kernel/locking/rtmutex_api.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * rtmutex API
   4  */
   5 #include <linux/spinlock.h>
   6 #include <linux/export.h>
   7
   8 #define RT_MUTEX_BUILD_MUTEX
   9 #include "rtmutex.c"
  10
  11 /*
  12  * Max number of times we'll walk the boosting chain:
  13  */
  14 int max_lock_depth = 1024;
  15
  16 /*
  17  * Debug aware fast / slowpath lock,trylock,unlock
  18  *
  19  * The atomic acquire/release ops are compiled away, when either the
  20  * architecture does not support cmpxchg or when debugging is enabled.
  21  */
  22 static __always_inline int __rt_mutex_lock_common(struct rt_mutex *lock,
  23                                                   unsigned int state,
  24                                                   struct lockdep_map *nest_lock,
  25                                                   unsigned int subclass)
  26 {
  27         int ret;
  28
  29         might_sleep();
  30         mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, _RET_IP_);
  31         ret = __rt_mutex_lock(&lock->rtmutex, state);
  32         if (ret)
  33                 mutex_release(&lock->dep_map, _RET_IP_);
  34         return ret;
  35 }
  36
  37 void rt_mutex_base_init(struct rt_mutex_base *rtb)
  38 {
  39         __rt_mutex_base_init(rtb);
  40 }
  41 EXPORT_SYMBOL(rt_mutex_base_init);
  42
  43 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  44 /**
  45  * rt_mutex_lock_nested - lock a rt_mutex
  46  *
  47  * @lock: the rt_mutex to be locked
  48  * @subclass: the lockdep subclass
  49  */
  50 void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
  51 {
  52         __rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, subclass);
  53 }
  54 EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
  55
  56 void __sched _rt_mutex_lock_nest_lock(struct rt_mutex *lock, struct lockdep_map *nest_lock)
  57 {
  58         __rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, nest_lock, 0);
  59 }
  60 EXPORT_SYMBOL_GPL(_rt_mutex_lock_nest_lock);
  61
  62 #else /* !CONFIG_DEBUG_LOCK_ALLOC */
  63
  64 /**
  65  * rt_mutex_lock - lock a rt_mutex
  66  *
  67  * @lock: the rt_mutex to be locked
  68  */
  69 void __sched rt_mutex_lock(struct rt_mutex *lock)
  70 {
  71         __rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, NULL, 0);
  72 }
  73 EXPORT_SYMBOL_GPL(rt_mutex_lock);
  74 #endif
  75
  76 /**
  77  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
  78  *
  79  * @lock:               the rt_mutex to be locked
  80  *
  81  * Returns:
  82  *  0           on success
  83  * -EINTR       when interrupted by a signal
  84  */
  85 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
  86 {
  87         return __rt_mutex_lock_common(lock, TASK_INTERRUPTIBLE, NULL, 0);
  88 }
  89 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
  90
  91 /**
  92  * rt_mutex_lock_killable - lock a rt_mutex killable
  93  *
  94  * @lock:               the rt_mutex to be locked
  95  *
  96  * Returns:
  97  *  0           on success
  98  * -EINTR       when interrupted by a signal
  99  */
 100 int __sched rt_mutex_lock_killable(struct rt_mutex *lock)
 101 {
 102         return __rt_mutex_lock_common(lock, TASK_KILLABLE, NULL, 0);
 103 }
 104 EXPORT_SYMBOL_GPL(rt_mutex_lock_killable);
 105
 106 /**
 107  * rt_mutex_trylock - try to lock a rt_mutex
 108  *
 109  * @lock:       the rt_mutex to be locked
 110  *
 111  * This function can only be called in thread context. It's safe to call it
 112  * from atomic regions, but not from hard or soft interrupt context.
 113  *
 114  * Returns:
 115  *  1 on success
 116  *  0 on contention
 117  */
 118 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 119 {
 120         int ret;
 121
 122         if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES) && WARN_ON_ONCE(!in_task()))
 123                 return 0;
 124
 125         ret = __rt_mutex_trylock(&lock->rtmutex);
 126         if (ret)
 127                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 128
 129         return ret;
 130 }
 131 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 132
 133 /**
 134  * rt_mutex_unlock - unlock a rt_mutex
 135  *
 136  * @lock: the rt_mutex to be unlocked
 137  */
 138 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 139 {
 140         mutex_release(&lock->dep_map, _RET_IP_);
 141         __rt_mutex_unlock(&lock->rtmutex);
 142 }
 143 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 144
 145 /*
 146  * Futex variants, must not use fastpath.
 147  */
 148 int __sched rt_mutex_futex_trylock(struct rt_mutex_base *lock)
 149 {
 150         return rt_mutex_slowtrylock(lock);
 151 }
 152
 153 int __sched __rt_mutex_futex_trylock(struct rt_mutex_base *lock)
 154 {
 155         return __rt_mutex_slowtrylock(lock);
 156 }
 157
 158 /**
 159  * __rt_mutex_futex_unlock - Futex variant, that since futex variants
 160  * do not use the fast-path, can be simple and will not need to retry.
 161  *
 162  * @lock:       The rt_mutex to be unlocked
 163  * @wqh:        The wake queue head from which to get the next lock waiter
 164  */
 165 bool __sched __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
 166                                      struct rt_wake_q_head *wqh)
 167 {
 168         lockdep_assert_held(&lock->wait_lock);
 169
 170         debug_rt_mutex_unlock(lock);
 171
 172         if (!rt_mutex_has_waiters(lock)) {
 173                 lock->owner = NULL;
 174                 return false; /* done */
 175         }
 176
 177         /*
 178          * We've already deboosted, mark_wakeup_next_waiter() will
 179          * retain preempt_disabled when we drop the wait_lock, to
 180          * avoid inversion prior to the wakeup.  preempt_disable()
 181          * therein pairs with rt_mutex_postunlock().
 182          */
 183         mark_wakeup_next_waiter(wqh, lock);
 184
 185         return true; /* call postunlock() */
 186 }
 187
 188 void __sched rt_mutex_futex_unlock(struct rt_mutex_base *lock)
 189 {
 190         DEFINE_RT_WAKE_Q(wqh);
 191         unsigned long flags;
 192         bool postunlock;
 193
 194         raw_spin_lock_irqsave(&lock->wait_lock, flags);
 195         postunlock = __rt_mutex_futex_unlock(lock, &wqh);
 196         raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 197
 198         if (postunlock)
 199                 rt_mutex_postunlock(&wqh);
 200 }
 201
 202 /**
 203  * __rt_mutex_init - initialize the rt_mutex
 204  *
 205  * @lock:       The rt_mutex to be initialized
 206  * @name:       The lock name used for debugging
 207  * @key:        The lock class key used for debugging
 208  *
 209  * Initialize the rt_mutex to unlocked state.
 210  *
 211  * Initializing of a locked rt_mutex is not allowed
 212  */
 213 void __sched __rt_mutex_init(struct rt_mutex *lock, const char *name,
 214                              struct lock_class_key *key)
 215 {
 216         debug_check_no_locks_freed((void *)lock, sizeof(*lock));
 217         __rt_mutex_base_init(&lock->rtmutex);
 218         lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
 219 }
 220 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 221
 222 /**
 223  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 224  *                              proxy owner
 225  *
 226  * @lock:       the rt_mutex to be locked
 227  * @proxy_owner:the task to set as owner
 228  *
 229  * No locking. Caller has to do serializing itself
 230  *
 231  * Special API call for PI-futex support. This initializes the rtmutex and
 232  * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
 233  * possible at this point because the pi_state which contains the rtmutex
 234  * is not yet visible to other tasks.
 235  */
 236 void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,
 237                                         struct task_struct *proxy_owner)
 238 {
 239         static struct lock_class_key pi_futex_key;
 240
 241         __rt_mutex_base_init(lock);
 242         /*
 243          * On PREEMPT_RT the futex hashbucket spinlock becomes 'sleeping'
 244          * and rtmutex based. That causes a lockdep false positive, because
 245          * some of the futex functions invoke spin_unlock(&hb->lock) with
 246          * the wait_lock of the rtmutex associated to the pi_futex held.
 247          * spin_unlock() in turn takes wait_lock of the rtmutex on which
 248          * the spinlock is based, which makes lockdep notice a lock
 249          * recursion. Give the futex/rtmutex wait_lock a separate key.
 250          */
 251         lockdep_set_class(&lock->wait_lock, &pi_futex_key);
 252         rt_mutex_set_owner(lock, proxy_owner);
 253 }
 254
 255 /**
 256  * rt_mutex_proxy_unlock - release a lock on behalf of owner
 257  *
 258  * @lock:       the rt_mutex to be locked
 259  *
 260  * No locking. Caller has to do serializing itself
 261  *
 262  * Special API call for PI-futex support. This just cleans up the rtmutex
 263  * (debugging) state. Concurrent operations on this rt_mutex are not
 264  * possible because it belongs to the pi_state which is about to be freed
 265  * and it is not longer visible to other tasks.
 266  */
 267 void __sched rt_mutex_proxy_unlock(struct rt_mutex_base *lock)
 268 {
 269         debug_rt_mutex_proxy_unlock(lock);
 270         rt_mutex_clear_owner(lock);
 271 }
 272
 273 /**
 274  * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 275  * @lock:               the rt_mutex to take
 276  * @waiter:             the pre-initialized rt_mutex_waiter
 277  * @task:               the task to prepare
 278  *
 279  * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
 280  * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
 281  *
 282  * NOTE: does _NOT_ remove the @waiter on failure; must either call
 283  * rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
 284  *
 285  * Returns:
 286  *  0 - task blocked on lock
 287  *  1 - acquired the lock for task, caller should wake it up
 288  * <0 - error
 289  *
 290  * Special API call for PI-futex support.
 291  */
 292 int __sched __rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
 293                                         struct rt_mutex_waiter *waiter,
 294                                         struct task_struct *task)
 295 {
 296         int ret;
 297
 298         lockdep_assert_held(&lock->wait_lock);
 299
 300         if (try_to_take_rt_mutex(lock, task, NULL))
 301                 return 1;
 302
 303         /* We enforce deadlock detection for futexes */
 304         ret = task_blocks_on_rt_mutex(lock, waiter, task, NULL,
 305                                       RT_MUTEX_FULL_CHAINWALK);
 306
 307         if (ret && !rt_mutex_owner(lock)) {
 308                 /*
 309                  * Reset the return value. We might have
 310                  * returned with -EDEADLK and the owner
 311                  * released the lock while we were walking the
 312                  * pi chain.  Let the waiter sort it out.
 313                  */
 314                 ret = 0;
 315         }
 316
 317         return ret;
 318 }
 319
 320 /**
 321  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 322  * @lock:               the rt_mutex to take
 323  * @waiter:             the pre-initialized rt_mutex_waiter
 324  * @task:               the task to prepare
 325  *
 326  * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
 327  * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
 328  *
 329  * NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
 330  * on failure.
 331  *
 332  * Returns:
 333  *  0 - task blocked on lock
 334  *  1 - acquired the lock for task, caller should wake it up
 335  * <0 - error
 336  *
 337  * Special API call for PI-futex support.
 338  */
 339 int __sched rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
 340                                       struct rt_mutex_waiter *waiter,
 341                                       struct task_struct *task)
 342 {
 343         int ret;
 344
 345         raw_spin_lock_irq(&lock->wait_lock);
 346         ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
 347         if (unlikely(ret))
 348                 remove_waiter(lock, waiter);
 349         raw_spin_unlock_irq(&lock->wait_lock);
 350
 351         return ret;
 352 }
 353
 354 /**
 355  * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
 356  * @lock:               the rt_mutex we were woken on
 357  * @to:                 the timeout, null if none. hrtimer should already have
 358  *                      been started.
 359  * @waiter:             the pre-initialized rt_mutex_waiter
 360  *
 361  * Wait for the lock acquisition started on our behalf by
 362  * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
 363  * rt_mutex_cleanup_proxy_lock().
 364  *
 365  * Returns:
 366  *  0 - success
 367  * <0 - error, one of -EINTR, -ETIMEDOUT
 368  *
 369  * Special API call for PI-futex support
 370  */
 371 int __sched rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock,
 372                                      struct hrtimer_sleeper *to,
 373                                      struct rt_mutex_waiter *waiter)
 374 {
 375         int ret;
 376
 377         raw_spin_lock_irq(&lock->wait_lock);
 378         /* sleep on the mutex */
 379         set_current_state(TASK_INTERRUPTIBLE);
 380         ret = rt_mutex_slowlock_block(lock, NULL, TASK_INTERRUPTIBLE, to, waiter);
 381         /*
 382          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 383          * have to fix that up.
 384          */
 385         fixup_rt_mutex_waiters(lock, true);
 386         raw_spin_unlock_irq(&lock->wait_lock);
 387
 388         return ret;
 389 }
 390
 391 /**
 392  * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
 393  * @lock:               the rt_mutex we were woken on
 394  * @waiter:             the pre-initialized rt_mutex_waiter
 395  *
 396  * Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
 397  * rt_mutex_wait_proxy_lock().
 398  *
 399  * Unless we acquired the lock; we're still enqueued on the wait-list and can
 400  * in fact still be granted ownership until we're removed. Therefore we can
 401  * find we are in fact the owner and must disregard the
 402  * rt_mutex_wait_proxy_lock() failure.
 403  *
 404  * Returns:
 405  *  true  - did the cleanup, we done.
 406  *  false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
 407  *          caller should disregards its return value.
 408  *
 409  * Special API call for PI-futex support
 410  */
 411 bool __sched rt_mutex_cleanup_proxy_lock(struct rt_mutex_base *lock,
 412                                          struct rt_mutex_waiter *waiter)
 413 {
 414         bool cleanup = false;
 415
 416         raw_spin_lock_irq(&lock->wait_lock);
 417         /*
 418          * Do an unconditional try-lock, this deals with the lock stealing
 419          * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
 420          * sets a NULL owner.
 421          *
 422          * We're not interested in the return value, because the subsequent
 423          * test on rt_mutex_owner() will infer that. If the trylock succeeded,
 424          * we will own the lock and it will have removed the waiter. If we
 425          * failed the trylock, we're still not owner and we need to remove
 426          * ourselves.
 427          */
 428         try_to_take_rt_mutex(lock, current, waiter);
 429         /*
 430          * Unless we're the owner; we're still enqueued on the wait_list.
 431          * So check if we became owner, if not, take us off the wait_list.
 432          */
 433         if (rt_mutex_owner(lock) != current) {
 434                 remove_waiter(lock, waiter);
 435                 cleanup = true;
 436         }
 437         /*
 438          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 439          * have to fix that up.
 440          */
 441         fixup_rt_mutex_waiters(lock, false);
 442
 443         raw_spin_unlock_irq(&lock->wait_lock);
 444
 445         return cleanup;
 446 }
 447
 448 /*
 449  * Recheck the pi chain, in case we got a priority setting
 450  *
 451  * Called from sched_setscheduler
 452  */
 453 void __sched rt_mutex_adjust_pi(struct task_struct *task)
 454 {
 455         struct rt_mutex_waiter *waiter;
 456         struct rt_mutex_base *next_lock;
 457         unsigned long flags;
 458
 459         raw_spin_lock_irqsave(&task->pi_lock, flags);
 460
 461         waiter = task->pi_blocked_on;
 462         if (!waiter || rt_waiter_node_equal(&waiter->tree, task_to_waiter_node(task))) {
 463                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 464                 return;
 465         }
 466         next_lock = waiter->lock;
 467         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 468
 469         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 470         get_task_struct(task);
 471
 472         rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
 473                                    next_lock, NULL, task);
 474 }
 475
 476 /*
 477  * Performs the wakeup of the top-waiter and re-enables preemption.
 478  */
 479 void __sched rt_mutex_postunlock(struct rt_wake_q_head *wqh)
 480 {
 481         rt_mutex_wake_up_q(wqh);
 482 }
 483
 484 #ifdef CONFIG_DEBUG_RT_MUTEXES
 485 void rt_mutex_debug_task_free(struct task_struct *task)
 486 {
 487         DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters.rb_root));
 488         DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
 489 }
 490 #endif
 491
 492 #ifdef CONFIG_PREEMPT_RT
 493 /* Mutexes */
 494 void __mutex_rt_init(struct mutex *mutex, const char *name,
 495                      struct lock_class_key *key)
 496 {
 497         debug_check_no_locks_freed((void *)mutex, sizeof(*mutex));
 498         lockdep_init_map_wait(&mutex->dep_map, name, key, 0, LD_WAIT_SLEEP);
 499 }
 500 EXPORT_SYMBOL(__mutex_rt_init);
 501
 502 static __always_inline int __mutex_lock_common(struct mutex *lock,
 503                                                unsigned int state,
 504                                                unsigned int subclass,
 505                                                struct lockdep_map *nest_lock,
 506                                                unsigned long ip)
 507 {
 508         int ret;
 509
 510         might_sleep();
 511         mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
 512         ret = __rt_mutex_lock(&lock->rtmutex, state);
 513         if (ret)
 514                 mutex_release(&lock->dep_map, ip);
 515         else
 516                 lock_acquired(&lock->dep_map, ip);
 517         return ret;
 518 }
 519
 520 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 521 void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 522 {
 523         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
 524 }
 525 EXPORT_SYMBOL_GPL(mutex_lock_nested);
 526
 527 void __sched _mutex_lock_nest_lock(struct mutex *lock,
 528                                    struct lockdep_map *nest_lock)
 529 {
 530         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, nest_lock, _RET_IP_);
 531 }
 532 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
 533
 534 int __sched mutex_lock_interruptible_nested(struct mutex *lock,
 535                                             unsigned int subclass)
 536 {
 537         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
 538 }
 539 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 540
 541 int __sched mutex_lock_killable_nested(struct mutex *lock,
 542                                             unsigned int subclass)
 543 {
 544         return __mutex_lock_common(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
 545 }
 546 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 547
 548 void __sched mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
 549 {
 550         int token;
 551
 552         might_sleep();
 553
 554         token = io_schedule_prepare();
 555         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
 556         io_schedule_finish(token);
 557 }
 558 EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
 559
 560 #else /* CONFIG_DEBUG_LOCK_ALLOC */
 561
 562 void __sched mutex_lock(struct mutex *lock)
 563 {
 564         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
 565 }
 566 EXPORT_SYMBOL(mutex_lock);
 567
 568 int __sched mutex_lock_interruptible(struct mutex *lock)
 569 {
 570         return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
 571 }
 572 EXPORT_SYMBOL(mutex_lock_interruptible);
 573
 574 int __sched mutex_lock_killable(struct mutex *lock)
 575 {
 576         return __mutex_lock_common(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
 577 }
 578 EXPORT_SYMBOL(mutex_lock_killable);
 579
 580 void __sched mutex_lock_io(struct mutex *lock)
 581 {
 582         int token = io_schedule_prepare();
 583
 584         __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
 585         io_schedule_finish(token);
 586 }
 587 EXPORT_SYMBOL(mutex_lock_io);
 588 #endif /* !CONFIG_DEBUG_LOCK_ALLOC */
 589
 590 int __sched mutex_trylock(struct mutex *lock)
 591 {
 592         int ret;
 593
 594         if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES) && WARN_ON_ONCE(!in_task()))
 595                 return 0;
 596
 597         ret = __rt_mutex_trylock(&lock->rtmutex);
 598         if (ret)
 599                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 600
 601         return ret;
 602 }
 603 EXPORT_SYMBOL(mutex_trylock);
 604
 605 void __sched mutex_unlock(struct mutex *lock)
 606 {
 607         mutex_release(&lock->dep_map, _RET_IP_);
 608         __rt_mutex_unlock(&lock->rtmutex);
 609 }
 610 EXPORT_SYMBOL(mutex_unlock);
 611
 612 #endif /* CONFIG_PREEMPT_RT */