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