Merge commit 'v2.6.26-rc9' into cpus4096
[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 <andrewm@uow.edu.au>
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
37 /*
38  * The per-CPU workqueue (if single thread, we always use the first
39  * possible cpu).
40  */
41 struct cpu_workqueue_struct {
42
43         spinlock_t lock;
44
45         struct list_head worklist;
46         wait_queue_head_t more_work;
47         struct work_struct *current_work;
48
49         struct workqueue_struct *wq;
50         struct task_struct *thread;
51
52         int run_depth;          /* Detect run_workqueue() recursion depth */
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 #ifdef CONFIG_LOCKDEP
66         struct lockdep_map lockdep_map;
67 #endif
68 };
69
70 /* Serializes the accesses to the list of workqueues. */
71 static DEFINE_SPINLOCK(workqueue_lock);
72 static LIST_HEAD(workqueues);
73
74 static int singlethread_cpu __read_mostly;
75 static cpumask_t cpu_singlethread_map __read_mostly;
76 /*
77  * _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
78  * flushes cwq->worklist. This means that flush_workqueue/wait_on_work
79  * which comes in between can't use for_each_online_cpu(). We could
80  * use cpu_possible_map, the cpumask below is more a documentation
81  * than optimization.
82  */
83 static cpumask_t cpu_populated_map __read_mostly;
84
85 /* If it's single threaded, it isn't in the list of workqueues. */
86 static inline int is_single_threaded(struct workqueue_struct *wq)
87 {
88         return wq->singlethread;
89 }
90
91 static const cpumask_t *wq_cpu_map(struct workqueue_struct *wq)
92 {
93         return is_single_threaded(wq)
94                 ? &cpu_singlethread_map : &cpu_populated_map;
95 }
96
97 static
98 struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
99 {
100         if (unlikely(is_single_threaded(wq)))
101                 cpu = singlethread_cpu;
102         return per_cpu_ptr(wq->cpu_wq, cpu);
103 }
104
105 /*
106  * Set the workqueue on which a work item is to be run
107  * - Must *only* be called if the pending flag is set
108  */
109 static inline void set_wq_data(struct work_struct *work,
110                                 struct cpu_workqueue_struct *cwq)
111 {
112         unsigned long new;
113
114         BUG_ON(!work_pending(work));
115
116         new = (unsigned long) cwq | (1UL << WORK_STRUCT_PENDING);
117         new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
118         atomic_long_set(&work->data, new);
119 }
120
121 static inline
122 struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
123 {
124         return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
125 }
126
127 static void insert_work(struct cpu_workqueue_struct *cwq,
128                                 struct work_struct *work, int tail)
129 {
130         set_wq_data(work, cwq);
131         /*
132          * Ensure that we get the right work->data if we see the
133          * result of list_add() below, see try_to_grab_pending().
134          */
135         smp_wmb();
136         if (tail)
137                 list_add_tail(&work->entry, &cwq->worklist);
138         else
139                 list_add(&work->entry, &cwq->worklist);
140         wake_up(&cwq->more_work);
141 }
142
143 /* Preempt must be disabled. */
144 static void __queue_work(struct cpu_workqueue_struct *cwq,
145                          struct work_struct *work)
146 {
147         unsigned long flags;
148
149         spin_lock_irqsave(&cwq->lock, flags);
150         insert_work(cwq, work, 1);
151         spin_unlock_irqrestore(&cwq->lock, flags);
152 }
153
154 /**
155  * queue_work - queue work on a workqueue
156  * @wq: workqueue to use
157  * @work: work to queue
158  *
159  * Returns 0 if @work was already on a queue, non-zero otherwise.
160  *
161  * We queue the work to the CPU on which it was submitted, but if the CPU dies
162  * it can be processed by another CPU.
163  */
164 int queue_work(struct workqueue_struct *wq, struct work_struct *work)
165 {
166         int ret = 0;
167
168         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
169                 BUG_ON(!list_empty(&work->entry));
170                 __queue_work(wq_per_cpu(wq, get_cpu()), work);
171                 put_cpu();
172                 ret = 1;
173         }
174         return ret;
175 }
176 EXPORT_SYMBOL_GPL(queue_work);
177
178 static void delayed_work_timer_fn(unsigned long __data)
179 {
180         struct delayed_work *dwork = (struct delayed_work *)__data;
181         struct cpu_workqueue_struct *cwq = get_wq_data(&dwork->work);
182         struct workqueue_struct *wq = cwq->wq;
183
184         __queue_work(wq_per_cpu(wq, smp_processor_id()), &dwork->work);
185 }
186
187 /**
188  * queue_delayed_work - queue work on a workqueue after delay
189  * @wq: workqueue to use
190  * @dwork: delayable work to queue
191  * @delay: number of jiffies to wait before queueing
192  *
193  * Returns 0 if @work was already on a queue, non-zero otherwise.
194  */
195 int queue_delayed_work(struct workqueue_struct *wq,
196                         struct delayed_work *dwork, unsigned long delay)
197 {
198         if (delay == 0)
199                 return queue_work(wq, &dwork->work);
200
201         return queue_delayed_work_on(-1, wq, dwork, delay);
202 }
203 EXPORT_SYMBOL_GPL(queue_delayed_work);
204
205 /**
206  * queue_delayed_work_on - queue work on specific CPU after delay
207  * @cpu: CPU number to execute work on
208  * @wq: workqueue to use
209  * @dwork: work to queue
210  * @delay: number of jiffies to wait before queueing
211  *
212  * Returns 0 if @work was already on a queue, non-zero otherwise.
213  */
214 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
215                         struct delayed_work *dwork, unsigned long delay)
216 {
217         int ret = 0;
218         struct timer_list *timer = &dwork->timer;
219         struct work_struct *work = &dwork->work;
220
221         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
222                 BUG_ON(timer_pending(timer));
223                 BUG_ON(!list_empty(&work->entry));
224
225                 timer_stats_timer_set_start_info(&dwork->timer);
226
227                 /* This stores cwq for the moment, for the timer_fn */
228                 set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
229                 timer->expires = jiffies + delay;
230                 timer->data = (unsigned long)dwork;
231                 timer->function = delayed_work_timer_fn;
232
233                 if (unlikely(cpu >= 0))
234                         add_timer_on(timer, cpu);
235                 else
236                         add_timer(timer);
237                 ret = 1;
238         }
239         return ret;
240 }
241 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
242
243 static void run_workqueue(struct cpu_workqueue_struct *cwq)
244 {
245         spin_lock_irq(&cwq->lock);
246         cwq->run_depth++;
247         if (cwq->run_depth > 3) {
248                 /* morton gets to eat his hat */
249                 printk("%s: recursion depth exceeded: %d\n",
250                         __func__, cwq->run_depth);
251                 dump_stack();
252         }
253         while (!list_empty(&cwq->worklist)) {
254                 struct work_struct *work = list_entry(cwq->worklist.next,
255                                                 struct work_struct, entry);
256                 work_func_t f = work->func;
257 #ifdef CONFIG_LOCKDEP
258                 /*
259                  * It is permissible to free the struct work_struct
260                  * from inside the function that is called from it,
261                  * this we need to take into account for lockdep too.
262                  * To avoid bogus "held lock freed" warnings as well
263                  * as problems when looking into work->lockdep_map,
264                  * make a copy and use that here.
265                  */
266                 struct lockdep_map lockdep_map = work->lockdep_map;
267 #endif
268
269                 cwq->current_work = work;
270                 list_del_init(cwq->worklist.next);
271                 spin_unlock_irq(&cwq->lock);
272
273                 BUG_ON(get_wq_data(work) != cwq);
274                 work_clear_pending(work);
275                 lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
276                 lock_acquire(&lockdep_map, 0, 0, 0, 2, _THIS_IP_);
277                 f(work);
278                 lock_release(&lockdep_map, 1, _THIS_IP_);
279                 lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);
280
281                 if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
282                         printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
283                                         "%s/0x%08x/%d\n",
284                                         current->comm, preempt_count(),
285                                         task_pid_nr(current));
286                         printk(KERN_ERR "    last function: ");
287                         print_symbol("%s\n", (unsigned long)f);
288                         debug_show_held_locks(current);
289                         dump_stack();
290                 }
291
292                 spin_lock_irq(&cwq->lock);
293                 cwq->current_work = NULL;
294         }
295         cwq->run_depth--;
296         spin_unlock_irq(&cwq->lock);
297 }
298
299 static int worker_thread(void *__cwq)
300 {
301         struct cpu_workqueue_struct *cwq = __cwq;
302         DEFINE_WAIT(wait);
303
304         if (cwq->wq->freezeable)
305                 set_freezable();
306
307         set_user_nice(current, -5);
308
309         for (;;) {
310                 prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
311                 if (!freezing(current) &&
312                     !kthread_should_stop() &&
313                     list_empty(&cwq->worklist))
314                         schedule();
315                 finish_wait(&cwq->more_work, &wait);
316
317                 try_to_freeze();
318
319                 if (kthread_should_stop())
320                         break;
321
322                 run_workqueue(cwq);
323         }
324
325         return 0;
326 }
327
328 struct wq_barrier {
329         struct work_struct      work;
330         struct completion       done;
331 };
332
333 static void wq_barrier_func(struct work_struct *work)
334 {
335         struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
336         complete(&barr->done);
337 }
338
339 static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
340                                         struct wq_barrier *barr, int tail)
341 {
342         INIT_WORK(&barr->work, wq_barrier_func);
343         __set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
344
345         init_completion(&barr->done);
346
347         insert_work(cwq, &barr->work, tail);
348 }
349
350 static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
351 {
352         int active;
353
354         if (cwq->thread == current) {
355                 /*
356                  * Probably keventd trying to flush its own queue. So simply run
357                  * it by hand rather than deadlocking.
358                  */
359                 run_workqueue(cwq);
360                 active = 1;
361         } else {
362                 struct wq_barrier barr;
363
364                 active = 0;
365                 spin_lock_irq(&cwq->lock);
366                 if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
367                         insert_wq_barrier(cwq, &barr, 1);
368                         active = 1;
369                 }
370                 spin_unlock_irq(&cwq->lock);
371
372                 if (active)
373                         wait_for_completion(&barr.done);
374         }
375
376         return active;
377 }
378
379 /**
380  * flush_workqueue - ensure that any scheduled work has run to completion.
381  * @wq: workqueue to flush
382  *
383  * Forces execution of the workqueue and blocks until its completion.
384  * This is typically used in driver shutdown handlers.
385  *
386  * We sleep until all works which were queued on entry have been handled,
387  * but we are not livelocked by new incoming ones.
388  *
389  * This function used to run the workqueues itself.  Now we just wait for the
390  * helper threads to do it.
391  */
392 void flush_workqueue(struct workqueue_struct *wq)
393 {
394         const cpumask_t *cpu_map = wq_cpu_map(wq);
395         int cpu;
396
397         might_sleep();
398         lock_acquire(&wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
399         lock_release(&wq->lockdep_map, 1, _THIS_IP_);
400         for_each_cpu_mask_nr(cpu, *cpu_map)
401                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
402 }
403 EXPORT_SYMBOL_GPL(flush_workqueue);
404
405 /*
406  * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
407  * so this work can't be re-armed in any way.
408  */
409 static int try_to_grab_pending(struct work_struct *work)
410 {
411         struct cpu_workqueue_struct *cwq;
412         int ret = -1;
413
414         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
415                 return 0;
416
417         /*
418          * The queueing is in progress, or it is already queued. Try to
419          * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
420          */
421
422         cwq = get_wq_data(work);
423         if (!cwq)
424                 return ret;
425
426         spin_lock_irq(&cwq->lock);
427         if (!list_empty(&work->entry)) {
428                 /*
429                  * This work is queued, but perhaps we locked the wrong cwq.
430                  * In that case we must see the new value after rmb(), see
431                  * insert_work()->wmb().
432                  */
433                 smp_rmb();
434                 if (cwq == get_wq_data(work)) {
435                         list_del_init(&work->entry);
436                         ret = 1;
437                 }
438         }
439         spin_unlock_irq(&cwq->lock);
440
441         return ret;
442 }
443
444 static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
445                                 struct work_struct *work)
446 {
447         struct wq_barrier barr;
448         int running = 0;
449
450         spin_lock_irq(&cwq->lock);
451         if (unlikely(cwq->current_work == work)) {
452                 insert_wq_barrier(cwq, &barr, 0);
453                 running = 1;
454         }
455         spin_unlock_irq(&cwq->lock);
456
457         if (unlikely(running))
458                 wait_for_completion(&barr.done);
459 }
460
461 static void wait_on_work(struct work_struct *work)
462 {
463         struct cpu_workqueue_struct *cwq;
464         struct workqueue_struct *wq;
465         const cpumask_t *cpu_map;
466         int cpu;
467
468         might_sleep();
469
470         lock_acquire(&work->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
471         lock_release(&work->lockdep_map, 1, _THIS_IP_);
472
473         cwq = get_wq_data(work);
474         if (!cwq)
475                 return;
476
477         wq = cwq->wq;
478         cpu_map = wq_cpu_map(wq);
479
480         for_each_cpu_mask_nr(cpu, *cpu_map)
481                 wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
482 }
483
484 static int __cancel_work_timer(struct work_struct *work,
485                                 struct timer_list* timer)
486 {
487         int ret;
488
489         do {
490                 ret = (timer && likely(del_timer(timer)));
491                 if (!ret)
492                         ret = try_to_grab_pending(work);
493                 wait_on_work(work);
494         } while (unlikely(ret < 0));
495
496         work_clear_pending(work);
497         return ret;
498 }
499
500 /**
501  * cancel_work_sync - block until a work_struct's callback has terminated
502  * @work: the work which is to be flushed
503  *
504  * Returns true if @work was pending.
505  *
506  * cancel_work_sync() will cancel the work if it is queued. If the work's
507  * callback appears to be running, cancel_work_sync() will block until it
508  * has completed.
509  *
510  * It is possible to use this function if the work re-queues itself. It can
511  * cancel the work even if it migrates to another workqueue, however in that
512  * case it only guarantees that work->func() has completed on the last queued
513  * workqueue.
514  *
515  * cancel_work_sync(&delayed_work->work) should be used only if ->timer is not
516  * pending, otherwise it goes into a busy-wait loop until the timer expires.
517  *
518  * The caller must ensure that workqueue_struct on which this work was last
519  * queued can't be destroyed before this function returns.
520  */
521 int cancel_work_sync(struct work_struct *work)
522 {
523         return __cancel_work_timer(work, NULL);
524 }
525 EXPORT_SYMBOL_GPL(cancel_work_sync);
526
527 /**
528  * cancel_delayed_work_sync - reliably kill off a delayed work.
529  * @dwork: the delayed work struct
530  *
531  * Returns true if @dwork was pending.
532  *
533  * It is possible to use this function if @dwork rearms itself via queue_work()
534  * or queue_delayed_work(). See also the comment for cancel_work_sync().
535  */
536 int cancel_delayed_work_sync(struct delayed_work *dwork)
537 {
538         return __cancel_work_timer(&dwork->work, &dwork->timer);
539 }
540 EXPORT_SYMBOL(cancel_delayed_work_sync);
541
542 static struct workqueue_struct *keventd_wq __read_mostly;
543
544 /**
545  * schedule_work - put work task in global workqueue
546  * @work: job to be done
547  *
548  * This puts a job in the kernel-global workqueue.
549  */
550 int schedule_work(struct work_struct *work)
551 {
552         return queue_work(keventd_wq, work);
553 }
554 EXPORT_SYMBOL(schedule_work);
555
556 /**
557  * schedule_delayed_work - put work task in global workqueue after delay
558  * @dwork: job to be done
559  * @delay: number of jiffies to wait or 0 for immediate execution
560  *
561  * After waiting for a given time this puts a job in the kernel-global
562  * workqueue.
563  */
564 int schedule_delayed_work(struct delayed_work *dwork,
565                                         unsigned long delay)
566 {
567         return queue_delayed_work(keventd_wq, dwork, delay);
568 }
569 EXPORT_SYMBOL(schedule_delayed_work);
570
571 /**
572  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
573  * @cpu: cpu to use
574  * @dwork: job to be done
575  * @delay: number of jiffies to wait
576  *
577  * After waiting for a given time this puts a job in the kernel-global
578  * workqueue on the specified CPU.
579  */
580 int schedule_delayed_work_on(int cpu,
581                         struct delayed_work *dwork, unsigned long delay)
582 {
583         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
584 }
585 EXPORT_SYMBOL(schedule_delayed_work_on);
586
587 /**
588  * schedule_on_each_cpu - call a function on each online CPU from keventd
589  * @func: the function to call
590  *
591  * Returns zero on success.
592  * Returns -ve errno on failure.
593  *
594  * schedule_on_each_cpu() is very slow.
595  */
596 int schedule_on_each_cpu(work_func_t func)
597 {
598         int cpu;
599         struct work_struct *works;
600
601         works = alloc_percpu(struct work_struct);
602         if (!works)
603                 return -ENOMEM;
604
605         get_online_cpus();
606         for_each_online_cpu(cpu) {
607                 struct work_struct *work = per_cpu_ptr(works, cpu);
608
609                 INIT_WORK(work, func);
610                 set_bit(WORK_STRUCT_PENDING, work_data_bits(work));
611                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), work);
612         }
613         flush_workqueue(keventd_wq);
614         put_online_cpus();
615         free_percpu(works);
616         return 0;
617 }
618
619 void flush_scheduled_work(void)
620 {
621         flush_workqueue(keventd_wq);
622 }
623 EXPORT_SYMBOL(flush_scheduled_work);
624
625 /**
626  * execute_in_process_context - reliably execute the routine with user context
627  * @fn:         the function to execute
628  * @ew:         guaranteed storage for the execute work structure (must
629  *              be available when the work executes)
630  *
631  * Executes the function immediately if process context is available,
632  * otherwise schedules the function for delayed execution.
633  *
634  * Returns:     0 - function was executed
635  *              1 - function was scheduled for execution
636  */
637 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
638 {
639         if (!in_interrupt()) {
640                 fn(&ew->work);
641                 return 0;
642         }
643
644         INIT_WORK(&ew->work, fn);
645         schedule_work(&ew->work);
646
647         return 1;
648 }
649 EXPORT_SYMBOL_GPL(execute_in_process_context);
650
651 int keventd_up(void)
652 {
653         return keventd_wq != NULL;
654 }
655
656 int current_is_keventd(void)
657 {
658         struct cpu_workqueue_struct *cwq;
659         int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
660         int ret = 0;
661
662         BUG_ON(!keventd_wq);
663
664         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
665         if (current == cwq->thread)
666                 ret = 1;
667
668         return ret;
669
670 }
671
672 static struct cpu_workqueue_struct *
673 init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
674 {
675         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
676
677         cwq->wq = wq;
678         spin_lock_init(&cwq->lock);
679         INIT_LIST_HEAD(&cwq->worklist);
680         init_waitqueue_head(&cwq->more_work);
681
682         return cwq;
683 }
684
685 static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
686 {
687         struct workqueue_struct *wq = cwq->wq;
688         const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d";
689         struct task_struct *p;
690
691         p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
692         /*
693          * Nobody can add the work_struct to this cwq,
694          *      if (caller is __create_workqueue)
695          *              nobody should see this wq
696          *      else // caller is CPU_UP_PREPARE
697          *              cpu is not on cpu_online_map
698          * so we can abort safely.
699          */
700         if (IS_ERR(p))
701                 return PTR_ERR(p);
702
703         cwq->thread = p;
704
705         return 0;
706 }
707
708 static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
709 {
710         struct task_struct *p = cwq->thread;
711
712         if (p != NULL) {
713                 if (cpu >= 0)
714                         kthread_bind(p, cpu);
715                 wake_up_process(p);
716         }
717 }
718
719 struct workqueue_struct *__create_workqueue_key(const char *name,
720                                                 int singlethread,
721                                                 int freezeable,
722                                                 struct lock_class_key *key,
723                                                 const char *lock_name)
724 {
725         struct workqueue_struct *wq;
726         struct cpu_workqueue_struct *cwq;
727         int err = 0, cpu;
728
729         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
730         if (!wq)
731                 return NULL;
732
733         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
734         if (!wq->cpu_wq) {
735                 kfree(wq);
736                 return NULL;
737         }
738
739         wq->name = name;
740         lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
741         wq->singlethread = singlethread;
742         wq->freezeable = freezeable;
743         INIT_LIST_HEAD(&wq->list);
744
745         if (singlethread) {
746                 cwq = init_cpu_workqueue(wq, singlethread_cpu);
747                 err = create_workqueue_thread(cwq, singlethread_cpu);
748                 start_workqueue_thread(cwq, -1);
749         } else {
750                 get_online_cpus();
751                 spin_lock(&workqueue_lock);
752                 list_add(&wq->list, &workqueues);
753                 spin_unlock(&workqueue_lock);
754
755                 for_each_possible_cpu(cpu) {
756                         cwq = init_cpu_workqueue(wq, cpu);
757                         if (err || !cpu_online(cpu))
758                                 continue;
759                         err = create_workqueue_thread(cwq, cpu);
760                         start_workqueue_thread(cwq, cpu);
761                 }
762                 put_online_cpus();
763         }
764
765         if (err) {
766                 destroy_workqueue(wq);
767                 wq = NULL;
768         }
769         return wq;
770 }
771 EXPORT_SYMBOL_GPL(__create_workqueue_key);
772
773 static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
774 {
775         /*
776          * Our caller is either destroy_workqueue() or CPU_DEAD,
777          * get_online_cpus() protects cwq->thread.
778          */
779         if (cwq->thread == NULL)
780                 return;
781
782         lock_acquire(&cwq->wq->lockdep_map, 0, 0, 0, 2, _THIS_IP_);
783         lock_release(&cwq->wq->lockdep_map, 1, _THIS_IP_);
784
785         flush_cpu_workqueue(cwq);
786         /*
787          * If the caller is CPU_DEAD and cwq->worklist was not empty,
788          * a concurrent flush_workqueue() can insert a barrier after us.
789          * However, in that case run_workqueue() won't return and check
790          * kthread_should_stop() until it flushes all work_struct's.
791          * When ->worklist becomes empty it is safe to exit because no
792          * more work_structs can be queued on this cwq: flush_workqueue
793          * checks list_empty(), and a "normal" queue_work() can't use
794          * a dead CPU.
795          */
796         kthread_stop(cwq->thread);
797         cwq->thread = NULL;
798 }
799
800 /**
801  * destroy_workqueue - safely terminate a workqueue
802  * @wq: target workqueue
803  *
804  * Safely destroy a workqueue. All work currently pending will be done first.
805  */
806 void destroy_workqueue(struct workqueue_struct *wq)
807 {
808         const cpumask_t *cpu_map = wq_cpu_map(wq);
809         int cpu;
810
811         get_online_cpus();
812         spin_lock(&workqueue_lock);
813         list_del(&wq->list);
814         spin_unlock(&workqueue_lock);
815
816         for_each_cpu_mask_nr(cpu, *cpu_map)
817                 cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
818         put_online_cpus();
819
820         free_percpu(wq->cpu_wq);
821         kfree(wq);
822 }
823 EXPORT_SYMBOL_GPL(destroy_workqueue);
824
825 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
826                                                 unsigned long action,
827                                                 void *hcpu)
828 {
829         unsigned int cpu = (unsigned long)hcpu;
830         struct cpu_workqueue_struct *cwq;
831         struct workqueue_struct *wq;
832
833         action &= ~CPU_TASKS_FROZEN;
834
835         switch (action) {
836         case CPU_UP_PREPARE:
837                 cpu_set(cpu, cpu_populated_map);
838         }
839
840         list_for_each_entry(wq, &workqueues, list) {
841                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
842
843                 switch (action) {
844                 case CPU_UP_PREPARE:
845                         if (!create_workqueue_thread(cwq, cpu))
846                                 break;
847                         printk(KERN_ERR "workqueue [%s] for %i failed\n",
848                                 wq->name, cpu);
849                         return NOTIFY_BAD;
850
851                 case CPU_ONLINE:
852                         start_workqueue_thread(cwq, cpu);
853                         break;
854
855                 case CPU_UP_CANCELED:
856                         start_workqueue_thread(cwq, -1);
857                 case CPU_DEAD:
858                         cleanup_workqueue_thread(cwq);
859                         break;
860                 }
861         }
862
863         switch (action) {
864         case CPU_UP_CANCELED:
865         case CPU_DEAD:
866                 cpu_clear(cpu, cpu_populated_map);
867         }
868
869         return NOTIFY_OK;
870 }
871
872 void __init init_workqueues(void)
873 {
874         cpu_populated_map = cpu_online_map;
875         singlethread_cpu = first_cpu(cpu_possible_map);
876         cpu_singlethread_map = cpumask_of_cpu(singlethread_cpu);
877         hotcpu_notifier(workqueue_cpu_callback, 0);
878         keventd_wq = create_workqueue("events");
879         BUG_ON(!keventd_wq);
880 }