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