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(task_t *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                                       __IP_DECL__)
 166 {
 167         struct rt_mutex *lock;
 168         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 169         int detect_deadlock, ret = 0, depth = 0;
 170         unsigned long flags;
 171
 172         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 173                                                          deadlock_detect);
 174
 175         /*
 176          * The (de)boosting is a step by step approach with a lot of
 177          * pitfalls. We want this to be preemptible and we want hold a
 178          * maximum of two locks per step. So we have to check
 179          * carefully whether things change under us.
 180          */
 181  again:
 182         if (++depth > max_lock_depth) {
 183                 static int prev_max;
 184
 185                 /*
 186                  * Print this only once. If the admin changes the limit,
 187                  * print a new message when reaching the limit again.
 188                  */
 189                 if (prev_max != max_lock_depth) {
 190                         prev_max = max_lock_depth;
 191                         printk(KERN_WARNING "Maximum lock depth %d reached "
 192                                "task: %s (%d)\n", max_lock_depth,
 193                                top_task->comm, top_task->pid);
 194                 }
 195                 put_task_struct(task);
 196
 197                 return deadlock_detect ? -EDEADLK : 0;
 198         }
 199  retry:
 200         /*
 201          * Task can not go away as we did a get_task() before !
 202          */
 203         spin_lock_irqsave(&task->pi_lock, flags);
 204
 205         waiter = task->pi_blocked_on;
 206         /*
 207          * Check whether the end of the boosting chain has been
 208          * reached or the state of the chain has changed while we
 209          * dropped the locks.
 210          */
 211         if (!waiter || !waiter->task)
 212                 goto out_unlock_pi;
 213
 214         if (top_waiter && (!task_has_pi_waiters(task) ||
 215                            top_waiter != task_top_pi_waiter(task)))
 216                 goto out_unlock_pi;
 217
 218         /*
 219          * When deadlock detection is off then we check, if further
 220          * priority adjustment is necessary.
 221          */
 222         if (!detect_deadlock && waiter->list_entry.prio == task->prio)
 223                 goto out_unlock_pi;
 224
 225         lock = waiter->lock;
 226         if (!spin_trylock(&lock->wait_lock)) {
 227                 spin_unlock_irqrestore(&task->pi_lock, flags);
 228                 cpu_relax();
 229                 goto retry;
 230         }
 231
 232         /* Deadlock detection */
 233         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 234                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 235                 spin_unlock(&lock->wait_lock);
 236                 ret = deadlock_detect ? -EDEADLK : 0;
 237                 goto out_unlock_pi;
 238         }
 239
 240         top_waiter = rt_mutex_top_waiter(lock);
 241
 242         /* Requeue the waiter */
 243         plist_del(&waiter->list_entry, &lock->wait_list);
 244         waiter->list_entry.prio = task->prio;
 245         plist_add(&waiter->list_entry, &lock->wait_list);
 246
 247         /* Release the task */
 248         spin_unlock_irqrestore(&task->pi_lock, flags);
 249         put_task_struct(task);
 250
 251         /* Grab the next task */
 252         task = rt_mutex_owner(lock);
 253         spin_lock_irqsave(&task->pi_lock, flags);
 254
 255         if (waiter == rt_mutex_top_waiter(lock)) {
 256                 /* Boost the owner */
 257                 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
 258                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 259                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 260                 __rt_mutex_adjust_prio(task);
 261
 262         } else if (top_waiter == waiter) {
 263                 /* Deboost the owner */
 264                 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
 265                 waiter = rt_mutex_top_waiter(lock);
 266                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 267                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 268                 __rt_mutex_adjust_prio(task);
 269         }
 270
 271         get_task_struct(task);
 272         spin_unlock_irqrestore(&task->pi_lock, flags);
 273
 274         top_waiter = rt_mutex_top_waiter(lock);
 275         spin_unlock(&lock->wait_lock);
 276
 277         if (!detect_deadlock && waiter != top_waiter)
 278                 goto out_put_task;
 279
 280         goto again;
 281
 282  out_unlock_pi:
 283         spin_unlock_irqrestore(&task->pi_lock, flags);
 284  out_put_task:
 285         put_task_struct(task);
 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 __IP_DECL__)
 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 __IP__);
 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                                    __IP_DECL__)
 407 {
 408         struct rt_mutex_waiter *top_waiter = waiter;
 409         task_t *owner = rt_mutex_owner(lock);
 410         int boost = 0, res;
 411         unsigned long flags;
 412
 413         spin_lock_irqsave(&current->pi_lock, flags);
 414         __rt_mutex_adjust_prio(current);
 415         waiter->task = current;
 416         waiter->lock = lock;
 417         plist_node_init(&waiter->list_entry, current->prio);
 418         plist_node_init(&waiter->pi_list_entry, current->prio);
 419
 420         /* Get the top priority waiter on the lock */
 421         if (rt_mutex_has_waiters(lock))
 422                 top_waiter = rt_mutex_top_waiter(lock);
 423         plist_add(&waiter->list_entry, &lock->wait_list);
 424
 425         current->pi_blocked_on = waiter;
 426
 427         spin_unlock_irqrestore(&current->pi_lock, flags);
 428
 429         if (waiter == rt_mutex_top_waiter(lock)) {
 430                 spin_lock_irqsave(&owner->pi_lock, flags);
 431                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
 432                 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
 433
 434                 __rt_mutex_adjust_prio(owner);
 435                 if (owner->pi_blocked_on) {
 436                         boost = 1;
 437                         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 438                         get_task_struct(owner);
 439                 }
 440                 spin_unlock_irqrestore(&owner->pi_lock, flags);
 441         }
 442         else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
 443                 spin_lock_irqsave(&owner->pi_lock, flags);
 444                 if (owner->pi_blocked_on) {
 445                         boost = 1;
 446                         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 447                         get_task_struct(owner);
 448                 }
 449                 spin_unlock_irqrestore(&owner->pi_lock, flags);
 450         }
 451         if (!boost)
 452                 return 0;
 453
 454         spin_unlock(&lock->wait_lock);
 455
 456         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
 457                                          current __IP__);
 458
 459         spin_lock(&lock->wait_lock);
 460
 461         return res;
 462 }
 463
 464 /*
 465  * Wake up the next waiter on the lock.
 466  *
 467  * Remove the top waiter from the current tasks waiter list and from
 468  * the lock waiter list. Set it as pending owner. Then wake it up.
 469  *
 470  * Called with lock->wait_lock held.
 471  */
 472 static void wakeup_next_waiter(struct rt_mutex *lock)
 473 {
 474         struct rt_mutex_waiter *waiter;
 475         struct task_struct *pendowner;
 476         unsigned long flags;
 477
 478         spin_lock_irqsave(&current->pi_lock, flags);
 479
 480         waiter = rt_mutex_top_waiter(lock);
 481         plist_del(&waiter->list_entry, &lock->wait_list);
 482
 483         /*
 484          * Remove it from current->pi_waiters. We do not adjust a
 485          * possible priority boost right now. We execute wakeup in the
 486          * boosted mode and go back to normal after releasing
 487          * lock->wait_lock.
 488          */
 489         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
 490         pendowner = waiter->task;
 491         waiter->task = NULL;
 492
 493         rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
 494
 495         spin_unlock_irqrestore(&current->pi_lock, flags);
 496
 497         /*
 498          * Clear the pi_blocked_on variable and enqueue a possible
 499          * waiter into the pi_waiters list of the pending owner. This
 500          * prevents that in case the pending owner gets unboosted a
 501          * waiter with higher priority than pending-owner->normal_prio
 502          * is blocked on the unboosted (pending) owner.
 503          */
 504         spin_lock_irqsave(&pendowner->pi_lock, flags);
 505
 506         WARN_ON(!pendowner->pi_blocked_on);
 507         WARN_ON(pendowner->pi_blocked_on != waiter);
 508         WARN_ON(pendowner->pi_blocked_on->lock != lock);
 509
 510         pendowner->pi_blocked_on = NULL;
 511
 512         if (rt_mutex_has_waiters(lock)) {
 513                 struct rt_mutex_waiter *next;
 514
 515                 next = rt_mutex_top_waiter(lock);
 516                 plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
 517         }
 518         spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 519
 520         wake_up_process(pendowner);
 521 }
 522
 523 /*
 524  * Remove a waiter from a lock
 525  *
 526  * Must be called with lock->wait_lock held
 527  */
 528 static void remove_waiter(struct rt_mutex *lock,
 529                           struct rt_mutex_waiter *waiter  __IP_DECL__)
 530 {
 531         int first = (waiter == rt_mutex_top_waiter(lock));
 532         int boost = 0;
 533         task_t *owner = rt_mutex_owner(lock);
 534         unsigned long flags;
 535
 536         spin_lock_irqsave(&current->pi_lock, flags);
 537         plist_del(&waiter->list_entry, &lock->wait_list);
 538         waiter->task = NULL;
 539         current->pi_blocked_on = NULL;
 540         spin_unlock_irqrestore(&current->pi_lock, flags);
 541
 542         if (first && owner != current) {
 543
 544                 spin_lock_irqsave(&owner->pi_lock, flags);
 545
 546                 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
 547
 548                 if (rt_mutex_has_waiters(lock)) {
 549                         struct rt_mutex_waiter *next;
 550
 551                         next = rt_mutex_top_waiter(lock);
 552                         plist_add(&next->pi_list_entry, &owner->pi_waiters);
 553                 }
 554                 __rt_mutex_adjust_prio(owner);
 555
 556                 if (owner->pi_blocked_on) {
 557                         boost = 1;
 558                         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 559                         get_task_struct(owner);
 560                 }
 561                 spin_unlock_irqrestore(&owner->pi_lock, flags);
 562         }
 563
 564         WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 565
 566         if (!boost)
 567                 return;
 568
 569         spin_unlock(&lock->wait_lock);
 570
 571         rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current __IP__);
 572
 573         spin_lock(&lock->wait_lock);
 574 }
 575
 576 /*
 577  * Recheck the pi chain, in case we got a priority setting
 578  *
 579  * Called from sched_setscheduler
 580  */
 581 void rt_mutex_adjust_pi(struct task_struct *task)
 582 {
 583         struct rt_mutex_waiter *waiter;
 584         unsigned long flags;
 585
 586         spin_lock_irqsave(&task->pi_lock, flags);
 587
 588         waiter = task->pi_blocked_on;
 589         if (!waiter || waiter->list_entry.prio == task->prio) {
 590                 spin_unlock_irqrestore(&task->pi_lock, flags);
 591                 return;
 592         }
 593
 594         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 595         get_task_struct(task);
 596         spin_unlock_irqrestore(&task->pi_lock, flags);
 597
 598         rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task __RET_IP__);
 599 }
 600
 601 /*
 602  * Slow path lock function:
 603  */
 604 static int __sched
 605 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 606                   struct hrtimer_sleeper *timeout,
 607                   int detect_deadlock __IP_DECL__)
 608 {
 609         struct rt_mutex_waiter waiter;
 610         int ret = 0;
 611
 612         debug_rt_mutex_init_waiter(&waiter);
 613         waiter.task = NULL;
 614
 615         spin_lock(&lock->wait_lock);
 616
 617         /* Try to acquire the lock again: */
 618         if (try_to_take_rt_mutex(lock __IP__)) {
 619                 spin_unlock(&lock->wait_lock);
 620                 return 0;
 621         }
 622
 623         set_current_state(state);
 624
 625         /* Setup the timer, when timeout != NULL */
 626         if (unlikely(timeout))
 627                 hrtimer_start(&timeout->timer, timeout->timer.expires,
 628                               HRTIMER_ABS);
 629
 630         for (;;) {
 631                 /* Try to acquire the lock: */
 632                 if (try_to_take_rt_mutex(lock __IP__))
 633                         break;
 634
 635                 /*
 636                  * TASK_INTERRUPTIBLE checks for signals and
 637                  * timeout. Ignored otherwise.
 638                  */
 639                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
 640                         /* Signal pending? */
 641                         if (signal_pending(current))
 642                                 ret = -EINTR;
 643                         if (timeout && !timeout->task)
 644                                 ret = -ETIMEDOUT;
 645                         if (ret)
 646                                 break;
 647                 }
 648
 649                 /*
 650                  * waiter.task is NULL the first time we come here and
 651                  * when we have been woken up by the previous owner
 652                  * but the lock got stolen by a higher prio task.
 653                  */
 654                 if (!waiter.task) {
 655                         ret = task_blocks_on_rt_mutex(lock, &waiter,
 656                                                       detect_deadlock __IP__);
 657                         /*
 658                          * If we got woken up by the owner then start loop
 659                          * all over without going into schedule to try
 660                          * to get the lock now:
 661                          */
 662                         if (unlikely(!waiter.task))
 663                                 continue;
 664
 665                         if (unlikely(ret))
 666                                 break;
 667                 }
 668
 669                 spin_unlock(&lock->wait_lock);
 670
 671                 debug_rt_mutex_print_deadlock(&waiter);
 672
 673                 if (waiter.task)
 674                         schedule_rt_mutex(lock);
 675
 676                 spin_lock(&lock->wait_lock);
 677                 set_current_state(state);
 678         }
 679
 680         set_current_state(TASK_RUNNING);
 681
 682         if (unlikely(waiter.task))
 683                 remove_waiter(lock, &waiter __IP__);
 684
 685         /*
 686          * try_to_take_rt_mutex() sets the waiter bit
 687          * unconditionally. We might have to fix that up.
 688          */
 689         fixup_rt_mutex_waiters(lock);
 690
 691         spin_unlock(&lock->wait_lock);
 692
 693         /* Remove pending timer: */
 694         if (unlikely(timeout))
 695                 hrtimer_cancel(&timeout->timer);
 696
 697         /*
 698          * Readjust priority, when we did not get the lock. We might
 699          * have been the pending owner and boosted. Since we did not
 700          * take the lock, the PI boost has to go.
 701          */
 702         if (unlikely(ret))
 703                 rt_mutex_adjust_prio(current);
 704
 705         debug_rt_mutex_free_waiter(&waiter);
 706
 707         return ret;
 708 }
 709
 710 /*
 711  * Slow path try-lock function:
 712  */
 713 static inline int
 714 rt_mutex_slowtrylock(struct rt_mutex *lock __IP_DECL__)
 715 {
 716         int ret = 0;
 717
 718         spin_lock(&lock->wait_lock);
 719
 720         if (likely(rt_mutex_owner(lock) != current)) {
 721
 722                 ret = try_to_take_rt_mutex(lock __IP__);
 723                 /*
 724                  * try_to_take_rt_mutex() sets the lock waiters
 725                  * bit unconditionally. Clean this up.
 726                  */
 727                 fixup_rt_mutex_waiters(lock);
 728         }
 729
 730         spin_unlock(&lock->wait_lock);
 731
 732         return ret;
 733 }
 734
 735 /*
 736  * Slow path to release a rt-mutex:
 737  */
 738 static void __sched
 739 rt_mutex_slowunlock(struct rt_mutex *lock)
 740 {
 741         spin_lock(&lock->wait_lock);
 742
 743         debug_rt_mutex_unlock(lock);
 744
 745         rt_mutex_deadlock_account_unlock(current);
 746
 747         if (!rt_mutex_has_waiters(lock)) {
 748                 lock->owner = NULL;
 749                 spin_unlock(&lock->wait_lock);
 750                 return;
 751         }
 752
 753         wakeup_next_waiter(lock);
 754
 755         spin_unlock(&lock->wait_lock);
 756
 757         /* Undo pi boosting if necessary: */
 758         rt_mutex_adjust_prio(current);
 759 }
 760
 761 /*
 762  * debug aware fast / slowpath lock,trylock,unlock
 763  *
 764  * The atomic acquire/release ops are compiled away, when either the
 765  * architecture does not support cmpxchg or when debugging is enabled.
 766  */
 767 static inline int
 768 rt_mutex_fastlock(struct rt_mutex *lock, int state,
 769                   int detect_deadlock,
 770                   int (*slowfn)(struct rt_mutex *lock, int state,
 771                                 struct hrtimer_sleeper *timeout,
 772                                 int detect_deadlock __IP_DECL__))
 773 {
 774         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 775                 rt_mutex_deadlock_account_lock(lock, current);
 776                 return 0;
 777         } else
 778                 return slowfn(lock, state, NULL, detect_deadlock __RET_IP__);
 779 }
 780
 781 static inline int
 782 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 783                         struct hrtimer_sleeper *timeout, int detect_deadlock,
 784                         int (*slowfn)(struct rt_mutex *lock, int state,
 785                                       struct hrtimer_sleeper *timeout,
 786                                       int detect_deadlock __IP_DECL__))
 787 {
 788         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 789                 rt_mutex_deadlock_account_lock(lock, current);
 790                 return 0;
 791         } else
 792                 return slowfn(lock, state, timeout, detect_deadlock __RET_IP__);
 793 }
 794
 795 static inline int
 796 rt_mutex_fasttrylock(struct rt_mutex *lock,
 797                      int (*slowfn)(struct rt_mutex *lock __IP_DECL__))
 798 {
 799         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 800                 rt_mutex_deadlock_account_lock(lock, current);
 801                 return 1;
 802         }
 803         return slowfn(lock __RET_IP__);
 804 }
 805
 806 static inline void
 807 rt_mutex_fastunlock(struct rt_mutex *lock,
 808                     void (*slowfn)(struct rt_mutex *lock))
 809 {
 810         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
 811                 rt_mutex_deadlock_account_unlock(current);
 812         else
 813                 slowfn(lock);
 814 }
 815
 816 /**
 817  * rt_mutex_lock - lock a rt_mutex
 818  *
 819  * @lock: the rt_mutex to be locked
 820  */
 821 void __sched rt_mutex_lock(struct rt_mutex *lock)
 822 {
 823         might_sleep();
 824
 825         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
 826 }
 827 EXPORT_SYMBOL_GPL(rt_mutex_lock);
 828
 829 /**
 830  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
 831  *
 832  * @lock:               the rt_mutex to be locked
 833  * @detect_deadlock:    deadlock detection on/off
 834  *
 835  * Returns:
 836  *  0           on success
 837  * -EINTR       when interrupted by a signal
 838  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 839  */
 840 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 841                                                  int detect_deadlock)
 842 {
 843         might_sleep();
 844
 845         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
 846                                  detect_deadlock, rt_mutex_slowlock);
 847 }
 848 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 849
 850 /**
 851  * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
 852  *                                     the timeout structure is provided
 853  *                                     by the caller
 854  *
 855  * @lock:               the rt_mutex to be locked
 856  * @timeout:            timeout structure or NULL (no timeout)
 857  * @detect_deadlock:    deadlock detection on/off
 858  *
 859  * Returns:
 860  *  0           on success
 861  * -EINTR       when interrupted by a signal
 862  * -ETIMEOUT    when the timeout expired
 863  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 864  */
 865 int
 866 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
 867                     int detect_deadlock)
 868 {
 869         might_sleep();
 870
 871         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
 872                                        detect_deadlock, rt_mutex_slowlock);
 873 }
 874 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
 875
 876 /**
 877  * rt_mutex_trylock - try to lock a rt_mutex
 878  *
 879  * @lock:       the rt_mutex to be locked
 880  *
 881  * Returns 1 on success and 0 on contention
 882  */
 883 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 884 {
 885         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 886 }
 887 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 888
 889 /**
 890  * rt_mutex_unlock - unlock a rt_mutex
 891  *
 892  * @lock: the rt_mutex to be unlocked
 893  */
 894 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 895 {
 896         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 897 }
 898 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 899
 900 /***
 901  * rt_mutex_destroy - mark a mutex unusable
 902  * @lock: the mutex to be destroyed
 903  *
 904  * This function marks the mutex uninitialized, and any subsequent
 905  * use of the mutex is forbidden. The mutex must not be locked when
 906  * this function is called.
 907  */
 908 void rt_mutex_destroy(struct rt_mutex *lock)
 909 {
 910         WARN_ON(rt_mutex_is_locked(lock));
 911 #ifdef CONFIG_DEBUG_RT_MUTEXES
 912         lock->magic = NULL;
 913 #endif
 914 }
 915
 916 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 917
 918 /**
 919  * __rt_mutex_init - initialize the rt lock
 920  *
 921  * @lock: the rt lock to be initialized
 922  *
 923  * Initialize the rt lock to unlocked state.
 924  *
 925  * Initializing of a locked rt lock is not allowed
 926  */
 927 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 928 {
 929         lock->owner = NULL;
 930         spin_lock_init(&lock->wait_lock);
 931         plist_head_init(&lock->wait_list, &lock->wait_lock);
 932
 933         debug_rt_mutex_init(lock, name);
 934 }
 935 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 936
 937 /**
 938  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 939  *                              proxy owner
 940  *
 941  * @lock:       the rt_mutex to be locked
 942  * @proxy_owner:the task to set as owner
 943  *
 944  * No locking. Caller has to do serializing itself
 945  * Special API call for PI-futex support
 946  */
 947 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 948                                 struct task_struct *proxy_owner)
 949 {
 950         __rt_mutex_init(lock, NULL);
 951         debug_rt_mutex_proxy_lock(lock, proxy_owner __RET_IP__);
 952         rt_mutex_set_owner(lock, proxy_owner, 0);
 953         rt_mutex_deadlock_account_lock(lock, proxy_owner);
 954 }
 955
 956 /**
 957  * rt_mutex_proxy_unlock - release a lock on behalf of owner
 958  *
 959  * @lock:       the rt_mutex to be locked
 960  *
 961  * No locking. Caller has to do serializing itself
 962  * Special API call for PI-futex support
 963  */
 964 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
 965                            struct task_struct *proxy_owner)
 966 {
 967         debug_rt_mutex_proxy_unlock(lock);
 968         rt_mutex_set_owner(lock, NULL, 0);
 969         rt_mutex_deadlock_account_unlock(proxy_owner);
 970 }
 971
 972 /**
 973  * rt_mutex_next_owner - return the next owner of the lock
 974  *
 975  * @lock: the rt lock query
 976  *
 977  * Returns the next owner of the lock or NULL
 978  *
 979  * Caller has to serialize against other accessors to the lock
 980  * itself.
 981  *
 982  * Special API call for PI-futex support
 983  */
 984 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
 985 {
 986         if (!rt_mutex_has_waiters(lock))
 987                 return NULL;
 988
 989         return rt_mutex_top_waiter(lock)->task;
 990 }