linux/include/linux/mutex.h
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   1/*
   2 * Mutexes: blocking mutual exclusion locks
   3 *
   4 * started by Ingo Molnar:
   5 *
   6 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   7 *
   8 * This file contains the main data structure and API definitions.
   9 */
  10#ifndef __LINUX_MUTEX_H
  11#define __LINUX_MUTEX_H
  12
  13#include <linux/list.h>
  14#include <linux/spinlock_types.h>
  15#include <linux/linkage.h>
  16#include <linux/lockdep.h>
  17
  18#include <linux/atomic.h>
  19
  20/*
  21 * Simple, straightforward mutexes with strict semantics:
  22 *
  23 * - only one task can hold the mutex at a time
  24 * - only the owner can unlock the mutex
  25 * - multiple unlocks are not permitted
  26 * - recursive locking is not permitted
  27 * - a mutex object must be initialized via the API
  28 * - a mutex object must not be initialized via memset or copying
  29 * - task may not exit with mutex held
  30 * - memory areas where held locks reside must not be freed
  31 * - held mutexes must not be reinitialized
  32 * - mutexes may not be used in hardware or software interrupt
  33 *   contexts such as tasklets and timers
  34 *
  35 * These semantics are fully enforced when DEBUG_MUTEXES is
  36 * enabled. Furthermore, besides enforcing the above rules, the mutex
  37 * debugging code also implements a number of additional features
  38 * that make lock debugging easier and faster:
  39 *
  40 * - uses symbolic names of mutexes, whenever they are printed in debug output
  41 * - point-of-acquire tracking, symbolic lookup of function names
  42 * - list of all locks held in the system, printout of them
  43 * - owner tracking
  44 * - detects self-recursing locks and prints out all relevant info
  45 * - detects multi-task circular deadlocks and prints out all affected
  46 *   locks and tasks (and only those tasks)
  47 */
  48struct mutex {
  49        /* 1: unlocked, 0: locked, negative: locked, possible waiters */
  50        atomic_t                count;
  51        spinlock_t              wait_lock;
  52        struct list_head        wait_list;
  53#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
  54        struct task_struct      *owner;
  55#endif
  56#ifdef CONFIG_DEBUG_MUTEXES
  57        const char              *name;
  58        void                    *magic;
  59#endif
  60#ifdef CONFIG_DEBUG_LOCK_ALLOC
  61        struct lockdep_map      dep_map;
  62#endif
  63};
  64
  65/*
  66 * This is the control structure for tasks blocked on mutex,
  67 * which resides on the blocked task's kernel stack:
  68 */
  69struct mutex_waiter {
  70        struct list_head        list;
  71        struct task_struct      *task;
  72#ifdef CONFIG_DEBUG_MUTEXES
  73        void                    *magic;
  74#endif
  75};
  76
  77#ifdef CONFIG_DEBUG_MUTEXES
  78# include <linux/mutex-debug.h>
  79#else
  80# define __DEBUG_MUTEX_INITIALIZER(lockname)
  81/**
  82 * mutex_init - initialize the mutex
  83 * @mutex: the mutex to be initialized
  84 *
  85 * Initialize the mutex to unlocked state.
  86 *
  87 * It is not allowed to initialize an already locked mutex.
  88 */
  89# define mutex_init(mutex) \
  90do {                                                    \
  91        static struct lock_class_key __key;             \
  92                                                        \
  93        __mutex_init((mutex), #mutex, &__key);          \
  94} while (0)
  95static inline void mutex_destroy(struct mutex *lock) {}
  96#endif
  97
  98#ifdef CONFIG_DEBUG_LOCK_ALLOC
  99# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 100                , .dep_map = { .name = #lockname }
 101#else
 102# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 103#endif
 104
 105#define __MUTEX_INITIALIZER(lockname) \
 106                { .count = ATOMIC_INIT(1) \
 107                , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 108                , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 109                __DEBUG_MUTEX_INITIALIZER(lockname) \
 110                __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 111
 112#define DEFINE_MUTEX(mutexname) \
 113        struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 114
 115extern void __mutex_init(struct mutex *lock, const char *name,
 116                         struct lock_class_key *key);
 117
 118/**
 119 * mutex_is_locked - is the mutex locked
 120 * @lock: the mutex to be queried
 121 *
 122 * Returns 1 if the mutex is locked, 0 if unlocked.
 123 */
 124static inline int mutex_is_locked(struct mutex *lock)
 125{
 126        return atomic_read(&lock->count) != 1;
 127}
 128
 129/*
 130 * See kernel/mutex.c for detailed documentation of these APIs.
 131 * Also see Documentation/mutex-design.txt.
 132 */
 133#ifdef CONFIG_DEBUG_LOCK_ALLOC
 134extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 135extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 136extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 137                                        unsigned int subclass);
 138extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 139                                        unsigned int subclass);
 140
 141#define mutex_lock(lock) mutex_lock_nested(lock, 0)
 142#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 143#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 144
 145#define mutex_lock_nest_lock(lock, nest_lock)                           \
 146do {                                                                    \
 147        typecheck(struct lockdep_map *, &(nest_lock)->dep_map);         \
 148        _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 149} while (0)
 150
 151#else
 152extern void mutex_lock(struct mutex *lock);
 153extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 154extern int __must_check mutex_lock_killable(struct mutex *lock);
 155
 156# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 157# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 158# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 159# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 160#endif
 161
 162/*
 163 * NOTE: mutex_trylock() follows the spin_trylock() convention,
 164 *       not the down_trylock() convention!
 165 *
 166 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 167 */
 168extern int mutex_trylock(struct mutex *lock);
 169extern void mutex_unlock(struct mutex *lock);
 170extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 171
 172#ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
 173#define arch_mutex_cpu_relax()  cpu_relax()
 174#endif
 175
 176#endif
 177
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