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/module.h>
  15 #include <linux/sched.h>
  16 #include <linux/timer.h>
  17
  18 #include "rtmutex_common.h"
  19
  20 #ifdef CONFIG_DEBUG_RT_MUTEXES
  21 # include "rtmutex-debug.h"
  22 #else
  23 # include "rtmutex.h"
  24 #endif
  25
  26 /*
  27  * lock->owner state tracking:
  28  *
  29  * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
  30  * are used to keep track of the "owner is pending" and "lock has
  31  * waiters" state.
  32  *
  33  * owner        bit1    bit0
  34  * NULL         0       0       lock is free (fast acquire possible)
  35  * NULL         0       1       invalid state
  36  * NULL         1       0       Transitional State*
  37  * NULL         1       1       invalid state
  38  * taskpointer  0       0       lock is held (fast release possible)
  39  * taskpointer  0       1       task is pending owner
  40  * taskpointer  1       0       lock is held and has waiters
  41  * taskpointer  1       1       task is pending owner and lock has more waiters
  42  *
  43  * Pending ownership is assigned to the top (highest priority)
  44  * waiter of the lock, when the lock is released. The thread is woken
  45  * up and can now take the lock. Until the lock is taken (bit 0
  46  * cleared) a competing higher priority thread can steal the lock
  47  * which puts the woken up thread back on the waiters list.
  48  *
  49  * The fast atomic compare exchange based acquire and release is only
  50  * possible when bit 0 and 1 of lock->owner are 0.
  51  *
  52  * (*) There's a small time where the owner can be NULL and the
  53  * "lock has waiters" bit is set.  This can happen when grabbing the lock.
  54  * To prevent a cmpxchg of the owner releasing the lock, we need to set this
  55  * bit before looking at the lock, hence the reason this is a transitional
  56  * state.
  57  */
  58
  59 static void
  60 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
  61                    unsigned long mask)
  62 {
  63         unsigned long val = (unsigned long)owner | mask;
  64
  65         if (rt_mutex_has_waiters(lock))
  66                 val |= RT_MUTEX_HAS_WAITERS;
  67
  68         lock->owner = (struct task_struct *)val;
  69 }
  70
  71 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  72 {
  73         lock->owner = (struct task_struct *)
  74                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  75 }
  76
  77 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  78 {
  79         if (!rt_mutex_has_waiters(lock))
  80                 clear_rt_mutex_waiters(lock);
  81 }
  82
  83 /*
  84  * We can speed up the acquire/release, if the architecture
  85  * supports cmpxchg and if there's no debugging state to be set up
  86  */
  87 #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  88 # define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
  89 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  90 {
  91         unsigned long owner, *p = (unsigned long *) &lock->owner;
  92
  93         do {
  94                 owner = *p;
  95         } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  96 }
  97 #else
  98 # define rt_mutex_cmpxchg(l,c,n)        (0)
  99 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 100 {
 101         lock->owner = (struct task_struct *)
 102                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 103 }
 104 #endif
 105
 106 /*
 107  * Calculate task priority from the waiter list priority
 108  *
 109  * Return task->normal_prio when the waiter list is empty or when
 110  * the waiter is not allowed to do priority boosting
 111  */
 112 int rt_mutex_getprio(struct task_struct *task)
 113 {
 114         if (likely(!task_has_pi_waiters(task)))
 115                 return task->normal_prio;
 116
 117         return min(task_top_pi_waiter(task)->pi_list_entry.prio,
 118                    task->normal_prio);
 119 }
 120
 121 /*
 122  * Adjust the priority of a task, after its pi_waiters got modified.
 123  *
 124  * This can be both boosting and unboosting. task->pi_lock must be held.
 125  */
 126 static void __rt_mutex_adjust_prio(struct task_struct *task)
 127 {
 128         int prio = rt_mutex_getprio(task);
 129
 130         if (task->prio != prio)
 131                 rt_mutex_setprio(task, prio);
 132 }
 133
 134 /*
 135  * Adjust task priority (undo boosting). Called from the exit path of
 136  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 137  *
 138  * (Note: We do this outside of the protection of lock->wait_lock to
 139  * allow the lock to be taken while or before we readjust the priority
 140  * of task. We do not use the spin_xx_mutex() variants here as we are
 141  * outside of the debug path.)
 142  */
 143 static void rt_mutex_adjust_prio(struct task_struct *task)
 144 {
 145         unsigned long flags;
 146
 147         spin_lock_irqsave(&task->pi_lock, flags);
 148         __rt_mutex_adjust_prio(task);
 149         spin_unlock_irqrestore(&task->pi_lock, flags);
 150 }
 151
 152 /*
 153  * Max number of times we'll walk the boosting chain:
 154  */
 155 int max_lock_depth = 1024;
 156
 157 /*
 158  * Adjust the priority chain. Also used for deadlock detection.
 159  * Decreases task's usage by one - may thus free the task.
 160  * Returns 0 or -EDEADLK.
 161  */
 162 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 163                                       int deadlock_detect,
 164                                       struct rt_mutex *orig_lock,
 165                                       struct rt_mutex_waiter *orig_waiter,
 166                                       struct task_struct *top_task)
 167 {
 168         struct rt_mutex *lock;
 169         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 170         int detect_deadlock, ret = 0, depth = 0;
 171         unsigned long flags;
 172
 173         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 174                                                          deadlock_detect);
 175
 176         /*
 177          * The (de)boosting is a step by step approach with a lot of
 178          * pitfalls. We want this to be preemptible and we want hold a
 179          * maximum of two locks per step. So we have to check
 180          * carefully whether things change under us.
 181          */
 182  again:
 183         if (++depth > max_lock_depth) {
 184                 static int prev_max;
 185
 186                 /*
 187                  * Print this only once. If the admin changes the limit,
 188                  * print a new message when reaching the limit again.
 189                  */
 190                 if (prev_max != max_lock_depth) {
 191                         prev_max = max_lock_depth;
 192                         printk(KERN_WARNING "Maximum lock depth %d reached "
 193                                "task: %s (%d)\n", max_lock_depth,
 194                                top_task->comm, top_task->pid);
 195                 }
 196                 put_task_struct(task);
 197
 198                 return deadlock_detect ? -EDEADLK : 0;
 199         }
 200  retry:
 201         /*
 202          * Task can not go away as we did a get_task() before !
 203          */
 204         spin_lock_irqsave(&task->pi_lock, flags);
 205
 206         waiter = task->pi_blocked_on;
 207         /*
 208          * Check whether the end of the boosting chain has been
 209          * reached or the state of the chain has changed while we
 210          * dropped the locks.
 211          */
 212         if (!waiter || !waiter->task)
 213                 goto out_unlock_pi;
 214
 215         /*
 216          * Check the orig_waiter state. After we dropped the locks,
 217          * the previous owner of the lock might have released the lock
 218          * and made us the pending owner:
 219          */
 220         if (orig_waiter && !orig_waiter->task)
 221                 goto out_unlock_pi;
 222
 223         /*
 224          * Drop out, when the task has no waiters. Note,
 225          * top_waiter can be NULL, when we are in the deboosting
 226          * mode!
 227          */
 228         if (top_waiter && (!task_has_pi_waiters(task) ||
 229                            top_waiter != task_top_pi_waiter(task)))
 230                 goto out_unlock_pi;
 231
 232         /*
 233          * When deadlock detection is off then we check, if further
 234          * priority adjustment is necessary.
 235          */
 236         if (!detect_deadlock && waiter->list_entry.prio == task->prio)
 237                 goto out_unlock_pi;
 238
 239         lock = waiter->lock;
 240         if (!spin_trylock(&lock->wait_lock)) {
 241                 spin_unlock_irqrestore(&task->pi_lock, flags);
 242                 cpu_relax();
 243                 goto retry;
 244         }
 245
 246         /* Deadlock detection */
 247         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 248                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 249                 spin_unlock(&lock->wait_lock);
 250                 ret = deadlock_detect ? -EDEADLK : 0;
 251                 goto out_unlock_pi;
 252         }
 253
 254         top_waiter = rt_mutex_top_waiter(lock);
 255
 256         /* Requeue the waiter */
 257         plist_del(&waiter->list_entry, &lock->wait_list);
 258         waiter->list_entry.prio = task->prio;
 259         plist_add(&waiter->list_entry, &lock->wait_list);
 260
 261         /* Release the task */
 262         spin_unlock_irqrestore(&task->pi_lock, flags);
 263         put_task_struct(task);
 264
 265         /* Grab the next task */
 266         task = rt_mutex_owner(lock);
 267         get_task_struct(task);
 268         spin_lock_irqsave(&task->pi_lock, flags);
 269
 270         if (waiter == rt_mutex_top_waiter(lock)) {
 271                 /* Boost the owner */
 272                 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
 273                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 274                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 275                 __rt_mutex_adjust_prio(task);
 276
 277         } else if (top_waiter == waiter) {
 278                 /* Deboost the owner */
 279                 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
 280                 waiter = rt_mutex_top_waiter(lock);
 281                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 282                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 283                 __rt_mutex_adjust_prio(task);
 284         }
 285
 286         spin_unlock_irqrestore(&task->pi_lock, flags);
 287
 288         top_waiter = rt_mutex_top_waiter(lock);
 289         spin_unlock(&lock->wait_lock);
 290
 291         if (!detect_deadlock && waiter != top_waiter)
 292                 goto out_put_task;
 293
 294         goto again;
 295
 296  out_unlock_pi:
 297         spin_unlock_irqrestore(&task->pi_lock, flags);
 298  out_put_task:
 299         put_task_struct(task);
 300
 301         return ret;
 302 }
 303
 304 /*
 305  * Optimization: check if we can steal the lock from the
 306  * assigned pending owner [which might not have taken the
 307  * lock yet]:
 308  */
 309 static inline int try_to_steal_lock(struct rt_mutex *lock)
 310 {
 311         struct task_struct *pendowner = rt_mutex_owner(lock);
 312         struct rt_mutex_waiter *next;
 313         unsigned long flags;
 314
 315         if (!rt_mutex_owner_pending(lock))
 316                 return 0;
 317
 318         if (pendowner == current)
 319                 return 1;
 320
 321         spin_lock_irqsave(&pendowner->pi_lock, flags);
 322         if (current->prio >= pendowner->prio) {
 323                 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 324                 return 0;
 325         }
 326
 327         /*
 328          * Check if a waiter is enqueued on the pending owners
 329          * pi_waiters list. Remove it and readjust pending owners
 330          * priority.
 331          */
 332         if (likely(!rt_mutex_has_waiters(lock))) {
 333                 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 334                 return 1;
 335         }
 336
 337         /* No chain handling, pending owner is not blocked on anything: */
 338         next = rt_mutex_top_waiter(lock);
 339         plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
 340         __rt_mutex_adjust_prio(pendowner);
 341         spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 342
 343         /*
 344          * We are going to steal the lock and a waiter was
 345          * enqueued on the pending owners pi_waiters queue. So
 346          * we have to enqueue this waiter into
 347          * current->pi_waiters list. This covers the case,
 348          * where current is boosted because it holds another
 349          * lock and gets unboosted because the booster is
 350          * interrupted, so we would delay a waiter with higher
 351          * priority as current->normal_prio.
 352          *
 353          * Note: in the rare case of a SCHED_OTHER task changing
 354          * its priority and thus stealing the lock, next->task
 355          * might be current:
 356          */
 357         if (likely(next->task != current)) {
 358                 spin_lock_irqsave(&current->pi_lock, flags);
 359                 plist_add(&next->pi_list_entry, &current->pi_waiters);
 360                 __rt_mutex_adjust_prio(current);
 361                 spin_unlock_irqrestore(&current->pi_lock, flags);
 362         }
 363         return 1;
 364 }
 365
 366 /*
 367  * Try to take an rt-mutex
 368  *
 369  * This fails
 370  * - when the lock has a real owner
 371  * - when a different pending owner exists and has higher priority than current
 372  *
 373  * Must be called with lock->wait_lock held.
 374  */
 375 static int try_to_take_rt_mutex(struct rt_mutex *lock)
 376 {
 377         /*
 378          * We have to be careful here if the atomic speedups are
 379          * enabled, such that, when
 380          *  - no other waiter is on the lock
 381          *  - the lock has been released since we did the cmpxchg
 382          * the lock can be released or taken while we are doing the
 383          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 384          *
 385          * The atomic acquire/release aware variant of
 386          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 387          * the WAITERS bit, the atomic release / acquire can not
 388          * happen anymore and lock->wait_lock protects us from the
 389          * non-atomic case.
 390          *
 391          * Note, that this might set lock->owner =
 392          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 393          * any more. This is fixed up when we take the ownership.
 394          * This is the transitional state explained at the top of this file.
 395          */
 396         mark_rt_mutex_waiters(lock);
 397
 398         if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
 399                 return 0;
 400
 401         /* We got the lock. */
 402         debug_rt_mutex_lock(lock);
 403
 404         rt_mutex_set_owner(lock, current, 0);
 405
 406         rt_mutex_deadlock_account_lock(lock, current);
 407
 408         return 1;
 409 }
 410
 411 /*
 412  * Task blocks on lock.
 413  *
 414  * Prepare waiter and propagate pi chain
 415  *
 416  * This must be called with lock->wait_lock held.
 417  */
 418 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 419                                    struct rt_mutex_waiter *waiter,
 420                                    int detect_deadlock)
 421 {
 422         struct task_struct *owner = rt_mutex_owner(lock);
 423         struct rt_mutex_waiter *top_waiter = waiter;
 424         unsigned long flags;
 425         int chain_walk = 0, res;
 426
 427         spin_lock_irqsave(&current->pi_lock, flags);
 428         __rt_mutex_adjust_prio(current);
 429         waiter->task = current;
 430         waiter->lock = lock;
 431         plist_node_init(&waiter->list_entry, current->prio);
 432         plist_node_init(&waiter->pi_list_entry, current->prio);
 433
 434         /* Get the top priority waiter on the lock */
 435         if (rt_mutex_has_waiters(lock))
 436                 top_waiter = rt_mutex_top_waiter(lock);
 437         plist_add(&waiter->list_entry, &lock->wait_list);
 438
 439         current->pi_blocked_on = waiter;
 440
 441         spin_unlock_irqrestore(&current->pi_lock, flags);
 442
 443         if (waiter == rt_mutex_top_waiter(lock)) {
 444                 spin_lock_irqsave(&owner->pi_lock, flags);
 445                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
 446                 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
 447
 448                 __rt_mutex_adjust_prio(owner);
 449                 if (owner->pi_blocked_on)
 450                         chain_walk = 1;
 451                 spin_unlock_irqrestore(&owner->pi_lock, flags);
 452         }
 453         else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
 454                 chain_walk = 1;
 455
 456         if (!chain_walk)
 457                 return 0;
 458
 459         /*
 460          * The owner can't disappear while holding a lock,
 461          * so the owner struct is protected by wait_lock.
 462          * Gets dropped in rt_mutex_adjust_prio_chain()!
 463          */
 464         get_task_struct(owner);
 465
 466         spin_unlock(&lock->wait_lock);
 467
 468         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
 469                                          current);
 470
 471         spin_lock(&lock->wait_lock);
 472
 473         return res;
 474 }
 475
 476 /*
 477  * Wake up the next waiter on the lock.
 478  *
 479  * Remove the top waiter from the current tasks waiter list and from
 480  * the lock waiter list. Set it as pending owner. Then wake it up.
 481  *
 482  * Called with lock->wait_lock held.
 483  */
 484 static void wakeup_next_waiter(struct rt_mutex *lock)
 485 {
 486         struct rt_mutex_waiter *waiter;
 487         struct task_struct *pendowner;
 488         unsigned long flags;
 489
 490         spin_lock_irqsave(&current->pi_lock, flags);
 491
 492         waiter = rt_mutex_top_waiter(lock);
 493         plist_del(&waiter->list_entry, &lock->wait_list);
 494
 495         /*
 496          * Remove it from current->pi_waiters. We do not adjust a
 497          * possible priority boost right now. We execute wakeup in the
 498          * boosted mode and go back to normal after releasing
 499          * lock->wait_lock.
 500          */
 501         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
 502         pendowner = waiter->task;
 503         waiter->task = NULL;
 504
 505         rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
 506
 507         spin_unlock_irqrestore(&current->pi_lock, flags);
 508
 509         /*
 510          * Clear the pi_blocked_on variable and enqueue a possible
 511          * waiter into the pi_waiters list of the pending owner. This
 512          * prevents that in case the pending owner gets unboosted a
 513          * waiter with higher priority than pending-owner->normal_prio
 514          * is blocked on the unboosted (pending) owner.
 515          */
 516         spin_lock_irqsave(&pendowner->pi_lock, flags);
 517
 518         WARN_ON(!pendowner->pi_blocked_on);
 519         WARN_ON(pendowner->pi_blocked_on != waiter);
 520         WARN_ON(pendowner->pi_blocked_on->lock != lock);
 521
 522         pendowner->pi_blocked_on = NULL;
 523
 524         if (rt_mutex_has_waiters(lock)) {
 525                 struct rt_mutex_waiter *next;
 526
 527                 next = rt_mutex_top_waiter(lock);
 528                 plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
 529         }
 530         spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 531
 532         wake_up_process(pendowner);
 533 }
 534
 535 /*
 536  * Remove a waiter from a lock
 537  *
 538  * Must be called with lock->wait_lock held
 539  */
 540 static void remove_waiter(struct rt_mutex *lock,
 541                           struct rt_mutex_waiter *waiter)
 542 {
 543         int first = (waiter == rt_mutex_top_waiter(lock));
 544         struct task_struct *owner = rt_mutex_owner(lock);
 545         unsigned long flags;
 546         int chain_walk = 0;
 547
 548         spin_lock_irqsave(&current->pi_lock, flags);
 549         plist_del(&waiter->list_entry, &lock->wait_list);
 550         waiter->task = NULL;
 551         current->pi_blocked_on = NULL;
 552         spin_unlock_irqrestore(&current->pi_lock, flags);
 553
 554         if (first && owner != current) {
 555
 556                 spin_lock_irqsave(&owner->pi_lock, flags);
 557
 558                 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
 559
 560                 if (rt_mutex_has_waiters(lock)) {
 561                         struct rt_mutex_waiter *next;
 562
 563                         next = rt_mutex_top_waiter(lock);
 564                         plist_add(&next->pi_list_entry, &owner->pi_waiters);
 565                 }
 566                 __rt_mutex_adjust_prio(owner);
 567
 568                 if (owner->pi_blocked_on)
 569                         chain_walk = 1;
 570
 571                 spin_unlock_irqrestore(&owner->pi_lock, flags);
 572         }
 573
 574         WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 575
 576         if (!chain_walk)
 577                 return;
 578
 579         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 580         get_task_struct(owner);
 581
 582         spin_unlock(&lock->wait_lock);
 583
 584         rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
 585
 586         spin_lock(&lock->wait_lock);
 587 }
 588
 589 /*
 590  * Recheck the pi chain, in case we got a priority setting
 591  *
 592  * Called from sched_setscheduler
 593  */
 594 void rt_mutex_adjust_pi(struct task_struct *task)
 595 {
 596         struct rt_mutex_waiter *waiter;
 597         unsigned long flags;
 598
 599         spin_lock_irqsave(&task->pi_lock, flags);
 600
 601         waiter = task->pi_blocked_on;
 602         if (!waiter || waiter->list_entry.prio == task->prio) {
 603                 spin_unlock_irqrestore(&task->pi_lock, flags);
 604                 return;
 605         }
 606
 607         spin_unlock_irqrestore(&task->pi_lock, flags);
 608
 609         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 610         get_task_struct(task);
 611         rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
 612 }
 613
 614 /*
 615  * Slow path lock function:
 616  */
 617 static int __sched
 618 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 619                   struct hrtimer_sleeper *timeout,
 620                   int detect_deadlock)
 621 {
 622         struct rt_mutex_waiter waiter;
 623         int ret = 0;
 624
 625         debug_rt_mutex_init_waiter(&waiter);
 626         waiter.task = NULL;
 627
 628         spin_lock(&lock->wait_lock);
 629
 630         /* Try to acquire the lock again: */
 631         if (try_to_take_rt_mutex(lock)) {
 632                 spin_unlock(&lock->wait_lock);
 633                 return 0;
 634         }
 635
 636         set_current_state(state);
 637
 638         /* Setup the timer, when timeout != NULL */
 639         if (unlikely(timeout))
 640                 hrtimer_start(&timeout->timer, timeout->timer.expires,
 641                               HRTIMER_MODE_ABS);
 642
 643         for (;;) {
 644                 /* Try to acquire the lock: */
 645                 if (try_to_take_rt_mutex(lock))
 646                         break;
 647
 648                 /*
 649                  * TASK_INTERRUPTIBLE checks for signals and
 650                  * timeout. Ignored otherwise.
 651                  */
 652                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 653                         /* Signal pending? */
 654                         if (signal_pending(current))
 655                                 ret = -EINTR;
 656                         if (timeout && !timeout->task)
 657                                 ret = -ETIMEDOUT;
 658                         if (ret)
 659                                 break;
 660                 }
 661
 662                 /*
 663                  * waiter.task is NULL the first time we come here and
 664                  * when we have been woken up by the previous owner
 665                  * but the lock got stolen by a higher prio task.
 666                  */
 667                 if (!waiter.task) {
 668                         ret = task_blocks_on_rt_mutex(lock, &waiter,
 669                                                       detect_deadlock);
 670                         /*
 671                          * If we got woken up by the owner then start loop
 672                          * all over without going into schedule to try
 673                          * to get the lock now:
 674                          */
 675                         if (unlikely(!waiter.task)) {
 676                                 /*
 677                                  * Reset the return value. We might
 678                                  * have returned with -EDEADLK and the
 679                                  * owner released the lock while we
 680                                  * were walking the pi chain.
 681                                  */
 682                                 ret = 0;
 683                                 continue;
 684                         }
 685                         if (unlikely(ret))
 686                                 break;
 687                 }
 688
 689                 spin_unlock(&lock->wait_lock);
 690
 691                 debug_rt_mutex_print_deadlock(&waiter);
 692
 693                 if (waiter.task)
 694                         schedule_rt_mutex(lock);
 695
 696                 spin_lock(&lock->wait_lock);
 697                 set_current_state(state);
 698         }
 699
 700         set_current_state(TASK_RUNNING);
 701
 702         if (unlikely(waiter.task))
 703                 remove_waiter(lock, &waiter);
 704
 705         /*
 706          * try_to_take_rt_mutex() sets the waiter bit
 707          * unconditionally. We might have to fix that up.
 708          */
 709         fixup_rt_mutex_waiters(lock);
 710
 711         spin_unlock(&lock->wait_lock);
 712
 713         /* Remove pending timer: */
 714         if (unlikely(timeout))
 715                 hrtimer_cancel(&timeout->timer);
 716
 717         /*
 718          * Readjust priority, when we did not get the lock. We might
 719          * have been the pending owner and boosted. Since we did not
 720          * take the lock, the PI boost has to go.
 721          */
 722         if (unlikely(ret))
 723                 rt_mutex_adjust_prio(current);
 724
 725         debug_rt_mutex_free_waiter(&waiter);
 726
 727         return ret;
 728 }
 729
 730 /*
 731  * Slow path try-lock function:
 732  */
 733 static inline int
 734 rt_mutex_slowtrylock(struct rt_mutex *lock)
 735 {
 736         int ret = 0;
 737
 738         spin_lock(&lock->wait_lock);
 739
 740         if (likely(rt_mutex_owner(lock) != current)) {
 741
 742                 ret = try_to_take_rt_mutex(lock);
 743                 /*
 744                  * try_to_take_rt_mutex() sets the lock waiters
 745                  * bit unconditionally. Clean this up.
 746                  */
 747                 fixup_rt_mutex_waiters(lock);
 748         }
 749
 750         spin_unlock(&lock->wait_lock);
 751
 752         return ret;
 753 }
 754
 755 /*
 756  * Slow path to release a rt-mutex:
 757  */
 758 static void __sched
 759 rt_mutex_slowunlock(struct rt_mutex *lock)
 760 {
 761         spin_lock(&lock->wait_lock);
 762
 763         debug_rt_mutex_unlock(lock);
 764
 765         rt_mutex_deadlock_account_unlock(current);
 766
 767         if (!rt_mutex_has_waiters(lock)) {
 768                 lock->owner = NULL;
 769                 spin_unlock(&lock->wait_lock);
 770                 return;
 771         }
 772
 773         wakeup_next_waiter(lock);
 774
 775         spin_unlock(&lock->wait_lock);
 776
 777         /* Undo pi boosting if necessary: */
 778         rt_mutex_adjust_prio(current);
 779 }
 780
 781 /*
 782  * debug aware fast / slowpath lock,trylock,unlock
 783  *
 784  * The atomic acquire/release ops are compiled away, when either the
 785  * architecture does not support cmpxchg or when debugging is enabled.
 786  */
 787 static inline int
 788 rt_mutex_fastlock(struct rt_mutex *lock, int state,
 789                   int detect_deadlock,
 790                   int (*slowfn)(struct rt_mutex *lock, int state,
 791                                 struct hrtimer_sleeper *timeout,
 792                                 int detect_deadlock))
 793 {
 794         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 795                 rt_mutex_deadlock_account_lock(lock, current);
 796                 return 0;
 797         } else
 798                 return slowfn(lock, state, NULL, detect_deadlock);
 799 }
 800
 801 static inline int
 802 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 803                         struct hrtimer_sleeper *timeout, int detect_deadlock,
 804                         int (*slowfn)(struct rt_mutex *lock, int state,
 805                                       struct hrtimer_sleeper *timeout,
 806                                       int detect_deadlock))
 807 {
 808         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 809                 rt_mutex_deadlock_account_lock(lock, current);
 810                 return 0;
 811         } else
 812                 return slowfn(lock, state, timeout, detect_deadlock);
 813 }
 814
 815 static inline int
 816 rt_mutex_fasttrylock(struct rt_mutex *lock,
 817                      int (*slowfn)(struct rt_mutex *lock))
 818 {
 819         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 820                 rt_mutex_deadlock_account_lock(lock, current);
 821                 return 1;
 822         }
 823         return slowfn(lock);
 824 }
 825
 826 static inline void
 827 rt_mutex_fastunlock(struct rt_mutex *lock,
 828                     void (*slowfn)(struct rt_mutex *lock))
 829 {
 830         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
 831                 rt_mutex_deadlock_account_unlock(current);
 832         else
 833                 slowfn(lock);
 834 }
 835
 836 /**
 837  * rt_mutex_lock - lock a rt_mutex
 838  *
 839  * @lock: the rt_mutex to be locked
 840  */
 841 void __sched rt_mutex_lock(struct rt_mutex *lock)
 842 {
 843         might_sleep();
 844
 845         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
 846 }
 847 EXPORT_SYMBOL_GPL(rt_mutex_lock);
 848
 849 /**
 850  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
 851  *
 852  * @lock:               the rt_mutex to be locked
 853  * @detect_deadlock:    deadlock detection on/off
 854  *
 855  * Returns:
 856  *  0           on success
 857  * -EINTR       when interrupted by a signal
 858  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 859  */
 860 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 861                                                  int detect_deadlock)
 862 {
 863         might_sleep();
 864
 865         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
 866                                  detect_deadlock, rt_mutex_slowlock);
 867 }
 868 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 869
 870 /**
 871  * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
 872  *                                     the timeout structure is provided
 873  *                                     by the caller
 874  *
 875  * @lock:               the rt_mutex to be locked
 876  * @timeout:            timeout structure or NULL (no timeout)
 877  * @detect_deadlock:    deadlock detection on/off
 878  *
 879  * Returns:
 880  *  0           on success
 881  * -EINTR       when interrupted by a signal
 882  * -ETIMEOUT    when the timeout expired
 883  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 884  */
 885 int
 886 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
 887                     int detect_deadlock)
 888 {
 889         might_sleep();
 890
 891         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
 892                                        detect_deadlock, rt_mutex_slowlock);
 893 }
 894 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
 895
 896 /**
 897  * rt_mutex_trylock - try to lock a rt_mutex
 898  *
 899  * @lock:       the rt_mutex to be locked
 900  *
 901  * Returns 1 on success and 0 on contention
 902  */
 903 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 904 {
 905         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 906 }
 907 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 908
 909 /**
 910  * rt_mutex_unlock - unlock a rt_mutex
 911  *
 912  * @lock: the rt_mutex to be unlocked
 913  */
 914 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 915 {
 916         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 917 }
 918 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 919
 920 /***
 921  * rt_mutex_destroy - mark a mutex unusable
 922  * @lock: the mutex to be destroyed
 923  *
 924  * This function marks the mutex uninitialized, and any subsequent
 925  * use of the mutex is forbidden. The mutex must not be locked when
 926  * this function is called.
 927  */
 928 void rt_mutex_destroy(struct rt_mutex *lock)
 929 {
 930         WARN_ON(rt_mutex_is_locked(lock));
 931 #ifdef CONFIG_DEBUG_RT_MUTEXES
 932         lock->magic = NULL;
 933 #endif
 934 }
 935
 936 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 937
 938 /**
 939  * __rt_mutex_init - initialize the rt lock
 940  *
 941  * @lock: the rt lock to be initialized
 942  *
 943  * Initialize the rt lock to unlocked state.
 944  *
 945  * Initializing of a locked rt lock is not allowed
 946  */
 947 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 948 {
 949         lock->owner = NULL;
 950         spin_lock_init(&lock->wait_lock);
 951         plist_head_init(&lock->wait_list, &lock->wait_lock);
 952
 953         debug_rt_mutex_init(lock, name);
 954 }
 955 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 956
 957 /**
 958  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 959  *                              proxy owner
 960  *
 961  * @lock:       the rt_mutex to be locked
 962  * @proxy_owner:the task to set as owner
 963  *
 964  * No locking. Caller has to do serializing itself
 965  * Special API call for PI-futex support
 966  */
 967 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 968                                 struct task_struct *proxy_owner)
 969 {
 970         __rt_mutex_init(lock, NULL);
 971         debug_rt_mutex_proxy_lock(lock, proxy_owner);
 972         rt_mutex_set_owner(lock, proxy_owner, 0);
 973         rt_mutex_deadlock_account_lock(lock, proxy_owner);
 974 }
 975
 976 /**
 977  * rt_mutex_proxy_unlock - release a lock on behalf of owner
 978  *
 979  * @lock:       the rt_mutex to be locked
 980  *
 981  * No locking. Caller has to do serializing itself
 982  * Special API call for PI-futex support
 983  */
 984 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
 985                            struct task_struct *proxy_owner)
 986 {
 987         debug_rt_mutex_proxy_unlock(lock);
 988         rt_mutex_set_owner(lock, NULL, 0);
 989         rt_mutex_deadlock_account_unlock(proxy_owner);
 990 }
 991
 992 /**
 993  * rt_mutex_next_owner - return the next owner of the lock
 994  *
 995  * @lock: the rt lock query
 996  *
 997  * Returns the next owner of the lock or NULL
 998  *
 999  * Caller has to serialize against other accessors to the lock
1000  * itself.
1001  *
1002  * Special API call for PI-futex support
1003  */
1004 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1005 {
1006         if (!rt_mutex_has_waiters(lock))
1007                 return NULL;
1008
1009         return rt_mutex_top_waiter(lock)->task;
1010 }