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