Loading...
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}
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/mm.h>
17#include <linux/notifier.h>
18#include <linux/percpu.h>
19#include <linux/cpu.h>
20#include <linux/freezer.h>
21#include <linux/kthread.h>
22#include <linux/rcupdate.h>
23#include <linux/ftrace.h>
24#include <linux/smp.h>
25#include <linux/smpboot.h>
26#include <linux/tick.h>
27#include <linux/irq.h>
28
29#define CREATE_TRACE_POINTS
30#include <trace/events/irq.h>
31
32/*
33 - No shared variables, all the data are CPU local.
34 - If a softirq needs serialization, let it serialize itself
35 by its own spinlocks.
36 - Even if softirq is serialized, only local cpu is marked for
37 execution. Hence, we get something sort of weak cpu binding.
38 Though it is still not clear, will it result in better locality
39 or will not.
40
41 Examples:
42 - NET RX softirq. It is multithreaded and does not require
43 any global serialization.
44 - NET TX softirq. It kicks software netdevice queues, hence
45 it is logically serialized per device, but this serialization
46 is invisible to common code.
47 - Tasklets: serialized wrt itself.
48 */
49
50#ifndef __ARCH_IRQ_STAT
51DEFINE_PER_CPU_ALIGNED(irq_cpustat_t, irq_stat);
52EXPORT_PER_CPU_SYMBOL(irq_stat);
53#endif
54
55static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
56
57DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
58
59const char * const softirq_to_name[NR_SOFTIRQS] = {
60 "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "IRQ_POLL",
61 "TASKLET", "SCHED", "HRTIMER", "RCU"
62};
63
64/*
65 * we cannot loop indefinitely here to avoid userspace starvation,
66 * but we also don't want to introduce a worst case 1/HZ latency
67 * to the pending events, so lets the scheduler to balance
68 * the softirq load for us.
69 */
70static void wakeup_softirqd(void)
71{
72 /* Interrupts are disabled: no need to stop preemption */
73 struct task_struct *tsk = __this_cpu_read(ksoftirqd);
74
75 if (tsk && tsk->state != TASK_RUNNING)
76 wake_up_process(tsk);
77}
78
79/*
80 * If ksoftirqd is scheduled, we do not want to process pending softirqs
81 * right now. Let ksoftirqd handle this at its own rate, to get fairness,
82 * unless we're doing some of the synchronous softirqs.
83 */
84#define SOFTIRQ_NOW_MASK ((1 << HI_SOFTIRQ) | (1 << TASKLET_SOFTIRQ))
85static bool ksoftirqd_running(unsigned long pending)
86{
87 struct task_struct *tsk = __this_cpu_read(ksoftirqd);
88
89 if (pending & SOFTIRQ_NOW_MASK)
90 return false;
91 return tsk && (tsk->state == TASK_RUNNING) &&
92 !__kthread_should_park(tsk);
93}
94
95/*
96 * preempt_count and SOFTIRQ_OFFSET usage:
97 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
98 * softirq processing.
99 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
100 * on local_bh_disable or local_bh_enable.
101 * This lets us distinguish between whether we are currently processing
102 * softirq and whether we just have bh disabled.
103 */
104
105/*
106 * This one is for softirq.c-internal use,
107 * where hardirqs are disabled legitimately:
108 */
109#ifdef CONFIG_TRACE_IRQFLAGS
110
111DEFINE_PER_CPU(int, hardirqs_enabled);
112DEFINE_PER_CPU(int, hardirq_context);
113EXPORT_PER_CPU_SYMBOL_GPL(hardirqs_enabled);
114EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
115
116void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
117{
118 unsigned long flags;
119
120 WARN_ON_ONCE(in_irq());
121
122 raw_local_irq_save(flags);
123 /*
124 * The preempt tracer hooks into preempt_count_add and will break
125 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
126 * is set and before current->softirq_enabled is cleared.
127 * We must manually increment preempt_count here and manually
128 * call the trace_preempt_off later.
129 */
130 __preempt_count_add(cnt);
131 /*
132 * Were softirqs turned off above:
133 */
134 if (softirq_count() == (cnt & SOFTIRQ_MASK))
135 lockdep_softirqs_off(ip);
136 raw_local_irq_restore(flags);
137
138 if (preempt_count() == cnt) {
139#ifdef CONFIG_DEBUG_PREEMPT
140 current->preempt_disable_ip = get_lock_parent_ip();
141#endif
142 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
143 }
144}
145EXPORT_SYMBOL(__local_bh_disable_ip);
146#endif /* CONFIG_TRACE_IRQFLAGS */
147
148static void __local_bh_enable(unsigned int cnt)
149{
150 lockdep_assert_irqs_disabled();
151
152 if (preempt_count() == cnt)
153 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
154
155 if (softirq_count() == (cnt & SOFTIRQ_MASK))
156 lockdep_softirqs_on(_RET_IP_);
157
158 __preempt_count_sub(cnt);
159}
160
161/*
162 * Special-case - softirqs can safely be enabled by __do_softirq(),
163 * without processing still-pending softirqs:
164 */
165void _local_bh_enable(void)
166{
167 WARN_ON_ONCE(in_irq());
168 __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
169}
170EXPORT_SYMBOL(_local_bh_enable);
171
172void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
173{
174 WARN_ON_ONCE(in_irq());
175 lockdep_assert_irqs_enabled();
176#ifdef CONFIG_TRACE_IRQFLAGS
177 local_irq_disable();
178#endif
179 /*
180 * Are softirqs going to be turned on now:
181 */
182 if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
183 lockdep_softirqs_on(ip);
184 /*
185 * Keep preemption disabled until we are done with
186 * softirq processing:
187 */
188 preempt_count_sub(cnt - 1);
189
190 if (unlikely(!in_interrupt() && local_softirq_pending())) {
191 /*
192 * Run softirq if any pending. And do it in its own stack
193 * as we may be calling this deep in a task call stack already.
194 */
195 do_softirq();
196 }
197
198 preempt_count_dec();
199#ifdef CONFIG_TRACE_IRQFLAGS
200 local_irq_enable();
201#endif
202 preempt_check_resched();
203}
204EXPORT_SYMBOL(__local_bh_enable_ip);
205
206/*
207 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
208 * but break the loop if need_resched() is set or after 2 ms.
209 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
210 * certain cases, such as stop_machine(), jiffies may cease to
211 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
212 * well to make sure we eventually return from this method.
213 *
214 * These limits have been established via experimentation.
215 * The two things to balance is latency against fairness -
216 * we want to handle softirqs as soon as possible, but they
217 * should not be able to lock up the box.
218 */
219#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2)
220#define MAX_SOFTIRQ_RESTART 10
221
222#ifdef CONFIG_TRACE_IRQFLAGS
223/*
224 * When we run softirqs from irq_exit() and thus on the hardirq stack we need
225 * to keep the lockdep irq context tracking as tight as possible in order to
226 * not miss-qualify lock contexts and miss possible deadlocks.
227 */
228
229static inline bool lockdep_softirq_start(void)
230{
231 bool in_hardirq = false;
232
233 if (lockdep_hardirq_context()) {
234 in_hardirq = true;
235 lockdep_hardirq_exit();
236 }
237
238 lockdep_softirq_enter();
239
240 return in_hardirq;
241}
242
243static inline void lockdep_softirq_end(bool in_hardirq)
244{
245 lockdep_softirq_exit();
246
247 if (in_hardirq)
248 lockdep_hardirq_enter();
249}
250#else
251static inline bool lockdep_softirq_start(void) { return false; }
252static inline void lockdep_softirq_end(bool in_hardirq) { }
253#endif
254
255asmlinkage __visible void __softirq_entry __do_softirq(void)
256{
257 unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
258 unsigned long old_flags = current->flags;
259 int max_restart = MAX_SOFTIRQ_RESTART;
260 struct softirq_action *h;
261 bool in_hardirq;
262 __u32 pending;
263 int softirq_bit;
264
265 /*
266 * Mask out PF_MEMALLOC as the current task context is borrowed for the
267 * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
268 * again if the socket is related to swapping.
269 */
270 current->flags &= ~PF_MEMALLOC;
271
272 pending = local_softirq_pending();
273 account_irq_enter_time(current);
274
275 __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
276 in_hardirq = lockdep_softirq_start();
277
278restart:
279 /* Reset the pending bitmask before enabling irqs */
280 set_softirq_pending(0);
281
282 local_irq_enable();
283
284 h = softirq_vec;
285
286 while ((softirq_bit = ffs(pending))) {
287 unsigned int vec_nr;
288 int prev_count;
289
290 h += softirq_bit - 1;
291
292 vec_nr = h - softirq_vec;
293 prev_count = preempt_count();
294
295 kstat_incr_softirqs_this_cpu(vec_nr);
296
297 trace_softirq_entry(vec_nr);
298 h->action(h);
299 trace_softirq_exit(vec_nr);
300 if (unlikely(prev_count != preempt_count())) {
301 pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
302 vec_nr, softirq_to_name[vec_nr], h->action,
303 prev_count, preempt_count());
304 preempt_count_set(prev_count);
305 }
306 h++;
307 pending >>= softirq_bit;
308 }
309
310 if (__this_cpu_read(ksoftirqd) == current)
311 rcu_softirq_qs();
312 local_irq_disable();
313
314 pending = local_softirq_pending();
315 if (pending) {
316 if (time_before(jiffies, end) && !need_resched() &&
317 --max_restart)
318 goto restart;
319
320 wakeup_softirqd();
321 }
322
323 lockdep_softirq_end(in_hardirq);
324 account_irq_exit_time(current);
325 __local_bh_enable(SOFTIRQ_OFFSET);
326 WARN_ON_ONCE(in_interrupt());
327 current_restore_flags(old_flags, PF_MEMALLOC);
328}
329
330asmlinkage __visible void do_softirq(void)
331{
332 __u32 pending;
333 unsigned long flags;
334
335 if (in_interrupt())
336 return;
337
338 local_irq_save(flags);
339
340 pending = local_softirq_pending();
341
342 if (pending && !ksoftirqd_running(pending))
343 do_softirq_own_stack();
344
345 local_irq_restore(flags);
346}
347
348/**
349 * irq_enter_rcu - Enter an interrupt context with RCU watching
350 */
351void irq_enter_rcu(void)
352{
353 if (is_idle_task(current) && !in_interrupt()) {
354 /*
355 * Prevent raise_softirq from needlessly waking up ksoftirqd
356 * here, as softirq will be serviced on return from interrupt.
357 */
358 local_bh_disable();
359 tick_irq_enter();
360 _local_bh_enable();
361 }
362 __irq_enter();
363}
364
365/**
366 * irq_enter - Enter an interrupt context including RCU update
367 */
368void irq_enter(void)
369{
370 rcu_irq_enter();
371 irq_enter_rcu();
372}
373
374static inline void invoke_softirq(void)
375{
376 if (ksoftirqd_running(local_softirq_pending()))
377 return;
378
379 if (!force_irqthreads) {
380#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
381 /*
382 * We can safely execute softirq on the current stack if
383 * it is the irq stack, because it should be near empty
384 * at this stage.
385 */
386 __do_softirq();
387#else
388 /*
389 * Otherwise, irq_exit() is called on the task stack that can
390 * be potentially deep already. So call softirq in its own stack
391 * to prevent from any overrun.
392 */
393 do_softirq_own_stack();
394#endif
395 } else {
396 wakeup_softirqd();
397 }
398}
399
400static inline void tick_irq_exit(void)
401{
402#ifdef CONFIG_NO_HZ_COMMON
403 int cpu = smp_processor_id();
404
405 /* Make sure that timer wheel updates are propagated */
406 if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
407 if (!in_irq())
408 tick_nohz_irq_exit();
409 }
410#endif
411}
412
413static inline void __irq_exit_rcu(void)
414{
415#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
416 local_irq_disable();
417#else
418 lockdep_assert_irqs_disabled();
419#endif
420 account_irq_exit_time(current);
421 preempt_count_sub(HARDIRQ_OFFSET);
422 if (!in_interrupt() && local_softirq_pending())
423 invoke_softirq();
424
425 tick_irq_exit();
426}
427
428/**
429 * irq_exit_rcu() - Exit an interrupt context without updating RCU
430 *
431 * Also processes softirqs if needed and possible.
432 */
433void irq_exit_rcu(void)
434{
435 __irq_exit_rcu();
436 /* must be last! */
437 lockdep_hardirq_exit();
438}
439
440/**
441 * irq_exit - Exit an interrupt context, update RCU and lockdep
442 *
443 * Also processes softirqs if needed and possible.
444 */
445void irq_exit(void)
446{
447 __irq_exit_rcu();
448 rcu_irq_exit();
449 /* must be last! */
450 lockdep_hardirq_exit();
451}
452
453/*
454 * This function must run with irqs disabled!
455 */
456inline void raise_softirq_irqoff(unsigned int nr)
457{
458 __raise_softirq_irqoff(nr);
459
460 /*
461 * If we're in an interrupt or softirq, we're done
462 * (this also catches softirq-disabled code). We will
463 * actually run the softirq once we return from
464 * the irq or softirq.
465 *
466 * Otherwise we wake up ksoftirqd to make sure we
467 * schedule the softirq soon.
468 */
469 if (!in_interrupt())
470 wakeup_softirqd();
471}
472
473void raise_softirq(unsigned int nr)
474{
475 unsigned long flags;
476
477 local_irq_save(flags);
478 raise_softirq_irqoff(nr);
479 local_irq_restore(flags);
480}
481
482void __raise_softirq_irqoff(unsigned int nr)
483{
484 trace_softirq_raise(nr);
485 or_softirq_pending(1UL << nr);
486}
487
488void open_softirq(int nr, void (*action)(struct softirq_action *))
489{
490 softirq_vec[nr].action = action;
491}
492
493/*
494 * Tasklets
495 */
496struct tasklet_head {
497 struct tasklet_struct *head;
498 struct tasklet_struct **tail;
499};
500
501static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
502static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
503
504static void __tasklet_schedule_common(struct tasklet_struct *t,
505 struct tasklet_head __percpu *headp,
506 unsigned int softirq_nr)
507{
508 struct tasklet_head *head;
509 unsigned long flags;
510
511 local_irq_save(flags);
512 head = this_cpu_ptr(headp);
513 t->next = NULL;
514 *head->tail = t;
515 head->tail = &(t->next);
516 raise_softirq_irqoff(softirq_nr);
517 local_irq_restore(flags);
518}
519
520void __tasklet_schedule(struct tasklet_struct *t)
521{
522 __tasklet_schedule_common(t, &tasklet_vec,
523 TASKLET_SOFTIRQ);
524}
525EXPORT_SYMBOL(__tasklet_schedule);
526
527void __tasklet_hi_schedule(struct tasklet_struct *t)
528{
529 __tasklet_schedule_common(t, &tasklet_hi_vec,
530 HI_SOFTIRQ);
531}
532EXPORT_SYMBOL(__tasklet_hi_schedule);
533
534static void tasklet_action_common(struct softirq_action *a,
535 struct tasklet_head *tl_head,
536 unsigned int softirq_nr)
537{
538 struct tasklet_struct *list;
539
540 local_irq_disable();
541 list = tl_head->head;
542 tl_head->head = NULL;
543 tl_head->tail = &tl_head->head;
544 local_irq_enable();
545
546 while (list) {
547 struct tasklet_struct *t = list;
548
549 list = list->next;
550
551 if (tasklet_trylock(t)) {
552 if (!atomic_read(&t->count)) {
553 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
554 &t->state))
555 BUG();
556 if (t->use_callback)
557 t->callback(t);
558 else
559 t->func(t->data);
560 tasklet_unlock(t);
561 continue;
562 }
563 tasklet_unlock(t);
564 }
565
566 local_irq_disable();
567 t->next = NULL;
568 *tl_head->tail = t;
569 tl_head->tail = &t->next;
570 __raise_softirq_irqoff(softirq_nr);
571 local_irq_enable();
572 }
573}
574
575static __latent_entropy void tasklet_action(struct softirq_action *a)
576{
577 tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
578}
579
580static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
581{
582 tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
583}
584
585void tasklet_setup(struct tasklet_struct *t,
586 void (*callback)(struct tasklet_struct *))
587{
588 t->next = NULL;
589 t->state = 0;
590 atomic_set(&t->count, 0);
591 t->callback = callback;
592 t->use_callback = true;
593 t->data = 0;
594}
595EXPORT_SYMBOL(tasklet_setup);
596
597void tasklet_init(struct tasklet_struct *t,
598 void (*func)(unsigned long), unsigned long data)
599{
600 t->next = NULL;
601 t->state = 0;
602 atomic_set(&t->count, 0);
603 t->func = func;
604 t->use_callback = false;
605 t->data = data;
606}
607EXPORT_SYMBOL(tasklet_init);
608
609void tasklet_kill(struct tasklet_struct *t)
610{
611 if (in_interrupt())
612 pr_notice("Attempt to kill tasklet from interrupt\n");
613
614 while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
615 do {
616 yield();
617 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
618 }
619 tasklet_unlock_wait(t);
620 clear_bit(TASKLET_STATE_SCHED, &t->state);
621}
622EXPORT_SYMBOL(tasklet_kill);
623
624void __init softirq_init(void)
625{
626 int cpu;
627
628 for_each_possible_cpu(cpu) {
629 per_cpu(tasklet_vec, cpu).tail =
630 &per_cpu(tasklet_vec, cpu).head;
631 per_cpu(tasklet_hi_vec, cpu).tail =
632 &per_cpu(tasklet_hi_vec, cpu).head;
633 }
634
635 open_softirq(TASKLET_SOFTIRQ, tasklet_action);
636 open_softirq(HI_SOFTIRQ, tasklet_hi_action);
637}
638
639static int ksoftirqd_should_run(unsigned int cpu)
640{
641 return local_softirq_pending();
642}
643
644static void run_ksoftirqd(unsigned int cpu)
645{
646 local_irq_disable();
647 if (local_softirq_pending()) {
648 /*
649 * We can safely run softirq on inline stack, as we are not deep
650 * in the task stack here.
651 */
652 __do_softirq();
653 local_irq_enable();
654 cond_resched();
655 return;
656 }
657 local_irq_enable();
658}
659
660#ifdef CONFIG_HOTPLUG_CPU
661/*
662 * tasklet_kill_immediate is called to remove a tasklet which can already be
663 * scheduled for execution on @cpu.
664 *
665 * Unlike tasklet_kill, this function removes the tasklet
666 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
667 *
668 * When this function is called, @cpu must be in the CPU_DEAD state.
669 */
670void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
671{
672 struct tasklet_struct **i;
673
674 BUG_ON(cpu_online(cpu));
675 BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
676
677 if (!test_bit(TASKLET_STATE_SCHED, &t->state))
678 return;
679
680 /* CPU is dead, so no lock needed. */
681 for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
682 if (*i == t) {
683 *i = t->next;
684 /* If this was the tail element, move the tail ptr */
685 if (*i == NULL)
686 per_cpu(tasklet_vec, cpu).tail = i;
687 return;
688 }
689 }
690 BUG();
691}
692
693static int takeover_tasklets(unsigned int cpu)
694{
695 /* CPU is dead, so no lock needed. */
696 local_irq_disable();
697
698 /* Find end, append list for that CPU. */
699 if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
700 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
701 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
702 per_cpu(tasklet_vec, cpu).head = NULL;
703 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
704 }
705 raise_softirq_irqoff(TASKLET_SOFTIRQ);
706
707 if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
708 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
709 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
710 per_cpu(tasklet_hi_vec, cpu).head = NULL;
711 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
712 }
713 raise_softirq_irqoff(HI_SOFTIRQ);
714
715 local_irq_enable();
716 return 0;
717}
718#else
719#define takeover_tasklets NULL
720#endif /* CONFIG_HOTPLUG_CPU */
721
722static struct smp_hotplug_thread softirq_threads = {
723 .store = &ksoftirqd,
724 .thread_should_run = ksoftirqd_should_run,
725 .thread_fn = run_ksoftirqd,
726 .thread_comm = "ksoftirqd/%u",
727};
728
729static __init int spawn_ksoftirqd(void)
730{
731 cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
732 takeover_tasklets);
733 BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
734
735 return 0;
736}
737early_initcall(spawn_ksoftirqd);
738
739/*
740 * [ These __weak aliases are kept in a separate compilation unit, so that
741 * GCC does not inline them incorrectly. ]
742 */
743
744int __init __weak early_irq_init(void)
745{
746 return 0;
747}
748
749int __init __weak arch_probe_nr_irqs(void)
750{
751 return NR_IRQS_LEGACY;
752}
753
754int __init __weak arch_early_irq_init(void)
755{
756 return 0;
757}
758
759unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
760{
761 return from;
762}