Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/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
 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         WARN_ON_ONCE(!irqs_disabled());
141 
142         if (softirq_count() == (cnt & SOFTIRQ_MASK))
143                 trace_softirqs_on(_RET_IP_);
144         preempt_count_sub(cnt);
145 }
146 
147 /*
148  * Special-case - softirqs can safely be enabled in
149  * cond_resched_softirq(), or by __do_softirq(),
150  * without processing still-pending softirqs:
151  */
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() || irqs_disabled());
162 #ifdef CONFIG_TRACE_IRQFLAGS
163         local_irq_disable();
164 #endif
165         /*
166          * Are softirqs going to be turned on now:
167          */
168         if (softirq_count() == SOFTIRQ_DISABLE_OFFSET)
169                 trace_softirqs_on(ip);
170         /*
171          * Keep preemption disabled until we are done with
172          * softirq processing:
173          */
174         preempt_count_sub(cnt - 1);
175 
176         if (unlikely(!in_interrupt() && local_softirq_pending())) {
177                 /*
178                  * Run softirq if any pending. And do it in its own stack
179                  * as we may be calling this deep in a task call stack already.
180                  */
181                 do_softirq();
182         }
183 
184         preempt_count_dec();
185 #ifdef CONFIG_TRACE_IRQFLAGS
186         local_irq_enable();
187 #endif
188         preempt_check_resched();
189 }
190 EXPORT_SYMBOL(__local_bh_enable_ip);
191 
192 /*
193  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
194  * but break the loop if need_resched() is set or after 2 ms.
195  * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
196  * certain cases, such as stop_machine(), jiffies may cease to
197  * increment and so we need the MAX_SOFTIRQ_RESTART limit as
198  * well to make sure we eventually return from this method.
199  *
200  * These limits have been established via experimentation.
201  * The two things to balance is latency against fairness -
202  * we want to handle softirqs as soon as possible, but they
203  * should not be able to lock up the box.
204  */
205 #define MAX_SOFTIRQ_TIME  msecs_to_jiffies(2)
206 #define MAX_SOFTIRQ_RESTART 10
207 
208 #ifdef CONFIG_TRACE_IRQFLAGS
209 /*
210  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
211  * to keep the lockdep irq context tracking as tight as possible in order to
212  * not miss-qualify lock contexts and miss possible deadlocks.
213  */
214 
215 static inline bool lockdep_softirq_start(void)
216 {
217         bool in_hardirq = false;
218 
219         if (trace_hardirq_context(current)) {
220                 in_hardirq = true;
221                 trace_hardirq_exit();
222         }
223 
224         lockdep_softirq_enter();
225 
226         return in_hardirq;
227 }
228 
229 static inline void lockdep_softirq_end(bool in_hardirq)
230 {
231         lockdep_softirq_exit();
232 
233         if (in_hardirq)
234                 trace_hardirq_enter();
235 }
236 #else
237 static inline bool lockdep_softirq_start(void) { return false; }
238 static inline void lockdep_softirq_end(bool in_hardirq) { }
239 #endif
240 
241 asmlinkage __visible void __softirq_entry __do_softirq(void)
242 {
243         unsigned long end = jiffies + MAX_SOFTIRQ_TIME;
244         unsigned long old_flags = current->flags;
245         int max_restart = MAX_SOFTIRQ_RESTART;
246         struct softirq_action *h;
247         bool in_hardirq;
248         __u32 pending;
249         int softirq_bit;
250 
251         /*
252          * Mask out PF_MEMALLOC s current task context is borrowed for the
253          * softirq. A softirq handled such as network RX might set PF_MEMALLOC
254          * again if the socket is related to swap
255          */
256         current->flags &= ~PF_MEMALLOC;
257 
258         pending = local_softirq_pending();
259         account_irq_enter_time(current);
260 
261         __local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
262         in_hardirq = lockdep_softirq_start();
263 
264 restart:
265         /* Reset the pending bitmask before enabling irqs */
266         set_softirq_pending(0);
267 
268         local_irq_enable();
269 
270         h = softirq_vec;
271 
272         while ((softirq_bit = ffs(pending))) {
273                 unsigned int vec_nr;
274                 int prev_count;
275 
276                 h += softirq_bit - 1;
277 
278                 vec_nr = h - softirq_vec;
279                 prev_count = preempt_count();
280 
281                 kstat_incr_softirqs_this_cpu(vec_nr);
282 
283                 trace_softirq_entry(vec_nr);
284                 h->action(h);
285                 trace_softirq_exit(vec_nr);
286                 if (unlikely(prev_count != preempt_count())) {
287                         pr_err("huh, entered softirq %u %s %p with preempt_count %08x, exited with %08x?\n",
288                                vec_nr, softirq_to_name[vec_nr], h->action,
289                                prev_count, preempt_count());
290                         preempt_count_set(prev_count);
291                 }
292                 h++;
293                 pending >>= softirq_bit;
294         }
295 
296         rcu_bh_qs();
297         local_irq_disable();
298 
299         pending = local_softirq_pending();
300         if (pending) {
301                 if (time_before(jiffies, end) && !need_resched() &&
302                     --max_restart)
303                         goto restart;
304 
305                 wakeup_softirqd();
306         }
307 
308         lockdep_softirq_end(in_hardirq);
309         account_irq_exit_time(current);
310         __local_bh_enable(SOFTIRQ_OFFSET);
311         WARN_ON_ONCE(in_interrupt());
312         tsk_restore_flags(current, old_flags, PF_MEMALLOC);
313 }
314 
315 asmlinkage __visible void do_softirq(void)
316 {
317         __u32 pending;
318         unsigned long flags;
319 
320         if (in_interrupt())
321                 return;
322 
323         local_irq_save(flags);
324 
325         pending = local_softirq_pending();
326 
327         if (pending && !ksoftirqd_running())
328                 do_softirq_own_stack();
329 
330         local_irq_restore(flags);
331 }
332 
333 /*
334  * Enter an interrupt context.
335  */
336 void irq_enter(void)
337 {
338         rcu_irq_enter();
339         if (is_idle_task(current) && !in_interrupt()) {
340                 /*
341                  * Prevent raise_softirq from needlessly waking up ksoftirqd
342                  * here, as softirq will be serviced on return from interrupt.
343                  */
344                 local_bh_disable();
345                 tick_irq_enter();
346                 _local_bh_enable();
347         }
348 
349         __irq_enter();
350 }
351 
352 static inline void invoke_softirq(void)
353 {
354         if (ksoftirqd_running())
355                 return;
356 
357         if (!force_irqthreads) {
358 #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
359                 /*
360                  * We can safely execute softirq on the current stack if
361                  * it is the irq stack, because it should be near empty
362                  * at this stage.
363                  */
364                 __do_softirq();
365 #else
366                 /*
367                  * Otherwise, irq_exit() is called on the task stack that can
368                  * be potentially deep already. So call softirq in its own stack
369                  * to prevent from any overrun.
370                  */
371                 do_softirq_own_stack();
372 #endif
373         } else {
374                 wakeup_softirqd();
375         }
376 }
377 
378 static inline void tick_irq_exit(void)
379 {
380 #ifdef CONFIG_NO_HZ_COMMON
381         int cpu = smp_processor_id();
382 
383         /* Make sure that timer wheel updates are propagated */
384         if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) {
385                 if (!in_interrupt())
386                         tick_nohz_irq_exit();
387         }
388 #endif
389 }
390 
391 /*
392  * Exit an interrupt context. Process softirqs if needed and possible:
393  */
394 void irq_exit(void)
395 {
396 #ifndef __ARCH_IRQ_EXIT_IRQS_DISABLED
397         local_irq_disable();
398 #else
399         WARN_ON_ONCE(!irqs_disabled());
400 #endif
401 
402         account_irq_exit_time(current);
403         preempt_count_sub(HARDIRQ_OFFSET);
404         if (!in_interrupt() && local_softirq_pending())
405                 invoke_softirq();
406 
407         tick_irq_exit();
408         rcu_irq_exit();
409         trace_hardirq_exit(); /* must be last! */
410 }
411 
412 /*
413  * This function must run with irqs disabled!
414  */
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 void __tasklet_hi_schedule_first(struct tasklet_struct *t)
490 {
491         BUG_ON(!irqs_disabled());
492 
493         t->next = __this_cpu_read(tasklet_hi_vec.head);
494         __this_cpu_write(tasklet_hi_vec.head, t);
495         __raise_softirq_irqoff(HI_SOFTIRQ);
496 }
497 EXPORT_SYMBOL(__tasklet_hi_schedule_first);
498 
499 static __latent_entropy void tasklet_action(struct softirq_action *a)
500 {
501         struct tasklet_struct *list;
502 
503         local_irq_disable();
504         list = __this_cpu_read(tasklet_vec.head);
505         __this_cpu_write(tasklet_vec.head, NULL);
506         __this_cpu_write(tasklet_vec.tail, this_cpu_ptr(&tasklet_vec.head));
507         local_irq_enable();
508 
509         while (list) {
510                 struct tasklet_struct *t = list;
511 
512                 list = list->next;
513 
514                 if (tasklet_trylock(t)) {
515                         if (!atomic_read(&t->count)) {
516                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
517                                                         &t->state))
518                                         BUG();
519                                 t->func(t->data);
520                                 tasklet_unlock(t);
521                                 continue;
522                         }
523                         tasklet_unlock(t);
524                 }
525 
526                 local_irq_disable();
527                 t->next = NULL;
528                 *__this_cpu_read(tasklet_vec.tail) = t;
529                 __this_cpu_write(tasklet_vec.tail, &(t->next));
530                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
531                 local_irq_enable();
532         }
533 }
534 
535 static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
536 {
537         struct tasklet_struct *list;
538 
539         local_irq_disable();
540         list = __this_cpu_read(tasklet_hi_vec.head);
541         __this_cpu_write(tasklet_hi_vec.head, NULL);
542         __this_cpu_write(tasklet_hi_vec.tail, this_cpu_ptr(&tasklet_hi_vec.head));
543         local_irq_enable();
544 
545         while (list) {
546                 struct tasklet_struct *t = list;
547 
548                 list = list->next;
549 
550                 if (tasklet_trylock(t)) {
551                         if (!atomic_read(&t->count)) {
552                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED,
553                                                         &t->state))
554                                         BUG();
555                                 t->func(t->data);
556                                 tasklet_unlock(t);
557                                 continue;
558                         }
559                         tasklet_unlock(t);
560                 }
561 
562                 local_irq_disable();
563                 t->next = NULL;
564                 *__this_cpu_read(tasklet_hi_vec.tail) = t;
565                 __this_cpu_write(tasklet_hi_vec.tail, &(t->next));
566                 __raise_softirq_irqoff(HI_SOFTIRQ);
567                 local_irq_enable();
568         }
569 }
570 
571 void tasklet_init(struct tasklet_struct *t,
572                   void (*func)(unsigned long), unsigned long data)
573 {
574         t->next = NULL;
575         t->state = 0;
576         atomic_set(&t->count, 0);
577         t->func = func;
578         t->data = data;
579 }
580 EXPORT_SYMBOL(tasklet_init);
581 
582 void tasklet_kill(struct tasklet_struct *t)
583 {
584         if (in_interrupt())
585                 pr_notice("Attempt to kill tasklet from interrupt\n");
586 
587         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
588                 do {
589                         yield();
590                 } while (test_bit(TASKLET_STATE_SCHED, &t->state));
591         }
592         tasklet_unlock_wait(t);
593         clear_bit(TASKLET_STATE_SCHED, &t->state);
594 }
595 EXPORT_SYMBOL(tasklet_kill);
596 
597 /*
598  * tasklet_hrtimer
599  */
600 
601 /*
602  * The trampoline is called when the hrtimer expires. It schedules a tasklet
603  * to run __tasklet_hrtimer_trampoline() which in turn will call the intended
604  * hrtimer callback, but from softirq context.
605  */
606 static enum hrtimer_restart __hrtimer_tasklet_trampoline(struct hrtimer *timer)
607 {
608         struct tasklet_hrtimer *ttimer =
609                 container_of(timer, struct tasklet_hrtimer, timer);
610 
611         tasklet_hi_schedule(&ttimer->tasklet);
612         return HRTIMER_NORESTART;
613 }
614 
615 /*
616  * Helper function which calls the hrtimer callback from
617  * tasklet/softirq context
618  */
619 static void __tasklet_hrtimer_trampoline(unsigned long data)
620 {
621         struct tasklet_hrtimer *ttimer = (void *)data;
622         enum hrtimer_restart restart;
623 
624         restart = ttimer->function(&ttimer->timer);
625         if (restart != HRTIMER_NORESTART)
626                 hrtimer_restart(&ttimer->timer);
627 }
628 
629 /**
630  * tasklet_hrtimer_init - Init a tasklet/hrtimer combo for softirq callbacks
631  * @ttimer:      tasklet_hrtimer which is initialized
632  * @function:    hrtimer callback function which gets called from softirq context
633  * @which_clock: clock id (CLOCK_MONOTONIC/CLOCK_REALTIME)
634  * @mode:        hrtimer mode (HRTIMER_MODE_ABS/HRTIMER_MODE_REL)
635  */
636 void tasklet_hrtimer_init(struct tasklet_hrtimer *ttimer,
637                           enum hrtimer_restart (*function)(struct hrtimer *),
638                           clockid_t which_clock, enum hrtimer_mode mode)
639 {
640         hrtimer_init(&ttimer->timer, which_clock, mode);
641         ttimer->timer.function = __hrtimer_tasklet_trampoline;
642         tasklet_init(&ttimer->tasklet, __tasklet_hrtimer_trampoline,
643                      (unsigned long)ttimer);
644         ttimer->function = function;
645 }
646 EXPORT_SYMBOL_GPL(tasklet_hrtimer_init);
647 
648 void __init softirq_init(void)
649 {
650         int cpu;
651 
652         for_each_possible_cpu(cpu) {
653                 per_cpu(tasklet_vec, cpu).tail =
654                         &per_cpu(tasklet_vec, cpu).head;
655                 per_cpu(tasklet_hi_vec, cpu).tail =
656                         &per_cpu(tasklet_hi_vec, cpu).head;
657         }
658 
659         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
660         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
661 }
662 
663 static int ksoftirqd_should_run(unsigned int cpu)
664 {
665         return local_softirq_pending();
666 }
667 
668 static void run_ksoftirqd(unsigned int cpu)
669 {
670         local_irq_disable();
671         if (local_softirq_pending()) {
672                 /*
673                  * We can safely run softirq on inline stack, as we are not deep
674                  * in the task stack here.
675                  */
676                 __do_softirq();
677                 local_irq_enable();
678                 cond_resched_rcu_qs();
679                 return;
680         }
681         local_irq_enable();
682 }
683 
684 #ifdef CONFIG_HOTPLUG_CPU
685 /*
686  * tasklet_kill_immediate is called to remove a tasklet which can already be
687  * scheduled for execution on @cpu.
688  *
689  * Unlike tasklet_kill, this function removes the tasklet
690  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
691  *
692  * When this function is called, @cpu must be in the CPU_DEAD state.
693  */
694 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
695 {
696         struct tasklet_struct **i;
697 
698         BUG_ON(cpu_online(cpu));
699         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
700 
701         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
702                 return;
703 
704         /* CPU is dead, so no lock needed. */
705         for (i = &per_cpu(tasklet_vec, cpu).head; *i; i = &(*i)->next) {
706                 if (*i == t) {
707                         *i = t->next;
708                         /* If this was the tail element, move the tail ptr */
709                         if (*i == NULL)
710                                 per_cpu(tasklet_vec, cpu).tail = i;
711                         return;
712                 }
713         }
714         BUG();
715 }
716 
717 static int takeover_tasklets(unsigned int cpu)
718 {
719         /* CPU is dead, so no lock needed. */
720         local_irq_disable();
721 
722         /* Find end, append list for that CPU. */
723         if (&per_cpu(tasklet_vec, cpu).head != per_cpu(tasklet_vec, cpu).tail) {
724                 *__this_cpu_read(tasklet_vec.tail) = per_cpu(tasklet_vec, cpu).head;
725                 this_cpu_write(tasklet_vec.tail, per_cpu(tasklet_vec, cpu).tail);
726                 per_cpu(tasklet_vec, cpu).head = NULL;
727                 per_cpu(tasklet_vec, cpu).tail = &per_cpu(tasklet_vec, cpu).head;
728         }
729         raise_softirq_irqoff(TASKLET_SOFTIRQ);
730 
731         if (&per_cpu(tasklet_hi_vec, cpu).head != per_cpu(tasklet_hi_vec, cpu).tail) {
732                 *__this_cpu_read(tasklet_hi_vec.tail) = per_cpu(tasklet_hi_vec, cpu).head;
733                 __this_cpu_write(tasklet_hi_vec.tail, per_cpu(tasklet_hi_vec, cpu).tail);
734                 per_cpu(tasklet_hi_vec, cpu).head = NULL;
735                 per_cpu(tasklet_hi_vec, cpu).tail = &per_cpu(tasklet_hi_vec, cpu).head;
736         }
737         raise_softirq_irqoff(HI_SOFTIRQ);
738 
739         local_irq_enable();
740         return 0;
741 }
742 #else
743 #define takeover_tasklets       NULL
744 #endif /* CONFIG_HOTPLUG_CPU */
745 
746 static 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 
753 static __init int spawn_ksoftirqd(void)
754 {
755         cpuhp_setup_state_nocalls(CPUHP_SOFTIRQ_DEAD, "softirq:dead", NULL,
756                                   takeover_tasklets);
757         BUG_ON(smpboot_register_percpu_thread(&softirq_threads));
758 
759         return 0;
760 }
761 early_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 
768 int __init __weak early_irq_init(void)
769 {
770         return 0;
771 }
772 
773 int __init __weak arch_probe_nr_irqs(void)
774 {
775         return NR_IRQS_LEGACY;
776 }
777 
778 int __init __weak arch_early_irq_init(void)
779 {
780         return 0;
781 }
782 
783 unsigned int __weak arch_dynirq_lower_bound(unsigned int from)
784 {
785         return from;
786 }
787 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us