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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 <asm/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 thread_info *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)
95# define mutex_destroy(mutex) do { } while (0)
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 int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
136 unsigned int subclass);
137extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
138 unsigned int subclass);
139
140#define mutex_lock(lock) mutex_lock_nested(lock, 0)
141#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
142#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
143#else
144extern void mutex_lock(struct mutex *lock);
145extern int __must_check mutex_lock_interruptible(struct mutex *lock);
146extern int __must_check mutex_lock_killable(struct mutex *lock);
147
148# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
149# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
150# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
151#endif
152
153/*
154 * NOTE: mutex_trylock() follows the spin_trylock() convention,
155 * not the down_trylock() convention!
156 *
157 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
158 */
159extern int mutex_trylock(struct mutex *lock);
160extern void mutex_unlock(struct mutex *lock);
161extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
162
163#endif