/*
* 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 <mingo@redhat.com>
*
* 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 <linux/mutex.h>
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)
{
__mutex_init(&lock->base, ww_class->mutex_name, &ww_class->mutex_key);
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
