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
  13  *   Kai Petzke <wpp@marie.physik.tu-berlin.de>
  14  *   Theodore Ts'o <tytso@mit.edu>
  15  *
  16  * Made to use alloc_percpu by Christoph Lameter.
  17  */
  18
  19 #include <linux/module.h>
  20 #include <linux/kernel.h>
  21 #include <linux/sched.h>
  22 #include <linux/init.h>
  23 #include <linux/signal.h>
  24 #include <linux/completion.h>
  25 #include <linux/workqueue.h>
  26 #include <linux/slab.h>
  27 #include <linux/cpu.h>
  28 #include <linux/notifier.h>
  29 #include <linux/kthread.h>
  30 #include <linux/hardirq.h>
  31 #include <linux/mempolicy.h>
  32 #include <linux/freezer.h>
  33 #include <linux/kallsyms.h>
  34 #include <linux/debug_locks.h>
  35 #include <linux/lockdep.h>
  36 #define CREATE_TRACE_POINTS
  37 #include <trace/events/workqueue.h>
  38
  39 /*
  40  * The per-CPU workqueue (if single thread, we always use the first
  41  * possible cpu).
  42  */
  43 struct cpu_workqueue_struct {
  44
  45         spinlock_t lock;
  46
  47         struct list_head worklist;
  48         wait_queue_head_t more_work;
  49         struct work_struct *current_work;
  50
  51         struct workqueue_struct *wq;
  52         struct task_struct *thread;
  53 } ____cacheline_aligned;
  54
  55 /*
  56  * The externally visible workqueue abstraction is an array of
  57  * per-CPU workqueues:
  58  */
  59 struct workqueue_struct {
  60         struct cpu_workqueue_struct *cpu_wq;
  61         struct list_head list;
  62         const char *name;
  63         int singlethread;
  64         int freezeable;         /* Freeze threads during suspend */
  65         int rt;
  66 #ifdef CONFIG_LOCKDEP
  67         struct lockdep_map lockdep_map;
  68 #endif
  69 };
  70
  71 #ifdef CONFIG_LOCKDEP
  72 /**
  73  * in_workqueue_context() - in context of specified workqueue?
  74  * @wq: the workqueue of interest
  75  *
  76  * Checks lockdep state to see if the current task is executing from
  77  * within a workqueue item.  This function exists only if lockdep is
  78  * enabled.
  79  */
  80 int in_workqueue_context(struct workqueue_struct *wq)
  81 {
  82         return lock_is_held(&wq->lockdep_map);
  83 }
  84 #endif
  85
  86 #ifdef CONFIG_DEBUG_OBJECTS_WORK
  87
  88 static struct debug_obj_descr work_debug_descr;
  89
  90 /*
  91  * fixup_init is called when:
  92  * - an active object is initialized
  93  */
  94 static int work_fixup_init(void *addr, enum debug_obj_state state)
  95 {
  96         struct work_struct *work = addr;
  97
  98         switch (state) {
  99         case ODEBUG_STATE_ACTIVE:
 100                 cancel_work_sync(work);
 101                 debug_object_init(work, &work_debug_descr);
 102                 return 1;
 103         default:
 104                 return 0;
 105         }
 106 }
 107
 108 /*
 109  * fixup_activate is called when:
 110  * - an active object is activated
 111  * - an unknown object is activated (might be a statically initialized object)
 112  */
 113 static int work_fixup_activate(void *addr, enum debug_obj_state state)
 114 {
 115         struct work_struct *work = addr;
 116
 117         switch (state) {
 118
 119         case ODEBUG_STATE_NOTAVAILABLE:
 120                 /*
 121                  * This is not really a fixup. The work struct was
 122                  * statically initialized. We just make sure that it
 123                  * is tracked in the object tracker.
 124                  */
 125                 if (test_bit(WORK_STRUCT_STATIC, work_data_bits(work))) {
 126                         debug_object_init(work, &work_debug_descr);
 127                         debug_object_activate(work, &work_debug_descr);
 128                         return 0;
 129                 }
 130                 WARN_ON_ONCE(1);
 131                 return 0;
 132
 133         case ODEBUG_STATE_ACTIVE:
 134                 WARN_ON(1);
 135
 136         default:
 137                 return 0;
 138         }
 139 }
 140
 141 /*
 142  * fixup_free is called when:
 143  * - an active object is freed
 144  */
 145 static int work_fixup_free(void *addr, enum debug_obj_state state)
 146 {
 147         struct work_struct *work = addr;
 148
 149         switch (state) {
 150         case ODEBUG_STATE_ACTIVE:
 151                 cancel_work_sync(work);
 152                 debug_object_free(work, &work_debug_descr);
 153                 return 1;
 154         default:
 155                 return 0;
 156         }
 157 }
 158
 159 static struct debug_obj_descr work_debug_descr = {
 160         .name           = "work_struct",
 161         .fixup_init     = work_fixup_init,
 162         .fixup_activate = work_fixup_activate,
 163         .fixup_free     = work_fixup_free,
 164 };
 165
 166 static inline void debug_work_activate(struct work_struct *work)
 167 {
 168         debug_object_activate(work, &work_debug_descr);
 169 }
 170
 171 static inline void debug_work_deactivate(struct work_struct *work)
 172 {
 173         debug_object_deactivate(work, &work_debug_descr);
 174 }
 175
 176 void __init_work(struct work_struct *work, int onstack)
 177 {
 178         if (onstack)
 179                 debug_object_init_on_stack(work, &work_debug_descr);
 180         else
 181                 debug_object_init(work, &work_debug_descr);
 182 }
 183 EXPORT_SYMBOL_GPL(__init_work);
 184
 185 void destroy_work_on_stack(struct work_struct *work)
 186 {
 187         debug_object_free(work, &work_debug_descr);
 188 }
 189 EXPORT_SYMBOL_GPL(destroy_work_on_stack);
 190
 191 #else
 192 static inline void debug_work_activate(struct work_struct *work) { }
 193 static inline void debug_work_deactivate(struct work_struct *work) { }
 194 #endif
 195
 196 /* Serializes the accesses to the list of workqueues. */
 197 static DEFINE_SPINLOCK(workqueue_lock);
 198 static LIST_HEAD(workqueues);
 199
 200 static int singlethread_cpu __read_mostly;
 201 static const struct cpumask *cpu_singlethread_map __read_mostly;
 202 /*
 203  * _cpu_down() first removes CPU from cpu_online_map, then CPU_DEAD
 204  * flushes cwq->worklist. This means that flush_workqueue/wait_on_work
 205  * which comes in between can't use for_each_online_cpu(). We could
 206  * use cpu_possible_map, the cpumask below is more a documentation
 207  * than optimization.
 208  */
 209 static cpumask_var_t cpu_populated_map __read_mostly;
 210
 211 /* If it's single threaded, it isn't in the list of workqueues. */
 212 static inline int is_wq_single_threaded(struct workqueue_struct *wq)
 213 {
 214         return wq->singlethread;
 215 }
 216
 217 static const struct cpumask *wq_cpu_map(struct workqueue_struct *wq)
 218 {
 219         return is_wq_single_threaded(wq)
 220                 ? cpu_singlethread_map : cpu_populated_map;
 221 }
 222
 223 static
 224 struct cpu_workqueue_struct *wq_per_cpu(struct workqueue_struct *wq, int cpu)
 225 {
 226         if (unlikely(is_wq_single_threaded(wq)))
 227                 cpu = singlethread_cpu;
 228         return per_cpu_ptr(wq->cpu_wq, cpu);
 229 }
 230
 231 /*
 232  * Set the workqueue on which a work item is to be run
 233  * - Must *only* be called if the pending flag is set
 234  */
 235 static inline void set_wq_data(struct work_struct *work,
 236                                 struct cpu_workqueue_struct *cwq)
 237 {
 238         unsigned long new;
 239
 240         BUG_ON(!work_pending(work));
 241
 242         new = (unsigned long) cwq | (1UL << WORK_STRUCT_PENDING);
 243         new |= WORK_STRUCT_FLAG_MASK & *work_data_bits(work);
 244         atomic_long_set(&work->data, new);
 245 }
 246
 247 /*
 248  * Clear WORK_STRUCT_PENDING and the workqueue on which it was queued.
 249  */
 250 static inline void clear_wq_data(struct work_struct *work)
 251 {
 252         unsigned long flags = *work_data_bits(work) &
 253                                 (1UL << WORK_STRUCT_STATIC);
 254         atomic_long_set(&work->data, flags);
 255 }
 256
 257 static inline
 258 struct cpu_workqueue_struct *get_wq_data(struct work_struct *work)
 259 {
 260         return (void *) (atomic_long_read(&work->data) & WORK_STRUCT_WQ_DATA_MASK);
 261 }
 262
 263 static void insert_work(struct cpu_workqueue_struct *cwq,
 264                         struct work_struct *work, struct list_head *head)
 265 {
 266         trace_workqueue_insertion(cwq->thread, work);
 267
 268         set_wq_data(work, cwq);
 269         /*
 270          * Ensure that we get the right work->data if we see the
 271          * result of list_add() below, see try_to_grab_pending().
 272          */
 273         smp_wmb();
 274         list_add_tail(&work->entry, head);
 275         wake_up(&cwq->more_work);
 276 }
 277
 278 static void __queue_work(struct cpu_workqueue_struct *cwq,
 279                          struct work_struct *work)
 280 {
 281         unsigned long flags;
 282
 283         debug_work_activate(work);
 284         spin_lock_irqsave(&cwq->lock, flags);
 285         insert_work(cwq, work, &cwq->worklist);
 286         spin_unlock_irqrestore(&cwq->lock, flags);
 287 }
 288
 289 /**
 290  * queue_work - queue work on a workqueue
 291  * @wq: workqueue to use
 292  * @work: work to queue
 293  *
 294  * Returns 0 if @work was already on a queue, non-zero otherwise.
 295  *
 296  * We queue the work to the CPU on which it was submitted, but if the CPU dies
 297  * it can be processed by another CPU.
 298  */
 299 int queue_work(struct workqueue_struct *wq, struct work_struct *work)
 300 {
 301         int ret;
 302
 303         ret = queue_work_on(get_cpu(), wq, work);
 304         put_cpu();
 305
 306         return ret;
 307 }
 308 EXPORT_SYMBOL_GPL(queue_work);
 309
 310 /**
 311  * queue_work_on - queue work on specific cpu
 312  * @cpu: CPU number to execute work on
 313  * @wq: workqueue to use
 314  * @work: work to queue
 315  *
 316  * Returns 0 if @work was already on a queue, non-zero otherwise.
 317  *
 318  * We queue the work to a specific CPU, the caller must ensure it
 319  * can't go away.
 320  */
 321 int
 322 queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
 323 {
 324         int ret = 0;
 325
 326         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 327                 BUG_ON(!list_empty(&work->entry));
 328                 __queue_work(wq_per_cpu(wq, cpu), work);
 329                 ret = 1;
 330         }
 331         return ret;
 332 }
 333 EXPORT_SYMBOL_GPL(queue_work_on);
 334
 335 static void delayed_work_timer_fn(unsigned long __data)
 336 {
 337         struct delayed_work *dwork = (struct delayed_work *)__data;
 338         struct cpu_workqueue_struct *cwq = get_wq_data(&dwork->work);
 339         struct workqueue_struct *wq = cwq->wq;
 340
 341         __queue_work(wq_per_cpu(wq, smp_processor_id()), &dwork->work);
 342 }
 343
 344 /**
 345  * queue_delayed_work - queue work on a workqueue after delay
 346  * @wq: workqueue to use
 347  * @dwork: delayable work to queue
 348  * @delay: number of jiffies to wait before queueing
 349  *
 350  * Returns 0 if @work was already on a queue, non-zero otherwise.
 351  */
 352 int queue_delayed_work(struct workqueue_struct *wq,
 353                         struct delayed_work *dwork, unsigned long delay)
 354 {
 355         if (delay == 0)
 356                 return queue_work(wq, &dwork->work);
 357
 358         return queue_delayed_work_on(-1, wq, dwork, delay);
 359 }
 360 EXPORT_SYMBOL_GPL(queue_delayed_work);
 361
 362 /**
 363  * queue_delayed_work_on - queue work on specific CPU after delay
 364  * @cpu: CPU number to execute work on
 365  * @wq: workqueue to use
 366  * @dwork: work to queue
 367  * @delay: number of jiffies to wait before queueing
 368  *
 369  * Returns 0 if @work was already on a queue, non-zero otherwise.
 370  */
 371 int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
 372                         struct delayed_work *dwork, unsigned long delay)
 373 {
 374         int ret = 0;
 375         struct timer_list *timer = &dwork->timer;
 376         struct work_struct *work = &dwork->work;
 377
 378         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
 379                 BUG_ON(timer_pending(timer));
 380                 BUG_ON(!list_empty(&work->entry));
 381
 382                 timer_stats_timer_set_start_info(&dwork->timer);
 383
 384                 /* This stores cwq for the moment, for the timer_fn */
 385                 set_wq_data(work, wq_per_cpu(wq, raw_smp_processor_id()));
 386                 timer->expires = jiffies + delay;
 387                 timer->data = (unsigned long)dwork;
 388                 timer->function = delayed_work_timer_fn;
 389
 390                 if (unlikely(cpu >= 0))
 391                         add_timer_on(timer, cpu);
 392                 else
 393                         add_timer(timer);
 394                 ret = 1;
 395         }
 396         return ret;
 397 }
 398 EXPORT_SYMBOL_GPL(queue_delayed_work_on);
 399
 400 static void run_workqueue(struct cpu_workqueue_struct *cwq)
 401 {
 402         spin_lock_irq(&cwq->lock);
 403         while (!list_empty(&cwq->worklist)) {
 404                 struct work_struct *work = list_entry(cwq->worklist.next,
 405                                                 struct work_struct, entry);
 406                 work_func_t f = work->func;
 407 #ifdef CONFIG_LOCKDEP
 408                 /*
 409                  * It is permissible to free the struct work_struct
 410                  * from inside the function that is called from it,
 411                  * this we need to take into account for lockdep too.
 412                  * To avoid bogus "held lock freed" warnings as well
 413                  * as problems when looking into work->lockdep_map,
 414                  * make a copy and use that here.
 415                  */
 416                 struct lockdep_map lockdep_map = work->lockdep_map;
 417 #endif
 418                 trace_workqueue_execution(cwq->thread, work);
 419                 debug_work_deactivate(work);
 420                 cwq->current_work = work;
 421                 list_del_init(cwq->worklist.next);
 422                 spin_unlock_irq(&cwq->lock);
 423
 424                 BUG_ON(get_wq_data(work) != cwq);
 425                 work_clear_pending(work);
 426                 lock_map_acquire(&cwq->wq->lockdep_map);
 427                 lock_map_acquire(&lockdep_map);
 428                 f(work);
 429                 lock_map_release(&lockdep_map);
 430                 lock_map_release(&cwq->wq->lockdep_map);
 431
 432                 if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
 433                         printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
 434                                         "%s/0x%08x/%d\n",
 435                                         current->comm, preempt_count(),
 436                                         task_pid_nr(current));
 437                         printk(KERN_ERR "    last function: ");
 438                         print_symbol("%s\n", (unsigned long)f);
 439                         debug_show_held_locks(current);
 440                         dump_stack();
 441                 }
 442
 443                 spin_lock_irq(&cwq->lock);
 444                 cwq->current_work = NULL;
 445         }
 446         spin_unlock_irq(&cwq->lock);
 447 }
 448
 449 static int worker_thread(void *__cwq)
 450 {
 451         struct cpu_workqueue_struct *cwq = __cwq;
 452         DEFINE_WAIT(wait);
 453
 454         if (cwq->wq->freezeable)
 455                 set_freezable();
 456
 457         for (;;) {
 458                 prepare_to_wait(&cwq->more_work, &wait, TASK_INTERRUPTIBLE);
 459                 if (!freezing(current) &&
 460                     !kthread_should_stop() &&
 461                     list_empty(&cwq->worklist))
 462                         schedule();
 463                 finish_wait(&cwq->more_work, &wait);
 464
 465                 try_to_freeze();
 466
 467                 if (kthread_should_stop())
 468                         break;
 469
 470                 run_workqueue(cwq);
 471         }
 472
 473         return 0;
 474 }
 475
 476 struct wq_barrier {
 477         struct work_struct      work;
 478         struct completion       done;
 479 };
 480
 481 static void wq_barrier_func(struct work_struct *work)
 482 {
 483         struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
 484         complete(&barr->done);
 485 }
 486
 487 static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
 488                         struct wq_barrier *barr, struct list_head *head)
 489 {
 490         /*
 491          * debugobject calls are safe here even with cwq->lock locked
 492          * as we know for sure that this will not trigger any of the
 493          * checks and call back into the fixup functions where we
 494          * might deadlock.
 495          */
 496         INIT_WORK_ON_STACK(&barr->work, wq_barrier_func);
 497         __set_bit(WORK_STRUCT_PENDING, work_data_bits(&barr->work));
 498
 499         init_completion(&barr->done);
 500
 501         debug_work_activate(&barr->work);
 502         insert_work(cwq, &barr->work, head);
 503 }
 504
 505 static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
 506 {
 507         int active = 0;
 508         struct wq_barrier barr;
 509
 510         WARN_ON(cwq->thread == current);
 511
 512         spin_lock_irq(&cwq->lock);
 513         if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) {
 514                 insert_wq_barrier(cwq, &barr, &cwq->worklist);
 515                 active = 1;
 516         }
 517         spin_unlock_irq(&cwq->lock);
 518
 519         if (active) {
 520                 wait_for_completion(&barr.done);
 521                 destroy_work_on_stack(&barr.work);
 522         }
 523
 524         return active;
 525 }
 526
 527 /**
 528  * flush_workqueue - ensure that any scheduled work has run to completion.
 529  * @wq: workqueue to flush
 530  *
 531  * Forces execution of the workqueue and blocks until its completion.
 532  * This is typically used in driver shutdown handlers.
 533  *
 534  * We sleep until all works which were queued on entry have been handled,
 535  * but we are not livelocked by new incoming ones.
 536  *
 537  * This function used to run the workqueues itself.  Now we just wait for the
 538  * helper threads to do it.
 539  */
 540 void flush_workqueue(struct workqueue_struct *wq)
 541 {
 542         const struct cpumask *cpu_map = wq_cpu_map(wq);
 543         int cpu;
 544
 545         might_sleep();
 546         lock_map_acquire(&wq->lockdep_map);
 547         lock_map_release(&wq->lockdep_map);
 548         for_each_cpu(cpu, cpu_map)
 549                 flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
 550 }
 551 EXPORT_SYMBOL_GPL(flush_workqueue);
 552
 553 /**
 554  * flush_work - block until a work_struct's callback has terminated
 555  * @work: the work which is to be flushed
 556  *
 557  * Returns false if @work has already terminated.
 558  *
 559  * It is expected that, prior to calling flush_work(), the caller has
 560  * arranged for the work to not be requeued, otherwise it doesn't make
 561  * sense to use this function.
 562  */
 563 int flush_work(struct work_struct *work)
 564 {
 565         struct cpu_workqueue_struct *cwq;
 566         struct list_head *prev;
 567         struct wq_barrier barr;
 568
 569         might_sleep();
 570         cwq = get_wq_data(work);
 571         if (!cwq)
 572                 return 0;
 573
 574         lock_map_acquire(&cwq->wq->lockdep_map);
 575         lock_map_release(&cwq->wq->lockdep_map);
 576
 577         prev = NULL;
 578         spin_lock_irq(&cwq->lock);
 579         if (!list_empty(&work->entry)) {
 580                 /*
 581                  * See the comment near try_to_grab_pending()->smp_rmb().
 582                  * If it was re-queued under us we are not going to wait.
 583                  */
 584                 smp_rmb();
 585                 if (unlikely(cwq != get_wq_data(work)))
 586                         goto out;
 587                 prev = &work->entry;
 588         } else {
 589                 if (cwq->current_work != work)
 590                         goto out;
 591                 prev = &cwq->worklist;
 592         }
 593         insert_wq_barrier(cwq, &barr, prev->next);
 594 out:
 595         spin_unlock_irq(&cwq->lock);
 596         if (!prev)
 597                 return 0;
 598
 599         wait_for_completion(&barr.done);
 600         destroy_work_on_stack(&barr.work);
 601         return 1;
 602 }
 603 EXPORT_SYMBOL_GPL(flush_work);
 604
 605 /*
 606  * Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
 607  * so this work can't be re-armed in any way.
 608  */
 609 static int try_to_grab_pending(struct work_struct *work)
 610 {
 611         struct cpu_workqueue_struct *cwq;
 612         int ret = -1;
 613
 614         if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
 615                 return 0;
 616
 617         /*
 618          * The queueing is in progress, or it is already queued. Try to
 619          * steal it from ->worklist without clearing WORK_STRUCT_PENDING.
 620          */
 621
 622         cwq = get_wq_data(work);
 623         if (!cwq)
 624                 return ret;
 625
 626         spin_lock_irq(&cwq->lock);
 627         if (!list_empty(&work->entry)) {
 628                 /*
 629                  * This work is queued, but perhaps we locked the wrong cwq.
 630                  * In that case we must see the new value after rmb(), see
 631                  * insert_work()->wmb().
 632                  */
 633                 smp_rmb();
 634                 if (cwq == get_wq_data(work)) {
 635                         debug_work_deactivate(work);
 636                         list_del_init(&work->entry);
 637                         ret = 1;
 638                 }
 639         }
 640         spin_unlock_irq(&cwq->lock);
 641
 642         return ret;
 643 }
 644
 645 static void wait_on_cpu_work(struct cpu_workqueue_struct *cwq,
 646                                 struct work_struct *work)
 647 {
 648         struct wq_barrier barr;
 649         int running = 0;
 650
 651         spin_lock_irq(&cwq->lock);
 652         if (unlikely(cwq->current_work == work)) {
 653                 insert_wq_barrier(cwq, &barr, cwq->worklist.next);
 654                 running = 1;
 655         }
 656         spin_unlock_irq(&cwq->lock);
 657
 658         if (unlikely(running)) {
 659                 wait_for_completion(&barr.done);
 660                 destroy_work_on_stack(&barr.work);
 661         }
 662 }
 663
 664 static void wait_on_work(struct work_struct *work)
 665 {
 666         struct cpu_workqueue_struct *cwq;
 667         struct workqueue_struct *wq;
 668         const struct cpumask *cpu_map;
 669         int cpu;
 670
 671         might_sleep();
 672
 673         lock_map_acquire(&work->lockdep_map);
 674         lock_map_release(&work->lockdep_map);
 675
 676         cwq = get_wq_data(work);
 677         if (!cwq)
 678                 return;
 679
 680         wq = cwq->wq;
 681         cpu_map = wq_cpu_map(wq);
 682
 683         for_each_cpu(cpu, cpu_map)
 684                 wait_on_cpu_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
 685 }
 686
 687 static int __cancel_work_timer(struct work_struct *work,
 688                                 struct timer_list* timer)
 689 {
 690         int ret;
 691
 692         do {
 693                 ret = (timer && likely(del_timer(timer)));
 694                 if (!ret)
 695                         ret = try_to_grab_pending(work);
 696                 wait_on_work(work);
 697         } while (unlikely(ret < 0));
 698
 699         clear_wq_data(work);
 700         return ret;
 701 }
 702
 703 /**
 704  * cancel_work_sync - block until a work_struct's callback has terminated
 705  * @work: the work which is to be flushed
 706  *
 707  * Returns true if @work was pending.
 708  *
 709  * cancel_work_sync() will cancel the work if it is queued. If the work's
 710  * callback appears to be running, cancel_work_sync() will block until it
 711  * has completed.
 712  *
 713  * It is possible to use this function if the work re-queues itself. It can
 714  * cancel the work even if it migrates to another workqueue, however in that
 715  * case it only guarantees that work->func() has completed on the last queued
 716  * workqueue.
 717  *
 718  * cancel_work_sync(&delayed_work->work) should be used only if ->timer is not
 719  * pending, otherwise it goes into a busy-wait loop until the timer expires.
 720  *
 721  * The caller must ensure that workqueue_struct on which this work was last
 722  * queued can't be destroyed before this function returns.
 723  */
 724 int cancel_work_sync(struct work_struct *work)
 725 {
 726         return __cancel_work_timer(work, NULL);
 727 }
 728 EXPORT_SYMBOL_GPL(cancel_work_sync);
 729
 730 /**
 731  * cancel_delayed_work_sync - reliably kill off a delayed work.
 732  * @dwork: the delayed work struct
 733  *
 734  * Returns true if @dwork was pending.
 735  *
 736  * It is possible to use this function if @dwork rearms itself via queue_work()
 737  * or queue_delayed_work(). See also the comment for cancel_work_sync().
 738  */
 739 int cancel_delayed_work_sync(struct delayed_work *dwork)
 740 {
 741         return __cancel_work_timer(&dwork->work, &dwork->timer);
 742 }
 743 EXPORT_SYMBOL(cancel_delayed_work_sync);
 744
 745 static struct workqueue_struct *keventd_wq __read_mostly;
 746
 747 /**
 748  * schedule_work - put work task in global workqueue
 749  * @work: job to be done
 750  *
 751  * Returns zero if @work was already on the kernel-global workqueue and
 752  * non-zero otherwise.
 753  *
 754  * This puts a job in the kernel-global workqueue if it was not already
 755  * queued and leaves it in the same position on the kernel-global
 756  * workqueue otherwise.
 757  */
 758 int schedule_work(struct work_struct *work)
 759 {
 760         return queue_work(keventd_wq, work);
 761 }
 762 EXPORT_SYMBOL(schedule_work);
 763
 764 /*
 765  * schedule_work_on - put work task on a specific cpu
 766  * @cpu: cpu to put the work task on
 767  * @work: job to be done
 768  *
 769  * This puts a job on a specific cpu
 770  */
 771 int schedule_work_on(int cpu, struct work_struct *work)
 772 {
 773         return queue_work_on(cpu, keventd_wq, work);
 774 }
 775 EXPORT_SYMBOL(schedule_work_on);
 776
 777 /**
 778  * schedule_delayed_work - put work task in global workqueue after delay
 779  * @dwork: job to be done
 780  * @delay: number of jiffies to wait or 0 for immediate execution
 781  *
 782  * After waiting for a given time this puts a job in the kernel-global
 783  * workqueue.
 784  */
 785 int schedule_delayed_work(struct delayed_work *dwork,
 786                                         unsigned long delay)
 787 {
 788         return queue_delayed_work(keventd_wq, dwork, delay);
 789 }
 790 EXPORT_SYMBOL(schedule_delayed_work);
 791
 792 /**
 793  * flush_delayed_work - block until a dwork_struct's callback has terminated
 794  * @dwork: the delayed work which is to be flushed
 795  *
 796  * Any timeout is cancelled, and any pending work is run immediately.
 797  */
 798 void flush_delayed_work(struct delayed_work *dwork)
 799 {
 800         if (del_timer_sync(&dwork->timer)) {
 801                 struct cpu_workqueue_struct *cwq;
 802                 cwq = wq_per_cpu(get_wq_data(&dwork->work)->wq, get_cpu());
 803                 __queue_work(cwq, &dwork->work);
 804                 put_cpu();
 805         }
 806         flush_work(&dwork->work);
 807 }
 808 EXPORT_SYMBOL(flush_delayed_work);
 809
 810 /**
 811  * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
 812  * @cpu: cpu to use
 813  * @dwork: job to be done
 814  * @delay: number of jiffies to wait
 815  *
 816  * After waiting for a given time this puts a job in the kernel-global
 817  * workqueue on the specified CPU.
 818  */
 819 int schedule_delayed_work_on(int cpu,
 820                         struct delayed_work *dwork, unsigned long delay)
 821 {
 822         return queue_delayed_work_on(cpu, keventd_wq, dwork, delay);
 823 }
 824 EXPORT_SYMBOL(schedule_delayed_work_on);
 825
 826 /**
 827  * schedule_on_each_cpu - call a function on each online CPU from keventd
 828  * @func: the function to call
 829  *
 830  * Returns zero on success.
 831  * Returns -ve errno on failure.
 832  *
 833  * schedule_on_each_cpu() is very slow.
 834  */
 835 int schedule_on_each_cpu(work_func_t func)
 836 {
 837         int cpu;
 838         int orig = -1;
 839         struct work_struct *works;
 840
 841         works = alloc_percpu(struct work_struct);
 842         if (!works)
 843                 return -ENOMEM;
 844
 845         get_online_cpus();
 846
 847         /*
 848          * When running in keventd don't schedule a work item on
 849          * itself.  Can just call directly because the work queue is
 850          * already bound.  This also is faster.
 851          */
 852         if (current_is_keventd())
 853                 orig = raw_smp_processor_id();
 854
 855         for_each_online_cpu(cpu) {
 856                 struct work_struct *work = per_cpu_ptr(works, cpu);
 857
 858                 INIT_WORK(work, func);
 859                 if (cpu != orig)
 860                         schedule_work_on(cpu, work);
 861         }
 862         if (orig >= 0)
 863                 func(per_cpu_ptr(works, orig));
 864
 865         for_each_online_cpu(cpu)
 866                 flush_work(per_cpu_ptr(works, cpu));
 867
 868         put_online_cpus();
 869         free_percpu(works);
 870         return 0;
 871 }
 872
 873 /**
 874  * flush_scheduled_work - ensure that any scheduled work has run to completion.
 875  *
 876  * Forces execution of the kernel-global workqueue and blocks until its
 877  * completion.
 878  *
 879  * Think twice before calling this function!  It's very easy to get into
 880  * trouble if you don't take great care.  Either of the following situations
 881  * will lead to deadlock:
 882  *
 883  *      One of the work items currently on the workqueue needs to acquire
 884  *      a lock held by your code or its caller.
 885  *
 886  *      Your code is running in the context of a work routine.
 887  *
 888  * They will be detected by lockdep when they occur, but the first might not
 889  * occur very often.  It depends on what work items are on the workqueue and
 890  * what locks they need, which you have no control over.
 891  *
 892  * In most situations flushing the entire workqueue is overkill; you merely
 893  * need to know that a particular work item isn't queued and isn't running.
 894  * In such cases you should use cancel_delayed_work_sync() or
 895  * cancel_work_sync() instead.
 896  */
 897 void flush_scheduled_work(void)
 898 {
 899         flush_workqueue(keventd_wq);
 900 }
 901 EXPORT_SYMBOL(flush_scheduled_work);
 902
 903 /**
 904  * execute_in_process_context - reliably execute the routine with user context
 905  * @fn:         the function to execute
 906  * @ew:         guaranteed storage for the execute work structure (must
 907  *              be available when the work executes)
 908  *
 909  * Executes the function immediately if process context is available,
 910  * otherwise schedules the function for delayed execution.
 911  *
 912  * Returns:     0 - function was executed
 913  *              1 - function was scheduled for execution
 914  */
 915 int execute_in_process_context(work_func_t fn, struct execute_work *ew)
 916 {
 917         if (!in_interrupt()) {
 918                 fn(&ew->work);
 919                 return 0;
 920         }
 921
 922         INIT_WORK(&ew->work, fn);
 923         schedule_work(&ew->work);
 924
 925         return 1;
 926 }
 927 EXPORT_SYMBOL_GPL(execute_in_process_context);
 928
 929 int keventd_up(void)
 930 {
 931         return keventd_wq != NULL;
 932 }
 933
 934 int current_is_keventd(void)
 935 {
 936         struct cpu_workqueue_struct *cwq;
 937         int cpu = raw_smp_processor_id(); /* preempt-safe: keventd is per-cpu */
 938         int ret = 0;
 939
 940         BUG_ON(!keventd_wq);
 941
 942         cwq = per_cpu_ptr(keventd_wq->cpu_wq, cpu);
 943         if (current == cwq->thread)
 944                 ret = 1;
 945
 946         return ret;
 947
 948 }
 949
 950 static struct cpu_workqueue_struct *
 951 init_cpu_workqueue(struct workqueue_struct *wq, int cpu)
 952 {
 953         struct cpu_workqueue_struct *cwq = per_cpu_ptr(wq->cpu_wq, cpu);
 954
 955         cwq->wq = wq;
 956         spin_lock_init(&cwq->lock);
 957         INIT_LIST_HEAD(&cwq->worklist);
 958         init_waitqueue_head(&cwq->more_work);
 959
 960         return cwq;
 961 }
 962
 963 static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 964 {
 965         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 966         struct workqueue_struct *wq = cwq->wq;
 967         const char *fmt = is_wq_single_threaded(wq) ? "%s" : "%s/%d";
 968         struct task_struct *p;
 969
 970         p = kthread_create(worker_thread, cwq, fmt, wq->name, cpu);
 971         /*
 972          * Nobody can add the work_struct to this cwq,
 973          *      if (caller is __create_workqueue)
 974          *              nobody should see this wq
 975          *      else // caller is CPU_UP_PREPARE
 976          *              cpu is not on cpu_online_map
 977          * so we can abort safely.
 978          */
 979         if (IS_ERR(p))
 980                 return PTR_ERR(p);
 981         if (cwq->wq->rt)
 982                 sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
 983         cwq->thread = p;
 984
 985         trace_workqueue_creation(cwq->thread, cpu);
 986
 987         return 0;
 988 }
 989
 990 static void start_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 991 {
 992         struct task_struct *p = cwq->thread;
 993
 994         if (p != NULL) {
 995                 if (cpu >= 0)
 996                         kthread_bind(p, cpu);
 997                 wake_up_process(p);
 998         }
 999 }
1000
1001 struct workqueue_struct *__create_workqueue_key(const char *name,
1002                                                 int singlethread,
1003                                                 int freezeable,
1004                                                 int rt,
1005                                                 struct lock_class_key *key,
1006                                                 const char *lock_name)
1007 {
1008         struct workqueue_struct *wq;
1009         struct cpu_workqueue_struct *cwq;
1010         int err = 0, cpu;
1011
1012         wq = kzalloc(sizeof(*wq), GFP_KERNEL);
1013         if (!wq)
1014                 return NULL;
1015
1016         wq->cpu_wq = alloc_percpu(struct cpu_workqueue_struct);
1017         if (!wq->cpu_wq) {
1018                 kfree(wq);
1019                 return NULL;
1020         }
1021
1022         wq->name = name;
1023         lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
1024         wq->singlethread = singlethread;
1025         wq->freezeable = freezeable;
1026         wq->rt = rt;
1027         INIT_LIST_HEAD(&wq->list);
1028
1029         if (singlethread) {
1030                 cwq = init_cpu_workqueue(wq, singlethread_cpu);
1031                 err = create_workqueue_thread(cwq, singlethread_cpu);
1032                 start_workqueue_thread(cwq, -1);
1033         } else {
1034                 cpu_maps_update_begin();
1035                 /*
1036                  * We must place this wq on list even if the code below fails.
1037                  * cpu_down(cpu) can remove cpu from cpu_populated_map before
1038                  * destroy_workqueue() takes the lock, in that case we leak
1039                  * cwq[cpu]->thread.
1040                  */
1041                 spin_lock(&workqueue_lock);
1042                 list_add(&wq->list, &workqueues);
1043                 spin_unlock(&workqueue_lock);
1044                 /*
1045                  * We must initialize cwqs for each possible cpu even if we
1046                  * are going to call destroy_workqueue() finally. Otherwise
1047                  * cpu_up() can hit the uninitialized cwq once we drop the
1048                  * lock.
1049                  */
1050                 for_each_possible_cpu(cpu) {
1051                         cwq = init_cpu_workqueue(wq, cpu);
1052                         if (err || !cpu_online(cpu))
1053                                 continue;
1054                         err = create_workqueue_thread(cwq, cpu);
1055                         start_workqueue_thread(cwq, cpu);
1056                 }
1057                 cpu_maps_update_done();
1058         }
1059
1060         if (err) {
1061                 destroy_workqueue(wq);
1062                 wq = NULL;
1063         }
1064         return wq;
1065 }
1066 EXPORT_SYMBOL_GPL(__create_workqueue_key);
1067
1068 static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
1069 {
1070         /*
1071          * Our caller is either destroy_workqueue() or CPU_POST_DEAD,
1072          * cpu_add_remove_lock protects cwq->thread.
1073          */
1074         if (cwq->thread == NULL)
1075                 return;
1076
1077         lock_map_acquire(&cwq->wq->lockdep_map);
1078         lock_map_release(&cwq->wq->lockdep_map);
1079
1080         flush_cpu_workqueue(cwq);
1081         /*
1082          * If the caller is CPU_POST_DEAD and cwq->worklist was not empty,
1083          * a concurrent flush_workqueue() can insert a barrier after us.
1084          * However, in that case run_workqueue() won't return and check
1085          * kthread_should_stop() until it flushes all work_struct's.
1086          * When ->worklist becomes empty it is safe to exit because no
1087          * more work_structs can be queued on this cwq: flush_workqueue
1088          * checks list_empty(), and a "normal" queue_work() can't use
1089          * a dead CPU.
1090          */
1091         trace_workqueue_destruction(cwq->thread);
1092         kthread_stop(cwq->thread);
1093         cwq->thread = NULL;
1094 }
1095
1096 /**
1097  * destroy_workqueue - safely terminate a workqueue
1098  * @wq: target workqueue
1099  *
1100  * Safely destroy a workqueue. All work currently pending will be done first.
1101  */
1102 void destroy_workqueue(struct workqueue_struct *wq)
1103 {
1104         const struct cpumask *cpu_map = wq_cpu_map(wq);
1105         int cpu;
1106
1107         cpu_maps_update_begin();
1108         spin_lock(&workqueue_lock);
1109         list_del(&wq->list);
1110         spin_unlock(&workqueue_lock);
1111
1112         for_each_cpu(cpu, cpu_map)
1113                 cleanup_workqueue_thread(per_cpu_ptr(wq->cpu_wq, cpu));
1114         cpu_maps_update_done();
1115
1116         free_percpu(wq->cpu_wq);
1117         kfree(wq);
1118 }
1119 EXPORT_SYMBOL_GPL(destroy_workqueue);
1120
1121 static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
1122                                                 unsigned long action,
1123                                                 void *hcpu)
1124 {
1125         unsigned int cpu = (unsigned long)hcpu;
1126         struct cpu_workqueue_struct *cwq;
1127         struct workqueue_struct *wq;
1128         int err = 0;
1129
1130         action &= ~CPU_TASKS_FROZEN;
1131
1132         switch (action) {
1133         case CPU_UP_PREPARE:
1134                 cpumask_set_cpu(cpu, cpu_populated_map);
1135         }
1136 undo:
1137         list_for_each_entry(wq, &workqueues, list) {
1138                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
1139
1140                 switch (action) {
1141                 case CPU_UP_PREPARE:
1142                         err = create_workqueue_thread(cwq, cpu);
1143                         if (!err)
1144                                 break;
1145                         printk(KERN_ERR "workqueue [%s] for %i failed\n",
1146                                 wq->name, cpu);
1147                         action = CPU_UP_CANCELED;
1148                         err = -ENOMEM;
1149                         goto undo;
1150
1151                 case CPU_ONLINE:
1152                         start_workqueue_thread(cwq, cpu);
1153                         break;
1154
1155                 case CPU_UP_CANCELED:
1156                         start_workqueue_thread(cwq, -1);
1157                 case CPU_POST_DEAD:
1158                         cleanup_workqueue_thread(cwq);
1159                         break;
1160                 }
1161         }
1162
1163         switch (action) {
1164         case CPU_UP_CANCELED:
1165         case CPU_POST_DEAD:
1166                 cpumask_clear_cpu(cpu, cpu_populated_map);
1167         }
1168
1169         return notifier_from_errno(err);
1170 }
1171
1172 #ifdef CONFIG_SMP
1173
1174 struct work_for_cpu {
1175         struct completion completion;
1176         long (*fn)(void *);
1177         void *arg;
1178         long ret;
1179 };
1180
1181 static int do_work_for_cpu(void *_wfc)
1182 {
1183         struct work_for_cpu *wfc = _wfc;
1184         wfc->ret = wfc->fn(wfc->arg);
1185         complete(&wfc->completion);
1186         return 0;
1187 }
1188
1189 /**
1190  * work_on_cpu - run a function in user context on a particular cpu
1191  * @cpu: the cpu to run on
1192  * @fn: the function to run
1193  * @arg: the function arg
1194  *
1195  * This will return the value @fn returns.
1196  * It is up to the caller to ensure that the cpu doesn't go offline.
1197  * The caller must not hold any locks which would prevent @fn from completing.
1198  */
1199 long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
1200 {
1201         struct task_struct *sub_thread;
1202         struct work_for_cpu wfc = {
1203                 .completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
1204                 .fn = fn,
1205                 .arg = arg,
1206         };
1207
1208         sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
1209         if (IS_ERR(sub_thread))
1210                 return PTR_ERR(sub_thread);
1211         kthread_bind(sub_thread, cpu);
1212         wake_up_process(sub_thread);
1213         wait_for_completion(&wfc.completion);
1214         return wfc.ret;
1215 }
1216 EXPORT_SYMBOL_GPL(work_on_cpu);
1217 #endif /* CONFIG_SMP */
1218
1219 void __init init_workqueues(void)
1220 {
1221         alloc_cpumask_var(&cpu_populated_map, GFP_KERNEL);
1222
1223         cpumask_copy(cpu_populated_map, cpu_online_mask);
1224         singlethread_cpu = cpumask_first(cpu_possible_mask);
1225         cpu_singlethread_map = cpumask_of(singlethread_cpu);
1226         hotcpu_notifier(workqueue_cpu_callback, 0);
1227         keventd_wq = create_workqueue("events");
1228         BUG_ON(!keventd_wq);
1229 }