kernel/sched/wait.c

   1 /*
   2  * Generic waiting primitives.
   3  *
   4  * (C) 2004 Nadia Yvette Chambers, Oracle
   5  */
   6 #include <linux/init.h>
   7 #include <linux/export.h>
   8 #include <linux/sched/signal.h>
   9 #include <linux/sched/debug.h>
  10 #include <linux/mm.h>
  11 #include <linux/wait.h>
  12 #include <linux/hash.h>
  13 #include <linux/kthread.h>
  14
  15 void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
  16 {
  17         spin_lock_init(&q->lock);
  18         lockdep_set_class_and_name(&q->lock, key, name);
  19         INIT_LIST_HEAD(&q->task_list);
  20 }
  21
  22 EXPORT_SYMBOL(__init_waitqueue_head);
  23
  24 void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  25 {
  26         unsigned long flags;
  27
  28         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  29         spin_lock_irqsave(&q->lock, flags);
  30         __add_wait_queue(q, wait);
  31         spin_unlock_irqrestore(&q->lock, flags);
  32 }
  33 EXPORT_SYMBOL(add_wait_queue);
  34
  35 void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
  36 {
  37         unsigned long flags;
  38
  39         wait->flags |= WQ_FLAG_EXCLUSIVE;
  40         spin_lock_irqsave(&q->lock, flags);
  41         __add_wait_queue_tail(q, wait);
  42         spin_unlock_irqrestore(&q->lock, flags);
  43 }
  44 EXPORT_SYMBOL(add_wait_queue_exclusive);
  45
  46 void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  47 {
  48         unsigned long flags;
  49
  50         spin_lock_irqsave(&q->lock, flags);
  51         __remove_wait_queue(q, wait);
  52         spin_unlock_irqrestore(&q->lock, flags);
  53 }
  54 EXPORT_SYMBOL(remove_wait_queue);
  55
  56
  57 /*
  58  * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
  59  * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
  60  * number) then we wake all the non-exclusive tasks and one exclusive task.
  61  *
  62  * There are circumstances in which we can try to wake a task which has already
  63  * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
  64  * zero in this (rare) case, and we handle it by continuing to scan the queue.
  65  */
  66 static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
  67                         int nr_exclusive, int wake_flags, void *key)
  68 {
  69         wait_queue_t *curr, *next;
  70
  71         list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
  72                 unsigned flags = curr->flags;
  73
  74                 if (curr->func(curr, mode, wake_flags, key) &&
  75                                 (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
  76                         break;
  77         }
  78 }
  79
  80 /**
  81  * __wake_up - wake up threads blocked on a waitqueue.
  82  * @q: the waitqueue
  83  * @mode: which threads
  84  * @nr_exclusive: how many wake-one or wake-many threads to wake up
  85  * @key: is directly passed to the wakeup function
  86  *
  87  * It may be assumed that this function implies a write memory barrier before
  88  * changing the task state if and only if any tasks are woken up.
  89  */
  90 void __wake_up(wait_queue_head_t *q, unsigned int mode,
  91                         int nr_exclusive, void *key)
  92 {
  93         unsigned long flags;
  94
  95         spin_lock_irqsave(&q->lock, flags);
  96         __wake_up_common(q, mode, nr_exclusive, 0, key);
  97         spin_unlock_irqrestore(&q->lock, flags);
  98 }
  99 EXPORT_SYMBOL(__wake_up);
 100
 101 /*
 102  * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
 103  */
 104 void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
 105 {
 106         __wake_up_common(q, mode, nr, 0, NULL);
 107 }
 108 EXPORT_SYMBOL_GPL(__wake_up_locked);
 109
 110 void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
 111 {
 112         __wake_up_common(q, mode, 1, 0, key);
 113 }
 114 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
 115
 116 /**
 117  * __wake_up_sync_key - wake up threads blocked on a waitqueue.
 118  * @q: the waitqueue
 119  * @mode: which threads
 120  * @nr_exclusive: how many wake-one or wake-many threads to wake up
 121  * @key: opaque value to be passed to wakeup targets
 122  *
 123  * The sync wakeup differs that the waker knows that it will schedule
 124  * away soon, so while the target thread will be woken up, it will not
 125  * be migrated to another CPU - ie. the two threads are 'synchronized'
 126  * with each other. This can prevent needless bouncing between CPUs.
 127  *
 128  * On UP it can prevent extra preemption.
 129  *
 130  * It may be assumed that this function implies a write memory barrier before
 131  * changing the task state if and only if any tasks are woken up.
 132  */
 133 void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
 134                         int nr_exclusive, void *key)
 135 {
 136         unsigned long flags;
 137         int wake_flags = 1; /* XXX WF_SYNC */
 138
 139         if (unlikely(!q))
 140                 return;
 141
 142         if (unlikely(nr_exclusive != 1))
 143                 wake_flags = 0;
 144
 145         spin_lock_irqsave(&q->lock, flags);
 146         __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
 147         spin_unlock_irqrestore(&q->lock, flags);
 148 }
 149 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
 150
 151 /*
 152  * __wake_up_sync - see __wake_up_sync_key()
 153  */
 154 void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
 155 {
 156         __wake_up_sync_key(q, mode, nr_exclusive, NULL);
 157 }
 158 EXPORT_SYMBOL_GPL(__wake_up_sync);      /* For internal use only */
 159
 160 /*
 161  * Note: we use "set_current_state()" _after_ the wait-queue add,
 162  * because we need a memory barrier there on SMP, so that any
 163  * wake-function that tests for the wait-queue being active
 164  * will be guaranteed to see waitqueue addition _or_ subsequent
 165  * tests in this thread will see the wakeup having taken place.
 166  *
 167  * The spin_unlock() itself is semi-permeable and only protects
 168  * one way (it only protects stuff inside the critical region and
 169  * stops them from bleeding out - it would still allow subsequent
 170  * loads to move into the critical region).
 171  */
 172 void
 173 prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
 174 {
 175         unsigned long flags;
 176
 177         wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 178         spin_lock_irqsave(&q->lock, flags);
 179         if (list_empty(&wait->task_list))
 180                 __add_wait_queue(q, wait);
 181         set_current_state(state);
 182         spin_unlock_irqrestore(&q->lock, flags);
 183 }
 184 EXPORT_SYMBOL(prepare_to_wait);
 185
 186 void
 187 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 188 {
 189         unsigned long flags;
 190
 191         wait->flags |= WQ_FLAG_EXCLUSIVE;
 192         spin_lock_irqsave(&q->lock, flags);
 193         if (list_empty(&wait->task_list))
 194                 __add_wait_queue_tail(q, wait);
 195         set_current_state(state);
 196         spin_unlock_irqrestore(&q->lock, flags);
 197 }
 198 EXPORT_SYMBOL(prepare_to_wait_exclusive);
 199
 200 void init_wait_entry(wait_queue_t *wait, int flags)
 201 {
 202         wait->flags = flags;
 203         wait->private = current;
 204         wait->func = autoremove_wake_function;
 205         INIT_LIST_HEAD(&wait->task_list);
 206 }
 207 EXPORT_SYMBOL(init_wait_entry);
 208
 209 long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
 210 {
 211         unsigned long flags;
 212         long ret = 0;
 213
 214         spin_lock_irqsave(&q->lock, flags);
 215         if (unlikely(signal_pending_state(state, current))) {
 216                 /*
 217                  * Exclusive waiter must not fail if it was selected by wakeup,
 218                  * it should "consume" the condition we were waiting for.
 219                  *
 220                  * The caller will recheck the condition and return success if
 221                  * we were already woken up, we can not miss the event because
 222                  * wakeup locks/unlocks the same q->lock.
 223                  *
 224                  * But we need to ensure that set-condition + wakeup after that
 225                  * can't see us, it should wake up another exclusive waiter if
 226                  * we fail.
 227                  */
 228                 list_del_init(&wait->task_list);
 229                 ret = -ERESTARTSYS;
 230         } else {
 231                 if (list_empty(&wait->task_list)) {
 232                         if (wait->flags & WQ_FLAG_EXCLUSIVE)
 233                                 __add_wait_queue_tail(q, wait);
 234                         else
 235                                 __add_wait_queue(q, wait);
 236                 }
 237                 set_current_state(state);
 238         }
 239         spin_unlock_irqrestore(&q->lock, flags);
 240
 241         return ret;
 242 }
 243 EXPORT_SYMBOL(prepare_to_wait_event);
 244
 245 /**
 246  * finish_wait - clean up after waiting in a queue
 247  * @q: waitqueue waited on
 248  * @wait: wait descriptor
 249  *
 250  * Sets current thread back to running state and removes
 251  * the wait descriptor from the given waitqueue if still
 252  * queued.
 253  */
 254 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
 255 {
 256         unsigned long flags;
 257
 258         __set_current_state(TASK_RUNNING);
 259         /*
 260          * We can check for list emptiness outside the lock
 261          * IFF:
 262          *  - we use the "careful" check that verifies both
 263          *    the next and prev pointers, so that there cannot
 264          *    be any half-pending updates in progress on other
 265          *    CPU's that we haven't seen yet (and that might
 266          *    still change the stack area.
 267          * and
 268          *  - all other users take the lock (ie we can only
 269          *    have _one_ other CPU that looks at or modifies
 270          *    the list).
 271          */
 272         if (!list_empty_careful(&wait->task_list)) {
 273                 spin_lock_irqsave(&q->lock, flags);
 274                 list_del_init(&wait->task_list);
 275                 spin_unlock_irqrestore(&q->lock, flags);
 276         }
 277 }
 278 EXPORT_SYMBOL(finish_wait);
 279
 280 int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
 281 {
 282         int ret = default_wake_function(wait, mode, sync, key);
 283
 284         if (ret)
 285                 list_del_init(&wait->task_list);
 286         return ret;
 287 }
 288 EXPORT_SYMBOL(autoremove_wake_function);
 289
 290 static inline bool is_kthread_should_stop(void)
 291 {
 292         return (current->flags & PF_KTHREAD) && kthread_should_stop();
 293 }
 294
 295 /*
 296  * DEFINE_WAIT_FUNC(wait, woken_wake_func);
 297  *
 298  * add_wait_queue(&wq, &wait);
 299  * for (;;) {
 300  *     if (condition)
 301  *         break;
 302  *
 303  *     p->state = mode;                         condition = true;
 304  *     smp_mb(); // A                           smp_wmb(); // C
 305  *     if (!wait->flags & WQ_FLAG_WOKEN)        wait->flags |= WQ_FLAG_WOKEN;
 306  *         schedule()                           try_to_wake_up();
 307  *     p->state = TASK_RUNNING;             ~~~~~~~~~~~~~~~~~~
 308  *     wait->flags &= ~WQ_FLAG_WOKEN;           condition = true;
 309  *     smp_mb() // B                            smp_wmb(); // C
 310  *                                              wait->flags |= WQ_FLAG_WOKEN;
 311  * }
 312  * remove_wait_queue(&wq, &wait);
 313  *
 314  */
 315 long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
 316 {
 317         set_current_state(mode); /* A */
 318         /*
 319          * The above implies an smp_mb(), which matches with the smp_wmb() from
 320          * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
 321          * also observe all state before the wakeup.
 322          */
 323         if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
 324                 timeout = schedule_timeout(timeout);
 325         __set_current_state(TASK_RUNNING);
 326
 327         /*
 328          * The below implies an smp_mb(), it too pairs with the smp_wmb() from
 329          * woken_wake_function() such that we must either observe the wait
 330          * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
 331          * an event.
 332          */
 333         smp_store_mb(wait->flags, wait->flags & ~WQ_FLAG_WOKEN); /* B */
 334
 335         return timeout;
 336 }
 337 EXPORT_SYMBOL(wait_woken);
 338
 339 int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
 340 {
 341         /*
 342          * Although this function is called under waitqueue lock, LOCK
 343          * doesn't imply write barrier and the users expects write
 344          * barrier semantics on wakeup functions.  The following
 345          * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
 346          * and is paired with smp_store_mb() in wait_woken().
 347          */
 348         smp_wmb(); /* C */
 349         wait->flags |= WQ_FLAG_WOKEN;
 350
 351         return default_wake_function(wait, mode, sync, key);
 352 }
 353 EXPORT_SYMBOL(woken_wake_function);
 354
 355 int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
 356 {
 357         struct wait_bit_key *key = arg;
 358         struct wait_bit_queue *wait_bit
 359                 = container_of(wait, struct wait_bit_queue, wait);
 360
 361         if (wait_bit->key.flags != key->flags ||
 362                         wait_bit->key.bit_nr != key->bit_nr ||
 363                         test_bit(key->bit_nr, key->flags))
 364                 return 0;
 365         else
 366                 return autoremove_wake_function(wait, mode, sync, key);
 367 }
 368 EXPORT_SYMBOL(wake_bit_function);
 369
 370 /*
 371  * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 372  * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 373  * permitted return codes. Nonzero return codes halt waiting and return.
 374  */
 375 int __sched
 376 __wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
 377               wait_bit_action_f *action, unsigned mode)
 378 {
 379         int ret = 0;
 380
 381         do {
 382                 prepare_to_wait(wq, &q->wait, mode);
 383                 if (test_bit(q->key.bit_nr, q->key.flags))
 384                         ret = (*action)(&q->key, mode);
 385         } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 386         finish_wait(wq, &q->wait);
 387         return ret;
 388 }
 389 EXPORT_SYMBOL(__wait_on_bit);
 390
 391 int __sched out_of_line_wait_on_bit(void *word, int bit,
 392                                     wait_bit_action_f *action, unsigned mode)
 393 {
 394         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 395         DEFINE_WAIT_BIT(wait, word, bit);
 396
 397         return __wait_on_bit(wq, &wait, action, mode);
 398 }
 399 EXPORT_SYMBOL(out_of_line_wait_on_bit);
 400
 401 int __sched out_of_line_wait_on_bit_timeout(
 402         void *word, int bit, wait_bit_action_f *action,
 403         unsigned mode, unsigned long timeout)
 404 {
 405         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 406         DEFINE_WAIT_BIT(wait, word, bit);
 407
 408         wait.key.timeout = jiffies + timeout;
 409         return __wait_on_bit(wq, &wait, action, mode);
 410 }
 411 EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
 412
 413 int __sched
 414 __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 415                         wait_bit_action_f *action, unsigned mode)
 416 {
 417         int ret = 0;
 418
 419         for (;;) {
 420                 prepare_to_wait_exclusive(wq, &q->wait, mode);
 421                 if (test_bit(q->key.bit_nr, q->key.flags)) {
 422                         ret = action(&q->key, mode);
 423                         /*
 424                          * See the comment in prepare_to_wait_event().
 425                          * finish_wait() does not necessarily takes wq->lock,
 426                          * but test_and_set_bit() implies mb() which pairs with
 427                          * smp_mb__after_atomic() before wake_up_page().
 428                          */
 429                         if (ret)
 430                                 finish_wait(wq, &q->wait);
 431                 }
 432                 if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
 433                         if (!ret)
 434                                 finish_wait(wq, &q->wait);
 435                         return 0;
 436                 } else if (ret) {
 437                         return ret;
 438                 }
 439         }
 440 }
 441 EXPORT_SYMBOL(__wait_on_bit_lock);
 442
 443 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
 444                                          wait_bit_action_f *action, unsigned mode)
 445 {
 446         wait_queue_head_t *wq = bit_waitqueue(word, bit);
 447         DEFINE_WAIT_BIT(wait, word, bit);
 448
 449         return __wait_on_bit_lock(wq, &wait, action, mode);
 450 }
 451 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 452
 453 void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
 454 {
 455         struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
 456         if (waitqueue_active(wq))
 457                 __wake_up(wq, TASK_NORMAL, 1, &key);
 458 }
 459 EXPORT_SYMBOL(__wake_up_bit);
 460
 461 /**
 462  * wake_up_bit - wake up a waiter on a bit
 463  * @word: the word being waited on, a kernel virtual address
 464  * @bit: the bit of the word being waited on
 465  *
 466  * There is a standard hashed waitqueue table for generic use. This
 467  * is the part of the hashtable's accessor API that wakes up waiters
 468  * on a bit. For instance, if one were to have waiters on a bitflag,
 469  * one would call wake_up_bit() after clearing the bit.
 470  *
 471  * In order for this to function properly, as it uses waitqueue_active()
 472  * internally, some kind of memory barrier must be done prior to calling
 473  * this. Typically, this will be smp_mb__after_atomic(), but in some
 474  * cases where bitflags are manipulated non-atomically under a lock, one
 475  * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 476  * because spin_unlock() does not guarantee a memory barrier.
 477  */
 478 void wake_up_bit(void *word, int bit)
 479 {
 480         __wake_up_bit(bit_waitqueue(word, bit), word, bit);
 481 }
 482 EXPORT_SYMBOL(wake_up_bit);
 483
 484 /*
 485  * Manipulate the atomic_t address to produce a better bit waitqueue table hash
 486  * index (we're keying off bit -1, but that would produce a horrible hash
 487  * value).
 488  */
 489 static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
 490 {
 491         if (BITS_PER_LONG == 64) {
 492                 unsigned long q = (unsigned long)p;
 493                 return bit_waitqueue((void *)(q & ~1), q & 1);
 494         }
 495         return bit_waitqueue(p, 0);
 496 }
 497
 498 static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
 499                                   void *arg)
 500 {
 501         struct wait_bit_key *key = arg;
 502         struct wait_bit_queue *wait_bit
 503                 = container_of(wait, struct wait_bit_queue, wait);
 504         atomic_t *val = key->flags;
 505
 506         if (wait_bit->key.flags != key->flags ||
 507             wait_bit->key.bit_nr != key->bit_nr ||
 508             atomic_read(val) != 0)
 509                 return 0;
 510         return autoremove_wake_function(wait, mode, sync, key);
 511 }
 512
 513 /*
 514  * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
 515  * the actions of __wait_on_atomic_t() are permitted return codes.  Nonzero
 516  * return codes halt waiting and return.
 517  */
 518 static __sched
 519 int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
 520                        int (*action)(atomic_t *), unsigned mode)
 521 {
 522         atomic_t *val;
 523         int ret = 0;
 524
 525         do {
 526                 prepare_to_wait(wq, &q->wait, mode);
 527                 val = q->key.flags;
 528                 if (atomic_read(val) == 0)
 529                         break;
 530                 ret = (*action)(val);
 531         } while (!ret && atomic_read(val) != 0);
 532         finish_wait(wq, &q->wait);
 533         return ret;
 534 }
 535
 536 #define DEFINE_WAIT_ATOMIC_T(name, p)                                   \
 537         struct wait_bit_queue name = {                                  \
 538                 .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),              \
 539                 .wait   = {                                             \
 540                         .private        = current,                      \
 541                         .func           = wake_atomic_t_function,       \
 542                         .task_list      =                               \
 543                                 LIST_HEAD_INIT((name).wait.task_list),  \
 544                 },                                                      \
 545         }
 546
 547 __sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
 548                                          unsigned mode)
 549 {
 550         wait_queue_head_t *wq = atomic_t_waitqueue(p);
 551         DEFINE_WAIT_ATOMIC_T(wait, p);
 552
 553         return __wait_on_atomic_t(wq, &wait, action, mode);
 554 }
 555 EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
 556
 557 /**
 558  * wake_up_atomic_t - Wake up a waiter on a atomic_t
 559  * @p: The atomic_t being waited on, a kernel virtual address
 560  *
 561  * Wake up anyone waiting for the atomic_t to go to zero.
 562  *
 563  * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
 564  * check is done by the waiter's wake function, not the by the waker itself).
 565  */
 566 void wake_up_atomic_t(atomic_t *p)
 567 {
 568         __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
 569 }
 570 EXPORT_SYMBOL(wake_up_atomic_t);
 571
 572 __sched int bit_wait(struct wait_bit_key *word, int mode)
 573 {
 574         schedule();
 575         if (signal_pending_state(mode, current))
 576                 return -EINTR;
 577         return 0;
 578 }
 579 EXPORT_SYMBOL(bit_wait);
 580
 581 __sched int bit_wait_io(struct wait_bit_key *word, int mode)
 582 {
 583         io_schedule();
 584         if (signal_pending_state(mode, current))
 585                 return -EINTR;
 586         return 0;
 587 }
 588 EXPORT_SYMBOL(bit_wait_io);
 589
 590 __sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
 591 {
 592         unsigned long now = READ_ONCE(jiffies);
 593         if (time_after_eq(now, word->timeout))
 594                 return -EAGAIN;
 595         schedule_timeout(word->timeout - now);
 596         if (signal_pending_state(mode, current))
 597                 return -EINTR;
 598         return 0;
 599 }
 600 EXPORT_SYMBOL_GPL(bit_wait_timeout);
 601
 602 __sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
 603 {
 604         unsigned long now = READ_ONCE(jiffies);
 605         if (time_after_eq(now, word->timeout))
 606                 return -EAGAIN;
 607         io_schedule_timeout(word->timeout - now);
 608         if (signal_pending_state(mode, current))
 609                 return -EINTR;
 610         return 0;
 611 }
 612 EXPORT_SYMBOL_GPL(bit_wait_io_timeout);