/* * 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/locking/mutex-design.txt. */ #include #include #include #include #include #include #include #include #include #include #include #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, 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, 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; if (!use_ww_ctx) ww_ctx = NULL; might_sleep(); ww = container_of(lock, struct ww_mutex, base); if (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, NULL)) { /* got the lock, yay! */ lock_acquired(&lock->dep_map, ip); if (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 (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 (unlikely(signal_pending_state(state, current))) { ret = -EINTR; goto err; } if (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 (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, &waiter))) break; spin_lock(&lock->wait_lock); } spin_lock(&lock->wait_lock); acquired: __set_current_state(TASK_RUNNING); if (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 (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);