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  * Called by sched_setscheduler() to check whether the priority change
 269  * is overruled by a possible priority boosting.
 270  */
 271 int rt_mutex_check_prio(struct task_struct *task, int newprio)
 272 {
 273         if (!task_has_pi_waiters(task))
 274                 return 0;
 275
 276         return task_top_pi_waiter(task)->task->prio <= newprio;
 277 }
 278
 279 /*
 280  * Adjust the priority of a task, after its pi_waiters got modified.
 281  *
 282  * This can be both boosting and unboosting. task->pi_lock must be held.
 283  */
 284 static void __rt_mutex_adjust_prio(struct task_struct *task)
 285 {
 286         int prio = rt_mutex_getprio(task);
 287
 288         if (task->prio != prio || dl_prio(prio))
 289                 rt_mutex_setprio(task, prio);
 290 }
 291
 292 /*
 293  * Adjust task priority (undo boosting). Called from the exit path of
 294  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 295  *
 296  * (Note: We do this outside of the protection of lock->wait_lock to
 297  * allow the lock to be taken while or before we readjust the priority
 298  * of task. We do not use the spin_xx_mutex() variants here as we are
 299  * outside of the debug path.)
 300  */
 301 static void rt_mutex_adjust_prio(struct task_struct *task)
 302 {
 303         unsigned long flags;
 304
 305         raw_spin_lock_irqsave(&task->pi_lock, flags);
 306         __rt_mutex_adjust_prio(task);
 307         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 308 }
 309
 310 /*
 311  * Max number of times we'll walk the boosting chain:
 312  */
 313 int max_lock_depth = 1024;
 314
 315 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 316 {
 317         return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 318 }
 319
 320 /*
 321  * Adjust the priority chain. Also used for deadlock detection.
 322  * Decreases task's usage by one - may thus free the task.
 323  *
 324  * @task:       the task owning the mutex (owner) for which a chain walk is
 325  *              probably needed
 326  * @deadlock_detect: do we have to carry out deadlock detection?
 327  * @orig_lock:  the mutex (can be NULL if we are walking the chain to recheck
 328  *              things for a task that has just got its priority adjusted, and
 329  *              is waiting on a mutex)
 330  * @next_lock:  the mutex on which the owner of @orig_lock was blocked before
 331  *              we dropped its pi_lock. Is never dereferenced, only used for
 332  *              comparison to detect lock chain changes.
 333  * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 334  *              its priority to the mutex owner (can be NULL in the case
 335  *              depicted above or if the top waiter is gone away and we are
 336  *              actually deboosting the owner)
 337  * @top_task:   the current top waiter
 338  *
 339  * Returns 0 or -EDEADLK.
 340  */
 341 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 342                                       int deadlock_detect,
 343                                       struct rt_mutex *orig_lock,
 344                                       struct rt_mutex *next_lock,
 345                                       struct rt_mutex_waiter *orig_waiter,
 346                                       struct task_struct *top_task)
 347 {
 348         struct rt_mutex *lock;
 349         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 350         int detect_deadlock, ret = 0, depth = 0;
 351         unsigned long flags;
 352
 353         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 354                                                          deadlock_detect);
 355
 356         /*
 357          * The (de)boosting is a step by step approach with a lot of
 358          * pitfalls. We want this to be preemptible and we want hold a
 359          * maximum of two locks per step. So we have to check
 360          * carefully whether things change under us.
 361          */
 362  again:
 363         if (++depth > max_lock_depth) {
 364                 static int prev_max;
 365
 366                 /*
 367                  * Print this only once. If the admin changes the limit,
 368                  * print a new message when reaching the limit again.
 369                  */
 370                 if (prev_max != max_lock_depth) {
 371                         prev_max = max_lock_depth;
 372                         printk(KERN_WARNING "Maximum lock depth %d reached "
 373                                "task: %s (%d)\n", max_lock_depth,
 374                                top_task->comm, task_pid_nr(top_task));
 375                 }
 376                 put_task_struct(task);
 377
 378                 return -EDEADLK;
 379         }
 380  retry:
 381         /*
 382          * Task can not go away as we did a get_task() before !
 383          */
 384         raw_spin_lock_irqsave(&task->pi_lock, flags);
 385
 386         waiter = task->pi_blocked_on;
 387         /*
 388          * Check whether the end of the boosting chain has been
 389          * reached or the state of the chain has changed while we
 390          * dropped the locks.
 391          */
 392         if (!waiter)
 393                 goto out_unlock_pi;
 394
 395         /*
 396          * Check the orig_waiter state. After we dropped the locks,
 397          * the previous owner of the lock might have released the lock.
 398          */
 399         if (orig_waiter && !rt_mutex_owner(orig_lock))
 400                 goto out_unlock_pi;
 401
 402         /*
 403          * We dropped all locks after taking a refcount on @task, so
 404          * the task might have moved on in the lock chain or even left
 405          * the chain completely and blocks now on an unrelated lock or
 406          * on @orig_lock.
 407          *
 408          * We stored the lock on which @task was blocked in @next_lock,
 409          * so we can detect the chain change.
 410          */
 411         if (next_lock != waiter->lock)
 412                 goto out_unlock_pi;
 413
 414         /*
 415          * Drop out, when the task has no waiters. Note,
 416          * top_waiter can be NULL, when we are in the deboosting
 417          * mode!
 418          */
 419         if (top_waiter) {
 420                 if (!task_has_pi_waiters(task))
 421                         goto out_unlock_pi;
 422                 /*
 423                  * If deadlock detection is off, we stop here if we
 424                  * are not the top pi waiter of the task.
 425                  */
 426                 if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
 427                         goto out_unlock_pi;
 428         }
 429
 430         /*
 431          * When deadlock detection is off then we check, if further
 432          * priority adjustment is necessary.
 433          */
 434         if (!detect_deadlock && waiter->prio == task->prio)
 435                 goto out_unlock_pi;
 436
 437         lock = waiter->lock;
 438         if (!raw_spin_trylock(&lock->wait_lock)) {
 439                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 440                 cpu_relax();
 441                 goto retry;
 442         }
 443
 444         /*
 445          * Deadlock detection. If the lock is the same as the original
 446          * lock which caused us to walk the lock chain or if the
 447          * current lock is owned by the task which initiated the chain
 448          * walk, we detected a deadlock.
 449          */
 450         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 451                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 452                 raw_spin_unlock(&lock->wait_lock);
 453                 ret = -EDEADLK;
 454                 goto out_unlock_pi;
 455         }
 456
 457         top_waiter = rt_mutex_top_waiter(lock);
 458
 459         /* Requeue the waiter */
 460         rt_mutex_dequeue(lock, waiter);
 461         waiter->prio = task->prio;
 462         rt_mutex_enqueue(lock, waiter);
 463
 464         /* Release the task */
 465         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 466         if (!rt_mutex_owner(lock)) {
 467                 /*
 468                  * If the requeue above changed the top waiter, then we need
 469                  * to wake the new top waiter up to try to get the lock.
 470                  */
 471
 472                 if (top_waiter != rt_mutex_top_waiter(lock))
 473                         wake_up_process(rt_mutex_top_waiter(lock)->task);
 474                 raw_spin_unlock(&lock->wait_lock);
 475                 goto out_put_task;
 476         }
 477         put_task_struct(task);
 478
 479         /* Grab the next task */
 480         task = rt_mutex_owner(lock);
 481         get_task_struct(task);
 482         raw_spin_lock_irqsave(&task->pi_lock, flags);
 483
 484         if (waiter == rt_mutex_top_waiter(lock)) {
 485                 /* Boost the owner */
 486                 rt_mutex_dequeue_pi(task, top_waiter);
 487                 rt_mutex_enqueue_pi(task, waiter);
 488                 __rt_mutex_adjust_prio(task);
 489
 490         } else if (top_waiter == waiter) {
 491                 /* Deboost the owner */
 492                 rt_mutex_dequeue_pi(task, waiter);
 493                 waiter = rt_mutex_top_waiter(lock);
 494                 rt_mutex_enqueue_pi(task, waiter);
 495                 __rt_mutex_adjust_prio(task);
 496         }
 497
 498         /*
 499          * Check whether the task which owns the current lock is pi
 500          * blocked itself. If yes we store a pointer to the lock for
 501          * the lock chain change detection above. After we dropped
 502          * task->pi_lock next_lock cannot be dereferenced anymore.
 503          */
 504         next_lock = task_blocked_on_lock(task);
 505
 506         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 507
 508         top_waiter = rt_mutex_top_waiter(lock);
 509         raw_spin_unlock(&lock->wait_lock);
 510
 511         /*
 512          * We reached the end of the lock chain. Stop right here. No
 513          * point to go back just to figure that out.
 514          */
 515         if (!next_lock)
 516                 goto out_put_task;
 517
 518         if (!detect_deadlock && waiter != top_waiter)
 519                 goto out_put_task;
 520
 521         goto again;
 522
 523  out_unlock_pi:
 524         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 525  out_put_task:
 526         put_task_struct(task);
 527
 528         return ret;
 529 }
 530
 531 /*
 532  * Try to take an rt-mutex
 533  *
 534  * Must be called with lock->wait_lock held.
 535  *
 536  * @lock:   the lock to be acquired.
 537  * @task:   the task which wants to acquire the lock
 538  * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
 539  */
 540 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 541                 struct rt_mutex_waiter *waiter)
 542 {
 543         /*
 544          * We have to be careful here if the atomic speedups are
 545          * enabled, such that, when
 546          *  - no other waiter is on the lock
 547          *  - the lock has been released since we did the cmpxchg
 548          * the lock can be released or taken while we are doing the
 549          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 550          *
 551          * The atomic acquire/release aware variant of
 552          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 553          * the WAITERS bit, the atomic release / acquire can not
 554          * happen anymore and lock->wait_lock protects us from the
 555          * non-atomic case.
 556          *
 557          * Note, that this might set lock->owner =
 558          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 559          * any more. This is fixed up when we take the ownership.
 560          * This is the transitional state explained at the top of this file.
 561          */
 562         mark_rt_mutex_waiters(lock);
 563
 564         if (rt_mutex_owner(lock))
 565                 return 0;
 566
 567         /*
 568          * It will get the lock because of one of these conditions:
 569          * 1) there is no waiter
 570          * 2) higher priority than waiters
 571          * 3) it is top waiter
 572          */
 573         if (rt_mutex_has_waiters(lock)) {
 574                 if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
 575                         if (!waiter || waiter != rt_mutex_top_waiter(lock))
 576                                 return 0;
 577                 }
 578         }
 579
 580         if (waiter || rt_mutex_has_waiters(lock)) {
 581                 unsigned long flags;
 582                 struct rt_mutex_waiter *top;
 583
 584                 raw_spin_lock_irqsave(&task->pi_lock, flags);
 585
 586                 /* remove the queued waiter. */
 587                 if (waiter) {
 588                         rt_mutex_dequeue(lock, waiter);
 589                         task->pi_blocked_on = NULL;
 590                 }
 591
 592                 /*
 593                  * We have to enqueue the top waiter(if it exists) into
 594                  * task->pi_waiters list.
 595                  */
 596                 if (rt_mutex_has_waiters(lock)) {
 597                         top = rt_mutex_top_waiter(lock);
 598                         rt_mutex_enqueue_pi(task, top);
 599                 }
 600                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 601         }
 602
 603         /* We got the lock. */
 604         debug_rt_mutex_lock(lock);
 605
 606         rt_mutex_set_owner(lock, task);
 607
 608         rt_mutex_deadlock_account_lock(lock, task);
 609
 610         return 1;
 611 }
 612
 613 /*
 614  * Task blocks on lock.
 615  *
 616  * Prepare waiter and propagate pi chain
 617  *
 618  * This must be called with lock->wait_lock held.
 619  */
 620 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 621                                    struct rt_mutex_waiter *waiter,
 622                                    struct task_struct *task,
 623                                    int detect_deadlock)
 624 {
 625         struct task_struct *owner = rt_mutex_owner(lock);
 626         struct rt_mutex_waiter *top_waiter = waiter;
 627         struct rt_mutex *next_lock;
 628         int chain_walk = 0, res;
 629         unsigned long flags;
 630
 631         /*
 632          * Early deadlock detection. We really don't want the task to
 633          * enqueue on itself just to untangle the mess later. It's not
 634          * only an optimization. We drop the locks, so another waiter
 635          * can come in before the chain walk detects the deadlock. So
 636          * the other will detect the deadlock and return -EDEADLOCK,
 637          * which is wrong, as the other waiter is not in a deadlock
 638          * situation.
 639          */
 640         if (owner == task)
 641                 return -EDEADLK;
 642
 643         raw_spin_lock_irqsave(&task->pi_lock, flags);
 644         __rt_mutex_adjust_prio(task);
 645         waiter->task = task;
 646         waiter->lock = lock;
 647         waiter->prio = task->prio;
 648
 649         /* Get the top priority waiter on the lock */
 650         if (rt_mutex_has_waiters(lock))
 651                 top_waiter = rt_mutex_top_waiter(lock);
 652         rt_mutex_enqueue(lock, waiter);
 653
 654         task->pi_blocked_on = waiter;
 655
 656         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 657
 658         if (!owner)
 659                 return 0;
 660
 661         raw_spin_lock_irqsave(&owner->pi_lock, flags);
 662         if (waiter == rt_mutex_top_waiter(lock)) {
 663                 rt_mutex_dequeue_pi(owner, top_waiter);
 664                 rt_mutex_enqueue_pi(owner, waiter);
 665
 666                 __rt_mutex_adjust_prio(owner);
 667                 if (owner->pi_blocked_on)
 668                         chain_walk = 1;
 669         } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
 670                 chain_walk = 1;
 671         }
 672
 673         /* Store the lock on which owner is blocked or NULL */
 674         next_lock = task_blocked_on_lock(owner);
 675
 676         raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 677         /*
 678          * Even if full deadlock detection is on, if the owner is not
 679          * blocked itself, we can avoid finding this out in the chain
 680          * walk.
 681          */
 682         if (!chain_walk || !next_lock)
 683                 return 0;
 684
 685         /*
 686          * The owner can't disappear while holding a lock,
 687          * so the owner struct is protected by wait_lock.
 688          * Gets dropped in rt_mutex_adjust_prio_chain()!
 689          */
 690         get_task_struct(owner);
 691
 692         raw_spin_unlock(&lock->wait_lock);
 693
 694         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
 695                                          next_lock, waiter, task);
 696
 697         raw_spin_lock(&lock->wait_lock);
 698
 699         return res;
 700 }
 701
 702 /*
 703  * Wake up the next waiter on the lock.
 704  *
 705  * Remove the top waiter from the current tasks pi waiter list and
 706  * wake it up.
 707  *
 708  * Called with lock->wait_lock held.
 709  */
 710 static void wakeup_next_waiter(struct rt_mutex *lock)
 711 {
 712         struct rt_mutex_waiter *waiter;
 713         unsigned long flags;
 714
 715         raw_spin_lock_irqsave(&current->pi_lock, flags);
 716
 717         waiter = rt_mutex_top_waiter(lock);
 718
 719         /*
 720          * Remove it from current->pi_waiters. We do not adjust a
 721          * possible priority boost right now. We execute wakeup in the
 722          * boosted mode and go back to normal after releasing
 723          * lock->wait_lock.
 724          */
 725         rt_mutex_dequeue_pi(current, waiter);
 726
 727         /*
 728          * As we are waking up the top waiter, and the waiter stays
 729          * queued on the lock until it gets the lock, this lock
 730          * obviously has waiters. Just set the bit here and this has
 731          * the added benefit of forcing all new tasks into the
 732          * slow path making sure no task of lower priority than
 733          * the top waiter can steal this lock.
 734          */
 735         lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
 736
 737         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 738
 739         /*
 740          * It's safe to dereference waiter as it cannot go away as
 741          * long as we hold lock->wait_lock. The waiter task needs to
 742          * acquire it in order to dequeue the waiter.
 743          */
 744         wake_up_process(waiter->task);
 745 }
 746
 747 /*
 748  * Remove a waiter from a lock and give up
 749  *
 750  * Must be called with lock->wait_lock held and
 751  * have just failed to try_to_take_rt_mutex().
 752  */
 753 static void remove_waiter(struct rt_mutex *lock,
 754                           struct rt_mutex_waiter *waiter)
 755 {
 756         int first = (waiter == rt_mutex_top_waiter(lock));
 757         struct task_struct *owner = rt_mutex_owner(lock);
 758         struct rt_mutex *next_lock = NULL;
 759         unsigned long flags;
 760
 761         raw_spin_lock_irqsave(&current->pi_lock, flags);
 762         rt_mutex_dequeue(lock, waiter);
 763         current->pi_blocked_on = NULL;
 764         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 765
 766         if (!owner)
 767                 return;
 768
 769         if (first) {
 770
 771                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 772
 773                 rt_mutex_dequeue_pi(owner, waiter);
 774
 775                 if (rt_mutex_has_waiters(lock)) {
 776                         struct rt_mutex_waiter *next;
 777
 778                         next = rt_mutex_top_waiter(lock);
 779                         rt_mutex_enqueue_pi(owner, next);
 780                 }
 781                 __rt_mutex_adjust_prio(owner);
 782
 783                 /* Store the lock on which owner is blocked or NULL */
 784                 next_lock = task_blocked_on_lock(owner);
 785
 786                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 787         }
 788
 789         if (!next_lock)
 790                 return;
 791
 792         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 793         get_task_struct(owner);
 794
 795         raw_spin_unlock(&lock->wait_lock);
 796
 797         rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
 798
 799         raw_spin_lock(&lock->wait_lock);
 800 }
 801
 802 /*
 803  * Recheck the pi chain, in case we got a priority setting
 804  *
 805  * Called from sched_setscheduler
 806  */
 807 void rt_mutex_adjust_pi(struct task_struct *task)
 808 {
 809         struct rt_mutex_waiter *waiter;
 810         struct rt_mutex *next_lock;
 811         unsigned long flags;
 812
 813         raw_spin_lock_irqsave(&task->pi_lock, flags);
 814
 815         waiter = task->pi_blocked_on;
 816         if (!waiter || (waiter->prio == task->prio &&
 817                         !dl_prio(task->prio))) {
 818                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 819                 return;
 820         }
 821         next_lock = waiter->lock;
 822         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 823
 824         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 825         get_task_struct(task);
 826
 827         rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
 828 }
 829
 830 /**
 831  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 832  * @lock:                the rt_mutex to take
 833  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 834  *                       or TASK_UNINTERRUPTIBLE)
 835  * @timeout:             the pre-initialized and started timer, or NULL for none
 836  * @waiter:              the pre-initialized rt_mutex_waiter
 837  *
 838  * lock->wait_lock must be held by the caller.
 839  */
 840 static int __sched
 841 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
 842                     struct hrtimer_sleeper *timeout,
 843                     struct rt_mutex_waiter *waiter)
 844 {
 845         int ret = 0;
 846
 847         for (;;) {
 848                 /* Try to acquire the lock: */
 849                 if (try_to_take_rt_mutex(lock, current, waiter))
 850                         break;
 851
 852                 /*
 853                  * TASK_INTERRUPTIBLE checks for signals and
 854                  * timeout. Ignored otherwise.
 855                  */
 856                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 857                         /* Signal pending? */
 858                         if (signal_pending(current))
 859                                 ret = -EINTR;
 860                         if (timeout && !timeout->task)
 861                                 ret = -ETIMEDOUT;
 862                         if (ret)
 863                                 break;
 864                 }
 865
 866                 raw_spin_unlock(&lock->wait_lock);
 867
 868                 debug_rt_mutex_print_deadlock(waiter);
 869
 870                 schedule_rt_mutex(lock);
 871
 872                 raw_spin_lock(&lock->wait_lock);
 873                 set_current_state(state);
 874         }
 875
 876         return ret;
 877 }
 878
 879 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
 880                                      struct rt_mutex_waiter *w)
 881 {
 882         /*
 883          * If the result is not -EDEADLOCK or the caller requested
 884          * deadlock detection, nothing to do here.
 885          */
 886         if (res != -EDEADLOCK || detect_deadlock)
 887                 return;
 888
 889         /*
 890          * Yell lowdly and stop the task right here.
 891          */
 892         rt_mutex_print_deadlock(w);
 893         while (1) {
 894                 set_current_state(TASK_INTERRUPTIBLE);
 895                 schedule();
 896         }
 897 }
 898
 899 /*
 900  * Slow path lock function:
 901  */
 902 static int __sched
 903 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 904                   struct hrtimer_sleeper *timeout,
 905                   int detect_deadlock)
 906 {
 907         struct rt_mutex_waiter waiter;
 908         int ret = 0;
 909
 910         debug_rt_mutex_init_waiter(&waiter);
 911         RB_CLEAR_NODE(&waiter.pi_tree_entry);
 912         RB_CLEAR_NODE(&waiter.tree_entry);
 913
 914         raw_spin_lock(&lock->wait_lock);
 915
 916         /* Try to acquire the lock again: */
 917         if (try_to_take_rt_mutex(lock, current, NULL)) {
 918                 raw_spin_unlock(&lock->wait_lock);
 919                 return 0;
 920         }
 921
 922         set_current_state(state);
 923
 924         /* Setup the timer, when timeout != NULL */
 925         if (unlikely(timeout)) {
 926                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 927                 if (!hrtimer_active(&timeout->timer))
 928                         timeout->task = NULL;
 929         }
 930
 931         ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
 932
 933         if (likely(!ret))
 934                 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 935
 936         set_current_state(TASK_RUNNING);
 937
 938         if (unlikely(ret)) {
 939                 remove_waiter(lock, &waiter);
 940                 rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
 941         }
 942
 943         /*
 944          * try_to_take_rt_mutex() sets the waiter bit
 945          * unconditionally. We might have to fix that up.
 946          */
 947         fixup_rt_mutex_waiters(lock);
 948
 949         raw_spin_unlock(&lock->wait_lock);
 950
 951         /* Remove pending timer: */
 952         if (unlikely(timeout))
 953                 hrtimer_cancel(&timeout->timer);
 954
 955         debug_rt_mutex_free_waiter(&waiter);
 956
 957         return ret;
 958 }
 959
 960 /*
 961  * Slow path try-lock function:
 962  */
 963 static inline int
 964 rt_mutex_slowtrylock(struct rt_mutex *lock)
 965 {
 966         int ret = 0;
 967
 968         raw_spin_lock(&lock->wait_lock);
 969
 970         if (likely(rt_mutex_owner(lock) != current)) {
 971
 972                 ret = try_to_take_rt_mutex(lock, current, NULL);
 973                 /*
 974                  * try_to_take_rt_mutex() sets the lock waiters
 975                  * bit unconditionally. Clean this up.
 976                  */
 977                 fixup_rt_mutex_waiters(lock);
 978         }
 979
 980         raw_spin_unlock(&lock->wait_lock);
 981
 982         return ret;
 983 }
 984
 985 /*
 986  * Slow path to release a rt-mutex:
 987  */
 988 static void __sched
 989 rt_mutex_slowunlock(struct rt_mutex *lock)
 990 {
 991         raw_spin_lock(&lock->wait_lock);
 992
 993         debug_rt_mutex_unlock(lock);
 994
 995         rt_mutex_deadlock_account_unlock(current);
 996
 997         /*
 998          * We must be careful here if the fast path is enabled. If we
 999          * have no waiters queued we cannot set owner to NULL here
1000          * because of:
1001          *
1002          * foo->lock->owner = NULL;
1003          *                      rtmutex_lock(foo->lock);   <- fast path
1004          *                      free = atomic_dec_and_test(foo->refcnt);
1005          *                      rtmutex_unlock(foo->lock); <- fast path
1006          *                      if (free)
1007          *                              kfree(foo);
1008          * raw_spin_unlock(foo->lock->wait_lock);
1009          *
1010          * So for the fastpath enabled kernel:
1011          *
1012          * Nothing can set the waiters bit as long as we hold
1013          * lock->wait_lock. So we do the following sequence:
1014          *
1015          *      owner = rt_mutex_owner(lock);
1016          *      clear_rt_mutex_waiters(lock);
1017          *      raw_spin_unlock(&lock->wait_lock);
1018          *      if (cmpxchg(&lock->owner, owner, 0) == owner)
1019          *              return;
1020          *      goto retry;
1021          *
1022          * The fastpath disabled variant is simple as all access to
1023          * lock->owner is serialized by lock->wait_lock:
1024          *
1025          *      lock->owner = NULL;
1026          *      raw_spin_unlock(&lock->wait_lock);
1027          */
1028         while (!rt_mutex_has_waiters(lock)) {
1029                 /* Drops lock->wait_lock ! */
1030                 if (unlock_rt_mutex_safe(lock) == true)
1031                         return;
1032                 /* Relock the rtmutex and try again */
1033                 raw_spin_lock(&lock->wait_lock);
1034         }
1035
1036         /*
1037          * The wakeup next waiter path does not suffer from the above
1038          * race. See the comments there.
1039          */
1040         wakeup_next_waiter(lock);
1041
1042         raw_spin_unlock(&lock->wait_lock);
1043
1044         /* Undo pi boosting if necessary: */
1045         rt_mutex_adjust_prio(current);
1046 }
1047
1048 /*
1049  * debug aware fast / slowpath lock,trylock,unlock
1050  *
1051  * The atomic acquire/release ops are compiled away, when either the
1052  * architecture does not support cmpxchg or when debugging is enabled.
1053  */
1054 static inline int
1055 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1056                   int detect_deadlock,
1057                   int (*slowfn)(struct rt_mutex *lock, int state,
1058                                 struct hrtimer_sleeper *timeout,
1059                                 int detect_deadlock))
1060 {
1061         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1062                 rt_mutex_deadlock_account_lock(lock, current);
1063                 return 0;
1064         } else
1065                 return slowfn(lock, state, NULL, detect_deadlock);
1066 }
1067
1068 static inline int
1069 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1070                         struct hrtimer_sleeper *timeout, int detect_deadlock,
1071                         int (*slowfn)(struct rt_mutex *lock, int state,
1072                                       struct hrtimer_sleeper *timeout,
1073                                       int detect_deadlock))
1074 {
1075         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1076                 rt_mutex_deadlock_account_lock(lock, current);
1077                 return 0;
1078         } else
1079                 return slowfn(lock, state, timeout, detect_deadlock);
1080 }
1081
1082 static inline int
1083 rt_mutex_fasttrylock(struct rt_mutex *lock,
1084                      int (*slowfn)(struct rt_mutex *lock))
1085 {
1086         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1087                 rt_mutex_deadlock_account_lock(lock, current);
1088                 return 1;
1089         }
1090         return slowfn(lock);
1091 }
1092
1093 static inline void
1094 rt_mutex_fastunlock(struct rt_mutex *lock,
1095                     void (*slowfn)(struct rt_mutex *lock))
1096 {
1097         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
1098                 rt_mutex_deadlock_account_unlock(current);
1099         else
1100                 slowfn(lock);
1101 }
1102
1103 /**
1104  * rt_mutex_lock - lock a rt_mutex
1105  *
1106  * @lock: the rt_mutex to be locked
1107  */
1108 void __sched rt_mutex_lock(struct rt_mutex *lock)
1109 {
1110         might_sleep();
1111
1112         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
1113 }
1114 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1115
1116 /**
1117  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1118  *
1119  * @lock:               the rt_mutex to be locked
1120  * @detect_deadlock:    deadlock detection on/off
1121  *
1122  * Returns:
1123  *  0           on success
1124  * -EINTR       when interrupted by a signal
1125  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1126  */
1127 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
1128                                                  int detect_deadlock)
1129 {
1130         might_sleep();
1131
1132         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
1133                                  detect_deadlock, rt_mutex_slowlock);
1134 }
1135 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1136
1137 /**
1138  * rt_mutex_timed_lock - lock a rt_mutex interruptible
1139  *                      the timeout structure is provided
1140  *                      by the caller
1141  *
1142  * @lock:               the rt_mutex to be locked
1143  * @timeout:            timeout structure or NULL (no timeout)
1144  * @detect_deadlock:    deadlock detection on/off
1145  *
1146  * Returns:
1147  *  0           on success
1148  * -EINTR       when interrupted by a signal
1149  * -ETIMEDOUT   when the timeout expired
1150  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1151  */
1152 int
1153 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
1154                     int detect_deadlock)
1155 {
1156         might_sleep();
1157
1158         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1159                                        detect_deadlock, rt_mutex_slowlock);
1160 }
1161 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1162
1163 /**
1164  * rt_mutex_trylock - try to lock a rt_mutex
1165  *
1166  * @lock:       the rt_mutex to be locked
1167  *
1168  * Returns 1 on success and 0 on contention
1169  */
1170 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1171 {
1172         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1173 }
1174 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1175
1176 /**
1177  * rt_mutex_unlock - unlock a rt_mutex
1178  *
1179  * @lock: the rt_mutex to be unlocked
1180  */
1181 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1182 {
1183         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1184 }
1185 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1186
1187 /**
1188  * rt_mutex_destroy - mark a mutex unusable
1189  * @lock: the mutex to be destroyed
1190  *
1191  * This function marks the mutex uninitialized, and any subsequent
1192  * use of the mutex is forbidden. The mutex must not be locked when
1193  * this function is called.
1194  */
1195 void rt_mutex_destroy(struct rt_mutex *lock)
1196 {
1197         WARN_ON(rt_mutex_is_locked(lock));
1198 #ifdef CONFIG_DEBUG_RT_MUTEXES
1199         lock->magic = NULL;
1200 #endif
1201 }
1202
1203 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1204
1205 /**
1206  * __rt_mutex_init - initialize the rt lock
1207  *
1208  * @lock: the rt lock to be initialized
1209  *
1210  * Initialize the rt lock to unlocked state.
1211  *
1212  * Initializing of a locked rt lock is not allowed
1213  */
1214 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1215 {
1216         lock->owner = NULL;
1217         raw_spin_lock_init(&lock->wait_lock);
1218         lock->waiters = RB_ROOT;
1219         lock->waiters_leftmost = NULL;
1220
1221         debug_rt_mutex_init(lock, name);
1222 }
1223 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1224
1225 /**
1226  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1227  *                              proxy owner
1228  *
1229  * @lock:       the rt_mutex to be locked
1230  * @proxy_owner:the task to set as owner
1231  *
1232  * No locking. Caller has to do serializing itself
1233  * Special API call for PI-futex support
1234  */
1235 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1236                                 struct task_struct *proxy_owner)
1237 {
1238         __rt_mutex_init(lock, NULL);
1239         debug_rt_mutex_proxy_lock(lock, proxy_owner);
1240         rt_mutex_set_owner(lock, proxy_owner);
1241         rt_mutex_deadlock_account_lock(lock, proxy_owner);
1242 }
1243
1244 /**
1245  * rt_mutex_proxy_unlock - release a lock on behalf of owner
1246  *
1247  * @lock:       the rt_mutex to be locked
1248  *
1249  * No locking. Caller has to do serializing itself
1250  * Special API call for PI-futex support
1251  */
1252 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1253                            struct task_struct *proxy_owner)
1254 {
1255         debug_rt_mutex_proxy_unlock(lock);
1256         rt_mutex_set_owner(lock, NULL);
1257         rt_mutex_deadlock_account_unlock(proxy_owner);
1258 }
1259
1260 /**
1261  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1262  * @lock:               the rt_mutex to take
1263  * @waiter:             the pre-initialized rt_mutex_waiter
1264  * @task:               the task to prepare
1265  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1266  *
1267  * Returns:
1268  *  0 - task blocked on lock
1269  *  1 - acquired the lock for task, caller should wake it up
1270  * <0 - error
1271  *
1272  * Special API call for FUTEX_REQUEUE_PI support.
1273  */
1274 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1275                               struct rt_mutex_waiter *waiter,
1276                               struct task_struct *task, int detect_deadlock)
1277 {
1278         int ret;
1279
1280         raw_spin_lock(&lock->wait_lock);
1281
1282         if (try_to_take_rt_mutex(lock, task, NULL)) {
1283                 raw_spin_unlock(&lock->wait_lock);
1284                 return 1;
1285         }
1286
1287         /* We enforce deadlock detection for futexes */
1288         ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
1289
1290         if (ret && !rt_mutex_owner(lock)) {
1291                 /*
1292                  * Reset the return value. We might have
1293                  * returned with -EDEADLK and the owner
1294                  * released the lock while we were walking the
1295                  * pi chain.  Let the waiter sort it out.
1296                  */
1297                 ret = 0;
1298         }
1299
1300         if (unlikely(ret))
1301                 remove_waiter(lock, waiter);
1302
1303         raw_spin_unlock(&lock->wait_lock);
1304
1305         debug_rt_mutex_print_deadlock(waiter);
1306
1307         return ret;
1308 }
1309
1310 /**
1311  * rt_mutex_next_owner - return the next owner of the lock
1312  *
1313  * @lock: the rt lock query
1314  *
1315  * Returns the next owner of the lock or NULL
1316  *
1317  * Caller has to serialize against other accessors to the lock
1318  * itself.
1319  *
1320  * Special API call for PI-futex support
1321  */
1322 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1323 {
1324         if (!rt_mutex_has_waiters(lock))
1325                 return NULL;
1326
1327         return rt_mutex_top_waiter(lock)->task;
1328 }
1329
1330 /**
1331  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1332  * @lock:               the rt_mutex we were woken on
1333  * @to:                 the timeout, null if none. hrtimer should already have
1334  *                      been started.
1335  * @waiter:             the pre-initialized rt_mutex_waiter
1336  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1337  *
1338  * Complete the lock acquisition started our behalf by another thread.
1339  *
1340  * Returns:
1341  *  0 - success
1342  * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1343  *
1344  * Special API call for PI-futex requeue support
1345  */
1346 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1347                                struct hrtimer_sleeper *to,
1348                                struct rt_mutex_waiter *waiter,
1349                                int detect_deadlock)
1350 {
1351         int ret;
1352
1353         raw_spin_lock(&lock->wait_lock);
1354
1355         set_current_state(TASK_INTERRUPTIBLE);
1356
1357         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1358
1359         set_current_state(TASK_RUNNING);
1360
1361         if (unlikely(ret))
1362                 remove_waiter(lock, waiter);
1363
1364         /*
1365          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1366          * have to fix that up.
1367          */
1368         fixup_rt_mutex_waiters(lock);
1369
1370         raw_spin_unlock(&lock->wait_lock);
1371
1372         return ret;
1373 }