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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
110void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
111{
112 unsigned long flags;
113
114 WARN_ON_ONCE(in_irq());
115
116 raw_local_irq_save(flags);
117 /*
118 * The preempt tracer hooks into preempt_count_add and will break
119 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
120 * is set and before current->softirq_enabled is cleared.
121 * We must manually increment preempt_count here and manually
122 * call the trace_preempt_off later.
123 */
124 __preempt_count_add(cnt);
125 /*
126 * Were softirqs turned off above:
127 */
128 if (softirq_count() == (cnt & SOFTIRQ_MASK))
129 trace_softirqs_off(ip);
130 raw_local_irq_restore(flags);
131
132 if (preempt_count() == cnt) {
133#ifdef CONFIG_DEBUG_PREEMPT
134 current->preempt_disable_ip = get_lock_parent_ip();
135#endif
136 trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
137 }
138}
139EXPORT_SYMBOL(__local_bh_disable_ip);
140#endif /* CONFIG_TRACE_IRQFLAGS */
141
142static void __local_bh_enable(unsigned int cnt)
143{
144 lockdep_assert_irqs_disabled();
145
146 if (preempt_count() == cnt)
147 trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
148
149 if (softirq_count() == (cnt & SOFTIRQ_MASK))
150 trace_softirqs_on(_RET_IP_);
151
152 __preempt_count_sub(cnt);
153}
154
155/*
156 * Special-case - softirqs can safely be enabled by __do_softirq(),
157 * without processing still-pending softirqs:
158 */
159void _local_bh_enable(void)
160{
161 WARN_ON_ONCE(in_irq());
162 __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
163}
164EXPORT_SYMBOL(_local_bh_enable);
165
166void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
167{
168 WARN_ON_ONCE(in_irq());
169 lockdep_assert_irqs_enabled();
170#ifdef CONFIG_TRACE_IRQFLAGS
171 local_irq_disable();
172#endif
173 /*
174 * Are softirqs going to be turned on now:
175 */
176 if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
177 trace_softirqs_on(ip);
178 /*
179 * Keep preemption disabled until we are done with
180 * softirq processing:
181 */
182 preempt_count_sub(cnt - 1);
183
184 if (unlikely(!in_interrupt() && local_softirq_pending())) {
185 /*
186 * Run softirq if any pending. And do it in its own stack
187 * as we may be calling this deep in a task call stack already.
188 */
189 do_softirq();
190 }
191
192 preempt_count_dec();
193#ifdef CONFIG_TRACE_IRQFLAGS
194 local_irq_enable();
195#endif
196 preempt_check_resched();
197}
198EXPORT_SYMBOL(__local_bh_enable_ip);
199
200/*
201 * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
202 * but break the loop if need_resched() is set or after 2 ms.
203 * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
204 * certain cases, such as stop_machine(), jiffies may cease to
205 * increment and so we need the MAX_SOFTIRQ_RESTART limit as
206 * well to make sure we eventually return from this method.
207 *
208 * These limits have been established via experimentation.
209 * The two things to balance is latency against fairness -
210 * we want to handle softirqs as soon as possible, but they
211 * should not be able to lock up the box.
212 */
213#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2)
214#define MAX_SOFTIRQ_RESTART 10
215
216#ifdef CONFIG_TRACE_IRQFLAGS
217/*
218 * When we run softirqs from irq_exit() and thus on the hardirq stack we need
219 * to keep the lockdep irq context tracking as tight as possible in order to
220 * not miss-qualify lock contexts and miss possible deadlocks.
221 */
222
223static inline bool lockdep_softirq_start(void)
224{
225 bool in_hardirq = false;
226
227 if (trace_hardirq_context(current)) {
228 in_hardirq = true;
229 trace_hardirq_exit();
230 }
231
232 lockdep_softirq_enter();
233
234 return in_hardirq;
235}
236
237static inline void lockdep_softirq_end(bool in_hardirq)
238{
239 lockdep_softirq_exit();
240
241 if (in_hardirq)
242 trace_hardirq_enter();
243}
244#else
245static inline bool lockdep_softirq_start(void) { return false; }
246static inline void lockdep_softirq_end(bool in_hardirq) { }
247#endif
248
249asmlinkage __visible void __softirq_entry __do_softirq(void)
250{
251 unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
252 unsigned long old_flags = current->flags;
253 int max_restart = MAX_SOFTIRQ_RESTART;
254 struct softirq_action *h;
255 bool in_hardirq;
256 __u32 pending;
257 int softirq_bit;
258
259 /*
260 * Mask out PF_MEMALLOC as the current task context is borrowed for the
261 * softirq. A softirq handled, such as network RX, might set PF_MEMALLOC
262 * again if the socket is related to swapping.
263 */
264 current->flags &= ~PF_MEMALLOC;
265
266 pending = local_softirq_pending();
267 account_irq_enter_time(current);
268
269 __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
270 in_hardirq = lockdep_softirq_start();
271
272restart:
273 /* Reset the pending bitmask before enabling irqs */
274 set_softirq_pending(0);
275
276 local_irq_enable();
277
278 h = softirq_vec;
279
280 while ((softirq_bit = ffs(pending))) {
281 unsigned int vec_nr;
282 int prev_count;
283
284 h += softirq_bit - 1;
285
286 vec_nr = h - softirq_vec;
287 prev_count = preempt_count();
288
289 kstat_incr_softirqs_this_cpu(vec_nr);
290
291 trace_softirq_entry(vec_nr);
292 h->action(h);
293 trace_softirq_exit(vec_nr);
294 if (unlikely(prev_count != preempt_count())) {
295 pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
296 vec_nr, softirq_to_name[vec_nr], h->action,
297 prev_count, preempt_count());
298 preempt_count_set(prev_count);
299 }
300 h++;
301 pending >>= softirq_bit;
302 }
303
304 if (__this_cpu_read(ksoftirqd) == current)
305 rcu_softirq_qs();
306 local_irq_disable();
307
308 pending = local_softirq_pending();
309 if (pending) {
310 if (time_before(jiffies, end) && !need_resched() &&
311 --max_restart)
312 goto restart;
313
314 wakeup_softirqd();
315 }
316
317 lockdep_softirq_end(in_hardirq);
318 account_irq_exit_time(current);
319 __local_bh_enable(SOFTIRQ_OFFSET);
320 WARN_ON_ONCE(in_interrupt());
321 current_restore_flags(old_flags, PF_MEMALLOC);
322}
323
324asmlinkage __visible void do_softirq(void)
325{
326 __u32 pending;
327 unsigned long flags;
328
329 if (in_interrupt())
330 return;
331
332 local_irq_save(flags);
333
334 pending = local_softirq_pending();
335
336 if (pending && !ksoftirqd_running(pending))
337 do_softirq_own_stack();
338
339 local_irq_restore(flags);
340}
341
342/*
343 * Enter an interrupt context.
344 */
345void irq_enter(void)
346{
347 rcu_irq_enter();
348 if (is_idle_task(current) && !in_interrupt()) {
349 /*
350 * Prevent raise_softirq from needlessly waking up ksoftirqd
351 * here, as softirq will be serviced on return from interrupt.
352 */
353 local_bh_disable();
354 tick_irq_enter();
355 _local_bh_enable();
356 }
357
358 __irq_enter();
359}
360
361static inline void invoke_softirq(void)
362{
363 if (ksoftirqd_running(local_softirq_pending()))
364 return;
365
366 if (!force_irqthreads) {
367#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
368 /*
369 * We can safely execute softirq on the current stack if
370 * it is the irq stack, because it should be near empty
371 * at this stage.
372 */
373 __do_softirq();
374#else
375 /*
376 * Otherwise, irq_exit() is called on the task stack that can
377 * be potentially deep already. So call softirq in its own stack
378 * to prevent from any overrun.
379 */
380 do_softirq_own_stack();
381#endif
382 } else {
383 wakeup_softirqd();
384 }
385}
386
387static inline void tick_irq_exit(void)
388{
389#ifdef CONFIG_NO_HZ_COMMON
390 int cpu = smp_processor_id();
391
392 /* Make sure that timer wheel updates are propagated */
393 if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
394 if (!in_irq())
395 tick_nohz_irq_exit();
396 }
397#endif
398}
399
400/*
401 * Exit an interrupt context. Process softirqs if needed and possible:
402 */
403void irq_exit(void)
404{
405#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
406 local_irq_disable();
407#else
408 lockdep_assert_irqs_disabled();
409#endif
410 account_irq_exit_time(current);
411 preempt_count_sub(HARDIRQ_OFFSET);
412 if (!in_interrupt() && local_softirq_pending())
413 invoke_softirq();
414
415 tick_irq_exit();
416 rcu_irq_exit();
417 trace_hardirq_exit(); /* must be last! */
418}
419
420/*
421 * This function must run with irqs disabled!
422 */
423inline void raise_softirq_irqoff(unsigned int nr)
424{
425 __raise_softirq_irqoff(nr);
426
427 /*
428 * If we're in an interrupt or softirq, we're done
429 * (this also catches softirq-disabled code). We will
430 * actually run the softirq once we return from
431 * the irq or softirq.
432 *
433 * Otherwise we wake up ksoftirqd to make sure we
434 * schedule the softirq soon.
435 */
436 if (!in_interrupt())
437 wakeup_softirqd();
438}
439
440void raise_softirq(unsigned int nr)
441{
442 unsigned long flags;
443
444 local_irq_save(flags);
445 raise_softirq_irqoff(nr);
446 local_irq_restore(flags);
447}
448
449void __raise_softirq_irqoff(unsigned int nr)
450{
451 trace_softirq_raise(nr);
452 or_softirq_pending(1UL << nr);
453}
454
455void open_softirq(int nr, void (*action)(struct softirq_action *))
456{
457 softirq_vec[nr].action = action;
458}
459
460/*
461 * Tasklets
462 */
463struct tasklet_head {
464 struct tasklet_struct *head;
465 struct tasklet_struct **tail;
466};
467
468static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
469static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
470
471static void __tasklet_schedule_common(struct tasklet_struct *t,
472 struct tasklet_head __percpu *headp,
473 unsigned int softirq_nr)
474{
475 struct tasklet_head *head;
476 unsigned long flags;
477
478 local_irq_save(flags);
479 head = this_cpu_ptr(headp);
480 t->next = NULL;
481 *head->tail = t;
482 head->tail = &(t->next);
483 raise_softirq_irqoff(softirq_nr);
484 local_irq_restore(flags);
485}
486
487void __tasklet_schedule(struct tasklet_struct *t)
488{
489 __tasklet_schedule_common(t, &tasklet_vec,
490 TASKLET_SOFTIRQ);
491}
492EXPORT_SYMBOL(__tasklet_schedule);
493
494void __tasklet_hi_schedule(struct tasklet_struct *t)
495{
496 __tasklet_schedule_common(t, &tasklet_hi_vec,
497 HI_SOFTIRQ);
498}
499EXPORT_SYMBOL(__tasklet_hi_schedule);
500
501static void tasklet_action_common(struct softirq_action *a,
502 struct tasklet_head *tl_head,
503 unsigned int softirq_nr)
504{
505 struct tasklet_struct *list;
506
507 local_irq_disable();
508 list = tl_head->head;
509 tl_head->head = NULL;
510 tl_head->tail = &tl_head->head;
511 local_irq_enable();
512
513 while (list) {
514 struct tasklet_struct *t = list;
515
516 list = list->next;
517
518 if (tasklet_trylock(t)) {
519 if (!atomic_read(&t->count)) {
520 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
521 &t->state))
522 BUG();
523 t->func(t->data);
524 tasklet_unlock(t);
525 continue;
526 }
527 tasklet_unlock(t);
528 }
529
530 local_irq_disable();
531 t->next = NULL;
532 *tl_head->tail = t;
533 tl_head->tail = &t->next;
534 __raise_softirq_irqoff(softirq_nr);
535 local_irq_enable();
536 }
537}
538
539static __latent_entropy void tasklet_action(struct softirq_action *a)
540{
541 tasklet_action_common(a, this_cpu_ptr(&tasklet_vec), TASKLET_SOFTIRQ);
542}
543
544static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
545{
546 tasklet_action_common(a, this_cpu_ptr(&tasklet_hi_vec), HI_SOFTIRQ);
547}
548
549void tasklet_init(struct tasklet_struct *t,
550 void (*func)(unsigned long), unsigned long data)
551{
552 t->next = NULL;
553 t->state = 0;
554 atomic_set(&t->count, 0);
555 t->func = func;
556 t->data = data;
557}
558EXPORT_SYMBOL(tasklet_init);
559
560void tasklet_kill(struct tasklet_struct *t)
561{
562 if (in_interrupt())
563 pr_notice("Attempt to kill tasklet from interrupt\n");
564
565 while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
566 do {
567 yield();
568 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
569 }
570 tasklet_unlock_wait(t);
571 clear_bit(TASKLET_STATE_SCHED, &t->state);
572}
573EXPORT_SYMBOL(tasklet_kill);
574
575void __init softirq_init(void)
576{
577 int cpu;
578
579 for_each_possible_cpu(cpu) {
580 per_cpu(tasklet_vec, cpu).tail =
581 &per_cpu(tasklet_vec, cpu).head;
582 per_cpu(tasklet_hi_vec, cpu).tail =
583 &per_cpu(tasklet_hi_vec, cpu).head;
584 }
585
586 open_softirq(TASKLET_SOFTIRQ, tasklet_action);
587 open_softirq(HI_SOFTIRQ, tasklet_hi_action);
588}
589
590static int ksoftirqd_should_run(unsigned int cpu)
591{
592 return local_softirq_pending();
593}
594
595static void run_ksoftirqd(unsigned int cpu)
596{
597 local_irq_disable();
598 if (local_softirq_pending()) {
599 /*
600 * We can safely run softirq on inline stack, as we are not deep
601 * in the task stack here.
602 */
603 __do_softirq();
604 local_irq_enable();
605 cond_resched();
606 return;
607 }
608 local_irq_enable();
609}
610
611#ifdef CONFIG_HOTPLUG_CPU
612/*
613 * tasklet_kill_immediate is called to remove a tasklet which can already be
614 * scheduled for execution on @cpu.
615 *
616 * Unlike tasklet_kill, this function removes the tasklet
617 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
618 *
619 * When this function is called, @cpu must be in the CPU_DEAD state.
620 */
621void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
622{
623 struct tasklet_struct **i;
624
625 BUG_ON(cpu_online(cpu));
626 BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
627
628 if (!test_bit(TASKLET_STATE_SCHED, &t->state))
629 return;
630
631 /* CPU is dead, so no lock needed. */
632 for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
633 if (*i == t) {
634 *i = t->next;
635 /* If this was the tail element, move the tail ptr */
636 if (*i == NULL)
637 per_cpu(tasklet_vec, cpu).tail = i;
638 return;
639 }
640 }
641 BUG();
642}
643
644static int takeover_tasklets(unsigned int cpu)
645{
646 /* CPU is dead, so no lock needed. */
647 local_irq_disable();
648
649 /* Find end, append list for that CPU. */
650 if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
651 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
652 __this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
653 per_cpu(tasklet_vec, cpu).head = NULL;
654 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
655 }
656 raise_softirq_irqoff(TASKLET_SOFTIRQ);
657
658 if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
659 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
660 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
661 per_cpu(tasklet_hi_vec, cpu).head = NULL;
662 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
663 }
664 raise_softirq_irqoff(HI_SOFTIRQ);
665
666 local_irq_enable();
667 return 0;
668}
669#else
670#define takeover_tasklets NULL
671#endif /* CONFIG_HOTPLUG_CPU */
672
673static struct smp_hotplug_thread softirq_threads = {
674 .store = &ksoftirqd,
675 .thread_should_run = ksoftirqd_should_run,
676 .thread_fn = run_ksoftirqd,
677 .thread_comm = "ksoftirqd/%u",
678};
679
680static __init int spawn_ksoftirqd(void)
681{
682 cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
683 takeover_tasklets);
684 BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
685
686 return 0;
687}
688early_initcall(spawn_ksoftirqd);
689
690/*
691 * [ These __weak aliases are kept in a separate compilation unit, so that
692 * GCC does not inline them incorrectly. ]
693 */
694
695int __init __weak early_irq_init(void)
696{
697 return 0;
698}
699
700int __init __weak arch_probe_nr_irqs(void)
701{
702 return NR_IRQS_LEGACY;
703}
704
705int __init __weak arch_early_irq_init(void)
706{
707 return 0;
708}
709
710unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
711{
712 return from;
713}
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 * Remote softirq infrastructure is by Jens Axboe.
11 */
12
13#include <linux/module.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/tick.h>
27
28#define CREATE_TRACE_POINTS
29#include <trace/events/irq.h>
30
31#include <asm/irq.h>
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
51irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
52EXPORT_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
59char *softirq_to_name[NR_SOFTIRQS] = {
60 "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
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 * preempt_count and SOFTIRQ_OFFSET usage:
81 * - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
82 * softirq processing.
83 * - preempt_count is changed by SOFTIRQ_DISABLE_OFFSET (= 2 * SOFTIRQ_OFFSET)
84 * on local_bh_disable or local_bh_enable.
85 * This lets us distinguish between whether we are currently processing
86 * softirq and whether we just have bh disabled.
87 */
88
89/*
90 * This one is for softirq.c-internal use,
91 * where hardirqs are disabled legitimately:
92 */
93#ifdef CONFIG_TRACE_IRQFLAGS
94static void __local_bh_disable(unsigned long ip, unsigned int cnt)
95{
96 unsigned long flags;
97
98 WARN_ON_ONCE(in_irq());
99
100 raw_local_irq_save(flags);
101 /*
102 * The preempt tracer hooks into add_preempt_count and will break
103 * lockdep because it calls back into lockdep after SOFTIRQ_OFFSET
104 * is set and before current->softirq_enabled is cleared.
105 * We must manually increment preempt_count here and manually
106 * call the trace_preempt_off later.
107 */
108 preempt_count() += cnt;
109 /*
110 * Were softirqs turned off above:
111 */
112 if (softirq_count() == cnt)
113 trace_softirqs_off(ip);
114 raw_local_irq_restore(flags);
115
116 if (preempt_count() == cnt)
117 trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
118}
119#else /* !CONFIG_TRACE_IRQFLAGS */
120static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
121{
122 add_preempt_count(cnt);
123 barrier();
124}
125#endif /* CONFIG_TRACE_IRQFLAGS */
126
127void local_bh_disable(void)
128{
129 __local_bh_disable((unsigned long)__builtin_return_address(0),
130 SOFTIRQ_DISABLE_OFFSET);
131}
132
133EXPORT_SYMBOL(local_bh_disable);
134
135static void __local_bh_enable(unsigned int cnt)
136{
137 WARN_ON_ONCE(in_irq());
138 WARN_ON_ONCE(!irqs_disabled());
139
140 if (softirq_count() == cnt)
141 trace_softirqs_on((unsigned long)__builtin_return_address(0));
142 sub_preempt_count(cnt);
143}
144
145/*
146 * Special-case - softirqs can safely be enabled in
147 * cond_resched_softirq(), or by __do_softirq(),
148 * without processing still-pending softirqs:
149 */
150void _local_bh_enable(void)
151{
152 __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
153}
154
155EXPORT_SYMBOL(_local_bh_enable);
156
157static inline void _local_bh_enable_ip(unsigned long ip)
158{
159 WARN_ON_ONCE(in_irq() || irqs_disabled());
160#ifdef CONFIG_TRACE_IRQFLAGS
161 local_irq_disable();
162#endif
163 /*
164 * Are softirqs going to be turned on now:
165 */
166 if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
167 trace_softirqs_on(ip);
168 /*
169 * Keep preemption disabled until we are done with
170 * softirq processing:
171 */
172 sub_preempt_count(SOFTIRQ_DISABLE_OFFSET - 1);
173
174 if (unlikely(!in_interrupt() && local_softirq_pending()))
175 do_softirq();
176
177 dec_preempt_count();
178#ifdef CONFIG_TRACE_IRQFLAGS
179 local_irq_enable();
180#endif
181 preempt_check_resched();
182}
183
184void local_bh_enable(void)
185{
186 _local_bh_enable_ip((unsigned long)__builtin_return_address(0));
187}
188EXPORT_SYMBOL(local_bh_enable);
189
190void local_bh_enable_ip(unsigned long ip)
191{
192 _local_bh_enable_ip(ip);
193}
194EXPORT_SYMBOL(local_bh_enable_ip);
195
196/*
197 * We restart softirq processing MAX_SOFTIRQ_RESTART times,
198 * and we fall back to softirqd after that.
199 *
200 * This number has 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_RESTART 10
206
207asmlinkage void __do_softirq(void)
208{
209 struct softirq_action *h;
210 __u32 pending;
211 int max_restart = MAX_SOFTIRQ_RESTART;
212 int cpu;
213
214 pending = local_softirq_pending();
215 account_system_vtime(current);
216
217 __local_bh_disable((unsigned long)__builtin_return_address(0),
218 SOFTIRQ_OFFSET);
219 lockdep_softirq_enter();
220
221 cpu = smp_processor_id();
222restart:
223 /* Reset the pending bitmask before enabling irqs */
224 set_softirq_pending(0);
225
226 local_irq_enable();
227
228 h = softirq_vec;
229
230 do {
231 if (pending & 1) {
232 unsigned int vec_nr = h - softirq_vec;
233 int prev_count = preempt_count();
234
235 kstat_incr_softirqs_this_cpu(vec_nr);
236
237 trace_softirq_entry(vec_nr);
238 h->action(h);
239 trace_softirq_exit(vec_nr);
240 if (unlikely(prev_count != preempt_count())) {
241 printk(KERN_ERR "huh, entered softirq %u %s %p"
242 "with preempt_count %08x,"
243 " exited with %08x?\n", vec_nr,
244 softirq_to_name[vec_nr], h->action,
245 prev_count, preempt_count());
246 preempt_count() = prev_count;
247 }
248
249 rcu_bh_qs(cpu);
250 }
251 h++;
252 pending >>= 1;
253 } while (pending);
254
255 local_irq_disable();
256
257 pending = local_softirq_pending();
258 if (pending && --max_restart)
259 goto restart;
260
261 if (pending)
262 wakeup_softirqd();
263
264 lockdep_softirq_exit();
265
266 account_system_vtime(current);
267 __local_bh_enable(SOFTIRQ_OFFSET);
268}
269
270#ifndef __ARCH_HAS_DO_SOFTIRQ
271
272asmlinkage void do_softirq(void)
273{
274 __u32 pending;
275 unsigned long flags;
276
277 if (in_interrupt())
278 return;
279
280 local_irq_save(flags);
281
282 pending = local_softirq_pending();
283
284 if (pending)
285 __do_softirq();
286
287 local_irq_restore(flags);
288}
289
290#endif
291
292/*
293 * Enter an interrupt context.
294 */
295void irq_enter(void)
296{
297 int cpu = smp_processor_id();
298
299 rcu_irq_enter();
300 if (idle_cpu(cpu) && !in_interrupt()) {
301 /*
302 * Prevent raise_softirq from needlessly waking up ksoftirqd
303 * here, as softirq will be serviced on return from interrupt.
304 */
305 local_bh_disable();
306 tick_check_idle(cpu);
307 _local_bh_enable();
308 }
309
310 __irq_enter();
311}
312
313#ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
314static inline void invoke_softirq(void)
315{
316 if (!force_irqthreads)
317 __do_softirq();
318 else {
319 __local_bh_disable((unsigned long)__builtin_return_address(0),
320 SOFTIRQ_OFFSET);
321 wakeup_softirqd();
322 __local_bh_enable(SOFTIRQ_OFFSET);
323 }
324}
325#else
326static inline void invoke_softirq(void)
327{
328 if (!force_irqthreads)
329 do_softirq();
330 else {
331 __local_bh_disable((unsigned long)__builtin_return_address(0),
332 SOFTIRQ_OFFSET);
333 wakeup_softirqd();
334 __local_bh_enable(SOFTIRQ_OFFSET);
335 }
336}
337#endif
338
339/*
340 * Exit an interrupt context. Process softirqs if needed and possible:
341 */
342void irq_exit(void)
343{
344 account_system_vtime(current);
345 trace_hardirq_exit();
346 sub_preempt_count(IRQ_EXIT_OFFSET);
347 if (!in_interrupt() && local_softirq_pending())
348 invoke_softirq();
349
350 rcu_irq_exit();
351#ifdef CONFIG_NO_HZ
352 /* Make sure that timer wheel updates are propagated */
353 if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched())
354 tick_nohz_stop_sched_tick(0);
355#endif
356 preempt_enable_no_resched();
357}
358
359/*
360 * This function must run with irqs disabled!
361 */
362inline void raise_softirq_irqoff(unsigned int nr)
363{
364 __raise_softirq_irqoff(nr);
365
366 /*
367 * If we're in an interrupt or softirq, we're done
368 * (this also catches softirq-disabled code). We will
369 * actually run the softirq once we return from
370 * the irq or softirq.
371 *
372 * Otherwise we wake up ksoftirqd to make sure we
373 * schedule the softirq soon.
374 */
375 if (!in_interrupt())
376 wakeup_softirqd();
377}
378
379void raise_softirq(unsigned int nr)
380{
381 unsigned long flags;
382
383 local_irq_save(flags);
384 raise_softirq_irqoff(nr);
385 local_irq_restore(flags);
386}
387
388void open_softirq(int nr, void (*action)(struct softirq_action *))
389{
390 softirq_vec[nr].action = action;
391}
392
393/*
394 * Tasklets
395 */
396struct tasklet_head
397{
398 struct tasklet_struct *head;
399 struct tasklet_struct **tail;
400};
401
402static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
403static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
404
405void __tasklet_schedule(struct tasklet_struct *t)
406{
407 unsigned long flags;
408
409 local_irq_save(flags);
410 t->next = NULL;
411 *__this_cpu_read(tasklet_vec.tail) = t;
412 __this_cpu_write(tasklet_vec.tail, &(t->next));
413 raise_softirq_irqoff(TASKLET_SOFTIRQ);
414 local_irq_restore(flags);
415}
416
417EXPORT_SYMBOL(__tasklet_schedule);
418
419void __tasklet_hi_schedule(struct tasklet_struct *t)
420{
421 unsigned long flags;
422
423 local_irq_save(flags);
424 t->next = NULL;
425 *__this_cpu_read(tasklet_hi_vec.tail) = t;
426 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
427 raise_softirq_irqoff(HI_SOFTIRQ);
428 local_irq_restore(flags);
429}
430
431EXPORT_SYMBOL(__tasklet_hi_schedule);
432
433void __tasklet_hi_schedule_first(struct tasklet_struct *t)
434{
435 BUG_ON(!irqs_disabled());
436
437 t->next = __this_cpu_read(tasklet_hi_vec.head);
438 __this_cpu_write(tasklet_hi_vec.head, t);
439 __raise_softirq_irqoff(HI_SOFTIRQ);
440}
441
442EXPORT_SYMBOL(__tasklet_hi_schedule_first);
443
444static void tasklet_action(struct softirq_action *a)
445{
446 struct tasklet_struct *list;
447
448 local_irq_disable();
449 list = __this_cpu_read(tasklet_vec.head);
450 __this_cpu_write(tasklet_vec.head, NULL);
451 __this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head);
452 local_irq_enable();
453
454 while (list) {
455 struct tasklet_struct *t = list;
456
457 list = list->next;
458
459 if (tasklet_trylock(t)) {
460 if (!atomic_read(&t->count)) {
461 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
462 BUG();
463 t->func(t->data);
464 tasklet_unlock(t);
465 continue;
466 }
467 tasklet_unlock(t);
468 }
469
470 local_irq_disable();
471 t->next = NULL;
472 *__this_cpu_read(tasklet_vec.tail) = t;
473 __this_cpu_write(tasklet_vec.tail, &(t->next));
474 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
475 local_irq_enable();
476 }
477}
478
479static void tasklet_hi_action(struct softirq_action *a)
480{
481 struct tasklet_struct *list;
482
483 local_irq_disable();
484 list = __this_cpu_read(tasklet_hi_vec.head);
485 __this_cpu_write(tasklet_hi_vec.head, NULL);
486 __this_cpu_write(tasklet_hi_vec.tail, &__get_cpu_var(tasklet_hi_vec).head);
487 local_irq_enable();
488
489 while (list) {
490 struct tasklet_struct *t = list;
491
492 list = list->next;
493
494 if (tasklet_trylock(t)) {
495 if (!atomic_read(&t->count)) {
496 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
497 BUG();
498 t->func(t->data);
499 tasklet_unlock(t);
500 continue;
501 }
502 tasklet_unlock(t);
503 }
504
505 local_irq_disable();
506 t->next = NULL;
507 *__this_cpu_read(tasklet_hi_vec.tail) = t;
508 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
509 __raise_softirq_irqoff(HI_SOFTIRQ);
510 local_irq_enable();
511 }
512}
513
514
515void tasklet_init(struct tasklet_struct *t,
516 void (*func)(unsigned long), unsigned long data)
517{
518 t->next = NULL;
519 t->state = 0;
520 atomic_set(&t->count, 0);
521 t->func = func;
522 t->data = data;
523}
524
525EXPORT_SYMBOL(tasklet_init);
526
527void tasklet_kill(struct tasklet_struct *t)
528{
529 if (in_interrupt())
530 printk("Attempt to kill tasklet from interrupt\n");
531
532 while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
533 do {
534 yield();
535 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
536 }
537 tasklet_unlock_wait(t);
538 clear_bit(TASKLET_STATE_SCHED, &t->state);
539}
540
541EXPORT_SYMBOL(tasklet_kill);
542
543/*
544 * tasklet_hrtimer
545 */
546
547/*
548 * The trampoline is called when the hrtimer expires. It schedules a tasklet
549 * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
550 * hrtimer callback, but from softirq context.
551 */
552static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
553{
554 struct tasklet_hrtimer *ttimer =
555 container_of(timer, struct tasklet_hrtimer, timer);
556
557 tasklet_hi_schedule(&ttimer->tasklet);
558 return HRTIMER_NORESTART;
559}
560
561/*
562 * Helper function which calls the hrtimer callback from
563 * tasklet/softirq context
564 */
565static void __tasklet_hrtimer_trampoline(unsigned long data)
566{
567 struct tasklet_hrtimer *ttimer = (void *)data;
568 enum hrtimer_restart restart;
569
570 restart = ttimer->function(&ttimer->timer);
571 if (restart != HRTIMER_NORESTART)
572 hrtimer_restart(&ttimer->timer);
573}
574
575/**
576 * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
577 * @ttimer: tasklet_hrtimer which is initialized
578 * @function: hrtimer callback function which gets called from softirq context
579 * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
580 * @mode: hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
581 */
582void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
583 enum hrtimer_restart (*function)(struct hrtimer *),
584 clockid_t which_clock, enum hrtimer_mode mode)
585{
586 hrtimer_init(&ttimer->timer, which_clock, mode);
587 ttimer->timer.function = __hrtimer_tasklet_trampoline;
588 tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
589 (unsigned long)ttimer);
590 ttimer->function = function;
591}
592EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
593
594/*
595 * Remote softirq bits
596 */
597
598DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
599EXPORT_PER_CPU_SYMBOL(softirq_work_list);
600
601static void __local_trigger(struct call_single_data *cp, int softirq)
602{
603 struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
604
605 list_add_tail(&cp->list, head);
606
607 /* Trigger the softirq only if the list was previously empty. */
608 if (head->next == &cp->list)
609 raise_softirq_irqoff(softirq);
610}
611
612#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
613static void remote_softirq_receive(void *data)
614{
615 struct call_single_data *cp = data;
616 unsigned long flags;
617 int softirq;
618
619 softirq = cp->priv;
620
621 local_irq_save(flags);
622 __local_trigger(cp, softirq);
623 local_irq_restore(flags);
624}
625
626static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
627{
628 if (cpu_online(cpu)) {
629 cp->func = remote_softirq_receive;
630 cp->info = cp;
631 cp->flags = 0;
632 cp->priv = softirq;
633
634 __smp_call_function_single(cpu, cp, 0);
635 return 0;
636 }
637 return 1;
638}
639#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
640static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
641{
642 return 1;
643}
644#endif
645
646/**
647 * __send_remote_softirq - try to schedule softirq work on a remote cpu
648 * @cp: private SMP call function data area
649 * @cpu: the remote cpu
650 * @this_cpu: the currently executing cpu
651 * @softirq: the softirq for the work
652 *
653 * Attempt to schedule softirq work on a remote cpu. If this cannot be
654 * done, the work is instead queued up on the local cpu.
655 *
656 * Interrupts must be disabled.
657 */
658void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
659{
660 if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
661 __local_trigger(cp, softirq);
662}
663EXPORT_SYMBOL(__send_remote_softirq);
664
665/**
666 * send_remote_softirq - try to schedule softirq work on a remote cpu
667 * @cp: private SMP call function data area
668 * @cpu: the remote cpu
669 * @softirq: the softirq for the work
670 *
671 * Like __send_remote_softirq except that disabling interrupts and
672 * computing the current cpu is done for the caller.
673 */
674void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
675{
676 unsigned long flags;
677 int this_cpu;
678
679 local_irq_save(flags);
680 this_cpu = smp_processor_id();
681 __send_remote_softirq(cp, cpu, this_cpu, softirq);
682 local_irq_restore(flags);
683}
684EXPORT_SYMBOL(send_remote_softirq);
685
686static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
687 unsigned long action, void *hcpu)
688{
689 /*
690 * If a CPU goes away, splice its entries to the current CPU
691 * and trigger a run of the softirq
692 */
693 if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
694 int cpu = (unsigned long) hcpu;
695 int i;
696
697 local_irq_disable();
698 for (i = 0; i < NR_SOFTIRQS; i++) {
699 struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
700 struct list_head *local_head;
701
702 if (list_empty(head))
703 continue;
704
705 local_head = &__get_cpu_var(softirq_work_list[i]);
706 list_splice_init(head, local_head);
707 raise_softirq_irqoff(i);
708 }
709 local_irq_enable();
710 }
711
712 return NOTIFY_OK;
713}
714
715static struct notifier_block __cpuinitdata remote_softirq_cpu_notifier = {
716 .notifier_call = remote_softirq_cpu_notify,
717};
718
719void __init softirq_init(void)
720{
721 int cpu;
722
723 for_each_possible_cpu(cpu) {
724 int i;
725
726 per_cpu(tasklet_vec, cpu).tail =
727 &per_cpu(tasklet_vec, cpu).head;
728 per_cpu(tasklet_hi_vec, cpu).tail =
729 &per_cpu(tasklet_hi_vec, cpu).head;
730 for (i = 0; i < NR_SOFTIRQS; i++)
731 INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
732 }
733
734 register_hotcpu_notifier(&remote_softirq_cpu_notifier);
735
736 open_softirq(TASKLET_SOFTIRQ, tasklet_action);
737 open_softirq(HI_SOFTIRQ, tasklet_hi_action);
738}
739
740static int run_ksoftirqd(void * __bind_cpu)
741{
742 set_current_state(TASK_INTERRUPTIBLE);
743
744 while (!kthread_should_stop()) {
745 preempt_disable();
746 if (!local_softirq_pending()) {
747 preempt_enable_no_resched();
748 schedule();
749 preempt_disable();
750 }
751
752 __set_current_state(TASK_RUNNING);
753
754 while (local_softirq_pending()) {
755 /* Preempt disable stops cpu going offline.
756 If already offline, we'll be on wrong CPU:
757 don't process */
758 if (cpu_is_offline((long)__bind_cpu))
759 goto wait_to_die;
760 local_irq_disable();
761 if (local_softirq_pending())
762 __do_softirq();
763 local_irq_enable();
764 preempt_enable_no_resched();
765 cond_resched();
766 preempt_disable();
767 rcu_note_context_switch((long)__bind_cpu);
768 }
769 preempt_enable();
770 set_current_state(TASK_INTERRUPTIBLE);
771 }
772 __set_current_state(TASK_RUNNING);
773 return 0;
774
775wait_to_die:
776 preempt_enable();
777 /* Wait for kthread_stop */
778 set_current_state(TASK_INTERRUPTIBLE);
779 while (!kthread_should_stop()) {
780 schedule();
781 set_current_state(TASK_INTERRUPTIBLE);
782 }
783 __set_current_state(TASK_RUNNING);
784 return 0;
785}
786
787#ifdef CONFIG_HOTPLUG_CPU
788/*
789 * tasklet_kill_immediate is called to remove a tasklet which can already be
790 * scheduled for execution on @cpu.
791 *
792 * Unlike tasklet_kill, this function removes the tasklet
793 * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
794 *
795 * When this function is called, @cpu must be in the CPU_DEAD state.
796 */
797void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
798{
799 struct tasklet_struct **i;
800
801 BUG_ON(cpu_online(cpu));
802 BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
803
804 if (!test_bit(TASKLET_STATE_SCHED, &t->state))
805 return;
806
807 /* CPU is dead, so no lock needed. */
808 for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
809 if (*i == t) {
810 *i = t->next;
811 /* If this was the tail element, move the tail ptr */
812 if (*i == NULL)
813 per_cpu(tasklet_vec, cpu).tail = i;
814 return;
815 }
816 }
817 BUG();
818}
819
820static void takeover_tasklets(unsigned int cpu)
821{
822 /* CPU is dead, so no lock needed. */
823 local_irq_disable();
824
825 /* Find end, append list for that CPU. */
826 if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
827 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
828 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
829 per_cpu(tasklet_vec, cpu).head = NULL;
830 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
831 }
832 raise_softirq_irqoff(TASKLET_SOFTIRQ);
833
834 if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
835 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
836 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
837 per_cpu(tasklet_hi_vec, cpu).head = NULL;
838 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
839 }
840 raise_softirq_irqoff(HI_SOFTIRQ);
841
842 local_irq_enable();
843}
844#endif /* CONFIG_HOTPLUG_CPU */
845
846static int __cpuinit cpu_callback(struct notifier_block *nfb,
847 unsigned long action,
848 void *hcpu)
849{
850 int hotcpu = (unsigned long)hcpu;
851 struct task_struct *p;
852
853 switch (action) {
854 case CPU_UP_PREPARE:
855 case CPU_UP_PREPARE_FROZEN:
856 p = kthread_create_on_node(run_ksoftirqd,
857 hcpu,
858 cpu_to_node(hotcpu),
859 "ksoftirqd/%d", hotcpu);
860 if (IS_ERR(p)) {
861 printk("ksoftirqd for %i failed\n", hotcpu);
862 return notifier_from_errno(PTR_ERR(p));
863 }
864 kthread_bind(p, hotcpu);
865 per_cpu(ksoftirqd, hotcpu) = p;
866 break;
867 case CPU_ONLINE:
868 case CPU_ONLINE_FROZEN:
869 wake_up_process(per_cpu(ksoftirqd, hotcpu));
870 break;
871#ifdef CONFIG_HOTPLUG_CPU
872 case CPU_UP_CANCELED:
873 case CPU_UP_CANCELED_FROZEN:
874 if (!per_cpu(ksoftirqd, hotcpu))
875 break;
876 /* Unbind so it can run. Fall thru. */
877 kthread_bind(per_cpu(ksoftirqd, hotcpu),
878 cpumask_any(cpu_online_mask));
879 case CPU_DEAD:
880 case CPU_DEAD_FROZEN: {
881 static const struct sched_param param = {
882 .sched_priority = MAX_RT_PRIO-1
883 };
884
885 p = per_cpu(ksoftirqd, hotcpu);
886 per_cpu(ksoftirqd, hotcpu) = NULL;
887 sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m);
888 kthread_stop(p);
889 takeover_tasklets(hotcpu);
890 break;
891 }
892#endif /* CONFIG_HOTPLUG_CPU */
893 }
894 return NOTIFY_OK;
895}
896
897static struct notifier_block __cpuinitdata cpu_nfb = {
898 .notifier_call = cpu_callback
899};
900
901static __init int spawn_ksoftirqd(void)
902{
903 void *cpu = (void *)(long)smp_processor_id();
904 int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
905
906 BUG_ON(err != NOTIFY_OK);
907 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
908 register_cpu_notifier(&cpu_nfb);
909 return 0;
910}
911early_initcall(spawn_ksoftirqd);
912
913/*
914 * [ These __weak aliases are kept in a separate compilation unit, so that
915 * GCC does not inline them incorrectly. ]
916 */
917
918int __init __weak early_irq_init(void)
919{
920 return 0;
921}
922
923#ifdef CONFIG_GENERIC_HARDIRQS
924int __init __weak arch_probe_nr_irqs(void)
925{
926 return NR_IRQS_LEGACY;
927}
928
929int __init __weak arch_early_irq_init(void)
930{
931 return 0;
932}
933#endif