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 if the
 539  *          callsite called task_blocked_on_lock(), otherwise NULL
 540  */
 541 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 542                                 struct rt_mutex_waiter *waiter)
 543 {
 544         unsigned long flags;
 545
 546         /*
 547          * Before testing whether we can acquire @lock, we set the
 548          * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
 549          * other tasks which try to modify @lock into the slow path
 550          * and they serialize on @lock->wait_lock.
 551          *
 552          * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
 553          * as explained at the top of this file if and only if:
 554          *
 555          * - There is a lock owner. The caller must fixup the
 556          *   transient state if it does a trylock or leaves the lock
 557          *   function due to a signal or timeout.
 558          *
 559          * - @task acquires the lock and there are no other
 560          *   waiters. This is undone in rt_mutex_set_owner(@task) at
 561          *   the end of this function.
 562          */
 563         mark_rt_mutex_waiters(lock);
 564
 565         /*
 566          * If @lock has an owner, give up.
 567          */
 568         if (rt_mutex_owner(lock))
 569                 return 0;
 570
 571         /*
 572          * If @waiter != NULL, @task has already enqueued the waiter
 573          * into @lock waiter list. If @waiter == NULL then this is a
 574          * trylock attempt.
 575          */
 576         if (waiter) {
 577                 /*
 578                  * If waiter is not the highest priority waiter of
 579                  * @lock, give up.
 580                  */
 581                 if (waiter != rt_mutex_top_waiter(lock))
 582                         return 0;
 583
 584                 /*
 585                  * We can acquire the lock. Remove the waiter from the
 586                  * lock waiters list.
 587                  */
 588                 rt_mutex_dequeue(lock, waiter);
 589
 590         } else {
 591                 /*
 592                  * If the lock has waiters already we check whether @task is
 593                  * eligible to take over the lock.
 594                  *
 595                  * If there are no other waiters, @task can acquire
 596                  * the lock.  @task->pi_blocked_on is NULL, so it does
 597                  * not need to be dequeued.
 598                  */
 599                 if (rt_mutex_has_waiters(lock)) {
 600                         /*
 601                          * If @task->prio is greater than or equal to
 602                          * the top waiter priority (kernel view),
 603                          * @task lost.
 604                          */
 605                         if (task->prio >= rt_mutex_top_waiter(lock)->prio)
 606                                 return 0;
 607
 608                         /*
 609                          * The current top waiter stays enqueued. We
 610                          * don't have to change anything in the lock
 611                          * waiters order.
 612                          */
 613                 } else {
 614                         /*
 615                          * No waiters. Take the lock without the
 616                          * pi_lock dance.@task->pi_blocked_on is NULL
 617                          * and we have no waiters to enqueue in @task
 618                          * pi waiters list.
 619                          */
 620                         goto takeit;
 621                 }
 622         }
 623
 624         /*
 625          * Clear @task->pi_blocked_on. Requires protection by
 626          * @task->pi_lock. Redundant operation for the @waiter == NULL
 627          * case, but conditionals are more expensive than a redundant
 628          * store.
 629          */
 630         raw_spin_lock_irqsave(&task->pi_lock, flags);
 631         task->pi_blocked_on = NULL;
 632         /*
 633          * Finish the lock acquisition. @task is the new owner. If
 634          * other waiters exist we have to insert the highest priority
 635          * waiter into @task->pi_waiters list.
 636          */
 637         if (rt_mutex_has_waiters(lock))
 638                 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
 639         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 640
 641 takeit:
 642         /* We got the lock. */
 643         debug_rt_mutex_lock(lock);
 644
 645         /*
 646          * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
 647          * are still waiters or clears it.
 648          */
 649         rt_mutex_set_owner(lock, task);
 650
 651         rt_mutex_deadlock_account_lock(lock, task);
 652
 653         return 1;
 654 }
 655
 656 /*
 657  * Task blocks on lock.
 658  *
 659  * Prepare waiter and propagate pi chain
 660  *
 661  * This must be called with lock->wait_lock held.
 662  */
 663 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 664                                    struct rt_mutex_waiter *waiter,
 665                                    struct task_struct *task,
 666                                    int detect_deadlock)
 667 {
 668         struct task_struct *owner = rt_mutex_owner(lock);
 669         struct rt_mutex_waiter *top_waiter = waiter;
 670         struct rt_mutex *next_lock;
 671         int chain_walk = 0, res;
 672         unsigned long flags;
 673
 674         /*
 675          * Early deadlock detection. We really don't want the task to
 676          * enqueue on itself just to untangle the mess later. It's not
 677          * only an optimization. We drop the locks, so another waiter
 678          * can come in before the chain walk detects the deadlock. So
 679          * the other will detect the deadlock and return -EDEADLOCK,
 680          * which is wrong, as the other waiter is not in a deadlock
 681          * situation.
 682          */
 683         if (owner == task)
 684                 return -EDEADLK;
 685
 686         raw_spin_lock_irqsave(&task->pi_lock, flags);
 687         __rt_mutex_adjust_prio(task);
 688         waiter->task = task;
 689         waiter->lock = lock;
 690         waiter->prio = task->prio;
 691
 692         /* Get the top priority waiter on the lock */
 693         if (rt_mutex_has_waiters(lock))
 694                 top_waiter = rt_mutex_top_waiter(lock);
 695         rt_mutex_enqueue(lock, waiter);
 696
 697         task->pi_blocked_on = waiter;
 698
 699         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 700
 701         if (!owner)
 702                 return 0;
 703
 704         raw_spin_lock_irqsave(&owner->pi_lock, flags);
 705         if (waiter == rt_mutex_top_waiter(lock)) {
 706                 rt_mutex_dequeue_pi(owner, top_waiter);
 707                 rt_mutex_enqueue_pi(owner, waiter);
 708
 709                 __rt_mutex_adjust_prio(owner);
 710                 if (owner->pi_blocked_on)
 711                         chain_walk = 1;
 712         } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
 713                 chain_walk = 1;
 714         }
 715
 716         /* Store the lock on which owner is blocked or NULL */
 717         next_lock = task_blocked_on_lock(owner);
 718
 719         raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 720         /*
 721          * Even if full deadlock detection is on, if the owner is not
 722          * blocked itself, we can avoid finding this out in the chain
 723          * walk.
 724          */
 725         if (!chain_walk || !next_lock)
 726                 return 0;
 727
 728         /*
 729          * The owner can't disappear while holding a lock,
 730          * so the owner struct is protected by wait_lock.
 731          * Gets dropped in rt_mutex_adjust_prio_chain()!
 732          */
 733         get_task_struct(owner);
 734
 735         raw_spin_unlock(&lock->wait_lock);
 736
 737         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
 738                                          next_lock, waiter, task);
 739
 740         raw_spin_lock(&lock->wait_lock);
 741
 742         return res;
 743 }
 744
 745 /*
 746  * Wake up the next waiter on the lock.
 747  *
 748  * Remove the top waiter from the current tasks pi waiter list and
 749  * wake it up.
 750  *
 751  * Called with lock->wait_lock held.
 752  */
 753 static void wakeup_next_waiter(struct rt_mutex *lock)
 754 {
 755         struct rt_mutex_waiter *waiter;
 756         unsigned long flags;
 757
 758         raw_spin_lock_irqsave(&current->pi_lock, flags);
 759
 760         waiter = rt_mutex_top_waiter(lock);
 761
 762         /*
 763          * Remove it from current->pi_waiters. We do not adjust a
 764          * possible priority boost right now. We execute wakeup in the
 765          * boosted mode and go back to normal after releasing
 766          * lock->wait_lock.
 767          */
 768         rt_mutex_dequeue_pi(current, waiter);
 769
 770         /*
 771          * As we are waking up the top waiter, and the waiter stays
 772          * queued on the lock until it gets the lock, this lock
 773          * obviously has waiters. Just set the bit here and this has
 774          * the added benefit of forcing all new tasks into the
 775          * slow path making sure no task of lower priority than
 776          * the top waiter can steal this lock.
 777          */
 778         lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
 779
 780         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 781
 782         /*
 783          * It's safe to dereference waiter as it cannot go away as
 784          * long as we hold lock->wait_lock. The waiter task needs to
 785          * acquire it in order to dequeue the waiter.
 786          */
 787         wake_up_process(waiter->task);
 788 }
 789
 790 /*
 791  * Remove a waiter from a lock and give up
 792  *
 793  * Must be called with lock->wait_lock held and
 794  * have just failed to try_to_take_rt_mutex().
 795  */
 796 static void remove_waiter(struct rt_mutex *lock,
 797                           struct rt_mutex_waiter *waiter)
 798 {
 799         int first = (waiter == rt_mutex_top_waiter(lock));
 800         struct task_struct *owner = rt_mutex_owner(lock);
 801         struct rt_mutex *next_lock = NULL;
 802         unsigned long flags;
 803
 804         raw_spin_lock_irqsave(&current->pi_lock, flags);
 805         rt_mutex_dequeue(lock, waiter);
 806         current->pi_blocked_on = NULL;
 807         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 808
 809         if (!owner)
 810                 return;
 811
 812         if (first) {
 813
 814                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 815
 816                 rt_mutex_dequeue_pi(owner, waiter);
 817
 818                 if (rt_mutex_has_waiters(lock)) {
 819                         struct rt_mutex_waiter *next;
 820
 821                         next = rt_mutex_top_waiter(lock);
 822                         rt_mutex_enqueue_pi(owner, next);
 823                 }
 824                 __rt_mutex_adjust_prio(owner);
 825
 826                 /* Store the lock on which owner is blocked or NULL */
 827                 next_lock = task_blocked_on_lock(owner);
 828
 829                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 830         }
 831
 832         if (!next_lock)
 833                 return;
 834
 835         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 836         get_task_struct(owner);
 837
 838         raw_spin_unlock(&lock->wait_lock);
 839
 840         rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
 841
 842         raw_spin_lock(&lock->wait_lock);
 843 }
 844
 845 /*
 846  * Recheck the pi chain, in case we got a priority setting
 847  *
 848  * Called from sched_setscheduler
 849  */
 850 void rt_mutex_adjust_pi(struct task_struct *task)
 851 {
 852         struct rt_mutex_waiter *waiter;
 853         struct rt_mutex *next_lock;
 854         unsigned long flags;
 855
 856         raw_spin_lock_irqsave(&task->pi_lock, flags);
 857
 858         waiter = task->pi_blocked_on;
 859         if (!waiter || (waiter->prio == task->prio &&
 860                         !dl_prio(task->prio))) {
 861                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 862                 return;
 863         }
 864         next_lock = waiter->lock;
 865         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 866
 867         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 868         get_task_struct(task);
 869
 870         rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
 871 }
 872
 873 /**
 874  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 875  * @lock:                the rt_mutex to take
 876  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 877  *                       or TASK_UNINTERRUPTIBLE)
 878  * @timeout:             the pre-initialized and started timer, or NULL for none
 879  * @waiter:              the pre-initialized rt_mutex_waiter
 880  *
 881  * lock->wait_lock must be held by the caller.
 882  */
 883 static int __sched
 884 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
 885                     struct hrtimer_sleeper *timeout,
 886                     struct rt_mutex_waiter *waiter)
 887 {
 888         int ret = 0;
 889
 890         for (;;) {
 891                 /* Try to acquire the lock: */
 892                 if (try_to_take_rt_mutex(lock, current, waiter))
 893                         break;
 894
 895                 /*
 896                  * TASK_INTERRUPTIBLE checks for signals and
 897                  * timeout. Ignored otherwise.
 898                  */
 899                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 900                         /* Signal pending? */
 901                         if (signal_pending(current))
 902                                 ret = -EINTR;
 903                         if (timeout && !timeout->task)
 904                                 ret = -ETIMEDOUT;
 905                         if (ret)
 906                                 break;
 907                 }
 908
 909                 raw_spin_unlock(&lock->wait_lock);
 910
 911                 debug_rt_mutex_print_deadlock(waiter);
 912
 913                 schedule_rt_mutex(lock);
 914
 915                 raw_spin_lock(&lock->wait_lock);
 916                 set_current_state(state);
 917         }
 918
 919         return ret;
 920 }
 921
 922 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
 923                                      struct rt_mutex_waiter *w)
 924 {
 925         /*
 926          * If the result is not -EDEADLOCK or the caller requested
 927          * deadlock detection, nothing to do here.
 928          */
 929         if (res != -EDEADLOCK || detect_deadlock)
 930                 return;
 931
 932         /*
 933          * Yell lowdly and stop the task right here.
 934          */
 935         rt_mutex_print_deadlock(w);
 936         while (1) {
 937                 set_current_state(TASK_INTERRUPTIBLE);
 938                 schedule();
 939         }
 940 }
 941
 942 /*
 943  * Slow path lock function:
 944  */
 945 static int __sched
 946 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 947                   struct hrtimer_sleeper *timeout,
 948                   int detect_deadlock)
 949 {
 950         struct rt_mutex_waiter waiter;
 951         int ret = 0;
 952
 953         debug_rt_mutex_init_waiter(&waiter);
 954         RB_CLEAR_NODE(&waiter.pi_tree_entry);
 955         RB_CLEAR_NODE(&waiter.tree_entry);
 956
 957         raw_spin_lock(&lock->wait_lock);
 958
 959         /* Try to acquire the lock again: */
 960         if (try_to_take_rt_mutex(lock, current, NULL)) {
 961                 raw_spin_unlock(&lock->wait_lock);
 962                 return 0;
 963         }
 964
 965         set_current_state(state);
 966
 967         /* Setup the timer, when timeout != NULL */
 968         if (unlikely(timeout)) {
 969                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 970                 if (!hrtimer_active(&timeout->timer))
 971                         timeout->task = NULL;
 972         }
 973
 974         ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
 975
 976         if (likely(!ret))
 977                 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 978
 979         set_current_state(TASK_RUNNING);
 980
 981         if (unlikely(ret)) {
 982                 remove_waiter(lock, &waiter);
 983                 rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
 984         }
 985
 986         /*
 987          * try_to_take_rt_mutex() sets the waiter bit
 988          * unconditionally. We might have to fix that up.
 989          */
 990         fixup_rt_mutex_waiters(lock);
 991
 992         raw_spin_unlock(&lock->wait_lock);
 993
 994         /* Remove pending timer: */
 995         if (unlikely(timeout))
 996                 hrtimer_cancel(&timeout->timer);
 997
 998         debug_rt_mutex_free_waiter(&waiter);
 999
1000         return ret;
1001 }
1002
1003 /*
1004  * Slow path try-lock function:
1005  */
1006 static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1007 {
1008         int ret;
1009
1010         /*
1011          * If the lock already has an owner we fail to get the lock.
1012          * This can be done without taking the @lock->wait_lock as
1013          * it is only being read, and this is a trylock anyway.
1014          */
1015         if (rt_mutex_owner(lock))
1016                 return 0;
1017
1018         /*
1019          * The mutex has currently no owner. Lock the wait lock and
1020          * try to acquire the lock.
1021          */
1022         raw_spin_lock(&lock->wait_lock);
1023
1024         ret = try_to_take_rt_mutex(lock, current, NULL);
1025
1026         /*
1027          * try_to_take_rt_mutex() sets the lock waiters bit
1028          * unconditionally. Clean this up.
1029          */
1030         fixup_rt_mutex_waiters(lock);
1031
1032         raw_spin_unlock(&lock->wait_lock);
1033
1034         return ret;
1035 }
1036
1037 /*
1038  * Slow path to release a rt-mutex:
1039  */
1040 static void __sched
1041 rt_mutex_slowunlock(struct rt_mutex *lock)
1042 {
1043         raw_spin_lock(&lock->wait_lock);
1044
1045         debug_rt_mutex_unlock(lock);
1046
1047         rt_mutex_deadlock_account_unlock(current);
1048
1049         /*
1050          * We must be careful here if the fast path is enabled. If we
1051          * have no waiters queued we cannot set owner to NULL here
1052          * because of:
1053          *
1054          * foo->lock->owner = NULL;
1055          *                      rtmutex_lock(foo->lock);   <- fast path
1056          *                      free = atomic_dec_and_test(foo->refcnt);
1057          *                      rtmutex_unlock(foo->lock); <- fast path
1058          *                      if (free)
1059          *                              kfree(foo);
1060          * raw_spin_unlock(foo->lock->wait_lock);
1061          *
1062          * So for the fastpath enabled kernel:
1063          *
1064          * Nothing can set the waiters bit as long as we hold
1065          * lock->wait_lock. So we do the following sequence:
1066          *
1067          *      owner = rt_mutex_owner(lock);
1068          *      clear_rt_mutex_waiters(lock);
1069          *      raw_spin_unlock(&lock->wait_lock);
1070          *      if (cmpxchg(&lock->owner, owner, 0) == owner)
1071          *              return;
1072          *      goto retry;
1073          *
1074          * The fastpath disabled variant is simple as all access to
1075          * lock->owner is serialized by lock->wait_lock:
1076          *
1077          *      lock->owner = NULL;
1078          *      raw_spin_unlock(&lock->wait_lock);
1079          */
1080         while (!rt_mutex_has_waiters(lock)) {
1081                 /* Drops lock->wait_lock ! */
1082                 if (unlock_rt_mutex_safe(lock) == true)
1083                         return;
1084                 /* Relock the rtmutex and try again */
1085                 raw_spin_lock(&lock->wait_lock);
1086         }
1087
1088         /*
1089          * The wakeup next waiter path does not suffer from the above
1090          * race. See the comments there.
1091          */
1092         wakeup_next_waiter(lock);
1093
1094         raw_spin_unlock(&lock->wait_lock);
1095
1096         /* Undo pi boosting if necessary: */
1097         rt_mutex_adjust_prio(current);
1098 }
1099
1100 /*
1101  * debug aware fast / slowpath lock,trylock,unlock
1102  *
1103  * The atomic acquire/release ops are compiled away, when either the
1104  * architecture does not support cmpxchg or when debugging is enabled.
1105  */
1106 static inline int
1107 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1108                   int detect_deadlock,
1109                   int (*slowfn)(struct rt_mutex *lock, int state,
1110                                 struct hrtimer_sleeper *timeout,
1111                                 int detect_deadlock))
1112 {
1113         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1114                 rt_mutex_deadlock_account_lock(lock, current);
1115                 return 0;
1116         } else
1117                 return slowfn(lock, state, NULL, detect_deadlock);
1118 }
1119
1120 static inline int
1121 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1122                         struct hrtimer_sleeper *timeout, int detect_deadlock,
1123                         int (*slowfn)(struct rt_mutex *lock, int state,
1124                                       struct hrtimer_sleeper *timeout,
1125                                       int detect_deadlock))
1126 {
1127         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1128                 rt_mutex_deadlock_account_lock(lock, current);
1129                 return 0;
1130         } else
1131                 return slowfn(lock, state, timeout, detect_deadlock);
1132 }
1133
1134 static inline int
1135 rt_mutex_fasttrylock(struct rt_mutex *lock,
1136                      int (*slowfn)(struct rt_mutex *lock))
1137 {
1138         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1139                 rt_mutex_deadlock_account_lock(lock, current);
1140                 return 1;
1141         }
1142         return slowfn(lock);
1143 }
1144
1145 static inline void
1146 rt_mutex_fastunlock(struct rt_mutex *lock,
1147                     void (*slowfn)(struct rt_mutex *lock))
1148 {
1149         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
1150                 rt_mutex_deadlock_account_unlock(current);
1151         else
1152                 slowfn(lock);
1153 }
1154
1155 /**
1156  * rt_mutex_lock - lock a rt_mutex
1157  *
1158  * @lock: the rt_mutex to be locked
1159  */
1160 void __sched rt_mutex_lock(struct rt_mutex *lock)
1161 {
1162         might_sleep();
1163
1164         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
1165 }
1166 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1167
1168 /**
1169  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1170  *
1171  * @lock:               the rt_mutex to be locked
1172  * @detect_deadlock:    deadlock detection on/off
1173  *
1174  * Returns:
1175  *  0           on success
1176  * -EINTR       when interrupted by a signal
1177  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1178  */
1179 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
1180                                                  int detect_deadlock)
1181 {
1182         might_sleep();
1183
1184         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
1185                                  detect_deadlock, rt_mutex_slowlock);
1186 }
1187 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1188
1189 /**
1190  * rt_mutex_timed_lock - lock a rt_mutex interruptible
1191  *                      the timeout structure is provided
1192  *                      by the caller
1193  *
1194  * @lock:               the rt_mutex to be locked
1195  * @timeout:            timeout structure or NULL (no timeout)
1196  * @detect_deadlock:    deadlock detection on/off
1197  *
1198  * Returns:
1199  *  0           on success
1200  * -EINTR       when interrupted by a signal
1201  * -ETIMEDOUT   when the timeout expired
1202  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
1203  */
1204 int
1205 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
1206                     int detect_deadlock)
1207 {
1208         might_sleep();
1209
1210         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1211                                        detect_deadlock, rt_mutex_slowlock);
1212 }
1213 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1214
1215 /**
1216  * rt_mutex_trylock - try to lock a rt_mutex
1217  *
1218  * @lock:       the rt_mutex to be locked
1219  *
1220  * Returns 1 on success and 0 on contention
1221  */
1222 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1223 {
1224         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1225 }
1226 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1227
1228 /**
1229  * rt_mutex_unlock - unlock a rt_mutex
1230  *
1231  * @lock: the rt_mutex to be unlocked
1232  */
1233 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1234 {
1235         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1236 }
1237 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1238
1239 /**
1240  * rt_mutex_destroy - mark a mutex unusable
1241  * @lock: the mutex to be destroyed
1242  *
1243  * This function marks the mutex uninitialized, and any subsequent
1244  * use of the mutex is forbidden. The mutex must not be locked when
1245  * this function is called.
1246  */
1247 void rt_mutex_destroy(struct rt_mutex *lock)
1248 {
1249         WARN_ON(rt_mutex_is_locked(lock));
1250 #ifdef CONFIG_DEBUG_RT_MUTEXES
1251         lock->magic = NULL;
1252 #endif
1253 }
1254
1255 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1256
1257 /**
1258  * __rt_mutex_init - initialize the rt lock
1259  *
1260  * @lock: the rt lock to be initialized
1261  *
1262  * Initialize the rt lock to unlocked state.
1263  *
1264  * Initializing of a locked rt lock is not allowed
1265  */
1266 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1267 {
1268         lock->owner = NULL;
1269         raw_spin_lock_init(&lock->wait_lock);
1270         lock->waiters = RB_ROOT;
1271         lock->waiters_leftmost = NULL;
1272
1273         debug_rt_mutex_init(lock, name);
1274 }
1275 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1276
1277 /**
1278  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1279  *                              proxy owner
1280  *
1281  * @lock:       the rt_mutex to be locked
1282  * @proxy_owner:the task to set as owner
1283  *
1284  * No locking. Caller has to do serializing itself
1285  * Special API call for PI-futex support
1286  */
1287 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1288                                 struct task_struct *proxy_owner)
1289 {
1290         __rt_mutex_init(lock, NULL);
1291         debug_rt_mutex_proxy_lock(lock, proxy_owner);
1292         rt_mutex_set_owner(lock, proxy_owner);
1293         rt_mutex_deadlock_account_lock(lock, proxy_owner);
1294 }
1295
1296 /**
1297  * rt_mutex_proxy_unlock - release a lock on behalf of owner
1298  *
1299  * @lock:       the rt_mutex to be locked
1300  *
1301  * No locking. Caller has to do serializing itself
1302  * Special API call for PI-futex support
1303  */
1304 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1305                            struct task_struct *proxy_owner)
1306 {
1307         debug_rt_mutex_proxy_unlock(lock);
1308         rt_mutex_set_owner(lock, NULL);
1309         rt_mutex_deadlock_account_unlock(proxy_owner);
1310 }
1311
1312 /**
1313  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1314  * @lock:               the rt_mutex to take
1315  * @waiter:             the pre-initialized rt_mutex_waiter
1316  * @task:               the task to prepare
1317  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1318  *
1319  * Returns:
1320  *  0 - task blocked on lock
1321  *  1 - acquired the lock for task, caller should wake it up
1322  * <0 - error
1323  *
1324  * Special API call for FUTEX_REQUEUE_PI support.
1325  */
1326 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1327                               struct rt_mutex_waiter *waiter,
1328                               struct task_struct *task, int detect_deadlock)
1329 {
1330         int ret;
1331
1332         raw_spin_lock(&lock->wait_lock);
1333
1334         if (try_to_take_rt_mutex(lock, task, NULL)) {
1335                 raw_spin_unlock(&lock->wait_lock);
1336                 return 1;
1337         }
1338
1339         /* We enforce deadlock detection for futexes */
1340         ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
1341
1342         if (ret && !rt_mutex_owner(lock)) {
1343                 /*
1344                  * Reset the return value. We might have
1345                  * returned with -EDEADLK and the owner
1346                  * released the lock while we were walking the
1347                  * pi chain.  Let the waiter sort it out.
1348                  */
1349                 ret = 0;
1350         }
1351
1352         if (unlikely(ret))
1353                 remove_waiter(lock, waiter);
1354
1355         raw_spin_unlock(&lock->wait_lock);
1356
1357         debug_rt_mutex_print_deadlock(waiter);
1358
1359         return ret;
1360 }
1361
1362 /**
1363  * rt_mutex_next_owner - return the next owner of the lock
1364  *
1365  * @lock: the rt lock query
1366  *
1367  * Returns the next owner of the lock or NULL
1368  *
1369  * Caller has to serialize against other accessors to the lock
1370  * itself.
1371  *
1372  * Special API call for PI-futex support
1373  */
1374 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1375 {
1376         if (!rt_mutex_has_waiters(lock))
1377                 return NULL;
1378
1379         return rt_mutex_top_waiter(lock)->task;
1380 }
1381
1382 /**
1383  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1384  * @lock:               the rt_mutex we were woken on
1385  * @to:                 the timeout, null if none. hrtimer should already have
1386  *                      been started.
1387  * @waiter:             the pre-initialized rt_mutex_waiter
1388  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1389  *
1390  * Complete the lock acquisition started our behalf by another thread.
1391  *
1392  * Returns:
1393  *  0 - success
1394  * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1395  *
1396  * Special API call for PI-futex requeue support
1397  */
1398 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1399                                struct hrtimer_sleeper *to,
1400                                struct rt_mutex_waiter *waiter,
1401                                int detect_deadlock)
1402 {
1403         int ret;
1404
1405         raw_spin_lock(&lock->wait_lock);
1406
1407         set_current_state(TASK_INTERRUPTIBLE);
1408
1409         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1410
1411         set_current_state(TASK_RUNNING);
1412
1413         if (unlikely(ret))
1414                 remove_waiter(lock, waiter);
1415
1416         /*
1417          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1418          * have to fix that up.
1419          */
1420         fixup_rt_mutex_waiters(lock);
1421
1422         raw_spin_unlock(&lock->wait_lock);
1423
1424         return ret;
1425 }