linux/kernel/mutex.c
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   1/*
   2 * kernel/mutex.c
   3 *
   4 * Mutexes: blocking mutual exclusion locks
   5 *
   6 * Started by Ingo Molnar:
   7 *
   8 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   9 *
  10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
  11 * David Howells for suggestions and improvements.
  12 *
  13 *  - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
  14 *    from the -rt tree, where it was originally implemented for rtmutexes
  15 *    by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
  16 *    and Sven Dietrich.
  17 *
  18 * Also see Documentation/mutex-design.txt.
  19 */
  20#include <linux/mutex.h>
  21#include <linux/ww_mutex.h>
  22#include <linux/sched.h>
  23#include <linux/sched/rt.h>
  24#include <linux/export.h>
  25#include <linux/spinlock.h>
  26#include <linux/interrupt.h>
  27#include <linux/debug_locks.h>
  28
  29/*
  30 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
  31 * which forces all calls into the slowpath:
  32 */
  33#ifdef CONFIG_DEBUG_MUTEXES
  34# include "mutex-debug.h"
  35# include <asm-generic/mutex-null.h>
  36#else
  37# include "mutex.h"
  38# include <asm/mutex.h>
  39#endif
  40
  41/*
  42 * A negative mutex count indicates that waiters are sleeping waiting for the
  43 * mutex.
  44 */
  45#define MUTEX_SHOW_NO_WAITER(mutex)     (atomic_read(&(mutex)->count) >= 0)
  46
  47void
  48__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
  49{
  50        atomic_set(&lock->count, 1);
  51        spin_lock_init(&lock->wait_lock);
  52        INIT_LIST_HEAD(&lock->wait_list);
  53        mutex_clear_owner(lock);
  54#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  55        lock->spin_mlock = NULL;
  56#endif
  57
  58        debug_mutex_init(lock, name, key);
  59}
  60
  61EXPORT_SYMBOL(__mutex_init);
  62
  63#ifndef CONFIG_DEBUG_LOCK_ALLOC
  64/*
  65 * We split the mutex lock/unlock logic into separate fastpath and
  66 * slowpath functions, to reduce the register pressure on the fastpath.
  67 * We also put the fastpath first in the kernel image, to make sure the
  68 * branch is predicted by the CPU as default-untaken.
  69 */
  70static __used noinline void __sched
  71__mutex_lock_slowpath(atomic_t *lock_count);
  72
  73/**
  74 * mutex_lock - acquire the mutex
  75 * @lock: the mutex to be acquired
  76 *
  77 * Lock the mutex exclusively for this task. If the mutex is not
  78 * available right now, it will sleep until it can get it.
  79 *
  80 * The mutex must later on be released by the same task that
  81 * acquired it. Recursive locking is not allowed. The task
  82 * may not exit without first unlocking the mutex. Also, kernel
  83 * memory where the mutex resides mutex must not be freed with
  84 * the mutex still locked. The mutex must first be initialized
  85 * (or statically defined) before it can be locked. memset()-ing
  86 * the mutex to 0 is not allowed.
  87 *
  88 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
  89 *   checks that will enforce the restrictions and will also do
  90 *   deadlock debugging. )
  91 *
  92 * This function is similar to (but not equivalent to) down().
  93 */
  94void __sched mutex_lock(struct mutex *lock)
  95{
  96        might_sleep();
  97        /*
  98         * The locking fastpath is the 1->0 transition from
  99         * 'unlocked' into 'locked' state.
 100         */
 101        __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
 102        mutex_set_owner(lock);
 103}
 104
 105EXPORT_SYMBOL(mutex_lock);
 106#endif
 107
 108#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 109/*
 110 * In order to avoid a stampede of mutex spinners from acquiring the mutex
 111 * more or less simultaneously, the spinners need to acquire a MCS lock
 112 * first before spinning on the owner field.
 113 *
 114 * We don't inline mspin_lock() so that perf can correctly account for the
 115 * time spent in this lock function.
 116 */
 117struct mspin_node {
 118        struct mspin_node *next ;
 119        int               locked;       /* 1 if lock acquired */
 120};
 121#define MLOCK(mutex)    ((struct mspin_node **)&((mutex)->spin_mlock))
 122
 123static noinline
 124void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
 125{
 126        struct mspin_node *prev;
 127
 128        /* Init node */
 129        node->locked = 0;
 130        node->next   = NULL;
 131
 132        prev = xchg(lock, node);
 133        if (likely(prev == NULL)) {
 134                /* Lock acquired */
 135                node->locked = 1;
 136                return;
 137        }
 138        ACCESS_ONCE(prev->next) = node;
 139        smp_wmb();
 140        /* Wait until the lock holder passes the lock down */
 141        while (!ACCESS_ONCE(node->locked))
 142                arch_mutex_cpu_relax();
 143}
 144
 145static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
 146{
 147        struct mspin_node *next = ACCESS_ONCE(node->next);
 148
 149        if (likely(!next)) {
 150                /*
 151                 * Release the lock by setting it to NULL
 152                 */
 153                if (cmpxchg(lock, node, NULL) == node)
 154                        return;
 155                /* Wait until the next pointer is set */
 156                while (!(next = ACCESS_ONCE(node->next)))
 157                        arch_mutex_cpu_relax();
 158        }
 159        ACCESS_ONCE(next->locked) = 1;
 160        smp_wmb();
 161}
 162
 163/*
 164 * Mutex spinning code migrated from kernel/sched/core.c
 165 */
 166
 167static inline bool owner_running(struct mutex *lock, struct task_struct *owner)
 168{
 169        if (lock->owner != owner)
 170                return false;
 171
 172        /*
 173         * Ensure we emit the owner->on_cpu, dereference _after_ checking
 174         * lock->owner still matches owner, if that fails, owner might
 175         * point to free()d memory, if it still matches, the rcu_read_lock()
 176         * ensures the memory stays valid.
 177         */
 178        barrier();
 179
 180        return owner->on_cpu;
 181}
 182
 183/*
 184 * Look out! "owner" is an entirely speculative pointer
 185 * access and not reliable.
 186 */
 187static noinline
 188int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
 189{
 190        rcu_read_lock();
 191        while (owner_running(lock, owner)) {
 192                if (need_resched())
 193                        break;
 194
 195                arch_mutex_cpu_relax();
 196        }
 197        rcu_read_unlock();
 198
 199        /*
 200         * We break out the loop above on need_resched() and when the
 201         * owner changed, which is a sign for heavy contention. Return
 202         * success only when lock->owner is NULL.
 203         */
 204        return lock->owner == NULL;
 205}
 206
 207/*
 208 * Initial check for entering the mutex spinning loop
 209 */
 210static inline int mutex_can_spin_on_owner(struct mutex *lock)
 211{
 212        struct task_struct *owner;
 213        int retval = 1;
 214
 215        rcu_read_lock();
 216        owner = ACCESS_ONCE(lock->owner);
 217        if (owner)
 218                retval = owner->on_cpu;
 219        rcu_read_unlock();
 220        /*
 221         * if lock->owner is not set, the mutex owner may have just acquired
 222         * it and not set the owner yet or the mutex has been released.
 223         */
 224        return retval;
 225}
 226#endif
 227
 228static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
 229
 230/**
 231 * mutex_unlock - release the mutex
 232 * @lock: the mutex to be released
 233 *
 234 * Unlock a mutex that has been locked by this task previously.
 235 *
 236 * This function must not be used in interrupt context. Unlocking
 237 * of a not locked mutex is not allowed.
 238 *
 239 * This function is similar to (but not equivalent to) up().
 240 */
 241void __sched mutex_unlock(struct mutex *lock)
 242{
 243        /*
 244         * The unlocking fastpath is the 0->1 transition from 'locked'
 245         * into 'unlocked' state:
 246         */
 247#ifndef CONFIG_DEBUG_MUTEXES
 248        /*
 249         * When debugging is enabled we must not clear the owner before time,
 250         * the slow path will always be taken, and that clears the owner field
 251         * after verifying that it was indeed current.
 252         */
 253        mutex_clear_owner(lock);
 254#endif
 255        __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
 256}
 257
 258EXPORT_SYMBOL(mutex_unlock);
 259
 260/**
 261 * ww_mutex_unlock - release the w/w mutex
 262 * @lock: the mutex to be released
 263 *
 264 * Unlock a mutex that has been locked by this task previously with any of the
 265 * ww_mutex_lock* functions (with or without an acquire context). It is
 266 * forbidden to release the locks after releasing the acquire context.
 267 *
 268 * This function must not be used in interrupt context. Unlocking
 269 * of a unlocked mutex is not allowed.
 270 */
 271void __sched ww_mutex_unlock(struct ww_mutex *lock)
 272{
 273        /*
 274         * The unlocking fastpath is the 0->1 transition from 'locked'
 275         * into 'unlocked' state:
 276         */
 277        if (lock->ctx) {
 278#ifdef CONFIG_DEBUG_MUTEXES
 279                DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
 280#endif
 281                if (lock->ctx->acquired > 0)
 282                        lock->ctx->acquired--;
 283                lock->ctx = NULL;
 284        }
 285
 286#ifndef CONFIG_DEBUG_MUTEXES
 287        /*
 288         * When debugging is enabled we must not clear the owner before time,
 289         * the slow path will always be taken, and that clears the owner field
 290         * after verifying that it was indeed current.
 291         */
 292        mutex_clear_owner(&lock->base);
 293#endif
 294        __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
 295}
 296EXPORT_SYMBOL(ww_mutex_unlock);
 297
 298static inline int __sched
 299__mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
 300{
 301        struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
 302        struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
 303
 304        if (!hold_ctx)
 305                return 0;
 306
 307        if (unlikely(ctx == hold_ctx))
 308                return -EALREADY;
 309
 310        if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
 311            (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
 312#ifdef CONFIG_DEBUG_MUTEXES
 313                DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
 314                ctx->contending_lock = ww;
 315#endif
 316                return -EDEADLK;
 317        }
 318
 319        return 0;
 320}
 321
 322static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
 323                                                   struct ww_acquire_ctx *ww_ctx)
 324{
 325#ifdef CONFIG_DEBUG_MUTEXES
 326        /*
 327         * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
 328         * but released with a normal mutex_unlock in this call.
 329         *
 330         * This should never happen, always use ww_mutex_unlock.
 331         */
 332        DEBUG_LOCKS_WARN_ON(ww->ctx);
 333
 334        /*
 335         * Not quite done after calling ww_acquire_done() ?
 336         */
 337        DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
 338
 339        if (ww_ctx->contending_lock) {
 340                /*
 341                 * After -EDEADLK you tried to
 342                 * acquire a different ww_mutex? Bad!
 343                 */
 344                DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
 345
 346                /*
 347                 * You called ww_mutex_lock after receiving -EDEADLK,
 348                 * but 'forgot' to unlock everything else first?
 349                 */
 350                DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
 351                ww_ctx->contending_lock = NULL;
 352        }
 353
 354        /*
 355         * Naughty, using a different class will lead to undefined behavior!
 356         */
 357        DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
 358#endif
 359        ww_ctx->acquired++;
 360}
 361
 362/*
 363 * after acquiring lock with fastpath or when we lost out in contested
 364 * slowpath, set ctx and wake up any waiters so they can recheck.
 365 *
 366 * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
 367 * as the fastpath and opportunistic spinning are disabled in that case.
 368 */
 369static __always_inline void
 370ww_mutex_set_context_fastpath(struct ww_mutex *lock,
 371                               struct ww_acquire_ctx *ctx)
 372{
 373        unsigned long flags;
 374        struct mutex_waiter *cur;
 375
 376        ww_mutex_lock_acquired(lock, ctx);
 377
 378        lock->ctx = ctx;
 379
 380        /*
 381         * The lock->ctx update should be visible on all cores before
 382         * the atomic read is done, otherwise contended waiters might be
 383         * missed. The contended waiters will either see ww_ctx == NULL
 384         * and keep spinning, or it will acquire wait_lock, add itself
 385         * to waiter list and sleep.
 386         */
 387        smp_mb(); /* ^^^ */
 388
 389        /*
 390         * Check if lock is contended, if not there is nobody to wake up
 391         */
 392        if (likely(atomic_read(&lock->base.count) == 0))
 393                return;
 394
 395        /*
 396         * Uh oh, we raced in fastpath, wake up everyone in this case,
 397         * so they can see the new lock->ctx.
 398         */
 399        spin_lock_mutex(&lock->base.wait_lock, flags);
 400        list_for_each_entry(cur, &lock->base.wait_list, list) {
 401                debug_mutex_wake_waiter(&lock->base, cur);
 402                wake_up_process(cur->task);
 403        }
 404        spin_unlock_mutex(&lock->base.wait_lock, flags);
 405}
 406
 407/*
 408 * Lock a mutex (possibly interruptible), slowpath:
 409 */
 410static __always_inline int __sched
 411__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 412                    struct lockdep_map *nest_lock, unsigned long ip,
 413                    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 414{
 415        struct task_struct *task = current;
 416        struct mutex_waiter waiter;
 417        unsigned long flags;
 418        int ret;
 419
 420        preempt_disable();
 421        mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
 422
 423#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 424        /*
 425         * Optimistic spinning.
 426         *
 427         * We try to spin for acquisition when we find that there are no
 428         * pending waiters and the lock owner is currently running on a
 429         * (different) CPU.
 430         *
 431         * The rationale is that if the lock owner is running, it is likely to
 432         * release the lock soon.
 433         *
 434         * Since this needs the lock owner, and this mutex implementation
 435         * doesn't track the owner atomically in the lock field, we need to
 436         * track it non-atomically.
 437         *
 438         * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
 439         * to serialize everything.
 440         *
 441         * The mutex spinners are queued up using MCS lock so that only one
 442         * spinner can compete for the mutex. However, if mutex spinning isn't
 443         * going to happen, there is no point in going through the lock/unlock
 444         * overhead.
 445         */
 446        if (!mutex_can_spin_on_owner(lock))
 447                goto slowpath;
 448
 449        for (;;) {
 450                struct task_struct *owner;
 451                struct mspin_node  node;
 452
 453                if (use_ww_ctx && ww_ctx->acquired > 0) {
 454                        struct ww_mutex *ww;
 455
 456                        ww = container_of(lock, struct ww_mutex, base);
 457                        /*
 458                         * If ww->ctx is set the contents are undefined, only
 459                         * by acquiring wait_lock there is a guarantee that
 460                         * they are not invalid when reading.
 461                         *
 462                         * As such, when deadlock detection needs to be
 463                         * performed the optimistic spinning cannot be done.
 464                         */
 465                        if (ACCESS_ONCE(ww->ctx))
 466                                goto slowpath;
 467                }
 468
 469                /*
 470                 * If there's an owner, wait for it to either
 471                 * release the lock or go to sleep.
 472                 */
 473                mspin_lock(MLOCK(lock), &node);
 474                owner = ACCESS_ONCE(lock->owner);
 475                if (owner && !mutex_spin_on_owner(lock, owner)) {
 476                        mspin_unlock(MLOCK(lock), &node);
 477                        goto slowpath;
 478                }
 479
 480                if ((atomic_read(&lock->count) == 1) &&
 481                    (atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
 482                        lock_acquired(&lock->dep_map, ip);
 483                        if (use_ww_ctx) {
 484                                struct ww_mutex *ww;
 485                                ww = container_of(lock, struct ww_mutex, base);
 486
 487                                ww_mutex_set_context_fastpath(ww, ww_ctx);
 488                        }
 489
 490                        mutex_set_owner(lock);
 491                        mspin_unlock(MLOCK(lock), &node);
 492                        preempt_enable();
 493                        return 0;
 494                }
 495                mspin_unlock(MLOCK(lock), &node);
 496
 497                /*
 498                 * When there's no owner, we might have preempted between the
 499                 * owner acquiring the lock and setting the owner field. If
 500                 * we're an RT task that will live-lock because we won't let
 501                 * the owner complete.
 502                 */
 503                if (!owner && (need_resched() || rt_task(task)))
 504                        goto slowpath;
 505
 506                /*
 507                 * The cpu_relax() call is a compiler barrier which forces
 508                 * everything in this loop to be re-loaded. We don't need
 509                 * memory barriers as we'll eventually observe the right
 510                 * values at the cost of a few extra spins.
 511                 */
 512                arch_mutex_cpu_relax();
 513        }
 514slowpath:
 515#endif
 516        spin_lock_mutex(&lock->wait_lock, flags);
 517
 518        /* once more, can we acquire the lock? */
 519        if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, 0) == 1))
 520                goto skip_wait;
 521
 522        debug_mutex_lock_common(lock, &waiter);
 523        debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
 524
 525        /* add waiting tasks to the end of the waitqueue (FIFO): */
 526        list_add_tail(&waiter.list, &lock->wait_list);
 527        waiter.task = task;
 528
 529        lock_contended(&lock->dep_map, ip);
 530
 531        for (;;) {
 532                /*
 533                 * Lets try to take the lock again - this is needed even if
 534                 * we get here for the first time (shortly after failing to
 535                 * acquire the lock), to make sure that we get a wakeup once
 536                 * it's unlocked. Later on, if we sleep, this is the
 537                 * operation that gives us the lock. We xchg it to -1, so
 538                 * that when we release the lock, we properly wake up the
 539                 * other waiters:
 540                 */
 541                if (MUTEX_SHOW_NO_WAITER(lock) &&
 542                    (atomic_xchg(&lock->count, -1) == 1))
 543                        break;
 544
 545                /*
 546                 * got a signal? (This code gets eliminated in the
 547                 * TASK_UNINTERRUPTIBLE case.)
 548                 */
 549                if (unlikely(signal_pending_state(state, task))) {
 550                        ret = -EINTR;
 551                        goto err;
 552                }
 553
 554                if (use_ww_ctx && ww_ctx->acquired > 0) {
 555                        ret = __mutex_lock_check_stamp(lock, ww_ctx);
 556                        if (ret)
 557                                goto err;
 558                }
 559
 560                __set_task_state(task, state);
 561
 562                /* didn't get the lock, go to sleep: */
 563                spin_unlock_mutex(&lock->wait_lock, flags);
 564                schedule_preempt_disabled();
 565                spin_lock_mutex(&lock->wait_lock, flags);
 566        }
 567        mutex_remove_waiter(lock, &waiter, current_thread_info());
 568        /* set it to 0 if there are no waiters left: */
 569        if (likely(list_empty(&lock->wait_list)))
 570                atomic_set(&lock->count, 0);
 571        debug_mutex_free_waiter(&waiter);
 572
 573skip_wait:
 574        /* got the lock - cleanup and rejoice! */
 575        lock_acquired(&lock->dep_map, ip);
 576        mutex_set_owner(lock);
 577
 578        if (use_ww_ctx) {
 579                struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
 580                struct mutex_waiter *cur;
 581
 582                /*
 583                 * This branch gets optimized out for the common case,
 584                 * and is only important for ww_mutex_lock.
 585                 */
 586                ww_mutex_lock_acquired(ww, ww_ctx);
 587                ww->ctx = ww_ctx;
 588
 589                /*
 590                 * Give any possible sleeping processes the chance to wake up,
 591                 * so they can recheck if they have to back off.
 592                 */
 593                list_for_each_entry(cur, &lock->wait_list, list) {
 594                        debug_mutex_wake_waiter(lock, cur);
 595                        wake_up_process(cur->task);
 596                }
 597        }
 598
 599        spin_unlock_mutex(&lock->wait_lock, flags);
 600        preempt_enable();
 601        return 0;
 602
 603err:
 604        mutex_remove_waiter(lock, &waiter, task_thread_info(task));
 605        spin_unlock_mutex(&lock->wait_lock, flags);
 606        debug_mutex_free_waiter(&waiter);
 607        mutex_release(&lock->dep_map, 1, ip);
 608        preempt_enable();
 609        return ret;
 610}
 611
 612#ifdef CONFIG_DEBUG_LOCK_ALLOC
 613void __sched
 614mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 615{
 616        might_sleep();
 617        __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
 618                            subclass, NULL, _RET_IP_, NULL, 0);
 619}
 620
 621EXPORT_SYMBOL_GPL(mutex_lock_nested);
 622
 623void __sched
 624_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
 625{
 626        might_sleep();
 627        __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
 628                            0, nest, _RET_IP_, NULL, 0);
 629}
 630
 631EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
 632
 633int __sched
 634mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 635{
 636        might_sleep();
 637        return __mutex_lock_common(lock, TASK_KILLABLE,
 638                                   subclass, NULL, _RET_IP_, NULL, 0);
 639}
 640EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 641
 642int __sched
 643mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 644{
 645        might_sleep();
 646        return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
 647                                   subclass, NULL, _RET_IP_, NULL, 0);
 648}
 649
 650EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 651
 652static inline int
 653ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 654{
 655#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 656        unsigned tmp;
 657
 658        if (ctx->deadlock_inject_countdown-- == 0) {
 659                tmp = ctx->deadlock_inject_interval;
 660                if (tmp > UINT_MAX/4)
 661                        tmp = UINT_MAX;
 662                else
 663                        tmp = tmp*2 + tmp + tmp/2;
 664
 665                ctx->deadlock_inject_interval = tmp;
 666                ctx->deadlock_inject_countdown = tmp;
 667                ctx->contending_lock = lock;
 668
 669                ww_mutex_unlock(lock);
 670
 671                return -EDEADLK;
 672        }
 673#endif
 674
 675        return 0;
 676}
 677
 678int __sched
 679__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 680{
 681        int ret;
 682
 683        might_sleep();
 684        ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
 685                                   0, &ctx->dep_map, _RET_IP_, ctx, 1);
 686        if (!ret && ctx->acquired > 1)
 687                return ww_mutex_deadlock_injection(lock, ctx);
 688
 689        return ret;
 690}
 691EXPORT_SYMBOL_GPL(__ww_mutex_lock);
 692
 693int __sched
 694__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 695{
 696        int ret;
 697
 698        might_sleep();
 699        ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
 700                                  0, &ctx->dep_map, _RET_IP_, ctx, 1);
 701
 702        if (!ret && ctx->acquired > 1)
 703                return ww_mutex_deadlock_injection(lock, ctx);
 704
 705        return ret;
 706}
 707EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
 708
 709#endif
 710
 711/*
 712 * Release the lock, slowpath:
 713 */
 714static inline void
 715__mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
 716{
 717        struct mutex *lock = container_of(lock_count, struct mutex, count);
 718        unsigned long flags;
 719
 720        spin_lock_mutex(&lock->wait_lock, flags);
 721        mutex_release(&lock->dep_map, nested, _RET_IP_);
 722        debug_mutex_unlock(lock);
 723
 724        /*
 725         * some architectures leave the lock unlocked in the fastpath failure
 726         * case, others need to leave it locked. In the later case we have to
 727         * unlock it here
 728         */
 729        if (__mutex_slowpath_needs_to_unlock())
 730                atomic_set(&lock->count, 1);
 731
 732        if (!list_empty(&lock->wait_list)) {
 733                /* get the first entry from the wait-list: */
 734                struct mutex_waiter *waiter =
 735                                list_entry(lock->wait_list.next,
 736                                           struct mutex_waiter, list);
 737
 738                debug_mutex_wake_waiter(lock, waiter);
 739
 740                wake_up_process(waiter->task);
 741        }
 742
 743        spin_unlock_mutex(&lock->wait_lock, flags);
 744}
 745
 746/*
 747 * Release the lock, slowpath:
 748 */
 749static __used noinline void
 750__mutex_unlock_slowpath(atomic_t *lock_count)
 751{
 752        __mutex_unlock_common_slowpath(lock_count, 1);
 753}
 754
 755#ifndef CONFIG_DEBUG_LOCK_ALLOC
 756/*
 757 * Here come the less common (and hence less performance-critical) APIs:
 758 * mutex_lock_interruptible() and mutex_trylock().
 759 */
 760static noinline int __sched
 761__mutex_lock_killable_slowpath(struct mutex *lock);
 762
 763static noinline int __sched
 764__mutex_lock_interruptible_slowpath(struct mutex *lock);
 765
 766/**
 767 * mutex_lock_interruptible - acquire the mutex, interruptible
 768 * @lock: the mutex to be acquired
 769 *
 770 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
 771 * been acquired or sleep until the mutex becomes available. If a
 772 * signal arrives while waiting for the lock then this function
 773 * returns -EINTR.
 774 *
 775 * This function is similar to (but not equivalent to) down_interruptible().
 776 */
 777int __sched mutex_lock_interruptible(struct mutex *lock)
 778{
 779        int ret;
 780
 781        might_sleep();
 782        ret =  __mutex_fastpath_lock_retval(&lock->count);
 783        if (likely(!ret)) {
 784                mutex_set_owner(lock);
 785                return 0;
 786        } else
 787                return __mutex_lock_interruptible_slowpath(lock);
 788}
 789
 790EXPORT_SYMBOL(mutex_lock_interruptible);
 791
 792int __sched mutex_lock_killable(struct mutex *lock)
 793{
 794        int ret;
 795
 796        might_sleep();
 797        ret = __mutex_fastpath_lock_retval(&lock->count);
 798        if (likely(!ret)) {
 799                mutex_set_owner(lock);
 800                return 0;
 801        } else
 802                return __mutex_lock_killable_slowpath(lock);
 803}
 804EXPORT_SYMBOL(mutex_lock_killable);
 805
 806static __used noinline void __sched
 807__mutex_lock_slowpath(atomic_t *lock_count)
 808{
 809        struct mutex *lock = container_of(lock_count, struct mutex, count);
 810
 811        __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
 812                            NULL, _RET_IP_, NULL, 0);
 813}
 814
 815static noinline int __sched
 816__mutex_lock_killable_slowpath(struct mutex *lock)
 817{
 818        return __mutex_lock_common(lock, TASK_KILLABLE, 0,
 819                                   NULL, _RET_IP_, NULL, 0);
 820}
 821
 822static noinline int __sched
 823__mutex_lock_interruptible_slowpath(struct mutex *lock)
 824{
 825        return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
 826                                   NULL, _RET_IP_, NULL, 0);
 827}
 828
 829static noinline int __sched
 830__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 831{
 832        return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
 833                                   NULL, _RET_IP_, ctx, 1);
 834}
 835
 836static noinline int __sched
 837__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
 838                                            struct ww_acquire_ctx *ctx)
 839{
 840        return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
 841                                   NULL, _RET_IP_, ctx, 1);
 842}
 843
 844#endif
 845
 846/*
 847 * Spinlock based trylock, we take the spinlock and check whether we
 848 * can get the lock:
 849 */
 850static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
 851{
 852        struct mutex *lock = container_of(lock_count, struct mutex, count);
 853        unsigned long flags;
 854        int prev;
 855
 856        spin_lock_mutex(&lock->wait_lock, flags);
 857
 858        prev = atomic_xchg(&lock->count, -1);
 859        if (likely(prev == 1)) {
 860                mutex_set_owner(lock);
 861                mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 862        }
 863
 864        /* Set it back to 0 if there are no waiters: */
 865        if (likely(list_empty(&lock->wait_list)))
 866                atomic_set(&lock->count, 0);
 867
 868        spin_unlock_mutex(&lock->wait_lock, flags);
 869
 870        return prev == 1;
 871}
 872
 873/**
 874 * mutex_trylock - try to acquire the mutex, without waiting
 875 * @lock: the mutex to be acquired
 876 *
 877 * Try to acquire the mutex atomically. Returns 1 if the mutex
 878 * has been acquired successfully, and 0 on contention.
 879 *
 880 * NOTE: this function follows the spin_trylock() convention, so
 881 * it is negated from the down_trylock() return values! Be careful
 882 * about this when converting semaphore users to mutexes.
 883 *
 884 * This function must not be used in interrupt context. The
 885 * mutex must be released by the same task that acquired it.
 886 */
 887int __sched mutex_trylock(struct mutex *lock)
 888{
 889        int ret;
 890
 891        ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
 892        if (ret)
 893                mutex_set_owner(lock);
 894
 895        return ret;
 896}
 897EXPORT_SYMBOL(mutex_trylock);
 898
 899#ifndef CONFIG_DEBUG_LOCK_ALLOC
 900int __sched
 901__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 902{
 903        int ret;
 904
 905        might_sleep();
 906
 907        ret = __mutex_fastpath_lock_retval(&lock->base.count);
 908
 909        if (likely(!ret)) {
 910                ww_mutex_set_context_fastpath(lock, ctx);
 911                mutex_set_owner(&lock->base);
 912        } else
 913                ret = __ww_mutex_lock_slowpath(lock, ctx);
 914        return ret;
 915}
 916EXPORT_SYMBOL(__ww_mutex_lock);
 917
 918int __sched
 919__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 920{
 921        int ret;
 922
 923        might_sleep();
 924
 925        ret = __mutex_fastpath_lock_retval(&lock->base.count);
 926
 927        if (likely(!ret)) {
 928                ww_mutex_set_context_fastpath(lock, ctx);
 929                mutex_set_owner(&lock->base);
 930        } else
 931                ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
 932        return ret;
 933}
 934EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
 935
 936#endif
 937
 938/**
 939 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
 940 * @cnt: the atomic which we are to dec
 941 * @lock: the mutex to return holding if we dec to 0
 942 *
 943 * return true and hold lock if we dec to 0, return false otherwise
 944 */
 945int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
 946{
 947        /* dec if we can't possibly hit 0 */
 948        if (atomic_add_unless(cnt, -1, 1))
 949                return 0;
 950        /* we might hit 0, so take the lock */
 951        mutex_lock(lock);
 952        if (!atomic_dec_and_test(cnt)) {
 953                /* when we actually did the dec, we didn't hit 0 */
 954                mutex_unlock(lock);
 955                return 0;
 956        }
 957        /* we hit 0, and we hold the lock */
 958        return 1;
 959}
 960EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
 961
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