| /* |
| * kernel/locking/mutex.c |
| * |
| * Mutexes: blocking mutual exclusion locks |
| * |
| * Started by Ingo Molnar: |
| * |
| * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
| * |
| * 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/locking/mutex-design.txt. |
| */ |
| #include <linux/mutex.h> |
| #include <linux/ww_mutex.h> |
| #include <linux/sched/signal.h> |
| #include <linux/sched/rt.h> |
| #include <linux/sched/wake_q.h> |
| #include <linux/sched/debug.h> |
| #include <linux/export.h> |
| #include <linux/spinlock.h> |
| #include <linux/interrupt.h> |
| #include <linux/debug_locks.h> |
| #include <linux/osq_lock.h> |
| |
| #ifdef CONFIG_DEBUG_MUTEXES |
| # include "mutex-debug.h" |
| #else |
| # include "mutex.h" |
| #endif |
| |
| void |
| __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) |
| { |
| atomic_long_set(&lock->owner, 0); |
| spin_lock_init(&lock->wait_lock); |
| INIT_LIST_HEAD(&lock->wait_list); |
| #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
| osq_lock_init(&lock->osq); |
| #endif |
| |
| debug_mutex_init(lock, name, key); |
| } |
| EXPORT_SYMBOL(__mutex_init); |
| |
| /* |
| * @owner: contains: 'struct task_struct *' to the current lock owner, |
| * NULL means not owned. Since task_struct pointers are aligned at |
| * at least L1_CACHE_BYTES, we have low bits to store extra state. |
| * |
| * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup. |
| * Bit1 indicates unlock needs to hand the lock to the top-waiter |
| * Bit2 indicates handoff has been done and we're waiting for pickup. |
| */ |
| #define MUTEX_FLAG_WAITERS 0x01 |
| #define MUTEX_FLAG_HANDOFF 0x02 |
| #define MUTEX_FLAG_PICKUP 0x04 |
| |
| #define MUTEX_FLAGS 0x07 |
| |
| static inline struct task_struct *__owner_task(unsigned long owner) |
| { |
| return (struct task_struct *)(owner & ~MUTEX_FLAGS); |
| } |
| |
| static inline unsigned long __owner_flags(unsigned long owner) |
| { |
| return owner & MUTEX_FLAGS; |
| } |
| |
| /* |
| * Trylock variant that retuns the owning task on failure. |
| */ |
| static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock) |
| { |
| unsigned long owner, curr = (unsigned long)current; |
| |
| owner = atomic_long_read(&lock->owner); |
| for (;;) { /* must loop, can race against a flag */ |
| unsigned long old, flags = __owner_flags(owner); |
| unsigned long task = owner & ~MUTEX_FLAGS; |
| |
| if (task) { |
| if (likely(task != curr)) |
| break; |
| |
| if (likely(!(flags & MUTEX_FLAG_PICKUP))) |
| break; |
| |
| flags &= ~MUTEX_FLAG_PICKUP; |
| } else { |
| #ifdef CONFIG_DEBUG_MUTEXES |
| DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP); |
| #endif |
| } |
| |
| /* |
| * We set the HANDOFF bit, we must make sure it doesn't live |
| * past the point where we acquire it. This would be possible |
| * if we (accidentally) set the bit on an unlocked mutex. |
| */ |
| flags &= ~MUTEX_FLAG_HANDOFF; |
| |
| old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags); |
| if (old == owner) |
| return NULL; |
| |
| owner = old; |
| } |
| |
| return __owner_task(owner); |
| } |
| |
| /* |
| * Actual trylock that will work on any unlocked state. |
| */ |
| static inline bool __mutex_trylock(struct mutex *lock) |
| { |
| return !__mutex_trylock_or_owner(lock); |
| } |
| |
| #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| /* |
| * Lockdep annotations are contained to the slow paths for simplicity. |
| * There is nothing that would stop spreading the lockdep annotations outwards |
| * except more code. |
| */ |
| |
| /* |
| * Optimistic trylock that only works in the uncontended case. Make sure to |
| * follow with a __mutex_trylock() before failing. |
| */ |
| static __always_inline bool __mutex_trylock_fast(struct mutex *lock) |
| { |
| unsigned long curr = (unsigned long)current; |
| unsigned long zero = 0UL; |
| |
| if (atomic_long_try_cmpxchg_acquire(&lock->owner, &zero, curr)) |
| return true; |
| |
| return false; |
| } |
| |
| static __always_inline bool __mutex_unlock_fast(struct mutex *lock) |
| { |
| unsigned long curr = (unsigned long)current; |
| |
| if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr) |
| return true; |
| |
| return false; |
| } |
| #endif |
| |
| static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag) |
| { |
| atomic_long_or(flag, &lock->owner); |
| } |
| |
| static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag) |
| { |
| atomic_long_andnot(flag, &lock->owner); |
| } |
| |
| static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter) |
| { |
| return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter; |
| } |
| |
| /* |
| * Add @waiter to a given location in the lock wait_list and set the |
| * FLAG_WAITERS flag if it's the first waiter. |
| */ |
| static void __sched |
| __mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter, |
| struct list_head *list) |
| { |
| debug_mutex_add_waiter(lock, waiter, current); |
| |
| list_add_tail(&waiter->list, list); |
| if (__mutex_waiter_is_first(lock, waiter)) |
| __mutex_set_flag(lock, MUTEX_FLAG_WAITERS); |
| } |
| |
| /* |
| * Give up ownership to a specific task, when @task = NULL, this is equivalent |
| * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves |
| * WAITERS. Provides RELEASE semantics like a regular unlock, the |
| * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff. |
| */ |
| static void __mutex_handoff(struct mutex *lock, struct task_struct *task) |
| { |
| unsigned long owner = atomic_long_read(&lock->owner); |
| |
| for (;;) { |
| unsigned long old, new; |
| |
| #ifdef CONFIG_DEBUG_MUTEXES |
| DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); |
| DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP); |
| #endif |
| |
| new = (owner & MUTEX_FLAG_WAITERS); |
| new |= (unsigned long)task; |
| if (task) |
| new |= MUTEX_FLAG_PICKUP; |
| |
| old = atomic_long_cmpxchg_release(&lock->owner, owner, new); |
| if (old == owner) |
| break; |
| |
| owner = old; |
| } |
| } |
| |
| #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. |
| */ |
| static void __sched __mutex_lock_slowpath(struct mutex *lock); |
| |
| /** |
| * 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 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(); |
| |
| if (!__mutex_trylock_fast(lock)) |
| __mutex_lock_slowpath(lock); |
| } |
| EXPORT_SYMBOL(mutex_lock); |
| #endif |
| |
| /* |
| * Wait-Die: |
| * The newer transactions are killed when: |
| * It (the new transaction) makes a request for a lock being held |
| * by an older transaction. |
| * |
| * Wound-Wait: |
| * The newer transactions are wounded when: |
| * An older transaction makes a request for a lock being held by |
| * the newer transaction. |
| */ |
| |
| /* |
| * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired |
| * it. |
| */ |
| 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++; |
| ww->ctx = ww_ctx; |
| } |
| |
| /* |
| * Determine if context @a is 'after' context @b. IOW, @a is a younger |
| * transaction than @b and depending on algorithm either needs to wait for |
| * @b or die. |
| */ |
| static inline bool __sched |
| __ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b) |
| { |
| |
| return (signed long)(a->stamp - b->stamp) > 0; |
| } |
| |
| /* |
| * Wait-Die; wake a younger waiter context (when locks held) such that it can |
| * die. |
| * |
| * Among waiters with context, only the first one can have other locks acquired |
| * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and |
| * __ww_mutex_check_kill() wake any but the earliest context. |
| */ |
| static bool __sched |
| __ww_mutex_die(struct mutex *lock, struct mutex_waiter *waiter, |
| struct ww_acquire_ctx *ww_ctx) |
| { |
| if (!ww_ctx->is_wait_die) |
| return false; |
| |
| if (waiter->ww_ctx->acquired > 0 && |
| __ww_ctx_stamp_after(waiter->ww_ctx, ww_ctx)) { |
| debug_mutex_wake_waiter(lock, waiter); |
| wake_up_process(waiter->task); |
| } |
| |
| return true; |
| } |
| |
| /* |
| * Wound-Wait; wound a younger @hold_ctx if it holds the lock. |
| * |
| * Wound the lock holder if there are waiters with older transactions than |
| * the lock holders. Even if multiple waiters may wound the lock holder, |
| * it's sufficient that only one does. |
| */ |
| static bool __ww_mutex_wound(struct mutex *lock, |
| struct ww_acquire_ctx *ww_ctx, |
| struct ww_acquire_ctx *hold_ctx) |
| { |
| struct task_struct *owner = __mutex_owner(lock); |
| |
| lockdep_assert_held(&lock->wait_lock); |
| |
| /* |
| * Possible through __ww_mutex_add_waiter() when we race with |
| * ww_mutex_set_context_fastpath(). In that case we'll get here again |
| * through __ww_mutex_check_waiters(). |
| */ |
| if (!hold_ctx) |
| return false; |
| |
| /* |
| * Can have !owner because of __mutex_unlock_slowpath(), but if owner, |
| * it cannot go away because we'll have FLAG_WAITERS set and hold |
| * wait_lock. |
| */ |
| if (!owner) |
| return false; |
| |
| if (ww_ctx->acquired > 0 && __ww_ctx_stamp_after(hold_ctx, ww_ctx)) { |
| hold_ctx->wounded = 1; |
| |
| /* |
| * wake_up_process() paired with set_current_state() |
| * inserts sufficient barriers to make sure @owner either sees |
| * it's wounded in __ww_mutex_check_kill() or has a |
| * wakeup pending to re-read the wounded state. |
| */ |
| if (owner != current) |
| wake_up_process(owner); |
| |
| return true; |
| } |
| |
| return false; |
| } |
| |
| /* |
| * We just acquired @lock under @ww_ctx, if there are later contexts waiting |
| * behind us on the wait-list, check if they need to die, or wound us. |
| * |
| * See __ww_mutex_add_waiter() for the list-order construction; basically the |
| * list is ordered by stamp, smallest (oldest) first. |
| * |
| * This relies on never mixing wait-die/wound-wait on the same wait-list; |
| * which is currently ensured by that being a ww_class property. |
| * |
| * The current task must not be on the wait list. |
| */ |
| static void __sched |
| __ww_mutex_check_waiters(struct mutex *lock, struct ww_acquire_ctx *ww_ctx) |
| { |
| struct mutex_waiter *cur; |
| |
| lockdep_assert_held(&lock->wait_lock); |
| |
| list_for_each_entry(cur, &lock->wait_list, list) { |
| if (!cur->ww_ctx) |
| continue; |
| |
| if (__ww_mutex_die(lock, cur, ww_ctx) || |
| __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx)) |
| break; |
| } |
| } |
| |
| /* |
| * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx |
| * and wake up any waiters so they can recheck. |
| */ |
| static __always_inline void |
| ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| { |
| ww_mutex_lock_acquired(lock, ctx); |
| |
| /* |
| * The lock->ctx update should be visible on all cores before |
| * the WAITERS check 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(); /* See comments above and below. */ |
| |
| /* |
| * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS |
| * MB MB |
| * [R] MUTEX_FLAG_WAITERS [R] ww->ctx |
| * |
| * The memory barrier above pairs with the memory barrier in |
| * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx |
| * and/or !empty list. |
| */ |
| if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS))) |
| return; |
| |
| /* |
| * Uh oh, we raced in fastpath, check if any of the waiters need to |
| * die or wound us. |
| */ |
| spin_lock(&lock->base.wait_lock); |
| __ww_mutex_check_waiters(&lock->base, ctx); |
| spin_unlock(&lock->base.wait_lock); |
| } |
| |
| #ifdef CONFIG_MUTEX_SPIN_ON_OWNER |
| |
| static inline |
| bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx, |
| struct mutex_waiter *waiter) |
| { |
| 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. |
| * |
| * Check this in every inner iteration because we may |
| * be racing against another thread's ww_mutex_lock. |
| */ |
| if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx)) |
| return false; |
| |
| /* |
| * If we aren't on the wait list yet, cancel the spin |
| * if there are waiters. We want to avoid stealing the |
| * lock from a waiter with an earlier stamp, since the |
| * other thread may already own a lock that we also |
| * need. |
| */ |
| if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS)) |
| return false; |
| |
| /* |
| * Similarly, stop spinning if we are no longer the |
| * first waiter. |
| */ |
| if (waiter && !__mutex_waiter_is_first(lock, waiter)) |
| return false; |
| |
| return true; |
| } |
| |
| /* |
| * Look out! "owner" is an entirely speculative pointer access and not |
| * reliable. |
| * |
| * "noinline" so that this function shows up on perf profiles. |
| */ |
| static noinline |
| bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner, |
| struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter) |
| { |
| bool ret = true; |
| |
| rcu_read_lock(); |
| while (__mutex_owner(lock) == owner) { |
| /* |
| * Ensure we emit the owner->on_cpu, dereference _after_ |
| * checking lock->owner still matches owner. If that fails, |
| * owner might point to freed memory. If it still matches, |
| * the rcu_read_lock() ensures the memory stays valid. |
| */ |
| barrier(); |
| |
| /* |
| * Use vcpu_is_preempted to detect lock holder preemption issue. |
| */ |
| if (!owner->on_cpu || need_resched() || |
| vcpu_is_preempted(task_cpu(owner))) { |
| ret = false; |
| break; |
| } |
| |
| if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) { |
| ret = false; |
| break; |
| } |
| |
| cpu_relax(); |
| } |
| rcu_read_unlock(); |
| |
| return ret; |
| } |
| |
| /* |
| * 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 = __mutex_owner(lock); |
| |
| /* |
| * As lock holder preemption issue, we both skip spinning if task is not |
| * on cpu or its cpu is preempted |
| */ |
| if (owner) |
| retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner)); |
| rcu_read_unlock(); |
| |
| /* |
| * If lock->owner is not set, the mutex has been released. Return true |
| * such that we'll trylock in the spin path, which is a faster option |
| * than the blocking slow path. |
| */ |
| return retval; |
| } |
| |
| /* |
| * 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. |
| * |
| * 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. |
| * |
| * Returns true when the lock was taken, otherwise false, indicating |
| * that we need to jump to the slowpath and sleep. |
| * |
| * The waiter flag is set to true if the spinner is a waiter in the wait |
| * queue. The waiter-spinner will spin on the lock directly and concurrently |
| * with the spinner at the head of the OSQ, if present, until the owner is |
| * changed to itself. |
| */ |
| static __always_inline bool |
| mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx, |
| const bool use_ww_ctx, struct mutex_waiter *waiter) |
| { |
| if (!waiter) { |
| /* |
| * The purpose of the mutex_can_spin_on_owner() function is |
| * to eliminate the overhead of osq_lock() and osq_unlock() |
| * in case spinning isn't possible. As a waiter-spinner |
| * is not going to take OSQ lock anyway, there is no need |
| * to call mutex_can_spin_on_owner(). |
| */ |
| if (!mutex_can_spin_on_owner(lock)) |
| goto fail; |
| |
| /* |
| * In order to avoid a stampede of mutex spinners trying to |
| * acquire the mutex all at once, the spinners need to take a |
| * MCS (queued) lock first before spinning on the owner field. |
| */ |
| if (!osq_lock(&lock->osq)) |
| goto fail; |
| } |
| |
| for (;;) { |
| struct task_struct *owner; |
| |
| /* Try to acquire the mutex... */ |
| owner = __mutex_trylock_or_owner(lock); |
| if (!owner) |
| break; |
| |
| /* |
| * There's an owner, wait for it to either |
| * release the lock or go to sleep. |
| */ |
| if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter)) |
| goto fail_unlock; |
| |
| /* |
| * 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. |
| */ |
| cpu_relax(); |
| } |
| |
| if (!waiter) |
| osq_unlock(&lock->osq); |
| |
| return true; |
| |
| |
| fail_unlock: |
| if (!waiter) |
| osq_unlock(&lock->osq); |
| |
| fail: |
| /* |
| * 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()) { |
| /* |
| * We _should_ have TASK_RUNNING here, but just in case |
| * we do not, make it so, otherwise we might get stuck. |
| */ |
| __set_current_state(TASK_RUNNING); |
| schedule_preempt_disabled(); |
| } |
| |
| return false; |
| } |
| #else |
| static __always_inline bool |
| mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx, |
| const bool use_ww_ctx, struct mutex_waiter *waiter) |
| { |
| return false; |
| } |
| #endif |
| |
| static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip); |
| |
| /** |
| * 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) |
| { |
| #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| if (__mutex_unlock_fast(lock)) |
| return; |
| #endif |
| __mutex_unlock_slowpath(lock, _RET_IP_); |
| } |
| 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; |
| } |
| |
| mutex_unlock(&lock->base); |
| } |
| EXPORT_SYMBOL(ww_mutex_unlock); |
| |
| |
| static __always_inline int __sched |
| __ww_mutex_kill(struct mutex *lock, struct ww_acquire_ctx *ww_ctx) |
| { |
| if (ww_ctx->acquired > 0) { |
| #ifdef CONFIG_DEBUG_MUTEXES |
| struct ww_mutex *ww; |
| |
| ww = container_of(lock, struct ww_mutex, base); |
| DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock); |
| ww_ctx->contending_lock = ww; |
| #endif |
| return -EDEADLK; |
| } |
| |
| return 0; |
| } |
| |
| |
| /* |
| * Check the wound condition for the current lock acquire. |
| * |
| * Wound-Wait: If we're wounded, kill ourself. |
| * |
| * Wait-Die: If we're trying to acquire a lock already held by an older |
| * context, kill ourselves. |
| * |
| * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to |
| * look at waiters before us in the wait-list. |
| */ |
| static inline int __sched |
| __ww_mutex_check_kill(struct mutex *lock, struct mutex_waiter *waiter, |
| struct ww_acquire_ctx *ctx) |
| { |
| struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); |
| struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx); |
| struct mutex_waiter *cur; |
| |
| if (ctx->acquired == 0) |
| return 0; |
| |
| if (!ctx->is_wait_die) { |
| if (ctx->wounded) |
| return __ww_mutex_kill(lock, ctx); |
| |
| return 0; |
| } |
| |
| if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx)) |
| return __ww_mutex_kill(lock, ctx); |
| |
| /* |
| * If there is a waiter in front of us that has a context, then its |
| * stamp is earlier than ours and we must kill ourself. |
| */ |
| cur = waiter; |
| list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) { |
| if (!cur->ww_ctx) |
| continue; |
| |
| return __ww_mutex_kill(lock, ctx); |
| } |
| |
| return 0; |
| } |
| |
| /* |
| * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest |
| * first. Such that older contexts are preferred to acquire the lock over |
| * younger contexts. |
| * |
| * Waiters without context are interspersed in FIFO order. |
| * |
| * Furthermore, for Wait-Die kill ourself immediately when possible (there are |
| * older contexts already waiting) to avoid unnecessary waiting and for |
| * Wound-Wait ensure we wound the owning context when it is younger. |
| */ |
| static inline int __sched |
| __ww_mutex_add_waiter(struct mutex_waiter *waiter, |
| struct mutex *lock, |
| struct ww_acquire_ctx *ww_ctx) |
| { |
| struct mutex_waiter *cur; |
| struct list_head *pos; |
| bool is_wait_die; |
| |
| if (!ww_ctx) { |
| __mutex_add_waiter(lock, waiter, &lock->wait_list); |
| return 0; |
| } |
| |
| is_wait_die = ww_ctx->is_wait_die; |
| |
| /* |
| * Add the waiter before the first waiter with a higher stamp. |
| * Waiters without a context are skipped to avoid starving |
| * them. Wait-Die waiters may die here. Wound-Wait waiters |
| * never die here, but they are sorted in stamp order and |
| * may wound the lock holder. |
| */ |
| pos = &lock->wait_list; |
| list_for_each_entry_reverse(cur, &lock->wait_list, list) { |
| if (!cur->ww_ctx) |
| continue; |
| |
| if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) { |
| /* |
| * Wait-Die: if we find an older context waiting, there |
| * is no point in queueing behind it, as we'd have to |
| * die the moment it would acquire the lock. |
| */ |
| if (is_wait_die) { |
| int ret = __ww_mutex_kill(lock, ww_ctx); |
| |
| if (ret) |
| return ret; |
| } |
| |
| break; |
| } |
| |
| pos = &cur->list; |
| |
| /* Wait-Die: ensure younger waiters die. */ |
| __ww_mutex_die(lock, cur, ww_ctx); |
| } |
| |
| __mutex_add_waiter(lock, waiter, pos); |
| |
| /* |
| * Wound-Wait: if we're blocking on a mutex owned by a younger context, |
| * wound that such that we might proceed. |
| */ |
| if (!is_wait_die) { |
| struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); |
| |
| /* |
| * See ww_mutex_set_context_fastpath(). Orders setting |
| * MUTEX_FLAG_WAITERS vs the ww->ctx load, |
| * such that either we or the fastpath will wound @ww->ctx. |
| */ |
| smp_mb(); |
| __ww_mutex_wound(lock, ww_ctx, ww->ctx); |
| } |
| |
| return 0; |
| } |
| |
| /* |
| * 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 mutex_waiter waiter; |
| bool first = false; |
| struct ww_mutex *ww; |
| int ret; |
| |
| might_sleep(); |
| |
| ww = container_of(lock, struct ww_mutex, base); |
| if (use_ww_ctx && ww_ctx) { |
| if (unlikely(ww_ctx == READ_ONCE(ww->ctx))) |
| return -EALREADY; |
| |
| /* |
| * Reset the wounded flag after a kill. No other process can |
| * race and wound us here since they can't have a valid owner |
| * pointer if we don't have any locks held. |
| */ |
| if (ww_ctx->acquired == 0) |
| ww_ctx->wounded = 0; |
| } |
| |
| preempt_disable(); |
| mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip); |
| |
| if (__mutex_trylock(lock) || |
| mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) { |
| /* got the lock, yay! */ |
| lock_acquired(&lock->dep_map, ip); |
| if (use_ww_ctx && ww_ctx) |
| ww_mutex_set_context_fastpath(ww, ww_ctx); |
| preempt_enable(); |
| return 0; |
| } |
| |
| spin_lock(&lock->wait_lock); |
| /* |
| * After waiting to acquire the wait_lock, try again. |
| */ |
| if (__mutex_trylock(lock)) { |
| if (use_ww_ctx && ww_ctx) |
| __ww_mutex_check_waiters(lock, ww_ctx); |
| |
| goto skip_wait; |
| } |
| |
| debug_mutex_lock_common(lock, &waiter); |
| |
| lock_contended(&lock->dep_map, ip); |
| |
| if (!use_ww_ctx) { |
| /* add waiting tasks to the end of the waitqueue (FIFO): */ |
| __mutex_add_waiter(lock, &waiter, &lock->wait_list); |
| |
| |
| #ifdef CONFIG_DEBUG_MUTEXES |
| waiter.ww_ctx = MUTEX_POISON_WW_CTX; |
| #endif |
| } else { |
| /* |
| * Add in stamp order, waking up waiters that must kill |
| * themselves. |
| */ |
| ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx); |
| if (ret) |
| goto err_early_kill; |
| |
| waiter.ww_ctx = ww_ctx; |
| } |
| |
| waiter.task = current; |
| |
| set_current_state(state); |
| for (;;) { |
| /* |
| * Once we hold wait_lock, we're serialized against |
| * mutex_unlock() handing the lock off to us, do a trylock |
| * before testing the error conditions to make sure we pick up |
| * the handoff. |
| */ |
| if (__mutex_trylock(lock)) |
| goto acquired; |
| |
| /* |
| * Check for signals and kill conditions while holding |
| * wait_lock. This ensures the lock cancellation is ordered |
| * against mutex_unlock() and wake-ups do not go missing. |
| */ |
| if (signal_pending_state(state, current)) { |
| ret = -EINTR; |
| goto err; |
| } |
| |
| if (use_ww_ctx && ww_ctx) { |
| ret = __ww_mutex_check_kill(lock, &waiter, ww_ctx); |
| if (ret) |
| goto err; |
| } |
| |
| spin_unlock(&lock->wait_lock); |
| schedule_preempt_disabled(); |
| |
| /* |
| * ww_mutex needs to always recheck its position since its waiter |
| * list is not FIFO ordered. |
| */ |
| if ((use_ww_ctx && ww_ctx) || !first) { |
| first = __mutex_waiter_is_first(lock, &waiter); |
| if (first) |
| __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF); |
| } |
| |
| set_current_state(state); |
| /* |
| * Here we order against unlock; we must either see it change |
| * state back to RUNNING and fall through the next schedule(), |
| * or we must see its unlock and acquire. |
| */ |
| if (__mutex_trylock(lock) || |
| (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter))) |
| break; |
| |
| spin_lock(&lock->wait_lock); |
| } |
| spin_lock(&lock->wait_lock); |
| acquired: |
| __set_current_state(TASK_RUNNING); |
| |
| if (use_ww_ctx && ww_ctx) { |
| /* |
| * Wound-Wait; we stole the lock (!first_waiter), check the |
| * waiters as anyone might want to wound us. |
| */ |
| if (!ww_ctx->is_wait_die && |
| !__mutex_waiter_is_first(lock, &waiter)) |
| __ww_mutex_check_waiters(lock, ww_ctx); |
| } |
| |
| mutex_remove_waiter(lock, &waiter, current); |
| if (likely(list_empty(&lock->wait_list))) |
| __mutex_clear_flag(lock, MUTEX_FLAGS); |
| |
| debug_mutex_free_waiter(&waiter); |
| |
| skip_wait: |
| /* got the lock - cleanup and rejoice! */ |
| lock_acquired(&lock->dep_map, ip); |
| |
| if (use_ww_ctx && ww_ctx) |
| ww_mutex_lock_acquired(ww, ww_ctx); |
| |
| spin_unlock(&lock->wait_lock); |
| preempt_enable(); |
| return 0; |
| |
| err: |
| __set_current_state(TASK_RUNNING); |
| mutex_remove_waiter(lock, &waiter, current); |
| err_early_kill: |
| spin_unlock(&lock->wait_lock); |
| debug_mutex_free_waiter(&waiter); |
| mutex_release(&lock->dep_map, 1, ip); |
| preempt_enable(); |
| return ret; |
| } |
| |
| static int __sched |
| __mutex_lock(struct mutex *lock, long state, unsigned int subclass, |
| struct lockdep_map *nest_lock, unsigned long ip) |
| { |
| return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false); |
| } |
| |
| static int __sched |
| __ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass, |
| struct lockdep_map *nest_lock, unsigned long ip, |
| struct ww_acquire_ctx *ww_ctx) |
| { |
| return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true); |
| } |
| |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| void __sched |
| mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
| { |
| __mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_); |
| } |
| |
| EXPORT_SYMBOL_GPL(mutex_lock_nested); |
| |
| void __sched |
| _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest) |
| { |
| __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_); |
| } |
| EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); |
| |
| int __sched |
| mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
| { |
| return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_); |
| } |
| EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
| |
| int __sched |
| mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
| { |
| return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_); |
| } |
| EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); |
| |
| void __sched |
| mutex_lock_io_nested(struct mutex *lock, unsigned int subclass) |
| { |
| int token; |
| |
| might_sleep(); |
| |
| token = io_schedule_prepare(); |
| __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, |
| subclass, NULL, _RET_IP_, NULL, 0); |
| io_schedule_finish(token); |
| } |
| EXPORT_SYMBOL_GPL(mutex_lock_io_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 = __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, |
| 0, ctx ? &ctx->dep_map : NULL, _RET_IP_, |
| ctx); |
| if (!ret && ctx && 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 = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, |
| 0, ctx ? &ctx->dep_map : NULL, _RET_IP_, |
| ctx); |
| |
| if (!ret && ctx && 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 noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip) |
| { |
| struct task_struct *next = NULL; |
| DEFINE_WAKE_Q(wake_q); |
| unsigned long owner; |
| |
| mutex_release(&lock->dep_map, 1, ip); |
| |
| /* |
| * Release the lock before (potentially) taking the spinlock such that |
| * other contenders can get on with things ASAP. |
| * |
| * Except when HANDOFF, in that case we must not clear the owner field, |
| * but instead set it to the top waiter. |
| */ |
| owner = atomic_long_read(&lock->owner); |
| for (;;) { |
| unsigned long old; |
| |
| #ifdef CONFIG_DEBUG_MUTEXES |
| DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current); |
| DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP); |
| #endif |
| |
| if (owner & MUTEX_FLAG_HANDOFF) |
| break; |
| |
| old = atomic_long_cmpxchg_release(&lock->owner, owner, |
| __owner_flags(owner)); |
| if (old == owner) { |
| if (owner & MUTEX_FLAG_WAITERS) |
| break; |
| |
| return; |
| } |
| |
| owner = old; |
| } |
| |
| spin_lock(&lock->wait_lock); |
| debug_mutex_unlock(lock); |
| if (!list_empty(&lock->wait_list)) { |
| /* get the first entry from the wait-list: */ |
| struct mutex_waiter *waiter = |
| list_first_entry(&lock->wait_list, |
| struct mutex_waiter, list); |
| |
| next = waiter->task; |
| |
| debug_mutex_wake_waiter(lock, waiter); |
| wake_q_add(&wake_q, next); |
| } |
| |
| if (owner & MUTEX_FLAG_HANDOFF) |
| __mutex_handoff(lock, next); |
| |
| spin_unlock(&lock->wait_lock); |
| |
| wake_up_q(&wake_q); |
| } |
| |
| #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 by signals. |
| * @lock: The mutex to be acquired. |
| * |
| * Lock the mutex like mutex_lock(). If a signal is delivered while the |
| * process is sleeping, this function will return without acquiring the |
| * mutex. |
| * |
| * Context: Process context. |
| * Return: 0 if the lock was successfully acquired or %-EINTR if a |
| * signal arrived. |
| */ |
| int __sched mutex_lock_interruptible(struct mutex *lock) |
| { |
| might_sleep(); |
| |
| if (__mutex_trylock_fast(lock)) |
| return 0; |
| |
| return __mutex_lock_interruptible_slowpath(lock); |
| } |
| |
| EXPORT_SYMBOL(mutex_lock_interruptible); |
| |
| /** |
| * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals. |
| * @lock: The mutex to be acquired. |
| * |
| * Lock the mutex like mutex_lock(). If a signal which will be fatal to |
| * the current process is delivered while the process is sleeping, this |
| * function will return without acquiring the mutex. |
| * |
| * Context: Process context. |
| * Return: 0 if the lock was successfully acquired or %-EINTR if a |
| * fatal signal arrived. |
| */ |
| int __sched mutex_lock_killable(struct mutex *lock) |
| { |
| might_sleep(); |
| |
| if (__mutex_trylock_fast(lock)) |
| return 0; |
| |
| return __mutex_lock_killable_slowpath(lock); |
| } |
| EXPORT_SYMBOL(mutex_lock_killable); |
| |
| /** |
| * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O |
| * @lock: The mutex to be acquired. |
| * |
| * Lock the mutex like mutex_lock(). While the task is waiting for this |
| * mutex, it will be accounted as being in the IO wait state by the |
| * scheduler. |
| * |
| * Context: Process context. |
| */ |
| void __sched mutex_lock_io(struct mutex *lock) |
| { |
| int token; |
| |
| token = io_schedule_prepare(); |
| mutex_lock(lock); |
| io_schedule_finish(token); |
| } |
| EXPORT_SYMBOL_GPL(mutex_lock_io); |
| |
| static noinline void __sched |
| __mutex_lock_slowpath(struct mutex *lock) |
| { |
| __mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_); |
| } |
| |
| static noinline int __sched |
| __mutex_lock_killable_slowpath(struct mutex *lock) |
| { |
| return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_); |
| } |
| |
| static noinline int __sched |
| __mutex_lock_interruptible_slowpath(struct mutex *lock) |
| { |
| return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_); |
| } |
| |
| static noinline int __sched |
| __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| { |
| return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL, |
| _RET_IP_, ctx); |
| } |
| |
| static noinline int __sched |
| __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock, |
| struct ww_acquire_ctx *ctx) |
| { |
| return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL, |
| _RET_IP_, ctx); |
| } |
| |
| #endif |
| |
| /** |
| * 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) |
| { |
| bool locked = __mutex_trylock(lock); |
| |
| if (locked) |
| mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
| |
| return locked; |
| } |
| EXPORT_SYMBOL(mutex_trylock); |
| |
| #ifndef CONFIG_DEBUG_LOCK_ALLOC |
| int __sched |
| ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| { |
| might_sleep(); |
| |
| if (__mutex_trylock_fast(&lock->base)) { |
| if (ctx) |
| ww_mutex_set_context_fastpath(lock, ctx); |
| return 0; |
| } |
| |
| return __ww_mutex_lock_slowpath(lock, ctx); |
| } |
| EXPORT_SYMBOL(ww_mutex_lock); |
| |
| int __sched |
| ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) |
| { |
| might_sleep(); |
| |
| if (__mutex_trylock_fast(&lock->base)) { |
| if (ctx) |
| ww_mutex_set_context_fastpath(lock, ctx); |
| return 0; |
| } |
| |
| return __ww_mutex_lock_interruptible_slowpath(lock, ctx); |
| } |
| 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); |