linux/kernel/rtmutex.c
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   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/export.h>
  15#include <linux/sched.h>
  16#include <linux/sched/rt.h>
  17#include <linux/timer.h>
  18
  19#include "rtmutex_common.h"
  20
  21/*
  22 * lock->owner state tracking:
  23 *
  24 * lock->owner holds the task_struct pointer of the owner. Bit 0
  25 * is used to keep track of the "lock has waiters" state.
  26 *
  27 * owner        bit0
  28 * NULL         0       lock is free (fast acquire possible)
  29 * NULL         1       lock is free and has waiters and the top waiter
  30 *                              is going to take the lock*
  31 * taskpointer  0       lock is held (fast release possible)
  32 * taskpointer  1       lock is held and has waiters**
  33 *
  34 * The fast atomic compare exchange based acquire and release is only
  35 * possible when bit 0 of lock->owner is 0.
  36 *
  37 * (*) It also can be a transitional state when grabbing the lock
  38 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  39 * we need to set the bit0 before looking at the lock, and the owner may be
  40 * NULL in this small time, hence this can be a transitional state.
  41 *
  42 * (**) There is a small time when bit 0 is set but there are no
  43 * waiters. This can happen when grabbing the lock in the slow path.
  44 * To prevent a cmpxchg of the owner releasing the lock, we need to
  45 * set this bit before looking at the lock.
  46 */
  47
  48static void
  49rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  50{
  51        unsigned long val = (unsigned long)owner;
  52
  53        if (rt_mutex_has_waiters(lock))
  54                val |= RT_MUTEX_HAS_WAITERS;
  55
  56        lock->owner = (struct task_struct *)val;
  57}
  58
  59static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  60{
  61        lock->owner = (struct task_struct *)
  62                        ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  63}
  64
  65static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  66{
  67        if (!rt_mutex_has_waiters(lock))
  68                clear_rt_mutex_waiters(lock);
  69}
  70
  71/*
  72 * We can speed up the acquire/release, if the architecture
  73 * supports cmpxchg and if there's no debugging state to be set up
  74 */
  75#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
  76# define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
  77static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  78{
  79        unsigned long owner, *p = (unsigned long *) &lock->owner;
  80
  81        do {
  82                owner = *p;
  83        } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
  84}
  85#else
  86# define rt_mutex_cmpxchg(l,c,n)        (0)
  87static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  88{
  89        lock->owner = (struct task_struct *)
  90                        ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
  91}
  92#endif
  93
  94/*
  95 * Calculate task priority from the waiter list priority
  96 *
  97 * Return task->normal_prio when the waiter list is empty or when
  98 * the waiter is not allowed to do priority boosting
  99 */
 100int rt_mutex_getprio(struct task_struct *task)
 101{
 102        if (likely(!task_has_pi_waiters(task)))
 103                return task->normal_prio;
 104
 105        return min(task_top_pi_waiter(task)->pi_list_entry.prio,
 106                   task->normal_prio);
 107}
 108
 109/*
 110 * Adjust the priority of a task, after its pi_waiters got modified.
 111 *
 112 * This can be both boosting and unboosting. task->pi_lock must be held.
 113 */
 114static void __rt_mutex_adjust_prio(struct task_struct *task)
 115{
 116        int prio = rt_mutex_getprio(task);
 117
 118        if (task->prio != prio)
 119                rt_mutex_setprio(task, prio);
 120}
 121
 122/*
 123 * Adjust task priority (undo boosting). Called from the exit path of
 124 * rt_mutex_slowunlock() and rt_mutex_slowlock().
 125 *
 126 * (Note: We do this outside of the protection of lock->wait_lock to
 127 * allow the lock to be taken while or before we readjust the priority
 128 * of task. We do not use the spin_xx_mutex() variants here as we are
 129 * outside of the debug path.)
 130 */
 131static void rt_mutex_adjust_prio(struct task_struct *task)
 132{
 133        unsigned long flags;
 134
 135        raw_spin_lock_irqsave(&task->pi_lock, flags);
 136        __rt_mutex_adjust_prio(task);
 137        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 138}
 139
 140/*
 141 * Max number of times we'll walk the boosting chain:
 142 */
 143int max_lock_depth = 1024;
 144
 145/*
 146 * Adjust the priority chain. Also used for deadlock detection.
 147 * Decreases task's usage by one - may thus free the task.
 148 * Returns 0 or -EDEADLK.
 149 */
 150static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 151                                      int deadlock_detect,
 152                                      struct rt_mutex *orig_lock,
 153                                      struct rt_mutex_waiter *orig_waiter,
 154                                      struct task_struct *top_task)
 155{
 156        struct rt_mutex *lock;
 157        struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 158        int detect_deadlock, ret = 0, depth = 0;
 159        unsigned long flags;
 160
 161        detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
 162                                                         deadlock_detect);
 163
 164        /*
 165         * The (de)boosting is a step by step approach with a lot of
 166         * pitfalls. We want this to be preemptible and we want hold a
 167         * maximum of two locks per step. So we have to check
 168         * carefully whether things change under us.
 169         */
 170 again:
 171        if (++depth > max_lock_depth) {
 172                static int prev_max;
 173
 174                /*
 175                 * Print this only once. If the admin changes the limit,
 176                 * print a new message when reaching the limit again.
 177                 */
 178                if (prev_max != max_lock_depth) {
 179                        prev_max = max_lock_depth;
 180                        printk(KERN_WARNING "Maximum lock depth %d reached "
 181                               "task: %s (%d)\n", max_lock_depth,
 182                               top_task->comm, task_pid_nr(top_task));
 183                }
 184                put_task_struct(task);
 185
 186                return deadlock_detect ? -EDEADLK : 0;
 187        }
 188 retry:
 189        /*
 190         * Task can not go away as we did a get_task() before !
 191         */
 192        raw_spin_lock_irqsave(&task->pi_lock, flags);
 193
 194        waiter = task->pi_blocked_on;
 195        /*
 196         * Check whether the end of the boosting chain has been
 197         * reached or the state of the chain has changed while we
 198         * dropped the locks.
 199         */
 200        if (!waiter)
 201                goto out_unlock_pi;
 202
 203        /*
 204         * Check the orig_waiter state. After we dropped the locks,
 205         * the previous owner of the lock might have released the lock.
 206         */
 207        if (orig_waiter && !rt_mutex_owner(orig_lock))
 208                goto out_unlock_pi;
 209
 210        /*
 211         * Drop out, when the task has no waiters. Note,
 212         * top_waiter can be NULL, when we are in the deboosting
 213         * mode!
 214         */
 215        if (top_waiter && (!task_has_pi_waiters(task) ||
 216                           top_waiter != task_top_pi_waiter(task)))
 217                goto out_unlock_pi;
 218
 219        /*
 220         * When deadlock detection is off then we check, if further
 221         * priority adjustment is necessary.
 222         */
 223        if (!detect_deadlock && waiter->list_entry.prio == task->prio)
 224                goto out_unlock_pi;
 225
 226        lock = waiter->lock;
 227        if (!raw_spin_trylock(&lock->wait_lock)) {
 228                raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 229                cpu_relax();
 230                goto retry;
 231        }
 232
 233        /* Deadlock detection */
 234        if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 235                debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 236                raw_spin_unlock(&lock->wait_lock);
 237                ret = deadlock_detect ? -EDEADLK : 0;
 238                goto out_unlock_pi;
 239        }
 240
 241        top_waiter = rt_mutex_top_waiter(lock);
 242
 243        /* Requeue the waiter */
 244        plist_del(&waiter->list_entry, &lock->wait_list);
 245        waiter->list_entry.prio = task->prio;
 246        plist_add(&waiter->list_entry, &lock->wait_list);
 247
 248        /* Release the task */
 249        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 250        if (!rt_mutex_owner(lock)) {
 251                /*
 252                 * If the requeue above changed the top waiter, then we need
 253                 * to wake the new top waiter up to try to get the lock.
 254                 */
 255
 256                if (top_waiter != rt_mutex_top_waiter(lock))
 257                        wake_up_process(rt_mutex_top_waiter(lock)->task);
 258                raw_spin_unlock(&lock->wait_lock);
 259                goto out_put_task;
 260        }
 261        put_task_struct(task);
 262
 263        /* Grab the next task */
 264        task = rt_mutex_owner(lock);
 265        get_task_struct(task);
 266        raw_spin_lock_irqsave(&task->pi_lock, flags);
 267
 268        if (waiter == rt_mutex_top_waiter(lock)) {
 269                /* Boost the owner */
 270                plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
 271                waiter->pi_list_entry.prio = waiter->list_entry.prio;
 272                plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 273                __rt_mutex_adjust_prio(task);
 274
 275        } else if (top_waiter == waiter) {
 276                /* Deboost the owner */
 277                plist_del(&waiter->pi_list_entry, &task->pi_waiters);
 278                waiter = rt_mutex_top_waiter(lock);
 279                waiter->pi_list_entry.prio = waiter->list_entry.prio;
 280                plist_add(&waiter->pi_list_entry, &task->pi_waiters);
 281                __rt_mutex_adjust_prio(task);
 282        }
 283
 284        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 285
 286        top_waiter = rt_mutex_top_waiter(lock);
 287        raw_spin_unlock(&lock->wait_lock);
 288
 289        if (!detect_deadlock && waiter != top_waiter)
 290                goto out_put_task;
 291
 292        goto again;
 293
 294 out_unlock_pi:
 295        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 296 out_put_task:
 297        put_task_struct(task);
 298
 299        return ret;
 300}
 301
 302/*
 303 * Try to take an rt-mutex
 304 *
 305 * Must be called with lock->wait_lock held.
 306 *
 307 * @lock:   the lock to be acquired.
 308 * @task:   the task which wants to acquire the lock
 309 * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
 310 */
 311static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 312                struct rt_mutex_waiter *waiter)
 313{
 314        /*
 315         * We have to be careful here if the atomic speedups are
 316         * enabled, such that, when
 317         *  - no other waiter is on the lock
 318         *  - the lock has been released since we did the cmpxchg
 319         * the lock can be released or taken while we are doing the
 320         * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
 321         *
 322         * The atomic acquire/release aware variant of
 323         * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
 324         * the WAITERS bit, the atomic release / acquire can not
 325         * happen anymore and lock->wait_lock protects us from the
 326         * non-atomic case.
 327         *
 328         * Note, that this might set lock->owner =
 329         * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
 330         * any more. This is fixed up when we take the ownership.
 331         * This is the transitional state explained at the top of this file.
 332         */
 333        mark_rt_mutex_waiters(lock);
 334
 335        if (rt_mutex_owner(lock))
 336                return 0;
 337
 338        /*
 339         * It will get the lock because of one of these conditions:
 340         * 1) there is no waiter
 341         * 2) higher priority than waiters
 342         * 3) it is top waiter
 343         */
 344        if (rt_mutex_has_waiters(lock)) {
 345                if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) {
 346                        if (!waiter || waiter != rt_mutex_top_waiter(lock))
 347                                return 0;
 348                }
 349        }
 350
 351        if (waiter || rt_mutex_has_waiters(lock)) {
 352                unsigned long flags;
 353                struct rt_mutex_waiter *top;
 354
 355                raw_spin_lock_irqsave(&task->pi_lock, flags);
 356
 357                /* remove the queued waiter. */
 358                if (waiter) {
 359                        plist_del(&waiter->list_entry, &lock->wait_list);
 360                        task->pi_blocked_on = NULL;
 361                }
 362
 363                /*
 364                 * We have to enqueue the top waiter(if it exists) into
 365                 * task->pi_waiters list.
 366                 */
 367                if (rt_mutex_has_waiters(lock)) {
 368                        top = rt_mutex_top_waiter(lock);
 369                        top->pi_list_entry.prio = top->list_entry.prio;
 370                        plist_add(&top->pi_list_entry, &task->pi_waiters);
 371                }
 372                raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 373        }
 374
 375        /* We got the lock. */
 376        debug_rt_mutex_lock(lock);
 377
 378        rt_mutex_set_owner(lock, task);
 379
 380        rt_mutex_deadlock_account_lock(lock, task);
 381
 382        return 1;
 383}
 384
 385/*
 386 * Task blocks on lock.
 387 *
 388 * Prepare waiter and propagate pi chain
 389 *
 390 * This must be called with lock->wait_lock held.
 391 */
 392static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 393                                   struct rt_mutex_waiter *waiter,
 394                                   struct task_struct *task,
 395                                   int detect_deadlock)
 396{
 397        struct task_struct *owner = rt_mutex_owner(lock);
 398        struct rt_mutex_waiter *top_waiter = waiter;
 399        unsigned long flags;
 400        int chain_walk = 0, res;
 401
 402        raw_spin_lock_irqsave(&task->pi_lock, flags);
 403        __rt_mutex_adjust_prio(task);
 404        waiter->task = task;
 405        waiter->lock = lock;
 406        plist_node_init(&waiter->list_entry, task->prio);
 407        plist_node_init(&waiter->pi_list_entry, task->prio);
 408
 409        /* Get the top priority waiter on the lock */
 410        if (rt_mutex_has_waiters(lock))
 411                top_waiter = rt_mutex_top_waiter(lock);
 412        plist_add(&waiter->list_entry, &lock->wait_list);
 413
 414        task->pi_blocked_on = waiter;
 415
 416        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 417
 418        if (!owner)
 419                return 0;
 420
 421        if (waiter == rt_mutex_top_waiter(lock)) {
 422                raw_spin_lock_irqsave(&owner->pi_lock, flags);
 423                plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
 424                plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
 425
 426                __rt_mutex_adjust_prio(owner);
 427                if (owner->pi_blocked_on)
 428                        chain_walk = 1;
 429                raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 430        }
 431        else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
 432                chain_walk = 1;
 433
 434        if (!chain_walk)
 435                return 0;
 436
 437        /*
 438         * The owner can't disappear while holding a lock,
 439         * so the owner struct is protected by wait_lock.
 440         * Gets dropped in rt_mutex_adjust_prio_chain()!
 441         */
 442        get_task_struct(owner);
 443
 444        raw_spin_unlock(&lock->wait_lock);
 445
 446        res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
 447                                         task);
 448
 449        raw_spin_lock(&lock->wait_lock);
 450
 451        return res;
 452}
 453
 454/*
 455 * Wake up the next waiter on the lock.
 456 *
 457 * Remove the top waiter from the current tasks waiter list and wake it up.
 458 *
 459 * Called with lock->wait_lock held.
 460 */
 461static void wakeup_next_waiter(struct rt_mutex *lock)
 462{
 463        struct rt_mutex_waiter *waiter;
 464        unsigned long flags;
 465
 466        raw_spin_lock_irqsave(&current->pi_lock, flags);
 467
 468        waiter = rt_mutex_top_waiter(lock);
 469
 470        /*
 471         * Remove it from current->pi_waiters. We do not adjust a
 472         * possible priority boost right now. We execute wakeup in the
 473         * boosted mode and go back to normal after releasing
 474         * lock->wait_lock.
 475         */
 476        plist_del(&waiter->pi_list_entry, &current->pi_waiters);
 477
 478        rt_mutex_set_owner(lock, NULL);
 479
 480        raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 481
 482        wake_up_process(waiter->task);
 483}
 484
 485/*
 486 * Remove a waiter from a lock and give up
 487 *
 488 * Must be called with lock->wait_lock held and
 489 * have just failed to try_to_take_rt_mutex().
 490 */
 491static void remove_waiter(struct rt_mutex *lock,
 492                          struct rt_mutex_waiter *waiter)
 493{
 494        int first = (waiter == rt_mutex_top_waiter(lock));
 495        struct task_struct *owner = rt_mutex_owner(lock);
 496        unsigned long flags;
 497        int chain_walk = 0;
 498
 499        raw_spin_lock_irqsave(&current->pi_lock, flags);
 500        plist_del(&waiter->list_entry, &lock->wait_list);
 501        current->pi_blocked_on = NULL;
 502        raw_spin_unlock_irqrestore(&current->pi_lock, flags);
 503
 504        if (!owner)
 505                return;
 506
 507        if (first) {
 508
 509                raw_spin_lock_irqsave(&owner->pi_lock, flags);
 510
 511                plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
 512
 513                if (rt_mutex_has_waiters(lock)) {
 514                        struct rt_mutex_waiter *next;
 515
 516                        next = rt_mutex_top_waiter(lock);
 517                        plist_add(&next->pi_list_entry, &owner->pi_waiters);
 518                }
 519                __rt_mutex_adjust_prio(owner);
 520
 521                if (owner->pi_blocked_on)
 522                        chain_walk = 1;
 523
 524                raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 525        }
 526
 527        WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 528
 529        if (!chain_walk)
 530                return;
 531
 532        /* gets dropped in rt_mutex_adjust_prio_chain()! */
 533        get_task_struct(owner);
 534
 535        raw_spin_unlock(&lock->wait_lock);
 536
 537        rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
 538
 539        raw_spin_lock(&lock->wait_lock);
 540}
 541
 542/*
 543 * Recheck the pi chain, in case we got a priority setting
 544 *
 545 * Called from sched_setscheduler
 546 */
 547void rt_mutex_adjust_pi(struct task_struct *task)
 548{
 549        struct rt_mutex_waiter *waiter;
 550        unsigned long flags;
 551
 552        raw_spin_lock_irqsave(&task->pi_lock, flags);
 553
 554        waiter = task->pi_blocked_on;
 555        if (!waiter || waiter->list_entry.prio == task->prio) {
 556                raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 557                return;
 558        }
 559
 560        raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 561
 562        /* gets dropped in rt_mutex_adjust_prio_chain()! */
 563        get_task_struct(task);
 564        rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
 565}
 566
 567/**
 568 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
 569 * @lock:                the rt_mutex to take
 570 * @state:               the state the task should block in (TASK_INTERRUPTIBLE
 571 *                       or TASK_UNINTERRUPTIBLE)
 572 * @timeout:             the pre-initialized and started timer, or NULL for none
 573 * @waiter:              the pre-initialized rt_mutex_waiter
 574 *
 575 * lock->wait_lock must be held by the caller.
 576 */
 577static int __sched
 578__rt_mutex_slowlock(struct rt_mutex *lock, int state,
 579                    struct hrtimer_sleeper *timeout,
 580                    struct rt_mutex_waiter *waiter)
 581{
 582        int ret = 0;
 583
 584        for (;;) {
 585                /* Try to acquire the lock: */
 586                if (try_to_take_rt_mutex(lock, current, waiter))
 587                        break;
 588
 589                /*
 590                 * TASK_INTERRUPTIBLE checks for signals and
 591                 * timeout. Ignored otherwise.
 592                 */
 593                if (unlikely(state == TASK_INTERRUPTIBLE)) {
 594                        /* Signal pending? */
 595                        if (signal_pending(current))
 596                                ret = -EINTR;
 597                        if (timeout && !timeout->task)
 598                                ret = -ETIMEDOUT;
 599                        if (ret)
 600                                break;
 601                }
 602
 603                raw_spin_unlock(&lock->wait_lock);
 604
 605                debug_rt_mutex_print_deadlock(waiter);
 606
 607                schedule_rt_mutex(lock);
 608
 609                raw_spin_lock(&lock->wait_lock);
 610                set_current_state(state);
 611        }
 612
 613        return ret;
 614}
 615
 616/*
 617 * Slow path lock function:
 618 */
 619static int __sched
 620rt_mutex_slowlock(struct rt_mutex *lock, int state,
 621                  struct hrtimer_sleeper *timeout,
 622                  int detect_deadlock)
 623{
 624        struct rt_mutex_waiter waiter;
 625        int ret = 0;
 626
 627        debug_rt_mutex_init_waiter(&waiter);
 628
 629        raw_spin_lock(&lock->wait_lock);
 630
 631        /* Try to acquire the lock again: */
 632        if (try_to_take_rt_mutex(lock, current, NULL)) {
 633                raw_spin_unlock(&lock->wait_lock);
 634                return 0;
 635        }
 636
 637        set_current_state(state);
 638
 639        /* Setup the timer, when timeout != NULL */
 640        if (unlikely(timeout)) {
 641                hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
 642                if (!hrtimer_active(&timeout->timer))
 643                        timeout->task = NULL;
 644        }
 645
 646        ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
 647
 648        if (likely(!ret))
 649                ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
 650
 651        set_current_state(TASK_RUNNING);
 652
 653        if (unlikely(ret))
 654                remove_waiter(lock, &waiter);
 655
 656        /*
 657         * try_to_take_rt_mutex() sets the waiter bit
 658         * unconditionally. We might have to fix that up.
 659         */
 660        fixup_rt_mutex_waiters(lock);
 661
 662        raw_spin_unlock(&lock->wait_lock);
 663
 664        /* Remove pending timer: */
 665        if (unlikely(timeout))
 666                hrtimer_cancel(&timeout->timer);
 667
 668        debug_rt_mutex_free_waiter(&waiter);
 669
 670        return ret;
 671}
 672
 673/*
 674 * Slow path try-lock function:
 675 */
 676static inline int
 677rt_mutex_slowtrylock(struct rt_mutex *lock)
 678{
 679        int ret = 0;
 680
 681        raw_spin_lock(&lock->wait_lock);
 682
 683        if (likely(rt_mutex_owner(lock) != current)) {
 684
 685                ret = try_to_take_rt_mutex(lock, current, NULL);
 686                /*
 687                 * try_to_take_rt_mutex() sets the lock waiters
 688                 * bit unconditionally. Clean this up.
 689                 */
 690                fixup_rt_mutex_waiters(lock);
 691        }
 692
 693        raw_spin_unlock(&lock->wait_lock);
 694
 695        return ret;
 696}
 697
 698/*
 699 * Slow path to release a rt-mutex:
 700 */
 701static void __sched
 702rt_mutex_slowunlock(struct rt_mutex *lock)
 703{
 704        raw_spin_lock(&lock->wait_lock);
 705
 706        debug_rt_mutex_unlock(lock);
 707
 708        rt_mutex_deadlock_account_unlock(current);
 709
 710        if (!rt_mutex_has_waiters(lock)) {
 711                lock->owner = NULL;
 712                raw_spin_unlock(&lock->wait_lock);
 713                return;
 714        }
 715
 716        wakeup_next_waiter(lock);
 717
 718        raw_spin_unlock(&lock->wait_lock);
 719
 720        /* Undo pi boosting if necessary: */
 721        rt_mutex_adjust_prio(current);
 722}
 723
 724/*
 725 * debug aware fast / slowpath lock,trylock,unlock
 726 *
 727 * The atomic acquire/release ops are compiled away, when either the
 728 * architecture does not support cmpxchg or when debugging is enabled.
 729 */
 730static inline int
 731rt_mutex_fastlock(struct rt_mutex *lock, int state,
 732                  int detect_deadlock,
 733                  int (*slowfn)(struct rt_mutex *lock, int state,
 734                                struct hrtimer_sleeper *timeout,
 735                                int detect_deadlock))
 736{
 737        if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 738                rt_mutex_deadlock_account_lock(lock, current);
 739                return 0;
 740        } else
 741                return slowfn(lock, state, NULL, detect_deadlock);
 742}
 743
 744static inline int
 745rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
 746                        struct hrtimer_sleeper *timeout, 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, timeout, detect_deadlock);
 756}
 757
 758static inline int
 759rt_mutex_fasttrylock(struct rt_mutex *lock,
 760                     int (*slowfn)(struct rt_mutex *lock))
 761{
 762        if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 763                rt_mutex_deadlock_account_lock(lock, current);
 764                return 1;
 765        }
 766        return slowfn(lock);
 767}
 768
 769static inline void
 770rt_mutex_fastunlock(struct rt_mutex *lock,
 771                    void (*slowfn)(struct rt_mutex *lock))
 772{
 773        if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
 774                rt_mutex_deadlock_account_unlock(current);
 775        else
 776                slowfn(lock);
 777}
 778
 779/**
 780 * rt_mutex_lock - lock a rt_mutex
 781 *
 782 * @lock: the rt_mutex to be locked
 783 */
 784void __sched rt_mutex_lock(struct rt_mutex *lock)
 785{
 786        might_sleep();
 787
 788        rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
 789}
 790EXPORT_SYMBOL_GPL(rt_mutex_lock);
 791
 792/**
 793 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
 794 *
 795 * @lock:               the rt_mutex to be locked
 796 * @detect_deadlock:    deadlock detection on/off
 797 *
 798 * Returns:
 799 *  0           on success
 800 * -EINTR       when interrupted by a signal
 801 * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 802 */
 803int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
 804                                                 int detect_deadlock)
 805{
 806        might_sleep();
 807
 808        return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
 809                                 detect_deadlock, rt_mutex_slowlock);
 810}
 811EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
 812
 813/**
 814 * rt_mutex_timed_lock - lock a rt_mutex interruptible
 815 *                      the timeout structure is provided
 816 *                      by the caller
 817 *
 818 * @lock:               the rt_mutex to be locked
 819 * @timeout:            timeout structure or NULL (no timeout)
 820 * @detect_deadlock:    deadlock detection on/off
 821 *
 822 * Returns:
 823 *  0           on success
 824 * -EINTR       when interrupted by a signal
 825 * -ETIMEDOUT   when the timeout expired
 826 * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
 827 */
 828int
 829rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
 830                    int detect_deadlock)
 831{
 832        might_sleep();
 833
 834        return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
 835                                       detect_deadlock, rt_mutex_slowlock);
 836}
 837EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
 838
 839/**
 840 * rt_mutex_trylock - try to lock a rt_mutex
 841 *
 842 * @lock:       the rt_mutex to be locked
 843 *
 844 * Returns 1 on success and 0 on contention
 845 */
 846int __sched rt_mutex_trylock(struct rt_mutex *lock)
 847{
 848        return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 849}
 850EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 851
 852/**
 853 * rt_mutex_unlock - unlock a rt_mutex
 854 *
 855 * @lock: the rt_mutex to be unlocked
 856 */
 857void __sched rt_mutex_unlock(struct rt_mutex *lock)
 858{
 859        rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 860}
 861EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 862
 863/**
 864 * rt_mutex_destroy - mark a mutex unusable
 865 * @lock: the mutex to be destroyed
 866 *
 867 * This function marks the mutex uninitialized, and any subsequent
 868 * use of the mutex is forbidden. The mutex must not be locked when
 869 * this function is called.
 870 */
 871void rt_mutex_destroy(struct rt_mutex *lock)
 872{
 873        WARN_ON(rt_mutex_is_locked(lock));
 874#ifdef CONFIG_DEBUG_RT_MUTEXES
 875        lock->magic = NULL;
 876#endif
 877}
 878
 879EXPORT_SYMBOL_GPL(rt_mutex_destroy);
 880
 881/**
 882 * __rt_mutex_init - initialize the rt lock
 883 *
 884 * @lock: the rt lock to be initialized
 885 *
 886 * Initialize the rt lock to unlocked state.
 887 *
 888 * Initializing of a locked rt lock is not allowed
 889 */
 890void __rt_mutex_init(struct rt_mutex *lock, const char *name)
 891{
 892        lock->owner = NULL;
 893        raw_spin_lock_init(&lock->wait_lock);
 894        plist_head_init(&lock->wait_list);
 895
 896        debug_rt_mutex_init(lock, name);
 897}
 898EXPORT_SYMBOL_GPL(__rt_mutex_init);
 899
 900/**
 901 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 902 *                              proxy owner
 903 *
 904 * @lock:       the rt_mutex to be locked
 905 * @proxy_owner:the task to set as owner
 906 *
 907 * No locking. Caller has to do serializing itself
 908 * Special API call for PI-futex support
 909 */
 910void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
 911                                struct task_struct *proxy_owner)
 912{
 913        __rt_mutex_init(lock, NULL);
 914        debug_rt_mutex_proxy_lock(lock, proxy_owner);
 915        rt_mutex_set_owner(lock, proxy_owner);
 916        rt_mutex_deadlock_account_lock(lock, proxy_owner);
 917}
 918
 919/**
 920 * rt_mutex_proxy_unlock - release a lock on behalf of owner
 921 *
 922 * @lock:       the rt_mutex to be locked
 923 *
 924 * No locking. Caller has to do serializing itself
 925 * Special API call for PI-futex support
 926 */
 927void rt_mutex_proxy_unlock(struct rt_mutex *lock,
 928                           struct task_struct *proxy_owner)
 929{
 930        debug_rt_mutex_proxy_unlock(lock);
 931        rt_mutex_set_owner(lock, NULL);
 932        rt_mutex_deadlock_account_unlock(proxy_owner);
 933}
 934
 935/**
 936 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 937 * @lock:               the rt_mutex to take
 938 * @waiter:             the pre-initialized rt_mutex_waiter
 939 * @task:               the task to prepare
 940 * @detect_deadlock:    perform deadlock detection (1) or not (0)
 941 *
 942 * Returns:
 943 *  0 - task blocked on lock
 944 *  1 - acquired the lock for task, caller should wake it up
 945 * <0 - error
 946 *
 947 * Special API call for FUTEX_REQUEUE_PI support.
 948 */
 949int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
 950                              struct rt_mutex_waiter *waiter,
 951                              struct task_struct *task, int detect_deadlock)
 952{
 953        int ret;
 954
 955        raw_spin_lock(&lock->wait_lock);
 956
 957        if (try_to_take_rt_mutex(lock, task, NULL)) {
 958                raw_spin_unlock(&lock->wait_lock);
 959                return 1;
 960        }
 961
 962        ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
 963
 964        if (ret && !rt_mutex_owner(lock)) {
 965                /*
 966                 * Reset the return value. We might have
 967                 * returned with -EDEADLK and the owner
 968                 * released the lock while we were walking the
 969                 * pi chain.  Let the waiter sort it out.
 970                 */
 971                ret = 0;
 972        }
 973
 974        if (unlikely(ret))
 975                remove_waiter(lock, waiter);
 976
 977        raw_spin_unlock(&lock->wait_lock);
 978
 979        debug_rt_mutex_print_deadlock(waiter);
 980
 981        return ret;
 982}
 983
 984/**
 985 * rt_mutex_next_owner - return the next owner of the lock
 986 *
 987 * @lock: the rt lock query
 988 *
 989 * Returns the next owner of the lock or NULL
 990 *
 991 * Caller has to serialize against other accessors to the lock
 992 * itself.
 993 *
 994 * Special API call for PI-futex support
 995 */
 996struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
 997{
 998        if (!rt_mutex_has_waiters(lock))
 999                return NULL;
1000
1001        return rt_mutex_top_waiter(lock)->task;
1002}
1003
1004/**
1005 * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1006 * @lock:               the rt_mutex we were woken on
1007 * @to:                 the timeout, null if none. hrtimer should already have
1008 *                      been started.
1009 * @waiter:             the pre-initialized rt_mutex_waiter
1010 * @detect_deadlock:    perform deadlock detection (1) or not (0)
1011 *
1012 * Complete the lock acquisition started our behalf by another thread.
1013 *
1014 * Returns:
1015 *  0 - success
1016 * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1017 *
1018 * Special API call for PI-futex requeue support
1019 */
1020int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1021                               struct hrtimer_sleeper *to,
1022                               struct rt_mutex_waiter *waiter,
1023                               int detect_deadlock)
1024{
1025        int ret;
1026
1027        raw_spin_lock(&lock->wait_lock);
1028
1029        set_current_state(TASK_INTERRUPTIBLE);
1030
1031        ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1032
1033        set_current_state(TASK_RUNNING);
1034
1035        if (unlikely(ret))
1036                remove_waiter(lock, waiter);
1037
1038        /*
1039         * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1040         * have to fix that up.
1041         */
1042        fixup_rt_mutex_waiters(lock);
1043
1044        raw_spin_unlock(&lock->wait_lock);
1045
1046        return ret;
1047}
1048
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