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TOMOYO Linux Cross Reference
Linux/kernel/softirq.c

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  1 /*
  2  *      linux/kernel/softirq.c
  3  *
  4  *      Copyright (C) 1992 Linus Torvalds
  5  *
  6  *      Distribute under GPLv2.
  7  *
  8  *      Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
  9  */
 10 
 11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 12 
 13 #include <linux/export.h>
 14 #include <linux/kernel_stat.h>
 15 #include <linux/interrupt.h>
 16 #include <linux/init.h>
 17 #include <linux/mm.h>
 18 #include <linux/notifier.h>
 19 #include <linux/percpu.h>
 20 #include <linux/cpu.h>
 21 #include <linux/freezer.h>
 22 #include <linux/kthread.h>
 23 #include <linux/rcupdate.h>
 24 #include <linux/ftrace.h>
 25 #include <linux/smp.h>
 26 #include <linux/smpboot.h>
 27 #include <linux/tick.h>
 28 #include <linux/irq.h>
 29 
 30 #define CREATE_TRACE_POINTS
 31 #include <trace/events/irq.h>
 32 
 33 /*
 34    - No shared variables, all the data are CPU local.
 35    - If a softirq needs serialization, let it serialize itself
 36      by its own spinlocks.
 37    - Even if softirq is serialized, only local cpu is marked for
 38      execution. Hence, we get something sort of weak cpu binding.
 39      Though it is still not clear, will it result in better locality
 40      or will not.
 41 
 42    Examples:
 43    - NET RX softirq. It is multithreaded and does not require
 44      any global serialization.
 45    - NET TX softirq. It kicks software netdevice queues, hence
 46      it is logically serialized per device, but this serialization
 47      is invisible to common code.
 48    - Tasklets: serialized wrt itself.
 49  */
 50 
 51 #ifndef __ARCH_IRQ_STAT
 52 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
 53 EXPORT_SYMBOL(irq_stat);
 54 #endif
 55 
 56 static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;
 57 
 58 DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
 59 
 60 const char * const softirq_to_name[NR_SOFTIRQS] = {
 61         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "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  */
 71 static void wakeup_softirqd(void)
 72 {
 73         /* Interrupts are disabled: no need to stop preemption */
 74         struct task_struct *tsk = __this_cpu_read(ksoftirqd);
 75 
 76         if (tsk && tsk->state != TASK_RUNNING)
 77                 wake_up_process(tsk);
 78 }
 79 
 80 /*
 81  * 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  */
 84 static 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
106 void __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 }
135 EXPORT_SYMBOL(__local_bh_disable_ip);
136 #endif /* CONFIG_TRACE_IRQFLAGS */
137 
138 static void __local_bh_enable(unsigned int cnt)
139 {
140         lockdep_assert_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  */
152 void _local_bh_enable(void)
153 {
154         WARN_ON_ONCE(in_irq());
155         __local_bh_enable(SOFTIRQ_DISABLE_OFFSET);
156 }
157 EXPORT_SYMBOL(_local_bh_enable);
158 
159 void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
160 {
161         WARN_ON_ONCE(in_irq());
162         lockdep_assert_irqs_enabled();
163 #ifdef CONFIG_TRACE_IRQFLAGS
164         local_irq_disable();
165 #endif
166         /*
167          * Are softirqs going to be turned on now:
168          */
169         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
170                 trace_softirqs_on(ip);
171         /*
172          * Keep preemption disabled until we are done with
173          * softirq processing:
174          */
175         preempt_count_sub(cnt - 1);
176 
177         if (unlikely(!in_interrupt() && local_softirq_pending())) {
178                 /*
179                  * Run softirq if any pending. And do it in its own stack
180                  * as we may be calling this deep in a task call stack already.
181                  */
182                 do_softirq();
183         }
184 
185         preempt_count_dec();
186 #ifdef CONFIG_TRACE_IRQFLAGS
187         local_irq_enable();
188 #endif
189         preempt_check_resched();
190 }
191 EXPORT_SYMBOL(__local_bh_enable_ip);
192 
193 /*
194  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
195  * but break the loop if need_resched() is set or after 2 ms.
196  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
197  * certain cases, such as stop_machine(), jiffies may cease to
198  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
199  * well to make sure we eventually return from this method.
200  *
201  * These limits have been established via experimentation.
202  * The two things to balance is latency against fairness -
203  * we want to handle softirqs as soon as possible, but they
204  * should not be able to lock up the box.
205  */
206 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
207 #define MAX_SOFTIRQ_RESTART 10
208 
209 #ifdef CONFIG_TRACE_IRQFLAGS
210 /*
211  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
212  * to keep the lockdep irq context tracking as tight as possible in order to
213  * not miss-qualify lock contexts and miss possible deadlocks.
214  */
215 
216 static inline bool lockdep_softirq_start(void)
217 {
218         bool in_hardirq = false;
219 
220         if (trace_hardirq_context(current)) {
221                 in_hardirq = true;
222                 trace_hardirq_exit();
223         }
224 
225         lockdep_softirq_enter();
226 
227         return in_hardirq;
228 }
229 
230 static inline void lockdep_softirq_end(bool in_hardirq)
231 {
232         lockdep_softirq_exit();
233 
234         if (in_hardirq)
235                 trace_hardirq_enter();
236 }
237 #else
238 static inline bool lockdep_softirq_start(void) { return false; }
239 static inline void lockdep_softirq_end(bool in_hardirq) { }
240 #endif
241 
242 asmlinkage __visible void __softirq_entry __do_softirq(void)
243 {
244         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
245         unsigned long old_flags = current->flags;
246         int max_restart = MAX_SOFTIRQ_RESTART;
247         struct softirq_action *h;
248         bool in_hardirq;
249         __u32 pending;
250         int softirq_bit;
251 
252         /*
253          * Mask out PF_MEMALLOC s current task context is borrowed for the
254          * softirq. A softirq handled such as network RX might set PF_MEMALLOC
255          * again if the socket is related to swap
256          */
257         current->flags &= ~PF_MEMALLOC;
258 
259         pending = local_softirq_pending();
260         account_irq_enter_time(current);
261 
262         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
263         in_hardirq = lockdep_softirq_start();
264 
265 restart:
266         /* Reset the pending bitmask before enabling irqs */
267         set_softirq_pending(0);
268 
269         local_irq_enable();
270 
271         h = softirq_vec;
272 
273         while ((softirq_bit = ffs(pending))) {
274                 unsigned int vec_nr;
275                 int prev_count;
276 
277                 h += softirq_bit - 1;
278 
279                 vec_nr = h - softirq_vec;
280                 prev_count = preempt_count();
281 
282                 kstat_incr_softirqs_this_cpu(vec_nr);
283 
284                 trace_softirq_entry(vec_nr);
285                 h->action(h);
286                 trace_softirq_exit(vec_nr);
287                 if (unlikely(prev_count != preempt_count())) {
288                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
289                                vec_nr, softirq_to_name[vec_nr], h->action,
290                                prev_count, preempt_count());
291                         preempt_count_set(prev_count);
292                 }
293                 h++;
294                 pending >>= softirq_bit;
295         }
296 
297         rcu_bh_qs();
298         local_irq_disable();
299 
300         pending = local_softirq_pending();
301         if (pending) {
302                 if (time_before(jiffies, end) && !need_resched() &&
303                     --max_restart)
304                         goto restart;
305 
306                 wakeup_softirqd();
307         }
308 
309         lockdep_softirq_end(in_hardirq);
310         account_irq_exit_time(current);
311         __local_bh_enable(SOFTIRQ_OFFSET);
312         WARN_ON_ONCE(in_interrupt());
313         current_restore_flags(old_flags, PF_MEMALLOC);
314 }
315 
316 asmlinkage __visible void do_softirq(void)
317 {
318         __u32 pending;
319         unsigned long flags;
320 
321         if (in_interrupt())
322                 return;
323 
324         local_irq_save(flags);
325 
326         pending = local_softirq_pending();
327 
328         if (pending && !ksoftirqd_running())
329                 do_softirq_own_stack();
330 
331         local_irq_restore(flags);
332 }
333 
334 /*
335  * Enter an interrupt context.
336  */
337 void irq_enter(void)
338 {
339         rcu_irq_enter();
340         if (is_idle_task(current) && !in_interrupt()) {
341                 /*
342                  * Prevent raise_softirq from needlessly waking up ksoftirqd
343                  * here, as softirq will be serviced on return from interrupt.
344                  */
345                 local_bh_disable();
346                 tick_irq_enter();
347                 _local_bh_enable();
348         }
349 
350         __irq_enter();
351 }
352 
353 static inline void invoke_softirq(void)
354 {
355         if (ksoftirqd_running())
356                 return;
357 
358         if (!force_irqthreads) {
359 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
360                 /*
361                  * We can safely execute softirq on the current stack if
362                  * it is the irq stack, because it should be near empty
363                  * at this stage.
364                  */
365                 __do_softirq();
366 #else
367                 /*
368                  * Otherwise, irq_exit() is called on the task stack that can
369                  * be potentially deep already. So call softirq in its own stack
370                  * to prevent from any overrun.
371                  */
372                 do_softirq_own_stack();
373 #endif
374         } else {
375                 wakeup_softirqd();
376         }
377 }
378 
379 static inline void tick_irq_exit(void)
380 {
381 #ifdef CONFIG_NO_HZ_COMMON
382         int cpu = smp_processor_id();
383 
384         /* Make sure that timer wheel updates are propagated */
385         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
386                 if (!in_interrupt())
387                         tick_nohz_irq_exit();
388         }
389 #endif
390 }
391 
392 /*
393  * Exit an interrupt context. Process softirqs if needed and possible:
394  */
395 void irq_exit(void)
396 {
397 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
398         local_irq_disable();
399 #else
400         lockdep_assert_irqs_disabled();
401 #endif
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  */
415 inline 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 
432 void 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 
441 void __raise_softirq_irqoff(unsigned int nr)
442 {
443         trace_softirq_raise(nr);
444         or_softirq_pending(1UL << nr);
445 }
446 
447 void open_softirq(int nr, void (*action)(struct softirq_action *))
448 {
449         softirq_vec[nr].action = action;
450 }
451 
452 /*
453  * Tasklets
454  */
455 struct tasklet_head {
456         struct tasklet_struct *head;
457         struct tasklet_struct **tail;
458 };
459 
460 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec);
461 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec);
462 
463 void __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 }
474 EXPORT_SYMBOL(__tasklet_schedule);
475 
476 void __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 }
487 EXPORT_SYMBOL(__tasklet_hi_schedule);
488 
489 static __latent_entropy void tasklet_action(struct softirq_action *a)
490 {
491         struct tasklet_struct *list;
492 
493         local_irq_disable();
494         list = __this_cpu_read(tasklet_vec.head);
495         __this_cpu_write(tasklet_vec.head, NULL);
496         __this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
497         local_irq_enable();
498 
499         while (list) {
500                 struct tasklet_struct *t = list;
501 
502                 list = list->next;
503 
504                 if (tasklet_trylock(t)) {
505                         if (!atomic_read(&t->count)) {
506                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
507                                                         &t->state))
508                                         BUG();
509                                 t->func(t->data);
510                                 tasklet_unlock(t);
511                                 continue;
512                         }
513                         tasklet_unlock(t);
514                 }
515 
516                 local_irq_disable();
517                 t->next = NULL;
518                 *__this_cpu_read(tasklet_vec.tail) = t;
519                 __this_cpu_write(tasklet_vec.tail, &(t->next));
520                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
521                 local_irq_enable();
522         }
523 }
524 
525 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
526 {
527         struct tasklet_struct *list;
528 
529         local_irq_disable();
530         list = __this_cpu_read(tasklet_hi_vec.head);
531         __this_cpu_write(tasklet_hi_vec.head, NULL);
532         __this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
533         local_irq_enable();
534 
535         while (list) {
536                 struct tasklet_struct *t = list;
537 
538                 list = list->next;
539 
540                 if (tasklet_trylock(t)) {
541                         if (!atomic_read(&t->count)) {
542                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
543                                                         &t->state))
544                                         BUG();
545                                 t->func(t->data);
546                                 tasklet_unlock(t);
547                                 continue;
548                         }
549                         tasklet_unlock(t);
550                 }
551 
552                 local_irq_disable();
553                 t->next = NULL;
554                 *__this_cpu_read(tasklet_hi_vec.tail) = t;
555                 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
556                 __raise_softirq_irqoff(HI_SOFTIRQ);
557                 local_irq_enable();
558         }
559 }
560 
561 void tasklet_init(struct tasklet_struct *t,
562                   void (*func)(unsigned long), unsigned long data)
563 {
564         t->next = NULL;
565         t->state = 0;
566         atomic_set(&t->count, 0);
567         t->func = func;
568         t->data = data;
569 }
570 EXPORT_SYMBOL(tasklet_init);
571 
572 void tasklet_kill(struct tasklet_struct *t)
573 {
574         if (in_interrupt())
575                 pr_notice("Attempt to kill tasklet from interrupt\n");
576 
577         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
578                 do {
579                         yield();
580                 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
581         }
582         tasklet_unlock_wait(t);
583         clear_bit(TASKLET_STATE_SCHED, &t->state);
584 }
585 EXPORT_SYMBOL(tasklet_kill);
586 
587 /*
588  * tasklet_hrtimer
589  */
590 
591 /*
592  * The trampoline is called when the hrtimer expires. It schedules a tasklet
593  * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
594  * hrtimer callback, but from softirq context.
595  */
596 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
597 {
598         struct tasklet_hrtimer *ttimer =
599                 container_of(timer, struct tasklet_hrtimer, timer);
600 
601         tasklet_hi_schedule(&ttimer->tasklet);
602         return HRTIMER_NORESTART;
603 }
604 
605 /*
606  * Helper function which calls the hrtimer callback from
607  * tasklet/softirq context
608  */
609 static void __tasklet_hrtimer_trampoline(unsigned long data)
610 {
611         struct tasklet_hrtimer *ttimer = (void *)data;
612         enum hrtimer_restart restart;
613 
614         restart = ttimer->function(&ttimer->timer);
615         if (restart != HRTIMER_NORESTART)
616                 hrtimer_restart(&ttimer->timer);
617 }
618 
619 /**
620  * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
621  * @ttimer:      tasklet_hrtimer which is initialized
622  * @function:    hrtimer callback function which gets called from softirq context
623  * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
624  * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
625  */
626 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
627                           enum hrtimer_restart (*function)(struct hrtimer *),
628                           clockid_t which_clock, enum hrtimer_mode mode)
629 {
630         hrtimer_init(&ttimer->timer, which_clock, mode);
631         ttimer->timer.function = __hrtimer_tasklet_trampoline;
632         tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
633                      (unsigned long)ttimer);
634         ttimer->function = function;
635 }
636 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
637 
638 void __init softirq_init(void)
639 {
640         int cpu;
641 
642         for_each_possible_cpu(cpu) {
643                 per_cpu(tasklet_vec, cpu).tail =
644                         &per_cpu(tasklet_vec, cpu).head;
645                 per_cpu(tasklet_hi_vec, cpu).tail =
646                         &per_cpu(tasklet_hi_vec, cpu).head;
647         }
648 
649         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
650         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
651 }
652 
653 static int ksoftirqd_should_run(unsigned int cpu)
654 {
655         return local_softirq_pending();
656 }
657 
658 static void run_ksoftirqd(unsigned int cpu)
659 {
660         local_irq_disable();
661         if (local_softirq_pending()) {
662                 /*
663                  * We can safely run softirq on inline stack, as we are not deep
664                  * in the task stack here.
665                  */
666                 __do_softirq();
667                 local_irq_enable();
668                 cond_resched_rcu_qs();
669                 return;
670         }
671         local_irq_enable();
672 }
673 
674 #ifdef CONFIG_HOTPLUG_CPU
675 /*
676  * tasklet_kill_immediate is called to remove a tasklet which can already be
677  * scheduled for execution on @cpu.
678  *
679  * Unlike tasklet_kill, this function removes the tasklet
680  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
681  *
682  * When this function is called, @cpu must be in the CPU_DEAD state.
683  */
684 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
685 {
686         struct tasklet_struct **i;
687 
688         BUG_ON(cpu_online(cpu));
689         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
690 
691         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
692                 return;
693 
694         /* CPU is dead, so no lock needed. */
695         for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
696                 if (*i == t) {
697                         *i = t->next;
698                         /* If this was the tail element, move the tail ptr */
699                         if (*i == NULL)
700                                 per_cpu(tasklet_vec, cpu).tail = i;
701                         return;
702                 }
703         }
704         BUG();
705 }
706 
707 static int takeover_tasklets(unsigned int cpu)
708 {
709         /* CPU is dead, so no lock needed. */
710         local_irq_disable();
711 
712         /* Find end, append list for that CPU. */
713         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
714                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
715                 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
716                 per_cpu(tasklet_vec, cpu).head = NULL;
717                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
718         }
719         raise_softirq_irqoff(TASKLET_SOFTIRQ);
720 
721         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
722                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
723                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
724                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
725                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
726         }
727         raise_softirq_irqoff(HI_SOFTIRQ);
728 
729         local_irq_enable();
730         return 0;
731 }
732 #else
733 #define takeover_tasklets       NULL
734 #endif /* CONFIG_HOTPLUG_CPU */
735 
736 static struct smp_hotplug_thread softirq_threads = {
737         .store                  = &ksoftirqd,
738         .thread_should_run      = ksoftirqd_should_run,
739         .thread_fn              = run_ksoftirqd,
740         .thread_comm            = "ksoftirqd/%u",
741 };
742 
743 static __init int spawn_ksoftirqd(void)
744 {
745         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
746                                   takeover_tasklets);
747         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
748 
749         return 0;
750 }
751 early_initcall(spawn_ksoftirqd);
752 
753 /*
754  * [ These __weak aliases are kept in a separate compilation unit, so that
755  *   GCC does not inline them incorrectly. ]
756  */
757 
758 int __init __weak early_irq_init(void)
759 {
760         return 0;
761 }
762 
763 int __init __weak arch_probe_nr_irqs(void)
764 {
765         return NR_IRQS_LEGACY;
766 }
767 
768 int __init __weak arch_early_irq_init(void)
769 {
770         return 0;
771 }
772 
773 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
774 {
775         return from;
776 }
777 

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