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 #include <linux/mempolicy.h>
  32
  33 /*
  34  * The per-CPU workqueue (if single thread, we always use the first
  35  * possible cpu).
  36  *
  37  * The sequence counters are for flush_scheduled_work().  It wants to wait
  38  * until all currently-scheduled works are completed, but it doesn't
  39  * want to be livelocked by new, incoming ones.  So it waits until
  40  * remove_sequence is >= the insert_sequence which pertained when
  41  * flush_scheduled_work() was called.
  42  */
  43 struct cpu_workqueue_struct {
  44
  45         spinlock_t lock;
  46
  47         long remove_sequence;   /* Least-recently added (next to run) */
  48         long insert_sequence;   /* Next to add */
  49
  50         struct list_head worklist;
  51         wait_queue_head_t more_work;
  52         wait_queue_head_t work_done;
  53
  54         struct workqueue_struct *wq;
  55         struct task_struct *thread;
  56
  57         int run_depth;          /* Detect run_workqueue() recursion depth */
  58 } ____cacheline_aligned;
  59
  60 /*
  61  * The externally visible workqueue abstraction is an array of
  62  * per-CPU workqueues:
  63  */
  64 struct workqueue_struct {
  65         struct cpu_workqueue_struct *cpu_wq;
  66         const char *name;
  67         struct list_head list;  /* Empty if single thread */
  68 };
  69
  70 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
  71    threads to each one as cpus come/go. */
  72 static DEFINE_MUTEX(workqueue_mutex);
  73 static LIST_HEAD(workqueues);
  74
  75 static int singlethread_cpu;
  76
  77 /* If it's single threaded, it isn't in the list of workqueues. */
  78 static inline int is_single_threaded(struct workqueue_struct *wq)
  79 {
  80         return list_empty(&wq->list);
  81 }
  82
  83 static inline void set_wq_data(struct work_struct *work, void *wq)
  84 {
  85         unsigned long new, old, res;
  86
  87         /* assume the pending flag is already set and that the task has already
  88          * been queued on this workqueue */
  89         new = (unsigned long) wq | (1UL << WORK_STRUCT_PENDING);
  90         res = work->management;
  91         if (res != new) {
  92                 do {
  93                         old = res;
  94                         new = (unsigned long) wq;
  95                         new |= (old & WORK_STRUCT_FLAG_MASK);
  96                         res = cmpxchg(&work->management, old, new);
  97                 } while (res != old);
  98         }
  99 }
 100
 101 static inline void *get_wq_data(struct work_struct *work)
 102 {
 103         return (void *) (work->management & WORK_STRUCT_WQ_DATA_MASK);
 104 }
 105
 106 /* Preempt must be disabled. */
 107 static void __queue_work(struct cpu_workqueue_struct *cwq,
 108                          struct work_struct *work)
 109 {
 110         unsigned long flags;
 111
 112         spin_lock_irqsave(&cwq->lock, flags);
 113         set_wq_data(work, cwq);
 114         list_add_tail(&work->entry, &cwq->worklist);
 115         cwq->insert_sequence++;
 116         wake_up(&cwq->more_work);
 117         spin_unlock_irqrestore(&cwq->lock, flags);
 118 }
 119
 120 /**
 121  * queue_work - queue work on a workqueue
 122  * @wq: workqueue to use
 123  * @work: work to queue
 124  *
 125  * Returns 0 if @work was already on a queue, non-zero otherwise.
 126  *
 127  * We queue the work to the CPU it was submitted, but there is no
 128  * guarantee that it will be processed by that CPU.
 129  */
 130 int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 131 {
 132         int ret = 0, cpu = get_cpu();
 133
 134         if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
 135                 if (unlikely(is_single_threaded(wq)))
 136                         cpu = singlethread_cpu;
 137                 BUG_ON(!list_empty(&work->entry));
 138                 __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 139                 ret = 1;
 140         }
 141         put_cpu();
 142         return ret;
 143 }
 144 EXPORT_SYMBOL_GPL(queue_work);
 145
 146 static void delayed_work_timer_fn(unsigned long __data)
 147 {
 148         struct delayed_work *dwork = (struct delayed_work *)__data;
 149         struct workqueue_struct *wq = get_wq_data(&dwork->work);
 150         int cpu = smp_processor_id();
 151
 152         if (unlikely(is_single_threaded(wq)))
 153                 cpu = singlethread_cpu;
 154
 155         __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), &dwork->work);
 156 }
 157
 158 /**
 159  * queue_delayed_work - queue work on a workqueue after delay
 160  * @wq: workqueue to use
 161  * @work: delayable work to queue
 162  * @delay: number of jiffies to wait before queueing
 163  *
 164  * Returns 0 if @work was already on a queue, non-zero otherwise.
 165  */
 166 int fastcall queue_delayed_work(struct workqueue_struct *wq,
 167                         struct delayed_work *dwork, unsigned long delay)
 168 {
 169         int ret = 0;
 170         struct timer_list *timer = &dwork->timer;
 171         struct work_struct *work = &dwork->work;
 172
 173         if (delay == 0)
 174                 return queue_work(wq, work);
 175
 176         if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
 177                 BUG_ON(timer_pending(timer));
 178                 BUG_ON(!list_empty(&work->entry));
 179
 180                 /* This stores wq for the moment, for the timer_fn */
 181                 set_wq_data(work, wq);
 182                 timer->expires = jiffies + delay;
 183                 timer->data = (unsigned long)dwork;
 184                 timer->function = delayed_work_timer_fn;
 185                 add_timer(timer);
 186                 ret = 1;
 187         }
 188         return ret;
 189 }
 190 EXPORT_SYMBOL_GPL(queue_delayed_work);
 191
 192 /**
 193  * queue_delayed_work_on - queue work on specific CPU after delay
 194  * @cpu: CPU number to execute work on
 195  * @wq: workqueue to use
 196  * @work: work to queue
 197  * @delay: number of jiffies to wait before queueing
 198  *
 199  * Returns 0 if @work was already on a queue, non-zero otherwise.
 200  */
 201 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 202                         struct delayed_work *dwork, unsigned long delay)
 203 {
 204         int ret = 0;
 205         struct timer_list *timer = &dwork->timer;
 206         struct work_struct *work = &dwork->work;
 207
 208         if (!test_and_set_bit(WORK_STRUCT_PENDING, &work->management)) {
 209                 BUG_ON(timer_pending(timer));
 210                 BUG_ON(!list_empty(&work->entry));
 211
 212                 /* This stores wq for the moment, for the timer_fn */
 213                 set_wq_data(work, wq);
 214                 timer->expires = jiffies + delay;
 215                 timer->data = (unsigned long)dwork;
 216                 timer->function = delayed_work_timer_fn;
 217                 add_timer_on(timer, cpu);
 218                 ret = 1;
 219         }
 220         return ret;
 221 }
 222 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
 223
 224 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 225 {
 226         unsigned long flags;
 227
 228         /*
 229          * Keep taking off work from the queue until
 230          * done.
 231          */
 232         spin_lock_irqsave(&cwq->lock, flags);
 233         cwq->run_depth++;
 234         if (cwq->run_depth > 3) {
 235                 /* morton gets to eat his hat */
 236                 printk("%s: recursion depth exceeded: %d\n",
 237                         __FUNCTION__, cwq->run_depth);
 238                 dump_stack();
 239         }
 240         while (!list_empty(&cwq->worklist)) {
 241                 struct work_struct *work = list_entry(cwq->worklist.next,
 242                                                 struct work_struct, entry);
 243                 work_func_t f = work->func;
 244
 245                 list_del_init(cwq->worklist.next);
 246                 spin_unlock_irqrestore(&cwq->lock, flags);
 247
 248                 BUG_ON(get_wq_data(work) != cwq);
 249                 if (!test_bit(WORK_STRUCT_NOAUTOREL, &work->management))
 250                         work_release(work);
 251                 f(work);
 252
 253                 spin_lock_irqsave(&cwq->lock, flags);
 254                 cwq->remove_sequence++;
 255                 wake_up(&cwq->work_done);
 256         }
 257         cwq->run_depth--;
 258         spin_unlock_irqrestore(&cwq->lock, flags);
 259 }
 260
 261 static int worker_thread(void *__cwq)
 262 {
 263         struct cpu_workqueue_struct *cwq = __cwq;
 264         DECLARE_WAITQUEUE(wait, current);
 265         struct k_sigaction sa;
 266         sigset_t blocked;
 267
 268         current->flags |= PF_NOFREEZE;
 269
 270         set_user_nice(current, -5);
 271
 272         /* Block and flush all signals */
 273         sigfillset(&blocked);
 274         sigprocmask(SIG_BLOCK, &blocked, NULL);
 275         flush_signals(current);
 276
 277         /*
 278          * We inherited MPOL_INTERLEAVE from the booting kernel.
 279          * Set MPOL_DEFAULT to insure node local allocations.
 280          */
 281         numa_default_policy();
 282
 283         /* SIG_IGN makes children autoreap: see do_notify_parent(). */
 284         sa.sa.sa_handler = SIG_IGN;
 285         sa.sa.sa_flags = 0;
 286         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 287         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 288
 289         set_current_state(TASK_INTERRUPTIBLE);
 290         while (!kthread_should_stop()) {
 291                 add_wait_queue(&cwq->more_work, &wait);
 292                 if (list_empty(&cwq->worklist))
 293                         schedule();
 294                 else
 295                         __set_current_state(TASK_RUNNING);
 296                 remove_wait_queue(&cwq->more_work, &wait);
 297
 298                 if (!list_empty(&cwq->worklist))
 299                         run_workqueue(cwq);
 300                 set_current_state(TASK_INTERRUPTIBLE);
 301         }
 302         __set_current_state(TASK_RUNNING);
 303         return 0;
 304 }
 305
 306 static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 307 {
 308         if (cwq->thread == current) {
 309                 /*
 310                  * Probably keventd trying to flush its own queue. So simply run
 311                  * it by hand rather than deadlocking.
 312                  */
 313                 run_workqueue(cwq);
 314         } else {
 315                 DEFINE_WAIT(wait);
 316                 long sequence_needed;
 317
 318                 spin_lock_irq(&cwq->lock);
 319                 sequence_needed = cwq->insert_sequence;
 320
 321                 while (sequence_needed - cwq->remove_sequence > 0) {
 322                         prepare_to_wait(&cwq->work_done, &wait,
 323                                         TASK_UNINTERRUPTIBLE);
 324                         spin_unlock_irq(&cwq->lock);
 325                         schedule();
 326                         spin_lock_irq(&cwq->lock);
 327                 }
 328                 finish_wait(&cwq->work_done, &wait);
 329                 spin_unlock_irq(&cwq->lock);
 330         }
 331 }
 332
 333 /**
 334  * flush_workqueue - ensure that any scheduled work has run to completion.
 335  * @wq: workqueue to flush
 336  *
 337  * Forces execution of the workqueue and blocks until its completion.
 338  * This is typically used in driver shutdown handlers.
 339  *
 340  * This function will sample each workqueue's current insert_sequence number and
 341  * will sleep until the head sequence is greater than or equal to that.  This
 342  * means that we sleep until all works which were queued on entry have been
 343  * handled, but we are not livelocked by new incoming ones.
 344  *
 345  * This function used to run the workqueues itself.  Now we just wait for the
 346  * helper threads to do it.
 347  */
 348 void fastcall flush_workqueue(struct workqueue_struct *wq)
 349 {
 350         might_sleep();
 351
 352         if (is_single_threaded(wq)) {
 353                 /* Always use first cpu's area. */
 354                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
 355         } else {
 356                 int cpu;
 357
 358                 mutex_lock(&workqueue_mutex);
 359                 for_each_online_cpu(cpu)
 360                         flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 361                 mutex_unlock(&workqueue_mutex);
 362         }
 363 }
 364 EXPORT_SYMBOL_GPL(flush_workqueue);
 365
 366 static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
 367                                                    int cpu)
 368 {
 369         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 370         struct task_struct *p;
 371
 372         spin_lock_init(&cwq->lock);
 373         cwq->wq = wq;
 374         cwq->thread = NULL;
 375         cwq->insert_sequence = 0;
 376         cwq->remove_sequence = 0;
 377         INIT_LIST_HEAD(&cwq->worklist);
 378         init_waitqueue_head(&cwq->more_work);
 379         init_waitqueue_head(&cwq->work_done);
 380
 381         if (is_single_threaded(wq))
 382                 p = kthread_create(worker_thread, cwq, "%s", wq->name);
 383         else
 384                 p = kthread_create(worker_thread, cwq, "%s/%d", wq->name, cpu);
 385         if (IS_ERR(p))
 386                 return NULL;
 387         cwq->thread = p;
 388         return p;
 389 }
 390
 391 struct workqueue_struct *__create_workqueue(const char *name,
 392                                             int singlethread)
 393 {
 394         int cpu, destroy = 0;
 395         struct workqueue_struct *wq;
 396         struct task_struct *p;
 397
 398         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
 399         if (!wq)
 400                 return NULL;
 401
 402         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
 403         if (!wq->cpu_wq) {
 404                 kfree(wq);
 405                 return NULL;
 406         }
 407
 408         wq->name = name;
 409         mutex_lock(&workqueue_mutex);
 410         if (singlethread) {
 411                 INIT_LIST_HEAD(&wq->list);
 412                 p = create_workqueue_thread(wq, singlethread_cpu);
 413                 if (!p)
 414                         destroy = 1;
 415                 else
 416                         wake_up_process(p);
 417         } else {
 418                 list_add(&wq->list, &workqueues);
 419                 for_each_online_cpu(cpu) {
 420                         p = create_workqueue_thread(wq, cpu);
 421                         if (p) {
 422                                 kthread_bind(p, cpu);
 423                                 wake_up_process(p);
 424                         } else
 425                                 destroy = 1;
 426                 }
 427         }
 428         mutex_unlock(&workqueue_mutex);
 429
 430         /*
 431          * Was there any error during startup? If yes then clean up:
 432          */
 433         if (destroy) {
 434                 destroy_workqueue(wq);
 435                 wq = NULL;
 436         }
 437         return wq;
 438 }
 439 EXPORT_SYMBOL_GPL(__create_workqueue);
 440
 441 static void cleanup_workqueue_thread(struct workqueue_struct *wq, int cpu)
 442 {
 443         struct cpu_workqueue_struct *cwq;
 444         unsigned long flags;
 445         struct task_struct *p;
 446
 447         cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 448         spin_lock_irqsave(&cwq->lock, flags);
 449         p = cwq->thread;
 450         cwq->thread = NULL;
 451         spin_unlock_irqrestore(&cwq->lock, flags);
 452         if (p)
 453                 kthread_stop(p);
 454 }
 455
 456 /**
 457  * destroy_workqueue - safely terminate a workqueue
 458  * @wq: target workqueue
 459  *
 460  * Safely destroy a workqueue. All work currently pending will be done first.
 461  */
 462 void destroy_workqueue(struct workqueue_struct *wq)
 463 {
 464         int cpu;
 465
 466         flush_workqueue(wq);
 467
 468         /* We don't need the distraction of CPUs appearing and vanishing. */
 469         mutex_lock(&workqueue_mutex);
 470         if (is_single_threaded(wq))
 471                 cleanup_workqueue_thread(wq, singlethread_cpu);
 472         else {
 473                 for_each_online_cpu(cpu)
 474                         cleanup_workqueue_thread(wq, cpu);
 475                 list_del(&wq->list);
 476         }
 477         mutex_unlock(&workqueue_mutex);
 478         free_percpu(wq->cpu_wq);
 479         kfree(wq);
 480 }
 481 EXPORT_SYMBOL_GPL(destroy_workqueue);
 482
 483 static struct workqueue_struct *keventd_wq;
 484
 485 /**
 486  * schedule_work - put work task in global workqueue
 487  * @work: job to be done
 488  *
 489  * This puts a job in the kernel-global workqueue.
 490  */
 491 int fastcall schedule_work(struct work_struct *work)
 492 {
 493         return queue_work(keventd_wq, work);
 494 }
 495 EXPORT_SYMBOL(schedule_work);
 496
 497 /**
 498  * schedule_delayed_work - put work task in global workqueue after delay
 499  * @dwork: job to be done
 500  * @delay: number of jiffies to wait or 0 for immediate execution
 501  *
 502  * After waiting for a given time this puts a job in the kernel-global
 503  * workqueue.
 504  */
 505 int fastcall schedule_delayed_work(struct delayed_work *dwork, unsigned long delay)
 506 {
 507         return queue_delayed_work(keventd_wq, dwork, delay);
 508 }
 509 EXPORT_SYMBOL(schedule_delayed_work);
 510
 511 /**
 512  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 513  * @cpu: cpu to use
 514  * @dwork: job to be done
 515  * @delay: number of jiffies to wait
 516  *
 517  * After waiting for a given time this puts a job in the kernel-global
 518  * workqueue on the specified CPU.
 519  */
 520 int schedule_delayed_work_on(int cpu,
 521                         struct delayed_work *dwork, unsigned long delay)
 522 {
 523         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
 524 }
 525 EXPORT_SYMBOL(schedule_delayed_work_on);
 526
 527 /**
 528  * schedule_on_each_cpu - call a function on each online CPU from keventd
 529  * @func: the function to call
 530  *
 531  * Returns zero on success.
 532  * Returns -ve errno on failure.
 533  *
 534  * Appears to be racy against CPU hotplug.
 535  *
 536  * schedule_on_each_cpu() is very slow.
 537  */
 538 int schedule_on_each_cpu(work_func_t func)
 539 {
 540         int cpu;
 541         struct work_struct *works;
 542
 543         works = alloc_percpu(struct work_struct);
 544         if (!works)
 545                 return -ENOMEM;
 546
 547         mutex_lock(&workqueue_mutex);
 548         for_each_online_cpu(cpu) {
 549                 INIT_WORK(per_cpu_ptr(works, cpu), func);
 550                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu),
 551                                 per_cpu_ptr(works, cpu));
 552         }
 553         mutex_unlock(&workqueue_mutex);
 554         flush_workqueue(keventd_wq);
 555         free_percpu(works);
 556         return 0;
 557 }
 558
 559 void flush_scheduled_work(void)
 560 {
 561         flush_workqueue(keventd_wq);
 562 }
 563 EXPORT_SYMBOL(flush_scheduled_work);
 564
 565 /**
 566  * cancel_rearming_delayed_workqueue - reliably kill off a delayed
 567  *                      work whose handler rearms the delayed work.
 568  * @wq:   the controlling workqueue structure
 569  * @dwork: the delayed work struct
 570  */
 571 void cancel_rearming_delayed_workqueue(struct workqueue_struct *wq,
 572                                        struct delayed_work *dwork)
 573 {
 574         while (!cancel_delayed_work(dwork))
 575                 flush_workqueue(wq);
 576 }
 577 EXPORT_SYMBOL(cancel_rearming_delayed_workqueue);
 578
 579 /**
 580  * cancel_rearming_delayed_work - reliably kill off a delayed keventd
 581  *                      work whose handler rearms the delayed work.
 582  * @dwork: the delayed work struct
 583  */
 584 void cancel_rearming_delayed_work(struct delayed_work *dwork)
 585 {
 586         cancel_rearming_delayed_workqueue(keventd_wq, dwork);
 587 }
 588 EXPORT_SYMBOL(cancel_rearming_delayed_work);
 589
 590 /**
 591  * execute_in_process_context - reliably execute the routine with user context
 592  * @fn:         the function to execute
 593  * @ew:         guaranteed storage for the execute work structure (must
 594  *              be available when the work executes)
 595  *
 596  * Executes the function immediately if process context is available,
 597  * otherwise schedules the function for delayed execution.
 598  *
 599  * Returns:     0 - function was executed
 600  *              1 - function was scheduled for execution
 601  */
 602 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 603 {
 604         if (!in_interrupt()) {
 605                 fn(&ew->work);
 606                 return 0;
 607         }
 608
 609         INIT_WORK(&ew->work, fn);
 610         schedule_work(&ew->work);
 611
 612         return 1;
 613 }
 614 EXPORT_SYMBOL_GPL(execute_in_process_context);
 615
 616 int keventd_up(void)
 617 {
 618         return keventd_wq != NULL;
 619 }
 620
 621 int current_is_keventd(void)
 622 {
 623         struct cpu_workqueue_struct *cwq;
 624         int cpu = smp_processor_id();   /* preempt-safe: keventd is per-cpu */
 625         int ret = 0;
 626
 627         BUG_ON(!keventd_wq);
 628
 629         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 630         if (current == cwq->thread)
 631                 ret = 1;
 632
 633         return ret;
 634
 635 }
 636
 637 #ifdef CONFIG_HOTPLUG_CPU
 638 /* Take the work from this (downed) CPU. */
 639 static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
 640 {
 641         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 642         struct list_head list;
 643         struct work_struct *work;
 644
 645         spin_lock_irq(&cwq->lock);
 646         list_replace_init(&cwq->worklist, &list);
 647
 648         while (!list_empty(&list)) {
 649                 printk("Taking work for %s\n", wq->name);
 650                 work = list_entry(list.next,struct work_struct,entry);
 651                 list_del(&work->entry);
 652                 __queue_work(per_cpu_ptr(wq->cpu_wq, smp_processor_id()), work);
 653         }
 654         spin_unlock_irq(&cwq->lock);
 655 }
 656
 657 /* We're holding the cpucontrol mutex here */
 658 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 659                                   unsigned long action,
 660                                   void *hcpu)
 661 {
 662         unsigned int hotcpu = (unsigned long)hcpu;
 663         struct workqueue_struct *wq;
 664
 665         switch (action) {
 666         case CPU_UP_PREPARE:
 667                 mutex_lock(&workqueue_mutex);
 668                 /* Create a new workqueue thread for it. */
 669                 list_for_each_entry(wq, &workqueues, list) {
 670                         if (!create_workqueue_thread(wq, hotcpu)) {
 671                                 printk("workqueue for %i failed\n", hotcpu);
 672                                 return NOTIFY_BAD;
 673                         }
 674                 }
 675                 break;
 676
 677         case CPU_ONLINE:
 678                 /* Kick off worker threads. */
 679                 list_for_each_entry(wq, &workqueues, list) {
 680                         struct cpu_workqueue_struct *cwq;
 681
 682                         cwq = per_cpu_ptr(wq->cpu_wq, hotcpu);
 683                         kthread_bind(cwq->thread, hotcpu);
 684                         wake_up_process(cwq->thread);
 685                 }
 686                 mutex_unlock(&workqueue_mutex);
 687                 break;
 688
 689         case CPU_UP_CANCELED:
 690                 list_for_each_entry(wq, &workqueues, list) {
 691                         if (!per_cpu_ptr(wq->cpu_wq, hotcpu)->thread)
 692                                 continue;
 693                         /* Unbind so it can run. */
 694                         kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread,
 695                                      any_online_cpu(cpu_online_map));
 696                         cleanup_workqueue_thread(wq, hotcpu);
 697                 }
 698                 mutex_unlock(&workqueue_mutex);
 699                 break;
 700
 701         case CPU_DOWN_PREPARE:
 702                 mutex_lock(&workqueue_mutex);
 703                 break;
 704
 705         case CPU_DOWN_FAILED:
 706                 mutex_unlock(&workqueue_mutex);
 707                 break;
 708
 709         case CPU_DEAD:
 710                 list_for_each_entry(wq, &workqueues, list)
 711                         cleanup_workqueue_thread(wq, hotcpu);
 712                 list_for_each_entry(wq, &workqueues, list)
 713                         take_over_work(wq, hotcpu);
 714                 mutex_unlock(&workqueue_mutex);
 715                 break;
 716         }
 717
 718         return NOTIFY_OK;
 719 }
 720 #endif
 721
 722 void init_workqueues(void)
 723 {
 724         singlethread_cpu = first_cpu(cpu_possible_map);
 725         hotcpu_notifier(workqueue_cpu_callback, 0);
 726         keventd_wq = create_workqueue("events");
 727         BUG_ON(!keventd_wq);
 728 }
 729