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1 /*
2  *	linux/kernel/softirq.c
3  *
4  *	Copyright (C) 1992 Linus Torvalds
5  *
6  *	Distribute under GPLv2.
7  *
8  *	Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
9  */
10 
11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
12 
13 #include <linux/export.h>
14 #include <linux/kernel_stat.h>
15 #include <linux/interrupt.h>
16 #include <linux/init.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 
30 #define CREATE_TRACE_POINTS
31 #include <trace/events/irq.h>
32 
33 /*
34    - No shared variables, all the data are CPU local.
35    - If a softirq needs serialization, let it serialize itself
36      by its own spinlocks.
37    - Even if softirq is serialized, only local cpu is marked for
38      execution. Hence, we get something sort of weak cpu binding.
39      Though it is still not clear, will it result in better locality
40      or will not.
41 
42    Examples:
43    - NET RX softirq. It is multithreaded and does not require
44      any global serialization.
45    - NET TX softirq. It kicks software netdevice queues, hence
46      it is logically serialized per device, but this serialization
47      is invisible to common code.
48    - Tasklets: serialized wrt itself.
49  */
50 
51 #ifndef __ARCH_IRQ_STAT
52 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
53 EXPORT_SYMBOL(irq_stat);
54 #endif
55 
56 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
57 
58 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
59 
60 const char * const softirq_to_name[NR_SOFTIRQS] = {
61 	"HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
62 	"TASKLET", "SCHED", "HRTIMER", "RCU"
63 };
64 
65 /*
66  * we cannot loop indefinitely here to avoid userspace starvation,
67  * but we also don't want to introduce a worst case 1/HZ latency
68  * to the pending events, so lets the scheduler to balance
69  * the softirq load for us.
70  */
wakeup_softirqd(void)71 static void wakeup_softirqd(void)
72 {
73 	/* Interrupts are disabled: no need to stop preemption */
74 	struct task_struct *tsk = __this_cpu_read(ksoftirqd);
75 
76 	if (tsk && tsk->state != TASK_RUNNING)
77 		wake_up_process(tsk);
78 }
79 
80 /*
81  * preempt_count and SOFTIRQ_OFFSET usage:
82  * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
83  *   softirq processing.
84  * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
85  *   on local_bh_disable or local_bh_enable.
86  * This lets us distinguish between whether we are currently processing
87  * softirq and whether we just have bh disabled.
88  */
89 
90 /*
91  * This one is for softirq.c-internal use,
92  * where hardirqs are disabled legitimately:
93  */
94 #ifdef CONFIG_TRACE_IRQFLAGS
__local_bh_disable_ip(unsigned long ip,unsigned int cnt)95 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
96 {
97 	unsigned long flags;
98 
99 	WARN_ON_ONCE(in_irq());
100 
101 	raw_local_irq_save(flags);
102 	/*
103 	 * The preempt tracer hooks into preempt_count_add and will break
104 	 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
105 	 * is set and before current->softirq_enabled is cleared.
106 	 * We must manually increment preempt_count here and manually
107 	 * call the trace_preempt_off later.
108 	 */
109 	__preempt_count_add(cnt);
110 	/*
111 	 * Were softirqs turned off above:
112 	 */
113 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
114 		trace_softirqs_off(ip);
115 	raw_local_irq_restore(flags);
116 
117 	if (preempt_count() == cnt)
118 		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
119 }
120 EXPORT_SYMBOL(__local_bh_disable_ip);
121 #endif /* CONFIG_TRACE_IRQFLAGS */
122 
__local_bh_enable(unsigned int cnt)123 static void __local_bh_enable(unsigned int cnt)
124 {
125 	WARN_ON_ONCE(!irqs_disabled());
126 
127 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
128 		trace_softirqs_on(_RET_IP_);
129 	preempt_count_sub(cnt);
130 }
131 
132 /*
133  * Special-case - softirqs can safely be enabled in
134  * cond_resched_softirq(), or by __do_softirq(),
135  * without processing still-pending softirqs:
136  */
_local_bh_enable(void)137 void _local_bh_enable(void)
138 {
139 	WARN_ON_ONCE(in_irq());
140 	__local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
141 }
142 EXPORT_SYMBOL(_local_bh_enable);
143 
__local_bh_enable_ip(unsigned long ip,unsigned int cnt)144 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
145 {
146 	WARN_ON_ONCE(in_irq() || irqs_disabled());
147 #ifdef CONFIG_TRACE_IRQFLAGS
148 	local_irq_disable();
149 #endif
150 	/*
151 	 * Are softirqs going to be turned on now:
152 	 */
153 	if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
154 		trace_softirqs_on(ip);
155 	/*
156 	 * Keep preemption disabled until we are done with
157 	 * softirq processing:
158 	 */
159 	preempt_count_sub(cnt - 1);
160 
161 	if (unlikely(!in_interrupt() && local_softirq_pending())) {
162 		/*
163 		 * Run softirq if any pending. And do it in its own stack
164 		 * as we may be calling this deep in a task call stack already.
165 		 */
166 		do_softirq();
167 	}
168 
169 	preempt_count_dec();
170 #ifdef CONFIG_TRACE_IRQFLAGS
171 	local_irq_enable();
172 #endif
173 	preempt_check_resched();
174 }
175 EXPORT_SYMBOL(__local_bh_enable_ip);
176 
177 /*
178  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
179  * but break the loop if need_resched() is set or after 2 ms.
180  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
181  * certain cases, such as stop_machine(), jiffies may cease to
182  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
183  * well to make sure we eventually return from this method.
184  *
185  * These limits have been established via experimentation.
186  * The two things to balance is latency against fairness -
187  * we want to handle softirqs as soon as possible, but they
188  * should not be able to lock up the box.
189  */
190 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
191 #define MAX_SOFTIRQ_RESTART 10
192 
193 #ifdef CONFIG_TRACE_IRQFLAGS
194 /*
195  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
196  * to keep the lockdep irq context tracking as tight as possible in order to
197  * not miss-qualify lock contexts and miss possible deadlocks.
198  */
199 
lockdep_softirq_start(void)200 static inline bool lockdep_softirq_start(void)
201 {
202 	bool in_hardirq = false;
203 
204 	if (trace_hardirq_context(current)) {
205 		in_hardirq = true;
206 		trace_hardirq_exit();
207 	}
208 
209 	lockdep_softirq_enter();
210 
211 	return in_hardirq;
212 }
213 
lockdep_softirq_end(bool in_hardirq)214 static inline void lockdep_softirq_end(bool in_hardirq)
215 {
216 	lockdep_softirq_exit();
217 
218 	if (in_hardirq)
219 		trace_hardirq_enter();
220 }
221 #else
lockdep_softirq_start(void)222 static inline bool lockdep_softirq_start(void) { return false; }
lockdep_softirq_end(bool in_hardirq)223 static inline void lockdep_softirq_end(bool in_hardirq) { }
224 #endif
225 
__do_softirq(void)226 asmlinkage __visible void __do_softirq(void)
227 {
228 	unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
229 	unsigned long old_flags = current->flags;
230 	int max_restart = MAX_SOFTIRQ_RESTART;
231 	struct softirq_action *h;
232 	bool in_hardirq;
233 	__u32 pending;
234 	int softirq_bit;
235 
236 	/*
237 	 * Mask out PF_MEMALLOC s current task context is borrowed for the
238 	 * softirq. A softirq handled such as network RX might set PF_MEMALLOC
239 	 * again if the socket is related to swap
240 	 */
241 	current->flags &= ~PF_MEMALLOC;
242 
243 	pending = local_softirq_pending();
244 	account_irq_enter_time(current);
245 
246 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
247 	in_hardirq = lockdep_softirq_start();
248 
249 restart:
250 	/* Reset the pending bitmask before enabling irqs */
251 	set_softirq_pending(0);
252 
253 	local_irq_enable();
254 
255 	h = softirq_vec;
256 
257 	while ((softirq_bit = ffs(pending))) {
258 		unsigned int vec_nr;
259 		int prev_count;
260 
261 		h += softirq_bit - 1;
262 
263 		vec_nr = h - softirq_vec;
264 		prev_count = preempt_count();
265 
266 		kstat_incr_softirqs_this_cpu(vec_nr);
267 
268 		trace_softirq_entry(vec_nr);
269 		h->action(h);
270 		trace_softirq_exit(vec_nr);
271 		if (unlikely(prev_count != preempt_count())) {
272 			pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
273 			       vec_nr, softirq_to_name[vec_nr], h->action,
274 			       prev_count, preempt_count());
275 			preempt_count_set(prev_count);
276 		}
277 		h++;
278 		pending >>= softirq_bit;
279 	}
280 
281 	rcu_bh_qs();
282 	local_irq_disable();
283 
284 	pending = local_softirq_pending();
285 	if (pending) {
286 		if (time_before(jiffies, end) && !need_resched() &&
287 		    --max_restart)
288 			goto restart;
289 
290 		wakeup_softirqd();
291 	}
292 
293 	lockdep_softirq_end(in_hardirq);
294 	account_irq_exit_time(current);
295 	__local_bh_enable(SOFTIRQ_OFFSET);
296 	WARN_ON_ONCE(in_interrupt());
297 	tsk_restore_flags(current, old_flags, PF_MEMALLOC);
298 }
299 
do_softirq(void)300 asmlinkage __visible void do_softirq(void)
301 {
302 	__u32 pending;
303 	unsigned long flags;
304 
305 	if (in_interrupt())
306 		return;
307 
308 	local_irq_save(flags);
309 
310 	pending = local_softirq_pending();
311 
312 	if (pending)
313 		do_softirq_own_stack();
314 
315 	local_irq_restore(flags);
316 }
317 
318 /*
319  * Enter an interrupt context.
320  */
irq_enter(void)321 void irq_enter(void)
322 {
323 	rcu_irq_enter();
324 	if (is_idle_task(current) && !in_interrupt()) {
325 		/*
326 		 * Prevent raise_softirq from needlessly waking up ksoftirqd
327 		 * here, as softirq will be serviced on return from interrupt.
328 		 */
329 		local_bh_disable();
330 		tick_irq_enter();
331 		_local_bh_enable();
332 	}
333 
334 	__irq_enter();
335 }
336 
invoke_softirq(void)337 static inline void invoke_softirq(void)
338 {
339 	if (!force_irqthreads) {
340 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
341 		/*
342 		 * We can safely execute softirq on the current stack if
343 		 * it is the irq stack, because it should be near empty
344 		 * at this stage.
345 		 */
346 		__do_softirq();
347 #else
348 		/*
349 		 * Otherwise, irq_exit() is called on the task stack that can
350 		 * be potentially deep already. So call softirq in its own stack
351 		 * to prevent from any overrun.
352 		 */
353 		do_softirq_own_stack();
354 #endif
355 	} else {
356 		wakeup_softirqd();
357 	}
358 }
359 
tick_irq_exit(void)360 static inline void tick_irq_exit(void)
361 {
362 #ifdef CONFIG_NO_HZ_COMMON
363 	int cpu = smp_processor_id();
364 
365 	/* Make sure that timer wheel updates are propagated */
366 	if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
367 		if (!in_interrupt())
368 			tick_nohz_irq_exit();
369 	}
370 #endif
371 }
372 
373 /*
374  * Exit an interrupt context. Process softirqs if needed and possible:
375  */
irq_exit(void)376 void irq_exit(void)
377 {
378 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
379 	local_irq_disable();
380 #else
381 	WARN_ON_ONCE(!irqs_disabled());
382 #endif
383 
384 	account_irq_exit_time(current);
385 	preempt_count_sub(HARDIRQ_OFFSET);
386 	if (!in_interrupt() && local_softirq_pending())
387 		invoke_softirq();
388 
389 	tick_irq_exit();
390 	rcu_irq_exit();
391 	trace_hardirq_exit(); /* must be last! */
392 }
393 
394 /*
395  * This function must run with irqs disabled!
396  */
raise_softirq_irqoff(unsigned int nr)397 inline void raise_softirq_irqoff(unsigned int nr)
398 {
399 	__raise_softirq_irqoff(nr);
400 
401 	/*
402 	 * If we're in an interrupt or softirq, we're done
403 	 * (this also catches softirq-disabled code). We will
404 	 * actually run the softirq once we return from
405 	 * the irq or softirq.
406 	 *
407 	 * Otherwise we wake up ksoftirqd to make sure we
408 	 * schedule the softirq soon.
409 	 */
410 	if (!in_interrupt())
411 		wakeup_softirqd();
412 }
413 
raise_softirq(unsigned int nr)414 void raise_softirq(unsigned int nr)
415 {
416 	unsigned long flags;
417 
418 	local_irq_save(flags);
419 	raise_softirq_irqoff(nr);
420 	local_irq_restore(flags);
421 }
422 
__raise_softirq_irqoff(unsigned int nr)423 void __raise_softirq_irqoff(unsigned int nr)
424 {
425 	trace_softirq_raise(nr);
426 	or_softirq_pending(1UL << nr);
427 }
428 
open_softirq(int nr,void (* action)(struct softirq_action *))429 void open_softirq(int nr, void (*action)(struct softirq_action *))
430 {
431 	softirq_vec[nr].action = action;
432 }
433 
434 /*
435  * Tasklets
436  */
437 struct tasklet_head {
438 	struct tasklet_struct *head;
439 	struct tasklet_struct **tail;
440 };
441 
442 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
443 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
444 
__tasklet_schedule(struct tasklet_struct * t)445 void __tasklet_schedule(struct tasklet_struct *t)
446 {
447 	unsigned long flags;
448 
449 	local_irq_save(flags);
450 	t->next = NULL;
451 	*__this_cpu_read(tasklet_vec.tail) = t;
452 	__this_cpu_write(tasklet_vec.tail, &(t->next));
453 	raise_softirq_irqoff(TASKLET_SOFTIRQ);
454 	local_irq_restore(flags);
455 }
456 EXPORT_SYMBOL(__tasklet_schedule);
457 
__tasklet_hi_schedule(struct tasklet_struct * t)458 void __tasklet_hi_schedule(struct tasklet_struct *t)
459 {
460 	unsigned long flags;
461 
462 	local_irq_save(flags);
463 	t->next = NULL;
464 	*__this_cpu_read(tasklet_hi_vec.tail) = t;
465 	__this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
466 	raise_softirq_irqoff(HI_SOFTIRQ);
467 	local_irq_restore(flags);
468 }
469 EXPORT_SYMBOL(__tasklet_hi_schedule);
470 
__tasklet_hi_schedule_first(struct tasklet_struct * t)471 void __tasklet_hi_schedule_first(struct tasklet_struct *t)
472 {
473 	BUG_ON(!irqs_disabled());
474 
475 	t->next = __this_cpu_read(tasklet_hi_vec.head);
476 	__this_cpu_write(tasklet_hi_vec.head, t);
477 	__raise_softirq_irqoff(HI_SOFTIRQ);
478 }
479 EXPORT_SYMBOL(__tasklet_hi_schedule_first);
480 
tasklet_action(struct softirq_action * a)481 static void tasklet_action(struct softirq_action *a)
482 {
483 	struct tasklet_struct *list;
484 
485 	local_irq_disable();
486 	list = __this_cpu_read(tasklet_vec.head);
487 	__this_cpu_write(tasklet_vec.head, NULL);
488 	__this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
489 	local_irq_enable();
490 
491 	while (list) {
492 		struct tasklet_struct *t = list;
493 
494 		list = list->next;
495 
496 		if (tasklet_trylock(t)) {
497 			if (!atomic_read(&t->count)) {
498 				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
499 							&t->state))
500 					BUG();
501 				t->func(t->data);
502 				tasklet_unlock(t);
503 				continue;
504 			}
505 			tasklet_unlock(t);
506 		}
507 
508 		local_irq_disable();
509 		t->next = NULL;
510 		*__this_cpu_read(tasklet_vec.tail) = t;
511 		__this_cpu_write(tasklet_vec.tail, &(t->next));
512 		__raise_softirq_irqoff(TASKLET_SOFTIRQ);
513 		local_irq_enable();
514 	}
515 }
516 
tasklet_hi_action(struct softirq_action * a)517 static void tasklet_hi_action(struct softirq_action *a)
518 {
519 	struct tasklet_struct *list;
520 
521 	local_irq_disable();
522 	list = __this_cpu_read(tasklet_hi_vec.head);
523 	__this_cpu_write(tasklet_hi_vec.head, NULL);
524 	__this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
525 	local_irq_enable();
526 
527 	while (list) {
528 		struct tasklet_struct *t = list;
529 
530 		list = list->next;
531 
532 		if (tasklet_trylock(t)) {
533 			if (!atomic_read(&t->count)) {
534 				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
535 							&t->state))
536 					BUG();
537 				t->func(t->data);
538 				tasklet_unlock(t);
539 				continue;
540 			}
541 			tasklet_unlock(t);
542 		}
543 
544 		local_irq_disable();
545 		t->next = NULL;
546 		*__this_cpu_read(tasklet_hi_vec.tail) = t;
547 		__this_cpu_write(tasklet_hi_vec.tail, &(t->next));
548 		__raise_softirq_irqoff(HI_SOFTIRQ);
549 		local_irq_enable();
550 	}
551 }
552 
tasklet_init(struct tasklet_struct * t,void (* func)(unsigned long),unsigned long data)553 void tasklet_init(struct tasklet_struct *t,
554 		  void (*func)(unsigned long), unsigned long data)
555 {
556 	t->next = NULL;
557 	t->state = 0;
558 	atomic_set(&t->count, 0);
559 	t->func = func;
560 	t->data = data;
561 }
562 EXPORT_SYMBOL(tasklet_init);
563 
tasklet_kill(struct tasklet_struct * t)564 void tasklet_kill(struct tasklet_struct *t)
565 {
566 	if (in_interrupt())
567 		pr_notice("Attempt to kill tasklet from interrupt\n");
568 
569 	while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
570 		do {
571 			yield();
572 		} while (test_bit(TASKLET_STATE_SCHED, &t->state));
573 	}
574 	tasklet_unlock_wait(t);
575 	clear_bit(TASKLET_STATE_SCHED, &t->state);
576 }
577 EXPORT_SYMBOL(tasklet_kill);
578 
579 /*
580  * tasklet_hrtimer
581  */
582 
583 /*
584  * The trampoline is called when the hrtimer expires. It schedules a tasklet
585  * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
586  * hrtimer callback, but from softirq context.
587  */
__hrtimer_tasklet_trampoline(struct hrtimer * timer)588 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
589 {
590 	struct tasklet_hrtimer *ttimer =
591 		container_of(timer, struct tasklet_hrtimer, timer);
592 
593 	tasklet_hi_schedule(&ttimer->tasklet);
594 	return HRTIMER_NORESTART;
595 }
596 
597 /*
598  * Helper function which calls the hrtimer callback from
599  * tasklet/softirq context
600  */
__tasklet_hrtimer_trampoline(unsigned long data)601 static void __tasklet_hrtimer_trampoline(unsigned long data)
602 {
603 	struct tasklet_hrtimer *ttimer = (void *)data;
604 	enum hrtimer_restart restart;
605 
606 	restart = ttimer->function(&ttimer->timer);
607 	if (restart != HRTIMER_NORESTART)
608 		hrtimer_restart(&ttimer->timer);
609 }
610 
611 /**
612  * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
613  * @ttimer:	 tasklet_hrtimer which is initialized
614  * @function:	 hrtimer callback function which gets called from softirq context
615  * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
616  * @mode:	 hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
617  */
tasklet_hrtimer_init(struct tasklet_hrtimer * ttimer,enum hrtimer_restart (* function)(struct hrtimer *),clockid_t which_clock,enum hrtimer_mode mode)618 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
619 			  enum hrtimer_restart (*function)(struct hrtimer *),
620 			  clockid_t which_clock, enum hrtimer_mode mode)
621 {
622 	hrtimer_init(&ttimer->timer, which_clock, mode);
623 	ttimer->timer.function = __hrtimer_tasklet_trampoline;
624 	tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
625 		     (unsigned long)ttimer);
626 	ttimer->function = function;
627 }
628 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
629 
softirq_init(void)630 void __init softirq_init(void)
631 {
632 	int cpu;
633 
634 	for_each_possible_cpu(cpu) {
635 		per_cpu(tasklet_vec, cpu).tail =
636 			&per_cpu(tasklet_vec, cpu).head;
637 		per_cpu(tasklet_hi_vec, cpu).tail =
638 			&per_cpu(tasklet_hi_vec, cpu).head;
639 	}
640 
641 	open_softirq(TASKLET_SOFTIRQ, tasklet_action);
642 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
643 }
644 
ksoftirqd_should_run(unsigned int cpu)645 static int ksoftirqd_should_run(unsigned int cpu)
646 {
647 	return local_softirq_pending();
648 }
649 
run_ksoftirqd(unsigned int cpu)650 static void run_ksoftirqd(unsigned int cpu)
651 {
652 	local_irq_disable();
653 	if (local_softirq_pending()) {
654 		/*
655 		 * We can safely run softirq on inline stack, as we are not deep
656 		 * in the task stack here.
657 		 */
658 		__do_softirq();
659 		local_irq_enable();
660 		cond_resched();
661 
662 		preempt_disable();
663 		rcu_note_context_switch(cpu);
664 		preempt_enable();
665 
666 		return;
667 	}
668 	local_irq_enable();
669 }
670 
671 #ifdef CONFIG_HOTPLUG_CPU
672 /*
673  * tasklet_kill_immediate is called to remove a tasklet which can already be
674  * scheduled for execution on @cpu.
675  *
676  * Unlike tasklet_kill, this function removes the tasklet
677  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
678  *
679  * When this function is called, @cpu must be in the CPU_DEAD state.
680  */
tasklet_kill_immediate(struct tasklet_struct * t,unsigned int cpu)681 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
682 {
683 	struct tasklet_struct **i;
684 
685 	BUG_ON(cpu_online(cpu));
686 	BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
687 
688 	if (!test_bit(TASKLET_STATE_SCHED, &t->state))
689 		return;
690 
691 	/* CPU is dead, so no lock needed. */
692 	for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
693 		if (*i == t) {
694 			*i = t->next;
695 			/* If this was the tail element, move the tail ptr */
696 			if (*i == NULL)
697 				per_cpu(tasklet_vec, cpu).tail = i;
698 			return;
699 		}
700 	}
701 	BUG();
702 }
703 
takeover_tasklets(unsigned int cpu)704 static void takeover_tasklets(unsigned int cpu)
705 {
706 	/* CPU is dead, so no lock needed. */
707 	local_irq_disable();
708 
709 	/* Find end, append list for that CPU. */
710 	if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
711 		*__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
712 		this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
713 		per_cpu(tasklet_vec, cpu).head = NULL;
714 		per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
715 	}
716 	raise_softirq_irqoff(TASKLET_SOFTIRQ);
717 
718 	if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
719 		*__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
720 		__this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
721 		per_cpu(tasklet_hi_vec, cpu).head = NULL;
722 		per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
723 	}
724 	raise_softirq_irqoff(HI_SOFTIRQ);
725 
726 	local_irq_enable();
727 }
728 #endif /* CONFIG_HOTPLUG_CPU */
729 
cpu_callback(struct notifier_block * nfb,unsigned long action,void * hcpu)730 static int cpu_callback(struct notifier_block *nfb, unsigned long action,
731 			void *hcpu)
732 {
733 	switch (action) {
734 #ifdef CONFIG_HOTPLUG_CPU
735 	case CPU_DEAD:
736 	case CPU_DEAD_FROZEN:
737 		takeover_tasklets((unsigned long)hcpu);
738 		break;
739 #endif /* CONFIG_HOTPLUG_CPU */
740 	}
741 	return NOTIFY_OK;
742 }
743 
744 static struct notifier_block cpu_nfb = {
745 	.notifier_call = cpu_callback
746 };
747 
748 static struct smp_hotplug_thread softirq_threads = {
749 	.store			= &ksoftirqd,
750 	.thread_should_run	= ksoftirqd_should_run,
751 	.thread_fn		= run_ksoftirqd,
752 	.thread_comm		= "ksoftirqd/%u",
753 };
754 
spawn_ksoftirqd(void)755 static __init int spawn_ksoftirqd(void)
756 {
757 	register_cpu_notifier(&cpu_nfb);
758 
759 	BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
760 
761 	return 0;
762 }
763 early_initcall(spawn_ksoftirqd);
764 
765 /*
766  * [ These __weak aliases are kept in a separate compilation unit, so that
767  *   GCC does not inline them incorrectly. ]
768  */
769 
early_irq_init(void)770 int __init __weak early_irq_init(void)
771 {
772 	return 0;
773 }
774 
arch_probe_nr_irqs(void)775 int __init __weak arch_probe_nr_irqs(void)
776 {
777 	return NR_IRQS_LEGACY;
778 }
779 
arch_early_irq_init(void)780 int __init __weak arch_early_irq_init(void)
781 {
782 	return 0;
783 }
784 
arch_dynirq_lower_bound(unsigned int from)785 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
786 {
787 	return from;
788 }
789