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 #include <linux/freezer.h>
  33 #include <linux/kallsyms.h>
  34 #include <linux/debug_locks.h>
  35
  36 /*
  37  * The per-CPU workqueue (if single thread, we always use the first
  38  * possible cpu).
  39  *
  40  * The sequence counters are for flush_scheduled_work().  It wants to wait
  41  * until all currently-scheduled works are completed, but it doesn't
  42  * want to be livelocked by new, incoming ones.  So it waits until
  43  * remove_sequence is >= the insert_sequence which pertained when
  44  * flush_scheduled_work() was called.
  45  */
  46 struct cpu_workqueue_struct {
  47
  48         spinlock_t lock;
  49
  50         long remove_sequence;   /* Least-recently added (next to run) */
  51         long insert_sequence;   /* Next to add */
  52
  53         struct list_head worklist;
  54         wait_queue_head_t more_work;
  55         wait_queue_head_t work_done;
  56
  57         struct workqueue_struct *wq;
  58         struct task_struct *thread;
  59
  60         int run_depth;          /* Detect run_workqueue() recursion depth */
  61
  62         int freezeable;         /* Freeze the thread during suspend */
  63 } ____cacheline_aligned;
  64
  65 /*
  66  * The externally visible workqueue abstraction is an array of
  67  * per-CPU workqueues:
  68  */
  69 struct workqueue_struct {
  70         struct cpu_workqueue_struct *cpu_wq;
  71         const char *name;
  72         struct list_head list;  /* Empty if single thread */
  73 };
  74
  75 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
  76    threads to each one as cpus come/go. */
  77 static DEFINE_MUTEX(workqueue_mutex);
  78 static LIST_HEAD(workqueues);
  79
  80 static int singlethread_cpu;
  81
  82 /* If it's single threaded, it isn't in the list of workqueues. */
  83 static inline int is_single_threaded(struct workqueue_struct *wq)
  84 {
  85         return list_empty(&wq->list);
  86 }
  87
  88 /*
  89  * Set the workqueue on which a work item is to be run
  90  * - Must *only* be called if the pending flag is set
  91  */
  92 static inline void set_wq_data(struct work_struct *work, void *wq)
  93 {
  94         unsigned long new;
  95
  96         BUG_ON(!work_pending(work));
  97
  98         new = (unsigned long) wq | (1UL << WORK_STRUCT_PENDING);
  99         new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
 100         atomic_long_set(&work->data, new);
 101 }
 102
 103 static inline void *get_wq_data(struct work_struct *work)
 104 {
 105         return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
 106 }
 107
 108 static int __run_work(struct cpu_workqueue_struct *cwq, struct work_struct *work)
 109 {
 110         int ret = 0;
 111         unsigned long flags;
 112
 113         spin_lock_irqsave(&cwq->lock, flags);
 114         /*
 115          * We need to re-validate the work info after we've gotten
 116          * the cpu_workqueue lock. We can run the work now iff:
 117          *
 118          *  - the wq_data still matches the cpu_workqueue_struct
 119          *  - AND the work is still marked pending
 120          *  - AND the work is still on a list (which will be this
 121          *    workqueue_struct list)
 122          *
 123          * All these conditions are important, because we
 124          * need to protect against the work being run right
 125          * now on another CPU (all but the last one might be
 126          * true if it's currently running and has not been
 127          * released yet, for example).
 128          */
 129         if (get_wq_data(work) == cwq
 130             && work_pending(work)
 131             && !list_empty(&work->entry)) {
 132                 work_func_t f = work->func;
 133                 list_del_init(&work->entry);
 134                 spin_unlock_irqrestore(&cwq->lock, flags);
 135
 136                 if (!test_bit(WORK_STRUCT_NOAUTOREL, work_data_bits(work)))
 137                         work_release(work);
 138                 f(work);
 139
 140                 spin_lock_irqsave(&cwq->lock, flags);
 141                 cwq->remove_sequence++;
 142                 wake_up(&cwq->work_done);
 143                 ret = 1;
 144         }
 145         spin_unlock_irqrestore(&cwq->lock, flags);
 146         return ret;
 147 }
 148
 149 /**
 150  * run_scheduled_work - run scheduled work synchronously
 151  * @work: work to run
 152  *
 153  * This checks if the work was pending, and runs it
 154  * synchronously if so. It returns a boolean to indicate
 155  * whether it had any scheduled work to run or not.
 156  *
 157  * NOTE! This _only_ works for normal work_structs. You
 158  * CANNOT use this for delayed work, because the wq data
 159  * for delayed work will not point properly to the per-
 160  * CPU workqueue struct, but will change!
 161  */
 162 int fastcall run_scheduled_work(struct work_struct *work)
 163 {
 164         for (;;) {
 165                 struct cpu_workqueue_struct *cwq;
 166
 167                 if (!work_pending(work))
 168                         return 0;
 169                 if (list_empty(&work->entry))
 170                         return 0;
 171                 /* NOTE! This depends intimately on __queue_work! */
 172                 cwq = get_wq_data(work);
 173                 if (!cwq)
 174                         return 0;
 175                 if (__run_work(cwq, work))
 176                         return 1;
 177         }
 178 }
 179 EXPORT_SYMBOL(run_scheduled_work);
 180
 181 /* Preempt must be disabled. */
 182 static void __queue_work(struct cpu_workqueue_struct *cwq,
 183                          struct work_struct *work)
 184 {
 185         unsigned long flags;
 186
 187         spin_lock_irqsave(&cwq->lock, flags);
 188         set_wq_data(work, cwq);
 189         list_add_tail(&work->entry, &cwq->worklist);
 190         cwq->insert_sequence++;
 191         wake_up(&cwq->more_work);
 192         spin_unlock_irqrestore(&cwq->lock, flags);
 193 }
 194
 195 /**
 196  * queue_work - queue work on a workqueue
 197  * @wq: workqueue to use
 198  * @work: work to queue
 199  *
 200  * Returns 0 if @work was already on a queue, non-zero otherwise.
 201  *
 202  * We queue the work to the CPU it was submitted, but there is no
 203  * guarantee that it will be processed by that CPU.
 204  */
 205 int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 206 {
 207         int ret = 0, cpu = get_cpu();
 208
 209         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 210                 if (unlikely(is_single_threaded(wq)))
 211                         cpu = singlethread_cpu;
 212                 BUG_ON(!list_empty(&work->entry));
 213                 __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 214                 ret = 1;
 215         }
 216         put_cpu();
 217         return ret;
 218 }
 219 EXPORT_SYMBOL_GPL(queue_work);
 220
 221 void delayed_work_timer_fn(unsigned long __data)
 222 {
 223         struct delayed_work *dwork = (struct delayed_work *)__data;
 224         struct workqueue_struct *wq = get_wq_data(&dwork->work);
 225         int cpu = smp_processor_id();
 226
 227         if (unlikely(is_single_threaded(wq)))
 228                 cpu = singlethread_cpu;
 229
 230         __queue_work(per_cpu_ptr(wq->cpu_wq, cpu), &dwork->work);
 231 }
 232
 233 /**
 234  * queue_delayed_work - queue work on a workqueue after delay
 235  * @wq: workqueue to use
 236  * @dwork: delayable work to queue
 237  * @delay: number of jiffies to wait before queueing
 238  *
 239  * Returns 0 if @work was already on a queue, non-zero otherwise.
 240  */
 241 int fastcall queue_delayed_work(struct workqueue_struct *wq,
 242                         struct delayed_work *dwork, unsigned long delay)
 243 {
 244         int ret = 0;
 245         struct timer_list *timer = &dwork->timer;
 246         struct work_struct *work = &dwork->work;
 247
 248         timer_stats_timer_set_start_info(timer);
 249         if (delay == 0)
 250                 return queue_work(wq, work);
 251
 252         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 253                 BUG_ON(timer_pending(timer));
 254                 BUG_ON(!list_empty(&work->entry));
 255
 256                 /* This stores wq for the moment, for the timer_fn */
 257                 set_wq_data(work, wq);
 258                 timer->expires = jiffies + delay;
 259                 timer->data = (unsigned long)dwork;
 260                 timer->function = delayed_work_timer_fn;
 261                 add_timer(timer);
 262                 ret = 1;
 263         }
 264         return ret;
 265 }
 266 EXPORT_SYMBOL_GPL(queue_delayed_work);
 267
 268 /**
 269  * queue_delayed_work_on - queue work on specific CPU after delay
 270  * @cpu: CPU number to execute work on
 271  * @wq: workqueue to use
 272  * @dwork: work to queue
 273  * @delay: number of jiffies to wait before queueing
 274  *
 275  * Returns 0 if @work was already on a queue, non-zero otherwise.
 276  */
 277 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 278                         struct delayed_work *dwork, unsigned long delay)
 279 {
 280         int ret = 0;
 281         struct timer_list *timer = &dwork->timer;
 282         struct work_struct *work = &dwork->work;
 283
 284         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 285                 BUG_ON(timer_pending(timer));
 286                 BUG_ON(!list_empty(&work->entry));
 287
 288                 /* This stores wq for the moment, for the timer_fn */
 289                 set_wq_data(work, wq);
 290                 timer->expires = jiffies + delay;
 291                 timer->data = (unsigned long)dwork;
 292                 timer->function = delayed_work_timer_fn;
 293                 add_timer_on(timer, cpu);
 294                 ret = 1;
 295         }
 296         return ret;
 297 }
 298 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
 299
 300 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 301 {
 302         unsigned long flags;
 303
 304         /*
 305          * Keep taking off work from the queue until
 306          * done.
 307          */
 308         spin_lock_irqsave(&cwq->lock, flags);
 309         cwq->run_depth++;
 310         if (cwq->run_depth > 3) {
 311                 /* morton gets to eat his hat */
 312                 printk("%s: recursion depth exceeded: %d\n",
 313                         __FUNCTION__, cwq->run_depth);
 314                 dump_stack();
 315         }
 316         while (!list_empty(&cwq->worklist)) {
 317                 struct work_struct *work = list_entry(cwq->worklist.next,
 318                                                 struct work_struct, entry);
 319                 work_func_t f = work->func;
 320
 321                 list_del_init(cwq->worklist.next);
 322                 spin_unlock_irqrestore(&cwq->lock, flags);
 323
 324                 BUG_ON(get_wq_data(work) != cwq);
 325                 if (!test_bit(WORK_STRUCT_NOAUTOREL, work_data_bits(work)))
 326                         work_release(work);
 327                 f(work);
 328
 329                 if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
 330                         printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
 331                                         "%s/0x%08x/%d\n",
 332                                         current->comm, preempt_count(),
 333                                         current->pid);
 334                         printk(KERN_ERR "    last function: ");
 335                         print_symbol("%s\n", (unsigned long)f);
 336                         debug_show_held_locks(current);
 337                         dump_stack();
 338                 }
 339
 340                 spin_lock_irqsave(&cwq->lock, flags);
 341                 cwq->remove_sequence++;
 342                 wake_up(&cwq->work_done);
 343         }
 344         cwq->run_depth--;
 345         spin_unlock_irqrestore(&cwq->lock, flags);
 346 }
 347
 348 static int worker_thread(void *__cwq)
 349 {
 350         struct cpu_workqueue_struct *cwq = __cwq;
 351         DECLARE_WAITQUEUE(wait, current);
 352         struct k_sigaction sa;
 353         sigset_t blocked;
 354
 355         if (!cwq->freezeable)
 356                 current->flags |= PF_NOFREEZE;
 357
 358         set_user_nice(current, -5);
 359
 360         /* Block and flush all signals */
 361         sigfillset(&blocked);
 362         sigprocmask(SIG_BLOCK, &blocked, NULL);
 363         flush_signals(current);
 364
 365         /*
 366          * We inherited MPOL_INTERLEAVE from the booting kernel.
 367          * Set MPOL_DEFAULT to insure node local allocations.
 368          */
 369         numa_default_policy();
 370
 371         /* SIG_IGN makes children autoreap: see do_notify_parent(). */
 372         sa.sa.sa_handler = SIG_IGN;
 373         sa.sa.sa_flags = 0;
 374         siginitset(&sa.sa.sa_mask, sigmask(SIGCHLD));
 375         do_sigaction(SIGCHLD, &sa, (struct k_sigaction *)0);
 376
 377         set_current_state(TASK_INTERRUPTIBLE);
 378         while (!kthread_should_stop()) {
 379                 if (cwq->freezeable)
 380                         try_to_freeze();
 381
 382                 add_wait_queue(&cwq->more_work, &wait);
 383                 if (list_empty(&cwq->worklist))
 384                         schedule();
 385                 else
 386                         __set_current_state(TASK_RUNNING);
 387                 remove_wait_queue(&cwq->more_work, &wait);
 388
 389                 if (!list_empty(&cwq->worklist))
 390                         run_workqueue(cwq);
 391                 set_current_state(TASK_INTERRUPTIBLE);
 392         }
 393         __set_current_state(TASK_RUNNING);
 394         return 0;
 395 }
 396
 397 static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 398 {
 399         if (cwq->thread == current) {
 400                 /*
 401                  * Probably keventd trying to flush its own queue. So simply run
 402                  * it by hand rather than deadlocking.
 403                  */
 404                 run_workqueue(cwq);
 405         } else {
 406                 DEFINE_WAIT(wait);
 407                 long sequence_needed;
 408
 409                 spin_lock_irq(&cwq->lock);
 410                 sequence_needed = cwq->insert_sequence;
 411
 412                 while (sequence_needed - cwq->remove_sequence > 0) {
 413                         prepare_to_wait(&cwq->work_done, &wait,
 414                                         TASK_UNINTERRUPTIBLE);
 415                         spin_unlock_irq(&cwq->lock);
 416                         schedule();
 417                         spin_lock_irq(&cwq->lock);
 418                 }
 419                 finish_wait(&cwq->work_done, &wait);
 420                 spin_unlock_irq(&cwq->lock);
 421         }
 422 }
 423
 424 /**
 425  * flush_workqueue - ensure that any scheduled work has run to completion.
 426  * @wq: workqueue to flush
 427  *
 428  * Forces execution of the workqueue and blocks until its completion.
 429  * This is typically used in driver shutdown handlers.
 430  *
 431  * This function will sample each workqueue's current insert_sequence number and
 432  * will sleep until the head sequence is greater than or equal to that.  This
 433  * means that we sleep until all works which were queued on entry have been
 434  * handled, but we are not livelocked by new incoming ones.
 435  *
 436  * This function used to run the workqueues itself.  Now we just wait for the
 437  * helper threads to do it.
 438  */
 439 void fastcall flush_workqueue(struct workqueue_struct *wq)
 440 {
 441         might_sleep();
 442
 443         if (is_single_threaded(wq)) {
 444                 /* Always use first cpu's area. */
 445                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
 446         } else {
 447                 int cpu;
 448
 449                 mutex_lock(&workqueue_mutex);
 450                 for_each_online_cpu(cpu)
 451                         flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 452                 mutex_unlock(&workqueue_mutex);
 453         }
 454 }
 455 EXPORT_SYMBOL_GPL(flush_workqueue);
 456
 457 static struct task_struct *create_workqueue_thread(struct workqueue_struct *wq,
 458                                                    int cpu, int freezeable)
 459 {
 460         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 461         struct task_struct *p;
 462
 463         spin_lock_init(&cwq->lock);
 464         cwq->wq = wq;
 465         cwq->thread = NULL;
 466         cwq->insert_sequence = 0;
 467         cwq->remove_sequence = 0;
 468         cwq->freezeable = freezeable;
 469         INIT_LIST_HEAD(&cwq->worklist);
 470         init_waitqueue_head(&cwq->more_work);
 471         init_waitqueue_head(&cwq->work_done);
 472
 473         if (is_single_threaded(wq))
 474                 p = kthread_create(worker_thread, cwq, "%s", wq->name);
 475         else
 476                 p = kthread_create(worker_thread, cwq, "%s/%d", wq->name, cpu);
 477         if (IS_ERR(p))
 478                 return NULL;
 479         cwq->thread = p;
 480         return p;
 481 }
 482
 483 struct workqueue_struct *__create_workqueue(const char *name,
 484                                             int singlethread, int freezeable)
 485 {
 486         int cpu, destroy = 0;
 487         struct workqueue_struct *wq;
 488         struct task_struct *p;
 489
 490         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
 491         if (!wq)
 492                 return NULL;
 493
 494         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
 495         if (!wq->cpu_wq) {
 496                 kfree(wq);
 497                 return NULL;
 498         }
 499
 500         wq->name = name;
 501         mutex_lock(&workqueue_mutex);
 502         if (singlethread) {
 503                 INIT_LIST_HEAD(&wq->list);
 504                 p = create_workqueue_thread(wq, singlethread_cpu, freezeable);
 505                 if (!p)
 506                         destroy = 1;
 507                 else
 508                         wake_up_process(p);
 509         } else {
 510                 list_add(&wq->list, &workqueues);
 511                 for_each_online_cpu(cpu) {
 512                         p = create_workqueue_thread(wq, cpu, freezeable);
 513                         if (p) {
 514                                 kthread_bind(p, cpu);
 515                                 wake_up_process(p);
 516                         } else
 517                                 destroy = 1;
 518                 }
 519         }
 520         mutex_unlock(&workqueue_mutex);
 521
 522         /*
 523          * Was there any error during startup? If yes then clean up:
 524          */
 525         if (destroy) {
 526                 destroy_workqueue(wq);
 527                 wq = NULL;
 528         }
 529         return wq;
 530 }
 531 EXPORT_SYMBOL_GPL(__create_workqueue);
 532
 533 static void cleanup_workqueue_thread(struct workqueue_struct *wq, int cpu)
 534 {
 535         struct cpu_workqueue_struct *cwq;
 536         unsigned long flags;
 537         struct task_struct *p;
 538
 539         cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 540         spin_lock_irqsave(&cwq->lock, flags);
 541         p = cwq->thread;
 542         cwq->thread = NULL;
 543         spin_unlock_irqrestore(&cwq->lock, flags);
 544         if (p)
 545                 kthread_stop(p);
 546 }
 547
 548 /**
 549  * destroy_workqueue - safely terminate a workqueue
 550  * @wq: target workqueue
 551  *
 552  * Safely destroy a workqueue. All work currently pending will be done first.
 553  */
 554 void destroy_workqueue(struct workqueue_struct *wq)
 555 {
 556         int cpu;
 557
 558         flush_workqueue(wq);
 559
 560         /* We don't need the distraction of CPUs appearing and vanishing. */
 561         mutex_lock(&workqueue_mutex);
 562         if (is_single_threaded(wq))
 563                 cleanup_workqueue_thread(wq, singlethread_cpu);
 564         else {
 565                 for_each_online_cpu(cpu)
 566                         cleanup_workqueue_thread(wq, cpu);
 567                 list_del(&wq->list);
 568         }
 569         mutex_unlock(&workqueue_mutex);
 570         free_percpu(wq->cpu_wq);
 571         kfree(wq);
 572 }
 573 EXPORT_SYMBOL_GPL(destroy_workqueue);
 574
 575 static struct workqueue_struct *keventd_wq;
 576
 577 /**
 578  * schedule_work - put work task in global workqueue
 579  * @work: job to be done
 580  *
 581  * This puts a job in the kernel-global workqueue.
 582  */
 583 int fastcall schedule_work(struct work_struct *work)
 584 {
 585         return queue_work(keventd_wq, work);
 586 }
 587 EXPORT_SYMBOL(schedule_work);
 588
 589 /**
 590  * schedule_delayed_work - put work task in global workqueue after delay
 591  * @dwork: job to be done
 592  * @delay: number of jiffies to wait or 0 for immediate execution
 593  *
 594  * After waiting for a given time this puts a job in the kernel-global
 595  * workqueue.
 596  */
 597 int fastcall schedule_delayed_work(struct delayed_work *dwork,
 598                                         unsigned long delay)
 599 {
 600         timer_stats_timer_set_start_info(&dwork->timer);
 601         return queue_delayed_work(keventd_wq, dwork, delay);
 602 }
 603 EXPORT_SYMBOL(schedule_delayed_work);
 604
 605 /**
 606  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 607  * @cpu: cpu to use
 608  * @dwork: job to be done
 609  * @delay: number of jiffies to wait
 610  *
 611  * After waiting for a given time this puts a job in the kernel-global
 612  * workqueue on the specified CPU.
 613  */
 614 int schedule_delayed_work_on(int cpu,
 615                         struct delayed_work *dwork, unsigned long delay)
 616 {
 617         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
 618 }
 619 EXPORT_SYMBOL(schedule_delayed_work_on);
 620
 621 /**
 622  * schedule_on_each_cpu - call a function on each online CPU from keventd
 623  * @func: the function to call
 624  *
 625  * Returns zero on success.
 626  * Returns -ve errno on failure.
 627  *
 628  * Appears to be racy against CPU hotplug.
 629  *
 630  * schedule_on_each_cpu() is very slow.
 631  */
 632 int schedule_on_each_cpu(work_func_t func)
 633 {
 634         int cpu;
 635         struct work_struct *works;
 636
 637         works = alloc_percpu(struct work_struct);
 638         if (!works)
 639                 return -ENOMEM;
 640
 641         mutex_lock(&workqueue_mutex);
 642         for_each_online_cpu(cpu) {
 643                 struct work_struct *work = per_cpu_ptr(works, cpu);
 644
 645                 INIT_WORK(work, func);
 646                 set_bit(WORK_STRUCT_PENDING, work_data_bits(work));
 647                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), work);
 648         }
 649         mutex_unlock(&workqueue_mutex);
 650         flush_workqueue(keventd_wq);
 651         free_percpu(works);
 652         return 0;
 653 }
 654
 655 void flush_scheduled_work(void)
 656 {
 657         flush_workqueue(keventd_wq);
 658 }
 659 EXPORT_SYMBOL(flush_scheduled_work);
 660
 661 /**
 662  * cancel_rearming_delayed_workqueue - reliably kill off a delayed work whose handler rearms the delayed work.
 663  * @wq:   the controlling workqueue structure
 664  * @dwork: the delayed work struct
 665  */
 666 void cancel_rearming_delayed_workqueue(struct workqueue_struct *wq,
 667                                        struct delayed_work *dwork)
 668 {
 669         while (!cancel_delayed_work(dwork))
 670                 flush_workqueue(wq);
 671 }
 672 EXPORT_SYMBOL(cancel_rearming_delayed_workqueue);
 673
 674 /**
 675  * cancel_rearming_delayed_work - reliably kill off a delayed keventd work whose handler rearms the delayed work.
 676  * @dwork: the delayed work struct
 677  */
 678 void cancel_rearming_delayed_work(struct delayed_work *dwork)
 679 {
 680         cancel_rearming_delayed_workqueue(keventd_wq, dwork);
 681 }
 682 EXPORT_SYMBOL(cancel_rearming_delayed_work);
 683
 684 /**
 685  * execute_in_process_context - reliably execute the routine with user context
 686  * @fn:         the function to execute
 687  * @ew:         guaranteed storage for the execute work structure (must
 688  *              be available when the work executes)
 689  *
 690  * Executes the function immediately if process context is available,
 691  * otherwise schedules the function for delayed execution.
 692  *
 693  * Returns:     0 - function was executed
 694  *              1 - function was scheduled for execution
 695  */
 696 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 697 {
 698         if (!in_interrupt()) {
 699                 fn(&ew->work);
 700                 return 0;
 701         }
 702
 703         INIT_WORK(&ew->work, fn);
 704         schedule_work(&ew->work);
 705
 706         return 1;
 707 }
 708 EXPORT_SYMBOL_GPL(execute_in_process_context);
 709
 710 int keventd_up(void)
 711 {
 712         return keventd_wq != NULL;
 713 }
 714
 715 int current_is_keventd(void)
 716 {
 717         struct cpu_workqueue_struct *cwq;
 718         int cpu = smp_processor_id();   /* preempt-safe: keventd is per-cpu */
 719         int ret = 0;
 720
 721         BUG_ON(!keventd_wq);
 722
 723         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 724         if (current == cwq->thread)
 725                 ret = 1;
 726
 727         return ret;
 728
 729 }
 730
 731 /* Take the work from this (downed) CPU. */
 732 static void take_over_work(struct workqueue_struct *wq, unsigned int cpu)
 733 {
 734         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 735         struct list_head list;
 736         struct work_struct *work;
 737
 738         spin_lock_irq(&cwq->lock);
 739         list_replace_init(&cwq->worklist, &list);
 740
 741         while (!list_empty(&list)) {
 742                 printk("Taking work for %s\n", wq->name);
 743                 work = list_entry(list.next,struct work_struct,entry);
 744                 list_del(&work->entry);
 745                 __queue_work(per_cpu_ptr(wq->cpu_wq, smp_processor_id()), work);
 746         }
 747         spin_unlock_irq(&cwq->lock);
 748 }
 749
 750 /* We're holding the cpucontrol mutex here */
 751 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 752                                   unsigned long action,
 753                                   void *hcpu)
 754 {
 755         unsigned int hotcpu = (unsigned long)hcpu;
 756         struct workqueue_struct *wq;
 757
 758         switch (action) {
 759         case CPU_UP_PREPARE:
 760                 mutex_lock(&workqueue_mutex);
 761                 /* Create a new workqueue thread for it. */
 762                 list_for_each_entry(wq, &workqueues, list) {
 763                         if (!create_workqueue_thread(wq, hotcpu, 0)) {
 764                                 printk("workqueue for %i failed\n", hotcpu);
 765                                 return NOTIFY_BAD;
 766                         }
 767                 }
 768                 break;
 769
 770         case CPU_ONLINE:
 771                 /* Kick off worker threads. */
 772                 list_for_each_entry(wq, &workqueues, list) {
 773                         struct cpu_workqueue_struct *cwq;
 774
 775                         cwq = per_cpu_ptr(wq->cpu_wq, hotcpu);
 776                         kthread_bind(cwq->thread, hotcpu);
 777                         wake_up_process(cwq->thread);
 778                 }
 779                 mutex_unlock(&workqueue_mutex);
 780                 break;
 781
 782         case CPU_UP_CANCELED:
 783                 list_for_each_entry(wq, &workqueues, list) {
 784                         if (!per_cpu_ptr(wq->cpu_wq, hotcpu)->thread)
 785                                 continue;
 786                         /* Unbind so it can run. */
 787                         kthread_bind(per_cpu_ptr(wq->cpu_wq, hotcpu)->thread,
 788                                      any_online_cpu(cpu_online_map));
 789                         cleanup_workqueue_thread(wq, hotcpu);
 790                 }
 791                 mutex_unlock(&workqueue_mutex);
 792                 break;
 793
 794         case CPU_DOWN_PREPARE:
 795                 mutex_lock(&workqueue_mutex);
 796                 break;
 797
 798         case CPU_DOWN_FAILED:
 799                 mutex_unlock(&workqueue_mutex);
 800                 break;
 801
 802         case CPU_DEAD:
 803                 list_for_each_entry(wq, &workqueues, list)
 804                         cleanup_workqueue_thread(wq, hotcpu);
 805                 list_for_each_entry(wq, &workqueues, list)
 806                         take_over_work(wq, hotcpu);
 807                 mutex_unlock(&workqueue_mutex);
 808                 break;
 809         }
 810
 811         return NOTIFY_OK;
 812 }
 813
 814 void init_workqueues(void)
 815 {
 816         singlethread_cpu = first_cpu(cpu_possible_map);
 817         hotcpu_notifier(workqueue_cpu_callback, 0);
 818         keventd_wq = create_workqueue("events");
 819         BUG_ON(!keventd_wq);
 820 }
 821