098 		return;
1099 
1100 	if (!early && !new_log_buf_len)
1101 		log_buf_add_cpu();
1102 
1103 	if (!new_log_buf_len)
1104 		return;
1105 
1106 	new_descs_count = new_log_buf_len >> PRB_AVGBITS;
1107 	if (new_descs_count == 0) {
1108 		pr_err("new_log_buf_len: %lu too small\n", new_log_buf_len);
1109 		return;
1110 	}
1111 
1112 	new_log_buf = memblock_alloc(new_log_buf_len, LOG_ALIGN);
1113 	if (unlikely(!new_log_buf)) {
1114 		pr_err("log_buf_len: %lu text bytes not available\n",
1115 		       new_log_buf_len);
1116 		return;
1117 	}
1118 
1119 	new_descs_size = new_descs_count * sizeof(struct prb_desc);
1120 	new_descs = memblock_alloc(new_descs_size, LOG_ALIGN);
1121 	if (unlikely(!new_descs)) {
1122 		pr_err("log_buf_len: %zu desc bytes not available\n",
1123 		       new_descs_size);
1124 		goto err_free_log_buf;
1125 	}
1126 
1127 	new_infos_size = new_descs_count * sizeof(struct printk_info);
1128 	new_infos = memblock_alloc(new_infos_size, LOG_ALIGN);
1129 	if (unlikely(!new_infos)) {
1130 		pr_err("log_buf_len: %zu info bytes not available\n",
1131 		       new_infos_size);
1132 		goto err_free_descs;
1133 	}
1134 
1135 	prb_rec_init_rd(&r, &info, &setup_text_buf[0], sizeof(setup_text_buf));
1136 
1137 	prb_init(&printk_rb_dynamic,
1138 		 new_log_buf, ilog2(new_log_buf_len),
1139 		 new_descs, ilog2(new_descs_count),
1140 		 new_infos);
1141 
1142 	local_irq_save(flags);
1143 
1144 	log_buf_len = new_log_buf_len;
1145 	log_buf = new_log_buf;
1146 	new_log_buf_len = 0;
1147 
1148 	free = __LOG_BUF_LEN;
1149 	prb_for_each_record(0, &printk_rb_static, seq, &r) {
1150 		text_size = add_to_rb(&printk_rb_dynamic, &r);
1151 		if (text_size > free)
1152 			free = 0;
1153 		else
1154 			free -= text_size;
1155 	}
1156 
1157 	prb = &printk_rb_dynamic;
1158 
1159 	local_irq_restore(flags);
1160 
1161 	/*
1162 	 * Copy any remaining messages that might have appeared from
1163 	 * NMI context after copying but before switching to the
1164 	 * dynamic buffer.
1165 	 */
1166 	prb_for_each_record(seq, &printk_rb_static, seq, &r) {
1167 		text_size = add_to_rb(&printk_rb_dynamic, &r);
1168 		if (text_size > free)
1169 			free = 0;
1170 		else
1171 			free -= text_size;
1172 	}
1173 
1174 	if (seq != prb_next_seq(&printk_rb_static)) {
1175 		pr_err("dropped %llu messages\n",
1176 		       prb_next_seq(&printk_rb_static) - seq);
1177 	}
1178 
1179 	pr_info("log_buf_len: %u bytes\n", log_buf_len);
1180 	pr_info("early log buf free: %u(%u%%)\n",
1181 		free, (free * 100) / __LOG_BUF_LEN);
1182 	return;
1183 
1184 err_free_descs:
1185 	memblock_free(new_descs, new_descs_size);
1186 err_free_log_buf:
1187 	memblock_free(new_log_buf, new_log_buf_len);
1188 }
1189 
1190 static bool __read_mostly ignore_loglevel;
1191 
ignore_loglevel_setup(char * str)1192 static int __init ignore_loglevel_setup(char *str)
1193 {
1194 	ignore_loglevel = true;
1195 	pr_info("debug: ignoring loglevel setting.\n");
1196 
1197 	return 0;
1198 }
1199 
1200 early_param("ignore_loglevel", ignore_loglevel_setup);
1201 module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);
1202 MODULE_PARM_DESC(ignore_loglevel,
1203 		 "ignore loglevel setting (prints all kernel messages to the console)");
1204 
suppress_message_printing(int level)1205 static bool suppress_message_printing(int level)
1206 {
1207 	return (level >= console_loglevel && !ignore_loglevel);
1208 }
1209 
1210 #ifdef CONFIG_BOOT_PRINTK_DELAY
1211 
1212 static int boot_delay; /* msecs delay after each printk during bootup */
1213 static unsigned long long loops_per_msec;	/* based on boot_delay */
1214 
boot_delay_setup(char * str)1215 static int __init boot_delay_setup(char *str)
1216 {
1217 	unsigned long lpj;
1218 
1219 	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
1220 	loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
1221 
1222 	get_option(&str, &boot_delay);
1223 	if (boot_delay > 10 * 1000)
1224 		boot_delay = 0;
1225 
1226 	pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
1227 		"HZ: %d, loops_per_msec: %llu\n",
1228 		boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
1229 	return 0;
1230 }
1231 early_param("boot_delay", boot_delay_setup);
1232 
boot_delay_msec(int level)1233 static void boot_delay_msec(int level)
1234 {
1235 	unsigned long long k;
1236 	unsigned long timeout;
1237 
1238 	if ((boot_delay == 0 || system_state >= SYSTEM_RUNNING)
1239 		|| suppress_message_printing(level)) {
1240 		return;
1241 	}
1242 
1243 	k = (unsigned long long)loops_per_msec * boot_delay;
1244 
1245 	timeout = jiffies + msecs_to_jiffies(boot_delay);
1246 	while (k) {
1247 		k--;
1248 		cpu_relax();
1249 		/*
1250 		 * use (volatile) jiffies to prevent
1251 		 * compiler reduction; loop termination via jiffies
1252 		 * is secondary and may or may not happen.
1253 		 */
1254 		if (time_after(jiffies, timeout))
1255 			break;
1256 		touch_nmi_watchdog();
1257 	}
1258 }
1259 #else
boot_delay_msec(int level)1260 static inline void boot_delay_msec(int level)
1261 {
1262 }
1263 #endif
1264 
1265 static bool printk_time = IS_ENABLED(CONFIG_PRINTK_TIME);
1266 module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
1267 
print_syslog(unsigned int level,char * buf)1268 static size_t print_syslog(unsigned int level, char *buf)
1269 {
1270 	return sprintf(buf, "<%u>", level);
1271 }
1272 
print_time(u64 ts,char * buf)1273 static size_t print_time(u64 ts, char *buf)
1274 {
1275 	unsigned long rem_nsec = do_div(ts, 1000000000);
1276 
1277 	return sprintf(buf, "[%5lu.%06lu]",
1278 		       (unsigned long)ts, rem_nsec / 1000);
1279 }
1280 
1281 #ifdef CONFIG_PRINTK_CALLER
print_caller(u32 id,char * buf)1282 static size_t print_caller(u32 id, char *buf)
1283 {
1284 	char caller[12];
1285 
1286 	snprintf(caller, sizeof(caller), "%c%u",
1287 		 id & 0x80000000 ? 'C' : 'T', id & ~0x80000000);
1288 	return sprintf(buf, "[%6s]", caller);
1289 }
1290 #else
1291 #define print_caller(id, buf) 0
1292 #endif
1293 
info_print_prefix(const struct printk_info * info,bool syslog,bool time,char * buf)1294 static size_t info_print_prefix(const struct printk_info  *info, bool syslog,
1295 				bool time, char *buf)
1296 {
1297 	size_t len = 0;
1298 
1299 	if (syslog)
1300 		len = print_syslog((info->facility << 3) | info->level, buf);
1301 
1302 	if (time)
1303 		len += print_time(info->ts_nsec, buf + len);
1304 
1305 	len += print_caller(info->caller_id, buf + len);
1306 
1307 	if (IS_ENABLED(CONFIG_PRINTK_CALLER) || time) {
1308 		buf[len++] = ' ';
1309 		buf[len] = '\0';
1310 	}
1311 
1312 	return len;
1313 }
1314 
1315 /*
1316  * Prepare the record for printing. The text is shifted within the given
1317  * buffer to avoid a need for another one. The following operations are
1318  * done:
1319  *
1320  *   - Add prefix for each line.
1321  *   - Drop truncated lines that no longer fit into the buffer.
1322  *   - Add the trailing newline that has been removed in vprintk_store().
1323  *   - Add a string terminator.
1324  *
1325  * Since the produced string is always terminated, the maximum possible
1326  * return value is @r->text_buf_size - 1;
1327  *
1328  * Return: The length of the updated/prepared text, including the added
1329  * prefixes and the newline. The terminator is not counted. The dropped
1330  * line(s) are not counted.
1331  */
record_print_text(struct printk_record * r,bool syslog,bool time)1332 static size_t record_print_text(struct printk_record *r, bool syslog,
1333 				bool time)
1334 {
1335 	size_t text_len = r->info->text_len;
1336 	size_t buf_size = r->text_buf_size;
1337 	char *text = r->text_buf;
1338 	char prefix[PREFIX_MAX];
1339 	bool truncated = false;
1340 	size_t prefix_len;
1341 	size_t line_len;
1342 	size_t len = 0;
1343 	char *next;
1344 
1345 	/*
1346 	 * If the message was truncated because the buffer was not large
1347 	 * enough, treat the available text as if it were the full text.
1348 	 */
1349 	if (text_len > buf_size)
1350 		text_len = buf_size;
1351 
1352 	prefix_len = info_print_prefix(r->info, syslog, time, prefix);
1353 
1354 	/*
1355 	 * @text_len: bytes of unprocessed text
1356 	 * @line_len: bytes of current line _without_ newline
1357 	 * @text:     pointer to beginning of current line
1358 	 * @len:      number of bytes prepared in r->text_buf
1359 	 */
1360 	for (;;) {
1361 		next = memchr(text, '\n', text_len);
1362 		if (next) {
1363 			line_len = next - text;
1364 		} else {
1365 			/* Drop truncated line(s). */
1366 			if (truncated)
1367 				break;
1368 			line_len = text_len;
1369 		}
1370 
1371 		/*
1372 		 * Truncate the text if there is not enough space to add the
1373 		 * prefix and a trailing newline and a terminator.
1374 		 */
1375 		if (len + prefix_len + text_len + 1 + 1 > buf_size) {
1376 			/* Drop even the current line if no space. */
1377 			if (len + prefix_len + line_len + 1 + 1 > buf_size)
1378 				break;
1379 
1380 			text_len = buf_size - len - prefix_len - 1 - 1;
1381 			truncated = true;
1382 		}
1383 
1384 		memmove(text + prefix_len, text, text_len);
1385 		memcpy(text, prefix, prefix_len);
1386 
1387 		/*
1388 		 * Increment the prepared length to include the text and
1389 		 * prefix that were just moved+copied. Also increment for the
1390 		 * newline at the end of this line. If this is the last line,
1391 		 * there is no newline, but it will be added immediately below.
1392 		 */
1393 		len += prefix_len + line_len + 1;
1394 		if (text_len == line_len) {
1395 			/*
1396 			 * This is the last line. Add the trailing newline
1397 			 * removed in vprintk_store().
1398 			 */
1399 			text[prefix_len + line_len] = '\n';
1400 			break;
1401 		}
1402 
1403 		/*
1404 		 * Advance beyond the added prefix and the related line with
1405 		 * its newline.
1406 		 */
1407 		text += prefix_len + line_len + 1;
1408 
1409 		/*
1410 		 * The remaining text has only decreased by the line with its
1411 		 * newline.
1412 		 *
1413 		 * Note that @text_len can become zero. It happens when @text
1414 		 * ended with a newline (either due to truncation or the
1415 		 * original string ending with "\n\n"). The loop is correctly
1416 		 * repeated and (if not truncated) an empty line with a prefix
1417 		 * will be prepared.
1418 		 */
1419 		text_len -= line_len + 1;
1420 	}
1421 
1422 	/*
1423 	 * If a buffer was provided, it will be terminated. Space for the
1424 	 * string terminator is guaranteed to be available. The terminator is
1425 	 * not counted in the return value.
1426 	 */
1427 	if (buf_size > 0)
1428 		r->text_buf[len] = 0;
1429 
1430 	return len;
1431 }
1432 
get_record_print_text_size(struct printk_info * info,unsigned int line_count,bool syslog,bool time)1433 static size_t get_record_print_text_size(struct printk_info *info,
1434 					 unsigned int line_count,
1435 					 bool syslog, bool time)
1436 {
1437 	char prefix[PREFIX_MAX];
1438 	size_t prefix_len;
1439 
1440 	prefix_len = info_print_prefix(info, syslog, time, prefix);
1441 
1442 	/*
1443 	 * Each line will be preceded with a prefix. The intermediate
1444 	 * newlines are already within the text, but a final trailing
1445 	 * newline will be added.
1446 	 */
1447 	return ((prefix_len * line_count) + info->text_len + 1);
1448 }
1449 
1450 /*
1451  * Beginning with @start_seq, find the first record where it and all following
1452  * records up to (but not including) @max_seq fit into @size.
1453  *
1454  * @max_seq is simply an upper bound and does not need to exist. If the caller
1455  * does not require an upper bound, -1 can be used for @max_seq.
1456  */
find_first_fitting_seq(u64 start_seq,u64 max_seq,size_t size,bool syslog,bool time)1457 static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
1458 				  bool syslog, bool time)
1459 {
1460 	struct printk_info info;
1461 	unsigned int line_count;
1462 	size_t len = 0;
1463 	u64 seq;
1464 
1465 	/* Determine the size of the records up to @max_seq. */
1466 	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1467 		if (info.seq >= max_seq)
1468 			break;
1469 		len += get_record_print_text_size(&info, line_count, syslog, time);
1470 	}
1471 
1472 	/*
1473 	 * Adjust the upper bound for the next loop to avoid subtracting
1474 	 * lengths that were never added.
1475 	 */
1476 	if (seq < max_seq)
1477 		max_seq = seq;
1478 
1479 	/*
1480 	 * Move first record forward until length fits into the buffer. Ignore
1481 	 * newest messages that were not counted in the above cycle. Messages
1482 	 * might appear and get lost in the meantime. This is a best effort
1483 	 * that prevents an infinite loop that could occur with a retry.
1484 	 */
1485 	prb_for_each_info(start_seq, prb, seq, &info, &line_count) {
1486 		if (len <= size || info.seq >= max_seq)
1487 			break;
1488 		len -= get_record_print_text_size(&info, line_count, syslog, time);
1489 	}
1490 
1491 	return seq;
1492 }
1493 
1494 /* The caller is responsible for making sure @size is greater than 0. */
syslog_print(char __user * buf,int size)1495 static int syslog_print(char __user *buf, int size)
1496 {
1497 	struct printk_info info;
1498 	struct printk_record r;
1499 	char *text;
1500 	int len = 0;
1501 	u64 seq;
1502 
1503 	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1504 	if (!text)
1505 		return -ENOMEM;
1506 
1507 	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1508 
1509 	mutex_lock(&syslog_lock);
1510 
1511 	/*
1512 	 * Wait for the @syslog_seq record to be available. @syslog_seq may
1513 	 * change while waiting.
1514 	 */
1515 	do {
1516 		seq = syslog_seq;
1517 
1518 		mutex_unlock(&syslog_lock);
1519 		/*
1520 		 * Guarantee this task is visible on the waitqueue before
1521 		 * checking the wake condition.
1522 		 *
1523 		 * The full memory barrier within set_current_state() of
1524 		 * prepare_to_wait_event() pairs with the full memory barrier
1525 		 * within wq_has_sleeper().
1526 		 *
1527 		 * This pairs with __wake_up_klogd:A.
1528 		 */
1529 		len = wait_event_interruptible(log_wait,
1530 				prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
1531 		mutex_lock(&syslog_lock);
1532 
1533 		if (len)
1534 			goto out;
1535 	} while (syslog_seq != seq);
1536 
1537 	/*
1538 	 * Copy records that fit into the buffer. The above cycle makes sure
1539 	 * that the first record is always available.
1540 	 */
1541 	do {
1542 		size_t n;
1543 		size_t skip;
1544 		int err;
1545 
1546 		if (!prb_read_valid(prb, syslog_seq, &r))
1547 			break;
1548 
1549 		if (r.info->seq != syslog_seq) {
1550 			/* message is gone, move to next valid one */
1551 			syslog_seq = r.info->seq;
1552 			syslog_partial = 0;
1553 		}
1554 
1555 		/*
1556 		 * To keep reading/counting partial line consistent,
1557 		 * use printk_time value as of the beginning of a line.
1558 		 */
1559 		if (!syslog_partial)
1560 			syslog_time = printk_time;
1561 
1562 		skip = syslog_partial;
1563 		n = record_print_text(&r, true, syslog_time);
1564 		if (n - syslog_partial <= size) {
1565 			/* message fits into buffer, move forward */
1566 			syslog_seq = r.info->seq + 1;
1567 			n -= syslog_partial;
1568 			syslog_partial = 0;
1569 		} else if (!len){
1570 			/* partial read(), remember position */
1571 			n = size;
1572 			syslog_partial += n;
1573 		} else
1574 			n = 0;
1575 
1576 		if (!n)
1577 			break;
1578 
1579 		mutex_unlock(&syslog_lock);
1580 		err = copy_to_user(buf, text + skip, n);
1581 		mutex_lock(&syslog_lock);
1582 
1583 		if (err) {
1584 			if (!len)
1585 				len = -EFAULT;
1586 			break;
1587 		}
1588 
1589 		len += n;
1590 		size -= n;
1591 		buf += n;
1592 	} while (size);
1593 out:
1594 	mutex_unlock(&syslog_lock);
1595 	kfree(text);
1596 	return len;
1597 }
1598 
syslog_print_all(char __user * buf,int size,bool clear)1599 static int syslog_print_all(char __user *buf, int size, bool clear)
1600 {
1601 	struct printk_info info;
1602 	struct printk_record r;
1603 	char *text;
1604 	int len = 0;
1605 	u64 seq;
1606 	bool time;
1607 
1608 	text = kmalloc(CONSOLE_LOG_MAX, GFP_KERNEL);
1609 	if (!text)
1610 		return -ENOMEM;
1611 
1612 	time = printk_time;
1613 	/*
1614 	 * Find first record that fits, including all following records,
1615 	 * into the user-provided buffer for this dump.
1616 	 */
1617 	seq = find_first_fitting_seq(latched_seq_read_nolock(&clear_seq), -1,
1618 				     size, true, time);
1619 
1620 	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
1621 
1622 	len = 0;
1623 	prb_for_each_record(seq, prb, seq, &r) {
1624 		int textlen;
1625 
1626 		textlen = record_print_text(&r, true, time);
1627 
1628 		if (len + textlen > size) {
1629 			seq--;
1630 			break;
1631 		}
1632 
1633 		if (copy_to_user(buf + len, text, textlen))
1634 			len = -EFAULT;
1635 		else
1636 			len += textlen;
1637 
1638 		if (len < 0)
1639 			break;
1640 	}
1641 
1642 	if (clear) {
1643 		mutex_lock(&syslog_lock);
1644 		latched_seq_write(&clear_seq, seq);
1645 		mutex_unlock(&syslog_lock);
1646 	}
1647 
1648 	kfree(text);
1649 	return len;
1650 }
1651 
syslog_clear(void)1652 static void syslog_clear(void)
1653 {
1654 	mutex_lock(&syslog_lock);
1655 	latched_seq_write(&clear_seq, prb_next_seq(prb));
1656 	mutex_unlock(&syslog_lock);
1657 }
1658 
do_syslog(int type,char __user * buf,int len,int source)1659 int do_syslog(int type, char __user *buf, int len, int source)
1660 {
1661 	struct printk_info info;
1662 	bool clear = false;
1663 	static int saved_console_loglevel = LOGLEVEL_DEFAULT;
1664 	int error;
1665 
1666 	error = check_syslog_permissions(type, source);
1667 	if (error)
1668 		return error;
1669 
1670 	switch (type) {
1671 	case SYSLOG_ACTION_CLOSE:	/* Close log */
1672 		break;
1673 	case SYSLOG_ACTION_OPEN:	/* Open log */
1674 		break;
1675 	case SYSLOG_ACTION_READ:	/* Read from log */
1676 		if (!buf || len < 0)
1677 			return -EINVAL;
1678 		if (!len)
1679 			return 0;
1680 		if (!access_ok(buf, len))
1681 			return -EFAULT;
1682 		error = syslog_print(buf, len);
1683 		break;
1684 	/* Read/clear last kernel messages */
1685 	case SYSLOG_ACTION_READ_CLEAR:
1686 		clear = true;
1687 		fallthrough;
1688 	/* Read last kernel messages */
1689 	case SYSLOG_ACTION_READ_ALL:
1690 		if (!buf || len < 0)
1691 			return -EINVAL;
1692 		if (!len)
1693 			return 0;
1694 		if (!access_ok(buf, len))
1695 			return -EFAULT;
1696 		error = syslog_print_all(buf, len, clear);
1697 		break;
1698 	/* Clear ring buffer */
1699 	case SYSLOG_ACTION_CLEAR:
1700 		syslog_clear();
1701 		break;
1702 	/* Disable logging to console */
1703 	case SYSLOG_ACTION_CONSOLE_OFF:
1704 		if (saved_console_loglevel == LOGLEVEL_DEFAULT)
1705 			saved_console_loglevel = console_loglevel;
1706 		console_loglevel = minimum_console_loglevel;
1707 		break;
1708 	/* Enable logging to console */
1709 	case SYSLOG_ACTION_CONSOLE_ON:
1710 		if (saved_console_loglevel != LOGLEVEL_DEFAULT) {
1711 			console_loglevel = saved_console_loglevel;
1712 			saved_console_loglevel = LOGLEVEL_DEFAULT;
1713 		}
1714 		break;
1715 	/* Set level of messages printed to console */
1716 	case SYSLOG_ACTION_CONSOLE_LEVEL:
1717 		if (len < 1 || len > 8)
1718 			return -EINVAL;
1719 		if (len < minimum_console_loglevel)
1720 			len = minimum_console_loglevel;
1721 		console_loglevel = len;
1722 		/* Implicitly re-enable logging to console */
1723 		saved_console_loglevel = LOGLEVEL_DEFAULT;
1724 		break;
1725 	/* Number of chars in the log buffer */
1726 	case SYSLOG_ACTION_SIZE_UNREAD:
1727 		mutex_lock(&syslog_lock);
1728 		if (!prb_read_valid_info(prb, syslog_seq, &info, NULL)) {
1729 			/* No unread messages. */
1730 			mutex_unlock(&syslog_lock);
1731 			return 0;
1732 		}
1733 		if (info.seq != syslog_seq) {
1734 			/* messages are gone, move to first one */
1735 			syslog_seq = info.seq;
1736 			syslog_partial = 0;
1737 		}
1738 		if (source == SYSLOG_FROM_PROC) {
1739 			/*
1740 			 * Short-cut for poll(/"proc/kmsg") which simply checks
1741 			 * for pending data, not the size; return the count of
1742 			 * records, not the length.
1743 			 */
1744 			error = prb_next_seq(prb) - syslog_seq;
1745 		} else {
1746 			bool time = syslog_partial ? syslog_time : printk_time;
1747 			unsigned int line_count;
1748 			u64 seq;
1749 
1750 			prb_for_each_info(syslog_seq, prb, seq, &info,
1751 					  &line_count) {
1752 				error += get_record_print_text_size(&info, line_count,
1753 								    true, time);
1754 				time = printk_time;
1755 			}
1756 			error -= syslog_partial;
1757 		}
1758 		mutex_unlock(&syslog_lock);
1759 		break;
1760 	/* Size of the log buffer */
1761 	case SYSLOG_ACTION_SIZE_BUFFER:
1762 		error = log_buf_len;
1763 		break;
1764 	default:
1765 		error = -EINVAL;
1766 		break;
1767 	}
1768 
1769 	return error;
1770 }
1771 
SYSCALL_DEFINE3(syslog,int,type,char __user *,buf,int,len)1772 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
1773 {
1774 	return do_syslog(type, buf, len, SYSLOG_FROM_READER);
1775 }
1776 
1777 /*
1778  * Special console_lock variants that help to reduce the risk of soft-lockups.
1779  * They allow to pass console_lock to another printk() call using a busy wait.
1780  */
1781 
1782 #ifdef CONFIG_LOCKDEP
1783 static struct lockdep_map console_owner_dep_map = {
1784 	.name = "console_owner"
1785 };
1786 #endif
1787 
1788 static DEFINE_RAW_SPINLOCK(console_owner_lock);
1789 static struct task_struct *console_owner;
1790 static bool console_waiter;
1791 
1792 /**
1793  * console_lock_spinning_enable - mark beginning of code where another
1794  *	thread might safely busy wait
1795  *
1796  * This basically converts console_lock into a spinlock. This marks
1797  * the section where the console_lock owner can not sleep, because
1798  * there may be a waiter spinning (like a spinlock). Also it must be
1799  * ready to hand over the lock at the end of the section.
1800  */
console_lock_spinning_enable(void)1801 static void console_lock_spinning_enable(void)
1802 {
1803 	raw_spin_lock(&console_owner_lock);
1804 	console_owner = current;
1805 	raw_spin_unlock(&console_owner_lock);
1806 
1807 	/* The waiter may spin on us after setting console_owner */
1808 	spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1809 }
1810 
1811 /**
1812  * console_lock_spinning_disable_and_check - mark end of code where another
1813  *	thread was able to busy wait and check if there is a waiter
1814  *
1815  * This is called at the end of the section where spinning is allowed.
1816  * It has two functions. First, it is a signal that it is no longer
1817  * safe to start busy waiting for the lock. Second, it checks if
1818  * there is a busy waiter and passes the lock rights to her.
1819  *
1820  * Important: Callers lose the lock if there was a busy waiter.
1821  *	They must not touch items synchronized by console_lock
1822  *	in this case.
1823  *
1824  * Return: 1 if the lock rights were passed, 0 otherwise.
1825  */
console_lock_spinning_disable_and_check(void)1826 static int console_lock_spinning_disable_and_check(void)
1827 {
1828 	int waiter;
1829 
1830 	raw_spin_lock(&console_owner_lock);
1831 	waiter = READ_ONCE(console_waiter);
1832 	console_owner = NULL;
1833 	raw_spin_unlock(&console_owner_lock);
1834 
1835 	if (!waiter) {
1836 		spin_release(&console_owner_dep_map, _THIS_IP_);
1837 		return 0;
1838 	}
1839 
1840 	/* The waiter is now free to continue */
1841 	WRITE_ONCE(console_waiter, false);
1842 
1843 	spin_release(&console_owner_dep_map, _THIS_IP_);
1844 
1845 	/*
1846 	 * Hand off console_lock to waiter. The waiter will perform
1847 	 * the up(). After this, the waiter is the console_lock owner.
1848 	 */
1849 	mutex_release(&console_lock_dep_map, _THIS_IP_);
1850 	return 1;
1851 }
1852 
1853 /**
1854  * console_trylock_spinning - try to get console_lock by busy waiting
1855  *
1856  * This allows to busy wait for the console_lock when the current
1857  * owner is running in specially marked sections. It means that
1858  * the current owner is running and cannot reschedule until it
1859  * is ready to lose the lock.
1860  *
1861  * Return: 1 if we got the lock, 0 othrewise
1862  */
console_trylock_spinning(void)1863 static int console_trylock_spinning(void)
1864 {
1865 	struct task_struct *owner = NULL;
1866 	bool waiter;
1867 	bool spin = false;
1868 	unsigned long flags;
1869 
1870 	if (console_trylock())
1871 		return 1;
1872 
1873 	/*
1874 	 * It's unsafe to spin once a panic has begun. If we are the
1875 	 * panic CPU, we may have already halted the owner of the
1876 	 * console_sem. If we are not the panic CPU, then we should
1877 	 * avoid taking console_sem, so the panic CPU has a better
1878 	 * chance of cleanly acquiring it later.
1879 	 */
1880 	if (panic_in_progress())
1881 		return 0;
1882 
1883 	printk_safe_enter_irqsave(flags);
1884 
1885 	raw_spin_lock(&console_owner_lock);
1886 	owner = READ_ONCE(console_owner);
1887 	waiter = READ_ONCE(console_waiter);
1888 	if (!waiter && owner && owner != current) {
1889 		WRITE_ONCE(console_waiter, true);
1890 		spin = true;
1891 	}
1892 	raw_spin_unlock(&console_owner_lock);
1893 
1894 	/*
1895 	 * If there is an active printk() writing to the
1896 	 * consoles, instead of having it write our data too,
1897 	 * see if we can offload that load from the active
1898 	 * printer, and do some printing ourselves.
1899 	 * Go into a spin only if there isn't already a waiter
1900 	 * spinning, and there is an active printer, and
1901 	 * that active printer isn't us (recursive printk?).
1902 	 */
1903 	if (!spin) {
1904 		printk_safe_exit_irqrestore(flags);
1905 		return 0;
1906 	}
1907 
1908 	/* We spin waiting for the owner to release us */
1909 	spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_);
1910 	/* Owner will clear console_waiter on hand off */
1911 	while (READ_ONCE(console_waiter))
1912 		cpu_relax();
1913 	spin_release(&console_owner_dep_map, _THIS_IP_);
1914 
1915 	printk_safe_exit_irqrestore(flags);
1916 	/*
1917 	 * The owner passed the console lock to us.
1918 	 * Since we did not spin on console lock, annotate
1919 	 * this as a trylock. Otherwise lockdep will
1920 	 * complain.
1921 	 */
1922 	mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_);
1923 
1924 	return 1;
1925 }
1926 
1927 /*
1928  * Call the specified console driver, asking it to write out the specified
1929  * text and length. If @dropped_text is non-NULL and any records have been
1930  * dropped, a dropped message will be written out first.
1931  */
call_console_driver(struct console * con,const char * text,size_t len,char * dropped_text)1932 static void call_console_driver(struct console *con, const char *text, size_t len,
1933 				char *dropped_text)
1934 {
1935 	size_t dropped_len;
1936 
1937 	if (con->dropped && dropped_text) {
1938 		dropped_len = snprintf(dropped_text, DROPPED_TEXT_MAX,
1939 				       "** %lu printk messages dropped **\n",
1940 				       con->dropped);
1941 		con->dropped = 0;
1942 		con->write(con, dropped_text, dropped_len);
1943 	}
1944 
1945 	con->write(con, text, len);
1946 }
1947 
1948 /*
1949  * Recursion is tracked separately on each CPU. If NMIs are supported, an
1950  * additional NMI context per CPU is also separately tracked. Until per-CPU
1951  * is available, a separate "early tracking" is performed.
1952  */
1953 static DEFINE_PER_CPU(u8, printk_count);
1954 static u8 printk_count_early;
1955 #ifdef CONFIG_HAVE_NMI
1956 static DEFINE_PER_CPU(u8, printk_count_nmi);
1957 static u8 printk_count_nmi_early;
1958 #endif
1959 
1960 /*
1961  * Recursion is limited to keep the output sane. printk() should not require
1962  * more than 1 level of recursion (allowing, for example, printk() to trigger
1963  * a WARN), but a higher value is used in case some printk-internal errors
1964  * exist, such as the ringbuffer validation checks failing.
1965  */
1966 #define PRINTK_MAX_RECURSION 3
1967 
1968 /*
1969  * Return a pointer to the dedicated counter for the CPU+context of the
1970  * caller.
1971  */
__printk_recursion_counter(void)1972 static u8 *__printk_recursion_counter(void)
1973 {
1974 #ifdef CONFIG_HAVE_NMI
1975 	if (in_nmi()) {
1976 		if (printk_percpu_data_ready())
1977 			return this_cpu_ptr(&printk_count_nmi);
1978 		return &printk_count_nmi_early;
1979 	}
1980 #endif
1981 	if (printk_percpu_data_ready())
1982 		return this_cpu_ptr(&printk_count);
1983 	return &printk_count_early;
1984 }
1985 
1986 /*
1987  * Enter recursion tracking. Interrupts are disabled to simplify tracking.
1988  * The caller must check the boolean return value to see if the recursion is
1989  * allowed. On failure, interrupts are not disabled.
1990  *
1991  * @recursion_ptr must be a variable of type (u8 *) and is the same variable
1992  * that is passed to printk_exit_irqrestore().
1993  */
1994 #define printk_enter_irqsave(recursion_ptr, flags)	\
1995 ({							\
1996 	bool success = true;				\
1997 							\
1998 	typecheck(u8 *, recursion_ptr);			\
1999 	local_irq_save(flags);				\
2000 	(recursion_ptr) = __printk_recursion_counter();	\
2001 	if (*(recursion_ptr) > PRINTK_MAX_RECURSION) {	\
2002 		local_irq_restore(flags);		\
2003 		success = false;			\
2004 	} else {					\
2005 		(*(recursion_ptr))++;			\
2006 	}						\
2007 	success;					\
2008 })
2009 
2010 /* Exit recursion tracking, restoring interrupts. */
2011 #define printk_exit_irqrestore(recursion_ptr, flags)	\
2012 	do {						\
2013 		typecheck(u8 *, recursion_ptr);		\
2014 		(*(recursion_ptr))--;			\
2015 		local_irq_restore(flags);		\
2016 	} while (0)
2017 
2018 int printk_delay_msec __read_mostly;
2019 
printk_delay(int level)2020 static inline void printk_delay(int level)
2021 {
2022 	boot_delay_msec(level);
2023 
2024 	if (unlikely(printk_delay_msec)) {
2025 		int m = printk_delay_msec;
2026 
2027 		while (m--) {
2028 			mdelay(1);
2029 			touch_nmi_watchdog();
2030 		}
2031 	}
2032 }
2033 
printk_caller_id(void)2034 static inline u32 printk_caller_id(void)
2035 {
2036 	return in_task() ? task_pid_nr(current) :
2037 		0x80000000 + smp_processor_id();
2038 }
2039 
2040 /**
2041  * printk_parse_prefix - Parse level and control flags.
2042  *
2043  * @text:     The terminated text message.
2044  * @level:    A pointer to the current level value, will be updated.
2045  * @flags:    A pointer to the current printk_info flags, will be updated.
2046  *
2047  * @level may be NULL if the caller is not interested in the parsed value.
2048  * Otherwise the variable pointed to by @level must be set to
2049  * LOGLEVEL_DEFAULT in order to be updated with the parsed value.
2050  *
2051  * @flags may be NULL if the caller is not interested in the parsed value.
2052  * Otherwise the variable pointed to by @flags will be OR'd with the parsed
2053  * value.
2054  *
2055  * Return: The length of the parsed level and control flags.
2056  */
printk_parse_prefix(const char * text,int * level,enum printk_info_flags * flags)2057 u16 printk_parse_prefix(const char *text, int *level,
2058 			enum printk_info_flags *flags)
2059 {
2060 	u16 prefix_len = 0;
2061 	int kern_level;
2062 
2063 	while (*text) {
2064 		kern_level = printk_get_level(text);
2065 		if (!kern_level)
2066 			break;
2067 
2068 		switch (kern_level) {
2069 		case '0' ... '7':
2070 			if (level && *level == LOGLEVEL_DEFAULT)
2071 				*level = kern_level - '0';
2072 			break;
2073 		case 'c':	/* KERN_CONT */
2074 			if (flags)
2075 				*flags |= LOG_CONT;
2076 		}
2077 
2078 		prefix_len += 2;
2079 		text += 2;
2080 	}
2081 
2082 	return prefix_len;
2083 }
2084 
2085 __printf(5, 0)
printk_sprint(char * text,u16 size,int facility,enum printk_info_flags * flags,const char * fmt,va_list args)2086 static u16 printk_sprint(char *text, u16 size, int facility,
2087 			 enum printk_info_flags *flags, const char *fmt,
2088 			 va_list args)
2089 {
2090 	u16 text_len;
2091 
2092 	text_len = vscnprintf(text, size, fmt, args);
2093 
2094 	/* Mark and strip a trailing newline. */
2095 	if (text_len && text[text_len - 1] == '\n') {
2096 		text_len--;
2097 		*flags |= LOG_NEWLINE;
2098 	}
2099 
2100 	/* Strip log level and control flags. */
2101 	if (facility == 0) {
2102 		u16 prefix_len;
2103 
2104 		prefix_len = printk_parse_prefix(text, NULL, NULL);
2105 		if (prefix_len) {
2106 			text_len -= prefix_len;
2107 			memmove(text, text + prefix_len, text_len);
2108 		}
2109 	}
2110 
2111 	trace_console_rcuidle(text, text_len);
2112 
2113 	return text_len;
2114 }
2115 
2116 __printf(4, 0)
vprintk_store(int facility,int level,const struct dev_printk_info * dev_info,const char * fmt,va_list args)2117 int vprintk_store(int facility, int level,
2118 		  const struct dev_printk_info *dev_info,
2119 		  const char *fmt, va_list args)
2120 {
2121 	struct prb_reserved_entry e;
2122 	enum printk_info_flags flags = 0;
2123 	struct printk_record r;
2124 	unsigned long irqflags;
2125 	u16 trunc_msg_len = 0;
2126 	char prefix_buf[8];
2127 	u8 *recursion_ptr;
2128 	u16 reserve_size;
2129 	va_list args2;
2130 	u32 caller_id;
2131 	u16 text_len;
2132 	int ret = 0;
2133 	u64 ts_nsec;
2134 
2135 	if (!printk_enter_irqsave(recursion_ptr, irqflags))
2136 		return 0;
2137 
2138 	/*
2139 	 * Since the duration of printk() can vary depending on the message
2140 	 * and state of the ringbuffer, grab the timestamp now so that it is
2141 	 * close to the call of printk(). This provides a more deterministic
2142 	 * timestamp with respect to the caller.
2143 	 */
2144 	ts_nsec = local_clock();
2145 
2146 	caller_id = printk_caller_id();
2147 
2148 	/*
2149 	 * The sprintf needs to come first since the syslog prefix might be
2150 	 * passed in as a parameter. An extra byte must be reserved so that
2151 	 * later the vscnprintf() into the reserved buffer has room for the
2152 	 * terminating '\0', which is not counted by vsnprintf().
2153 	 */
2154 	va_copy(args2, args);
2155 	reserve_size = vsnprintf(&prefix_buf[0], sizeof(prefix_buf), fmt, args2) + 1;
2156 	va_end(args2);
2157 
2158 	if (reserve_size > LOG_LINE_MAX)
2159 		reserve_size = LOG_LINE_MAX;
2160 
2161 	/* Extract log level or control flags. */
2162 	if (facility == 0)
2163 		printk_parse_prefix(&prefix_buf[0], &level, &flags);
2164 
2165 	if (level == LOGLEVEL_DEFAULT)
2166 		level = default_message_loglevel;
2167 
2168 	if (dev_info)
2169 		flags |= LOG_NEWLINE;
2170 
2171 	if (flags & LOG_CONT) {
2172 		prb_rec_init_wr(&r, reserve_size);
2173 		if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {
2174 			text_len = printk_sprint(&r.text_buf[r.info->text_len], reserve_size,
2175 						 facility, &flags, fmt, args);
2176 			r.info->text_len += text_len;
2177 
2178 			if (flags & LOG_NEWLINE) {
2179 				r.info->flags |= LOG_NEWLINE;
2180 				prb_final_commit(&e);
2181 			} else {
2182 				prb_commit(&e);
2183 			}
2184 
2185 			ret = text_len;
2186 			goto out;
2187 		}
2188 	}
2189 
2190 	/*
2191 	 * Explicitly initialize the record before every prb_reserve() call.
2192 	 * prb_reserve_in_last() and prb_reserve() purposely invalidate the
2193 	 * structure when they fail.
2194 	 */
2195 	prb_rec_init_wr(&r, reserve_size);
2196 	if (!prb_reserve(&e, prb, &r)) {
2197 		/* truncate the message if it is too long for empty buffer */
2198 		truncate_msg(&reserve_size, &trunc_msg_len);
2199 
2200 		prb_rec_init_wr(&r, reserve_size + trunc_msg_len);
2201 		if (!prb_reserve(&e, prb, &r))
2202 			goto out;
2203 	}
2204 
2205 	/* fill message */
2206 	text_len = printk_sprint(&r.text_buf[0], reserve_size, facility, &flags, fmt, args);
2207 	if (trunc_msg_len)
2208 		memcpy(&r.text_buf[text_len], trunc_msg, trunc_msg_len);
2209 	r.info->text_len = text_len + trunc_msg_len;
2210 	r.info->facility = facility;
2211 	r.info->level = level & 7;
2212 	r.info->flags = flags & 0x1f;
2213 	r.info->ts_nsec = ts_nsec;
2214 	r.info->caller_id = caller_id;
2215 	if (dev_info)
2216 		memcpy(&r.info->dev_info, dev_info, sizeof(r.info->dev_info));
2217 
2218 	/* A message without a trailing newline can be continued. */
2219 	if (!(flags & LOG_NEWLINE))
2220 		prb_commit(&e);
2221 	else
2222 		prb_final_commit(&e);
2223 
2224 	ret = text_len + trunc_msg_len;
2225 out:
2226 	printk_exit_irqrestore(recursion_ptr, irqflags);
2227 	return ret;
2228 }
2229 
vprintk_emit(int facility,int level,const struct dev_printk_info * dev_info,const char * fmt,va_list args)2230 asmlinkage int vprintk_emit(int facility, int level,
2231 			    const struct dev_printk_info *dev_info,
2232 			    const char *fmt, va_list args)
2233 {
2234 	int printed_len;
2235 	bool in_sched = false;
2236 
2237 	/* Suppress unimportant messages after panic happens */
2238 	if (unlikely(suppress_printk))
2239 		return 0;
2240 
2241 	if (unlikely(suppress_panic_printk) &&
2242 	    atomic_read(&panic_cpu) != raw_smp_processor_id())
2243 		return 0;
2244 
2245 	if (level == LOGLEVEL_SCHED) {
2246 		level = LOGLEVEL_DEFAULT;
2247 		in_sched = true;
2248 	}
2249 
2250 	printk_delay(level);
2251 
2252 	printed_len = vprintk_store(facility, level, dev_info, fmt, args);
2253 
2254 	/* If called from the scheduler, we can not call up(). */
2255 	if (!in_sched) {
2256 		/*
2257 		 * The caller may be holding system-critical or
2258 		 * timing-sensitive locks. Disable preemption during
2259 		 * printing of all remaining records to all consoles so that
2260 		 * this context can return as soon as possible. Hopefully
2261 		 * another printk() caller will take over the printing.
2262 		 */
2263 		preempt_disable();
2264 		/*
2265 		 * Try to acquire and then immediately release the console
2266 		 * semaphore. The release will print out buffers. With the
2267 		 * spinning variant, this context tries to take over the
2268 		 * printing from another printing context.
2269 		 */
2270 		if (console_trylock_spinning())
2271 			console_unlock();
2272 		preempt_enable();
2273 	}
2274 
2275 	wake_up_klogd();
2276 	return printed_len;
2277 }
2278 EXPORT_SYMBOL(vprintk_emit);
2279 
vprintk_default(const char * fmt,va_list args)2280 int vprintk_default(const char *fmt, va_list args)
2281 {
2282 	return vprintk_emit(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
2283 }
2284 EXPORT_SYMBOL_GPL(vprintk_default);
2285 
_printk(const char * fmt,...)2286 asmlinkage __visible int _printk(const char *fmt, ...)
2287 {
2288 	va_list args;
2289 	int r;
2290 
2291 	va_start(args, fmt);
2292 	r = vprintk(fmt, args);
2293 	va_end(args);
2294 
2295 	return r;
2296 }
2297 EXPORT_SYMBOL(_printk);
2298 
2299 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
2300 
2301 #else /* CONFIG_PRINTK */
2302 
2303 #define CONSOLE_LOG_MAX		0
2304 #define DROPPED_TEXT_MAX	0
2305 #define printk_time		false
2306 
2307 #define prb_read_valid(rb, seq, r)	false
2308 #define prb_first_valid_seq(rb)		0
2309 #define prb_next_seq(rb)		0
2310 
2311 static u64 syslog_seq;
2312 
record_print_text(const struct printk_record * r,bool syslog,bool time)2313 static size_t record_print_text(const struct printk_record *r,
2314 				bool syslog, bool time)
2315 {
2316 	return 0;
2317 }
info_print_ext_header(char * buf,size_t size,struct printk_info * info)2318 static ssize_t info_print_ext_header(char *buf, size_t size,
2319 				     struct printk_info *info)
2320 {
2321 	return 0;
2322 }
msg_print_ext_body(char * buf,size_t size,char * text,size_t text_len,struct dev_printk_info * dev_info)2323 static ssize_t msg_print_ext_body(char *buf, size_t size,
2324 				  char *text, size_t text_len,
2325 				  struct dev_printk_info *dev_info) { return 0; }
console_lock_spinning_enable(void)2326 static void console_lock_spinning_enable(void) { }
console_lock_spinning_disable_and_check(void)2327 static int console_lock_spinning_disable_and_check(void) { return 0; }
call_console_driver(struct console * con,const char * text,size_t len,char * dropped_text)2328 static void call_console_driver(struct console *con, const char *text, size_t len,
2329 				char *dropped_text)
2330 {
2331 }
suppress_message_printing(int level)2332 static bool suppress_message_printing(int level) { return false; }
__pr_flush(struct console * con,int timeout_ms,bool reset_on_progress)2333 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
2334 
2335 #endif /* CONFIG_PRINTK */
2336 
2337 #ifdef CONFIG_EARLY_PRINTK
2338 struct console *early_console;
2339 
early_printk(const char * fmt,...)2340 asmlinkage __visible void early_printk(const char *fmt, ...)
2341 {
2342 	va_list ap;
2343 	char buf[512];
2344 	int n;
2345 
2346 	if (!early_console)
2347 		return;
2348 
2349 	va_start(ap, fmt);
2350 	n = vscnprintf(buf, sizeof(buf), fmt, ap);
2351 	va_end(ap);
2352 
2353 	early_console->write(early_console, buf, n);
2354 }
2355 #endif
2356 
set_user_specified(struct console_cmdline * c,bool user_specified)2357 static void set_user_specified(struct console_cmdline *c, bool user_specified)
2358 {
2359 	if (!user_specified)
2360 		return;
2361 
2362 	/*
2363 	 * @c console was defined by the user on the command line.
2364 	 * Do not clear when added twice also by SPCR or the device tree.
2365 	 */
2366 	c->user_specified = true;
2367 	/* At least one console defined by the user on the command line. */
2368 	console_set_on_cmdline = 1;
2369 }
2370 
__add_preferred_console(char * name,int idx,char * options,char * brl_options,bool user_specified)2371 static int __add_preferred_console(char *name, int idx, char *options,
2372 				   char *brl_options, bool user_specified)
2373 {
2374 	struct console_cmdline *c;
2375 	int i;
2376 
2377 	/*
2378 	 *	See if this tty is not yet registered, and
2379 	 *	if we have a slot free.
2380 	 */
2381 	for (i = 0, c = console_cmdline;
2382 	     i < MAX_CMDLINECONSOLES && c->name[0];
2383 	     i++, c++) {
2384 		if (strcmp(c->name, name) == 0 && c->index == idx) {
2385 			if (!brl_options)
2386 				preferred_console = i;
2387 			set_user_specified(c, user_specified);
2388 			return 0;
2389 		}
2390 	}
2391 	if (i == MAX_CMDLINECONSOLES)
2392 		return -E2BIG;
2393 	if (!brl_options)
2394 		preferred_console = i;
2395 	strlcpy(c->name, name, sizeof(c->name));
2396 	c->options = options;
2397 	set_user_specified(c, user_specified);
2398 	braille_set_options(c, brl_options);
2399 
2400 	c->index = idx;
2401 	return 0;
2402 }
2403 
console_msg_format_setup(char * str)2404 static int __init console_msg_format_setup(char *str)
2405 {
2406 	if (!strcmp(str, "syslog"))
2407 		console_msg_format = MSG_FORMAT_SYSLOG;
2408 	if (!strcmp(str, "default"))
2409 		console_msg_format = MSG_FORMAT_DEFAULT;
2410 	return 1;
2411 }
2412 __setup("console_msg_format=", console_msg_format_setup);
2413 
2414 /*
2415  * Set up a console.  Called via do_early_param() in init/main.c
2416  * for each "console=" parameter in the boot command line.
2417  */
console_setup(char * str)2418 static int __init console_setup(char *str)
2419 {
2420 	char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for "ttyS" */
2421 	char *s, *options, *brl_options = NULL;
2422 	int idx;
2423 
2424 	/*
2425 	 * console="" or console=null have been suggested as a way to
2426 	 * disable console output. Use ttynull that has been created
2427 	 * for exactly this purpose.
2428 	 */
2429 	if (str[0] == 0 || strcmp(str, "null") == 0) {
2430 		__add_preferred_console("ttynull", 0, NULL, NULL, true);
2431 		return 1;
2432 	}
2433 
2434 	if (_braille_console_setup(&str, &brl_options))
2435 		return 1;
2436 
2437 	/*
2438 	 * Decode str into name, index, options.
2439 	 */
2440 	if (str[0] >= '0' && str[0] <= '9') {
2441 		strcpy(buf, "ttyS");
2442 		strncpy(buf + 4, str, sizeof(buf) - 5);
2443 	} else {
2444 		strncpy(buf, str, sizeof(buf) - 1);
2445 	}
2446 	buf[sizeof(buf) - 1] = 0;
2447 	options = strchr(str, ',');
2448 	if (options)
2449 		*(options++) = 0;
2450 #ifdef __sparc__
2451 	if (!strcmp(str, "ttya"))
2452 		strcpy(buf, "ttyS0");
2453 	if (!strcmp(str, "ttyb"))
2454 		strcpy(buf, "ttyS1");
2455 #endif
2456 	for (s = buf; *s; s++)
2457 		if (isdigit(*s) || *s == ',')
2458 			break;
2459 	idx = simple_strtoul(s, NULL, 10);
2460 	*s = 0;
2461 
2462 	__add_preferred_console(buf, idx, options, brl_options, true);
2463 	return 1;
2464 }
2465 __setup("console=", console_setup);
2466 
2467 /**
2468  * add_preferred_console - add a device to the list of preferred consoles.
2469  * @name: device name
2470  * @idx: device index
2471  * @options: options for this console
2472  *
2473  * The last preferred console added will be used for kernel messages
2474  * and stdin/out/err for init.  Normally this is used by console_setup
2475  * above to handle user-supplied console arguments; however it can also
2476  * be used by arch-specific code either to override the user or more
2477  * commonly to provide a default console (ie from PROM variables) when
2478  * the user has not supplied one.
2479  */
add_preferred_console(char * name,int idx,char * options)2480 int add_preferred_console(char *name, int idx, char *options)
2481 {
2482 	return __add_preferred_console(name, idx, options, NULL, false);
2483 }
2484 
2485 bool console_suspend_enabled = true;
2486 EXPORT_SYMBOL(console_suspend_enabled);
2487 
console_suspend_disable(char * str)2488 static int __init console_suspend_disable(char *str)
2489 {
2490 	console_suspend_enabled = false;
2491 	return 1;
2492 }
2493 __setup("no_console_suspend", console_suspend_disable);
2494 module_param_named(console_suspend, console_suspend_enabled,
2495 		bool, S_IRUGO | S_IWUSR);
2496 MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
2497 	" and hibernate operations");
2498 
2499 static bool printk_console_no_auto_verbose;
2500 
console_verbose(void)2501 void console_verbose(void)
2502 {
2503 	if (console_loglevel && !printk_console_no_auto_verbose)
2504 		console_loglevel = CONSOLE_LOGLEVEL_MOTORMOUTH;
2505 }
2506 EXPORT_SYMBOL_GPL(console_verbose);
2507 
2508 module_param_named(console_no_auto_verbose, printk_console_no_auto_verbose, bool, 0644);
2509 MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to highest on oops/panic/etc");
2510 
2511 /**
2512  * suspend_console - suspend the console subsystem
2513  *
2514  * This disables printk() while we go into suspend states
2515  */
suspend_console(void)2516 void suspend_console(void)
2517 {
2518 	if (!console_suspend_enabled)
2519 		return;
2520 	pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
2521 	pr_flush(1000, true);
2522 	console_lock();
2523 	console_suspended = 1;
2524 	up_console_sem();
2525 }
2526 
resume_console(void)2527 void resume_console(void)
2528 {
2529 	if (!console_suspend_enabled)
2530 		return;
2531 	down_console_sem();
2532 	console_suspended = 0;
2533 	console_unlock();
2534 	pr_flush(1000, true);
2535 }
2536 
2537 /**
2538  * console_cpu_notify - print deferred console messages after CPU hotplug
2539  * @cpu: unused
2540  *
2541  * If printk() is called from a CPU that is not online yet, the messages
2542  * will be printed on the console only if there are CON_ANYTIME consoles.
2543  * This function is called when a new CPU comes online (or fails to come
2544  * up) or goes offline.
2545  */
console_cpu_notify(unsigned int cpu)2546 static int console_cpu_notify(unsigned int cpu)
2547 {
2548 	if (!cpuhp_tasks_frozen) {
2549 		/* If trylock fails, someone else is doing the printing */
2550 		if (console_trylock())
2551 			console_unlock();
2552 	}
2553 	return 0;
2554 }
2555 
2556 /**
2557  * console_lock - lock the console system for exclusive use.
2558  *
2559  * Acquires a lock which guarantees that the caller has
2560  * exclusive access to the console system and the console_drivers list.
2561  *
2562  * Can sleep, returns nothing.
2563  */
console_lock(void)2564 void console_lock(void)
2565 {
2566 	might_sleep();
2567 
2568 	down_console_sem();
2569 	if (console_suspended)
2570 		return;
2571 	console_locked = 1;
2572 	console_may_schedule = 1;
2573 }
2574 EXPORT_SYMBOL(console_lock);
2575 
2576 /**
2577  * console_trylock - try to lock the console system for exclusive use.
2578  *
2579  * Try to acquire a lock which guarantees that the caller has exclusive
2580  * access to the console system and the console_drivers list.
2581  *
2582  * returns 1 on success, and 0 on failure to acquire the lock.
2583  */
console_trylock(void)2584 int console_trylock(void)
2585 {
2586 	if (down_trylock_console_sem())
2587 		return 0;
2588 	if (console_suspended) {
2589 		up_console_sem();
2590 		return 0;
2591 	}
2592 	console_locked = 1;
2593 	console_may_schedule = 0;
2594 	return 1;
2595 }
2596 EXPORT_SYMBOL(console_trylock);
2597 
is_console_locked(void)2598 int is_console_locked(void)
2599 {
2600 	return console_locked;
2601 }
2602 EXPORT_SYMBOL(is_console_locked);
2603 
2604 /*
2605  * Return true when this CPU should unlock console_sem without pushing all
2606  * messages to the console. This reduces the chance that the console is
2607  * locked when the panic CPU tries to use it.
2608  */
abandon_console_lock_in_panic(void)2609 static bool abandon_console_lock_in_panic(void)
2610 {
2611 	if (!panic_in_progress())
2612 		return false;
2613 
2614 	/*
2615 	 * We can use raw_smp_processor_id() here because it is impossible for
2616 	 * the task to be migrated to the panic_cpu, or away from it. If
2617 	 * panic_cpu has already been set, and we're not currently executing on
2618 	 * that CPU, then we never will be.
2619 	 */
2620 	return atomic_read(&panic_cpu) != raw_smp_processor_id();
2621 }
2622 
2623 /*
2624  * Check if the given console is currently capable and allowed to print
2625  * records.
2626  *
2627  * Requires the console_lock.
2628  */
console_is_usable(struct console * con)2629 static inline bool console_is_usable(struct console *con)
2630 {
2631 	if (!(con->flags & CON_ENABLED))
2632 		return false;
2633 
2634 	if (!con->write)
2635 		return false;
2636 
2637 	/*
2638 	 * Console drivers may assume that per-cpu resources have been
2639 	 * allocated. So unless they're explicitly marked as being able to
2640 	 * cope (CON_ANYTIME) don't call them until this CPU is officially up.
2641 	 */
2642 	if (!cpu_online(raw_smp_processor_id()) &&
2643 	    !(con->flags & CON_ANYTIME))
2644 		return false;
2645 
2646 	return true;
2647 }
2648 
__console_unlock(void)2649 static void __console_unlock(void)
2650 {
2651 	console_locked = 0;
2652 	up_console_sem();
2653 }
2654 
2655 /*
2656  * Print one record for the given console. The record printed is whatever
2657  * record is the next available record for the given console.
2658  *
2659  * @text is a buffer of size CONSOLE_LOG_MAX.
2660  *
2661  * If extended messages should be printed, @ext_text is a buffer of size
2662  * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
2663  *
2664  * If dropped messages should be printed, @dropped_text is a buffer of size
2665  * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
2666  *
2667  * @handover will be set to true if a printk waiter has taken over the
2668  * console_lock, in which case the caller is no longer holding the
2669  * console_lock. Otherwise it is set to false.
2670  *
2671  * Returns false if the given console has no next record to print, otherwise
2672  * true.
2673  *
2674  * Requires the console_lock.
2675  */
console_emit_next_record(struct console * con,char * text,char * ext_text,char * dropped_text,bool * handover)2676 static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
2677 				     char *dropped_text, bool *handover)
2678 {
2679 	static int panic_console_dropped;
2680 	struct printk_info info;
2681 	struct printk_record r;
2682 	unsigned long flags;
2683 	char *write_text;
2684 	size_t len;
2685 
2686 	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
2687 
2688 	*handover = false;
2689 
2690 	if (!prb_read_valid(prb, con->seq, &r))
2691 		return false;
2692 
2693 	if (con->seq != r.info->seq) {
2694 		con->dropped += r.info->seq - con->seq;
2695 		con->seq = r.info->seq;
2696 		if (panic_in_progress() && panic_console_dropped++ > 10) {
2697 			suppress_panic_printk = 1;
2698 			pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
2699 		}
2700 	}
2701 
2702 	/* Skip record that has level above the console loglevel. */
2703 	if (suppress_message_printing(r.info->level)) {
2704 		con->seq++;
2705 		goto skip;
2706 	}
2707 
2708 	if (ext_text) {
2709 		write_text = ext_text;
2710 		len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
2711 		len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
2712 					  &r.text_buf[0], r.info->text_len, &r.info->dev_info);
2713 	} else {
2714 		write_text = text;
2715 		len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
2716 	}
2717 
2718 	/*
2719 	 * While actively printing out messages, if another printk()
2720 	 * were to occur on another CPU, it may wait for this one to
2721 	 * finish. This task can not be preempted if there is a
2722 	 * waiter waiting to take over.
2723 	 *
2724 	 * Interrupts are disabled because the hand over to a waiter
2725 	 * must not be interrupted until the hand over is completed
2726 	 * (@console_waiter is cleared).
2727 	 */
2728 	printk_safe_enter_irqsave(flags);
2729 	console_lock_spinning_enable();
2730 
2731 	stop_critical_timings();	/* don't trace print latency */
2732 	call_console_driver(con, write_text, len, dropped_text);
2733 	start_critical_timings();
2734 
2735 	con->seq++;
2736 
2737 	*handover = console_lock_spinning_disable_and_check();
2738 	printk_safe_exit_irqrestore(flags);
2739 skip:
2740 	return true;
2741 }
2742 
2743 /*
2744  * Print out all remaining records to all consoles.
2745  *
2746  * @do_cond_resched is set by the caller. It can be true only in schedulable
2747  * context.
2748  *
2749  * @next_seq is set to the sequence number after the last available record.
2750  * The value is valid only when this function returns true. It means that all
2751  * usable consoles are completely flushed.
2752  *
2753  * @handover will be set to true if a printk waiter has taken over the
2754  * console_lock, in which case the caller is no longer holding the
2755  * console_lock. Otherwise it is set to false.
2756  *
2757  * Returns true when there was at least one usable console and all messages
2758  * were flushed to all usable consoles. A returned false informs the caller
2759  * that everything was not flushed (either there were no usable consoles or
2760  * another context has taken over printing or it is a panic situation and this
2761  * is not the panic CPU). Regardless the reason, the caller should assume it
2762  * is not useful to immediately try again.
2763  *
2764  * Requires the console_lock.
2765  */
console_flush_all(bool do_cond_resched,u64 * next_seq,bool * handover)2766 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
2767 {
2768 	static char dropped_text[DROPPED_TEXT_MAX];
2769 	static char ext_text[CONSOLE_EXT_LOG_MAX];
2770 	static char text[CONSOLE_LOG_MAX];
2771 	bool any_usable = false;
2772 	struct console *con;
2773 	bool any_progress;
2774 
2775 	*next_seq = 0;
2776 	*handover = false;
2777 
2778 	do {
2779 		any_progress = false;
2780 
2781 		for_each_console(con) {
2782 			bool progress;
2783 
2784 			if (!console_is_usable(con))
2785 				continue;
2786 			any_usable = true;
2787 
2788 			if (con->flags & CON_EXTENDED) {
2789 				/* Extended consoles do not print "dropped messages". */
2790 				progress = console_emit_next_record(con, &text[0],
2791 								    &ext_text[0], NULL,
2792 								    handover);
2793 			} else {
2794 				progress = console_emit_next_record(con, &text[0],
2795 								    NULL, &dropped_text[0],
2796 								    handover);
2797 			}
2798 			if (*handover)
2799 				return false;
2800 
2801 			/* Track the next of the highest seq flushed. */
2802 			if (con->seq > *next_seq)
2803 				*next_seq = con->seq;
2804 
2805 			if (!progress)
2806 				continue;
2807 			any_progress = true;
2808 
2809 			/* Allow panic_cpu to take over the consoles safely. */
2810 			if (abandon_console_lock_in_panic())
2811 				return false;
2812 
2813 			if (do_cond_resched)
2814 				cond_resched();
2815 		}
2816 	} while (any_progress);
2817 
2818 	return any_usable;
2819 }
2820 
2821 /**
2822  * console_unlock - unlock the console system
2823  *
2824  * Releases the console_lock which the caller holds on the console system
2825  * and the console driver list.
2826  *
2827  * While the console_lock was held, console output may have been buffered
2828  * by printk().  If this is the case, console_unlock(); emits
2829  * the output prior to releasing the lock.
2830  *
2831  * console_unlock(); may be called from any context.
2832  */
console_unlock(void)2833 void console_unlock(void)
2834 {
2835 	bool do_cond_resched;
2836 	bool handover;
2837 	bool flushed;
2838 	u64 next_seq;
2839 
2840 	if (console_suspended) {
2841 		up_console_sem();
2842 		return;
2843 	}
2844 
2845 	/*
2846 	 * Console drivers are called with interrupts disabled, so
2847 	 * @console_may_schedule should be cleared before; however, we may
2848 	 * end up dumping a lot of lines, for example, if called from
2849 	 * console registration path, and should invoke cond_resched()
2850 	 * between lines if allowable.  Not doing so can cause a very long
2851 	 * scheduling stall on a slow console leading to RCU stall and
2852 	 * softlockup warnings which exacerbate the issue with more
2853 	 * messages practically incapacitating the system. Therefore, create
2854 	 * a local to use for the printing loop.
2855 	 */
2856 	do_cond_resched = console_may_schedule;
2857 
2858 	do {
2859 		console_may_schedule = 0;
2860 
2861 		flushed = console_flush_all(do_cond_resched, &next_seq, &handover);
2862 		if (!handover)
2863 			__console_unlock();
2864 
2865 		/*
2866 		 * Abort if there was a failure to flush all messages to all
2867 		 * usable consoles. Either it is not possible to flush (in
2868 		 * which case it would be an infinite loop of retrying) or
2869 		 * another context has taken over printing.
2870 		 */
2871 		if (!flushed)
2872 			break;
2873 
2874 		/*
2875 		 * Some context may have added new records after
2876 		 * console_flush_all() but before unlocking the console.
2877 		 * Re-check if there is a new record to flush. If the trylock
2878 		 * fails, another context is already handling the printing.
2879 		 */
2880 	} while (prb_read_valid(prb, next_seq, NULL) && console_trylock());
2881 }
2882 EXPORT_SYMBOL(console_unlock);
2883 
2884 /**
2885  * console_conditional_schedule - yield the CPU if required
2886  *
2887  * If the console code is currently allowed to sleep, and
2888  * if this CPU should yield the CPU to another task, do
2889  * so here.
2890  *
2891  * Must be called within console_lock();.
2892  */
console_conditional_schedule(void)2893 void __sched console_conditional_schedule(void)
2894 {
2895 	if (console_may_schedule)
2896 		cond_resched();
2897 }
2898 EXPORT_SYMBOL(console_conditional_schedule);
2899 
console_unblank(void)2900 void console_unblank(void)
2901 {
2902 	struct console *c;
2903 
2904 	/*
2905 	 * console_unblank can no longer be called in interrupt context unless
2906 	 * oops_in_progress is set to 1..
2907 	 */
2908 	if (oops_in_progress) {
2909 		if (down_trylock_console_sem() != 0)
2910 			return;
2911 	} else
2912 		console_lock();
2913 
2914 	console_locked = 1;
2915 	console_may_schedule = 0;
2916 	for_each_console(c)
2917 		if ((c->flags & CON_ENABLED) && c->unblank)
2918 			c->unblank();
2919 	console_unlock();
2920 
2921 	if (!oops_in_progress)
2922 		pr_flush(1000, true);
2923 }
2924 
2925 /**
2926  * console_flush_on_panic - flush console content on panic
2927  * @mode: flush all messages in buffer or just the pending ones
2928  *
2929  * Immediately output all pending messages no matter what.
2930  */
console_flush_on_panic(enum con_flush_mode mode)2931 void console_flush_on_panic(enum con_flush_mode mode)
2932 {
2933 	/*
2934 	 * If someone else is holding the console lock, trylock will fail
2935 	 * and may_schedule may be set.  Ignore and proceed to unlock so
2936 	 * that messages are flushed out.  As this can be called from any
2937 	 * context and we don't want to get preempted while flushing,
2938 	 * ensure may_schedule is cleared.
2939 	 */
2940 	console_trylock();
2941 	console_may_schedule = 0;
2942 
2943 	if (mode == CONSOLE_REPLAY_ALL) {
2944 		struct console *c;
2945 		u64 seq;
2946 
2947 		seq = prb_first_valid_seq(prb);
2948 		for_each_console(c)
2949 			c->seq = seq;
2950 	}
2951 	console_unlock();
2952 }
2953 
2954 /*
2955  * Return the console tty driver structure and its associated index
2956  */
console_device(int * index)2957 struct tty_driver *console_device(int *index)
2958 {
2959 	struct console *c;
2960 	struct tty_driver *driver = NULL;
2961 
2962 	console_lock();
2963 	for_each_console(c) {
2964 		if (!c->device)
2965 			continue;
2966 		driver = c->device(c, index);
2967 		if (driver)
2968 			break;
2969 	}
2970 	console_unlock();
2971 	return driver;
2972 }
2973 
2974 /*
2975  * Prevent further output on the passed console device so that (for example)
2976  * serial drivers can disable console output before suspending a port, and can
2977  * re-enable output afterwards.
2978  */
console_stop(struct console * console)2979 void console_stop(struct console *console)
2980 {
2981 	__pr_flush(console, 1000, true);
2982 	console_lock();
2983 	console->flags &= ~CON_ENABLED;
2984 	console_unlock();
2985 }
2986 EXPORT_SYMBOL(console_stop);
2987 
console_start(struct console * console)2988 void console_start(struct console *console)
2989 {
2990 	console_lock();
2991 	console->flags |= CON_ENABLED;
2992 	console_unlock();
2993 	__pr_flush(console, 1000, true);
2994 }
2995 EXPORT_SYMBOL(console_start);
2996 
2997 static int __read_mostly keep_bootcon;
2998 
keep_bootcon_setup(char * str)2999 static int __init keep_bootcon_setup(char *str)
3000 {
3001 	keep_bootcon = 1;
3002 	pr_info("debug: skip boot console de-registration.\n");
3003 
3004 	return 0;
3005 }
3006 
3007 early_param("keep_bootcon", keep_bootcon_setup);
3008 
3009 /*
3010  * This is called by register_console() to try to match
3011  * the newly registered console with any of the ones selected
3012  * by either the command line or add_preferred_console() and
3013  * setup/enable it.
3014  *
3015  * Care need to be taken with consoles that are statically
3016  * enabled such as netconsole
3017  */
try_enable_preferred_console(struct console * newcon,bool user_specified)3018 static int try_enable_preferred_console(struct console *newcon,
3019 					bool user_specified)
3020 {
3021 	struct console_cmdline *c;
3022 	int i, err;
3023 
3024 	for (i = 0, c = console_cmdline;
3025 	     i < MAX_CMDLINECONSOLES && c->name[0];
3026 	     i++, c++) {
3027 		if (c->user_specified != user_specified)
3028 			continue;
3029 		if (!newcon->match ||
3030 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
3031 			/* default matching */
3032 			BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
3033 			if (strcmp(c->name, newcon->name) != 0)
3034 				continue;
3035 			if (newcon->index >= 0 &&
3036 			    newcon->index != c->index)
3037 				continue;
3038 			if (newcon->index < 0)
3039 				newcon->index = c->index;
3040 
3041 			if (_braille_register_console(newcon, c))
3042 				return 0;
3043 
3044 			if (newcon->setup &&
3045 			    (err = newcon->setup(newcon, c->options)) != 0)
3046 				return err;
3047 		}
3048 		newcon->flags |= CON_ENABLED;
3049 		if (i == preferred_console)
3050 			newcon->flags |= CON_CONSDEV;
3051 		return 0;
3052 	}
3053 
3054 	/*
3055 	 * Some consoles, such as pstore and netconsole, can be enabled even
3056 	 * without matching. Accept the pre-enabled consoles only when match()
3057 	 * and setup() had a chance to be called.
3058 	 */
3059 	if (newcon->flags & CON_ENABLED && c->user_specified ==	user_specified)
3060 		return 0;
3061 
3062 	return -ENOENT;
3063 }
3064 
3065 /* Try to enable the console unconditionally */
try_enable_default_console(struct console * newcon)3066 static void try_enable_default_console(struct console *newcon)
3067 {
3068 	if (newcon->index < 0)
3069 		newcon->index = 0;
3070 
3071 	if (newcon->setup && newcon->setup(newcon, NULL) != 0)
3072 		return;
3073 
3074 	newcon->flags |= CON_ENABLED;
3075 
3076 	if (newcon->device)
3077 		newcon->flags |= CON_CONSDEV;
3078 }
3079 
3080 #define con_printk(lvl, con, fmt, ...)			\
3081 	printk(lvl pr_fmt("%sconsole [%s%d] " fmt),	\
3082 	       (con->flags & CON_BOOT) ? "boot" : "",	\
3083 	       con->name, con->index, ##__VA_ARGS__)
3084 
3085 /*
3086  * The console driver calls this routine during kernel initialization
3087  * to register the console printing procedure with printk() and to
3088  * print any messages that were printed by the kernel before the
3089  * console driver was initialized.
3090  *
3091  * This can happen pretty early during the boot process (because of
3092  * early_printk) - sometimes before setup_arch() completes - be careful
3093  * of what kernel features are used - they may not be initialised yet.
3094  *
3095  * There are two types of consoles - bootconsoles (early_printk) and
3096  * "real" consoles (everything which is not a bootconsole) which are
3097  * handled differently.
3098  *  - Any number of bootconsoles can be registered at any time.
3099  *  - As soon as a "real" console is registered, all bootconsoles
3100  *    will be unregistered automatically.
3101  *  - Once a "real" console is registered, any attempt to register a
3102  *    bootconsoles will be rejected
3103  */
register_console(struct console * newcon)3104 void register_console(struct console *newcon)
3105 {
3106 	struct console *con;
3107 	bool bootcon_enabled = false;
3108 	bool realcon_enabled = false;
3109 	int err;
3110 
3111 	for_each_console(con) {
3112 		if (WARN(con == newcon, "console '%s%d' already registered\n",
3113 					 con->name, con->index))
3114 			return;
3115 	}
3116 
3117 	for_each_console(con) {
3118 		if (con->flags & CON_BOOT)
3119 			bootcon_enabled = true;
3120 		else
3121 			realcon_enabled = true;
3122 	}
3123 
3124 	/* Do not register boot consoles when there already is a real one. */
3125 	if (newcon->flags & CON_BOOT && realcon_enabled) {
3126 		pr_info("Too late to register bootconsole %s%d\n",
3127 			newcon->name, newcon->index);
3128 		return;
3129 	}
3130 
3131 	/*
3132 	 * See if we want to enable this console driver by default.
3133 	 *
3134 	 * Nope when a console is preferred by the command line, device
3135 	 * tree, or SPCR.
3136 	 *
3137 	 * The first real console with tty binding (driver) wins. More
3138 	 * consoles might get enabled before the right one is found.
3139 	 *
3140 	 * Note that a console with tty binding will have CON_CONSDEV
3141 	 * flag set and will be first in the list.
3142 	 */
3143 	if (preferred_console < 0) {
3144 		if (!console_drivers || !console_drivers->device ||
3145 		    console_drivers->flags & CON_BOOT) {
3146 			try_enable_default_console(newcon);
3147 		}
3148 	}
3149 
3150 	/* See if this console matches one we selected on the command line */
3151 	err = try_enable_preferred_console(newcon, true);
3152 
3153 	/* If not, try to match against the platform default(s) */
3154 	if (err == -ENOENT)
3155 		err = try_enable_preferred_console(newcon, false);
3156 
3157 	/* printk() messages are not printed to the Braille console. */
3158 	if (err || newcon->flags & CON_BRL)
3159 		return;
3160 
3161 	/*
3162 	 * If we have a bootconsole, and are switching to a real console,
3163 	 * don't print everything out again, since when the boot console, and
3164 	 * the real console are the same physical device, it's annoying to
3165 	 * see the beginning boot messages twice
3166 	 */
3167 	if (bootcon_enabled &&
3168 	    ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
3169 		newcon->flags &= ~CON_PRINTBUFFER;
3170 	}
3171 
3172 	/*
3173 	 *	Put this console in the list - keep the
3174 	 *	preferred driver at the head of the list.
3175 	 */
3176 	console_lock();
3177 	if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
3178 		newcon->next = console_drivers;
3179 		console_drivers = newcon;
3180 		if (newcon->next)
3181 			newcon->next->flags &= ~CON_CONSDEV;
3182 		/* Ensure this flag is always set for the head of the list */
3183 		newcon->flags |= CON_CONSDEV;
3184 	} else {
3185 		newcon->next = console_drivers->next;
3186 		console_drivers->next = newcon;
3187 	}
3188 
3189 	if (newcon->flags & CON_EXTENDED)
3190 		nr_ext_console_drivers++;
3191 
3192 	newcon->dropped = 0;
3193 	if (newcon->flags & CON_PRINTBUFFER) {
3194 		/* Get a consistent copy of @syslog_seq. */
3195 		mutex_lock(&syslog_lock);
3196 		newcon->seq = syslog_seq;
3197 		mutex_unlock(&syslog_lock);
3198 	} else {
3199 		/* Begin with next message. */
3200 		newcon->seq = prb_next_seq(prb);
3201 	}
3202 	console_unlock();
3203 	console_sysfs_notify();
3204 
3205 	/*
3206 	 * By unregistering the bootconsoles after we enable the real console
3207 	 * we get the "console xxx enabled" message on all the consoles -
3208 	 * boot consoles, real consoles, etc - this is to ensure that end
3209 	 * users know there might be something in the kernel's log buffer that
3210 	 * went to the bootconsole (that they do not see on the real console)
3211 	 */
3212 	con_printk(KERN_INFO, newcon, "enabled\n");
3213 	if (bootcon_enabled &&
3214 	    ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV) &&
3215 	    !keep_bootcon) {
3216 		/* We need to iterate through all boot consoles, to make
3217 		 * sure we print everything out, before we unregister them.
3218 		 */
3219 		for_each_console(con)
3220 			if (con->flags & CON_BOOT)
3221 				unregister_console(con);
3222 	}
3223 }
3224 EXPORT_SYMBOL(register_console);
3225 
unregister_console(struct console * console)3226 int unregister_console(struct console *console)
3227 {
3228 	struct console *con;
3229 	int res;
3230 
3231 	con_printk(KERN_INFO, console, "disabled\n");
3232 
3233 	res = _braille_unregister_console(console);
3234 	if (res < 0)
3235 		return res;
3236 	if (res > 0)
3237 		return 0;
3238 
3239 	res = -ENODEV;
3240 	console_lock();
3241 	if (console_drivers == console) {
3242 		console_drivers=console->next;
3243 		res = 0;
3244 	} else {
3245 		for_each_console(con) {
3246 			if (con->next == console) {
3247 				con->next = console->next;
3248 				res = 0;
3249 				break;
3250 			}
3251 		}
3252 	}
3253 
3254 	if (res)
3255 		goto out_disable_unlock;
3256 
3257 	if (console->flags & CON_EXTENDED)
3258 		nr_ext_console_drivers--;
3259 
3260 	/*
3261 	 * If this isn't the last console and it has CON_CONSDEV set, we
3262 	 * need to set it on the next preferred console.
3263 	 */
3264 	if (console_drivers != NULL && console->flags & CON_CONSDEV)
3265 		console_drivers->flags |= CON_CONSDEV;
3266 
3267 	console->flags &= ~CON_ENABLED;
3268 	console_unlock();
3269 	console_sysfs_notify();
3270 
3271 	if (console->exit)
3272 		res = console->exit(console);
3273 
3274 	return res;
3275 
3276 out_disable_unlock:
3277 	console->flags &= ~CON_ENABLED;
3278 	console_unlock();
3279 
3280 	return res;
3281 }
3282 EXPORT_SYMBOL(unregister_console);
3283 
3284 /*
3285  * Initialize the console device. This is called *early*, so
3286  * we can't necessarily depend on lots of kernel help here.
3287  * Just do some early initializations, and do the complex setup
3288  * later.
3289  */
console_init(void)3290 void __init console_init(void)
3291 {
3292 	int ret;
3293 	initcall_t call;
3294 	initcall_entry_t *ce;
3295 
3296 	/* Setup the default TTY line discipline. */
3297 	n_tty_init();
3298 
3299 	/*
3300 	 * set up the console device so that later boot sequences can
3301 	 * inform about problems etc..
3302 	 */
3303 	ce = __con_initcall_start;
3304 	trace_initcall_level("console");
3305 	while (ce < __con_initcall_end) {
3306 		call = initcall_from_entry(ce);
3307 		trace_initcall_start(call);
3308 		ret = call();
3309 		trace_initcall_finish(call, ret);
3310 		ce++;
3311 	}
3312 }
3313 
3314 /*
3315  * Some boot consoles access data that is in the init section and which will
3316  * be discarded after the initcalls have been run. To make sure that no code
3317  * will access this data, unregister the boot consoles in a late initcall.
3318  *
3319  * If for some reason, such as deferred probe or the driver being a loadable
3320  * module, the real console hasn't registered yet at this point, there will
3321  * be a brief interval in which no messages are logged to the console, which
3322  * makes it difficult to diagnose problems that occur during this time.
3323  *
3324  * To mitigate this problem somewhat, only unregister consoles whose memory
3325  * intersects with the init section. Note that all other boot consoles will
3326  * get unregistered when the real preferred console is registered.
3327  */
printk_late_init(void)3328 static int __init printk_late_init(void)
3329 {
3330 	struct console *con;
3331 	int ret;
3332 
3333 	for_each_console(con) {
3334 		if (!(con->flags & CON_BOOT))
3335 			continue;
3336 
3337 		/* Check addresses that might be used for enabled consoles. */
3338 		if (init_section_intersects(con, sizeof(*con)) ||
3339 		    init_section_contains(con->write, 0) ||
3340 		    init_section_contains(con->read, 0) ||
3341 		    init_section_contains(con->device, 0) ||
3342 		    init_section_contains(con->unblank, 0) ||
3343 		    init_section_contains(con->data, 0)) {
3344 			/*
3345 			 * Please, consider moving the reported consoles out
3346 			 * of the init section.
3347 			 */
3348 			pr_warn("bootconsole [%s%d] uses init memory and must be disabled even before the real one is ready\n",
3349 				con->name, con->index);
3350 			unregister_console(con);
3351 		}
3352 	}
3353 	ret = cpuhp_setup_state_nocalls(CPUHP_PRINTK_DEAD, "printk:dead", NULL,
3354 					console_cpu_notify);
3355 	WARN_ON(ret < 0);
3356 	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "printk:online",
3357 					console_cpu_notify, NULL);
3358 	WARN_ON(ret < 0);
3359 	printk_sysctl_init();
3360 	return 0;
3361 }
3362 late_initcall(printk_late_init);
3363 
3364 #if defined CONFIG_PRINTK
3365 /* If @con is specified, only wait for that console. Otherwise wait for all. */
__pr_flush(struct console * con,int timeout_ms,bool reset_on_progress)3366 static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress)
3367 {
3368 	int remaining = timeout_ms;
3369 	struct console *c;
3370 	u64 last_diff = 0;
3371 	u64 printk_seq;
3372 	u64 diff;
3373 	u64 seq;
3374 
3375 	might_sleep();
3376 
3377 	seq = prb_next_seq(prb);
3378 
3379 	for (;;) {
3380 		diff = 0;
3381 
3382 		console_lock();
3383 
3384 		for_each_console(c) {
3385 			if (con && con != c)
3386 				continue;
3387 			if (!console_is_usable(c))
3388 				continue;
3389 			printk_seq = c->seq;
3390 			if (printk_seq < seq)
3391 				diff += seq - printk_seq;
3392 		}
3393 
3394 		/*
3395 		 * If consoles are suspended, it cannot be expected that they
3396 		 * make forward progress, so timeout immediately. @diff is
3397 		 * still used to return a valid flush status.
3398 		 */
3399 		if (console_suspended)
3400 			remaining = 0;
3401 		else if (diff != last_diff && reset_on_progress)
3402 			remaining = timeout_ms;
3403 
3404 		console_unlock();
3405 
3406 		if (diff == 0 || remaining == 0)
3407 			break;
3408 
3409 		if (remaining < 0) {
3410 			/* no timeout limit */
3411 			msleep(100);
3412 		} else if (remaining < 100) {
3413 			msleep(remaining);
3414 			remaining = 0;
3415 		} else {
3416 			msleep(100);
3417 			remaining -= 100;
3418 		}
3419 
3420 		last_diff = diff;
3421 	}
3422 
3423 	return (diff == 0);
3424 }
3425 
3426 /**
3427  * pr_flush() - Wait for printing threads to catch up.
3428  *
3429  * @timeout_ms:        The maximum time (in ms) to wait.
3430  * @reset_on_progress: Reset the timeout if forward progress is seen.
3431  *
3432  * A value of 0 for @timeout_ms means no waiting will occur. A value of -1
3433  * represents infinite waiting.
3434  *
3435  * If @reset_on_progress is true, the timeout will be reset whenever any
3436  * printer has been seen to make some forward progress.
3437  *
3438  * Context: Process context. May sleep while acquiring console lock.
3439  * Return: true if all enabled printers are caught up.
3440  */
pr_flush(int timeout_ms,bool reset_on_progress)3441 bool pr_flush(int timeout_ms, bool reset_on_progress)
3442 {
3443 	return __pr_flush(NULL, timeout_ms, reset_on_progress);
3444 }
3445 EXPORT_SYMBOL(pr_flush);
3446 
3447 /*
3448  * Delayed printk version, for scheduler-internal messages:
3449  */
3450 #define PRINTK_PENDING_WAKEUP	0x01
3451 #define PRINTK_PENDING_OUTPUT	0x02
3452 
3453 static DEFINE_PER_CPU(int, printk_pending);
3454 
wake_up_klogd_work_func(struct irq_work * irq_work)3455 static void wake_up_klogd_work_func(struct irq_work *irq_work)
3456 {
3457 	int pending = this_cpu_xchg(printk_pending, 0);
3458 
3459 	if (pending & PRINTK_PENDING_OUTPUT) {
3460 		/* If trylock fails, someone else is doing the printing */
3461 		if (console_trylock())
3462 			console_unlock();
3463 	}
3464 
3465 	if (pending & PRINTK_PENDING_WAKEUP)
3466 		wake_up_interruptible(&log_wait);
3467 }
3468 
3469 static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
3470 	IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
3471 
__wake_up_klogd(int val)3472 static void __wake_up_klogd(int val)
3473 {
3474 	if (!printk_percpu_data_ready())
3475 		return;
3476 
3477 	preempt_disable();
3478 	/*
3479 	 * Guarantee any new records can be seen by tasks preparing to wait
3480 	 * before this context checks if the wait queue is empty.
3481 	 *
3482 	 * The full memory barrier within wq_has_sleeper() pairs with the full
3483 	 * memory barrier within set_current_state() of
3484 	 * prepare_to_wait_event(), which is called after ___wait_event() adds
3485 	 * the waiter but before it has checked the wait condition.
3486 	 *
3487 	 * This pairs with devkmsg_read:A and syslog_print:A.
3488 	 */
3489 	if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
3490 	    (val & PRINTK_PENDING_OUTPUT)) {
3491 		this_cpu_or(printk_pending, val);
3492 		irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
3493 	}
3494 	preempt_enable();
3495 }
3496 
wake_up_klogd(void)3497 void wake_up_klogd(void)
3498 {
3499 	__wake_up_klogd(PRINTK_PENDING_WAKEUP);
3500 }
3501 
defer_console_output(void)3502 void defer_console_output(void)
3503 {
3504 	/*
3505 	 * New messages may have been added directly to the ringbuffer
3506 	 * using vprintk_store(), so wake any waiters as well.
3507 	 */
3508 	__wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
3509 }
3510 
printk_trigger_flush(void)3511 void printk_trigger_flush(void)
3512 {
3513 	defer_console_output();
3514 }
3515 
vprintk_deferred(const char * fmt,va_list args)3516 int vprintk_deferred(const char *fmt, va_list args)
3517 {
3518 	int r;
3519 
3520 	r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args);
3521 	defer_console_output();
3522 
3523 	return r;
3524 }
3525 
_printk_deferred(const char * fmt,...)3526 int _printk_deferred(const char *fmt, ...)
3527 {
3528 	va_list args;
3529 	int r;
3530 
3531 	va_start(args, fmt);
3532 	r = vprintk_deferred(fmt, args);
3533 	va_end(args);
3534 
3535 	return r;
3536 }
3537 
3538 /*
3539  * printk rate limiting, lifted from the networking subsystem.
3540  *
3541  * This enforces a rate limit: not more than 10 kernel messages
3542  * every 5s to make a denial-of-service attack impossible.
3543  */
3544 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
3545 
__printk_ratelimit(const char * func)3546 int __printk_ratelimit(const char *func)
3547 {
3548 	return ___ratelimit(&printk_ratelimit_state, func);
3549 }
3550 EXPORT_SYMBOL(__printk_ratelimit);
3551 
3552 /**
3553  * printk_timed_ratelimit - caller-controlled printk ratelimiting
3554  * @caller_jiffies: pointer to caller's state
3555  * @interval_msecs: minimum interval between prints
3556  *
3557  * printk_timed_ratelimit() returns true if more than @interval_msecs
3558  * milliseconds have elapsed since the last time printk_timed_ratelimit()
3559  * returned true.
3560  */
printk_timed_ratelimit(unsigned long * caller_jiffies,unsigned int interval_msecs)3561 bool printk_timed_ratelimit(unsigned long *caller_jiffies,
3562 			unsigned int interval_msecs)
3563 {
3564 	unsigned long elapsed = jiffies - *caller_jiffies;
3565 
3566 	if (*caller_jiffies && elapsed <= msecs_to_jiffies(interval_msecs))
3567 		return false;
3568 
3569 	*caller_jiffies = jiffies;
3570 	return true;
3571 }
3572 EXPORT_SYMBOL(printk_timed_ratelimit);
3573 
3574 static DEFINE_SPINLOCK(dump_list_lock);
3575 static LIST_HEAD(dump_list);
3576 
3577 /**
3578  * kmsg_dump_register - register a kernel log dumper.
3579  * @dumper: pointer to the kmsg_dumper structure
3580  *
3581  * Adds a kernel log dumper to the system. The dump callback in the
3582  * structure will be called when the kernel oopses or panics and must be
3583  * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
3584  */
kmsg_dump_register(struct kmsg_dumper * dumper)3585 int kmsg_dump_register(struct kmsg_dumper *dumper)
3586 {
3587 	unsigned long flags;
3588 	int err = -EBUSY;
3589 
3590 	/* The dump callback needs to be set */
3591 	if (!dumper->dump)
3592 		return -EINVAL;
3593 
3594 	spin_lock_irqsave(&dump_list_lock, flags);
3595 	/* Don't allow registering multiple times */
3596 	if (!dumper->registered) {
3597 		dumper->registered = 1;
3598 		list_add_tail_rcu(&dumper->list, &dump_list);
3599 		err = 0;
3600 	}
3601 	spin_unlock_irqrestore(&dump_list_lock, flags);
3602 
3603 	return err;
3604 }
3605 EXPORT_SYMBOL_GPL(kmsg_dump_register);
3606 
3607 /**
3608  * kmsg_dump_unregister - unregister a kmsg dumper.
3609  * @dumper: pointer to the kmsg_dumper structure
3610  *
3611  * Removes a dump device from the system. Returns zero on success and
3612  * %-EINVAL otherwise.
3613  */
kmsg_dump_unregister(struct kmsg_dumper * dumper)3614 int kmsg_dump_unregister(struct kmsg_dumper *dumper)
3615 {
3616 	unsigned long flags;
3617 	int err = -EINVAL;
3618 
3619 	spin_lock_irqsave(&dump_list_lock, flags);
3620 	if (dumper->registered) {
3621 		dumper->registered = 0;
3622 		list_del_rcu(&dumper->list);
3623 		err = 0;
3624 	}
3625 	spin_unlock_irqrestore(&dump_list_lock, flags);
3626 	synchronize_rcu();
3627 
3628 	return err;
3629 }
3630 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
3631 
3632 static bool always_kmsg_dump;
3633 module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
3634 
kmsg_dump_reason_str(enum kmsg_dump_reason reason)3635 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
3636 {
3637 	switch (reason) {
3638 	case KMSG_DUMP_PANIC:
3639 		return "Panic";
3640 	case KMSG_DUMP_OOPS:
3641 		return "Oops";
3642 	case KMSG_DUMP_EMERG:
3643 		return "Emergency";
3644 	case KMSG_DUMP_SHUTDOWN:
3645 		return "Shutdown";
3646 	default:
3647 		return "Unknown";
3648 	}
3649 }
3650 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
3651 
3652 /**
3653  * kmsg_dump - dump kernel log to kernel message dumpers.
3654  * @reason: the reason (oops, panic etc) for dumping
3655  *
3656  * Call each of the registered dumper's dump() callback, which can
3657  * retrieve the kmsg records with kmsg_dump_get_line() or
3658  * kmsg_dump_get_buffer().
3659  */
kmsg_dump(enum kmsg_dump_reason reason)3660 void kmsg_dump(enum kmsg_dump_reason reason)
3661 {
3662 	struct kmsg_dumper *dumper;
3663 
3664 	rcu_read_lock();
3665 	list_for_each_entry_rcu(dumper, &dump_list, list) {
3666 		enum kmsg_dump_reason max_reason = dumper->max_reason;
3667 
3668 		/*
3669 		 * If client has not provided a specific max_reason, default
3670 		 * to KMSG_DUMP_OOPS, unless always_kmsg_dump was set.
3671 		 */
3672 		if (max_reason == KMSG_DUMP_UNDEF) {
3673 			max_reason = always_kmsg_dump ? KMSG_DUMP_MAX :
3674 							KMSG_DUMP_OOPS;
3675 		}
3676 		if (reason > max_reason)
3677 			continue;
3678 
3679 		/* invoke dumper which will iterate over records */
3680 		dumper->dump(dumper, reason);
3681 	}
3682 	rcu_read_unlock();
3683 }
3684 
3685 /**
3686  * kmsg_dump_get_line - retrieve one kmsg log line
3687  * @iter: kmsg dump iterator
3688  * @syslog: include the "<4>" prefixes
3689  * @line: buffer to copy the line to
3690  * @size: maximum size of the buffer
3691  * @len: length of line placed into buffer
3692  *
3693  * Start at the beginning of the kmsg buffer, with the oldest kmsg
3694  * record, and copy one record into the provided buffer.
3695  *
3696  * Consecutive calls will return the next available record moving
3697  * towards the end of the buffer with the youngest messages.
3698  *
3699  * A return value of FALSE indicates that there are no more records to
3700  * read.
3701  */
kmsg_dump_get_line(struct kmsg_dump_iter * iter,bool syslog,char * line,size_t size,size_t * len)3702 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
3703 			char *line, size_t size, size_t *len)
3704 {
3705 	u64 min_seq = latched_seq_read_nolock(&clear_seq);
3706 	struct printk_info info;
3707 	unsigned int line_count;
3708 	struct printk_record r;
3709 	size_t l = 0;
3710 	bool ret = false;
3711 
3712 	if (iter->cur_seq < min_seq)
3713 		iter->cur_seq = min_seq;
3714 
3715 	prb_rec_init_rd(&r, &info, line, size);
3716 
3717 	/* Read text or count text lines? */
3718 	if (line) {
3719 		if (!prb_read_valid(prb, iter->cur_seq, &r))
3720 			goto out;
3721 		l = record_print_text(&r, syslog, printk_time);
3722 	} else {
3723 		if (!prb_read_valid_info(prb, iter->cur_seq,
3724 					 &info, &line_count)) {
3725 			goto out;
3726 		}
3727 		l = get_record_print_text_size(&info, line_count, syslog,
3728 					       printk_time);
3729 
3730 	}
3731 
3732 	iter->cur_seq = r.info->seq + 1;
3733 	ret = true;
3734 out:
3735 	if (len)
3736 		*len = l;
3737 	return ret;
3738 }
3739 EXPORT_SYMBOL_GPL(kmsg_dump_get_line);
3740 
3741 /**
3742  * kmsg_dump_get_buffer - copy kmsg log lines
3743  * @iter: kmsg dump iterator
3744  * @syslog: include the "<4>" prefixes
3745  * @buf: buffer to copy the line to
3746  * @size: maximum size of the buffer
3747  * @len_out: length of line placed into buffer
3748  *
3749  * Start at the end of the kmsg buffer and fill the provided buffer
3750  * with as many of the *youngest* kmsg records that fit into it.
3751  * If the buffer is large enough, all available kmsg records will be
3752  * copied with a single call.
3753  *
3754  * Consecutive calls will fill the buffer with the next block of
3755  * available older records, not including the earlier retrieved ones.
3756  *
3757  * A return value of FALSE indicates that there are no more records to
3758  * read.
3759  */
kmsg_dump_get_buffer(struct kmsg_dump_iter * iter,bool syslog,char * buf,size_t size,size_t * len_out)3760 bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
3761 			  char *buf, size_t size, size_t *len_out)
3762 {
3763 	u64 min_seq = latched_seq_read_nolock(&clear_seq);
3764 	struct printk_info info;
3765 	struct printk_record r;
3766 	u64 seq;
3767 	u64 next_seq;
3768 	size_t len = 0;
3769 	bool ret = false;
3770 	bool time = printk_time;
3771 
3772 	if (!buf || !size)
3773 		goto out;
3774 
3775 	if (iter->cur_seq < min_seq)
3776 		iter->cur_seq = min_seq;
3777 
3778 	if (prb_read_valid_info(prb, iter->cur_seq, &info, NULL)) {
3779 		if (info.seq != iter->cur_seq) {
3780 			/* messages are gone, move to first available one */
3781 			iter->cur_seq = info.seq;
3782 		}
3783 	}
3784 
3785 	/* last entry */
3786 	if (iter->cur_seq >= iter->next_seq)
3787 		goto out;
3788 
3789 	/*
3790 	 * Find first record that fits, including all following records,
3791 	 * into the user-provided buffer for this dump. Pass in size-1
3792 	 * because this function (by way of record_print_text()) will
3793 	 * not write more than size-1 bytes of text into @buf.
3794 	 */
3795 	seq = find_first_fitting_seq(iter->cur_seq, iter->next_seq,
3796 				     size - 1, syslog, time);
3797 
3798 	/*
3799 	 * Next kmsg_dump_get_buffer() invocation will dump block of
3800 	 * older records stored right before this one.
3801 	 */
3802 	next_seq = seq;
3803 
3804 	prb_rec_init_rd(&r, &info, buf, size);
3805 
3806 	len = 0;
3807 	prb_for_each_record(seq, prb, seq, &r) {
3808 		if (r.info->seq >= iter->next_seq)
3809 			break;
3810 
3811 		len += record_print_text(&r, syslog, time);
3812 
3813 		/* Adjust record to store to remaining buffer space. */
3814 		prb_rec_init_rd(&r, &info, buf + len, size - len);
3815 	}
3816 
3817 	iter->next_seq = next_seq;
3818 	ret = true;
3819 out:
3820 	if (len_out)
3821 		*len_out = len;
3822 	return ret;
3823 }
3824 EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);
3825 
3826 /**
3827  * kmsg_dump_rewind - reset the iterator
3828  * @iter: kmsg dump iterator
3829  *
3830  * Reset the dumper's iterator so that kmsg_dump_get_line() and
3831  * kmsg_dump_get_buffer() can be called again and used multiple
3832  * times within the same dumper.dump() callback.
3833  */
kmsg_dump_rewind(struct kmsg_dump_iter * iter)3834 void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
3835 {
3836 	iter->cur_seq = latched_seq_read_nolock(&clear_seq);
3837 	iter->next_seq = prb_next_seq(prb);
3838 }
3839 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
3840 
3841 #endif
3842 
3843 #ifdef CONFIG_SMP
3844 static atomic_t printk_cpu_sync_owner = ATOMIC_INIT(-1);
3845 static atomic_t printk_cpu_sync_nested = ATOMIC_INIT(0);
3846 
3847 /**
3848  * __printk_cpu_sync_wait() - Busy wait until the printk cpu-reentrant
3849  *                            spinning lock is not owned by any CPU.
3850  *
3851  * Context: Any context.
3852  */
__printk_cpu_sync_wait(void)3853 void __printk_cpu_sync_wait(void)
3854 {
3855 	do {
3856 		cpu_relax();
3857 	} while (atomic_read(&printk_cpu_sync_owner) != -1);
3858 }
3859 EXPORT_SYMBOL(__printk_cpu_sync_wait);
3860 
3861 /**
3862  * __printk_cpu_sync_try_get() - Try to acquire the printk cpu-reentrant
3863  *                               spinning lock.
3864  *
3865  * If no processor has the lock, the calling processor takes the lock and
3866  * becomes the owner. If the calling processor is already the owner of the
3867  * lock, this function succeeds immediately.
3868  *
3869  * Context: Any context. Expects interrupts to be disabled.
3870  * Return: 1 on success, otherwise 0.
3871  */
__printk_cpu_sync_try_get(void)3872 int __printk_cpu_sync_try_get(void)
3873 {
3874 	int cpu;
3875 	int old;
3876 
3877 	cpu = smp_processor_id();
3878 
3879 	/*
3880 	 * Guarantee loads and stores from this CPU when it is the lock owner
3881 	 * are _not_ visible to the previous lock owner. This pairs with
3882 	 * __printk_cpu_sync_put:B.
3883 	 *
3884 	 * Memory barrier involvement:
3885 	 *
3886 	 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
3887 	 * then __printk_cpu_sync_put:A can never read from
3888 	 * __printk_cpu_sync_try_get:B.
3889 	 *
3890 	 * Relies on:
3891 	 *
3892 	 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
3893 	 * of the previous CPU
3894 	 *    matching
3895 	 * ACQUIRE from __printk_cpu_sync_try_get:A to
3896 	 * __printk_cpu_sync_try_get:B of this CPU
3897 	 */
3898 	old = atomic_cmpxchg_acquire(&printk_cpu_sync_owner, -1,
3899 				     cpu); /* LMM(__printk_cpu_sync_try_get:A) */
3900 	if (old == -1) {
3901 		/*
3902 		 * This CPU is now the owner and begins loading/storing
3903 		 * data: LMM(__printk_cpu_sync_try_get:B)
3904 		 */
3905 		return 1;
3906 
3907 	} else if (old == cpu) {
3908 		/* This CPU is already the owner. */
3909 		atomic_inc(&printk_cpu_sync_nested);
3910 		return 1;
3911 	}
3912 
3913 	return 0;
3914 }
3915 EXPORT_SYMBOL(__printk_cpu_sync_try_get);
3916 
3917 /**
3918  * __printk_cpu_sync_put() - Release the printk cpu-reentrant spinning lock.
3919  *
3920  * The calling processor must be the owner of the lock.
3921  *
3922  * Context: Any context. Expects interrupts to be disabled.
3923  */
__printk_cpu_sync_put(void)3924 void __printk_cpu_sync_put(void)
3925 {
3926 	if (atomic_read(&printk_cpu_sync_nested)) {
3927 		atomic_dec(&printk_cpu_sync_nested);
3928 		return;
3929 	}
3930 
3931 	/*
3932 	 * This CPU is finished loading/storing data:
3933 	 * LMM(__printk_cpu_sync_put:A)
3934 	 */
3935 
3936 	/*
3937 	 * Guarantee loads and stores from this CPU when it was the
3938 	 * lock owner are visible to the next lock owner. This pairs
3939 	 * with __printk_cpu_sync_try_get:A.
3940 	 *
3941 	 * Memory barrier involvement:
3942 	 *
3943 	 * If __printk_cpu_sync_try_get:A reads from __printk_cpu_sync_put:B,
3944 	 * then __printk_cpu_sync_try_get:B reads from __printk_cpu_sync_put:A.
3945 	 *
3946 	 * Relies on:
3947 	 *
3948 	 * RELEASE from __printk_cpu_sync_put:A to __printk_cpu_sync_put:B
3949 	 * of this CPU
3950 	 *    matching
3951 	 * ACQUIRE from __printk_cpu_sync_try_get:A to
3952 	 * __printk_cpu_sync_try_get:B of the next CPU
3953 	 */
3954 	atomic_set_release(&printk_cpu_sync_owner,
3955 			   -1); /* LMM(__printk_cpu_sync_put:B) */
3956 }
3957 EXPORT_SYMBOL(__printk_cpu_sync_put);
3958 #endif /* CONFIG_SMP */
3959