/* * kernel/locking/mutex.c * * Mutexes: blocking mutual exclusion locks * * Started by Ingo Molnar: * * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar * * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and * David Howells for suggestions and improvements. * * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline * from the -rt tree, where it was originally implemented for rtmutexes * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale * and Sven Dietrich. * * Also see Documentation/mutex-design.txt. */ #include #include #include #include #include #include #include #include #include "mcs_spinlock.h" /* * In the DEBUG case we are using the "NULL fastpath" for mutexes, * which forces all calls into the slowpath: */ #ifdef CONFIG_DEBUG_MUTEXES # include "mutex-debug.h" # include /* * Must be 0 for the debug case so we do not do the unlock outside of the * wait_lock region. debug_mutex_unlock() will do the actual unlock in this * case. */ # undef __mutex_slowpath_needs_to_unlock # define __mutex_slowpath_needs_to_unlock() 0 #else # include "mutex.h" # include #endif void __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) { atomic_set(&lock->count, 1); spin_lock_init(&lock->wait_lock); INIT_LIST_HEAD(&lock->wait_list); mutex_clear_owner(lock); #ifdef CONFIG_MUTEX_SPIN_ON_OWNER lock->osq = NULL; #endif debug_mutex_init(lock, name, key); } EXPORT_SYMBOL(__mutex_init); #ifndef CONFIG_DEBUG_LOCK_ALLOC /* * We split the mutex lock/unlock logic into separate fastpath and * slowpath functions, to reduce the register pressure on the fastpath. * We also put the fastpath first in the kernel image, to make sure the * branch is predicted by the CPU as default-untaken. */ __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count); /** * mutex_lock - acquire the mutex * @lock: the mutex to be acquired * * Lock the mutex exclusively for this task. If the mutex is not * available right now, it will sleep until it can get it. * * The mutex must later on be released by the same task that * acquired it. Recursive locking is not allowed. The task * may not exit without first unlocking the mutex. Also, kernel * memory where the mutex resides mutex must not be freed with * the mutex still locked. The mutex must first be initialized * (or statically defined) before it can be locked. memset()-ing * the mutex to 0 is not allowed. * * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging * checks that will enforce the restrictions and will also do * deadlock debugging. ) * * This function is similar to (but not equivalent to) down(). */ void __sched mutex_lock(struct mutex *lock) { might_sleep(); /* * The locking fastpath is the 1->0 transition from * 'unlocked' into 'locked' state. */ __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); mutex_set_owner(lock); } EXPORT_SYMBOL(mutex_lock); #endif #ifdef CONFIG_MUTEX_SPIN_ON_OWNER /* * In order to avoid a stampede of mutex spinners from acquiring the mutex * more or less simultaneously, the spinners need to acquire a MCS lock * first before spinning on the owner field. * */ /* * Mutex spinning code migrated from kernel/sched/core.c */ static inline bool owner_running(struct mutex *lock, struct task_struct *owner) { if (lock->owner != owner) return false; /* * Ensure we emit the owner->on_cpu, dereference _after_ checking * lock->owner still matches owner, if that fails, owner might * point to free()d memory, if it still matches, the rcu_read_lock() * ensures the memory stays valid. */ barrier(); return owner->on_cpu; } /* * Look out! "owner" is an entirely speculative pointer * access and not reliable. */ static noinline int mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner) { rcu_read_lock(); while (owner_running(lock, owner)) { if (need_resched()) break; arch_mutex_cpu_relax(); } rcu_read_unlock(); /* * We break out the loop above on need_resched() and when the * owner changed, which is a sign for heavy contention. Return * success only when lock->owner is NULL. */ return lock->owner == NULL; } /* * Initial check for entering the mutex spinning loop */ static inline int mutex_can_spin_on_owner(struct mutex *lock) { struct task_struct *owner; int retval = 1; if (need_resched()) return 0; rcu_read_lock(); owner = ACCESS_ONCE(lock->owner); if (owner) retval = owner->on_cpu; rcu_read_unlock(); /* * if lock->owner is not set, the mutex owner may have just acquired * it and not set the owner yet or the mutex has been released. */ return retval; } #endif __visible __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); /** * mutex_unlock - release the mutex * @lock: the mutex to be released * * Unlock a mutex that has been locked by this task previously. * * This function must not be used in interrupt context. Unlocking * of a not locked mutex is not allowed. * * This function is similar to (but not equivalent to) up(). */ void __sched mutex_unlock(struct mutex *lock) { /* * The unlocking fastpath is the 0->1 transition from 'locked' * into 'unlocked' state: */ #ifndef CONFIG_DEBUG_MUTEXES /* * When debugging is enabled we must not clear the owner before time, * the slow path will always be taken, and that clears the owner field * after verifying that it was indeed current. */ mutex_clear_owner(lock); #endif __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); } EXPORT_SYMBOL(mutex_unlock); /** * ww_mutex_unlock - release the w/w mutex * @lock: the mutex to be released * * Unlock a mutex that has been locked by this task previously with any of the * ww_mutex_lock* functions (with or without an acquire context). It is * forbidden to release the locks after releasing the acquire context. * * This function must not be used in interrupt context. Unlocking * of a unlocked mutex is not allowed. */ void __sched ww_mutex_unlock(struct ww_mutex *lock) { /* * The unlocking fastpath is the 0->1 transition from 'locked' * into 'unlocked' state: */ if (lock->ctx) { #ifdef CONFIG_DEBUG_MUTEXES DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired); #endif if (lock->ctx->acquired > 0) lock->ctx->acquired--; lock->ctx = NULL; } #ifndef CONFIG_DEBUG_MUTEXES /* * When debugging is enabled we must not clear the owner before time, * the slow path will always be taken, and that clears the owner field * after verifying that it was indeed current. */ mutex_clear_owner(&lock->base); #endif __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath); } EXPORT_SYMBOL(ww_mutex_unlock); static inline int __sched __mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) { struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx); if (!hold_ctx) return 0; if (unlikely(ctx == hold_ctx)) return -EALREADY; if (ctx->stamp - hold_ctx->stamp <= LONG_MAX && (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) { #ifdef CONFIG_DEBUG_MUTEXES DEBUG_LOCKS_WARN_ON(ctx->contending_lock); ctx->contending_lock = ww; #endif return -EDEADLK; } return 0; } static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) { #ifdef CONFIG_DEBUG_MUTEXES /* * If this WARN_ON triggers, you used ww_mutex_lock to acquire, * but released with a normal mutex_unlock in this call. * * This should never happen, always use ww_mutex_unlock. */ DEBUG_LOCKS_WARN_ON(ww->ctx); /* * Not quite done after calling ww_acquire_done() ? */ DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire); if (ww_ctx->contending_lock) { /* * After -EDEADLK you tried to * acquire a different ww_mutex? Bad! */ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww); /* * You called ww_mutex_lock after receiving -EDEADLK, * but 'forgot' to unlock everything else first? */ DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0); ww_ctx->contending_lock = NULL; } /* * Naughty, using a different class will lead to undefined behavior! */ DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class); #endif ww_ctx->acquired++; } /* * after acquiring lock with fastpath or when we lost out in contested * slowpath, set ctx and wake up any waiters so they can recheck. * * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set, * as the fastpath and opportunistic spinning are disabled in that case. */ static __always_inline void ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { unsigned long flags; struct mutex_waiter *cur; ww_mutex_lock_acquired(lock, ctx); lock->ctx = ctx; /* * The lock->ctx update should be visible on all cores before * the atomic read is done, otherwise contended waiters might be * missed. The contended waiters will either see ww_ctx == NULL * and keep spinning, or it will acquire wait_lock, add itself * to waiter list and sleep. */ smp_mb(); /* ^^^ */ /* * Check if lock is contended, if not there is nobody to wake up */ if (likely(atomic_read(&lock->base.count) == 0)) return; /* * Uh oh, we raced in fastpath, wake up everyone in this case, * so they can see the new lock->ctx. */ spin_lock_mutex(&lock->base.wait_lock, flags); list_for_each_entry(cur, &lock->base.wait_list, list) { debug_mutex_wake_waiter(&lock->base, cur); wake_up_process(cur->task); } spin_unlock_mutex(&lock->base.wait_lock, flags); } /* * Lock a mutex (possibly interruptible), slowpath: */ static __always_inline int __sched __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, struct lockdep_map *nest_lock, unsigned long ip, struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx) { struct task_struct *task = current; struct mutex_waiter waiter; unsigned long flags; int ret; preempt_disable(); mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); #ifdef CONFIG_MUTEX_SPIN_ON_OWNER /* * Optimistic spinning. * * We try to spin for acquisition when we find that the lock owner * is currently running on a (different) CPU and while we don't * need to reschedule. The rationale is that if the lock owner is * running, it is likely to release the lock soon. * * Since this needs the lock owner, and this mutex implementation * doesn't track the owner atomically in the lock field, we need to * track it non-atomically. * * We can't do this for DEBUG_MUTEXES because that relies on wait_lock * to serialize everything. * * The mutex spinners are queued up using MCS lock so that only one * spinner can compete for the mutex. However, if mutex spinning isn't * going to happen, there is no point in going through the lock/unlock * overhead. */ if (!mutex_can_spin_on_owner(lock)) goto slowpath; if (!osq_lock(&lock->osq)) goto slowpath; for (;;) { struct task_struct *owner; if (use_ww_ctx && ww_ctx->acquired > 0) { struct ww_mutex *ww; ww = container_of(lock, struct ww_mutex, base); /* * If ww->ctx is set the contents are undefined, only * by acquiring wait_lock there is a guarantee that * they are not invalid when reading. * * As such, when deadlock detection needs to be * performed the optimistic spinning cannot be done. */ if (ACCESS_ONCE(ww->ctx)) break; } /* * If there's an owner, wait for it to either * release the lock or go to sleep. */ owner = ACCESS_ONCE(lock->owner); if (owner && !mutex_spin_on_owner(lock, owner)) break; /* Try to acquire the mutex if it is unlocked. */ if (!mutex_is_locked(lock) && (atomic_cmpxchg(&lock->count, 1, 0) == 1)) { lock_acquired(&lock->dep_map, ip); if (use_ww_ctx) { struct ww_mutex *ww; ww = container_of(lock, struct ww_mutex, base); ww_mutex_set_context_fastpath(ww, ww_ctx); } mutex_set_owner(lock); osq_unlock(&lock->osq); preempt_enable(); return 0; } /* * When there's no owner, we might have preempted between the * owner acquiring the lock and setting the owner field. If * we're an RT task that will live-lock because we won't let * the owner complete. */ if (!owner && (need_resched() || rt_task(task))) break; /* * The cpu_relax() call is a compiler barrier which forces * everything in this loop to be re-loaded. We don't need * memory barriers as we'll eventually observe the right * values at the cost of a few extra spins. */ arch_mutex_cpu_relax(); } osq_unlock(&lock->osq); slowpath: /* * If we fell out of the spin path because of need_resched(), * reschedule now, before we try-lock the mutex. This avoids getting * scheduled out right after we obtained the mutex. */ if (need_resched()) schedule_preempt_disabled(); #endif spin_lock_mutex(&lock->wait_lock, flags); /* * Once more, try to acquire the lock. Only try-lock the mutex if * it is unlocked to reduce unnecessary xchg() operations. */ if (!mutex_is_locked(lock) && (atomic_xchg(&lock->count, 0) == 1)) goto skip_wait; debug_mutex_lock_common(lock, &waiter); debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); /* add waiting tasks to the end of the waitqueue (FIFO): */ list_add_tail(&waiter.list, &lock->wait_list); waiter.task = task; lock_contended(&lock->dep_map, ip); for (;;) { /* * Lets try to take the lock again - this is needed even if * we get here for the first time (shortly after failing to * acquire the lock), to make sure that we get a wakeup once * it's unlocked. Later on, if we sleep, this is the * operation that gives us the lock. We xchg it to -1, so * that when we release the lock, we properly wake up the * other waiters. We only attempt the xchg if the count is * non-negative in order to avoid unnecessary xchg operations: */ if (atomic_read(&lock->count) >= 0 && (atomic_xchg(&lock->count, -1) == 1)) break; /* * got a signal? (This code gets eliminated in the * TASK_UNINTERRUPTIBLE case.) */ if (unlikely(signal_pending_state(state, task))) { ret = -EINTR; goto err; } if (use_ww_ctx && ww_ctx->acquired > 0) { ret = __mutex_lock_check_stamp(lock, ww_ctx); if (ret) goto err; } __set_task_state(task, state); /* didn't get the lock, go to sleep: */ spin_unlock_mutex(&lock->wait_lock, flags); schedule_preempt_disabled(); spin_lock_mutex(&lock->wait_lock, flags); } mutex_remove_waiter(lock, &waiter, current_thread_info()); /* set it to 0 if there are no waiters left: */ if (likely(list_empty(&lock->wait_list))) atomic_set(&lock->count, 0); debug_mutex_free_waiter(&waiter); skip_wait: /* got the lock - cleanup and rejoice! */ lock_acquired(&lock->dep_map, ip); mutex_set_owner(lock); if (use_ww_ctx) { struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); struct mutex_waiter *cur; /* * This branch gets optimized out for the common case, * and is only important for ww_mutex_lock. */ ww_mutex_lock_acquired(ww, ww_ctx); ww->ctx = ww_ctx; /* * Give any possible sleeping processes the chance to wake up, * so they can recheck if they have to back off. */ list_for_each_entry(cur, &lock->wait_list, list) { debug_mutex_wake_waiter(lock, cur); wake_up_process(cur->task); } } spin_unlock_mutex(&lock->wait_lock, flags); preempt_enable(); return 0; err: mutex_remove_waiter(lock, &waiter, task_thread_info(task)); spin_unlock_mutex(&lock->wait_lock, flags); debug_mutex_free_waiter(&waiter); mutex_release(&lock->dep_map, 1, ip); preempt_enable(); return ret; } #ifdef CONFIG_DEBUG_LOCK_ALLOC void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass) { might_sleep(); __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_, NULL, 0); } EXPORT_SYMBOL_GPL(mutex_lock_nested); void __sched _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) { might_sleep(); __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_, NULL, 0); } EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); int __sched mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) { might_sleep(); return __mutex_lock_common(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_, NULL, 0); } EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); int __sched mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) { might_sleep(); return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_, NULL, 0); } EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); static inline int ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH unsigned tmp; if (ctx->deadlock_inject_countdown-- == 0) { tmp = ctx->deadlock_inject_interval; if (tmp > UINT_MAX/4) tmp = UINT_MAX; else tmp = tmp*2 + tmp + tmp/2; ctx->deadlock_inject_interval = tmp; ctx->deadlock_inject_countdown = tmp; ctx->contending_lock = lock; ww_mutex_unlock(lock); return -EDEADLK; } #endif return 0; } int __sched __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { int ret; might_sleep(); ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, &ctx->dep_map, _RET_IP_, ctx, 1); if (!ret && ctx->acquired > 1) return ww_mutex_deadlock_injection(lock, ctx); return ret; } EXPORT_SYMBOL_GPL(__ww_mutex_lock); int __sched __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { int ret; might_sleep(); ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0, &ctx->dep_map, _RET_IP_, ctx, 1); if (!ret && ctx->acquired > 1) return ww_mutex_deadlock_injection(lock, ctx); return ret; } EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible); #endif /* * Release the lock, slowpath: */ static inline void __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) { struct mutex *lock = container_of(lock_count, struct mutex, count); unsigned long flags; /* * some architectures leave the lock unlocked in the fastpath failure * case, others need to leave it locked. In the later case we have to * unlock it here */ if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1); spin_lock_mutex(&lock->wait_lock, flags); mutex_release(&lock->dep_map, nested, _RET_IP_); debug_mutex_unlock(lock); if (!list_empty(&lock->wait_list)) { /* get the first entry from the wait-list: */ struct mutex_waiter *waiter = list_entry(lock->wait_list.next, struct mutex_waiter, list); debug_mutex_wake_waiter(lock, waiter); wake_up_process(waiter->task); } spin_unlock_mutex(&lock->wait_lock, flags); } /* * Release the lock, slowpath: */ __visible void __mutex_unlock_slowpath(atomic_t *lock_count) { __mutex_unlock_common_slowpath(lock_count, 1); } #ifndef CONFIG_DEBUG_LOCK_ALLOC /* * Here come the less common (and hence less performance-critical) APIs: * mutex_lock_interruptible() and mutex_trylock(). */ static noinline int __sched __mutex_lock_killable_slowpath(struct mutex *lock); static noinline int __sched __mutex_lock_interruptible_slowpath(struct mutex *lock); /** * mutex_lock_interruptible - acquire the mutex, interruptible * @lock: the mutex to be acquired * * Lock the mutex like mutex_lock(), and return 0 if the mutex has * been acquired or sleep until the mutex becomes available. If a * signal arrives while waiting for the lock then this function * returns -EINTR. * * This function is similar to (but not equivalent to) down_interruptible(). */ int __sched mutex_lock_interruptible(struct mutex *lock) { int ret; might_sleep(); ret = __mutex_fastpath_lock_retval(&lock->count); if (likely(!ret)) { mutex_set_owner(lock); return 0; } else return __mutex_lock_interruptible_slowpath(lock); } EXPORT_SYMBOL(mutex_lock_interruptible); int __sched mutex_lock_killable(struct mutex *lock) { int ret; might_sleep(); ret = __mutex_fastpath_lock_retval(&lock->count); if (likely(!ret)) { mutex_set_owner(lock); return 0; } else return __mutex_lock_killable_slowpath(lock); } EXPORT_SYMBOL(mutex_lock_killable); __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count) { struct mutex *lock = container_of(lock_count, struct mutex, count); __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_, NULL, 0); } static noinline int __sched __mutex_lock_killable_slowpath(struct mutex *lock) { return __mutex_lock_common(lock, TASK_KILLABLE, 0, NULL, _RET_IP_, NULL, 0); } static noinline int __sched __mutex_lock_interruptible_slowpath(struct mutex *lock) { return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_, NULL, 0); } static noinline int __sched __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_, ctx, 1); } static noinline int __sched __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_, ctx, 1); } #endif /* * Spinlock based trylock, we take the spinlock and check whether we * can get the lock: */ static inline int __mutex_trylock_slowpath(atomic_t *lock_count) { struct mutex *lock = container_of(lock_count, struct mutex, count); unsigned long flags; int prev; spin_lock_mutex(&lock->wait_lock, flags); prev = atomic_xchg(&lock->count, -1); if (likely(prev == 1)) { mutex_set_owner(lock); mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); } /* Set it back to 0 if there are no waiters: */ if (likely(list_empty(&lock->wait_list))) atomic_set(&lock->count, 0); spin_unlock_mutex(&lock->wait_lock, flags); return prev == 1; } /** * mutex_trylock - try to acquire the mutex, without waiting * @lock: the mutex to be acquired * * Try to acquire the mutex atomically. Returns 1 if the mutex * has been acquired successfully, and 0 on contention. * * NOTE: this function follows the spin_trylock() convention, so * it is negated from the down_trylock() return values! Be careful * about this when converting semaphore users to mutexes. * * This function must not be used in interrupt context. The * mutex must be released by the same task that acquired it. */ int __sched mutex_trylock(struct mutex *lock) { int ret; ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); if (ret) mutex_set_owner(lock); return ret; } EXPORT_SYMBOL(mutex_trylock); #ifndef CONFIG_DEBUG_LOCK_ALLOC int __sched __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { int ret; might_sleep(); ret = __mutex_fastpath_lock_retval(&lock->base.count); if (likely(!ret)) { ww_mutex_set_context_fastpath(lock, ctx); mutex_set_owner(&lock->base); } else ret = __ww_mutex_lock_slowpath(lock, ctx); return ret; } EXPORT_SYMBOL(__ww_mutex_lock); int __sched __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { int ret; might_sleep(); ret = __mutex_fastpath_lock_retval(&lock->base.count); if (likely(!ret)) { ww_mutex_set_context_fastpath(lock, ctx); mutex_set_owner(&lock->base); } else ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx); return ret; } EXPORT_SYMBOL(__ww_mutex_lock_interruptible); #endif /** * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 * @cnt: the atomic which we are to dec * @lock: the mutex to return holding if we dec to 0 * * return true and hold lock if we dec to 0, return false otherwise */ int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) { /* dec if we can't possibly hit 0 */ if (atomic_add_unless(cnt, -1, 1)) return 0; /* we might hit 0, so take the lock */ mutex_lock(lock); if (!atomic_dec_and_test(cnt)) { /* when we actually did the dec, we didn't hit 0 */ mutex_unlock(lock); return 0; } /* we hit 0, and we hold the lock */ return 1; } EXPORT_SYMBOL(atomic_dec_and_mutex_lock);