kernel/rtmutex.c

   1 /*
   2  * RT-Mutexes: simple blocking mutual exclusion locks with PI support
   3  *
   4  * started by Ingo Molnar and Thomas Gleixner.
   5  *
   6  *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   7  *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   8  *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
   9  *  Copyright (C) 2006 Esben Nielsen
  10  *
  11  *  See Documentation/rt-mutex-design.txt for details.
  12  */
  13 #include <linux/spinlock.h>
  14 #include <linux/export.h>
  15 #include <linux/sched.h>
  16 #include <linux/sched/rt.h>
  17 #include <linux/timer.h>
  18
  19 #include "rtmutex_common.h"
  20
  21 /*
  22  * lock->owner state tracking:
  23  *
  24  * lock->owner holds the task_struct pointer of the owner. Bit 0
  25  * is used to keep track of the "lock has waiters" state.
  26  *
  27  * owner        bit0
  28  * NULL         0       lock is free (fast acquire possible)
  29  * NULL         1       lock is free and has waiters and the top waiter
  30  *                              is going to take the lock*
  31  * taskpointer  0       lock is held (fast release possible)
  32  * taskpointer  1       lock is held and has waiters**
  33  *
  34  * The fast atomic compare exchange based acquire and release is only
  35  * possible when bit 0 of lock->owner is 0.
  36  *
  37  * (*) It also can be a transitional state when grabbing the lock
  38  * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  39  * we need to set the bit0 before looking at the lock, and the owner may be
  40  * NULL in this small time, hence this can be a transitional state.
  41  *
  42  * (**) There is a small time when bit 0 is set but there are no
  43  * waiters. This can happen when grabbing the lock in the slow path.
  44  * To prevent a cmpxchg of the owner releasing the lock, we need to
  45  * set this bit before looking at the lock.
  46  */
  47
  48 static void
  49 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  50 {
  51         unsigned long val = (unsigned long)owner;
  52
  53         if (rt_mutex_has_waiters(lock))
  54                 val |= RT_MUTEX_HAS_WAITERS;
  55
  56         lock->owner = (struct task_struct *)val;
  57 }
  58
  59 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  60 {
  61         lock->owner = (struct task_struct *)
  62                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  63 }
  64
  65 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  66 {
  67         if (!rt_mutex_has_waiters(lock))
  68                 clear_rt_mutex_waiters(lock);
  69 }
  70
  71 /*
  72  * We can speed up the acquire/release, if the architecture
  73  * supports cmpxchg and if there's no debugging state to be set up
  74  */
  75 #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  76 # define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
  77 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  78 {
  79         unsigned long owner, *p = (unsigned long *) &lock->owner;
  80
  81         do {
  82                 owner = *p;
  83         } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  84 }
  85 #else
  86 # define rt_mutex_cmpxchg(l,c,n)        (0)
  87 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  88 {
  89         lock->owner = (struct task_struct *)
  90                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
  91 }
  92 #endif
  93
  94 /*
  95  * Calculate task priority from the waiter list priority
  96  *
  97  * Return task->normal_prio when the waiter list is empty or when
  98  * the waiter is not allowed to do priority boosting
  99  */
 100 int rt_mutex_getprio(struct task_struct *task)
 101 {
 102         if (likely(!task_has_pi_waiters(task)))
 103                 return task->normal_prio;
 104
 105         return min(task_top_pi_waiter(task)->pi_list_entry.prio,
 106                    task->normal_prio);
 107 }
 108
 109 /*
 110  * Adjust the priority of a task, after its pi_waiters got modified.
 111  *
 112  * This can be both boosting and unboosting. task->pi_lock must be held.
 113  */
 114 static void __rt_mutex_adjust_prio(struct task_struct *task)
 115 {
 116         int prio = rt_mutex_getprio(task);
 117
 118         if (task->prio != prio)
 119                 rt_mutex_setprio(task, prio);
 120 }
 121
 122 /*
 123  * Adjust task priority (undo boosting). Called from the exit path of
 124  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 125  *
 126  * (Note: We do this outside of the protection of lock->wait_lock to
 127  * allow the lock to be taken while or before we readjust the priority
 128  * of task. We do not use the spin_xx_mutex() variants here as we are
 129  * outside of the debug path.)
 130  */
 131 static void rt_mutex_adjust_prio(struct task_struct *task)
 132 {
 133         unsigned long flags;
 134
 135         raw_spin_lock_irqsave(&task->pi_lock, flags);
 136         __rt_mutex_adjust_prio(task);
 137         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 138 }
 139
 140 /*
 141  * Max number of times we'll walk the boosting chain:
 142  */
 143 int max_lock_depth = 1024;
 144
 145 /*
 146  * Adjust the priority chain. Also used for deadlock detection.
 147  * Decreases task's usage by one - may thus free the task.
 148  *
 149  * @task: the task owning the mutex (owner) for which a chain walk is probably
 150  *        needed
 151  * @deadlock_detect: do we have to carry out deadlock detection?
 152  * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
 153  *             things for a task that has just got its priority adjusted, and
 154  *             is waiting on a mutex)
 155  * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 156  *               its priority to the mutex owner (can be NULL in the case
 157  *               depicted above or if the top waiter is gone away and we are
 158  *               actually deboosting the owner)
 159  * @top_task: the current top waiter
 160  *
 161  * Returns 0 or -EDEADLK.
 162  */
 163 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 164                                       int deadlock_detect,
 165                                       struct rt_mutex *orig_lock,
 166                                       struct rt_mutex_waiter *orig_waiter,
 167                                       struct task_struct *top_task)
 168 {
 169         struct rt_mutex *lock;
 170         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 171         int detect_deadlock, ret = 0, depth = 0;
 172         unsigned long flags;
 173
 174         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 175                                                          deadlock_detect);
 176
 177         /*
 178          * The (de)boosting is a step by step approach with a lot of
 179          * pitfalls. We want this to be preemptible and we want hold a
 180          * maximum of two locks per step. So we have to check
 181          * carefully whether things change under us.
 182          */
 183  again:
 184         if (++depth > max_lock_depth) {
 185                 static int prev_max;
 186
 187                 /*
 188                  * Print this only once. If the admin changes the limit,
 189                  * print a new message when reaching the limit again.
 190                  */
 191                 if (prev_max != max_lock_depth) {
 192                         prev_max = max_lock_depth;
 193                         printk(KERN_WARNING "Maximum lock depth %d reached "
 194                                "task: %s (%d)\n", max_lock_depth,
 195                                top_task->comm, task_pid_nr(top_task));
 196                 }
 197                 put_task_struct(task);
 198
 199                 return deadlock_detect ? -EDEADLK : 0;
 200         }
 201  retry:
 202         /*
 203          * Task can not go away as we did a get_task() before !
 204          */
 205         raw_spin_lock_irqsave(&task->pi_lock, flags);
 206
 207         waiter = task->pi_blocked_on;
 208         /*
 209          * Check whether the end of the boosting chain has been
 210          * reached or the state of the chain has changed while we
 211          * dropped the locks.
 212          */
 213         if (!waiter)
 214                 goto out_unlock_pi;
 215
 216         /*
 217          * Check the orig_waiter state. After we dropped the locks,
 218          * the previous owner of the lock might have released the lock.
 219          */
 220         if (orig_waiter && !rt_mutex_owner(orig_lock))
 221                 goto out_unlock_pi;
 222
 223         /*
 224          * Drop out, when the task has no waiters. Note,
 225          * top_waiter can be NULL, when we are in the deboosting
 226          * mode!
 227          */
 228         if (top_waiter && (!task_has_pi_waiters(task) ||
 229                            top_waiter != task_top_pi_waiter(task)))
 230                 goto out_unlock_pi;
 231
 232         /*
 233          * When deadlock detection is off then we check, if further
 234          * priority adjustment is necessary.
 235          */
 236         if (!detect_deadlock && waiter->list_entry.prio == task->prio)
 237                 goto out_unlock_pi;
 238
 239         lock = waiter->lock;
 240         if (!raw_spin_trylock(&lock->wait_lock)) {
 241                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 242                 cpu_relax();
 243                 goto retry;
 244         }
 245
 246         /* Deadlock detection */
 247         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 248                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 249                 raw_spin_unlock(&lock->wait_lock);
 250                 ret = deadlock_detect ? -EDEADLK : 0;
 251                 goto out_unlock_pi;
 252         }
 253
 254         top_waiter = rt_mutex_top_waiter(lock);
 255
 256         /* Requeue the waiter */
 257         plist_del(&waiter->list_entry, &lock->wait_list);
 258         waiter->list_entry.prio = task->prio;
 259         plist_add(&waiter->list_entry, &lock->wait_list);
 260
 261         /* Release the task */
 262         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 263         if (!rt_mutex_owner(lock)) {
 264                 /*
 265                  * If the requeue above changed the top waiter, then we need
 266                  * to wake the new top waiter up to try to get the lock.
 267                  */
 268
 269                 if (top_waiter != rt_mutex_top_waiter(lock))
 270                         wake_up_process(rt_mutex_top_waiter(lock)->task);
 271                 raw_spin_unlock(&lock->wait_lock);
 272                 goto out_put_task;
 273         }
 274         put_task_struct(task);
 275
 276         /* Grab the next task */
 277         task = rt_mutex_owner(lock);
 278         get_task_struct(task);
 279         raw_spin_lock_irqsave(&task->pi_lock, flags);
 280
 281         if (waiter == rt_mutex_top_waiter(lock)) {
 282                 /* Boost the owner */
 283                 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
 284                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 285                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 286                 __rt_mutex_adjust_prio(task);
 287
 288         } else if (top_waiter == waiter) {
 289                 /* Deboost the owner */
 290                 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
 291                 waiter = rt_mutex_top_waiter(lock);
 292                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 293                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 294                 __rt_mutex_adjust_prio(task);
 295         }
 296
 297         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 298
 299         top_waiter = rt_mutex_top_waiter(lock);
 300         raw_spin_unlock(&lock->wait_lock);
 301
 302         if (!detect_deadlock && waiter != top_waiter)
 303                 goto out_put_task;
 304
 305         goto again;
 306
 307  out_unlock_pi:
 308         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 309  out_put_task:
 310         put_task_struct(task);
 311
 312         return ret;
 313 }
 314
 315 /*
 316  * Try to take an rt-mutex
 317  *
 318  * Must be called with lock->wait_lock held.
 319  *
 320  * @lock:   the lock to be acquired.
 321  * @task:   the task which wants to acquire the lock
 322  * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
 323  */
 324 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 325                 struct rt_mutex_waiter *waiter)
 326 {
 327         /*
 328          * We have to be careful here if the atomic speedups are
 329          * enabled, such that, when
 330          *  - no other waiter is on the lock
 331          *  - the lock has been released since we did the cmpxchg
 332          * the lock can be released or taken while we are doing the
 333          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 334          *
 335          * The atomic acquire/release aware variant of
 336          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 337          * the WAITERS bit, the atomic release / acquire can not
 338          * happen anymore and lock->wait_lock protects us from the
 339          * non-atomic case.
 340          *
 341          * Note, that this might set lock->owner =
 342          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 343          * any more. This is fixed up when we take the ownership.
 344          * This is the transitional state explained at the top of this file.
 345          */
 346         mark_rt_mutex_waiters(lock);
 347
 348         if (rt_mutex_owner(lock))
 349                 return 0;
 350
 351         /*
 352          * It will get the lock because of one of these conditions:
 353          * 1) there is no waiter
 354          * 2) higher priority than waiters
 355          * 3) it is top waiter
 356          */
 357         if (rt_mutex_has_waiters(lock)) {
 358                 if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
 359                         if (!waiter || waiter != rt_mutex_top_waiter(lock))
 360                                 return 0;
 361                 }
 362         }
 363
 364         if (waiter || rt_mutex_has_waiters(lock)) {
 365                 unsigned long flags;
 366                 struct rt_mutex_waiter *top;
 367
 368                 raw_spin_lock_irqsave(&task->pi_lock, flags);
 369
 370                 /* remove the queued waiter. */
 371                 if (waiter) {
 372                         plist_del(&waiter->list_entry, &lock->wait_list);
 373                         task->pi_blocked_on = NULL;
 374                 }
 375
 376                 /*
 377                  * We have to enqueue the top waiter(if it exists) into
 378                  * task->pi_waiters list.
 379                  */
 380                 if (rt_mutex_has_waiters(lock)) {
 381                         top = rt_mutex_top_waiter(lock);
 382                         top->pi_list_entry.prio = top->list_entry.prio;
 383                         plist_add(&top->pi_list_entry, &task->pi_waiters);
 384                 }
 385                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 386         }
 387
 388         /* We got the lock. */
 389         debug_rt_mutex_lock(lock);
 390
 391         rt_mutex_set_owner(lock, task);
 392
 393         rt_mutex_deadlock_account_lock(lock, task);
 394
 395         return 1;
 396 }
 397
 398 /*
 399  * Task blocks on lock.
 400  *
 401  * Prepare waiter and propagate pi chain
 402  *
 403  * This must be called with lock->wait_lock held.
 404  */
 405 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 406                                    struct rt_mutex_waiter *waiter,
 407                                    struct task_struct *task,
 408                                    int detect_deadlock)
 409 {
 410         struct task_struct *owner = rt_mutex_owner(lock);
 411         struct rt_mutex_waiter *top_waiter = waiter;
 412         unsigned long flags;
 413         int chain_walk = 0, res;
 414
 415         raw_spin_lock_irqsave(&task->pi_lock, flags);
 416         __rt_mutex_adjust_prio(task);
 417         waiter->task = task;
 418         waiter->lock = lock;
 419         plist_node_init(&waiter->list_entry, task->prio);
 420         plist_node_init(&waiter->pi_list_entry, task->prio);
 421
 422         /* Get the top priority waiter on the lock */
 423         if (rt_mutex_has_waiters(lock))
 424                 top_waiter = rt_mutex_top_waiter(lock);
 425         plist_add(&waiter->list_entry, &lock->wait_list);
 426
 427         task->pi_blocked_on = waiter;
 428
 429         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 430
 431         if (!owner)
 432                 return 0;
 433
 434         if (waiter == rt_mutex_top_waiter(lock)) {
 435                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 436                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
 437                 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
 438
 439                 __rt_mutex_adjust_prio(owner);
 440                 if (owner->pi_blocked_on)
 441                         chain_walk = 1;
 442                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 443         }
 444         else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
 445                 chain_walk = 1;
 446
 447         if (!chain_walk)
 448                 return 0;
 449
 450         /*
 451          * The owner can't disappear while holding a lock,
 452          * so the owner struct is protected by wait_lock.
 453          * Gets dropped in rt_mutex_adjust_prio_chain()!
 454          */
 455         get_task_struct(owner);
 456
 457         raw_spin_unlock(&lock->wait_lock);
 458
 459         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
 460                                          task);
 461
 462         raw_spin_lock(&lock->wait_lock);
 463
 464         return res;
 465 }
 466
 467 /*
 468  * Wake up the next waiter on the lock.
 469  *
 470  * Remove the top waiter from the current tasks waiter list and wake it up.
 471  *
 472  * Called with lock->wait_lock held.
 473  */
 474 static void wakeup_next_waiter(struct rt_mutex *lock)
 475 {
 476         struct rt_mutex_waiter *waiter;
 477         unsigned long flags;
 478
 479         raw_spin_lock_irqsave(&current->pi_lock, flags);
 480
 481         waiter = rt_mutex_top_waiter(lock);
 482
 483         /*
 484          * Remove it from current->pi_waiters. We do not adjust a
 485          * possible priority boost right now. We execute wakeup in the
 486          * boosted mode and go back to normal after releasing
 487          * lock->wait_lock.
 488          */
 489         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
 490
 491         rt_mutex_set_owner(lock, NULL);
 492
 493         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 494
 495         wake_up_process(waiter->task);
 496 }
 497
 498 /*
 499  * Remove a waiter from a lock and give up
 500  *
 501  * Must be called with lock->wait_lock held and
 502  * have just failed to try_to_take_rt_mutex().
 503  */
 504 static void remove_waiter(struct rt_mutex *lock,
 505                           struct rt_mutex_waiter *waiter)
 506 {
 507         int first = (waiter == rt_mutex_top_waiter(lock));
 508         struct task_struct *owner = rt_mutex_owner(lock);
 509         unsigned long flags;
 510         int chain_walk = 0;
 511
 512         raw_spin_lock_irqsave(&current->pi_lock, flags);
 513         plist_del(&waiter->list_entry, &lock->wait_list);
 514         current->pi_blocked_on = NULL;
 515         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 516
 517         if (!owner)
 518                 return;
 519
 520         if (first) {
 521
 522                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 523
 524                 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
 525
 526                 if (rt_mutex_has_waiters(lock)) {
 527                         struct rt_mutex_waiter *next;
 528
 529                         next = rt_mutex_top_waiter(lock);
 530                         plist_add(&next->pi_list_entry, &owner->pi_waiters);
 531                 }
 532                 __rt_mutex_adjust_prio(owner);
 533
 534                 if (owner->pi_blocked_on)
 535                         chain_walk = 1;
 536
 537                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 538         }
 539
 540         WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 541
 542         if (!chain_walk)
 543                 return;
 544
 545         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 546         get_task_struct(owner);
 547
 548         raw_spin_unlock(&lock->wait_lock);
 549
 550         rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
 551
 552         raw_spin_lock(&lock->wait_lock);
 553 }
 554
 555 /*
 556  * Recheck the pi chain, in case we got a priority setting
 557  *
 558  * Called from sched_setscheduler
 559  */
 560 void rt_mutex_adjust_pi(struct task_struct *task)
 561 {
 562         struct rt_mutex_waiter *waiter;
 563         unsigned long flags;
 564
 565         raw_spin_lock_irqsave(&task->pi_lock, flags);
 566
 567         waiter = task->pi_blocked_on;
 568         if (!waiter || waiter->list_entry.prio == task->prio) {
 569                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 570                 return;
 571         }
 572
 573         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 574
 575         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 576         get_task_struct(task);
 577         rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
 578 }
 579
 580 /**
 581  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 582  * @lock:                the rt_mutex to take
 583  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 584  *                       or TASK_UNINTERRUPTIBLE)
 585  * @timeout:             the pre-initialized and started timer, or NULL for none
 586  * @waiter:              the pre-initialized rt_mutex_waiter
 587  *
 588  * lock->wait_lock must be held by the caller.
 589  */
 590 static int __sched
 591 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
 592                     struct hrtimer_sleeper *timeout,
 593                     struct rt_mutex_waiter *waiter)
 594 {
 595         int ret = 0;
 596
 597         for (;;) {
 598                 /* Try to acquire the lock: */
 599                 if (try_to_take_rt_mutex(lock, current, waiter))
 600                         break;
 601
 602                 /*
 603                  * TASK_INTERRUPTIBLE checks for signals and
 604                  * timeout. Ignored otherwise.
 605                  */
 606                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 607                         /* Signal pending? */
 608                         if (signal_pending(current))
 609                                 ret = -EINTR;
 610                         if (timeout && !timeout->task)
 611                                 ret = -ETIMEDOUT;
 612                         if (ret)
 613                                 break;
 614                 }
 615
 616                 raw_spin_unlock(&lock->wait_lock);
 617
 618                 debug_rt_mutex_print_deadlock(waiter);
 619
 620                 schedule_rt_mutex(lock);
 621
 622                 raw_spin_lock(&lock->wait_lock);
 623                 set_current_state(state);
 624         }
 625
 626         return ret;
 627 }
 628
 629 /*
 630  * Slow path lock function:
 631  */
 632 static int __sched
 633 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 634                   struct hrtimer_sleeper *timeout,
 635                   int detect_deadlock)
 636 {
 637         struct rt_mutex_waiter waiter;
 638         int ret = 0;
 639
 640         debug_rt_mutex_init_waiter(&waiter);
 641
 642         raw_spin_lock(&lock->wait_lock);
 643
 644         /* Try to acquire the lock again: */
 645         if (try_to_take_rt_mutex(lock, current, NULL)) {
 646                 raw_spin_unlock(&lock->wait_lock);
 647                 return 0;
 648         }
 649
 650         set_current_state(state);
 651
 652         /* Setup the timer, when timeout != NULL */
 653         if (unlikely(timeout)) {
 654                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 655                 if (!hrtimer_active(&timeout->timer))
 656                         timeout->task = NULL;
 657         }
 658
 659         ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
 660
 661         if (likely(!ret))
 662                 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 663
 664         set_current_state(TASK_RUNNING);
 665
 666         if (unlikely(ret))
 667                 remove_waiter(lock, &waiter);
 668
 669         /*
 670          * try_to_take_rt_mutex() sets the waiter bit
 671          * unconditionally. We might have to fix that up.
 672          */
 673         fixup_rt_mutex_waiters(lock);
 674
 675         raw_spin_unlock(&lock->wait_lock);
 676
 677         /* Remove pending timer: */
 678         if (unlikely(timeout))
 679                 hrtimer_cancel(&timeout->timer);
 680
 681         debug_rt_mutex_free_waiter(&waiter);
 682
 683         return ret;
 684 }
 685
 686 /*
 687  * Slow path try-lock function:
 688  */
 689 static inline int
 690 rt_mutex_slowtrylock(struct rt_mutex *lock)
 691 {
 692         int ret = 0;
 693
 694         raw_spin_lock(&lock->wait_lock);
 695
 696         if (likely(rt_mutex_owner(lock) != current)) {
 697
 698                 ret = try_to_take_rt_mutex(lock, current, NULL);
 699                 /*
 700                  * try_to_take_rt_mutex() sets the lock waiters
 701                  * bit unconditionally. Clean this up.
 702                  */
 703                 fixup_rt_mutex_waiters(lock);
 704         }
 705
 706         raw_spin_unlock(&lock->wait_lock);
 707
 708         return ret;
 709 }
 710
 711 /*
 712  * Slow path to release a rt-mutex:
 713  */
 714 static void __sched
 715 rt_mutex_slowunlock(struct rt_mutex *lock)
 716 {
 717         raw_spin_lock(&lock->wait_lock);
 718
 719         debug_rt_mutex_unlock(lock);
 720
 721         rt_mutex_deadlock_account_unlock(current);
 722
 723         if (!rt_mutex_has_waiters(lock)) {
 724                 lock->owner = NULL;
 725                 raw_spin_unlock(&lock->wait_lock);
 726                 return;
 727         }
 728
 729         wakeup_next_waiter(lock);
 730
 731         raw_spin_unlock(&lock->wait_lock);
 732
 733         /* Undo pi boosting if necessary: */
 734         rt_mutex_adjust_prio(current);
 735 }
 736
 737 /*
 738  * debug aware fast / slowpath lock,trylock,unlock
 739  *
 740  * The atomic acquire/release ops are compiled away, when either the
 741  * architecture does not support cmpxchg or when debugging is enabled.
 742  */
 743 static inline int
 744 rt_mutex_fastlock(struct rt_mutex *lock, int state,
 745                   int detect_deadlock,
 746                   int (*slowfn)(struct rt_mutex *lock, int state,
 747                                 struct hrtimer_sleeper *timeout,
 748                                 int detect_deadlock))
 749 {
 750         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 751                 rt_mutex_deadlock_account_lock(lock, current);
 752                 return 0;
 753         } else
 754                 return slowfn(lock, state, NULL, detect_deadlock);
 755 }
 756
 757 static inline int
 758 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 759                         struct hrtimer_sleeper *timeout, int detect_deadlock,
 760                         int (*slowfn)(struct rt_mutex *lock, int state,
 761                                       struct hrtimer_sleeper *timeout,
 762                                       int detect_deadlock))
 763 {
 764         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 765                 rt_mutex_deadlock_account_lock(lock, current);
 766                 return 0;
 767         } else
 768                 return slowfn(lock, state, timeout, detect_deadlock);
 769 }
 770
 771 static inline int
 772 rt_mutex_fasttrylock(struct rt_mutex *lock,
 773                      int (*slowfn)(struct rt_mutex *lock))
 774 {
 775         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 776                 rt_mutex_deadlock_account_lock(lock, current);
 777                 return 1;
 778         }
 779         return slowfn(lock);
 780 }
 781
 782 static inline void
 783 rt_mutex_fastunlock(struct rt_mutex *lock,
 784                     void (*slowfn)(struct rt_mutex *lock))
 785 {
 786         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
 787                 rt_mutex_deadlock_account_unlock(current);
 788         else
 789                 slowfn(lock);
 790 }
 791
 792 /**
 793  * rt_mutex_lock - lock a rt_mutex
 794  *
 795  * @lock: the rt_mutex to be locked
 796  */
 797 void __sched rt_mutex_lock(struct rt_mutex *lock)
 798 {
 799         might_sleep();
 800
 801         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
 802 }
 803 EXPORT_SYMBOL_GPL(rt_mutex_lock);
 804
 805 /**
 806  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
 807  *
 808  * @lock:               the rt_mutex to be locked
 809  * @detect_deadlock:    deadlock detection on/off
 810  *
 811  * Returns:
 812  *  0           on success
 813  * -EINTR       when interrupted by a signal
 814  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 815  */
 816 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 817                                                  int detect_deadlock)
 818 {
 819         might_sleep();
 820
 821         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
 822                                  detect_deadlock, rt_mutex_slowlock);
 823 }
 824 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 825
 826 /**
 827  * rt_mutex_timed_lock - lock a rt_mutex interruptible
 828  *                      the timeout structure is provided
 829  *                      by the caller
 830  *
 831  * @lock:               the rt_mutex to be locked
 832  * @timeout:            timeout structure or NULL (no timeout)
 833  * @detect_deadlock:    deadlock detection on/off
 834  *
 835  * Returns:
 836  *  0           on success
 837  * -EINTR       when interrupted by a signal
 838  * -ETIMEDOUT   when the timeout expired
 839  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 840  */
 841 int
 842 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
 843                     int detect_deadlock)
 844 {
 845         might_sleep();
 846
 847         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
 848                                        detect_deadlock, rt_mutex_slowlock);
 849 }
 850 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
 851
 852 /**
 853  * rt_mutex_trylock - try to lock a rt_mutex
 854  *
 855  * @lock:       the rt_mutex to be locked
 856  *
 857  * Returns 1 on success and 0 on contention
 858  */
 859 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 860 {
 861         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 862 }
 863 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 864
 865 /**
 866  * rt_mutex_unlock - unlock a rt_mutex
 867  *
 868  * @lock: the rt_mutex to be unlocked
 869  */
 870 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 871 {
 872         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 873 }
 874 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 875
 876 /**
 877  * rt_mutex_destroy - mark a mutex unusable
 878  * @lock: the mutex to be destroyed
 879  *
 880  * This function marks the mutex uninitialized, and any subsequent
 881  * use of the mutex is forbidden. The mutex must not be locked when
 882  * this function is called.
 883  */
 884 void rt_mutex_destroy(struct rt_mutex *lock)
 885 {
 886         WARN_ON(rt_mutex_is_locked(lock));
 887 #ifdef CONFIG_DEBUG_RT_MUTEXES
 888         lock->magic = NULL;
 889 #endif
 890 }
 891
 892 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 893
 894 /**
 895  * __rt_mutex_init - initialize the rt lock
 896  *
 897  * @lock: the rt lock to be initialized
 898  *
 899  * Initialize the rt lock to unlocked state.
 900  *
 901  * Initializing of a locked rt lock is not allowed
 902  */
 903 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 904 {
 905         lock->owner = NULL;
 906         raw_spin_lock_init(&lock->wait_lock);
 907         plist_head_init(&lock->wait_list);
 908
 909         debug_rt_mutex_init(lock, name);
 910 }
 911 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 912
 913 /**
 914  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 915  *                              proxy owner
 916  *
 917  * @lock:       the rt_mutex to be locked
 918  * @proxy_owner:the task to set as owner
 919  *
 920  * No locking. Caller has to do serializing itself
 921  * Special API call for PI-futex support
 922  */
 923 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 924                                 struct task_struct *proxy_owner)
 925 {
 926         __rt_mutex_init(lock, NULL);
 927         debug_rt_mutex_proxy_lock(lock, proxy_owner);
 928         rt_mutex_set_owner(lock, proxy_owner);
 929         rt_mutex_deadlock_account_lock(lock, proxy_owner);
 930 }
 931
 932 /**
 933  * rt_mutex_proxy_unlock - release a lock on behalf of owner
 934  *
 935  * @lock:       the rt_mutex to be locked
 936  *
 937  * No locking. Caller has to do serializing itself
 938  * Special API call for PI-futex support
 939  */
 940 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
 941                            struct task_struct *proxy_owner)
 942 {
 943         debug_rt_mutex_proxy_unlock(lock);
 944         rt_mutex_set_owner(lock, NULL);
 945         rt_mutex_deadlock_account_unlock(proxy_owner);
 946 }
 947
 948 /**
 949  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 950  * @lock:               the rt_mutex to take
 951  * @waiter:             the pre-initialized rt_mutex_waiter
 952  * @task:               the task to prepare
 953  * @detect_deadlock:    perform deadlock detection (1) or not (0)
 954  *
 955  * Returns:
 956  *  0 - task blocked on lock
 957  *  1 - acquired the lock for task, caller should wake it up
 958  * <0 - error
 959  *
 960  * Special API call for FUTEX_REQUEUE_PI support.
 961  */
 962 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 963                               struct rt_mutex_waiter *waiter,
 964                               struct task_struct *task, int detect_deadlock)
 965 {
 966         int ret;
 967
 968         raw_spin_lock(&lock->wait_lock);
 969
 970         if (try_to_take_rt_mutex(lock, task, NULL)) {
 971                 raw_spin_unlock(&lock->wait_lock);
 972                 return 1;
 973         }
 974
 975         ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 976
 977         if (ret && !rt_mutex_owner(lock)) {
 978                 /*
 979                  * Reset the return value. We might have
 980                  * returned with -EDEADLK and the owner
 981                  * released the lock while we were walking the
 982                  * pi chain.  Let the waiter sort it out.
 983                  */
 984                 ret = 0;
 985         }
 986
 987         if (unlikely(ret))
 988                 remove_waiter(lock, waiter);
 989
 990         raw_spin_unlock(&lock->wait_lock);
 991
 992         debug_rt_mutex_print_deadlock(waiter);
 993
 994         return ret;
 995 }
 996
 997 /**
 998  * rt_mutex_next_owner - return the next owner of the lock
 999  *
1000  * @lock: the rt lock query
1001  *
1002  * Returns the next owner of the lock or NULL
1003  *
1004  * Caller has to serialize against other accessors to the lock
1005  * itself.
1006  *
1007  * Special API call for PI-futex support
1008  */
1009 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1010 {
1011         if (!rt_mutex_has_waiters(lock))
1012                 return NULL;
1013
1014         return rt_mutex_top_waiter(lock)->task;
1015 }
1016
1017 /**
1018  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1019  * @lock:               the rt_mutex we were woken on
1020  * @to:                 the timeout, null if none. hrtimer should already have
1021  *                      been started.
1022  * @waiter:             the pre-initialized rt_mutex_waiter
1023  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1024  *
1025  * Complete the lock acquisition started our behalf by another thread.
1026  *
1027  * Returns:
1028  *  0 - success
1029  * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1030  *
1031  * Special API call for PI-futex requeue support
1032  */
1033 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1034                                struct hrtimer_sleeper *to,
1035                                struct rt_mutex_waiter *waiter,
1036                                int detect_deadlock)
1037 {
1038         int ret;
1039
1040         raw_spin_lock(&lock->wait_lock);
1041
1042         set_current_state(TASK_INTERRUPTIBLE);
1043
1044         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1045
1046         set_current_state(TASK_RUNNING);
1047
1048         if (unlikely(ret))
1049                 remove_waiter(lock, waiter);
1050
1051         /*
1052          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1053          * have to fix that up.
1054          */
1055         fixup_rt_mutex_waiters(lock);
1056
1057         raw_spin_unlock(&lock->wait_lock);
1058
1059         return ret;
1060 }