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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 #include <linux/module.h>
12 #include <linux/kernel_stat.h>
13 #include <linux/interrupt.h>
14 #include <linux/init.h>
15 #include <linux/mm.h>
16 #include <linux/notifier.h>
17 #include <linux/percpu.h>
18 #include <linux/cpu.h>
19 #include <linux/freezer.h>
20 #include <linux/kthread.h>
21 #include <linux/rcupdate.h>
22 #include <linux/smp.h>
23 #include <linux/tick.h>
24
25 #include <asm/irq.h>
26 /*
27    - No shared variables, all the data are CPU local.
28    - If a softirq needs serialization, let it serialize itself
29      by its own spinlocks.
30    - Even if softirq is serialized, only local cpu is marked for
31      execution. Hence, we get something sort of weak cpu binding.
32      Though it is still not clear, will it result in better locality
33      or will not.
34
35    Examples:
36    - NET RX softirq. It is multithreaded and does not require
37      any global serialization.
38    - NET TX softirq. It kicks software netdevice queues, hence
39      it is logically serialized per device, but this serialization
40      is invisible to common code.
41    - Tasklets: serialized wrt itself.
42  */
43
44 #ifndef __ARCH_IRQ_STAT
45 irq_cpustat_t irq_stat[NR_CPUS] ____cacheline_aligned;
46 EXPORT_SYMBOL(irq_stat);
47 #endif
48
49 static struct softirq_action softirq_vec[32] __cacheline_aligned_in_smp;
50
51 static DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
52
53 /*
54  * we cannot loop indefinitely here to avoid userspace starvation,
55  * but we also don't want to introduce a worst case 1/HZ latency
56  * to the pending events, so lets the scheduler to balance
57  * the softirq load for us.
58  */
59 static inline void wakeup_softirqd(void)
60 {
61         /* Interrupts are disabled: no need to stop preemption */
62         struct task_struct *tsk = __get_cpu_var(ksoftirqd);
63
64         if (tsk && tsk->state != TASK_RUNNING)
65                 wake_up_process(tsk);
66 }
67
68 /*
69  * This one is for softirq.c-internal use,
70  * where hardirqs are disabled legitimately:
71  */
72 #ifdef CONFIG_TRACE_IRQFLAGS
73 static void __local_bh_disable(unsigned long ip)
74 {
75         unsigned long flags;
76
77         WARN_ON_ONCE(in_irq());
78
79         raw_local_irq_save(flags);
80         add_preempt_count(SOFTIRQ_OFFSET);
81         /*
82          * Were softirqs turned off above:
83          */
84         if (softirq_count() == SOFTIRQ_OFFSET)
85                 trace_softirqs_off(ip);
86         raw_local_irq_restore(flags);
87 }
88 #else /* !CONFIG_TRACE_IRQFLAGS */
89 static inline void __local_bh_disable(unsigned long ip)
90 {
91         add_preempt_count(SOFTIRQ_OFFSET);
92         barrier();
93 }
94 #endif /* CONFIG_TRACE_IRQFLAGS */
95
96 void local_bh_disable(void)
97 {
98         __local_bh_disable((unsigned long)__builtin_return_address(0));
99 }
100
101 EXPORT_SYMBOL(local_bh_disable);
102
103 void __local_bh_enable(void)
104 {
105         WARN_ON_ONCE(in_irq());
106
107         /*
108          * softirqs should never be enabled by __local_bh_enable(),
109          * it always nests inside local_bh_enable() sections:
110          */
111         WARN_ON_ONCE(softirq_count() == SOFTIRQ_OFFSET);
112
113         sub_preempt_count(SOFTIRQ_OFFSET);
114 }
115 EXPORT_SYMBOL_GPL(__local_bh_enable);
116
117 /*
118  * Special-case - softirqs can safely be enabled in
119  * cond_resched_softirq(), or by __do_softirq(),
120  * without processing still-pending softirqs:
121  */
122 void _local_bh_enable(void)
123 {
124         WARN_ON_ONCE(in_irq());
125         WARN_ON_ONCE(!irqs_disabled());
126
127         if (softirq_count() == SOFTIRQ_OFFSET)
128                 trace_softirqs_on((unsigned long)__builtin_return_address(0));
129         sub_preempt_count(SOFTIRQ_OFFSET);
130 }
131
132 EXPORT_SYMBOL(_local_bh_enable);
133
134 void local_bh_enable(void)
135 {
136 #ifdef CONFIG_TRACE_IRQFLAGS
137         unsigned long flags;
138
139         WARN_ON_ONCE(in_irq());
140 #endif
141         WARN_ON_ONCE(irqs_disabled());
142
143 #ifdef CONFIG_TRACE_IRQFLAGS
144         local_irq_save(flags);
145 #endif
146         /*
147          * Are softirqs going to be turned on now:
148          */
149         if (softirq_count() == SOFTIRQ_OFFSET)
150                 trace_softirqs_on((unsigned long)__builtin_return_address(0));
151         /*
152          * Keep preemption disabled until we are done with
153          * softirq processing:
154          */
155         sub_preempt_count(SOFTIRQ_OFFSET - 1);
156
157         if (unlikely(!in_interrupt() && local_softirq_pending()))
158                 do_softirq();
159
160         dec_preempt_count();
161 #ifdef CONFIG_TRACE_IRQFLAGS
162         local_irq_restore(flags);
163 #endif
164         preempt_check_resched();
165 }
166 EXPORT_SYMBOL(local_bh_enable);
167
168 void local_bh_enable_ip(unsigned long ip)
169 {
170 #ifdef CONFIG_TRACE_IRQFLAGS
171         unsigned long flags;
172
173         WARN_ON_ONCE(in_irq());
174
175         local_irq_save(flags);
176 #endif
177         /*
178          * Are softirqs going to be turned on now:
179          */
180         if (softirq_count() == SOFTIRQ_OFFSET)
181                 trace_softirqs_on(ip);
182         /*
183          * Keep preemption disabled until we are done with
184          * softirq processing:
185          */
186         sub_preempt_count(SOFTIRQ_OFFSET - 1);
187
188         if (unlikely(!in_interrupt() && local_softirq_pending()))
189                 do_softirq();
190
191         dec_preempt_count();
192 #ifdef CONFIG_TRACE_IRQFLAGS
193         local_irq_restore(flags);
194 #endif
195         preempt_check_resched();
196 }
197 EXPORT_SYMBOL(local_bh_enable_ip);
198
199 /*
200  * We restart softirq processing MAX_SOFTIRQ_RESTART times,
201  * and we fall back to softirqd after that.
202  *
203  * This number has been established via experimentation.
204  * The two things to balance is latency against fairness -
205  * we want to handle softirqs as soon as possible, but they
206  * should not be able to lock up the box.
207  */
208 #define MAX_SOFTIRQ_RESTART 10
209
210 asmlinkage void __do_softirq(void)
211 {
212         struct softirq_action *h;
213         __u32 pending;
214         int max_restart = MAX_SOFTIRQ_RESTART;
215         int cpu;
216
217         pending = local_softirq_pending();
218         account_system_vtime(current);
219
220         __local_bh_disable((unsigned long)__builtin_return_address(0));
221         trace_softirq_enter();
222
223         cpu = smp_processor_id();
224 restart:
225         /* Reset the pending bitmask before enabling irqs */
226         set_softirq_pending(0);
227
228         local_irq_enable();
229
230         h = softirq_vec;
231
232         do {
233                 if (pending & 1) {
234                         h->action(h);
235                         rcu_bh_qsctr_inc(cpu);
236                 }
237                 h++;
238                 pending >>= 1;
239         } while (pending);
240
241         local_irq_disable();
242
243         pending = local_softirq_pending();
244         if (pending && --max_restart)
245                 goto restart;
246
247         if (pending)
248                 wakeup_softirqd();
249
250         trace_softirq_exit();
251
252         account_system_vtime(current);
253         _local_bh_enable();
254 }
255
256 #ifndef __ARCH_HAS_DO_SOFTIRQ
257
258 asmlinkage void do_softirq(void)
259 {
260         __u32 pending;
261         unsigned long flags;
262
263         if (in_interrupt())
264                 return;
265
266         local_irq_save(flags);
267
268         pending = local_softirq_pending();
269
270         if (pending)
271                 __do_softirq();
272
273         local_irq_restore(flags);
274 }
275
276 #endif
277
278 /*
279  * Enter an interrupt context.
280  */
281 void irq_enter(void)
282 {
283 #ifdef CONFIG_NO_HZ
284         int cpu = smp_processor_id();
285         if (idle_cpu(cpu) && !in_interrupt())
286                 tick_nohz_stop_idle(cpu);
287 #endif
288         __irq_enter();
289 #ifdef CONFIG_NO_HZ
290         if (idle_cpu(cpu))
291                 tick_nohz_update_jiffies();
292 #endif
293 }
294
295 #ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
296 # define invoke_softirq()       __do_softirq()
297 #else
298 # define invoke_softirq()       do_softirq()
299 #endif
300
301 /*
302  * Exit an interrupt context. Process softirqs if needed and possible:
303  */
304 void irq_exit(void)
305 {
306         account_system_vtime(current);
307         trace_hardirq_exit();
308         sub_preempt_count(IRQ_EXIT_OFFSET);
309         if (!in_interrupt() && local_softirq_pending())
310                 invoke_softirq();
311
312 #ifdef CONFIG_NO_HZ
313         /* Make sure that timer wheel updates are propagated */
314         if (!in_interrupt() && idle_cpu(smp_processor_id()) && !need_resched())
315                 tick_nohz_stop_sched_tick();
316         rcu_irq_exit();
317 #endif
318         preempt_enable_no_resched();
319 }
320
321 /*
322  * This function must run with irqs disabled!
323  */
324 inline void raise_softirq_irqoff(unsigned int nr)
325 {
326         __raise_softirq_irqoff(nr);
327
328         /*
329          * If we're in an interrupt or softirq, we're done
330          * (this also catches softirq-disabled code). We will
331          * actually run the softirq once we return from
332          * the irq or softirq.
333          *
334          * Otherwise we wake up ksoftirqd to make sure we
335          * schedule the softirq soon.
336          */
337         if (!in_interrupt())
338                 wakeup_softirqd();
339 }
340
341 void raise_softirq(unsigned int nr)
342 {
343         unsigned long flags;
344
345         local_irq_save(flags);
346         raise_softirq_irqoff(nr);
347         local_irq_restore(flags);
348 }
349
350 void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
351 {
352         softirq_vec[nr].data = data;
353         softirq_vec[nr].action = action;
354 }
355
356 /* Tasklets */
357 struct tasklet_head
358 {
359         struct tasklet_struct *list;
360 };
361
362 /* Some compilers disobey section attribute on statics when not
363    initialized -- RR */
364 static DEFINE_PER_CPU(struct tasklet_head, tasklet_vec) = { NULL };
365 static DEFINE_PER_CPU(struct tasklet_head, tasklet_hi_vec) = { NULL };
366
367 void __tasklet_schedule(struct tasklet_struct *t)
368 {
369         unsigned long flags;
370
371         local_irq_save(flags);
372         t->next = __get_cpu_var(tasklet_vec).list;
373         __get_cpu_var(tasklet_vec).list = t;
374         raise_softirq_irqoff(TASKLET_SOFTIRQ);
375         local_irq_restore(flags);
376 }
377
378 EXPORT_SYMBOL(__tasklet_schedule);
379
380 void __tasklet_hi_schedule(struct tasklet_struct *t)
381 {
382         unsigned long flags;
383
384         local_irq_save(flags);
385         t->next = __get_cpu_var(tasklet_hi_vec).list;
386         __get_cpu_var(tasklet_hi_vec).list = t;
387         raise_softirq_irqoff(HI_SOFTIRQ);
388         local_irq_restore(flags);
389 }
390
391 EXPORT_SYMBOL(__tasklet_hi_schedule);
392
393 static void tasklet_action(struct softirq_action *a)
394 {
395         struct tasklet_struct *list;
396
397         local_irq_disable();
398         list = __get_cpu_var(tasklet_vec).list;
399         __get_cpu_var(tasklet_vec).list = NULL;
400         local_irq_enable();
401
402         while (list) {
403                 struct tasklet_struct *t = list;
404
405                 list = list->next;
406
407                 if (tasklet_trylock(t)) {
408                         if (!atomic_read(&t->count)) {
409                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
410                                         BUG();
411                                 t->func(t->data);
412                                 tasklet_unlock(t);
413                                 continue;
414                         }
415                         tasklet_unlock(t);
416                 }
417
418                 local_irq_disable();
419                 t->next = __get_cpu_var(tasklet_vec).list;
420                 __get_cpu_var(tasklet_vec).list = t;
421                 __raise_softirq_irqoff(TASKLET_SOFTIRQ);
422                 local_irq_enable();
423         }
424 }
425
426 static void tasklet_hi_action(struct softirq_action *a)
427 {
428         struct tasklet_struct *list;
429
430         local_irq_disable();
431         list = __get_cpu_var(tasklet_hi_vec).list;
432         __get_cpu_var(tasklet_hi_vec).list = NULL;
433         local_irq_enable();
434
435         while (list) {
436                 struct tasklet_struct *t = list;
437
438                 list = list->next;
439
440                 if (tasklet_trylock(t)) {
441                         if (!atomic_read(&t->count)) {
442                                 if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
443                                         BUG();
444                                 t->func(t->data);
445                                 tasklet_unlock(t);
446                                 continue;
447                         }
448                         tasklet_unlock(t);
449                 }
450
451                 local_irq_disable();
452                 t->next = __get_cpu_var(tasklet_hi_vec).list;
453                 __get_cpu_var(tasklet_hi_vec).list = t;
454                 __raise_softirq_irqoff(HI_SOFTIRQ);
455                 local_irq_enable();
456         }
457 }
458
459
460 void tasklet_init(struct tasklet_struct *t,
461                   void (*func)(unsigned long), unsigned long data)
462 {
463         t->next = NULL;
464         t->state = 0;
465         atomic_set(&t->count, 0);
466         t->func = func;
467         t->data = data;
468 }
469
470 EXPORT_SYMBOL(tasklet_init);
471
472 void tasklet_kill(struct tasklet_struct *t)
473 {
474         if (in_interrupt())
475                 printk("Attempt to kill tasklet from interrupt\n");
476
477         while (test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
478                 do
479                         yield();
480                 while (test_bit(TASKLET_STATE_SCHED, &t->state));
481         }
482         tasklet_unlock_wait(t);
483         clear_bit(TASKLET_STATE_SCHED, &t->state);
484 }
485
486 EXPORT_SYMBOL(tasklet_kill);
487
488 void __init softirq_init(void)
489 {
490         open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
491         open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
492 }
493
494 static int ksoftirqd(void * __bind_cpu)
495 {
496         set_current_state(TASK_INTERRUPTIBLE);
497
498         while (!kthread_should_stop()) {
499                 preempt_disable();
500                 if (!local_softirq_pending()) {
501                         preempt_enable_no_resched();
502                         schedule();
503                         preempt_disable();
504                 }
505
506                 __set_current_state(TASK_RUNNING);
507
508                 while (local_softirq_pending()) {
509                         /* Preempt disable stops cpu going offline.
510                            If already offline, we'll be on wrong CPU:
511                            don't process */
512                         if (cpu_is_offline((long)__bind_cpu))
513                                 goto wait_to_die;
514                         do_softirq();
515                         preempt_enable_no_resched();
516                         cond_resched();
517                         preempt_disable();
518                 }
519                 preempt_enable();
520                 set_current_state(TASK_INTERRUPTIBLE);
521         }
522         __set_current_state(TASK_RUNNING);
523         return 0;
524
525 wait_to_die:
526         preempt_enable();
527         /* Wait for kthread_stop */
528         set_current_state(TASK_INTERRUPTIBLE);
529         while (!kthread_should_stop()) {
530                 schedule();
531                 set_current_state(TASK_INTERRUPTIBLE);
532         }
533         __set_current_state(TASK_RUNNING);
534         return 0;
535 }
536
537 #ifdef CONFIG_HOTPLUG_CPU
538 /*
539  * tasklet_kill_immediate is called to remove a tasklet which can already be
540  * scheduled for execution on @cpu.
541  *
542  * Unlike tasklet_kill, this function removes the tasklet
543  * _immediately_, even if the tasklet is in TASKLET_STATE_SCHED state.
544  *
545  * When this function is called, @cpu must be in the CPU_DEAD state.
546  */
547 void tasklet_kill_immediate(struct tasklet_struct *t, unsigned int cpu)
548 {
549         struct tasklet_struct **i;
550
551         BUG_ON(cpu_online(cpu));
552         BUG_ON(test_bit(TASKLET_STATE_RUN, &t->state));
553
554         if (!test_bit(TASKLET_STATE_SCHED, &t->state))
555                 return;
556
557         /* CPU is dead, so no lock needed. */
558         for (i = &per_cpu(tasklet_vec, cpu).list; *i; i = &(*i)->next) {
559                 if (*i == t) {
560                         *i = t->next;
561                         return;
562                 }
563         }
564         BUG();
565 }
566
567 static void takeover_tasklets(unsigned int cpu)
568 {
569         struct tasklet_struct **i;
570
571         /* CPU is dead, so no lock needed. */
572         local_irq_disable();
573
574         /* Find end, append list for that CPU. */
575         for (i = &__get_cpu_var(tasklet_vec).list; *i; i = &(*i)->next);
576         *i = per_cpu(tasklet_vec, cpu).list;
577         per_cpu(tasklet_vec, cpu).list = NULL;
578         raise_softirq_irqoff(TASKLET_SOFTIRQ);
579
580         for (i = &__get_cpu_var(tasklet_hi_vec).list; *i; i = &(*i)->next);
581         *i = per_cpu(tasklet_hi_vec, cpu).list;
582         per_cpu(tasklet_hi_vec, cpu).list = NULL;
583         raise_softirq_irqoff(HI_SOFTIRQ);
584
585         local_irq_enable();
586 }
587 #endif /* CONFIG_HOTPLUG_CPU */
588
589 static int __cpuinit cpu_callback(struct notifier_block *nfb,
590                                   unsigned long action,
591                                   void *hcpu)
592 {
593         int hotcpu = (unsigned long)hcpu;
594         struct task_struct *p;
595
596         switch (action) {
597         case CPU_UP_PREPARE:
598         case CPU_UP_PREPARE_FROZEN:
599                 p = kthread_create(ksoftirqd, hcpu, "ksoftirqd/%d", hotcpu);
600                 if (IS_ERR(p)) {
601                         printk("ksoftirqd for %i failed\n", hotcpu);
602                         return NOTIFY_BAD;
603                 }
604                 kthread_bind(p, hotcpu);
605                 per_cpu(ksoftirqd, hotcpu) = p;
606                 break;
607         case CPU_ONLINE:
608         case CPU_ONLINE_FROZEN:
609                 wake_up_process(per_cpu(ksoftirqd, hotcpu));
610                 break;
611 #ifdef CONFIG_HOTPLUG_CPU
612         case CPU_UP_CANCELED:
613         case CPU_UP_CANCELED_FROZEN:
614                 if (!per_cpu(ksoftirqd, hotcpu))
615                         break;
616                 /* Unbind so it can run.  Fall thru. */
617                 kthread_bind(per_cpu(ksoftirqd, hotcpu),
618                              any_online_cpu(cpu_online_map));
619         case CPU_DEAD:
620         case CPU_DEAD_FROZEN: {
621                 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
622
623                 p = per_cpu(ksoftirqd, hotcpu);
624                 per_cpu(ksoftirqd, hotcpu) = NULL;
625                 sched_setscheduler(p, SCHED_FIFO, &param);
626                 kthread_stop(p);
627                 takeover_tasklets(hotcpu);
628                 break;
629         }
630 #endif /* CONFIG_HOTPLUG_CPU */
631         }
632         return NOTIFY_OK;
633 }
634
635 static struct notifier_block __cpuinitdata cpu_nfb = {
636         .notifier_call = cpu_callback
637 };
638
639 __init int spawn_ksoftirqd(void)
640 {
641         void *cpu = (void *)(long)smp_processor_id();
642         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
643
644         BUG_ON(err == NOTIFY_BAD);
645         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
646         register_cpu_notifier(&cpu_nfb);
647         return 0;
648 }
649
650 #ifdef CONFIG_SMP
651 /*
652  * Call a function on all processors
653  */
654 int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait)
655 {
656         int ret = 0;
657
658         preempt_disable();
659         ret = smp_call_function(func, info, retry, wait);
660         local_irq_disable();
661         func(info);
662         local_irq_enable();
663         preempt_enable();
664         return ret;
665 }
666 EXPORT_SYMBOL(on_each_cpu);
667 #endif