kernel/futex/waitwake.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2
   3 #include <linux/sched/task.h>
   4 #include <linux/sched/signal.h>
   5 #include <linux/freezer.h>
   6
   7 #include "futex.h"
   8
   9 /*
  10  * READ this before attempting to hack on futexes!
  11  *
  12  * Basic futex operation and ordering guarantees
  13  * =============================================
  14  *
  15  * The waiter reads the futex value in user space and calls
  16  * futex_wait(). This function computes the hash bucket and acquires
  17  * the hash bucket lock. After that it reads the futex user space value
  18  * again and verifies that the data has not changed. If it has not changed
  19  * it enqueues itself into the hash bucket, releases the hash bucket lock
  20  * and schedules.
  21  *
  22  * The waker side modifies the user space value of the futex and calls
  23  * futex_wake(). This function computes the hash bucket and acquires the
  24  * hash bucket lock. Then it looks for waiters on that futex in the hash
  25  * bucket and wakes them.
  26  *
  27  * In futex wake up scenarios where no tasks are blocked on a futex, taking
  28  * the hb spinlock can be avoided and simply return. In order for this
  29  * optimization to work, ordering guarantees must exist so that the waiter
  30  * being added to the list is acknowledged when the list is concurrently being
  31  * checked by the waker, avoiding scenarios like the following:
  32  *
  33  * CPU 0                               CPU 1
  34  * val = *futex;
  35  * sys_futex(WAIT, futex, val);
  36  *   futex_wait(futex, val);
  37  *   uval = *futex;
  38  *                                     *futex = newval;
  39  *                                     sys_futex(WAKE, futex);
  40  *                                       futex_wake(futex);
  41  *                                       if (queue_empty())
  42  *                                         return;
  43  *   if (uval == val)
  44  *      lock(hash_bucket(futex));
  45  *      queue();
  46  *     unlock(hash_bucket(futex));
  47  *     schedule();
  48  *
  49  * This would cause the waiter on CPU 0 to wait forever because it
  50  * missed the transition of the user space value from val to newval
  51  * and the waker did not find the waiter in the hash bucket queue.
  52  *
  53  * The correct serialization ensures that a waiter either observes
  54  * the changed user space value before blocking or is woken by a
  55  * concurrent waker:
  56  *
  57  * CPU 0                                 CPU 1
  58  * val = *futex;
  59  * sys_futex(WAIT, futex, val);
  60  *   futex_wait(futex, val);
  61  *
  62  *   waiters++; (a)
  63  *   smp_mb(); (A) <-- paired with -.
  64  *                                  |
  65  *   lock(hash_bucket(futex));      |
  66  *                                  |
  67  *   uval = *futex;                 |
  68  *                                  |        *futex = newval;
  69  *                                  |        sys_futex(WAKE, futex);
  70  *                                  |          futex_wake(futex);
  71  *                                  |
  72  *                                  `--------> smp_mb(); (B)
  73  *   if (uval == val)
  74  *     queue();
  75  *     unlock(hash_bucket(futex));
  76  *     schedule();                         if (waiters)
  77  *                                           lock(hash_bucket(futex));
  78  *   else                                    wake_waiters(futex);
  79  *     waiters--; (b)                        unlock(hash_bucket(futex));
  80  *
  81  * Where (A) orders the waiters increment and the futex value read through
  82  * atomic operations (see futex_hb_waiters_inc) and where (B) orders the write
  83  * to futex and the waiters read (see futex_hb_waiters_pending()).
  84  *
  85  * This yields the following case (where X:=waiters, Y:=futex):
  86  *
  87  *      X = Y = 0
  88  *
  89  *      w[X]=1          w[Y]=1
  90  *      MB              MB
  91  *      r[Y]=y          r[X]=x
  92  *
  93  * Which guarantees that x==0 && y==0 is impossible; which translates back into
  94  * the guarantee that we cannot both miss the futex variable change and the
  95  * enqueue.
  96  *
  97  * Note that a new waiter is accounted for in (a) even when it is possible that
  98  * the wait call can return error, in which case we backtrack from it in (b).
  99  * Refer to the comment in futex_q_lock().
 100  *
 101  * Similarly, in order to account for waiters being requeued on another
 102  * address we always increment the waiters for the destination bucket before
 103  * acquiring the lock. It then decrements them again  after releasing it -
 104  * the code that actually moves the futex(es) between hash buckets (requeue_futex)
 105  * will do the additional required waiter count housekeeping. This is done for
 106  * double_lock_hb() and double_unlock_hb(), respectively.
 107  */
 108
 109 bool __futex_wake_mark(struct futex_q *q)
 110 {
 111         if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
 112                 return false;
 113
 114         __futex_unqueue(q);
 115         /*
 116          * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
 117          * is written, without taking any locks. This is possible in the event
 118          * of a spurious wakeup, for example. A memory barrier is required here
 119          * to prevent the following store to lock_ptr from getting ahead of the
 120          * plist_del in __futex_unqueue().
 121          */
 122         smp_store_release(&q->lock_ptr, NULL);
 123
 124         return true;
 125 }
 126
 127 /*
 128  * The hash bucket lock must be held when this is called.
 129  * Afterwards, the futex_q must not be accessed. Callers
 130  * must ensure to later call wake_up_q() for the actual
 131  * wakeups to occur.
 132  */
 133 void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q)
 134 {
 135         struct task_struct *p = q->task;
 136
 137         get_task_struct(p);
 138
 139         if (!__futex_wake_mark(q)) {
 140                 put_task_struct(p);
 141                 return;
 142         }
 143
 144         /*
 145          * Queue the task for later wakeup for after we've released
 146          * the hb->lock.
 147          */
 148         wake_q_add_safe(wake_q, p);
 149 }
 150
 151 /*
 152  * Wake up waiters matching bitset queued on this futex (uaddr).
 153  */
 154 int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
 155 {
 156         struct futex_hash_bucket *hb;
 157         struct futex_q *this, *next;
 158         union futex_key key = FUTEX_KEY_INIT;
 159         DEFINE_WAKE_Q(wake_q);
 160         int ret;
 161
 162         if (!bitset)
 163                 return -EINVAL;
 164
 165         ret = get_futex_key(uaddr, flags, &key, FUTEX_READ);
 166         if (unlikely(ret != 0))
 167                 return ret;
 168
 169         if ((flags & FLAGS_STRICT) && !nr_wake)
 170                 return 0;
 171
 172         hb = futex_hash(&key);
 173
 174         /* Make sure we really have tasks to wakeup */
 175         if (!futex_hb_waiters_pending(hb))
 176                 return ret;
 177
 178         spin_lock(&hb->lock);
 179
 180         plist_for_each_entry_safe(this, next, &hb->chain, list) {
 181                 if (futex_match (&this->key, &key)) {
 182                         if (this->pi_state || this->rt_waiter) {
 183                                 ret = -EINVAL;
 184                                 break;
 185                         }
 186
 187                         /* Check if one of the bits is set in both bitsets */
 188                         if (!(this->bitset & bitset))
 189                                 continue;
 190
 191                         this->wake(&wake_q, this);
 192                         if (++ret >= nr_wake)
 193                                 break;
 194                 }
 195         }
 196
 197         spin_unlock(&hb->lock);
 198         wake_up_q(&wake_q);
 199         return ret;
 200 }
 201
 202 static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
 203 {
 204         unsigned int op =         (encoded_op & 0x70000000) >> 28;
 205         unsigned int cmp =        (encoded_op & 0x0f000000) >> 24;
 206         int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
 207         int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
 208         int oldval, ret;
 209
 210         if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
 211                 if (oparg < 0 || oparg > 31) {
 212                         char comm[sizeof(current->comm)];
 213                         /*
 214                          * kill this print and return -EINVAL when userspace
 215                          * is sane again
 216                          */
 217                         pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
 218                                         get_task_comm(comm, current), oparg);
 219                         oparg &= 31;
 220                 }
 221                 oparg = 1 << oparg;
 222         }
 223
 224         pagefault_disable();
 225         ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
 226         pagefault_enable();
 227         if (ret)
 228                 return ret;
 229
 230         switch (cmp) {
 231         case FUTEX_OP_CMP_EQ:
 232                 return oldval == cmparg;
 233         case FUTEX_OP_CMP_NE:
 234                 return oldval != cmparg;
 235         case FUTEX_OP_CMP_LT:
 236                 return oldval < cmparg;
 237         case FUTEX_OP_CMP_GE:
 238                 return oldval >= cmparg;
 239         case FUTEX_OP_CMP_LE:
 240                 return oldval <= cmparg;
 241         case FUTEX_OP_CMP_GT:
 242                 return oldval > cmparg;
 243         default:
 244                 return -ENOSYS;
 245         }
 246 }
 247
 248 /*
 249  * Wake up all waiters hashed on the physical page that is mapped
 250  * to this virtual address:
 251  */
 252 int futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
 253                   int nr_wake, int nr_wake2, int op)
 254 {
 255         union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
 256         struct futex_hash_bucket *hb1, *hb2;
 257         struct futex_q *this, *next;
 258         int ret, op_ret;
 259         DEFINE_WAKE_Q(wake_q);
 260
 261 retry:
 262         ret = get_futex_key(uaddr1, flags, &key1, FUTEX_READ);
 263         if (unlikely(ret != 0))
 264                 return ret;
 265         ret = get_futex_key(uaddr2, flags, &key2, FUTEX_WRITE);
 266         if (unlikely(ret != 0))
 267                 return ret;
 268
 269         hb1 = futex_hash(&key1);
 270         hb2 = futex_hash(&key2);
 271
 272 retry_private:
 273         double_lock_hb(hb1, hb2);
 274         op_ret = futex_atomic_op_inuser(op, uaddr2);
 275         if (unlikely(op_ret < 0)) {
 276                 double_unlock_hb(hb1, hb2);
 277
 278                 if (!IS_ENABLED(CONFIG_MMU) ||
 279                     unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
 280                         /*
 281                          * we don't get EFAULT from MMU faults if we don't have
 282                          * an MMU, but we might get them from range checking
 283                          */
 284                         ret = op_ret;
 285                         return ret;
 286                 }
 287
 288                 if (op_ret == -EFAULT) {
 289                         ret = fault_in_user_writeable(uaddr2);
 290                         if (ret)
 291                                 return ret;
 292                 }
 293
 294                 cond_resched();
 295                 if (!(flags & FLAGS_SHARED))
 296                         goto retry_private;
 297                 goto retry;
 298         }
 299
 300         plist_for_each_entry_safe(this, next, &hb1->chain, list) {
 301                 if (futex_match (&this->key, &key1)) {
 302                         if (this->pi_state || this->rt_waiter) {
 303                                 ret = -EINVAL;
 304                                 goto out_unlock;
 305                         }
 306                         this->wake(&wake_q, this);
 307                         if (++ret >= nr_wake)
 308                                 break;
 309                 }
 310         }
 311
 312         if (op_ret > 0) {
 313                 op_ret = 0;
 314                 plist_for_each_entry_safe(this, next, &hb2->chain, list) {
 315                         if (futex_match (&this->key, &key2)) {
 316                                 if (this->pi_state || this->rt_waiter) {
 317                                         ret = -EINVAL;
 318                                         goto out_unlock;
 319                                 }
 320                                 this->wake(&wake_q, this);
 321                                 if (++op_ret >= nr_wake2)
 322                                         break;
 323                         }
 324                 }
 325                 ret += op_ret;
 326         }
 327
 328 out_unlock:
 329         double_unlock_hb(hb1, hb2);
 330         wake_up_q(&wake_q);
 331         return ret;
 332 }
 333
 334 static long futex_wait_restart(struct restart_block *restart);
 335
 336 /**
 337  * futex_wait_queue() - futex_queue() and wait for wakeup, timeout, or signal
 338  * @hb:         the futex hash bucket, must be locked by the caller
 339  * @q:          the futex_q to queue up on
 340  * @timeout:    the prepared hrtimer_sleeper, or null for no timeout
 341  */
 342 void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
 343                             struct hrtimer_sleeper *timeout)
 344 {
 345         /*
 346          * The task state is guaranteed to be set before another task can
 347          * wake it. set_current_state() is implemented using smp_store_mb() and
 348          * futex_queue() calls spin_unlock() upon completion, both serializing
 349          * access to the hash list and forcing another memory barrier.
 350          */
 351         set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
 352         futex_queue(q, hb);
 353
 354         /* Arm the timer */
 355         if (timeout)
 356                 hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
 357
 358         /*
 359          * If we have been removed from the hash list, then another task
 360          * has tried to wake us, and we can skip the call to schedule().
 361          */
 362         if (likely(!plist_node_empty(&q->list))) {
 363                 /*
 364                  * If the timer has already expired, current will already be
 365                  * flagged for rescheduling. Only call schedule if there
 366                  * is no timeout, or if it has yet to expire.
 367                  */
 368                 if (!timeout || timeout->task)
 369                         schedule();
 370         }
 371         __set_current_state(TASK_RUNNING);
 372 }
 373
 374 /**
 375  * futex_unqueue_multiple - Remove various futexes from their hash bucket
 376  * @v:     The list of futexes to unqueue
 377  * @count: Number of futexes in the list
 378  *
 379  * Helper to unqueue a list of futexes. This can't fail.
 380  *
 381  * Return:
 382  *  - >=0 - Index of the last futex that was awoken;
 383  *  - -1  - No futex was awoken
 384  */
 385 int futex_unqueue_multiple(struct futex_vector *v, int count)
 386 {
 387         int ret = -1, i;
 388
 389         for (i = 0; i < count; i++) {
 390                 if (!futex_unqueue(&v[i].q))
 391                         ret = i;
 392         }
 393
 394         return ret;
 395 }
 396
 397 /**
 398  * futex_wait_multiple_setup - Prepare to wait and enqueue multiple futexes
 399  * @vs:         The futex list to wait on
 400  * @count:      The size of the list
 401  * @woken:      Index of the last woken futex, if any. Used to notify the
 402  *              caller that it can return this index to userspace (return parameter)
 403  *
 404  * Prepare multiple futexes in a single step and enqueue them. This may fail if
 405  * the futex list is invalid or if any futex was already awoken. On success the
 406  * task is ready to interruptible sleep.
 407  *
 408  * Return:
 409  *  -  1 - One of the futexes was woken by another thread
 410  *  -  0 - Success
 411  *  - <0 - -EFAULT, -EWOULDBLOCK or -EINVAL
 412  */
 413 int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken)
 414 {
 415         struct futex_hash_bucket *hb;
 416         bool retry = false;
 417         int ret, i;
 418         u32 uval;
 419
 420         /*
 421          * Enqueuing multiple futexes is tricky, because we need to enqueue
 422          * each futex on the list before dealing with the next one to avoid
 423          * deadlocking on the hash bucket. But, before enqueuing, we need to
 424          * make sure that current->state is TASK_INTERRUPTIBLE, so we don't
 425          * lose any wake events, which cannot be done before the get_futex_key
 426          * of the next key, because it calls get_user_pages, which can sleep.
 427          * Thus, we fetch the list of futexes keys in two steps, by first
 428          * pinning all the memory keys in the futex key, and only then we read
 429          * each key and queue the corresponding futex.
 430          *
 431          * Private futexes doesn't need to recalculate hash in retry, so skip
 432          * get_futex_key() when retrying.
 433          */
 434 retry:
 435         for (i = 0; i < count; i++) {
 436                 if (!(vs[i].w.flags & FLAGS_SHARED) && retry)
 437                         continue;
 438
 439                 ret = get_futex_key(u64_to_user_ptr(vs[i].w.uaddr),
 440                                     vs[i].w.flags,
 441                                     &vs[i].q.key, FUTEX_READ);
 442
 443                 if (unlikely(ret))
 444                         return ret;
 445         }
 446
 447         set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
 448
 449         for (i = 0; i < count; i++) {
 450                 u32 __user *uaddr = (u32 __user *)(unsigned long)vs[i].w.uaddr;
 451                 struct futex_q *q = &vs[i].q;
 452                 u32 val = vs[i].w.val;
 453
 454                 hb = futex_q_lock(q);
 455                 ret = futex_get_value_locked(&uval, uaddr);
 456
 457                 if (!ret && uval == val) {
 458                         /*
 459                          * The bucket lock can't be held while dealing with the
 460                          * next futex. Queue each futex at this moment so hb can
 461                          * be unlocked.
 462                          */
 463                         futex_queue(q, hb);
 464                         continue;
 465                 }
 466
 467                 futex_q_unlock(hb);
 468                 __set_current_state(TASK_RUNNING);
 469
 470                 /*
 471                  * Even if something went wrong, if we find out that a futex
 472                  * was woken, we don't return error and return this index to
 473                  * userspace
 474                  */
 475                 *woken = futex_unqueue_multiple(vs, i);
 476                 if (*woken >= 0)
 477                         return 1;
 478
 479                 if (ret) {
 480                         /*
 481                          * If we need to handle a page fault, we need to do so
 482                          * without any lock and any enqueued futex (otherwise
 483                          * we could lose some wakeup). So we do it here, after
 484                          * undoing all the work done so far. In success, we
 485                          * retry all the work.
 486                          */
 487                         if (get_user(uval, uaddr))
 488                                 return -EFAULT;
 489
 490                         retry = true;
 491                         goto retry;
 492                 }
 493
 494                 if (uval != val)
 495                         return -EWOULDBLOCK;
 496         }
 497
 498         return 0;
 499 }
 500
 501 /**
 502  * futex_sleep_multiple - Check sleeping conditions and sleep
 503  * @vs:    List of futexes to wait for
 504  * @count: Length of vs
 505  * @to:    Timeout
 506  *
 507  * Sleep if and only if the timeout hasn't expired and no futex on the list has
 508  * been woken up.
 509  */
 510 static void futex_sleep_multiple(struct futex_vector *vs, unsigned int count,
 511                                  struct hrtimer_sleeper *to)
 512 {
 513         if (to && !to->task)
 514                 return;
 515
 516         for (; count; count--, vs++) {
 517                 if (!READ_ONCE(vs->q.lock_ptr))
 518                         return;
 519         }
 520
 521         schedule();
 522 }
 523
 524 /**
 525  * futex_wait_multiple - Prepare to wait on and enqueue several futexes
 526  * @vs:         The list of futexes to wait on
 527  * @count:      The number of objects
 528  * @to:         Timeout before giving up and returning to userspace
 529  *
 530  * Entry point for the FUTEX_WAIT_MULTIPLE futex operation, this function
 531  * sleeps on a group of futexes and returns on the first futex that is
 532  * wake, or after the timeout has elapsed.
 533  *
 534  * Return:
 535  *  - >=0 - Hint to the futex that was awoken
 536  *  - <0  - On error
 537  */
 538 int futex_wait_multiple(struct futex_vector *vs, unsigned int count,
 539                         struct hrtimer_sleeper *to)
 540 {
 541         int ret, hint = 0;
 542
 543         if (to)
 544                 hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
 545
 546         while (1) {
 547                 ret = futex_wait_multiple_setup(vs, count, &hint);
 548                 if (ret) {
 549                         if (ret > 0) {
 550                                 /* A futex was woken during setup */
 551                                 ret = hint;
 552                         }
 553                         return ret;
 554                 }
 555
 556                 futex_sleep_multiple(vs, count, to);
 557
 558                 __set_current_state(TASK_RUNNING);
 559
 560                 ret = futex_unqueue_multiple(vs, count);
 561                 if (ret >= 0)
 562                         return ret;
 563
 564                 if (to && !to->task)
 565                         return -ETIMEDOUT;
 566                 else if (signal_pending(current))
 567                         return -ERESTARTSYS;
 568                 /*
 569                  * The final case is a spurious wakeup, for
 570                  * which just retry.
 571                  */
 572         }
 573 }
 574
 575 /**
 576  * futex_wait_setup() - Prepare to wait on a futex
 577  * @uaddr:      the futex userspace address
 578  * @val:        the expected value
 579  * @flags:      futex flags (FLAGS_SHARED, etc.)
 580  * @q:          the associated futex_q
 581  * @hb:         storage for hash_bucket pointer to be returned to caller
 582  *
 583  * Setup the futex_q and locate the hash_bucket.  Get the futex value and
 584  * compare it with the expected value.  Handle atomic faults internally.
 585  * Return with the hb lock held on success, and unlocked on failure.
 586  *
 587  * Return:
 588  *  -  0 - uaddr contains val and hb has been locked;
 589  *  - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
 590  */
 591 int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
 592                      struct futex_q *q, struct futex_hash_bucket **hb)
 593 {
 594         u32 uval;
 595         int ret;
 596
 597         /*
 598          * Access the page AFTER the hash-bucket is locked.
 599          * Order is important:
 600          *
 601          *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
 602          *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
 603          *
 604          * The basic logical guarantee of a futex is that it blocks ONLY
 605          * if cond(var) is known to be true at the time of blocking, for
 606          * any cond.  If we locked the hash-bucket after testing *uaddr, that
 607          * would open a race condition where we could block indefinitely with
 608          * cond(var) false, which would violate the guarantee.
 609          *
 610          * On the other hand, we insert q and release the hash-bucket only
 611          * after testing *uaddr.  This guarantees that futex_wait() will NOT
 612          * absorb a wakeup if *uaddr does not match the desired values
 613          * while the syscall executes.
 614          */
 615 retry:
 616         ret = get_futex_key(uaddr, flags, &q->key, FUTEX_READ);
 617         if (unlikely(ret != 0))
 618                 return ret;
 619
 620 retry_private:
 621         *hb = futex_q_lock(q);
 622
 623         ret = futex_get_value_locked(&uval, uaddr);
 624
 625         if (ret) {
 626                 futex_q_unlock(*hb);
 627
 628                 ret = get_user(uval, uaddr);
 629                 if (ret)
 630                         return ret;
 631
 632                 if (!(flags & FLAGS_SHARED))
 633                         goto retry_private;
 634
 635                 goto retry;
 636         }
 637
 638         if (uval != val) {
 639                 futex_q_unlock(*hb);
 640                 ret = -EWOULDBLOCK;
 641         }
 642
 643         return ret;
 644 }
 645
 646 int __futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
 647                  struct hrtimer_sleeper *to, u32 bitset)
 648 {
 649         struct futex_q q = futex_q_init;
 650         struct futex_hash_bucket *hb;
 651         int ret;
 652
 653         if (!bitset)
 654                 return -EINVAL;
 655
 656         q.bitset = bitset;
 657
 658 retry:
 659         /*
 660          * Prepare to wait on uaddr. On success, it holds hb->lock and q
 661          * is initialized.
 662          */
 663         ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
 664         if (ret)
 665                 return ret;
 666
 667         /* futex_queue and wait for wakeup, timeout, or a signal. */
 668         futex_wait_queue(hb, &q, to);
 669
 670         /* If we were woken (and unqueued), we succeeded, whatever. */
 671         if (!futex_unqueue(&q))
 672                 return 0;
 673
 674         if (to && !to->task)
 675                 return -ETIMEDOUT;
 676
 677         /*
 678          * We expect signal_pending(current), but we might be the
 679          * victim of a spurious wakeup as well.
 680          */
 681         if (!signal_pending(current))
 682                 goto retry;
 683
 684         return -ERESTARTSYS;
 685 }
 686
 687 int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val, ktime_t *abs_time, u32 bitset)
 688 {
 689         struct hrtimer_sleeper timeout, *to;
 690         struct restart_block *restart;
 691         int ret;
 692
 693         to = futex_setup_timer(abs_time, &timeout, flags,
 694                                current->timer_slack_ns);
 695
 696         ret = __futex_wait(uaddr, flags, val, to, bitset);
 697
 698         /* No timeout, nothing to clean up. */
 699         if (!to)
 700                 return ret;
 701
 702         hrtimer_cancel(&to->timer);
 703         destroy_hrtimer_on_stack(&to->timer);
 704
 705         if (ret == -ERESTARTSYS) {
 706                 restart = &current->restart_block;
 707                 restart->futex.uaddr = uaddr;
 708                 restart->futex.val = val;
 709                 restart->futex.time = *abs_time;
 710                 restart->futex.bitset = bitset;
 711                 restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
 712
 713                 return set_restart_fn(restart, futex_wait_restart);
 714         }
 715
 716         return ret;
 717 }
 718
 719 static long futex_wait_restart(struct restart_block *restart)
 720 {
 721         u32 __user *uaddr = restart->futex.uaddr;
 722         ktime_t t, *tp = NULL;
 723
 724         if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
 725                 t = restart->futex.time;
 726                 tp = &t;
 727         }
 728         restart->fn = do_no_restart_syscall;
 729
 730         return (long)futex_wait(uaddr, restart->futex.flags,
 731                                 restart->futex.val, tp, restart->futex.bitset);
 732 }
 733