1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *	linux/kernel/softirq.c
4  *
5  *	Copyright (C) 1992 Linus Torvalds
6  *
7  *	Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
8  */
9 
10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11 
12 #include <linux/export.h>
13 #include <linux/kernel_stat.h>
14 #include <linux/interrupt.h>
15 #include <linux/init.h>
16 #include <linux/local_lock.h>
17 #include <linux/mm.h>
18 #include <linux/notifier.h>
19 #include <linux/percpu.h>
20 #include <linux/cpu.h>
21 #include <linux/freezer.h>
22 #include <linux/kthread.h>
23 #include <linux/rcupdate.h>
24 #include <linux/ftrace.h>
25 #include <linux/smp.h>
26 #include <linux/smpboot.h>
27 #include <linux/tick.h>
28 #include <linux/irq.h>
29 #include <linux/wait_bit.h>
30 
31 #include <asm/softirq_stack.h>
32 
33 #define CREATE_TRACE_POINTS
34 #include <trace/events/irq.h>
35 
36 /*
37    - No shared variables, all the data are CPU local.
38    - If a softirq needs serialization, let it serialize itself
39      by its own spinlocks.
40    - Even if softirq is serialized, only local cpu is marked for
41      execution. Hence, we get something sort of weak cpu binding.
42      Though it is still not clear, will it result in better locality
43      or will not.
44 
45    Examples:
46    - NET RX softirq. It is multithreaded and does not require
47      any global serialization.
48    - NET TX softirq. It kicks software netdevice queues, hence
49      it is logically serialized per device, but this serialization
50      is invisible to common code.
51    - Tasklets: serialized wrt itself.
52  */
53 
54 #ifndef __ARCH_IRQ_STAT
55 DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat);
56 EXPORT_PER_CPU_SYMBOL(irq_stat);
57 #endif
58 
59 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
60 
61 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
62 
63 const char * const softirq_to_name[NR_SOFTIRQS] = {
64 	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
65 	"TASKLET", "SCHED", "HRTIMER", "RCU"
66 };
67 
68 /*
69  * we cannot loop indefinitely here to avoid userspace starvation,
70  * but we also don't want to introduce a worst case 1/HZ latency
71  * to the pending events, so lets the scheduler to balance
72  * the softirq load for us.
73  */
wakeup_softirqd(void)74 static void wakeup_softirqd(void)
75 {
76 	/* Interrupts are disabled: no need to stop preemption */
77 	struct task_struct *tsk = __this_cpu_read(ksoftirqd);
78 
79 	if (tsk)
80 		wake_up_process(tsk);
81 }
82 
83 #ifdef CONFIG_TRACE_IRQFLAGS
84 DEFINE_PER_CPU(int, hardirqs_enabled);
85 DEFINE_PER_CPU(int, hardirq_context);
86 EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
87 EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
88 #endif
89 
90 /*
91  * SOFTIRQ_OFFSET usage:
92  *
93  * On !RT kernels 'count' is the preempt counter, on RT kernels this applies
94  * to a per CPU counter and to task::softirqs_disabled_cnt.
95  *
96  * - count is changed by SOFTIRQ_OFFSET on entering or leaving softirq
97  *   processing.
98  *
99  * - count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
100  *   on local_bh_disable or local_bh_enable.
101  *
102  * This lets us distinguish between whether we are currently processing
103  * softirq and whether we just have bh disabled.
104  */
105 #ifdef CONFIG_PREEMPT_RT
106 
107 /*
108  * RT accounts for BH disabled sections in task::softirqs_disabled_cnt and
109  * also in per CPU softirq_ctrl::cnt. This is necessary to allow tasks in a
110  * softirq disabled section to be preempted.
111  *
112  * The per task counter is used for softirq_count(), in_softirq() and
113  * in_serving_softirqs() because these counts are only valid when the task
114  * holding softirq_ctrl::lock is running.
115  *
116  * The per CPU counter prevents pointless wakeups of ksoftirqd in case that
117  * the task which is in a softirq disabled section is preempted or blocks.
118  */
119 struct softirq_ctrl {
120 	local_lock_t	lock;
121 	int		cnt;
122 };
123 
124 static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = {
125 	.lock	= INIT_LOCAL_LOCK(softirq_ctrl.lock),
126 };
127 
128 /**
129  * local_bh_blocked() - Check for idle whether BH processing is blocked
130  *
131  * Returns false if the per CPU softirq::cnt is 0 otherwise true.
132  *
133  * This is invoked from the idle task to guard against false positive
134  * softirq pending warnings, which would happen when the task which holds
135  * softirq_ctrl::lock was the only running task on the CPU and blocks on
136  * some other lock.
137  */
local_bh_blocked(void)138 bool local_bh_blocked(void)
139 {
140 	return __this_cpu_read(softirq_ctrl.cnt) != 0;
141 }
142 
__local_bh_disable_ip(unsigned long ip,unsigned int cnt)143 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
144 {
145 	unsigned long flags;
146 	int newcnt;
147 
148 	WARN_ON_ONCE(in_hardirq());
149 
150 	/* First entry of a task into a BH disabled section? */
151 	if (!current->softirq_disable_cnt) {
152 		if (preemptible()) {
153 			local_lock(&softirq_ctrl.lock);
154 			/* Required to meet the RCU bottomhalf requirements. */
155 			rcu_read_lock();
156 		} else {
157 			DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt));
158 		}
159 	}
160 
161 	/*
162 	 * Track the per CPU softirq disabled state. On RT this is per CPU
163 	 * state to allow preemption of bottom half disabled sections.
164 	 */
165 	newcnt = __this_cpu_add_return(softirq_ctrl.cnt, cnt);
166 	/*
167 	 * Reflect the result in the task state to prevent recursion on the
168 	 * local lock and to make softirq_count() & al work.
169 	 */
170 	current->softirq_disable_cnt = newcnt;
171 
172 	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && newcnt == cnt) {
173 		raw_local_irq_save(flags);
174 		lockdep_softirqs_off(ip);
175 		raw_local_irq_restore(flags);
176 	}
177 }
178 EXPORT_SYMBOL(__local_bh_disable_ip);
179 
__local_bh_enable(unsigned int cnt,bool unlock)180 static void __local_bh_enable(unsigned int cnt, bool unlock)
181 {
182 	unsigned long flags;
183 	int newcnt;
184 
185 	DEBUG_LOCKS_WARN_ON(current->softirq_disable_cnt !=
186 			    this_cpu_read(softirq_ctrl.cnt));
187 
188 	if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS) && softirq_count() == cnt) {
189 		raw_local_irq_save(flags);
190 		lockdep_softirqs_on(_RET_IP_);
191 		raw_local_irq_restore(flags);
192 	}
193 
194 	newcnt = __this_cpu_sub_return(softirq_ctrl.cnt, cnt);
195 	current->softirq_disable_cnt = newcnt;
196 
197 	if (!newcnt && unlock) {
198 		rcu_read_unlock();
199 		local_unlock(&softirq_ctrl.lock);
200 	}
201 }
202 
__local_bh_enable_ip(unsigned long ip,unsigned int cnt)203 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
204 {
205 	bool preempt_on = preemptible();
206 	unsigned long flags;
207 	u32 pending;
208 	int curcnt;
209 
210 	WARN_ON_ONCE(in_hardirq());
211 	lockdep_assert_irqs_enabled();
212 
213 	local_irq_save(flags);
214 	curcnt = __this_cpu_read(softirq_ctrl.cnt);
215 
216 	/*
217 	 * If this is not reenabling soft interrupts, no point in trying to
218 	 * run pending ones.
219 	 */
220 	if (curcnt != cnt)
221 		goto out;
222 
223 	pending = local_softirq_pending();
224 	if (!pending)
225 		goto out;
226 
227 	/*
228 	 * If this was called from non preemptible context, wake up the
229 	 * softirq daemon.
230 	 */
231 	if (!preempt_on) {
232 		wakeup_softirqd();
233 		goto out;
234 	}
235 
236 	/*
237 	 * Adjust softirq count to SOFTIRQ_OFFSET which makes
238 	 * in_serving_softirq() become true.
239 	 */
240 	cnt = SOFTIRQ_OFFSET;
241 	__local_bh_enable(cnt, false);
242 	__do_softirq();
243 
244 out:
245 	__local_bh_enable(cnt, preempt_on);
246 	local_irq_restore(flags);
247 }
248 EXPORT_SYMBOL(__local_bh_enable_ip);
249 
250 /*
251  * Invoked from ksoftirqd_run() outside of the interrupt disabled section
252  * to acquire the per CPU local lock for reentrancy protection.
253  */
ksoftirqd_run_begin(void)254 static inline void ksoftirqd_run_begin(void)
255 {
256 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
257 	local_irq_disable();
258 }
259 
260 /* Counterpart to ksoftirqd_run_begin() */
ksoftirqd_run_end(void)261 static inline void ksoftirqd_run_end(void)
262 {
263 	__local_bh_enable(SOFTIRQ_OFFSET, true);
264 	WARN_ON_ONCE(in_interrupt());
265 	local_irq_enable();
266 }
267 
softirq_handle_begin(void)268 static inline void softirq_handle_begin(void) { }
softirq_handle_end(void)269 static inline void softirq_handle_end(void) { }
270 
should_wake_ksoftirqd(void)271 static inline bool should_wake_ksoftirqd(void)
272 {
273 	return !this_cpu_read(softirq_ctrl.cnt);
274 }
275 
invoke_softirq(void)276 static inline void invoke_softirq(void)
277 {
278 	if (should_wake_ksoftirqd())
279 		wakeup_softirqd();
280 }
281 
282 /*
283  * flush_smp_call_function_queue() can raise a soft interrupt in a function
284  * call. On RT kernels this is undesired and the only known functionality
285  * in the block layer which does this is disabled on RT. If soft interrupts
286  * get raised which haven't been raised before the flush, warn so it can be
287  * investigated.
288  */
do_softirq_post_smp_call_flush(unsigned int was_pending)289 void do_softirq_post_smp_call_flush(unsigned int was_pending)
290 {
291 	if (WARN_ON_ONCE(was_pending != local_softirq_pending()))
292 		invoke_softirq();
293 }
294 
295 #else /* CONFIG_PREEMPT_RT */
296 
297 /*
298  * This one is for softirq.c-internal use, where hardirqs are disabled
299  * legitimately:
300  */
301 #ifdef CONFIG_TRACE_IRQFLAGS
__local_bh_disable_ip(unsigned long ip,unsigned int cnt)302 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
303 {
304 	unsigned long flags;
305 
306 	WARN_ON_ONCE(in_hardirq());
307 
308 	raw_local_irq_save(flags);
309 	/*
310 	 * The preempt tracer hooks into preempt_count_add and will break
311 	 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
312 	 * is set and before current->softirq_enabled is cleared.
313 	 * We must manually increment preempt_count here and manually
314 	 * call the trace_preempt_off later.
315 	 */
316 	__preempt_count_add(cnt);
317 	/*
318 	 * Were softirqs turned off above:
319 	 */
320 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
321 		lockdep_softirqs_off(ip);
322 	raw_local_irq_restore(flags);
323 
324 	if (preempt_count() == cnt) {
325 #ifdef CONFIG_DEBUG_PREEMPT
326 		current->preempt_disable_ip = get_lock_parent_ip();
327 #endif
328 		trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
329 	}
330 }
331 EXPORT_SYMBOL(__local_bh_disable_ip);
332 #endif /* CONFIG_TRACE_IRQFLAGS */
333 
__local_bh_enable(unsigned int cnt)334 static void __local_bh_enable(unsigned int cnt)
335 {
336 	lockdep_assert_irqs_disabled();
337 
338 	if (preempt_count() == cnt)
339 		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
340 
341 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
342 		lockdep_softirqs_on(_RET_IP_);
343 
344 	__preempt_count_sub(cnt);
345 }
346 
347 /*
348  * Special-case - softirqs can safely be enabled by __do_softirq(),
349  * without processing still-pending softirqs:
350  */
_local_bh_enable(void)351 void _local_bh_enable(void)
352 {
353 	WARN_ON_ONCE(in_hardirq());
354 	__local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
355 }
356 EXPORT_SYMBOL(_local_bh_enable);
357 
__local_bh_enable_ip(unsigned long ip,unsigned int cnt)358 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
359 {
360 	WARN_ON_ONCE(in_hardirq());
361 	lockdep_assert_irqs_enabled();
362 #ifdef CONFIG_TRACE_IRQFLAGS
363 	local_irq_disable();
364 #endif
365 	/*
366 	 * Are softirqs going to be turned on now:
367 	 */
368 	if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
369 		lockdep_softirqs_on(ip);
370 	/*
371 	 * Keep preemption disabled until we are done with
372 	 * softirq processing:
373 	 */
374 	__preempt_count_sub(cnt - 1);
375 
376 	if (unlikely(!in_interrupt() && local_softirq_pending())) {
377 		/*
378 		 * Run softirq if any pending. And do it in its own stack
379 		 * as we may be calling this deep in a task call stack already.
380 		 */
381 		do_softirq();
382 	}
383 
384 	preempt_count_dec();
385 #ifdef CONFIG_TRACE_IRQFLAGS
386 	local_irq_enable();
387 #endif
388 	preempt_check_resched();
389 }
390 EXPORT_SYMBOL(__local_bh_enable_ip);
391 
softirq_handle_begin(void)392 static inline void softirq_handle_begin(void)
393 {
394 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
395 }
396 
softirq_handle_end(void)397 static inline void softirq_handle_end(void)
398 {
399 	__local_bh_enable(SOFTIRQ_OFFSET);
400 	WARN_ON_ONCE(in_interrupt());
401 }
402 
ksoftirqd_run_begin(void)403 static inline void ksoftirqd_run_begin(void)
404 {
405 	local_irq_disable();
406 }
407 
ksoftirqd_run_end(void)408 static inline void ksoftirqd_run_end(void)
409 {
410 	local_irq_enable();
411 }
412 
should_wake_ksoftirqd(void)413 static inline bool should_wake_ksoftirqd(void)
414 {
415 	return true;
416 }
417 
invoke_softirq(void)418 static inline void invoke_softirq(void)
419 {
420 	if (!force_irqthreads() || !__this_cpu_read(ksoftirqd)) {
421 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
422 		/*
423 		 * We can safely execute softirq on the current stack if
424 		 * it is the irq stack, because it should be near empty
425 		 * at this stage.
426 		 */
427 		__do_softirq();
428 #else
429 		/*
430 		 * Otherwise, irq_exit() is called on the task stack that can
431 		 * be potentially deep already. So call softirq in its own stack
432 		 * to prevent from any overrun.
433 		 */
434 		do_softirq_own_stack();
435 #endif
436 	} else {
437 		wakeup_softirqd();
438 	}
439 }
440 
do_softirq(void)441 asmlinkage __visible void do_softirq(void)
442 {
443 	__u32 pending;
444 	unsigned long flags;
445 
446 	if (in_interrupt())
447 		return;
448 
449 	local_irq_save(flags);
450 
451 	pending = local_softirq_pending();
452 
453 	if (pending)
454 		do_softirq_own_stack();
455 
456 	local_irq_restore(flags);
457 }
458 
459 #endif /* !CONFIG_PREEMPT_RT */
460 
461 /*
462  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
463  * but break the loop if need_resched() is set or after 2 ms.
464  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
465  * certain cases, such as stop_machine(), jiffies may cease to
466  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
467  * well to make sure we eventually return from this method.
468  *
469  * These limits have been established via experimentation.
470  * The two things to balance is latency against fairness -
471  * we want to handle softirqs as soon as possible, but they
472  * should not be able to lock up the box.
473  */
474 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
475 #define MAX_SOFTIRQ_RESTART 10
476 
477 #ifdef CONFIG_TRACE_IRQFLAGS
478 /*
479  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
480  * to keep the lockdep irq context tracking as tight as possible in order to
481  * not miss-qualify lock contexts and miss possible deadlocks.
482  */
483 
lockdep_softirq_start(void)484 static inline bool lockdep_softirq_start(void)
485 {
486 	bool in_hardirq = false;
487 
488 	if (lockdep_hardirq_context()) {
489 		in_hardirq = true;
490 		lockdep_hardirq_exit();
491 	}
492 
493 	lockdep_softirq_enter();
494 
495 	return in_hardirq;
496 }
497 
lockdep_softirq_end(bool in_hardirq)498 static inline void lockdep_softirq_end(bool in_hardirq)
499 {
500 	lockdep_softirq_exit();
501 
502 	if (in_hardirq)
503 		lockdep_hardirq_enter();
504 }
505 #else
lockdep_softirq_start(void)506 static inline bool lockdep_softirq_start(void) { return false; }
lockdep_softirq_end(bool in_hardirq)507 static inline void lockdep_softirq_end(bool in_hardirq) { }
508 #endif
509 
__do_softirq(void)510 asmlinkage __visible void __softirq_entry __do_softirq(void)
511 {
512 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
513 	unsigned long old_flags = current->flags;
514 	int max_restart = MAX_SOFTIRQ_RESTART;
515 	struct softirq_action *h;
516 	bool in_hardirq;
517 	__u32 pending;
518 	int softirq_bit;
519 
520 	/*
521 	 * Mask out PF_MEMALLOC as the current task context is borrowed for the
522 	 * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
523 	 * again if the socket is related to swapping.
524 	 */
525 	current->flags &= ~PF_MEMALLOC;
526 
527 	pending = local_softirq_pending();
528 
529 	softirq_handle_begin();
530 	in_hardirq = lockdep_softirq_start();
531 	account_softirq_enter(current);
532 
533 restart:
534 	/* Reset the pending bitmask before enabling irqs */
535 	set_softirq_pending(0);
536 
537 	local_irq_enable();
538 
539 	h = softirq_vec;
540 
541 	while ((softirq_bit = ffs(pending))) {
542 		unsigned int vec_nr;
543 		int prev_count;
544 
545 		h += softirq_bit - 1;
546 
547 		vec_nr = h - softirq_vec;
548 		prev_count = preempt_count();
549 
550 		kstat_incr_softirqs_this_cpu(vec_nr);
551 
552 		trace_softirq_entry(vec_nr);
553 		h->action(h);
554 		trace_softirq_exit(vec_nr);
555 		if (unlikely(prev_count != preempt_count())) {
556 			pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
557 			       vec_nr, softirq_to_name[vec_nr], h->action,
558 			       prev_count, preempt_count());
559 			preempt_count_set(prev_count);
560 		}
561 		h++;
562 		pending >>= softirq_bit;
563 	}
564 
565 	if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
566 	    __this_cpu_read(ksoftirqd) == current)
567 		rcu_softirq_qs();
568 
569 	local_irq_disable();
570 
571 	pending = local_softirq_pending();
572 	if (pending) {
573 		if (time_before(jiffies, end) && !need_resched() &&
574 		    --max_restart)
575 			goto restart;
576 
577 		wakeup_softirqd();
578 	}
579 
580 	account_softirq_exit(current);
581 	lockdep_softirq_end(in_hardirq);
582 	softirq_handle_end();
583 	current_restore_flags(old_flags, PF_MEMALLOC);
584 }
585 
586 /**
587  * irq_enter_rcu - Enter an interrupt context with RCU watching
588  */
irq_enter_rcu(void)589 void irq_enter_rcu(void)
590 {
591 	__irq_enter_raw();
592 
593 	if (tick_nohz_full_cpu(smp_processor_id()) ||
594 	    (is_idle_task(current) && (irq_count() == HARDIRQ_OFFSET)))
595 		tick_irq_enter();
596 
597 	account_hardirq_enter(current);
598 }
599 
600 /**
601  * irq_enter - Enter an interrupt context including RCU update
602  */
irq_enter(void)603 void irq_enter(void)
604 {
605 	ct_irq_enter();
606 	irq_enter_rcu();
607 }
608 
tick_irq_exit(void)609 static inline void tick_irq_exit(void)
610 {
611 #ifdef CONFIG_NO_HZ_COMMON
612 	int cpu = smp_processor_id();
613 
614 	/* Make sure that timer wheel updates are propagated */
615 	if ((sched_core_idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
616 		if (!in_hardirq())
617 			tick_nohz_irq_exit();
618 	}
619 #endif
620 }
621 
__irq_exit_rcu(void)622 static inline void __irq_exit_rcu(void)
623 {
624 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
625 	local_irq_disable();
626 #else
627 	lockdep_assert_irqs_disabled();
628 #endif
629 	account_hardirq_exit(current);
630 	preempt_count_sub(HARDIRQ_OFFSET);
631 	if (!in_interrupt() && local_softirq_pending())
632 		invoke_softirq();
633 
634 	tick_irq_exit();
635 }
636 
637 /**
638  * irq_exit_rcu() - Exit an interrupt context without updating RCU
639  *
640  * Also processes softirqs if needed and possible.
641  */
irq_exit_rcu(void)642 void irq_exit_rcu(void)
643 {
644 	__irq_exit_rcu();
645 	 /* must be last! */
646 	lockdep_hardirq_exit();
647 }
648 
649 /**
650  * irq_exit - Exit an interrupt context, update RCU and lockdep
651  *
652  * Also processes softirqs if needed and possible.
653  */
irq_exit(void)654 void irq_exit(void)
655 {
656 	__irq_exit_rcu();
657 	ct_irq_exit();
658 	 /* must be last! */
659 	lockdep_hardirq_exit();
660 }
661 
662 /*
663  * This function must run with irqs disabled!
664  */
raise_softirq_irqoff(unsigned int nr)665 inline void raise_softirq_irqoff(unsigned int nr)
666 {
667 	__raise_softirq_irqoff(nr);
668 
669 	/*
670 	 * If we're in an interrupt or softirq, we're done
671 	 * (this also catches softirq-disabled code). We will
672 	 * actually run the softirq once we return from
673 	 * the irq or softirq.
674 	 *
675 	 * Otherwise we wake up ksoftirqd to make sure we
676 	 * schedule the softirq soon.
677 	 */
678 	if (!in_interrupt() && should_wake_ksoftirqd())
679 		wakeup_softirqd();
680 }
681 
raise_softirq(unsigned int nr)682 void raise_softirq(unsigned int nr)
683 {
684 	unsigned long flags;
685 
686 	local_irq_save(flags);
687 	raise_softirq_irqoff(nr);
688 	local_irq_restore(flags);
689 }
690 
__raise_softirq_irqoff(unsigned int nr)691 void __raise_softirq_irqoff(unsigned int nr)
692 {
693 	lockdep_assert_irqs_disabled();
694 	trace_softirq_raise(nr);
695 	or_softirq_pending(1UL << nr);
696 }
697 
open_softirq(int nr,void (* action)(struct softirq_action *))698 void open_softirq(int nr, void (*action)(struct softirq_action *))
699 {
700 	softirq_vec[nr].action = action;
701 }
702 
703 /*
704  * Tasklets
705  */
706 struct tasklet_head {
707 	struct tasklet_struct *head;
708 	struct tasklet_struct **tail;
709 };
710 
711 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
712 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
713 
__tasklet_schedule_common(struct tasklet_struct * t,struct tasklet_head __percpu * headp,unsigned int softirq_nr)714 static void __tasklet_schedule_common(struct tasklet_struct *t,
715 				      struct tasklet_head __percpu *headp,
716 				      unsigned int softirq_nr)
717 {
718 	struct tasklet_head *head;
719 	unsigned long flags;
720 
721 	local_irq_save(flags);
722 	head = this_cpu_ptr(headp);
723 	t->next = NULL;
724 	*head->tail = t;
725 	head->tail = &(t->next);
726 	raise_softirq_irqoff(softirq_nr);
727 	local_irq_restore(flags);
728 }
729 
__tasklet_schedule(struct tasklet_struct * t)730 void __tasklet_schedule(struct tasklet_struct *t)
731 {
732 	__tasklet_schedule_common(t, &tasklet_vec,
733 				  TASKLET_SOFTIRQ);
734 }
735 EXPORT_SYMBOL(__tasklet_schedule);
736 
__tasklet_hi_schedule(struct tasklet_struct * t)737 void __tasklet_hi_schedule(struct tasklet_struct *t)
738 {
739 	__tasklet_schedule_common(t, &tasklet_hi_vec,
740 				  HI_SOFTIRQ);
741 }
742 EXPORT_SYMBOL(__tasklet_hi_schedule);
743 
tasklet_clear_sched(struct tasklet_struct * t)744 static bool tasklet_clear_sched(struct tasklet_struct *t)
745 {
746 	if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
747 		wake_up_var(&t->state);
748 		return true;
749 	}
750 
751 	WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
752 		  t->use_callback ? "callback" : "func",
753 		  t->use_callback ? (void *)t->callback : (void *)t->func);
754 
755 	return false;
756 }
757 
tasklet_action_common(struct softirq_action * a,struct tasklet_head * tl_head,unsigned int softirq_nr)758 static void tasklet_action_common(struct softirq_action *a,
759 				  struct tasklet_head *tl_head,
760 				  unsigned int softirq_nr)
761 {
762 	struct tasklet_struct *list;
763 
764 	local_irq_disable();
765 	list = tl_head->head;
766 	tl_head->head = NULL;
767 	tl_head->tail = &tl_head->head;
768 	local_irq_enable();
769 
770 	while (list) {
771 		struct tasklet_struct *t = list;
772 
773 		list = list->next;
774 
775 		if (tasklet_trylock(t)) {
776 			if (!atomic_read(&t->count)) {
777 				if (tasklet_clear_sched(t)) {
778 					if (t->use_callback) {
779 						trace_tasklet_entry(t, t->callback);
780 						t->callback(t);
781 						trace_tasklet_exit(t, t->callback);
782 					} else {
783 						trace_tasklet_entry(t, t->func);
784 						t->func(t->data);
785 						trace_tasklet_exit(t, t->func);
786 					}
787 				}
788 				tasklet_unlock(t);
789 				continue;
790 			}
791 			tasklet_unlock(t);
792 		}
793 
794 		local_irq_disable();
795 		t->next = NULL;
796 		*tl_head->tail = t;
797 		tl_head->tail = &t->next;
798 		__raise_softirq_irqoff(softirq_nr);
799 		local_irq_enable();
800 	}
801 }
802 
tasklet_action(struct softirq_action * a)803 static __latent_entropy void tasklet_action(struct softirq_action *a)
804 {
805 	tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
806 }
807 
tasklet_hi_action(struct softirq_action * a)808 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
809 {
810 	tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
811 }
812 
tasklet_setup(struct tasklet_struct * t,void (* callback)(struct tasklet_struct *))813 void tasklet_setup(struct tasklet_struct *t,
814 		   void (*callback)(struct tasklet_struct *))
815 {
816 	t->next = NULL;
817 	t->state = 0;
818 	atomic_set(&t->count, 0);
819 	t->callback = callback;
820 	t->use_callback = true;
821 	t->data = 0;
822 }
823 EXPORT_SYMBOL(tasklet_setup);
824 
tasklet_init(struct tasklet_struct * t,void (* func)(unsigned long),unsigned long data)825 void tasklet_init(struct tasklet_struct *t,
826 		  void (*func)(unsigned long), unsigned long data)
827 {
828 	t->next = NULL;
829 	t->state = 0;
830 	atomic_set(&t->count, 0);
831 	t->func = func;
832 	t->use_callback = false;
833 	t->data = data;
834 }
835 EXPORT_SYMBOL(tasklet_init);
836 
837 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
838 /*
839  * Do not use in new code. Waiting for tasklets from atomic contexts is
840  * error prone and should be avoided.
841  */
tasklet_unlock_spin_wait(struct tasklet_struct * t)842 void tasklet_unlock_spin_wait(struct tasklet_struct *t)
843 {
844 	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
845 		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
846 			/*
847 			 * Prevent a live lock when current preempted soft
848 			 * interrupt processing or prevents ksoftirqd from
849 			 * running. If the tasklet runs on a different CPU
850 			 * then this has no effect other than doing the BH
851 			 * disable/enable dance for nothing.
852 			 */
853 			local_bh_disable();
854 			local_bh_enable();
855 		} else {
856 			cpu_relax();
857 		}
858 	}
859 }
860 EXPORT_SYMBOL(tasklet_unlock_spin_wait);
861 #endif
862 
tasklet_kill(struct tasklet_struct * t)863 void tasklet_kill(struct tasklet_struct *t)
864 {
865 	if (in_interrupt())
866 		pr_notice("Attempt to kill tasklet from interrupt\n");
867 
868 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
869 		wait_var_event(&t->state, !test_bit(TASKLET_STATE_SCHED, &t->state));
870 
871 	tasklet_unlock_wait(t);
872 	tasklet_clear_sched(t);
873 }
874 EXPORT_SYMBOL(tasklet_kill);
875 
876 #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
tasklet_unlock(struct tasklet_struct * t)877 void tasklet_unlock(struct tasklet_struct *t)
878 {
879 	smp_mb__before_atomic();
880 	clear_bit(TASKLET_STATE_RUN, &t->state);
881 	smp_mb__after_atomic();
882 	wake_up_var(&t->state);
883 }
884 EXPORT_SYMBOL_GPL(tasklet_unlock);
885 
tasklet_unlock_wait(struct tasklet_struct * t)886 void tasklet_unlock_wait(struct tasklet_struct *t)
887 {
888 	wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state));
889 }
890 EXPORT_SYMBOL_GPL(tasklet_unlock_wait);
891 #endif
892 
softirq_init(void)893 void __init softirq_init(void)
894 {
895 	int cpu;
896 
897 	for_each_possible_cpu(cpu) {
898 		per_cpu(tasklet_vec, cpu).tail =
899 			&per_cpu(tasklet_vec, cpu).head;
900 		per_cpu(tasklet_hi_vec, cpu).tail =
901 			&per_cpu(tasklet_hi_vec, cpu).head;
902 	}
903 
904 	open_softirq(TASKLET_SOFTIRQ, tasklet_action);
905 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
906 }
907 
ksoftirqd_should_run(unsigned int cpu)908 static int ksoftirqd_should_run(unsigned int cpu)
909 {
910 	return local_softirq_pending();
911 }
912 
run_ksoftirqd(unsigned int cpu)913 static void run_ksoftirqd(unsigned int cpu)
914 {
915 	ksoftirqd_run_begin();
916 	if (local_softirq_pending()) {
917 		/*
918 		 * We can safely run softirq on inline stack, as we are not deep
919 		 * in the task stack here.
920 		 */
921 		__do_softirq();
922 		ksoftirqd_run_end();
923 		cond_resched();
924 		return;
925 	}
926 	ksoftirqd_run_end();
927 }
928 
929 #ifdef CONFIG_HOTPLUG_CPU
takeover_tasklets(unsigned int cpu)930 static int takeover_tasklets(unsigned int cpu)
931 {
932 	/* CPU is dead, so no lock needed. */
933 	local_irq_disable();
934 
935 	/* Find end, append list for that CPU. */
936 	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
937 		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
938 		__this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
939 		per_cpu(tasklet_vec, cpu).head = NULL;
940 		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
941 	}
942 	raise_softirq_irqoff(TASKLET_SOFTIRQ);
943 
944 	if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
945 		*__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
946 		__this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
947 		per_cpu(tasklet_hi_vec, cpu).head = NULL;
948 		per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
949 	}
950 	raise_softirq_irqoff(HI_SOFTIRQ);
951 
952 	local_irq_enable();
953 	return 0;
954 }
955 #else
956 #define takeover_tasklets	NULL
957 #endif /* CONFIG_HOTPLUG_CPU */
958 
959 static struct smp_hotplug_thread softirq_threads = {
960 	.store			= &ksoftirqd,
961 	.thread_should_run	= ksoftirqd_should_run,
962 	.thread_fn		= run_ksoftirqd,
963 	.thread_comm		= "ksoftirqd/%u",
964 };
965 
spawn_ksoftirqd(void)966 static __init int spawn_ksoftirqd(void)
967 {
968 	cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
969 				  takeover_tasklets);
970 	BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
971 
972 	return 0;
973 }
974 early_initcall(spawn_ksoftirqd);
975 
976 /*
977  * [ These __weak aliases are kept in a separate compilation unit, so that
978  *   GCC does not inline them incorrectly. ]
979  */
980 
early_irq_init(void)981 int __init __weak early_irq_init(void)
982 {
983 	return 0;
984 }
985 
arch_probe_nr_irqs(void)986 int __init __weak arch_probe_nr_irqs(void)
987 {
988 	return NR_IRQS_LEGACY;
989 }
990 
arch_early_irq_init(void)991 int __init __weak arch_early_irq_init(void)
992 {
993 	return 0;
994 }
995 
arch_dynirq_lower_bound(unsigned int from)996 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
997 {
998 	return from;
999 }
1000