Merge branch 'hwpoison-2.6.32' of git://git.kernel.org/pub/scm/linux/kernel/git/ak...
[linux-2.6.git] / kernel / workqueue.c
1 /*
2  * linux/kernel/workqueue.c
3  *
4  * Generic mechanism for defining kernel helper threads for running
5  * arbitrary tasks in process context.
6  *
7  * Started by Ingo Molnar, Copyright (C) 2002
8  *
9  * Derived from the taskqueue/keventd code by:
10  *
11  *   David Woodhouse <dwmw2@infradead.org>
12  *   Andrew Morton
13  *   Kai Petzke <wpp@marie.physik.tu-berlin.de>
14  *   Theodore Ts'o <tytso@mit.edu>
15  *
16  * Made to use alloc_percpu by Christoph Lameter.
17  */
18
19 #include <linux/module.h>
20 #include <linux/kernel.h>
21 #include <linux/sched.h>
22 #include <linux/init.h>
23 #include <linux/signal.h>
24 #include <linux/completion.h>
25 #include <linux/workqueue.h>
26 #include <linux/slab.h>
27 #include <linux/cpu.h>
28 #include <linux/notifier.h>
29 #include <linux/kthread.h>
30 #include <linux/hardirq.h>
31 #include <linux/mempolicy.h>
32 #include <linux/freezer.h>
33 #include <linux/kallsyms.h>
34 #include <linux/debug_locks.h>
35 #include <linux/lockdep.h>
36 #define CREATE_TRACE_POINTS
37 #include <trace/events/workqueue.h>
38
39 /*
40  * The per-CPU workqueue (if single thread, we always use the first
41  * possible cpu).
42  */
43 struct cpu_workqueue_struct {
44
45         spinlock_t lock;
46
47         struct list_head worklist;
48         wait_queue_head_t more_work;
49         struct work_struct *current_work;
50
51         struct workqueue_struct *wq;
52         struct task_struct *thread;
53 } ____cacheline_aligned;
54
55 /*
56  * The externally visible workqueue abstraction is an array of
57  * per-CPU workqueues:
58  */
59 struct workqueue_struct {
60         struct cpu_workqueue_struct *cpu_wq;
61         struct list_head list;
62         const char *name;
63         int singlethread;
64         int freezeable;         /* Freeze threads during suspend */
65         int rt;
66 #ifdef CONFIG_LOCKDEP
67         struct lockdep_map lockdep_map;
68 #endif
69 };
70
71 /* Serializes the accesses to the list of workqueues. */
72 static DEFINE_SPINLOCK(workqueue_lock);
73 static LIST_HEAD(workqueues);
74
75 static int singlethread_cpu __read_mostly;
76 static const struct cpumask *cpu_singlethread_map __read_mostly;
77 /*
78  * _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
79  * flushes cwq->worklist. This means that flush_workqueue/wait_on_work
80  * which comes in between can't use for_each_online_cpu(). We could
81  * use cpu_possible_map, the cpumask below is more a documentation
82  * than optimization.
83  */
84 static cpumask_var_t cpu_populated_map __read_mostly;
85
86 /* If it's single threaded, it isn't in the list of workqueues. */
87 static inline int is_wq_single_threaded(struct workqueue_struct *wq)
88 {
89         return wq->singlethread;
90 }
91
92 static const struct cpumask *wq_cpu_map(struct workqueue_struct *wq)
93 {
94         return is_wq_single_threaded(wq)
95                 ? cpu_singlethread_map : cpu_populated_map;
96 }
97
98 static
99 struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
100 {
101         if (unlikely(is_wq_single_threaded(wq)))
102                 cpu = singlethread_cpu;
103         return per_cpu_ptr(wq->cpu_wq, cpu);
104 }
105
106 /*
107  * Set the workqueue on which a work item is to be run
108  * - Must *only* be called if the pending flag is set
109  */
110 static inline void set_wq_data(struct work_struct *work,
111                                 struct cpu_workqueue_struct *cwq)
112 {
113         unsigned long new;
114
115         BUG_ON(!work_pending(work));
116
117         new = (unsigned long) cwq | (1UL << WORK_STRUCT_PENDING);
118         new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
119         atomic_long_set(&work->data, new);
120 }
121
122 static inline
123 struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
124 {
125         return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
126 }
127
128 static void insert_work(struct cpu_workqueue_struct *cwq,
129                         struct work_struct *work, struct list_head *head)
130 {
131         trace_workqueue_insertion(cwq->thread, work);
132
133         set_wq_data(work, cwq);
134         /*
135          * Ensure that we get the right work->data if we see the
136          * result of list_add() below, see try_to_grab_pending().
137          */
138         smp_wmb();
139         list_add_tail(&work->entry, head);
140         wake_up(&cwq->more_work);
141 }
142
143 static void __queue_work(struct cpu_workqueue_struct *cwq,
144                          struct work_struct *work)
145 {
146         unsigned long flags;
147
148         spin_lock_irqsave(&cwq->lock, flags);
149         insert_work(cwq, work, &cwq->worklist);
150         spin_unlock_irqrestore(&cwq->lock, flags);
151 }
152
153 /**
154  * queue_work - queue work on a workqueue
155  * @wq: workqueue to use
156  * @work: work to queue
157  *
158  * Returns 0 if @work was already on a queue, non-zero otherwise.
159  *
160  * We queue the work to the CPU on which it was submitted, but if the CPU dies
161  * it can be processed by another CPU.
162  */
163 int queue_work(struct workqueue_struct *wq, struct work_struct *work)
164 {
165         int ret;
166
167         ret = queue_work_on(get_cpu(), wq, work);
168         put_cpu();
169
170         return ret;
171 }
172 EXPORT_SYMBOL_GPL(queue_work);
173
174 /**
175  * queue_work_on - queue work on specific cpu
176  * @cpu: CPU number to execute work on
177  * @wq: workqueue to use
178  * @work: work to queue
179  *
180  * Returns 0 if @work was already on a queue, non-zero otherwise.
181  *
182  * We queue the work to a specific CPU, the caller must ensure it
183  * can't go away.
184  */
185 int
186 queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
187 {
188         int ret = 0;
189
190         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
191                 BUG_ON(!list_empty(&work->entry));
192                 __queue_work(wq_per_cpu(wq, cpu), work);
193                 ret = 1;
194         }
195         return ret;
196 }
197 EXPORT_SYMBOL_GPL(queue_work_on);
198
199 static void delayed_work_timer_fn(unsigned long __data)
200 {
201         struct delayed_work *dwork = (struct delayed_work *)__data;
202         struct cpu_workqueue_struct *cwq = get_wq_data(&dwork->work);
203         struct workqueue_struct *wq = cwq->wq;
204
205         __queue_work(wq_per_cpu(wq, smp_processor_id()), &dwork->work);
206 }
207
208 /**
209  * queue_delayed_work - queue work on a workqueue after delay
210  * @wq: workqueue to use
211  * @dwork: delayable work to queue
212  * @delay: number of jiffies to wait before queueing
213  *
214  * Returns 0 if @work was already on a queue, non-zero otherwise.
215  */
216 int queue_delayed_work(struct workqueue_struct *wq,
217                         struct delayed_work *dwork, unsigned long delay)
218 {
219         if (delay == 0)
220                 return queue_work(wq, &dwork->work);
221
222         return queue_delayed_work_on(-1, wq, dwork, delay);
223 }
224 EXPORT_SYMBOL_GPL(queue_delayed_work);
225
226 /**
227  * queue_delayed_work_on - queue work on specific CPU after delay
228  * @cpu: CPU number to execute work on
229  * @wq: workqueue to use
230  * @dwork: work to queue
231  * @delay: number of jiffies to wait before queueing
232  *
233  * Returns 0 if @work was already on a queue, non-zero otherwise.
234  */
235 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
236                         struct delayed_work *dwork, unsigned long delay)
237 {
238         int ret = 0;
239         struct timer_list *timer = &dwork->timer;
240         struct work_struct *work = &dwork->work;
241
242         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
243                 BUG_ON(timer_pending(timer));
244                 BUG_ON(!list_empty(&work->entry));
245
246                 timer_stats_timer_set_start_info(&dwork->timer);
247
248                 /* This stores cwq for the moment, for the timer_fn */
249                 set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
250                 timer->expires = jiffies + delay;
251                 timer->data = (unsigned long)dwork;
252                 timer->function = delayed_work_timer_fn;
253
254                 if (unlikely(cpu >= 0))
255                         add_timer_on(timer, cpu);
256                 else
257                         add_timer(timer);
258                 ret = 1;
259         }
260         return ret;
261 }
262 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
263
264 static void run_workqueue(struct cpu_workqueue_struct *cwq)
265 {
266         spin_lock_irq(&cwq->lock);
267         while (!list_empty(&cwq->worklist)) {
268                 struct work_struct *work = list_entry(cwq->worklist.next,
269                                                 struct work_struct, entry);
270                 work_func_t f = work->func;
271 #ifdef CONFIG_LOCKDEP
272                 /*
273                  * It is permissible to free the struct work_struct
274                  * from inside the function that is called from it,
275                  * this we need to take into account for lockdep too.
276                  * To avoid bogus "held lock freed" warnings as well
277                  * as problems when looking into work->lockdep_map,
278                  * make a copy and use that here.
279                  */
280                 struct lockdep_map lockdep_map = work->lockdep_map;
281 #endif
282                 trace_workqueue_execution(cwq->thread, work);
283                 cwq->current_work = work;
284                 list_del_init(cwq->worklist.next);
285                 spin_unlock_irq(&cwq->lock);
286
287                 BUG_ON(get_wq_data(work) != cwq);
288                 work_clear_pending(work);
289                 lock_map_acquire(&cwq->wq->lockdep_map);
290                 lock_map_acquire(&lockdep_map);
291                 f(work);
292                 lock_map_release(&lockdep_map);
293                 lock_map_release(&cwq->wq->lockdep_map);
294
295                 if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
296                         printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
297                                         "%s/0x%08x/%d\n",
298                                         current->comm, preempt_count(),
299                                         task_pid_nr(current));
300                         printk(KERN_ERR "    last function: ");
301                         print_symbol("%s\n", (unsigned long)f);
302                         debug_show_held_locks(current);
303                         dump_stack();
304                 }
305
306                 spin_lock_irq(&cwq->lock);
307                 cwq->current_work = NULL;
308         }
309         spin_unlock_irq(&cwq->lock);
310 }
311
312 static int worker_thread(void *__cwq)
313 {
314         struct cpu_workqueue_struct *cwq = __cwq;
315         DEFINE_WAIT(wait);
316
317         if (cwq->wq->freezeable)
318                 set_freezable();
319
320         for (;;) {
321                 prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
322                 if (!freezing(current) &&
323                     !kthread_should_stop() &&
324                     list_empty(&cwq->worklist))
325                         schedule();
326                 finish_wait(&cwq->more_work, &wait);
327
328                 try_to_freeze();
329
330                 if (kthread_should_stop())
331                         break;
332
333                 run_workqueue(cwq);
334         }
335
336         return 0;
337 }
338
339 struct wq_barrier {
340         struct work_struct      work;
341         struct completion       done;
342 };
343
344 static void wq_barrier_func(struct work_struct *work)
345 {
346         struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
347         complete(&barr->done);
348 }
349
350 static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
351                         struct wq_barrier *barr, struct list_head *head)
352 {
353         INIT_WORK(&barr->work, wq_barrier_func);
354         __set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
355
356         init_completion(&barr->done);
357
358         insert_work(cwq, &barr->work, head);
359 }
360
361 static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
362 {
363         int active = 0;
364         struct wq_barrier barr;
365
366         WARN_ON(cwq->thread == current);
367
368         spin_lock_irq(&cwq->lock);
369         if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
370                 insert_wq_barrier(cwq, &barr, &cwq->worklist);
371                 active = 1;
372         }
373         spin_unlock_irq(&cwq->lock);
374
375         if (active)
376                 wait_for_completion(&barr.done);
377
378         return active;
379 }
380
381 /**
382  * flush_workqueue - ensure that any scheduled work has run to completion.
383  * @wq: workqueue to flush
384  *
385  * Forces execution of the workqueue and blocks until its completion.
386  * This is typically used in driver shutdown handlers.
387  *
388  * We sleep until all works which were queued on entry have been handled,
389  * but we are not livelocked by new incoming ones.
390  *
391  * This function used to run the workqueues itself.  Now we just wait for the
392  * helper threads to do it.
393  */
394 void flush_workqueue(struct workqueue_struct *wq)
395 {
396         const struct cpumask *cpu_map = wq_cpu_map(wq);
397         int cpu;
398
399         might_sleep();
400         lock_map_acquire(&wq->lockdep_map);
401         lock_map_release(&wq->lockdep_map);
402         for_each_cpu(cpu, cpu_map)
403                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
404 }
405 EXPORT_SYMBOL_GPL(flush_workqueue);
406
407 /**
408  * flush_work - block until a work_struct's callback has terminated
409  * @work: the work which is to be flushed
410  *
411  * Returns false if @work has already terminated.
412  *
413  * It is expected that, prior to calling flush_work(), the caller has
414  * arranged for the work to not be requeued, otherwise it doesn't make
415  * sense to use this function.
416  */
417 int flush_work(struct work_struct *work)
418 {
419         struct cpu_workqueue_struct *cwq;
420         struct list_head *prev;
421         struct wq_barrier barr;
422
423         might_sleep();
424         cwq = get_wq_data(work);
425         if (!cwq)
426                 return 0;
427
428         lock_map_acquire(&cwq->wq->lockdep_map);
429         lock_map_release(&cwq->wq->lockdep_map);
430
431         prev = NULL;
432         spin_lock_irq(&cwq->lock);
433         if (!list_empty(&work->entry)) {
434                 /*
435                  * See the comment near try_to_grab_pending()->smp_rmb().
436                  * If it was re-queued under us we are not going to wait.
437                  */
438                 smp_rmb();
439                 if (unlikely(cwq != get_wq_data(work)))
440                         goto out;
441                 prev = &work->entry;
442         } else {
443                 if (cwq->current_work != work)
444                         goto out;
445                 prev = &cwq->worklist;
446         }
447         insert_wq_barrier(cwq, &barr, prev->next);
448 out:
449         spin_unlock_irq(&cwq->lock);
450         if (!prev)
451                 return 0;
452
453         wait_for_completion(&barr.done);
454         return 1;
455 }
456 EXPORT_SYMBOL_GPL(flush_work);
457
458 /*
459  * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
460  * so this work can't be re-armed in any way.
461  */
462 static int try_to_grab_pending(struct work_struct *work)
463 {
464         struct cpu_workqueue_struct *cwq;
465         int ret = -1;
466
467         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
468                 return 0;
469
470         /*
471          * The queueing is in progress, or it is already queued. Try to
472          * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
473          */
474
475         cwq = get_wq_data(work);
476         if (!cwq)
477                 return ret;
478
479         spin_lock_irq(&cwq->lock);
480         if (!list_empty(&work->entry)) {
481                 /*
482                  * This work is queued, but perhaps we locked the wrong cwq.
483                  * In that case we must see the new value after rmb(), see
484                  * insert_work()->wmb().
485                  */
486                 smp_rmb();
487                 if (cwq == get_wq_data(work)) {
488                         list_del_init(&work->entry);
489                         ret = 1;
490                 }
491         }
492         spin_unlock_irq(&cwq->lock);
493
494         return ret;
495 }
496
497 static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
498                                 struct work_struct *work)
499 {
500         struct wq_barrier barr;
501         int running = 0;
502
503         spin_lock_irq(&cwq->lock);
504         if (unlikely(cwq->current_work == work)) {
505                 insert_wq_barrier(cwq, &barr, cwq->worklist.next);
506                 running = 1;
507         }
508         spin_unlock_irq(&cwq->lock);
509
510         if (unlikely(running))
511                 wait_for_completion(&barr.done);
512 }
513
514 static void wait_on_work(struct work_struct *work)
515 {
516         struct cpu_workqueue_struct *cwq;
517         struct workqueue_struct *wq;
518         const struct cpumask *cpu_map;
519         int cpu;
520
521         might_sleep();
522
523         lock_map_acquire(&work->lockdep_map);
524         lock_map_release(&work->lockdep_map);
525
526         cwq = get_wq_data(work);
527         if (!cwq)
528                 return;
529
530         wq = cwq->wq;
531         cpu_map = wq_cpu_map(wq);
532
533         for_each_cpu(cpu, cpu_map)
534                 wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
535 }
536
537 static int __cancel_work_timer(struct work_struct *work,
538                                 struct timer_list* timer)
539 {
540         int ret;
541
542         do {
543                 ret = (timer && likely(del_timer(timer)));
544                 if (!ret)
545                         ret = try_to_grab_pending(work);
546                 wait_on_work(work);
547         } while (unlikely(ret < 0));
548
549         work_clear_pending(work);
550         return ret;
551 }
552
553 /**
554  * cancel_work_sync - block until a work_struct's callback has terminated
555  * @work: the work which is to be flushed
556  *
557  * Returns true if @work was pending.
558  *
559  * cancel_work_sync() will cancel the work if it is queued. If the work's
560  * callback appears to be running, cancel_work_sync() will block until it
561  * has completed.
562  *
563  * It is possible to use this function if the work re-queues itself. It can
564  * cancel the work even if it migrates to another workqueue, however in that
565  * case it only guarantees that work->func() has completed on the last queued
566  * workqueue.
567  *
568  * cancel_work_sync(&delayed_work->work) should be used only if ->timer is not
569  * pending, otherwise it goes into a busy-wait loop until the timer expires.
570  *
571  * The caller must ensure that workqueue_struct on which this work was last
572  * queued can't be destroyed before this function returns.
573  */
574 int cancel_work_sync(struct work_struct *work)
575 {
576         return __cancel_work_timer(work, NULL);
577 }
578 EXPORT_SYMBOL_GPL(cancel_work_sync);
579
580 /**
581  * cancel_delayed_work_sync - reliably kill off a delayed work.
582  * @dwork: the delayed work struct
583  *
584  * Returns true if @dwork was pending.
585  *
586  * It is possible to use this function if @dwork rearms itself via queue_work()
587  * or queue_delayed_work(). See also the comment for cancel_work_sync().
588  */
589 int cancel_delayed_work_sync(struct delayed_work *dwork)
590 {
591         return __cancel_work_timer(&dwork->work, &dwork->timer);
592 }
593 EXPORT_SYMBOL(cancel_delayed_work_sync);
594
595 static struct workqueue_struct *keventd_wq __read_mostly;
596
597 /**
598  * schedule_work - put work task in global workqueue
599  * @work: job to be done
600  *
601  * Returns zero if @work was already on the kernel-global workqueue and
602  * non-zero otherwise.
603  *
604  * This puts a job in the kernel-global workqueue if it was not already
605  * queued and leaves it in the same position on the kernel-global
606  * workqueue otherwise.
607  */
608 int schedule_work(struct work_struct *work)
609 {
610         return queue_work(keventd_wq, work);
611 }
612 EXPORT_SYMBOL(schedule_work);
613
614 /*
615  * schedule_work_on - put work task on a specific cpu
616  * @cpu: cpu to put the work task on
617  * @work: job to be done
618  *
619  * This puts a job on a specific cpu
620  */
621 int schedule_work_on(int cpu, struct work_struct *work)
622 {
623         return queue_work_on(cpu, keventd_wq, work);
624 }
625 EXPORT_SYMBOL(schedule_work_on);
626
627 /**
628  * schedule_delayed_work - put work task in global workqueue after delay
629  * @dwork: job to be done
630  * @delay: number of jiffies to wait or 0 for immediate execution
631  *
632  * After waiting for a given time this puts a job in the kernel-global
633  * workqueue.
634  */
635 int schedule_delayed_work(struct delayed_work *dwork,
636                                         unsigned long delay)
637 {
638         return queue_delayed_work(keventd_wq, dwork, delay);
639 }
640 EXPORT_SYMBOL(schedule_delayed_work);
641
642 /**
643  * flush_delayed_work - block until a dwork_struct's callback has terminated
644  * @dwork: the delayed work which is to be flushed
645  *
646  * Any timeout is cancelled, and any pending work is run immediately.
647  */
648 void flush_delayed_work(struct delayed_work *dwork)
649 {
650         if (del_timer_sync(&dwork->timer)) {
651                 struct cpu_workqueue_struct *cwq;
652                 cwq = wq_per_cpu(keventd_wq, get_cpu());
653                 __queue_work(cwq, &dwork->work);
654                 put_cpu();
655         }
656         flush_work(&dwork->work);
657 }
658 EXPORT_SYMBOL(flush_delayed_work);
659
660 /**
661  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
662  * @cpu: cpu to use
663  * @dwork: job to be done
664  * @delay: number of jiffies to wait
665  *
666  * After waiting for a given time this puts a job in the kernel-global
667  * workqueue on the specified CPU.
668  */
669 int schedule_delayed_work_on(int cpu,
670                         struct delayed_work *dwork, unsigned long delay)
671 {
672         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
673 }
674 EXPORT_SYMBOL(schedule_delayed_work_on);
675
676 /**
677  * schedule_on_each_cpu - call a function on each online CPU from keventd
678  * @func: the function to call
679  *
680  * Returns zero on success.
681  * Returns -ve errno on failure.
682  *
683  * schedule_on_each_cpu() is very slow.
684  */
685 int schedule_on_each_cpu(work_func_t func)
686 {
687         int cpu;
688         int orig = -1;
689         struct work_struct *works;
690
691         works = alloc_percpu(struct work_struct);
692         if (!works)
693                 return -ENOMEM;
694
695         /*
696          * when running in keventd don't schedule a work item on itself.
697          * Can just call directly because the work queue is already bound.
698          * This also is faster.
699          * Make this a generic parameter for other workqueues?
700          */
701         if (current_is_keventd()) {
702                 orig = raw_smp_processor_id();
703                 INIT_WORK(per_cpu_ptr(works, orig), func);
704                 func(per_cpu_ptr(works, orig));
705         }
706
707         get_online_cpus();
708         for_each_online_cpu(cpu) {
709                 struct work_struct *work = per_cpu_ptr(works, cpu);
710
711                 if (cpu == orig)
712                         continue;
713                 INIT_WORK(work, func);
714                 schedule_work_on(cpu, work);
715         }
716         for_each_online_cpu(cpu) {
717                 if (cpu != orig)
718                         flush_work(per_cpu_ptr(works, cpu));
719         }
720         put_online_cpus();
721         free_percpu(works);
722         return 0;
723 }
724
725 void flush_scheduled_work(void)
726 {
727         flush_workqueue(keventd_wq);
728 }
729 EXPORT_SYMBOL(flush_scheduled_work);
730
731 /**
732  * execute_in_process_context - reliably execute the routine with user context
733  * @fn:         the function to execute
734  * @ew:         guaranteed storage for the execute work structure (must
735  *              be available when the work executes)
736  *
737  * Executes the function immediately if process context is available,
738  * otherwise schedules the function for delayed execution.
739  *
740  * Returns:     0 - function was executed
741  *              1 - function was scheduled for execution
742  */
743 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
744 {
745         if (!in_interrupt()) {
746                 fn(&ew->work);
747                 return 0;
748         }
749
750         INIT_WORK(&ew->work, fn);
751         schedule_work(&ew->work);
752
753         return 1;
754 }
755 EXPORT_SYMBOL_GPL(execute_in_process_context);
756
757 int keventd_up(void)
758 {
759         return keventd_wq != NULL;
760 }
761
762 int current_is_keventd(void)
763 {
764         struct cpu_workqueue_struct *cwq;
765         int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
766         int ret = 0;
767
768         BUG_ON(!keventd_wq);
769
770         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
771         if (current == cwq->thread)
772                 ret = 1;
773
774         return ret;
775
776 }
777
778 static struct cpu_workqueue_struct *
779 init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
780 {
781         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
782
783         cwq->wq = wq;
784         spin_lock_init(&cwq->lock);
785         INIT_LIST_HEAD(&cwq->worklist);
786         init_waitqueue_head(&cwq->more_work);
787
788         return cwq;
789 }
790
791 static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
792 {
793         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
794         struct workqueue_struct *wq = cwq->wq;
795         const char *fmt = is_wq_single_threaded(wq) ? "%s" : "%s/%d";
796         struct task_struct *p;
797
798         p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
799         /*
800          * Nobody can add the work_struct to this cwq,
801          *      if (caller is __create_workqueue)
802          *              nobody should see this wq
803          *      else // caller is CPU_UP_PREPARE
804          *              cpu is not on cpu_online_map
805          * so we can abort safely.
806          */
807         if (IS_ERR(p))
808                 return PTR_ERR(p);
809         if (cwq->wq->rt)
810                 sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
811         cwq->thread = p;
812
813         trace_workqueue_creation(cwq->thread, cpu);
814
815         return 0;
816 }
817
818 static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
819 {
820         struct task_struct *p = cwq->thread;
821
822         if (p != NULL) {
823                 if (cpu >= 0)
824                         kthread_bind(p, cpu);
825                 wake_up_process(p);
826         }
827 }
828
829 struct workqueue_struct *__create_workqueue_key(const char *name,
830                                                 int singlethread,
831                                                 int freezeable,
832                                                 int rt,
833                                                 struct lock_class_key *key,
834                                                 const char *lock_name)
835 {
836         struct workqueue_struct *wq;
837         struct cpu_workqueue_struct *cwq;
838         int err = 0, cpu;
839
840         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
841         if (!wq)
842                 return NULL;
843
844         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
845         if (!wq->cpu_wq) {
846                 kfree(wq);
847                 return NULL;
848         }
849
850         wq->name = name;
851         lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
852         wq->singlethread = singlethread;
853         wq->freezeable = freezeable;
854         wq->rt = rt;
855         INIT_LIST_HEAD(&wq->list);
856
857         if (singlethread) {
858                 cwq = init_cpu_workqueue(wq, singlethread_cpu);
859                 err = create_workqueue_thread(cwq, singlethread_cpu);
860                 start_workqueue_thread(cwq, -1);
861         } else {
862                 cpu_maps_update_begin();
863                 /*
864                  * We must place this wq on list even if the code below fails.
865                  * cpu_down(cpu) can remove cpu from cpu_populated_map before
866                  * destroy_workqueue() takes the lock, in that case we leak
867                  * cwq[cpu]->thread.
868                  */
869                 spin_lock(&workqueue_lock);
870                 list_add(&wq->list, &workqueues);
871                 spin_unlock(&workqueue_lock);
872                 /*
873                  * We must initialize cwqs for each possible cpu even if we
874                  * are going to call destroy_workqueue() finally. Otherwise
875                  * cpu_up() can hit the uninitialized cwq once we drop the
876                  * lock.
877                  */
878                 for_each_possible_cpu(cpu) {
879                         cwq = init_cpu_workqueue(wq, cpu);
880                         if (err || !cpu_online(cpu))
881                                 continue;
882                         err = create_workqueue_thread(cwq, cpu);
883                         start_workqueue_thread(cwq, cpu);
884                 }
885                 cpu_maps_update_done();
886         }
887
888         if (err) {
889                 destroy_workqueue(wq);
890                 wq = NULL;
891         }
892         return wq;
893 }
894 EXPORT_SYMBOL_GPL(__create_workqueue_key);
895
896 static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
897 {
898         /*
899          * Our caller is either destroy_workqueue() or CPU_POST_DEAD,
900          * cpu_add_remove_lock protects cwq->thread.
901          */
902         if (cwq->thread == NULL)
903                 return;
904
905         lock_map_acquire(&cwq->wq->lockdep_map);
906         lock_map_release(&cwq->wq->lockdep_map);
907
908         flush_cpu_workqueue(cwq);
909         /*
910          * If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
911          * a concurrent flush_workqueue() can insert a barrier after us.
912          * However, in that case run_workqueue() won't return and check
913          * kthread_should_stop() until it flushes all work_struct's.
914          * When ->worklist becomes empty it is safe to exit because no
915          * more work_structs can be queued on this cwq: flush_workqueue
916          * checks list_empty(), and a "normal" queue_work() can't use
917          * a dead CPU.
918          */
919         trace_workqueue_destruction(cwq->thread);
920         kthread_stop(cwq->thread);
921         cwq->thread = NULL;
922 }
923
924 /**
925  * destroy_workqueue - safely terminate a workqueue
926  * @wq: target workqueue
927  *
928  * Safely destroy a workqueue. All work currently pending will be done first.
929  */
930 void destroy_workqueue(struct workqueue_struct *wq)
931 {
932         const struct cpumask *cpu_map = wq_cpu_map(wq);
933         int cpu;
934
935         cpu_maps_update_begin();
936         spin_lock(&workqueue_lock);
937         list_del(&wq->list);
938         spin_unlock(&workqueue_lock);
939
940         for_each_cpu(cpu, cpu_map)
941                 cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
942         cpu_maps_update_done();
943
944         free_percpu(wq->cpu_wq);
945         kfree(wq);
946 }
947 EXPORT_SYMBOL_GPL(destroy_workqueue);
948
949 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
950                                                 unsigned long action,
951                                                 void *hcpu)
952 {
953         unsigned int cpu = (unsigned long)hcpu;
954         struct cpu_workqueue_struct *cwq;
955         struct workqueue_struct *wq;
956         int ret = NOTIFY_OK;
957
958         action &= ~CPU_TASKS_FROZEN;
959
960         switch (action) {
961         case CPU_UP_PREPARE:
962                 cpumask_set_cpu(cpu, cpu_populated_map);
963         }
964 undo:
965         list_for_each_entry(wq, &workqueues, list) {
966                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
967
968                 switch (action) {
969                 case CPU_UP_PREPARE:
970                         if (!create_workqueue_thread(cwq, cpu))
971                                 break;
972                         printk(KERN_ERR "workqueue [%s] for %i failed\n",
973                                 wq->name, cpu);
974                         action = CPU_UP_CANCELED;
975                         ret = NOTIFY_BAD;
976                         goto undo;
977
978                 case CPU_ONLINE:
979                         start_workqueue_thread(cwq, cpu);
980                         break;
981
982                 case CPU_UP_CANCELED:
983                         start_workqueue_thread(cwq, -1);
984                 case CPU_POST_DEAD:
985                         cleanup_workqueue_thread(cwq);
986                         break;
987                 }
988         }
989
990         switch (action) {
991         case CPU_UP_CANCELED:
992         case CPU_POST_DEAD:
993                 cpumask_clear_cpu(cpu, cpu_populated_map);
994         }
995
996         return ret;
997 }
998
999 #ifdef CONFIG_SMP
1000
1001 struct work_for_cpu {
1002         struct completion completion;
1003         long (*fn)(void *);
1004         void *arg;
1005         long ret;
1006 };
1007
1008 static int do_work_for_cpu(void *_wfc)
1009 {
1010         struct work_for_cpu *wfc = _wfc;
1011         wfc->ret = wfc->fn(wfc->arg);
1012         complete(&wfc->completion);
1013         return 0;
1014 }
1015
1016 /**
1017  * work_on_cpu - run a function in user context on a particular cpu
1018  * @cpu: the cpu to run on
1019  * @fn: the function to run
1020  * @arg: the function arg
1021  *
1022  * This will return the value @fn returns.
1023  * It is up to the caller to ensure that the cpu doesn't go offline.
1024  * The caller must not hold any locks which would prevent @fn from completing.
1025  */
1026 long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
1027 {
1028         struct task_struct *sub_thread;
1029         struct work_for_cpu wfc = {
1030                 .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
1031                 .fn = fn,
1032                 .arg = arg,
1033         };
1034
1035         sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
1036         if (IS_ERR(sub_thread))
1037                 return PTR_ERR(sub_thread);
1038         kthread_bind(sub_thread, cpu);
1039         wake_up_process(sub_thread);
1040         wait_for_completion(&wfc.completion);
1041         return wfc.ret;
1042 }
1043 EXPORT_SYMBOL_GPL(work_on_cpu);
1044 #endif /* CONFIG_SMP */
1045
1046 void __init init_workqueues(void)
1047 {
1048         alloc_cpumask_var(&cpu_populated_map, GFP_KERNEL);
1049
1050         cpumask_copy(cpu_populated_map, cpu_online_mask);
1051         singlethread_cpu = cpumask_first(cpu_possible_mask);
1052         cpu_singlethread_map = cpumask_of(singlethread_cpu);
1053         hotcpu_notifier(workqueue_cpu_callback, 0);
1054         keventd_wq = create_workqueue("events");
1055         BUG_ON(!keventd_wq);
1056 }