Root/kernel/softirq.c

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}
787

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