/* SPDX-License-Identifier: GPL-2.0 */ /* * Wound/Wait Mutexes: blocking mutual exclusion locks with deadlock avoidance * * Original mutex implementation started by Ingo Molnar: * * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <[email protected]> * * Wait/Die implementation: * Copyright (C) 2013 Canonical Ltd. * Choice of algorithm: * Copyright (C) 2018 WMWare Inc. * * This file contains the main data structure and API definitions. */ #ifndef __LINUX_WW_MUTEX_H #define __LINUX_WW_MUTEX_H #include <linux/mutex.h> #include <linux/rtmutex.h> #if defined(CONFIG_DEBUG_MUTEXES) || \ (defined(CONFIG_PREEMPT_RT) && defined(CONFIG_DEBUG_RT_MUTEXES)) #define DEBUG_WW_MUTEXES #endif #ifndef CONFIG_PREEMPT_RT #define WW_MUTEX_BASE … #define ww_mutex_base_init(l,n,k) … #define ww_mutex_base_is_locked(b) … #else #define WW_MUTEX_BASE … #define ww_mutex_base_init … #define ww_mutex_base_is_locked … #endif struct ww_class { … }; struct ww_mutex { … }; struct ww_acquire_ctx { … }; #define __WW_CLASS_INITIALIZER(ww_class, _is_wait_die) … #define DEFINE_WD_CLASS(classname) … #define DEFINE_WW_CLASS(classname) … /** * ww_mutex_init - initialize the w/w mutex * @lock: the mutex to be initialized * @ww_class: the w/w class the mutex should belong to * * Initialize the w/w mutex to unlocked state and associate it with the given * class. Static define macro for w/w mutex is not provided and this function * is the only way to properly initialize the w/w mutex. * * It is not allowed to initialize an already locked mutex. */ static inline void ww_mutex_init(struct ww_mutex *lock, struct ww_class *ww_class) { … } /** * ww_acquire_init - initialize a w/w acquire context * @ctx: w/w acquire context to initialize * @ww_class: w/w class of the context * * Initializes an context to acquire multiple mutexes of the given w/w class. * * Context-based w/w mutex acquiring can be done in any order whatsoever within * a given lock class. Deadlocks will be detected and handled with the * wait/die logic. * * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can * result in undetected deadlocks and is so forbidden. Mixing different contexts * for the same w/w class when acquiring mutexes can also result in undetected * deadlocks, and is hence also forbidden. Both types of abuse will be caught by * enabling CONFIG_PROVE_LOCKING. * * Nesting of acquire contexts for _different_ w/w classes is possible, subject * to the usual locking rules between different lock classes. * * An acquire context must be released with ww_acquire_fini by the same task * before the memory is freed. It is recommended to allocate the context itself * on the stack. */ static inline void ww_acquire_init(struct ww_acquire_ctx *ctx, struct ww_class *ww_class) { … } /** * ww_acquire_done - marks the end of the acquire phase * @ctx: the acquire context * * Marks the end of the acquire phase, any further w/w mutex lock calls using * this context are forbidden. * * Calling this function is optional, it is just useful to document w/w mutex * code and clearly designated the acquire phase from actually using the locked * data structures. */ static inline void ww_acquire_done(struct ww_acquire_ctx *ctx) { … } /** * ww_acquire_fini - releases a w/w acquire context * @ctx: the acquire context to free * * Releases a w/w acquire context. This must be called _after_ all acquired w/w * mutexes have been released with ww_mutex_unlock. */ static inline void ww_acquire_fini(struct ww_acquire_ctx *ctx) { … } /** * ww_mutex_lock - acquire the w/w mutex * @lock: the mutex to be acquired * @ctx: w/w acquire context, or NULL to acquire only a single lock. * * Lock the w/w mutex exclusively for this task. * * Deadlocks within a given w/w class of locks are detected and handled with the * wait/die algorithm. If the lock isn't immediately available this function * will either sleep until it is (wait case). Or it selects the current context * for backing off by returning -EDEADLK (die case). Trying to acquire the * same lock with the same context twice is also detected and signalled by * returning -EALREADY. Returns 0 if the mutex was successfully acquired. * * In the die case the caller must release all currently held w/w mutexes for * the given context and then wait for this contending lock to be available by * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this * lock and proceed with trying to acquire further w/w mutexes (e.g. when * scanning through lru lists trying to free resources). * * The mutex must later on be released by the same task that * acquired it. 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 mutex must be * of the same w/w lock class as was used to initialize the acquire context. * * A mutex acquired with this function must be released with ww_mutex_unlock. */ extern int /* __must_check */ ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx); /** * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible * @lock: the mutex to be acquired * @ctx: w/w acquire context * * Lock the w/w mutex exclusively for this task. * * Deadlocks within a given w/w class of locks are detected and handled with the * wait/die algorithm. If the lock isn't immediately available this function * will either sleep until it is (wait case). Or it selects the current context * for backing off by returning -EDEADLK (die case). Trying to acquire the * same lock with the same context twice is also detected and signalled by * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a * signal arrives while waiting for the lock then this function returns -EINTR. * * In the die case the caller must release all currently held w/w mutexes for * the given context and then wait for this contending lock to be available by * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to * not acquire this lock and proceed with trying to acquire further w/w mutexes * (e.g. when scanning through lru lists trying to free resources). * * The mutex must later on be released by the same task that * acquired it. 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 mutex must be * of the same w/w lock class as was used to initialize the acquire context. * * A mutex acquired with this function must be released with ww_mutex_unlock. */ extern int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx); /** * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex * @lock: the mutex to be acquired * @ctx: w/w acquire context * * Acquires a w/w mutex with the given context after a die case. This function * will sleep until the lock becomes available. * * The caller must have released all w/w mutexes already acquired with the * context and then call this function on the contended lock. * * Afterwards the caller may continue to (re)acquire the other w/w mutexes it * needs with ww_mutex_lock. Note that the -EALREADY return code from * ww_mutex_lock can be used to avoid locking this contended mutex twice. * * It is forbidden to call this function with any other w/w mutexes associated * with the context held. It is forbidden to call this on anything else than the * contending mutex. * * Note that the slowpath lock acquiring can also be done by calling * ww_mutex_lock directly. This function here is simply to help w/w mutex * locking code readability by clearly denoting the slowpath. */ static inline void ww_mutex_lock_slow(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { … } /** * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex, interruptible * @lock: the mutex to be acquired * @ctx: w/w acquire context * * Acquires a w/w mutex with the given context after a die case. This function * will sleep until the lock becomes available and returns 0 when the lock has * been acquired. If a signal arrives while waiting for the lock then this * function returns -EINTR. * * The caller must have released all w/w mutexes already acquired with the * context and then call this function on the contended lock. * * Afterwards the caller may continue to (re)acquire the other w/w mutexes it * needs with ww_mutex_lock. Note that the -EALREADY return code from * ww_mutex_lock can be used to avoid locking this contended mutex twice. * * It is forbidden to call this function with any other w/w mutexes associated * with the given context held. It is forbidden to call this on anything else * than the contending mutex. * * Note that the slowpath lock acquiring can also be done by calling * ww_mutex_lock_interruptible directly. This function here is simply to help * w/w mutex locking code readability by clearly denoting the slowpath. */ static inline int __must_check ww_mutex_lock_slow_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { … } extern void ww_mutex_unlock(struct ww_mutex *lock); extern int __must_check ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx); /*** * ww_mutex_destroy - mark a w/w mutex unusable * @lock: the mutex to be destroyed * * This function marks the mutex uninitialized, and any subsequent * use of the mutex is forbidden. The mutex must not be locked when * this function is called. */ static inline void ww_mutex_destroy(struct ww_mutex *lock) { … } /** * ww_mutex_is_locked - is the w/w mutex locked * @lock: the mutex to be queried * * Returns 1 if the mutex is locked, 0 if unlocked. */ static inline bool ww_mutex_is_locked(struct ww_mutex *lock) { … } #endif
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