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