mutex.h

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/*
 * Mutexes: blocking mutual exclusion locks
 *
 * started by Ingo Molnar:
 *
 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <[email protected]>
 *
 * This file contains the main data structure and API definitions.
 */
#ifndef __LINUX_MUTEX_H
#define __LINUX_MUTEX_H

#include <linux/list.h>
#include <linux/spinlock_types.h>
#include <linux/linkage.h>
#include <linux/lockdep.h>

#include <linux/atomic.h>

/*
 * Simple, straightforward mutexes with strict semantics:
 *
 * - only one task can hold the mutex at a time
 * - only the owner can unlock the mutex
 * - multiple unlocks are not permitted
 * - recursive locking is not permitted
 * - a mutex object must be initialized via the API
 * - a mutex object must not be initialized via memset or copying
 * - task may not exit with mutex held
 * - memory areas where held locks reside must not be freed
 * - held mutexes must not be reinitialized
 * - mutexes may not be used in hardware or software interrupt
 *   contexts such as tasklets and timers
 *
 * These semantics are fully enforced when DEBUG_MUTEXES is
 * enabled. Furthermore, besides enforcing the above rules, the mutex
 * debugging code also implements a number of additional features
 * that make lock debugging easier and faster:
 *
 * - uses symbolic names of mutexes, whenever they are printed in debug output
 * - point-of-acquire tracking, symbolic lookup of function names
 * - list of all locks held in the system, printout of them
 * - owner tracking
 * - detects self-recursing locks and prints out all relevant info
 * - detects multi-task circular deadlocks and prints out all affected
 *   locks and tasks (and only those tasks)
 */
struct mutex {
    /* 1: unlocked, 0: locked, negative: locked, possible waiters */
    atomic_t        count;
    spinlock_t      wait_lock;
    struct list_head    wait_list;
#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
    struct task_struct  *owner;
#endif
#ifdef CONFIG_DEBUG_MUTEXES
    const char      *name;
    void            *magic;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
    struct lockdep_map  dep_map;
#endif
};

/*
 * This is the control structure for tasks blocked on mutex,
 * which resides on the blocked task's kernel stack:
 */
struct mutex_waiter {
    struct list_head    list;
    struct task_struct  *task;
#ifdef CONFIG_DEBUG_MUTEXES
    void            *magic;
#endif
};

#ifdef CONFIG_DEBUG_MUTEXES
# include <linux/mutex-debug.h>
#else
# define __DEBUG_MUTEX_INITIALIZER(lockname)

# define mutex_init(mutex) \
do {                            \
    static struct lock_class_key __key;     \
                            \
    __mutex_init((mutex), #mutex, &__key);      \
} while (0)
static inline void mutex_destroy(struct mutex *lock) {}
#endif

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
        , .dep_map = { .name = #lockname }
#else
# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
#endif

#define __MUTEX_INITIALIZER(lockname) \
        { .count = ATOMIC_INIT(1) \
        , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
        , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
        __DEBUG_MUTEX_INITIALIZER(lockname) \
        __DEP_MAP_MUTEX_INITIALIZER(lockname) }

#define DEFINE_MUTEX(mutexname) \
    struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)

extern void __mutex_init(struct mutex *lock, const char *name,
             struct lock_class_key *key);

static inline int mutex_is_locked(struct mutex *lock)
{
    return atomic_read(&lock->count) != 1;
}

/*
 * See kernel/mutex.c for detailed documentation of these APIs.
 * Also see Documentation/mutex-design.txt.
 */
#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
                    unsigned int subclass);
extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
                    unsigned int subclass);

#define mutex_lock(lock) mutex_lock_nested(lock, 0)
#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)

#define mutex_lock_nest_lock(lock, nest_lock)               \
do {                                    \
    typecheck(struct lockdep_map *, &(nest_lock)->dep_map);     \
    _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);     \
} while (0)

#else
extern void mutex_lock(struct mutex *lock);
extern int __must_check mutex_lock_interruptible(struct mutex *lock);
extern int __must_check mutex_lock_killable(struct mutex *lock);

# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
#endif

/*
 * NOTE: mutex_trylock() follows the spin_trylock() convention,
 *       not the down_trylock() convention!
 *
 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 */
extern int mutex_trylock(struct mutex *lock);
extern void mutex_unlock(struct mutex *lock);
extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);

#ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
#define arch_mutex_cpu_relax()  cpu_relax()
#endif

#endif