git.oblomov.eu Git - linux-2.6/blob - 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 struct cpu_workqueue_struct {
  41
  42         spinlock_t lock;
  43
  44         struct list_head worklist;
  45         wait_queue_head_t more_work;
  46         struct work_struct *current_work;
  47
  48         struct workqueue_struct *wq;
  49         struct task_struct *thread;
  50
  51         int run_depth;          /* Detect run_workqueue() recursion depth */
  52 } ____cacheline_aligned;
  53
  54 /*
  55  * The externally visible workqueue abstraction is an array of
  56  * per-CPU workqueues:
  57  */
  58 struct workqueue_struct {
  59         struct cpu_workqueue_struct *cpu_wq;
  60         struct list_head list;
  61         const char *name;
  62         int singlethread;
  63         int freezeable;         /* Freeze threads during suspend */
  64 };
  65
  66 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
  67    threads to each one as cpus come/go. */
  68 static DEFINE_MUTEX(workqueue_mutex);
  69 static LIST_HEAD(workqueues);
  70
  71 static int singlethread_cpu __read_mostly;
  72 static cpumask_t cpu_singlethread_map __read_mostly;
  73 /*
  74  * _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
  75  * flushes cwq->worklist. This means that flush_workqueue/wait_on_work
  76  * which comes in between can't use for_each_online_cpu(). We could
  77  * use cpu_possible_map, the cpumask below is more a documentation
  78  * than optimization.
  79  */
  80 static cpumask_t cpu_populated_map __read_mostly;
  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 wq->singlethread;
  86 }
  87
  88 static const cpumask_t *wq_cpu_map(struct workqueue_struct *wq)
  89 {
  90         return is_single_threaded(wq)
  91                 ? &cpu_singlethread_map : &cpu_populated_map;
  92 }
  93
  94 static
  95 struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
  96 {
  97         if (unlikely(is_single_threaded(wq)))
  98                 cpu = singlethread_cpu;
  99         return per_cpu_ptr(wq->cpu_wq, cpu);
 100 }
 101
 102 /*
 103  * Set the workqueue on which a work item is to be run
 104  * - Must *only* be called if the pending flag is set
 105  */
 106 static inline void set_wq_data(struct work_struct *work,
 107                                 struct cpu_workqueue_struct *cwq)
 108 {
 109         unsigned long new;
 110
 111         BUG_ON(!work_pending(work));
 112
 113         new = (unsigned long) cwq | (1UL << WORK_STRUCT_PENDING);
 114         new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
 115         atomic_long_set(&work->data, new);
 116 }
 117
 118 static inline
 119 struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
 120 {
 121         return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
 122 }
 123
 124 static void insert_work(struct cpu_workqueue_struct *cwq,
 125                                 struct work_struct *work, int tail)
 126 {
 127         set_wq_data(work, cwq);
 128         /*
 129          * Ensure that we get the right work->data if we see the
 130          * result of list_add() below, see try_to_grab_pending().
 131          */
 132         smp_wmb();
 133         if (tail)
 134                 list_add_tail(&work->entry, &cwq->worklist);
 135         else
 136                 list_add(&work->entry, &cwq->worklist);
 137         wake_up(&cwq->more_work);
 138 }
 139
 140 /* Preempt must be disabled. */
 141 static void __queue_work(struct cpu_workqueue_struct *cwq,
 142                          struct work_struct *work)
 143 {
 144         unsigned long flags;
 145
 146         spin_lock_irqsave(&cwq->lock, flags);
 147         insert_work(cwq, work, 1);
 148         spin_unlock_irqrestore(&cwq->lock, flags);
 149 }
 150
 151 /**
 152  * queue_work - queue work on a workqueue
 153  * @wq: workqueue to use
 154  * @work: work to queue
 155  *
 156  * Returns 0 if @work was already on a queue, non-zero otherwise.
 157  *
 158  * We queue the work to the CPU it was submitted, but there is no
 159  * guarantee that it will be processed by that CPU.
 160  */
 161 int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
 162 {
 163         int ret = 0;
 164
 165         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 166                 BUG_ON(!list_empty(&work->entry));
 167                 __queue_work(wq_per_cpu(wq, get_cpu()), work);
 168                 put_cpu();
 169                 ret = 1;
 170         }
 171         return ret;
 172 }
 173 EXPORT_SYMBOL_GPL(queue_work);
 174
 175 void delayed_work_timer_fn(unsigned long __data)
 176 {
 177         struct delayed_work *dwork = (struct delayed_work *)__data;
 178         struct cpu_workqueue_struct *cwq = get_wq_data(&dwork->work);
 179         struct workqueue_struct *wq = cwq->wq;
 180
 181         __queue_work(wq_per_cpu(wq, smp_processor_id()), &dwork->work);
 182 }
 183
 184 /**
 185  * queue_delayed_work - queue work on a workqueue after delay
 186  * @wq: workqueue to use
 187  * @dwork: delayable work to queue
 188  * @delay: number of jiffies to wait before queueing
 189  *
 190  * Returns 0 if @work was already on a queue, non-zero otherwise.
 191  */
 192 int fastcall queue_delayed_work(struct workqueue_struct *wq,
 193                         struct delayed_work *dwork, unsigned long delay)
 194 {
 195         timer_stats_timer_set_start_info(&dwork->timer);
 196         if (delay == 0)
 197                 return queue_work(wq, &dwork->work);
 198
 199         return queue_delayed_work_on(-1, wq, dwork, delay);
 200 }
 201 EXPORT_SYMBOL_GPL(queue_delayed_work);
 202
 203 /**
 204  * queue_delayed_work_on - queue work on specific CPU after delay
 205  * @cpu: CPU number to execute work on
 206  * @wq: workqueue to use
 207  * @dwork: work to queue
 208  * @delay: number of jiffies to wait before queueing
 209  *
 210  * Returns 0 if @work was already on a queue, non-zero otherwise.
 211  */
 212 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 213                         struct delayed_work *dwork, unsigned long delay)
 214 {
 215         int ret = 0;
 216         struct timer_list *timer = &dwork->timer;
 217         struct work_struct *work = &dwork->work;
 218
 219         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 220                 BUG_ON(timer_pending(timer));
 221                 BUG_ON(!list_empty(&work->entry));
 222
 223                 /* This stores cwq for the moment, for the timer_fn */
 224                 set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
 225                 timer->expires = jiffies + delay;
 226                 timer->data = (unsigned long)dwork;
 227                 timer->function = delayed_work_timer_fn;
 228
 229                 if (unlikely(cpu >= 0))
 230                         add_timer_on(timer, cpu);
 231                 else
 232                         add_timer(timer);
 233                 ret = 1;
 234         }
 235         return ret;
 236 }
 237 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
 238
 239 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 240 {
 241         spin_lock_irq(&cwq->lock);
 242         cwq->run_depth++;
 243         if (cwq->run_depth > 3) {
 244                 /* morton gets to eat his hat */
 245                 printk("%s: recursion depth exceeded: %d\n",
 246                         __FUNCTION__, cwq->run_depth);
 247                 dump_stack();
 248         }
 249         while (!list_empty(&cwq->worklist)) {
 250                 struct work_struct *work = list_entry(cwq->worklist.next,
 251                                                 struct work_struct, entry);
 252                 work_func_t f = work->func;
 253
 254                 cwq->current_work = work;
 255                 list_del_init(cwq->worklist.next);
 256                 spin_unlock_irq(&cwq->lock);
 257
 258                 BUG_ON(get_wq_data(work) != cwq);
 259                 work_clear_pending(work);
 260                 f(work);
 261
 262                 if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
 263                         printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
 264                                         "%s/0x%08x/%d\n",
 265                                         current->comm, preempt_count(),
 266                                         current->pid);
 267                         printk(KERN_ERR "    last function: ");
 268                         print_symbol("%s\n", (unsigned long)f);
 269                         debug_show_held_locks(current);
 270                         dump_stack();
 271                 }
 272
 273                 spin_lock_irq(&cwq->lock);
 274                 cwq->current_work = NULL;
 275         }
 276         cwq->run_depth--;
 277         spin_unlock_irq(&cwq->lock);
 278 }
 279
 280 static int worker_thread(void *__cwq)
 281 {
 282         struct cpu_workqueue_struct *cwq = __cwq;
 283         DEFINE_WAIT(wait);
 284
 285         if (!cwq->wq->freezeable)
 286                 current->flags |= PF_NOFREEZE;
 287
 288         set_user_nice(current, -5);
 289
 290         for (;;) {
 291                 prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
 292                 if (!freezing(current) &&
 293                     !kthread_should_stop() &&
 294                     list_empty(&cwq->worklist))
 295                         schedule();
 296                 finish_wait(&cwq->more_work, &wait);
 297
 298                 try_to_freeze();
 299
 300                 if (kthread_should_stop())
 301                         break;
 302
 303                 run_workqueue(cwq);
 304         }
 305
 306         return 0;
 307 }
 308
 309 struct wq_barrier {
 310         struct work_struct      work;
 311         struct completion       done;
 312 };
 313
 314 static void wq_barrier_func(struct work_struct *work)
 315 {
 316         struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
 317         complete(&barr->done);
 318 }
 319
 320 static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
 321                                         struct wq_barrier *barr, int tail)
 322 {
 323         INIT_WORK(&barr->work, wq_barrier_func);
 324         __set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
 325
 326         init_completion(&barr->done);
 327
 328         insert_work(cwq, &barr->work, tail);
 329 }
 330
 331 static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 332 {
 333         int active;
 334
 335         if (cwq->thread == current) {
 336                 /*
 337                  * Probably keventd trying to flush its own queue. So simply run
 338                  * it by hand rather than deadlocking.
 339                  */
 340                 run_workqueue(cwq);
 341                 active = 1;
 342         } else {
 343                 struct wq_barrier barr;
 344
 345                 active = 0;
 346                 spin_lock_irq(&cwq->lock);
 347                 if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
 348                         insert_wq_barrier(cwq, &barr, 1);
 349                         active = 1;
 350                 }
 351                 spin_unlock_irq(&cwq->lock);
 352
 353                 if (active)
 354                         wait_for_completion(&barr.done);
 355         }
 356
 357         return active;
 358 }
 359
 360 /**
 361  * flush_workqueue - ensure that any scheduled work has run to completion.
 362  * @wq: workqueue to flush
 363  *
 364  * Forces execution of the workqueue and blocks until its completion.
 365  * This is typically used in driver shutdown handlers.
 366  *
 367  * We sleep until all works which were queued on entry have been handled,
 368  * but we are not livelocked by new incoming ones.
 369  *
 370  * This function used to run the workqueues itself.  Now we just wait for the
 371  * helper threads to do it.
 372  */
 373 void fastcall flush_workqueue(struct workqueue_struct *wq)
 374 {
 375         const cpumask_t *cpu_map = wq_cpu_map(wq);
 376         int cpu;
 377
 378         might_sleep();
 379         for_each_cpu_mask(cpu, *cpu_map)
 380                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 381 }
 382 EXPORT_SYMBOL_GPL(flush_workqueue);
 383
 384 /*
 385  * Upon a successful return, the caller "owns" WORK_STRUCT_PENDING bit,
 386  * so this work can't be re-armed in any way.
 387  */
 388 static int try_to_grab_pending(struct work_struct *work)
 389 {
 390         struct cpu_workqueue_struct *cwq;
 391         int ret = 0;
 392
 393         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
 394                 return 1;
 395
 396         /*
 397          * The queueing is in progress, or it is already queued. Try to
 398          * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
 399          */
 400
 401         cwq = get_wq_data(work);
 402         if (!cwq)
 403                 return ret;
 404
 405         spin_lock_irq(&cwq->lock);
 406         if (!list_empty(&work->entry)) {
 407                 /*
 408                  * This work is queued, but perhaps we locked the wrong cwq.
 409                  * In that case we must see the new value after rmb(), see
 410                  * insert_work()->wmb().
 411                  */
 412                 smp_rmb();
 413                 if (cwq == get_wq_data(work)) {
 414                         list_del_init(&work->entry);
 415                         ret = 1;
 416                 }
 417         }
 418         spin_unlock_irq(&cwq->lock);
 419
 420         return ret;
 421 }
 422
 423 static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
 424                                 struct work_struct *work)
 425 {
 426         struct wq_barrier barr;
 427         int running = 0;
 428
 429         spin_lock_irq(&cwq->lock);
 430         if (unlikely(cwq->current_work == work)) {
 431                 insert_wq_barrier(cwq, &barr, 0);
 432                 running = 1;
 433         }
 434         spin_unlock_irq(&cwq->lock);
 435
 436         if (unlikely(running))
 437                 wait_for_completion(&barr.done);
 438 }
 439
 440 static void wait_on_work(struct work_struct *work)
 441 {
 442         struct cpu_workqueue_struct *cwq;
 443         struct workqueue_struct *wq;
 444         const cpumask_t *cpu_map;
 445         int cpu;
 446
 447         might_sleep();
 448
 449         cwq = get_wq_data(work);
 450         if (!cwq)
 451                 return;
 452
 453         wq = cwq->wq;
 454         cpu_map = wq_cpu_map(wq);
 455
 456         for_each_cpu_mask(cpu, *cpu_map)
 457                 wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 458 }
 459
 460 /**
 461  * cancel_work_sync - block until a work_struct's callback has terminated
 462  * @work: the work which is to be flushed
 463  *
 464  * cancel_work_sync() will cancel the work if it is queued. If the work's
 465  * callback appears to be running, cancel_work_sync() will block until it
 466  * has completed.
 467  *
 468  * It is possible to use this function if the work re-queues itself. It can
 469  * cancel the work even if it migrates to another workqueue, however in that
 470  * case it only guarantees that work->func() has completed on the last queued
 471  * workqueue.
 472  *
 473  * cancel_work_sync(&delayed_work->work) should be used only if ->timer is not
 474  * pending, otherwise it goes into a busy-wait loop until the timer expires.
 475  *
 476  * The caller must ensure that workqueue_struct on which this work was last
 477  * queued can't be destroyed before this function returns.
 478  */
 479 void cancel_work_sync(struct work_struct *work)
 480 {
 481         while (!try_to_grab_pending(work))
 482                 cpu_relax();
 483         wait_on_work(work);
 484         work_clear_pending(work);
 485 }
 486 EXPORT_SYMBOL_GPL(cancel_work_sync);
 487
 488 /**
 489  * cancel_rearming_delayed_work - reliably kill off a delayed work.
 490  * @dwork: the delayed work struct
 491  *
 492  * It is possible to use this function if @dwork rearms itself via queue_work()
 493  * or queue_delayed_work(). See also the comment for cancel_work_sync().
 494  */
 495 void cancel_rearming_delayed_work(struct delayed_work *dwork)
 496 {
 497         while (!del_timer(&dwork->timer) &&
 498                !try_to_grab_pending(&dwork->work))
 499                 cpu_relax();
 500         wait_on_work(&dwork->work);
 501         work_clear_pending(&dwork->work);
 502 }
 503 EXPORT_SYMBOL(cancel_rearming_delayed_work);
 504
 505 static struct workqueue_struct *keventd_wq __read_mostly;
 506
 507 /**
 508  * schedule_work - put work task in global workqueue
 509  * @work: job to be done
 510  *
 511  * This puts a job in the kernel-global workqueue.
 512  */
 513 int fastcall schedule_work(struct work_struct *work)
 514 {
 515         return queue_work(keventd_wq, work);
 516 }
 517 EXPORT_SYMBOL(schedule_work);
 518
 519 /**
 520  * schedule_delayed_work - put work task in global workqueue after delay
 521  * @dwork: job to be done
 522  * @delay: number of jiffies to wait or 0 for immediate execution
 523  *
 524  * After waiting for a given time this puts a job in the kernel-global
 525  * workqueue.
 526  */
 527 int fastcall schedule_delayed_work(struct delayed_work *dwork,
 528                                         unsigned long delay)
 529 {
 530         timer_stats_timer_set_start_info(&dwork->timer);
 531         return queue_delayed_work(keventd_wq, dwork, delay);
 532 }
 533 EXPORT_SYMBOL(schedule_delayed_work);
 534
 535 /**
 536  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 537  * @cpu: cpu to use
 538  * @dwork: job to be done
 539  * @delay: number of jiffies to wait
 540  *
 541  * After waiting for a given time this puts a job in the kernel-global
 542  * workqueue on the specified CPU.
 543  */
 544 int schedule_delayed_work_on(int cpu,
 545                         struct delayed_work *dwork, unsigned long delay)
 546 {
 547         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
 548 }
 549 EXPORT_SYMBOL(schedule_delayed_work_on);
 550
 551 /**
 552  * schedule_on_each_cpu - call a function on each online CPU from keventd
 553  * @func: the function to call
 554  *
 555  * Returns zero on success.
 556  * Returns -ve errno on failure.
 557  *
 558  * Appears to be racy against CPU hotplug.
 559  *
 560  * schedule_on_each_cpu() is very slow.
 561  */
 562 int schedule_on_each_cpu(work_func_t func)
 563 {
 564         int cpu;
 565         struct work_struct *works;
 566
 567         works = alloc_percpu(struct work_struct);
 568         if (!works)
 569                 return -ENOMEM;
 570
 571         preempt_disable();              /* CPU hotplug */
 572         for_each_online_cpu(cpu) {
 573                 struct work_struct *work = per_cpu_ptr(works, cpu);
 574
 575                 INIT_WORK(work, func);
 576                 set_bit(WORK_STRUCT_PENDING, work_data_bits(work));
 577                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), work);
 578         }
 579         preempt_enable();
 580         flush_workqueue(keventd_wq);
 581         free_percpu(works);
 582         return 0;
 583 }
 584
 585 void flush_scheduled_work(void)
 586 {
 587         flush_workqueue(keventd_wq);
 588 }
 589 EXPORT_SYMBOL(flush_scheduled_work);
 590
 591 /**
 592  * execute_in_process_context - reliably execute the routine with user context
 593  * @fn:         the function to execute
 594  * @ew:         guaranteed storage for the execute work structure (must
 595  *              be available when the work executes)
 596  *
 597  * Executes the function immediately if process context is available,
 598  * otherwise schedules the function for delayed execution.
 599  *
 600  * Returns:     0 - function was executed
 601  *              1 - function was scheduled for execution
 602  */
 603 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 604 {
 605         if (!in_interrupt()) {
 606                 fn(&ew->work);
 607                 return 0;
 608         }
 609
 610         INIT_WORK(&ew->work, fn);
 611         schedule_work(&ew->work);
 612
 613         return 1;
 614 }
 615 EXPORT_SYMBOL_GPL(execute_in_process_context);
 616
 617 int keventd_up(void)
 618 {
 619         return keventd_wq != NULL;
 620 }
 621
 622 int current_is_keventd(void)
 623 {
 624         struct cpu_workqueue_struct *cwq;
 625         int cpu = smp_processor_id();   /* preempt-safe: keventd is per-cpu */
 626         int ret = 0;
 627
 628         BUG_ON(!keventd_wq);
 629
 630         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 631         if (current == cwq->thread)
 632                 ret = 1;
 633
 634         return ret;
 635
 636 }
 637
 638 static struct cpu_workqueue_struct *
 639 init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
 640 {
 641         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 642
 643         cwq->wq = wq;
 644         spin_lock_init(&cwq->lock);
 645         INIT_LIST_HEAD(&cwq->worklist);
 646         init_waitqueue_head(&cwq->more_work);
 647
 648         return cwq;
 649 }
 650
 651 static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 652 {
 653         struct workqueue_struct *wq = cwq->wq;
 654         const char *fmt = is_single_threaded(wq) ? "%s" : "%s/%d";
 655         struct task_struct *p;
 656
 657         p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
 658         /*
 659          * Nobody can add the work_struct to this cwq,
 660          *      if (caller is __create_workqueue)
 661          *              nobody should see this wq
 662          *      else // caller is CPU_UP_PREPARE
 663          *              cpu is not on cpu_online_map
 664          * so we can abort safely.
 665          */
 666         if (IS_ERR(p))
 667                 return PTR_ERR(p);
 668
 669         cwq->thread = p;
 670
 671         return 0;
 672 }
 673
 674 static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 675 {
 676         struct task_struct *p = cwq->thread;
 677
 678         if (p != NULL) {
 679                 if (cpu >= 0)
 680                         kthread_bind(p, cpu);
 681                 wake_up_process(p);
 682         }
 683 }
 684
 685 struct workqueue_struct *__create_workqueue(const char *name,
 686                                             int singlethread, int freezeable)
 687 {
 688         struct workqueue_struct *wq;
 689         struct cpu_workqueue_struct *cwq;
 690         int err = 0, cpu;
 691
 692         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
 693         if (!wq)
 694                 return NULL;
 695
 696         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
 697         if (!wq->cpu_wq) {
 698                 kfree(wq);
 699                 return NULL;
 700         }
 701
 702         wq->name = name;
 703         wq->singlethread = singlethread;
 704         wq->freezeable = freezeable;
 705         INIT_LIST_HEAD(&wq->list);
 706
 707         if (singlethread) {
 708                 cwq = init_cpu_workqueue(wq, singlethread_cpu);
 709                 err = create_workqueue_thread(cwq, singlethread_cpu);
 710                 start_workqueue_thread(cwq, -1);
 711         } else {
 712                 mutex_lock(&workqueue_mutex);
 713                 list_add(&wq->list, &workqueues);
 714
 715                 for_each_possible_cpu(cpu) {
 716                         cwq = init_cpu_workqueue(wq, cpu);
 717                         if (err || !cpu_online(cpu))
 718                                 continue;
 719                         err = create_workqueue_thread(cwq, cpu);
 720                         start_workqueue_thread(cwq, cpu);
 721                 }
 722                 mutex_unlock(&workqueue_mutex);
 723         }
 724
 725         if (err) {
 726                 destroy_workqueue(wq);
 727                 wq = NULL;
 728         }
 729         return wq;
 730 }
 731 EXPORT_SYMBOL_GPL(__create_workqueue);
 732
 733 static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 734 {
 735         /*
 736          * Our caller is either destroy_workqueue() or CPU_DEAD,
 737          * workqueue_mutex protects cwq->thread
 738          */
 739         if (cwq->thread == NULL)
 740                 return;
 741
 742         /*
 743          * If the caller is CPU_DEAD the single flush_cpu_workqueue()
 744          * is not enough, a concurrent flush_workqueue() can insert a
 745          * barrier after us.
 746          * When ->worklist becomes empty it is safe to exit because no
 747          * more work_structs can be queued on this cwq: flush_workqueue
 748          * checks list_empty(), and a "normal" queue_work() can't use
 749          * a dead CPU.
 750          */
 751         while (flush_cpu_workqueue(cwq))
 752                 ;
 753
 754         kthread_stop(cwq->thread);
 755         cwq->thread = NULL;
 756 }
 757
 758 /**
 759  * destroy_workqueue - safely terminate a workqueue
 760  * @wq: target workqueue
 761  *
 762  * Safely destroy a workqueue. All work currently pending will be done first.
 763  */
 764 void destroy_workqueue(struct workqueue_struct *wq)
 765 {
 766         const cpumask_t *cpu_map = wq_cpu_map(wq);
 767         struct cpu_workqueue_struct *cwq;
 768         int cpu;
 769
 770         mutex_lock(&workqueue_mutex);
 771         list_del(&wq->list);
 772         mutex_unlock(&workqueue_mutex);
 773
 774         for_each_cpu_mask(cpu, *cpu_map) {
 775                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 776                 cleanup_workqueue_thread(cwq, cpu);
 777         }
 778
 779         free_percpu(wq->cpu_wq);
 780         kfree(wq);
 781 }
 782 EXPORT_SYMBOL_GPL(destroy_workqueue);
 783
 784 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 785                                                 unsigned long action,
 786                                                 void *hcpu)
 787 {
 788         unsigned int cpu = (unsigned long)hcpu;
 789         struct cpu_workqueue_struct *cwq;
 790         struct workqueue_struct *wq;
 791
 792         action &= ~CPU_TASKS_FROZEN;
 793
 794         switch (action) {
 795         case CPU_LOCK_ACQUIRE:
 796                 mutex_lock(&workqueue_mutex);
 797                 return NOTIFY_OK;
 798
 799         case CPU_LOCK_RELEASE:
 800                 mutex_unlock(&workqueue_mutex);
 801                 return NOTIFY_OK;
 802
 803         case CPU_UP_PREPARE:
 804                 cpu_set(cpu, cpu_populated_map);
 805         }
 806
 807         list_for_each_entry(wq, &workqueues, list) {
 808                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 809
 810                 switch (action) {
 811                 case CPU_UP_PREPARE:
 812                         if (!create_workqueue_thread(cwq, cpu))
 813                                 break;
 814                         printk(KERN_ERR "workqueue for %i failed\n", cpu);
 815                         return NOTIFY_BAD;
 816
 817                 case CPU_ONLINE:
 818                         start_workqueue_thread(cwq, cpu);
 819                         break;
 820
 821                 case CPU_UP_CANCELED:
 822                         start_workqueue_thread(cwq, -1);
 823                 case CPU_DEAD:
 824                         cleanup_workqueue_thread(cwq, cpu);
 825                         break;
 826                 }
 827         }
 828
 829         return NOTIFY_OK;
 830 }
 831
 832 void __init init_workqueues(void)
 833 {
 834         cpu_populated_map = cpu_online_map;
 835         singlethread_cpu = first_cpu(cpu_possible_map);
 836         cpu_singlethread_map = cpumask_of_cpu(singlethread_cpu);
 837         hotcpu_notifier(workqueue_cpu_callback, 0);
 838         keventd_wq = create_workqueue("events");
 839         BUG_ON(!keventd_wq);
 840 }