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 /*
  21  * lock->owner state tracking:
  22  *
  23  * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
  24  * are used to keep track of the "owner is pending" and "lock has
  25  * waiters" state.
  26  *
  27  * owner        bit1    bit0
  28  * NULL         0       0       lock is free (fast acquire possible)
  29  * NULL         0       1       invalid state
  30  * NULL         1       0       Transitional State*
  31  * NULL         1       1       invalid state
  32  * taskpointer  0       0       lock is held (fast release possible)
  33  * taskpointer  0       1       task is pending owner
  34  * taskpointer  1       0       lock is held and has waiters
  35  * taskpointer  1       1       task is pending owner and lock has more waiters
  36  *
  37  * Pending ownership is assigned to the top (highest priority)
  38  * waiter of the lock, when the lock is released. The thread is woken
  39  * up and can now take the lock. Until the lock is taken (bit 0
  40  * cleared) a competing higher priority thread can steal the lock
  41  * which puts the woken up thread back on the waiters list.
  42  *
  43  * The fast atomic compare exchange based acquire and release is only
  44  * possible when bit 0 and 1 of lock->owner are 0.
  45  *
  46  * (*) There's a small time where the owner can be NULL and the
  47  * "lock has waiters" bit is set.  This can happen when grabbing the lock.
  48  * To prevent a cmpxchg of the owner releasing the lock, we need to set this
  49  * bit before looking at the lock, hence the reason this is a transitional
  50  * state.
  51  */
  52
  53 static void
  54 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
  55                    unsigned long mask)
  56 {
  57         unsigned long val = (unsigned long)owner | mask;
  58
  59         if (rt_mutex_has_waiters(lock))
  60                 val |= RT_MUTEX_HAS_WAITERS;
  61
  62         lock->owner = (struct task_struct *)val;
  63 }
  64
  65 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  66 {
  67         lock->owner = (struct task_struct *)
  68                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  69 }
  70
  71 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  72 {
  73         if (!rt_mutex_has_waiters(lock))
  74                 clear_rt_mutex_waiters(lock);
  75 }
  76
  77 /*
  78  * We can speed up the acquire/release, if the architecture
  79  * supports cmpxchg and if there's no debugging state to be set up
  80  */
  81 #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  82 # define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
  83 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  84 {
  85         unsigned long owner, *p = (unsigned long *) &lock->owner;
  86
  87         do {
  88                 owner = *p;
  89         } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  90 }
  91 #else
  92 # define rt_mutex_cmpxchg(l,c,n)        (0)
  93 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  94 {
  95         lock->owner = (struct task_struct *)
  96                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
  97 }
  98 #endif
  99
 100 /*
 101  * Calculate task priority from the waiter list priority
 102  *
 103  * Return task->normal_prio when the waiter list is empty or when
 104  * the waiter is not allowed to do priority boosting
 105  */
 106 int rt_mutex_getprio(struct task_struct *task)
 107 {
 108         if (likely(!task_has_pi_waiters(task)))
 109                 return task->normal_prio;
 110
 111         return min(task_top_pi_waiter(task)->pi_list_entry.prio,
 112                    task->normal_prio);
 113 }
 114
 115 /*
 116  * Adjust the priority of a task, after its pi_waiters got modified.
 117  *
 118  * This can be both boosting and unboosting. task->pi_lock must be held.
 119  */
 120 static void __rt_mutex_adjust_prio(struct task_struct *task)
 121 {
 122         int prio = rt_mutex_getprio(task);
 123
 124         if (task->prio != prio)
 125                 rt_mutex_setprio(task, prio);
 126 }
 127
 128 /*
 129  * Adjust task priority (undo boosting). Called from the exit path of
 130  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 131  *
 132  * (Note: We do this outside of the protection of lock->wait_lock to
 133  * allow the lock to be taken while or before we readjust the priority
 134  * of task. We do not use the spin_xx_mutex() variants here as we are
 135  * outside of the debug path.)
 136  */
 137 static void rt_mutex_adjust_prio(struct task_struct *task)
 138 {
 139         unsigned long flags;
 140
 141         raw_spin_lock_irqsave(&task->pi_lock, flags);
 142         __rt_mutex_adjust_prio(task);
 143         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 144 }
 145
 146 /*
 147  * Max number of times we'll walk the boosting chain:
 148  */
 149 int max_lock_depth = 1024;
 150
 151 /*
 152  * Adjust the priority chain. Also used for deadlock detection.
 153  * Decreases task's usage by one - may thus free the task.
 154  * Returns 0 or -EDEADLK.
 155  */
 156 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 157                                       int deadlock_detect,
 158                                       struct rt_mutex *orig_lock,
 159                                       struct rt_mutex_waiter *orig_waiter,
 160                                       struct task_struct *top_task)
 161 {
 162         struct rt_mutex *lock;
 163         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 164         int detect_deadlock, ret = 0, depth = 0;
 165         unsigned long flags;
 166
 167         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 168                                                          deadlock_detect);
 169
 170         /*
 171          * The (de)boosting is a step by step approach with a lot of
 172          * pitfalls. We want this to be preemptible and we want hold a
 173          * maximum of two locks per step. So we have to check
 174          * carefully whether things change under us.
 175          */
 176  again:
 177         if (++depth > max_lock_depth) {
 178                 static int prev_max;
 179
 180                 /*
 181                  * Print this only once. If the admin changes the limit,
 182                  * print a new message when reaching the limit again.
 183                  */
 184                 if (prev_max != max_lock_depth) {
 185                         prev_max = max_lock_depth;
 186                         printk(KERN_WARNING "Maximum lock depth %d reached "
 187                                "task: %s (%d)\n", max_lock_depth,
 188                                top_task->comm, task_pid_nr(top_task));
 189                 }
 190                 put_task_struct(task);
 191
 192                 return deadlock_detect ? -EDEADLK : 0;
 193         }
 194  retry:
 195         /*
 196          * Task can not go away as we did a get_task() before !
 197          */
 198         raw_spin_lock_irqsave(&task->pi_lock, flags);
 199
 200         waiter = task->pi_blocked_on;
 201         /*
 202          * Check whether the end of the boosting chain has been
 203          * reached or the state of the chain has changed while we
 204          * dropped the locks.
 205          */
 206         if (!waiter || !waiter->task)
 207                 goto out_unlock_pi;
 208
 209         /*
 210          * Check the orig_waiter state. After we dropped the locks,
 211          * the previous owner of the lock might have released the lock
 212          * and made us the pending owner:
 213          */
 214         if (orig_waiter && !orig_waiter->task)
 215                 goto out_unlock_pi;
 216
 217         /*
 218          * Drop out, when the task has no waiters. Note,
 219          * top_waiter can be NULL, when we are in the deboosting
 220          * mode!
 221          */
 222         if (top_waiter && (!task_has_pi_waiters(task) ||
 223                            top_waiter != task_top_pi_waiter(task)))
 224                 goto out_unlock_pi;
 225
 226         /*
 227          * When deadlock detection is off then we check, if further
 228          * priority adjustment is necessary.
 229          */
 230         if (!detect_deadlock && waiter->list_entry.prio == task->prio)
 231                 goto out_unlock_pi;
 232
 233         lock = waiter->lock;
 234         if (!raw_spin_trylock(&lock->wait_lock)) {
 235                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 236                 cpu_relax();
 237                 goto retry;
 238         }
 239
 240         /* Deadlock detection */
 241         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 242                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 243                 raw_spin_unlock(&lock->wait_lock);
 244                 ret = deadlock_detect ? -EDEADLK : 0;
 245                 goto out_unlock_pi;
 246         }
 247
 248         top_waiter = rt_mutex_top_waiter(lock);
 249
 250         /* Requeue the waiter */
 251         plist_del(&waiter->list_entry, &lock->wait_list);
 252         waiter->list_entry.prio = task->prio;
 253         plist_add(&waiter->list_entry, &lock->wait_list);
 254
 255         /* Release the task */
 256         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 257         put_task_struct(task);
 258
 259         /* Grab the next task */
 260         task = rt_mutex_owner(lock);
 261         get_task_struct(task);
 262         raw_spin_lock_irqsave(&task->pi_lock, flags);
 263
 264         if (waiter == rt_mutex_top_waiter(lock)) {
 265                 /* Boost the owner */
 266                 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
 267                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 268                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 269                 __rt_mutex_adjust_prio(task);
 270
 271         } else if (top_waiter == waiter) {
 272                 /* Deboost the owner */
 273                 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
 274                 waiter = rt_mutex_top_waiter(lock);
 275                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
 276                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 277                 __rt_mutex_adjust_prio(task);
 278         }
 279
 280         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 281
 282         top_waiter = rt_mutex_top_waiter(lock);
 283         raw_spin_unlock(&lock->wait_lock);
 284
 285         if (!detect_deadlock && waiter != top_waiter)
 286                 goto out_put_task;
 287
 288         goto again;
 289
 290  out_unlock_pi:
 291         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 292  out_put_task:
 293         put_task_struct(task);
 294
 295         return ret;
 296 }
 297
 298 /*
 299  * Optimization: check if we can steal the lock from the
 300  * assigned pending owner [which might not have taken the
 301  * lock yet]:
 302  */
 303 static inline int try_to_steal_lock(struct rt_mutex *lock,
 304                                     struct task_struct *task)
 305 {
 306         struct task_struct *pendowner = rt_mutex_owner(lock);
 307         struct rt_mutex_waiter *next;
 308         unsigned long flags;
 309
 310         if (!rt_mutex_owner_pending(lock))
 311                 return 0;
 312
 313         if (pendowner == task)
 314                 return 1;
 315
 316         raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
 317         if (task->prio >= pendowner->prio) {
 318                 raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 319                 return 0;
 320         }
 321
 322         /*
 323          * Check if a waiter is enqueued on the pending owners
 324          * pi_waiters list. Remove it and readjust pending owners
 325          * priority.
 326          */
 327         if (likely(!rt_mutex_has_waiters(lock))) {
 328                 raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 329                 return 1;
 330         }
 331
 332         /* No chain handling, pending owner is not blocked on anything: */
 333         next = rt_mutex_top_waiter(lock);
 334         plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
 335         __rt_mutex_adjust_prio(pendowner);
 336         raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 337
 338         /*
 339          * We are going to steal the lock and a waiter was
 340          * enqueued on the pending owners pi_waiters queue. So
 341          * we have to enqueue this waiter into
 342          * task->pi_waiters list. This covers the case,
 343          * where task is boosted because it holds another
 344          * lock and gets unboosted because the booster is
 345          * interrupted, so we would delay a waiter with higher
 346          * priority as task->normal_prio.
 347          *
 348          * Note: in the rare case of a SCHED_OTHER task changing
 349          * its priority and thus stealing the lock, next->task
 350          * might be task:
 351          */
 352         if (likely(next->task != task)) {
 353                 raw_spin_lock_irqsave(&task->pi_lock, flags);
 354                 plist_add(&next->pi_list_entry, &task->pi_waiters);
 355                 __rt_mutex_adjust_prio(task);
 356                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 357         }
 358         return 1;
 359 }
 360
 361 /*
 362  * Try to take an rt-mutex
 363  *
 364  * This fails
 365  * - when the lock has a real owner
 366  * - when a different pending owner exists and has higher priority than current
 367  *
 368  * Must be called with lock->wait_lock held.
 369  */
 370 static int try_to_take_rt_mutex(struct rt_mutex *lock)
 371 {
 372         /*
 373          * We have to be careful here if the atomic speedups are
 374          * enabled, such that, when
 375          *  - no other waiter is on the lock
 376          *  - the lock has been released since we did the cmpxchg
 377          * the lock can be released or taken while we are doing the
 378          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 379          *
 380          * The atomic acquire/release aware variant of
 381          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 382          * the WAITERS bit, the atomic release / acquire can not
 383          * happen anymore and lock->wait_lock protects us from the
 384          * non-atomic case.
 385          *
 386          * Note, that this might set lock->owner =
 387          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 388          * any more. This is fixed up when we take the ownership.
 389          * This is the transitional state explained at the top of this file.
 390          */
 391         mark_rt_mutex_waiters(lock);
 392
 393         if (rt_mutex_owner(lock) && !try_to_steal_lock(lock, current))
 394                 return 0;
 395
 396         /* We got the lock. */
 397         debug_rt_mutex_lock(lock);
 398
 399         rt_mutex_set_owner(lock, current, 0);
 400
 401         rt_mutex_deadlock_account_lock(lock, current);
 402
 403         return 1;
 404 }
 405
 406 /*
 407  * Task blocks on lock.
 408  *
 409  * Prepare waiter and propagate pi chain
 410  *
 411  * This must be called with lock->wait_lock held.
 412  */
 413 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 414                                    struct rt_mutex_waiter *waiter,
 415                                    struct task_struct *task,
 416                                    int detect_deadlock)
 417 {
 418         struct task_struct *owner = rt_mutex_owner(lock);
 419         struct rt_mutex_waiter *top_waiter = waiter;
 420         unsigned long flags;
 421         int chain_walk = 0, res;
 422
 423         raw_spin_lock_irqsave(&task->pi_lock, flags);
 424         __rt_mutex_adjust_prio(task);
 425         waiter->task = task;
 426         waiter->lock = lock;
 427         plist_node_init(&waiter->list_entry, task->prio);
 428         plist_node_init(&waiter->pi_list_entry, task->prio);
 429
 430         /* Get the top priority waiter on the lock */
 431         if (rt_mutex_has_waiters(lock))
 432                 top_waiter = rt_mutex_top_waiter(lock);
 433         plist_add(&waiter->list_entry, &lock->wait_list);
 434
 435         task->pi_blocked_on = waiter;
 436
 437         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 438
 439         if (waiter == rt_mutex_top_waiter(lock)) {
 440                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 441                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
 442                 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
 443
 444                 __rt_mutex_adjust_prio(owner);
 445                 if (owner->pi_blocked_on)
 446                         chain_walk = 1;
 447                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 448         }
 449         else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
 450                 chain_walk = 1;
 451
 452         if (!chain_walk)
 453                 return 0;
 454
 455         /*
 456          * The owner can't disappear while holding a lock,
 457          * so the owner struct is protected by wait_lock.
 458          * Gets dropped in rt_mutex_adjust_prio_chain()!
 459          */
 460         get_task_struct(owner);
 461
 462         raw_spin_unlock(&lock->wait_lock);
 463
 464         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
 465                                          task);
 466
 467         raw_spin_lock(&lock->wait_lock);
 468
 469         return res;
 470 }
 471
 472 /*
 473  * Wake up the next waiter on the lock.
 474  *
 475  * Remove the top waiter from the current tasks waiter list and from
 476  * the lock waiter list. Set it as pending owner. Then wake it up.
 477  *
 478  * Called with lock->wait_lock held.
 479  */
 480 static void wakeup_next_waiter(struct rt_mutex *lock)
 481 {
 482         struct rt_mutex_waiter *waiter;
 483         struct task_struct *pendowner;
 484         unsigned long flags;
 485
 486         raw_spin_lock_irqsave(&current->pi_lock, flags);
 487
 488         waiter = rt_mutex_top_waiter(lock);
 489         plist_del(&waiter->list_entry, &lock->wait_list);
 490
 491         /*
 492          * Remove it from current->pi_waiters. We do not adjust a
 493          * possible priority boost right now. We execute wakeup in the
 494          * boosted mode and go back to normal after releasing
 495          * lock->wait_lock.
 496          */
 497         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
 498         pendowner = waiter->task;
 499         waiter->task = NULL;
 500
 501         rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
 502
 503         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 504
 505         /*
 506          * Clear the pi_blocked_on variable and enqueue a possible
 507          * waiter into the pi_waiters list of the pending owner. This
 508          * prevents that in case the pending owner gets unboosted a
 509          * waiter with higher priority than pending-owner->normal_prio
 510          * is blocked on the unboosted (pending) owner.
 511          */
 512         raw_spin_lock_irqsave(&pendowner->pi_lock, flags);
 513
 514         WARN_ON(!pendowner->pi_blocked_on);
 515         WARN_ON(pendowner->pi_blocked_on != waiter);
 516         WARN_ON(pendowner->pi_blocked_on->lock != lock);
 517
 518         pendowner->pi_blocked_on = NULL;
 519
 520         if (rt_mutex_has_waiters(lock)) {
 521                 struct rt_mutex_waiter *next;
 522
 523                 next = rt_mutex_top_waiter(lock);
 524                 plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
 525         }
 526         raw_spin_unlock_irqrestore(&pendowner->pi_lock, flags);
 527
 528         wake_up_process(pendowner);
 529 }
 530
 531 /*
 532  * Remove a waiter from a lock
 533  *
 534  * Must be called with lock->wait_lock held
 535  */
 536 static void remove_waiter(struct rt_mutex *lock,
 537                           struct rt_mutex_waiter *waiter)
 538 {
 539         int first = (waiter == rt_mutex_top_waiter(lock));
 540         struct task_struct *owner = rt_mutex_owner(lock);
 541         unsigned long flags;
 542         int chain_walk = 0;
 543
 544         raw_spin_lock_irqsave(&current->pi_lock, flags);
 545         plist_del(&waiter->list_entry, &lock->wait_list);
 546         waiter->task = NULL;
 547         current->pi_blocked_on = NULL;
 548         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 549
 550         if (first && owner != current) {
 551
 552                 raw_spin_lock_irqsave(&owner->pi_lock, flags);
 553
 554                 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
 555
 556                 if (rt_mutex_has_waiters(lock)) {
 557                         struct rt_mutex_waiter *next;
 558
 559                         next = rt_mutex_top_waiter(lock);
 560                         plist_add(&next->pi_list_entry, &owner->pi_waiters);
 561                 }
 562                 __rt_mutex_adjust_prio(owner);
 563
 564                 if (owner->pi_blocked_on)
 565                         chain_walk = 1;
 566
 567                 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 568         }
 569
 570         WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 571
 572         if (!chain_walk)
 573                 return;
 574
 575         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 576         get_task_struct(owner);
 577
 578         raw_spin_unlock(&lock->wait_lock);
 579
 580         rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
 581
 582         raw_spin_lock(&lock->wait_lock);
 583 }
 584
 585 /*
 586  * Recheck the pi chain, in case we got a priority setting
 587  *
 588  * Called from sched_setscheduler
 589  */
 590 void rt_mutex_adjust_pi(struct task_struct *task)
 591 {
 592         struct rt_mutex_waiter *waiter;
 593         unsigned long flags;
 594
 595         raw_spin_lock_irqsave(&task->pi_lock, flags);
 596
 597         waiter = task->pi_blocked_on;
 598         if (!waiter || waiter->list_entry.prio == task->prio) {
 599                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 600                 return;
 601         }
 602
 603         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 604
 605         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 606         get_task_struct(task);
 607         rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
 608 }
 609
 610 /**
 611  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 612  * @lock:                the rt_mutex to take
 613  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 614  *                       or TASK_UNINTERRUPTIBLE)
 615  * @timeout:             the pre-initialized and started timer, or NULL for none
 616  * @waiter:              the pre-initialized rt_mutex_waiter
 617  * @detect_deadlock:     passed to task_blocks_on_rt_mutex
 618  *
 619  * lock->wait_lock must be held by the caller.
 620  */
 621 static int __sched
 622 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
 623                     struct hrtimer_sleeper *timeout,
 624                     struct rt_mutex_waiter *waiter,
 625                     int detect_deadlock)
 626 {
 627         int ret = 0;
 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, current,
 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                                 /*
 663                                  * Reset the return value. We might
 664                                  * have returned with -EDEADLK and the
 665                                  * owner released the lock while we
 666                                  * were walking the pi chain.
 667                                  */
 668                                 ret = 0;
 669                                 continue;
 670                         }
 671                         if (unlikely(ret))
 672                                 break;
 673                 }
 674
 675                 raw_spin_unlock(&lock->wait_lock);
 676
 677                 debug_rt_mutex_print_deadlock(waiter);
 678
 679                 if (waiter->task)
 680                         schedule_rt_mutex(lock);
 681
 682                 raw_spin_lock(&lock->wait_lock);
 683                 set_current_state(state);
 684         }
 685
 686         return ret;
 687 }
 688
 689 /*
 690  * Slow path lock function:
 691  */
 692 static int __sched
 693 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 694                   struct hrtimer_sleeper *timeout,
 695                   int detect_deadlock)
 696 {
 697         struct rt_mutex_waiter waiter;
 698         int ret = 0;
 699
 700         debug_rt_mutex_init_waiter(&waiter);
 701         waiter.task = NULL;
 702
 703         raw_spin_lock(&lock->wait_lock);
 704
 705         /* Try to acquire the lock again: */
 706         if (try_to_take_rt_mutex(lock)) {
 707                 raw_spin_unlock(&lock->wait_lock);
 708                 return 0;
 709         }
 710
 711         set_current_state(state);
 712
 713         /* Setup the timer, when timeout != NULL */
 714         if (unlikely(timeout)) {
 715                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 716                 if (!hrtimer_active(&timeout->timer))
 717                         timeout->task = NULL;
 718         }
 719
 720         ret = __rt_mutex_slowlock(lock, state, timeout, &waiter,
 721                                   detect_deadlock);
 722
 723         set_current_state(TASK_RUNNING);
 724
 725         if (unlikely(waiter.task))
 726                 remove_waiter(lock, &waiter);
 727
 728         /*
 729          * try_to_take_rt_mutex() sets the waiter bit
 730          * unconditionally. We might have to fix that up.
 731          */
 732         fixup_rt_mutex_waiters(lock);
 733
 734         raw_spin_unlock(&lock->wait_lock);
 735
 736         /* Remove pending timer: */
 737         if (unlikely(timeout))
 738                 hrtimer_cancel(&timeout->timer);
 739
 740         /*
 741          * Readjust priority, when we did not get the lock. We might
 742          * have been the pending owner and boosted. Since we did not
 743          * take the lock, the PI boost has to go.
 744          */
 745         if (unlikely(ret))
 746                 rt_mutex_adjust_prio(current);
 747
 748         debug_rt_mutex_free_waiter(&waiter);
 749
 750         return ret;
 751 }
 752
 753 /*
 754  * Slow path try-lock function:
 755  */
 756 static inline int
 757 rt_mutex_slowtrylock(struct rt_mutex *lock)
 758 {
 759         int ret = 0;
 760
 761         raw_spin_lock(&lock->wait_lock);
 762
 763         if (likely(rt_mutex_owner(lock) != current)) {
 764
 765                 ret = try_to_take_rt_mutex(lock);
 766                 /*
 767                  * try_to_take_rt_mutex() sets the lock waiters
 768                  * bit unconditionally. Clean this up.
 769                  */
 770                 fixup_rt_mutex_waiters(lock);
 771         }
 772
 773         raw_spin_unlock(&lock->wait_lock);
 774
 775         return ret;
 776 }
 777
 778 /*
 779  * Slow path to release a rt-mutex:
 780  */
 781 static void __sched
 782 rt_mutex_slowunlock(struct rt_mutex *lock)
 783 {
 784         raw_spin_lock(&lock->wait_lock);
 785
 786         debug_rt_mutex_unlock(lock);
 787
 788         rt_mutex_deadlock_account_unlock(current);
 789
 790         if (!rt_mutex_has_waiters(lock)) {
 791                 lock->owner = NULL;
 792                 raw_spin_unlock(&lock->wait_lock);
 793                 return;
 794         }
 795
 796         wakeup_next_waiter(lock);
 797
 798         raw_spin_unlock(&lock->wait_lock);
 799
 800         /* Undo pi boosting if necessary: */
 801         rt_mutex_adjust_prio(current);
 802 }
 803
 804 /*
 805  * debug aware fast / slowpath lock,trylock,unlock
 806  *
 807  * The atomic acquire/release ops are compiled away, when either the
 808  * architecture does not support cmpxchg or when debugging is enabled.
 809  */
 810 static inline int
 811 rt_mutex_fastlock(struct rt_mutex *lock, int state,
 812                   int detect_deadlock,
 813                   int (*slowfn)(struct rt_mutex *lock, int state,
 814                                 struct hrtimer_sleeper *timeout,
 815                                 int detect_deadlock))
 816 {
 817         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 818                 rt_mutex_deadlock_account_lock(lock, current);
 819                 return 0;
 820         } else
 821                 return slowfn(lock, state, NULL, detect_deadlock);
 822 }
 823
 824 static inline int
 825 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 826                         struct hrtimer_sleeper *timeout, int detect_deadlock,
 827                         int (*slowfn)(struct rt_mutex *lock, int state,
 828                                       struct hrtimer_sleeper *timeout,
 829                                       int detect_deadlock))
 830 {
 831         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 832                 rt_mutex_deadlock_account_lock(lock, current);
 833                 return 0;
 834         } else
 835                 return slowfn(lock, state, timeout, detect_deadlock);
 836 }
 837
 838 static inline int
 839 rt_mutex_fasttrylock(struct rt_mutex *lock,
 840                      int (*slowfn)(struct rt_mutex *lock))
 841 {
 842         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 843                 rt_mutex_deadlock_account_lock(lock, current);
 844                 return 1;
 845         }
 846         return slowfn(lock);
 847 }
 848
 849 static inline void
 850 rt_mutex_fastunlock(struct rt_mutex *lock,
 851                     void (*slowfn)(struct rt_mutex *lock))
 852 {
 853         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
 854                 rt_mutex_deadlock_account_unlock(current);
 855         else
 856                 slowfn(lock);
 857 }
 858
 859 /**
 860  * rt_mutex_lock - lock a rt_mutex
 861  *
 862  * @lock: the rt_mutex to be locked
 863  */
 864 void __sched rt_mutex_lock(struct rt_mutex *lock)
 865 {
 866         might_sleep();
 867
 868         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
 869 }
 870 EXPORT_SYMBOL_GPL(rt_mutex_lock);
 871
 872 /**
 873  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
 874  *
 875  * @lock:               the rt_mutex to be locked
 876  * @detect_deadlock:    deadlock detection on/off
 877  *
 878  * Returns:
 879  *  0           on success
 880  * -EINTR       when interrupted by a signal
 881  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 882  */
 883 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 884                                                  int detect_deadlock)
 885 {
 886         might_sleep();
 887
 888         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
 889                                  detect_deadlock, rt_mutex_slowlock);
 890 }
 891 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 892
 893 /**
 894  * rt_mutex_timed_lock - lock a rt_mutex interruptible
 895  *                      the timeout structure is provided
 896  *                      by the caller
 897  *
 898  * @lock:               the rt_mutex to be locked
 899  * @timeout:            timeout structure or NULL (no timeout)
 900  * @detect_deadlock:    deadlock detection on/off
 901  *
 902  * Returns:
 903  *  0           on success
 904  * -EINTR       when interrupted by a signal
 905  * -ETIMEDOUT   when the timeout expired
 906  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 907  */
 908 int
 909 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
 910                     int detect_deadlock)
 911 {
 912         might_sleep();
 913
 914         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
 915                                        detect_deadlock, rt_mutex_slowlock);
 916 }
 917 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
 918
 919 /**
 920  * rt_mutex_trylock - try to lock a rt_mutex
 921  *
 922  * @lock:       the rt_mutex to be locked
 923  *
 924  * Returns 1 on success and 0 on contention
 925  */
 926 int __sched rt_mutex_trylock(struct rt_mutex *lock)
 927 {
 928         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 929 }
 930 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 931
 932 /**
 933  * rt_mutex_unlock - unlock a rt_mutex
 934  *
 935  * @lock: the rt_mutex to be unlocked
 936  */
 937 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 938 {
 939         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 940 }
 941 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 942
 943 /**
 944  * rt_mutex_destroy - mark a mutex unusable
 945  * @lock: the mutex to be destroyed
 946  *
 947  * This function marks the mutex uninitialized, and any subsequent
 948  * use of the mutex is forbidden. The mutex must not be locked when
 949  * this function is called.
 950  */
 951 void rt_mutex_destroy(struct rt_mutex *lock)
 952 {
 953         WARN_ON(rt_mutex_is_locked(lock));
 954 #ifdef CONFIG_DEBUG_RT_MUTEXES
 955         lock->magic = NULL;
 956 #endif
 957 }
 958
 959 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 960
 961 /**
 962  * __rt_mutex_init - initialize the rt lock
 963  *
 964  * @lock: the rt lock to be initialized
 965  *
 966  * Initialize the rt lock to unlocked state.
 967  *
 968  * Initializing of a locked rt lock is not allowed
 969  */
 970 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 971 {
 972         lock->owner = NULL;
 973         raw_spin_lock_init(&lock->wait_lock);
 974         plist_head_init_raw(&lock->wait_list, &lock->wait_lock);
 975
 976         debug_rt_mutex_init(lock, name);
 977 }
 978 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 979
 980 /**
 981  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 982  *                              proxy owner
 983  *
 984  * @lock:       the rt_mutex to be locked
 985  * @proxy_owner:the task to set as owner
 986  *
 987  * No locking. Caller has to do serializing itself
 988  * Special API call for PI-futex support
 989  */
 990 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 991                                 struct task_struct *proxy_owner)
 992 {
 993         __rt_mutex_init(lock, NULL);
 994         debug_rt_mutex_proxy_lock(lock, proxy_owner);
 995         rt_mutex_set_owner(lock, proxy_owner, 0);
 996         rt_mutex_deadlock_account_lock(lock, proxy_owner);
 997 }
 998
 999 /**
1000  * rt_mutex_proxy_unlock - release a lock on behalf of owner
1001  *
1002  * @lock:       the rt_mutex to be locked
1003  *
1004  * No locking. Caller has to do serializing itself
1005  * Special API call for PI-futex support
1006  */
1007 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1008                            struct task_struct *proxy_owner)
1009 {
1010         debug_rt_mutex_proxy_unlock(lock);
1011         rt_mutex_set_owner(lock, NULL, 0);
1012         rt_mutex_deadlock_account_unlock(proxy_owner);
1013 }
1014
1015 /**
1016  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1017  * @lock:               the rt_mutex to take
1018  * @waiter:             the pre-initialized rt_mutex_waiter
1019  * @task:               the task to prepare
1020  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1021  *
1022  * Returns:
1023  *  0 - task blocked on lock
1024  *  1 - acquired the lock for task, caller should wake it up
1025  * <0 - error
1026  *
1027  * Special API call for FUTEX_REQUEUE_PI support.
1028  */
1029 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1030                               struct rt_mutex_waiter *waiter,
1031                               struct task_struct *task, int detect_deadlock)
1032 {
1033         int ret;
1034
1035         raw_spin_lock(&lock->wait_lock);
1036
1037         mark_rt_mutex_waiters(lock);
1038
1039         if (!rt_mutex_owner(lock) || try_to_steal_lock(lock, task)) {
1040                 /* We got the lock for task. */
1041                 debug_rt_mutex_lock(lock);
1042                 rt_mutex_set_owner(lock, task, 0);
1043                 raw_spin_unlock(&lock->wait_lock);
1044                 rt_mutex_deadlock_account_lock(lock, task);
1045                 return 1;
1046         }
1047
1048         ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
1049
1050         if (ret && !waiter->task) {
1051                 /*
1052                  * Reset the return value. We might have
1053                  * returned with -EDEADLK and the owner
1054                  * released the lock while we were walking the
1055                  * pi chain.  Let the waiter sort it out.
1056                  */
1057                 ret = 0;
1058         }
1059         raw_spin_unlock(&lock->wait_lock);
1060
1061         debug_rt_mutex_print_deadlock(waiter);
1062
1063         return ret;
1064 }
1065
1066 /**
1067  * rt_mutex_next_owner - return the next owner of the lock
1068  *
1069  * @lock: the rt lock query
1070  *
1071  * Returns the next owner of the lock or NULL
1072  *
1073  * Caller has to serialize against other accessors to the lock
1074  * itself.
1075  *
1076  * Special API call for PI-futex support
1077  */
1078 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1079 {
1080         if (!rt_mutex_has_waiters(lock))
1081                 return NULL;
1082
1083         return rt_mutex_top_waiter(lock)->task;
1084 }
1085
1086 /**
1087  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1088  * @lock:               the rt_mutex we were woken on
1089  * @to:                 the timeout, null if none. hrtimer should already have
1090  *                      been started.
1091  * @waiter:             the pre-initialized rt_mutex_waiter
1092  * @detect_deadlock:    perform deadlock detection (1) or not (0)
1093  *
1094  * Complete the lock acquisition started our behalf by another thread.
1095  *
1096  * Returns:
1097  *  0 - success
1098  * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1099  *
1100  * Special API call for PI-futex requeue support
1101  */
1102 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1103                                struct hrtimer_sleeper *to,
1104                                struct rt_mutex_waiter *waiter,
1105                                int detect_deadlock)
1106 {
1107         int ret;
1108
1109         raw_spin_lock(&lock->wait_lock);
1110
1111         set_current_state(TASK_INTERRUPTIBLE);
1112
1113         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter,
1114                                   detect_deadlock);
1115
1116         set_current_state(TASK_RUNNING);
1117
1118         if (unlikely(waiter->task))
1119                 remove_waiter(lock, waiter);
1120
1121         /*
1122          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1123          * have to fix that up.
1124          */
1125         fixup_rt_mutex_waiters(lock);
1126
1127         raw_spin_unlock(&lock->wait_lock);
1128
1129         /*
1130          * Readjust priority, when we did not get the lock. We might have been
1131          * the pending owner and boosted. Since we did not take the lock, the
1132          * PI boost has to go.
1133          */
1134         if (unlikely(ret))
1135                 rt_mutex_adjust_prio(current);
1136
1137         return ret;
1138 }