kernel/locking/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/sched/deadline.h>
  18 #include <linux/timer.h>
  19
  20 #include "rtmutex_common.h"
  21
  22 /*
  23  * lock->owner state tracking:
  24  *
  25  * lock->owner holds the task_struct pointer of the owner. Bit 0
  26  * is used to keep track of the "lock has waiters" state.
  27  *
  28  * owner        bit0
  29  * NULL         0       lock is free (fast acquire possible)
  30  * NULL         1       lock is free and has waiters and the top waiter
  31  *                              is going to take the lock*
  32  * taskpointer  0       lock is held (fast release possible)
  33  * taskpointer  1       lock is held and has waiters**
  34  *
  35  * The fast atomic compare exchange based acquire and release is only
  36  * possible when bit 0 of lock->owner is 0.
  37  *
  38  * (*) It also can be a transitional state when grabbing the lock
  39  * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  40  * we need to set the bit0 before looking at the lock, and the owner may be
  41  * NULL in this small time, hence this can be a transitional state.
  42  *
  43  * (**) There is a small time when bit 0 is set but there are no
  44  * waiters. This can happen when grabbing the lock in the slow path.
  45  * To prevent a cmpxchg of the owner releasing the lock, we need to
  46  * set this bit before looking at the lock.
  47  */
  48
  49 static void
  50 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  51 {
  52         unsigned long val = (unsigned long)owner;
  53
  54         if (rt_mutex_has_waiters(lock))
  55                 val |= RT_MUTEX_HAS_WAITERS;
  56
  57         lock->owner = (struct task_struct *)val;
  58 }
  59
  60 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  61 {
  62         lock->owner = (struct task_struct *)
  63                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  64 }
  65
  66 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  67 {
  68         if (!rt_mutex_has_waiters(lock))
  69                 clear_rt_mutex_waiters(lock);
  70 }
  71
  72 /*
  73  * We can speed up the acquire/release, if the architecture
  74  * supports cmpxchg and if there's no debugging state to be set up
  75  */
  76 #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  77 # define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
  78 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  79 {
  80         unsigned long owner, *p = (unsigned long *) &lock->owner;
  81
  82         do {
  83                 owner = *p;
  84         } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  85 }
  86
  87 /*
  88  * Safe fastpath aware unlock:
  89  * 1) Clear the waiters bit
  90  * 2) Drop lock->wait_lock
  91  * 3) Try to unlock the lock with cmpxchg
  92  */
  93 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
  94         __releases(lock->wait_lock)
  95 {
  96         struct task_struct *owner = rt_mutex_owner(lock);
  97
  98         clear_rt_mutex_waiters(lock);
  99         raw_spin_unlock(&lock->wait_lock);
 100         /*
 101          * If a new waiter comes in between the unlock and the cmpxchg
 102          * we have two situations:
 103          *
 104          * unlock(wait_lock);
 105          *                                      lock(wait_lock);
 106          * cmpxchg(p, owner, 0) == owner
 107          *                                      mark_rt_mutex_waiters(lock);
 108          *                                      acquire(lock);
 109          * or:
 110          *
 111          * unlock(wait_lock);
 112          *                                      lock(wait_lock);
 113          *                                      mark_rt_mutex_waiters(lock);
 114          *
 115          * cmpxchg(p, owner, 0) != owner
 116          *                                      enqueue_waiter();
 117          *                                      unlock(wait_lock);
 118          * lock(wait_lock);
 119          * wake waiter();
 120          * unlock(wait_lock);
 121          *                                      lock(wait_lock);
 122          *                                      acquire(lock);
 123          */
 124         return rt_mutex_cmpxchg(lock, owner, NULL);
 125 }
 126
 127 #else
 128 # define rt_mutex_cmpxchg(l,c,n)        (0)
 129 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 130 {
 131         lock->owner = (struct task_struct *)
 132                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 133 }
 134
 135 /*
 136  * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 137  */
 138 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
 139         __releases(lock->wait_lock)
 140 {
 141         lock->owner = NULL;
 142         raw_spin_unlock(&lock->wait_lock);
 143         return true;
 144 }
 145 #endif
 146
 147 static inline int
 148 rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 149                      struct rt_mutex_waiter *right)
 150 {
 151         if (left->prio < right->prio)
 152                 return 1;
 153
 154         /*
 155          * If both waiters have dl_prio(), we check the deadlines of the
 156          * associated tasks.
 157          * If left waiter has a dl_prio(), and we didn't return 1 above,
 158          * then right waiter has a dl_prio() too.
 159          */
 160         if (dl_prio(left->prio))
 161                 return (left->task->dl.deadline < right->task->dl.deadline);
 162
 163         return 0;
 164 }
 165
 166 static void
 167 rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 168 {
 169         struct rb_node **link = &lock->waiters.rb_node;
 170         struct rb_node *parent = NULL;
 171         struct rt_mutex_waiter *entry;
 172         int leftmost = 1;
 173
 174         while (*link) {
 175                 parent = *link;
 176                 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
 177                 if (rt_mutex_waiter_less(waiter, entry)) {
 178                         link = &parent->rb_left;
 179                 } else {
 180                         link = &parent->rb_right;
 181                         leftmost = 0;
 182                 }
 183         }
 184
 185         if (leftmost)
 186                 lock->waiters_leftmost = &waiter->tree_entry;
 187
 188         rb_link_node(&waiter->tree_entry, parent, link);
 189         rb_insert_color(&waiter->tree_entry, &lock->waiters);
 190 }
 191
 192 static void
 193 rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 194 {
 195         if (RB_EMPTY_NODE(&waiter->tree_entry))
 196                 return;
 197
 198         if (lock->waiters_leftmost == &waiter->tree_entry)
 199                 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
 200
 201         rb_erase(&waiter->tree_entry, &lock->waiters);
 202         RB_CLEAR_NODE(&waiter->tree_entry);
 203 }
 204
 205 static void
 206 rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 207 {
 208         struct rb_node **link = &task->pi_waiters.rb_node;
 209         struct rb_node *parent = NULL;
 210         struct rt_mutex_waiter *entry;
 211         int leftmost = 1;
 212
 213         while (*link) {
 214                 parent = *link;
 215                 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
 216                 if (rt_mutex_waiter_less(waiter, entry)) {
 217                         link = &parent->rb_left;
 218                 } else {
 219                         link = &parent->rb_right;
 220                         leftmost = 0;
 221                 }
 222         }
 223
 224         if (leftmost)
 225                 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
 226
 227         rb_link_node(&waiter->pi_tree_entry, parent, link);
 228         rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
 229 }
 230
 231 static void
 232 rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 233 {
 234         if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
 235                 return;
 236
 237         if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
 238                 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
 239
 240         rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
 241         RB_CLEAR_NODE(&waiter->pi_tree_entry);
 242 }
 243
 244 /*
 245  * Calculate task priority from the waiter tree priority
 246  *
 247  * Return task->normal_prio when the waiter tree is empty or when
 248  * the waiter is not allowed to do priority boosting
 249  */
 250 int rt_mutex_getprio(struct task_struct *task)
 251 {
 252         if (likely(!task_has_pi_waiters(task)))
 253                 return task->normal_prio;
 254
 255         return min(task_top_pi_waiter(task)->prio,
 256                    task->normal_prio);
 257 }
 258
 259 struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
 260 {
 261         if (likely(!task_has_pi_waiters(task)))
 262                 return NULL;
 263
 264         return task_top_pi_waiter(task)->task;
 265 }
 266
 267 /*
 268  * Adjust the priority of a task, after its pi_waiters got modified.
 269  *
 270  * This can be both boosting and unboosting. task->pi_lock must be held.
 271  */
 272 static void __rt_mutex_adjust_prio(struct task_struct *task)
 273 {
 274         int prio = rt_mutex_getprio(task);
 275
 276         if (task->prio != prio || dl_prio(prio))
 277                 rt_mutex_setprio(task, prio);
 278 }
 279
 280 /*
 281  * Adjust task priority (undo boosting). Called from the exit path of
 282  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 283  *
 284  * (Note: We do this outside of the protection of lock->wait_lock to
 285  * allow the lock to be taken while or before we readjust the priority
 286  * of task. We do not use the spin_xx_mutex() variants here as we are
 287  * outside of the debug path.)
 288  */
 289 static void rt_mutex_adjust_prio(struct task_struct *task)
 290 {
 291         unsigned long flags;
 292
 293         raw_spin_lock_irqsave(&task->pi_lock, flags);
 294         __rt_mutex_adjust_prio(task);
 295         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 296 }
 297
 298 /*
 299  * Max number of times we'll walk the boosting chain:
 300  */
 301 int max_lock_depth = 1024;
 302
 303 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 304 {
 305         return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 306 }
 307
 308 /*
 309  * Adjust the priority chain. Also used for deadlock detection.
 310  * Decreases task's usage by one - may thus free the task.
 311  *
 312  * @task:       the task owning the mutex (owner) for which a chain walk is
 313  *              probably needed
 314  * @deadlock_detect: do we have to carry out deadlock detection?
 315  * @orig_lock:  the mutex (can be NULL if we are walking the chain to recheck
 316  *              things for a task that has just got its priority adjusted, and
 317  *              is waiting on a mutex)
 318  * @next_lock:  the mutex on which the owner of @orig_lock was blocked before
 319  *              we dropped its pi_lock. Is never dereferenced, only used for
 320  *              comparison to detect lock chain changes.
 321  * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 322  *              its priority to the mutex owner (can be NULL in the case
 323  *              depicted above or if the top waiter is gone away and we are
 324  *              actually deboosting the owner)
 325  * @top_task:   the current top waiter
 326  *
 327  * Returns 0 or -EDEADLK.
 328  */
 329 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 330                                       int deadlock_detect,
 331                                       struct rt_mutex *orig_lock,
 332                                       struct rt_mutex *next_lock,
 333                                       struct rt_mutex_waiter *orig_waiter,
 334                                       struct task_struct *top_task)
 335 {
 336         struct rt_mutex *lock;
 337         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 338         int detect_deadlock, ret = 0, depth = 0;
 339         unsigned long flags;
 340
 341         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 342                                                          deadlock_detect);
 343
 344         /*
 345          * The (de)boosting is a step by step approach with a lot of
 346          * pitfalls. We want this to be preemptible and we want hold a
 347          * maximum of two locks per step. So we have to check
 348          * carefully whether things change under us.
 349          */
 350  again:
 351         if (++depth > max_lock_depth) {
 352                 static int prev_max;
 353
 354                 /*
 355                  * Print this only once. If the admin changes the limit,
 356                  * print a new message when reaching the limit again.
 357                  */
 358                 if (prev_max != max_lock_depth) {
 359                         prev_max = max_lock_depth;
 360                         printk(KERN_WARNING "Maximum lock depth %d reached "
 361                                "task: %s (%d)\n", max_lock_depth,
 362                                top_task->comm, task_pid_nr(top_task));
 363                 }
 364                 put_task_struct(task);
 365
 366                 return -EDEADLK;
 367         }
 368  retry:
 369         /*
 370          * Task can not go away as we did a get_task() before !
 371          */
 372         raw_spin_lock_irqsave(&task->pi_lock, flags);
 373
 374         waiter = task->pi_blocked_on;
 375         /*
 376          * Check whether the end of the boosting chain has been
 377          * reached or the state of the chain has changed while we
 378          * dropped the locks.
 379          */
 380         if (!waiter)
 381                 goto out_unlock_pi;
 382
 383         /*
 384          * Check the orig_waiter state. After we dropped the locks,
 385          * the previous owner of the lock might have released the lock.
 386          */
 387         if (orig_waiter && !rt_mutex_owner(orig_lock))
 388                 goto out_unlock_pi;
 389
 390         /*
 391          * We dropped all locks after taking a refcount on @task, so
 392          * the task might have moved on in the lock chain or even left
 393          * the chain completely and blocks now on an unrelated lock or
 394          * on @orig_lock.
 395          *
 396          * We stored the lock on which @task was blocked in @next_lock,
 397          * so we can detect the chain change.
 398          */
 399         if (next_lock != waiter->lock)
 400                 goto out_unlock_pi;
 401
 402         /*
 403          * Drop out, when the task has no waiters. Note,
 404          * top_waiter can be NULL, when we are in the deboosting
 405          * mode!
 406          */
 407         if (top_waiter) {
 408                 if (!task_has_pi_waiters(task))
 409                         goto out_unlock_pi;
 410                 /*
 411                  * If deadlock detection is off, we stop here if we
 412                  * are not the top pi waiter of the task.
 413                  */
 414                 if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
 415                         goto out_unlock_pi;
 416         }
 417
 418         /*
 419          * When deadlock detection is off then we check, if further
 420          * priority adjustment is necessary.
 421          */
 422         if (!detect_deadlock && waiter->prio == task->prio)
 423                 goto out_unlock_pi;
 424
 425         lock = waiter->lock;
 426         if (!raw_spin_trylock(&lock->wait_lock)) {
 427                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 428                 cpu_relax();
 429                 goto retry;
 430         }
 431
 432         /*
 433          * Deadlock detection. If the lock is the same as the original
 434          * lock which caused us to walk the lock chain or if the
 435          * current lock is owned by the task which initiated the chain
 436          * walk, we detected a deadlock.
 437          */
 438         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 439                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 440                 raw_spin_unlock(&lock->wait_lock);
 441                 ret = -EDEADLK;
 442                 goto out_unlock_pi;
 443         }
 444
 445         top_waiter = rt_mutex_top_waiter(lock);
 446
 447         /* Requeue the waiter */
 448         rt_mutex_dequeue(lock, waiter);
 449         waiter->prio = task->prio;
 450         rt_mutex_enqueue(lock, waiter);
 451
 452         /* Release the task */
 453         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 454         if (!rt_mutex_owner(lock)) {
 455                 /*
 456                  * If the requeue above changed the top waiter, then we need
 457                  * to wake the new top waiter up to try to get the lock.
 458                  */
 459
 460                 if (top_waiter != rt_mutex_top_waiter(lock))
 461                         wake_up_process(rt_mutex_top_waiter(lock)->task);
 462                 raw_spin_unlock(&lock->wait_lock);
 463                 goto out_put_task;
 464         }
 465         put_task_struct(task);
 466
 467         /* Grab the next task */
 468         task = rt_mutex_owner(lock);
 469         get_task_struct(task);
 470         raw_spin_lock_irqsave(&task->pi_lock, flags);
 471
 472         if (waiter == rt_mutex_top_waiter(lock)) {
 473                 /* Boost the owner */
 474                 rt_mutex_dequeue_pi(task, top_waiter);
 475                 rt_mutex_enqueue_pi(task, waiter);
 476                 __rt_mutex_adjust_prio(task);
 477
 478         } else if (top_waiter == waiter) {
 479                 /* Deboost the owner */
 480                 rt_mutex_dequeue_pi(task, waiter);
 481                 waiter = rt_mutex_top_waiter(lock);
 482                 rt_mutex_enqueue_pi(task, waiter);
 483                 __rt_mutex_adjust_prio(task);
 484         }
 485
 486         /*
 487          * Check whether the task which owns the current lock is pi
 488          * blocked itself. If yes we store a pointer to the lock for
 489          * the lock chain change detection above. After we dropped
 490          * task->pi_lock next_lock cannot be dereferenced anymore.
 491          */
 492         next_lock = task_blocked_on_lock(task);
 493
 494         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 495
 496         top_waiter = rt_mutex_top_waiter(lock);
 497         raw_spin_unlock(&lock->wait_lock);
 498
 499         /*
 500          * We reached the end of the lock chain. Stop right here. No
 501          * point to go back just to figure that out.
 502          */
 503         if (!next_lock)
 504                 goto out_put_task;
 505
 506         if (!detect_deadlock && waiter != top_waiter)
 507                 goto out_put_task;
 508
 509         goto again;
 510
 511  out_unlock_pi:
 512         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 513  out_put_task:
 514         put_task_struct(task);
 515
 516         return ret;
 517 }
 518
 519 /*
 520  * Try to take an rt-mutex
 521  *
 522  * Must be called with lock->wait_lock held.
 523  *
 524  * @lock:   the lock to be acquired.
 525  * @task:   the task which wants to acquire the lock
 526  * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
 527  */
 528 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 529                 struct rt_mutex_waiter *waiter)
 530 {
 531         /*
 532          * We have to be careful here if the atomic speedups are
 533          * enabled, such that, when
 534          *  - no other waiter is on the lock
 535          *  - the lock has been released since we did the cmpxchg
 536          * the lock can be released or taken while we are doing the
 537          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 538          *
 539          * The atomic acquire/release aware variant of
 540          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 541          * the WAITERS bit, the atomic release / acquire can not
 542          * happen anymore and lock->wait_lock protects us from the
 543          * non-atomic case.
 544          *
 545          * Note, that this might set lock->owner =
 546          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 547          * any more. This is fixed up when we take the ownership.
 548          * This is the transitional state explained at the top of this file.
 549          */
 550         mark_rt_mutex_waiters(lock);
 551
 552         if (rt_mutex_owner(lock))
 553                 return 0;
 554
 555         /*
 556          * It will get the lock because of one of these conditions:
 557          * 1) there is no waiter
 558          * 2) higher priority than waiters
 559          * 3) it is top waiter
 560          */
 561         if (rt_mutex_has_waiters(lock)) {
 562                 if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
 563                         if (!waiter || waiter != rt_mutex_top_waiter(lock))
 564                                 return 0;
 565                 }
 566         }
 567
 568         if (waiter || rt_mutex_has_waiters(lock)) {
 569                 unsigned long flags;
 570                 struct rt_mutex_waiter *top;
 571
 572                 raw_spin_lock_irqsave(&task->pi_lock, flags);
 573
 574                 /* remove the queued waiter. */
 575                 if (waiter) {
 576                         rt_mutex_dequeue(lock, waiter);
 577                         task->pi_blocked_on = NULL;
 578                 }
 579
 580                 /*
 581                  * We have to enqueue the top waiter(if it exists) into
 582                  * task->pi_waiters list.
 583                  */
 584                 if (rt_mutex_has_waiters(lock)) {
 585                         top = rt_mutex_top_waiter(lock);
 586                         rt_mutex_enqueue_pi(task, top);
 587                 }
 588                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 589         }
 590
 591         /* We got the lock. */
 592         debug_rt_mutex_lock(lock);
 593
 594         rt_mutex_set_owner(lock, task);
 595
 596         rt_mutex_deadlock_account_lock(lock, task);
 597
 598         return 1;
 599 }
 600
 601 /*
 602  * Task blocks on lock.
 603  *
 604  * Prepare waiter and propagate pi chain
 605  *
 606  * This must be called with lock->wait_lock held.
 607  */
 608 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 609                                    struct rt_mutex_waiter *waiter,
 610                                    struct task_struct *task,
 611                                    int detect_deadlock)
 612 {
 613         struct task_struct *owner = rt_mutex_owner(lock);
 614         struct rt_mutex_waiter *top_waiter = waiter;
 615         struct rt_mutex *next_lock;
 616         int chain_walk = 0, res;
 617         unsigned long flags;
 618
 619         /*
 620          * Early deadlock detection. We really don't want the task to
 621          * enqueue on itself just to untangle the mess later. It's not
 622          * only an optimization. We drop the locks, so another waiter
 623          * can come in before the chain walk detects the deadlock. So
 624          * the other will detect the deadlock and return -EDEADLOCK,
 625          * which is wrong, as the other waiter is not in a deadlock
 626          * situation.
 627          */
 628         if (owner == task)
 629                 return -EDEADLK;
 630
 631         raw_spin_lock_irqsave(&task->pi_lock, flags);
 632         __rt_mutex_adjust_prio(task);
 633         waiter->task = task;
 634         waiter->lock = lock;
 635         waiter->prio = task->prio;
 636
 637         /* Get the top priority waiter on the lock */
 638         if (rt_mutex_has_waiters(lock))
 639                 top_waiter = rt_mutex_top_waiter(lock);
 640         rt_mutex_enqueue(lock, waiter);
 641
 642         task->pi_blocked_on = waiter;
 643
 644         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 645
 646         if (!owner)
 647                 return 0;
 648
 649         raw_spin_lock_irqsave(&owner->pi_lock, flags);
 650         if (waiter == rt_mutex_top_waiter(lock)) {
 651                 rt_mutex_dequeue_pi(owner, top_waiter);
 652                 rt_mutex_enqueue_pi(owner, waiter);
 653
 654                 __rt_mutex_adjust_prio(owner);
 655                 if (owner->pi_blocked_on)
 656                         chain_walk = 1;
 657         } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
 658                 chain_walk = 1;
 659         }
 660
 661         /* Store the lock on which owner is blocked or NULL */
 662         next_lock = task_blocked_on_lock(owner);
 663
 664         raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 665         /*
 666          * Even if full deadlock detection is on, if the owner is not
 667          * blocked itself, we can avoid finding this out in the chain
 668          * walk.
 669          */
 670         if (!chain_walk || !next_lock)
 671                 return 0;
 672
 673         /*
 674          * The owner can't disappear while holding a lock,
 675          * so the owner struct is protected by wait_lock.
 676          * Gets dropped in rt_mutex_adjust_prio_chain()!
 677          */
 678         get_task_struct(owner);
 679
 680         raw_spin_unlock(&lock->wait_lock);
 681
 682         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
 683                                          next_lock, waiter, task);
 684
 685         raw_spin_lock(&lock->wait_lock);
 686
 687         return res;
 688 }
 689
 690 /*
 691  * Wake up the next waiter on the lock.
 692  *
 693  * Remove the top waiter from the current tasks pi waiter list and
 694  * wake it up.
 695  *
 696  * Called with lock->wait_lock held.
 697  */
 698 static void wakeup_next_waiter(struct rt_mutex *lock)
 699 {
 700         struct rt_mutex_waiter *waiter;
 701         unsigned long flags;
 702
 703         raw_spin_lock_irqsave(&current->pi_lock, flags);
 704
 705         waiter = rt_mutex_top_waiter(lock);
 706
 707         /*
 708          * Remove it from current->pi_waiters. We do not adjust a
 709          * possible priority boost right now. We execute wakeup in the
 710          * boosted mode and go back to normal after releasing
 711          * lock->wait_lock.
 712          */
 713         rt_mutex_dequeue_pi(current, waiter);
 714
 715         /*
 716          * As we are waking up the top waiter, and the waiter stays
 717          * queued on the lock until it gets the lock, this lock
 718          * obviously has waiters. Just set the bit here and this has
 719          * the added benefit of forcing all new tasks into the
 720          * slow path making sure no task of lower priority than
 721          * the top waiter can steal this lock.
 722          */
 723         lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
 724
 725         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 726
 727         /*
 728          * It's safe to dereference waiter as it cannot go away as
 729          * long as we hold lock->wait_lock. The waiter task needs to
 730          * acquire it in order to dequeue the waiter.
 731          */
 732         wake_up_process(waiter->task);
 733 }
 734
 735 /*
 736  * Remove a waiter from a lock and give up
 737  *
 738  * Must be called with lock->wait_lock held and
 739  * have just failed to try_to_take_rt_mutex().
 740  */
 741 static void remove_waiter(struct rt_mutex *lock,
 742                           struct rt_mutex_waiter *waiter)
 743 {
 744         int first = (waiter == rt_mutex_top_waiter(lock));
 745         struct task_struct *owner = rt_mutex_owner(lock);
 746         struct rt_mutex *next_lock = NULL;
 747         unsigned long flags;
 748
 749         raw_spin_lock_irqsave(&current->pi_lock, flags);
 750         rt_mutex_dequeue(lock, waiter);
 751         current->pi_blocked_on = NULL;
 752         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 753
 754         if (!owner)
 755                 return;
 756
 757         if (first) {
 758
 759                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 760
 761                 rt_mutex_dequeue_pi(owner, waiter);
 762
 763                 if (rt_mutex_has_waiters(lock)) {
 764                         struct rt_mutex_waiter *next;
 765
 766                         next = rt_mutex_top_waiter(lock);
 767                         rt_mutex_enqueue_pi(owner, next);
 768                 }
 769                 __rt_mutex_adjust_prio(owner);
 770
 771                 /* Store the lock on which owner is blocked or NULL */
 772                 next_lock = task_blocked_on_lock(owner);
 773
 774                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 775         }
 776
 777         if (!next_lock)
 778                 return;
 779
 780         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 781         get_task_struct(owner);
 782
 783         raw_spin_unlock(&lock->wait_lock);
 784
 785         rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
 786
 787         raw_spin_lock(&lock->wait_lock);
 788 }
 789
 790 /*
 791  * Recheck the pi chain, in case we got a priority setting
 792  *
 793  * Called from sched_setscheduler
 794  */
 795 void rt_mutex_adjust_pi(struct task_struct *task)
 796 {
 797         struct rt_mutex_waiter *waiter;
 798         struct rt_mutex *next_lock;
 799         unsigned long flags;
 800
 801         raw_spin_lock_irqsave(&task->pi_lock, flags);
 802
 803         waiter = task->pi_blocked_on;
 804         if (!waiter || (waiter->prio == task->prio &&
 805                         !dl_prio(task->prio))) {
 806                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 807                 return;
 808         }
 809         next_lock = waiter->lock;
 810         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 811
 812         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 813         get_task_struct(task);
 814
 815         rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
 816 }
 817
 818 /**
 819  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 820  * @lock:                the rt_mutex to take
 821  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 822  *                       or TASK_UNINTERRUPTIBLE)
 823  * @timeout:             the pre-initialized and started timer, or NULL for none
 824  * @waiter:              the pre-initialized rt_mutex_waiter
 825  *
 826  * lock->wait_lock must be held by the caller.
 827  */
 828 static int __sched
 829 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
 830                     struct hrtimer_sleeper *timeout,
 831                     struct rt_mutex_waiter *waiter)
 832 {
 833         int ret = 0;
 834
 835         for (;;) {
 836                 /* Try to acquire the lock: */
 837                 if (try_to_take_rt_mutex(lock, current, waiter))
 838                         break;
 839
 840                 /*
 841                  * TASK_INTERRUPTIBLE checks for signals and
 842                  * timeout. Ignored otherwise.
 843                  */
 844                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 845                         /* Signal pending? */
 846                         if (signal_pending(current))
 847                                 ret = -EINTR;
 848                         if (timeout && !timeout->task)
 849                                 ret = -ETIMEDOUT;
 850                         if (ret)
 851                                 break;
 852                 }
 853
 854                 raw_spin_unlock(&lock->wait_lock);
 855
 856                 debug_rt_mutex_print_deadlock(waiter);
 857
 858                 schedule_rt_mutex(lock);
 859
 860                 raw_spin_lock(&lock->wait_lock);
 861                 set_current_state(state);
 862         }
 863
 864         return ret;
 865 }
 866
 867 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
 868                                      struct rt_mutex_waiter *w)
 869 {
 870         /*
 871          * If the result is not -EDEADLOCK or the caller requested
 872          * deadlock detection, nothing to do here.
 873          */
 874         if (res != -EDEADLOCK || detect_deadlock)
 875                 return;
 876
 877         /*
 878          * Yell lowdly and stop the task right here.
 879          */
 880         rt_mutex_print_deadlock(w);
 881         while (1) {
 882                 set_current_state(TASK_INTERRUPTIBLE);
 883                 schedule();
 884         }
 885 }
 886
 887 /*
 888  * Slow path lock function:
 889  */
 890 static int __sched
 891 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 892                   struct hrtimer_sleeper *timeout,
 893                   int detect_deadlock)
 894 {
 895         struct rt_mutex_waiter waiter;
 896         int ret = 0;
 897
 898         debug_rt_mutex_init_waiter(&waiter);
 899         RB_CLEAR_NODE(&waiter.pi_tree_entry);
 900         RB_CLEAR_NODE(&waiter.tree_entry);
 901
 902         raw_spin_lock(&lock->wait_lock);
 903
 904         /* Try to acquire the lock again: */
 905         if (try_to_take_rt_mutex(lock, current, NULL)) {
 906                 raw_spin_unlock(&lock->wait_lock);
 907                 return 0;
 908         }
 909
 910         set_current_state(state);
 911
 912         /* Setup the timer, when timeout != NULL */
 913         if (unlikely(timeout)) {
 914                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 915                 if (!hrtimer_active(&timeout->timer))
 916                         timeout->task = NULL;
 917         }
 918
 919         ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
 920
 921         if (likely(!ret))
 922                 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 923
 924         set_current_state(TASK_RUNNING);
 925
 926         if (unlikely(ret)) {
 927                 remove_waiter(lock, &waiter);
 928                 rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
 929         }
 930
 931         /*
 932          * try_to_take_rt_mutex() sets the waiter bit
 933          * unconditionally. We might have to fix that up.
 934          */
 935         fixup_rt_mutex_waiters(lock);
 936
 937         raw_spin_unlock(&lock->wait_lock);
 938
 939         /* Remove pending timer: */
 940         if (unlikely(timeout))
 941                 hrtimer_cancel(&timeout->timer);
 942
 943         debug_rt_mutex_free_waiter(&waiter);
 944
 945         return ret;
 946 }
 947
 948 /*
 949  * Slow path try-lock function:
 950  */
 951 static inline int
 952 rt_mutex_slowtrylock(struct rt_mutex *lock)
 953 {
 954         int ret = 0;
 955
 956         raw_spin_lock(&lock->wait_lock);
 957
 958         if (likely(rt_mutex_owner(lock) != current)) {
 959
 960                 ret = try_to_take_rt_mutex(lock, current, NULL);
 961                 /*
 962                  * try_to_take_rt_mutex() sets the lock waiters
 963                  * bit unconditionally. Clean this up.
 964                  */
 965                 fixup_rt_mutex_waiters(lock);
 966         }
 967
 968         raw_spin_unlock(&lock->wait_lock);
 969
 970         return ret;
 971 }
 972
 973 /*
 974  * Slow path to release a rt-mutex:
 975  */
 976 static void __sched
 977 rt_mutex_slowunlock(struct rt_mutex *lock)
 978 {
 979         raw_spin_lock(&lock->wait_lock);
 980
 981         debug_rt_mutex_unlock(lock);
 982
 983         rt_mutex_deadlock_account_unlock(current);
 984
 985         /*
 986          * We must be careful here if the fast path is enabled. If we
 987          * have no waiters queued we cannot set owner to NULL here
 988          * because of:
 989          *
 990          * foo->lock->owner = NULL;
 991          *                      rtmutex_lock(foo->lock);   <- fast path
 992          *                      free = atomic_dec_and_test(foo->refcnt);
 993          *                      rtmutex_unlock(foo->lock); <- fast path
 994          *                      if (free)
 995          *                              kfree(foo);
 996          * raw_spin_unlock(foo->lock->wait_lock);
 997          *
 998          * So for the fastpath enabled kernel:
 999          *
1000          * Nothing can set the waiters bit as long as we hold
1001          * lock->wait_lock. So we do the following sequence:
1002          *
1003          *      owner = rt_mutex_owner(lock);
1004          *      clear_rt_mutex_waiters(lock);
1005          *      raw_spin_unlock(&lock->wait_lock);
1006          *      if (cmpxchg(&lock->owner, owner, 0) == owner)
1007          *              return;
1008          *      goto retry;
1009          *
1010          * The fastpath disabled variant is simple as all access to
1011          * lock->owner is serialized by lock->wait_lock:
1012          *
1013          *      lock->owner = NULL;
1014          *      raw_spin_unlock(&lock->wait_lock);
1015          */
1016         while (!rt_mutex_has_waiters(lock)) {
1017                 /* Drops lock->wait_lock ! */
1018                 if (unlock_rt_mutex_safe(lock) == true)
1019                         return;
1020                 /* Relock the rtmutex and try again */
1021                 raw_spin_lock(&lock->wait_lock);
1022         }
1023
1024         /*
1025          * The wakeup next waiter path does not suffer from the above
1026          * race. See the comments there.
1027          */
1028         wakeup_next_waiter(lock);
1029
1030         raw_spin_unlock(&lock->wait_lock);
1031
1032         /* Undo pi boosting if necessary: */
1033         rt_mutex_adjust_prio(current);
1034 }
1035
1036 /*
1037  * debug aware fast / slowpath lock,trylock,unlock
1038  *
1039  * The atomic acquire/release ops are compiled away, when either the
1040  * architecture does not support cmpxchg or when debugging is enabled.
1041  */
1042 static inline int
1043 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1044                   int detect_deadlock,
1045                   int (*slowfn)(struct rt_mutex *lock, int state,
1046                                 struct hrtimer_sleeper *timeout,
1047                                 int detect_deadlock))
1048 {
1049         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1050                 rt_mutex_deadlock_account_lock(lock, current);
1051                 return 0;
1052         } else
1053                 return slowfn(lock, state, NULL, detect_deadlock);
1054 }
1055
1056 static inline int
1057 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1058                         struct hrtimer_sleeper *timeout, int detect_deadlock,
1059                         int (*slowfn)(struct rt_mutex *lock, int state,
1060                                       struct hrtimer_sleeper *timeout,
1061                                       int detect_deadlock))
1062 {
1063         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1064                 rt_mutex_deadlock_account_lock(lock, current);
1065                 return 0;
1066         } else
1067                 return slowfn(lock, state, timeout, detect_deadlock);
1068 }
1069
1070 static inline int
1071 rt_mutex_fasttrylock(struct rt_mutex *lock,
1072                      int (*slowfn)(struct rt_mutex *lock))
1073 {
1074         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1075                 rt_mutex_deadlock_account_lock(lock, current);
1076                 return 1;
1077         }
1078         return slowfn(lock);
1079 }
1080
1081 static inline void
1082 rt_mutex_fastunlock(struct rt_mutex *lock,
1083                     void (*slowfn)(struct rt_mutex *lock))
1084 {
1085         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
1086                 rt_mutex_deadlock_account_unlock(current);
1087         else
1088                 slowfn(lock);
1089 }
1090
1091 /**
1092  * rt_mutex_lock - lock a rt_mutex
1093  *
1094  * @lock: the rt_mutex to be locked
1095  */
1096 void __sched rt_mutex_lock(struct rt_mutex *lock)
1097 {
1098         might_sleep();
1099
1100         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
1101 }
1102 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1103
1104 /**
1105  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1106  *
1107  * @lock:               the rt_mutex to be locked
1108  * @detect_deadlock:    deadlock detection on/off
1109  *
1110  * Returns:
1111  *  0           on success
1112  * -EINTR       when interrupted by a signal
1113  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1114  */
1115 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
1116                                                  int detect_deadlock)
1117 {
1118         might_sleep();
1119
1120         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
1121                                  detect_deadlock, rt_mutex_slowlock);
1122 }
1123 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1124
1125 /**
1126  * rt_mutex_timed_lock - lock a rt_mutex interruptible
1127  *                      the timeout structure is provided
1128  *                      by the caller
1129  *
1130  * @lock:               the rt_mutex to be locked
1131  * @timeout:            timeout structure or NULL (no timeout)
1132  * @detect_deadlock:    deadlock detection on/off
1133  *
1134  * Returns:
1135  *  0           on success
1136  * -EINTR       when interrupted by a signal
1137  * -ETIMEDOUT   when the timeout expired
1138  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1139  */
1140 int
1141 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
1142                     int detect_deadlock)
1143 {
1144         might_sleep();
1145
1146         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1147                                        detect_deadlock, rt_mutex_slowlock);
1148 }
1149 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1150
1151 /**
1152  * rt_mutex_trylock - try to lock a rt_mutex
1153  *
1154  * @lock:       the rt_mutex to be locked
1155  *
1156  * Returns 1 on success and 0 on contention
1157  */
1158 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1159 {
1160         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1161 }
1162 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1163
1164 /**
1165  * rt_mutex_unlock - unlock a rt_mutex
1166  *
1167  * @lock: the rt_mutex to be unlocked
1168  */
1169 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1170 {
1171         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1172 }
1173 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1174
1175 /**
1176  * rt_mutex_destroy - mark a mutex unusable
1177  * @lock: the mutex to be destroyed
1178  *
1179  * This function marks the mutex uninitialized, and any subsequent
1180  * use of the mutex is forbidden. The mutex must not be locked when
1181  * this function is called.
1182  */
1183 void rt_mutex_destroy(struct rt_mutex *lock)
1184 {
1185         WARN_ON(rt_mutex_is_locked(lock));
1186 #ifdef CONFIG_DEBUG_RT_MUTEXES
1187         lock->magic = NULL;
1188 #endif
1189 }
1190
1191 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1192
1193 /**
1194  * __rt_mutex_init - initialize the rt lock
1195  *
1196  * @lock: the rt lock to be initialized
1197  *
1198  * Initialize the rt lock to unlocked state.
1199  *
1200  * Initializing of a locked rt lock is not allowed
1201  */
1202 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1203 {
1204         lock->owner = NULL;
1205         raw_spin_lock_init(&lock->wait_lock);
1206         lock->waiters = RB_ROOT;
1207         lock->waiters_leftmost = NULL;
1208
1209         debug_rt_mutex_init(lock, name);
1210 }
1211 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1212
1213 /**
1214  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1215  *                              proxy owner
1216  *
1217  * @lock:       the rt_mutex to be locked
1218  * @proxy_owner:the task to set as owner
1219  *
1220  * No locking. Caller has to do serializing itself
1221  * Special API call for PI-futex support
1222  */
1223 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1224                                 struct task_struct *proxy_owner)
1225 {
1226         __rt_mutex_init(lock, NULL);
1227         debug_rt_mutex_proxy_lock(lock, proxy_owner);
1228         rt_mutex_set_owner(lock, proxy_owner);
1229         rt_mutex_deadlock_account_lock(lock, proxy_owner);
1230 }
1231
1232 /**
1233  * rt_mutex_proxy_unlock - release a lock on behalf of owner
1234  *
1235  * @lock:       the rt_mutex to be locked
1236  *
1237  * No locking. Caller has to do serializing itself
1238  * Special API call for PI-futex support
1239  */
1240 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1241                            struct task_struct *proxy_owner)
1242 {
1243         debug_rt_mutex_proxy_unlock(lock);
1244         rt_mutex_set_owner(lock, NULL);
1245         rt_mutex_deadlock_account_unlock(proxy_owner);
1246 }
1247
1248 /**
1249  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1250  * @lock:               the rt_mutex to take
1251  * @waiter:             the pre-initialized rt_mutex_waiter
1252  * @task:               the task to prepare
1253  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1254  *
1255  * Returns:
1256  *  0 - task blocked on lock
1257  *  1 - acquired the lock for task, caller should wake it up
1258  * <0 - error
1259  *
1260  * Special API call for FUTEX_REQUEUE_PI support.
1261  */
1262 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1263                               struct rt_mutex_waiter *waiter,
1264                               struct task_struct *task, int detect_deadlock)
1265 {
1266         int ret;
1267
1268         raw_spin_lock(&lock->wait_lock);
1269
1270         if (try_to_take_rt_mutex(lock, task, NULL)) {
1271                 raw_spin_unlock(&lock->wait_lock);
1272                 return 1;
1273         }
1274
1275         /* We enforce deadlock detection for futexes */
1276         ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
1277
1278         if (ret && !rt_mutex_owner(lock)) {
1279                 /*
1280                  * Reset the return value. We might have
1281                  * returned with -EDEADLK and the owner
1282                  * released the lock while we were walking the
1283                  * pi chain.  Let the waiter sort it out.
1284                  */
1285                 ret = 0;
1286         }
1287
1288         if (unlikely(ret))
1289                 remove_waiter(lock, waiter);
1290
1291         raw_spin_unlock(&lock->wait_lock);
1292
1293         debug_rt_mutex_print_deadlock(waiter);
1294
1295         return ret;
1296 }
1297
1298 /**
1299  * rt_mutex_next_owner - return the next owner of the lock
1300  *
1301  * @lock: the rt lock query
1302  *
1303  * Returns the next owner of the lock or NULL
1304  *
1305  * Caller has to serialize against other accessors to the lock
1306  * itself.
1307  *
1308  * Special API call for PI-futex support
1309  */
1310 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1311 {
1312         if (!rt_mutex_has_waiters(lock))
1313                 return NULL;
1314
1315         return rt_mutex_top_waiter(lock)->task;
1316 }
1317
1318 /**
1319  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1320  * @lock:               the rt_mutex we were woken on
1321  * @to:                 the timeout, null if none. hrtimer should already have
1322  *                      been started.
1323  * @waiter:             the pre-initialized rt_mutex_waiter
1324  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1325  *
1326  * Complete the lock acquisition started our behalf by another thread.
1327  *
1328  * Returns:
1329  *  0 - success
1330  * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1331  *
1332  * Special API call for PI-futex requeue support
1333  */
1334 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1335                                struct hrtimer_sleeper *to,
1336                                struct rt_mutex_waiter *waiter,
1337                                int detect_deadlock)
1338 {
1339         int ret;
1340
1341         raw_spin_lock(&lock->wait_lock);
1342
1343         set_current_state(TASK_INTERRUPTIBLE);
1344
1345         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1346
1347         set_current_state(TASK_RUNNING);
1348
1349         if (unlikely(ret))
1350                 remove_waiter(lock, waiter);
1351
1352         /*
1353          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1354          * have to fix that up.
1355          */
1356         fixup_rt_mutex_waiters(lock);
1357
1358         raw_spin_unlock(&lock->wait_lock);
1359
1360         return ret;
1361 }