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 <clameter@sgi.com>.
  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
  32 /*
  33  * The per-CPU workqueue (if single thread, we always use the first
  34  * possible cpu).
  35  *
  36  * The sequence counters are for flush_scheduled_work().  It wants to wait
  37  * until until all currently-scheduled works are completed, but it doesn't
  38  * want to be livelocked by new, incoming ones.  So it waits until
  39  * remove_sequence is >= the insert_sequence which pertained when
  40  * flush_scheduled_work() was called.
  41  */
  42 struct cpu_workqueue_struct {
  43
  44         spinlock_t lock;
  45
  46         long remove_sequence;   /* Least-recently added (next to run) */
  47         long insert_sequence;   /* Next to add */
  48
  49         struct list_head worklist;
  50         wait_queue_head_t more_work;
  51         wait_queue_head_t work_done;
  52
  53         struct workqueue_struct *wq;
  54         struct task_struct *thread;
  55
  56         int run_depth;          /* Detect run_workqueue() recursion depth */
  57 } ____cacheline_aligned;
  58
  59 /*
  60  * The externally visible workqueue abstraction is an array of
  61  * per-CPU workqueues:
  62  */
  63 struct workqueue_struct {
  64         struct cpu_workqueue_struct *cpu_wq;
  65         const char *name;
  66         struct list_head list;  /* Empty if single thread */
  67 };
  68
  69 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
  70    threads to each one as cpus come/go. */
  71 static DEFINE_MUTEX(workqueue_mutex);
  72 static LIST_HEAD(workqueues);
  73
  74 static int singlethread_cpu;
  75
  76 /* If it's single threaded, it isn't in the list of workqueues. */
  77 static inline int is_single_threaded(struct workqueue_struct *wq)
  78 {
  79         return list_empty(&wq->list);
  80 }
  81
  82 /* Preempt must be disabled. */
  83 static void __queue_work(struct cpu_workqueue_struct *cwq,
  84                          struct work_struct *work)
  85 {
  86         unsigned long flags;
  87
  88         spin_lock_irqsave(&cwq->lock, flags);
  89         work->wq_data = cwq;
  90         list_add_tail(&work->entry, &cwq->worklist);
  91         cwq->insert_sequence++;
  92         wake_up(&cwq->more_work);
  93         spin_unlock_irqrestore(&cwq->lock, flags);
  94 }
  95
  96 /**
  97  * queue_work - queue work on a workqueue
  98  * @wq: workqueue to use
  99  * @work: work to queue
 100  *
 101  * Returns non-zero if it was successfully added.
 102  *
 103  * We queue the work to the CPU it was submitted, but there is no
 104  * guarantee that it will be processed by that CPU.
 105  */
 106 int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 107 {
 108         int ret = 0, cpu = get_cpu();
 109
 110         if (!test_and_set_bit(0, &work->pending)) {
 111                 if (unlikely(is_single_threaded(wq)))
 112                         cpu = singlethread_cpu;
 113                 BUG_ON(!list_empty(&work->entry));
 114                 __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 115                 ret = 1;
 116         }
 117         put_cpu();
 118         return ret;
 119 }
 120 EXPORT_SYMBOL_GPL(queue_work);
 121
 122 static void delayed_work_timer_fn(unsigned long __data)
 123 {
 124         struct work_struct *work = (struct work_struct *)__data;
 125         struct workqueue_struct *wq = work->wq_data;
 126         int cpu = smp_processor_id();
 127
 128         if (unlikely(is_single_threaded(wq)))
 129                 cpu = singlethread_cpu;
 130
 131         __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 132 }
 133
 134 /**
 135  * queue_delayed_work - queue work on a workqueue after delay
 136  * @wq: workqueue to use
 137  * @work: work to queue
 138  * @delay: number of jiffies to wait before queueing
 139  *
 140  * Returns non-zero if it was successfully added.
 141  */
 142 int fastcall queue_delayed_work(struct workqueue_struct *wq,
 143                         struct work_struct *work, unsigned long delay)
 144 {
 145         int ret = 0;
 146         struct timer_list *timer = &work->timer;
 147
 148         if (!test_and_set_bit(0, &work->pending)) {
 149                 BUG_ON(timer_pending(timer));
 150                 BUG_ON(!list_empty(&work->entry));
 151
 152                 /* This stores wq for the moment, for the timer_fn */
 153                 work->wq_data = wq;
 154                 timer->expires = jiffies + delay;
 155                 timer->data = (unsigned long)work;
 156                 timer->function = delayed_work_timer_fn;
 157                 add_timer(timer);
 158                 ret = 1;
 159         }
 160         return ret;
 161 }
 162 EXPORT_SYMBOL_GPL(queue_delayed_work);
 163
 164 /**
 165  * queue_delayed_work_on - queue work on specific CPU after delay
 166  * @cpu: CPU number to execute work on
 167  * @wq: workqueue to use
 168  * @work: work to queue
 169  * @delay: number of jiffies to wait before queueing
 170  *
 171  * Returns non-zero if it was successfully added.
 172  */
 173 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 174                         struct work_struct *work, unsigned long delay)
 175 {
 176         int ret = 0;
 177         struct timer_list *timer = &work->timer;
 178
 179         if (!test_and_set_bit(0, &work->pending)) {
 180                 BUG_ON(timer_pending(timer));
 181                 BUG_ON(!list_empty(&work->entry));
 182
 183                 /* This stores wq for the moment, for the timer_fn */
 184                 work->wq_data = wq;
 185                 timer->expires = jiffies + delay;
 186                 timer->data = (unsigned long)work;
 187                 timer->function = delayed_work_timer_fn;
 188                 add_timer_on(timer, cpu);
 189                 ret = 1;
 190         }
 191         return ret;
 192 }
 193 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
 194
 195 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 196 {
 197         unsigned long flags;
 198
 199         /*
 200          * Keep taking off work from the queue until
 201          * done.
 202          */
 203         spin_lock_irqsave(&cwq->lock, flags);
 204         cwq->run_depth++;
 205         if (cwq->run_depth > 3) {
 206                 /* morton gets to eat his hat */
 207                 printk("%s: recursion depth exceeded: %d\n",
 208                         __FUNCTION__, cwq->run_depth);
 209                 dump_stack();
 210         }
 211         while (!list_empty(&cwq->worklist)) {
 212                 struct work_struct *work = list_entry(cwq->worklist.next,
 213                                                 struct work_struct, entry);
 214                 void (*f) (void *) = work->func;
 215                 void *data = work->data;
 216
 217                 list_del_init(cwq->worklist.next);
 218                 spin_unlock_irqrestore(&cwq->lock, flags);
 219
 220                 BUG_ON(work->wq_data != cwq);
 221                 clear_bit(0, &work->pending);
 222                 f(data);
 223
 224                 spin_lock_irqsave(&cwq->lock, flags);
 225                 cwq->remove_sequence++;
 226                 wake_up(&cwq->work_done);
 227         }
 228         cwq->run_depth--;
 229         spin_unlock_irqrestore(&cwq->lock, flags);
 230 }
 231
 232 static int worker_thread(void *__cwq)
 233 {
 234         struct cpu_workqueue_struct *cwq = __cwq;
 235         DECLARE_WAITQUEUE(wait, current);
 236         struct k_sigaction sa;
 237         sigset_t blocked;
 238
 239         current->flags |= PF_NOFREEZE;
 240
 241         set_user_nice(current, -5);
 242
 243         /* Block and flush all signals */
 244         sigfillset(&blocked);
 245         sigprocmask(SIG_BLOCK, &blocked, NULL);
 246         flush_signals(current);
 247
 248         /* SIG_IGN makes children autoreap: see do_notify_parent(). */
 249         sa.sa.sa_handler = SIG_IGN;
 250         sa.sa.sa_flags = 0;
 251         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 252         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 253
 254         set_current_state(TASK_INTERRUPTIBLE);
 255         while (!kthread_should_stop()) {
 256                 add_wait_queue(&cwq->more_work, &wait);
 257                 if (list_empty(&cwq->worklist))
 258                         schedule();
 259                 else
 260                         __set_current_state(TASK_RUNNING);
 261                 remove_wait_queue(&cwq->more_work, &wait);
 262
 263                 if (!list_empty(&cwq->worklist))
 264                         run_workqueue(cwq);
 265                 set_current_state(TASK_INTERRUPTIBLE);
 266         }
 267         __set_current_state(TASK_RUNNING);
 268         return 0;
 269 }
 270
 271 static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 272 {
 273         if (cwq->thread == current) {
 274                 /*
 275                  * Probably keventd trying to flush its own queue. So simply run
 276                  * it by hand rather than deadlocking.
 277                  */
 278                 run_workqueue(cwq);
 279         } else {
 280                 DEFINE_WAIT(wait);
 281                 long sequence_needed;
 282
 283                 spin_lock_irq(&cwq->lock);
 284                 sequence_needed = cwq->insert_sequence;
 285
 286                 while (sequence_needed - cwq->remove_sequence > 0) {
 287                         prepare_to_wait(&cwq->work_done, &wait,
 288                                         TASK_UNINTERRUPTIBLE);
 289                         spin_unlock_irq(&cwq->lock);
 290                         schedule();
 291                         spin_lock_irq(&cwq->lock);
 292                 }
 293                 finish_wait(&cwq->work_done, &wait);
 294                 spin_unlock_irq(&cwq->lock);
 295         }
 296 }
 297
 298 /**
 299  * flush_workqueue - ensure that any scheduled work has run to completion.
 300  * @wq: workqueue to flush
 301  *
 302  * Forces execution of the workqueue and blocks until its completion.
 303  * This is typically used in driver shutdown handlers.
 304  *
 305  * This function will sample each workqueue's current insert_sequence number and
 306  * will sleep until the head sequence is greater than or equal to that.  This
 307  * means that we sleep until all works which were queued on entry have been
 308  * handled, but we are not livelocked by new incoming ones.
 309  *
 310  * This function used to run the workqueues itself.  Now we just wait for the
 311  * helper threads to do it.
 312  */
 313 void fastcall flush_workqueue(struct workqueue_struct *wq)
 314 {
 315         might_sleep();
 316
 317         if (is_single_threaded(wq)) {
 318                 /* Always use first cpu's area. */
 319                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
 320         } else {
 321                 int cpu;
 322
 323                 mutex_lock(&workqueue_mutex);
 324                 for_each_online_cpu(cpu)
 325                         flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 326                 mutex_unlock(&workqueue_mutex);
 327         }
 328 }
 329 EXPORT_SYMBOL_GPL(flush_workqueue);
 330
 331 static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
 332                                                    int cpu)
 333 {
 334         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 335         struct task_struct *p;
 336
 337         spin_lock_init(&cwq->lock);
 338         cwq->wq = wq;
 339         cwq->thread = NULL;
 340         cwq->insert_sequence = 0;
 341         cwq->remove_sequence = 0;
 342         INIT_LIST_HEAD(&cwq->worklist);
 343         init_waitqueue_head(&cwq->more_work);
 344         init_waitqueue_head(&cwq->work_done);
 345
 346         if (is_single_threaded(wq))
 347                 p = kthread_create(worker_thread, cwq, "%s", wq->name);
 348         else
 349                 p = kthread_create(worker_thread, cwq, "%s/%d", wq->name, cpu);
 350         if (IS_ERR(p))
 351                 return NULL;
 352         cwq->thread = p;
 353         return p;
 354 }
 355
 356 struct workqueue_struct *__create_workqueue(const char *name,
 357                                             int singlethread)
 358 {
 359         int cpu, destroy = 0;
 360         struct workqueue_struct *wq;
 361         struct task_struct *p;
 362
 363         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
 364         if (!wq)
 365                 return NULL;
 366
 367         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
 368         if (!wq->cpu_wq) {
 369                 kfree(wq);
 370                 return NULL;
 371         }
 372
 373         wq->name = name;
 374         mutex_lock(&workqueue_mutex);
 375         if (singlethread) {
 376                 INIT_LIST_HEAD(&wq->list);
 377                 p = create_workqueue_thread(wq, singlethread_cpu);
 378                 if (!p)
 379                         destroy = 1;
 380                 else
 381                         wake_up_process(p);
 382         } else {
 383                 list_add(&wq->list, &workqueues);
 384                 for_each_online_cpu(cpu) {
 385                         p = create_workqueue_thread(wq, cpu);
 386                         if (p) {
 387                                 kthread_bind(p, cpu);
 388                                 wake_up_process(p);
 389                         } else
 390                                 destroy = 1;
 391                 }
 392         }
 393         mutex_unlock(&workqueue_mutex);
 394
 395         /*
 396          * Was there any error during startup? If yes then clean up:
 397          */
 398         if (destroy) {
 399                 destroy_workqueue(wq);
 400                 wq = NULL;
 401         }
 402         return wq;
 403 }
 404 EXPORT_SYMBOL_GPL(__create_workqueue);
 405
 406 static void cleanup_workqueue_thread(struct workqueue_struct *wq, int cpu)
 407 {
 408         struct cpu_workqueue_struct *cwq;
 409         unsigned long flags;
 410         struct task_struct *p;
 411
 412         cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 413         spin_lock_irqsave(&cwq->lock, flags);
 414         p = cwq->thread;
 415         cwq->thread = NULL;
 416         spin_unlock_irqrestore(&cwq->lock, flags);
 417         if (p)
 418                 kthread_stop(p);
 419 }
 420
 421 /**
 422  * destroy_workqueue - safely terminate a workqueue
 423  * @wq: target workqueue
 424  *
 425  * Safely destroy a workqueue. All work currently pending will be done first.
 426  */
 427 void destroy_workqueue(struct workqueue_struct *wq)
 428 {
 429         int cpu;
 430
 431         flush_workqueue(wq);
 432
 433         /* We don't need the distraction of CPUs appearing and vanishing. */
 434         mutex_lock(&workqueue_mutex);
 435         if (is_single_threaded(wq))
 436                 cleanup_workqueue_thread(wq, singlethread_cpu);
 437         else {
 438                 for_each_online_cpu(cpu)
 439                         cleanup_workqueue_thread(wq, cpu);
 440                 list_del(&wq->list);
 441         }
 442         mutex_unlock(&workqueue_mutex);
 443         free_percpu(wq->cpu_wq);
 444         kfree(wq);
 445 }
 446 EXPORT_SYMBOL_GPL(destroy_workqueue);
 447
 448 static struct workqueue_struct *keventd_wq;
 449
 450 /**
 451  * schedule_work - put work task in global workqueue
 452  * @work: job to be done
 453  *
 454  * This puts a job in the kernel-global workqueue.
 455  */
 456 int fastcall schedule_work(struct work_struct *work)
 457 {
 458         return queue_work(keventd_wq, work);
 459 }
 460 EXPORT_SYMBOL(schedule_work);
 461
 462 /**
 463  * schedule_delayed_work - put work task in global workqueue after delay
 464  * @work: job to be done
 465  * @delay: number of jiffies to wait
 466  *
 467  * After waiting for a given time this puts a job in the kernel-global
 468  * workqueue.
 469  */
 470 int fastcall schedule_delayed_work(struct work_struct *work, unsigned long delay)
 471 {
 472         return queue_delayed_work(keventd_wq, work, delay);
 473 }
 474 EXPORT_SYMBOL(schedule_delayed_work);
 475
 476 /**
 477  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 478  * @cpu: cpu to use
 479  * @work: job to be done
 480  * @delay: number of jiffies to wait
 481  *
 482  * After waiting for a given time this puts a job in the kernel-global
 483  * workqueue on the specified CPU.
 484  */
 485 int schedule_delayed_work_on(int cpu,
 486                         struct work_struct *work, unsigned long delay)
 487 {
 488         return queue_delayed_work_on(cpu, keventd_wq, work, delay);
 489 }
 490 EXPORT_SYMBOL(schedule_delayed_work_on);
 491
 492 /**
 493  * schedule_on_each_cpu - call a function on each online CPU from keventd
 494  * @func: the function to call
 495  * @info: a pointer to pass to func()
 496  *
 497  * Returns zero on success.
 498  * Returns -ve errno on failure.
 499  *
 500  * Appears to be racy against CPU hotplug.
 501  *
 502  * schedule_on_each_cpu() is very slow.
 503  */
 504 int schedule_on_each_cpu(void (*func)(void *info), void *info)
 505 {
 506         int cpu;
 507         struct work_struct *works;
 508
 509         works = alloc_percpu(struct work_struct);
 510         if (!works)
 511                 return -ENOMEM;
 512
 513         mutex_lock(&workqueue_mutex);
 514         for_each_online_cpu(cpu) {
 515                 INIT_WORK(per_cpu_ptr(works, cpu), func, info);
 516                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu),
 517                                 per_cpu_ptr(works, cpu));
 518         }
 519         mutex_unlock(&workqueue_mutex);
 520         flush_workqueue(keventd_wq);
 521         free_percpu(works);
 522         return 0;
 523 }
 524
 525 void flush_scheduled_work(void)
 526 {
 527         flush_workqueue(keventd_wq);
 528 }
 529 EXPORT_SYMBOL(flush_scheduled_work);
 530
 531 /**
 532  * cancel_rearming_delayed_workqueue - reliably kill off a delayed
 533  *                      work whose handler rearms the delayed work.
 534  * @wq:   the controlling workqueue structure
 535  * @work: the delayed work struct
 536  */
 537 void cancel_rearming_delayed_workqueue(struct workqueue_struct *wq,
 538                                        struct work_struct *work)
 539 {
 540         while (!cancel_delayed_work(work))
 541                 flush_workqueue(wq);
 542 }
 543 EXPORT_SYMBOL(cancel_rearming_delayed_workqueue);
 544
 545 /**
 546  * cancel_rearming_delayed_work - reliably kill off a delayed keventd
 547  *                      work whose handler rearms the delayed work.
 548  * @work: the delayed work struct
 549  */
 550 void cancel_rearming_delayed_work(struct work_struct *work)
 551 {
 552         cancel_rearming_delayed_workqueue(keventd_wq, work);
 553 }
 554 EXPORT_SYMBOL(cancel_rearming_delayed_work);
 555
 556 /**
 557  * execute_in_process_context - reliably execute the routine with user context
 558  * @fn:         the function to execute
 559  * @data:       data to pass to the function
 560  * @ew:         guaranteed storage for the execute work structure (must
 561  *              be available when the work executes)
 562  *
 563  * Executes the function immediately if process context is available,
 564  * otherwise schedules the function for delayed execution.
 565  *
 566  * Returns:     0 - function was executed
 567  *              1 - function was scheduled for execution
 568  */
 569 int execute_in_process_context(void (*fn)(void *data), void *data,
 570                                struct execute_work *ew)
 571 {
 572         if (!in_interrupt()) {
 573                 fn(data);
 574                 return 0;
 575         }
 576
 577         INIT_WORK(&ew->work, fn, data);
 578         schedule_work(&ew->work);
 579
 580         return 1;
 581 }
 582 EXPORT_SYMBOL_GPL(execute_in_process_context);
 583
 584 int keventd_up(void)
 585 {
 586         return keventd_wq != NULL;
 587 }
 588
 589 int current_is_keventd(void)
 590 {
 591         struct cpu_workqueue_struct *cwq;
 592         int cpu = smp_processor_id();   /* preempt-safe: keventd is per-cpu */
 593         int ret = 0;
 594
 595         BUG_ON(!keventd_wq);
 596
 597         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 598         if (current == cwq->thread)
 599                 ret = 1;
 600
 601         return ret;
 602
 603 }
 604
 605 #ifdef CONFIG_HOTPLUG_CPU
 606 /* Take the work from this (downed) CPU. */
 607 static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
 608 {
 609         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 610         struct list_head list;
 611         struct work_struct *work;
 612
 613         spin_lock_irq(&cwq->lock);
 614         list_replace_init(&cwq->worklist, &list);
 615
 616         while (!list_empty(&list)) {
 617                 printk("Taking work for %s\n", wq->name);
 618                 work = list_entry(list.next,struct work_struct,entry);
 619                 list_del(&work->entry);
 620                 __queue_work(per_cpu_ptr(wq->cpu_wq, smp_processor_id()), work);
 621         }
 622         spin_unlock_irq(&cwq->lock);
 623 }
 624
 625 /* We're holding the cpucontrol mutex here */
 626 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 627                                   unsigned long action,
 628                                   void *hcpu)
 629 {
 630         unsigned int hotcpu = (unsigned long)hcpu;
 631         struct workqueue_struct *wq;
 632
 633         switch (action) {
 634         case CPU_UP_PREPARE:
 635                 mutex_lock(&workqueue_mutex);
 636                 /* Create a new workqueue thread for it. */
 637                 list_for_each_entry(wq, &workqueues, list) {
 638                         if (!create_workqueue_thread(wq, hotcpu)) {
 639                                 printk("workqueue for %i failed\n", hotcpu);
 640                                 return NOTIFY_BAD;
 641                         }
 642                 }
 643                 break;
 644
 645         case CPU_ONLINE:
 646                 /* Kick off worker threads. */
 647                 list_for_each_entry(wq, &workqueues, list) {
 648                         struct cpu_workqueue_struct *cwq;
 649
 650                         cwq = per_cpu_ptr(wq->cpu_wq, hotcpu);
 651                         kthread_bind(cwq->thread, hotcpu);
 652                         wake_up_process(cwq->thread);
 653                 }
 654                 mutex_unlock(&workqueue_mutex);
 655                 break;
 656
 657         case CPU_UP_CANCELED:
 658                 list_for_each_entry(wq, &workqueues, list) {
 659                         if (!per_cpu_ptr(wq->cpu_wq, hotcpu)->thread)
 660                                 continue;
 661                         /* Unbind so it can run. */
 662                         kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread,
 663                                      any_online_cpu(cpu_online_map));
 664                         cleanup_workqueue_thread(wq, hotcpu);
 665                 }
 666                 mutex_unlock(&workqueue_mutex);
 667                 break;
 668
 669         case CPU_DOWN_PREPARE:
 670                 mutex_lock(&workqueue_mutex);
 671                 break;
 672
 673         case CPU_DOWN_FAILED:
 674                 mutex_unlock(&workqueue_mutex);
 675                 break;
 676
 677         case CPU_DEAD:
 678                 list_for_each_entry(wq, &workqueues, list)
 679                         cleanup_workqueue_thread(wq, hotcpu);
 680                 list_for_each_entry(wq, &workqueues, list)
 681                         take_over_work(wq, hotcpu);
 682                 mutex_unlock(&workqueue_mutex);
 683                 break;
 684         }
 685
 686         return NOTIFY_OK;
 687 }
 688 #endif
 689
 690 void init_workqueues(void)
 691 {
 692         singlethread_cpu = first_cpu(cpu_possible_map);
 693         hotcpu_notifier(workqueue_cpu_callback, 0);
 694         keventd_wq = create_workqueue("events");
 695         BUG_ON(!keventd_wq);
 696 }
 697