kernel/rtmutex.c

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