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/*

 * 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 

 *

 * Wound/wait implementation:

 *  Copyright (C) 2013 Canonical Ltd.

 *

 * This file contains the main data structure and API definitions.

 */

#ifndef __LINUX_WW_MUTEX_H

#define __LINUX_WW_MUTEX_H

#include 

#include 

struct ww_class {

	atomic_long_t stamp;

	struct lock_class_key acquire_key;

	struct lock_class_key mutex_key;

	const char *acquire_name;

	const char *mutex_name;

};

struct ww_acquire_ctx {

	struct task_struct *task;

	unsigned long stamp;

	unsigned acquired;

#ifdef CONFIG_DEBUG_MUTEXES

	unsigned done_acquire;

	struct ww_class *ww_class;

	struct ww_mutex *contending_lock;

#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC

	struct lockdep_map dep_map;

#endif

#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH

	unsigned deadlock_inject_interval;

	unsigned deadlock_inject_countdown;

#endif

};

struct ww_mutex {

	struct mutex base;

	struct ww_acquire_ctx *ctx;

#ifdef CONFIG_DEBUG_MUTEXES

	struct ww_class *ww_class;

#endif

};

#ifdef CONFIG_DEBUG_LOCK_ALLOC

# define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class) \

		, .ww_class = &ww_class

#else

# define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class)

#endif

#define __WW_CLASS_INITIALIZER(ww_class) \

		{ .stamp = ATOMIC_LONG_INIT(0) \

		, .acquire_name = #ww_class "_acquire" \

		, .mutex_name = #ww_class "_mutex" }

#define __WW_MUTEX_INITIALIZER(lockname, class) \

		{ .base = { \__MUTEX_INITIALIZER(lockname) } \

		__WW_CLASS_MUTEX_INITIALIZER(lockname, class) }

#define DEFINE_WW_CLASS(classname) \

	struct ww_class classname = __WW_CLASS_INITIALIZER(classname)

#define DEFINE_WW_MUTEX(mutexname, ww_class) \

	struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)

/**

 * 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.

 *

 * 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)

{

    MutexInit(&lock->base);

	lock->ctx = NULL;

#ifdef CONFIG_DEBUG_MUTEXES

	lock->ww_class = ww_class;

#endif

}

/**

 * 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/wound 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)

{

	ctx->task = current;

	ctx->stamp = atomic_long_inc_return(&ww_class->stamp);

	ctx->acquired = 0;

#ifdef CONFIG_DEBUG_MUTEXES

	ctx->ww_class = ww_class;

	ctx->done_acquire = 0;

	ctx->contending_lock = NULL;

#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC

	debug_check_no_locks_freed((void *)ctx, sizeof(*ctx));

	lockdep_init_map(&ctx->dep_map, ww_class->acquire_name,

			 &ww_class->acquire_key, 0);

	mutex_acquire(&ctx->dep_map, 0, 0, _RET_IP_);

#endif

#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH

	ctx->deadlock_inject_interval = 1;

	ctx->deadlock_inject_countdown = ctx->stamp & 0xf;

#endif

}

/**

 * 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)

{

#ifdef CONFIG_DEBUG_MUTEXES

	lockdep_assert_held(ctx);

	DEBUG_LOCKS_WARN_ON(ctx->done_acquire);

	ctx->done_acquire = 1;

#endif

}

/**

 * 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)

{

#ifdef CONFIG_DEBUG_MUTEXES

	mutex_release(&ctx->dep_map, 0, _THIS_IP_);

	DEBUG_LOCKS_WARN_ON(ctx->acquired);

	if (!config_enabled(CONFIG_PROVE_LOCKING))

		/*

		 * lockdep will normally handle this,

		 * but fail without anyway

		 */

		ctx->done_acquire = 1;

	if (!config_enabled(CONFIG_DEBUG_LOCK_ALLOC))

		/* ensure ww_acquire_fini will still fail if called twice */

		ctx->acquired = ~0U;

#endif

}

extern int __must_check __ww_mutex_lock(struct ww_mutex *lock,

					struct ww_acquire_ctx *ctx);

extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock,

						      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/wound algorithm. If the lock isn't immediately avaiable this function

 * will either sleep until it is (wait case). Or it selects the current context

 * for backing off by returning -EDEADLK (wound 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 wound 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.

 */

static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

{

	if (ctx)

		return __ww_mutex_lock(lock, ctx);

	mutex_lock(&lock->base);

	return 0;

}

/**

 * 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/wound algorithm. If the lock isn't immediately avaiable this function

 * will either sleep until it is (wait case). Or it selects the current context

 * for backing off by returning -EDEADLK (wound 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 wound 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.

 */

static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock,

							   struct ww_acquire_ctx *ctx)

{

	if (ctx)

		return __ww_mutex_lock_interruptible(lock, ctx);

	else

		return mutex_lock_interruptible(&lock->base);

}

/**

 * 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 wound 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)

{

	int ret;

#ifdef CONFIG_DEBUG_MUTEXES

	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);

#endif

	ret = ww_mutex_lock(lock, ctx);

	(void)ret;

}

/**

 * 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 wound 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)

{

#ifdef CONFIG_DEBUG_MUTEXES

	DEBUG_LOCKS_WARN_ON(!ctx->contending_lock);

#endif

	return ww_mutex_lock_interruptible(lock, ctx);

}

extern void ww_mutex_unlock(struct ww_mutex *lock);

/**

 * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context

 * @lock: mutex to lock

 *

 * Trylocks a mutex without acquire context, so no deadlock detection is

 * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.

 */

static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock)

{

	return mutex_trylock(&lock->base);

}

/***

 * 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)

{

	mutex_destroy(&lock->base);

}

/**

 * 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)

{

	return mutex_is_locked(&lock->base);

}

#endif