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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_MUTEX_SPIN_ON_OWNER
57 void *spin_mlock; /* Spinner MCS lock */
58#endif
59#ifdef CONFIG_DEBUG_MUTEXES
60 const char *name;
61 void *magic;
62#endif
63#ifdef CONFIG_DEBUG_LOCK_ALLOC
64 struct lockdep_map dep_map;
65#endif
66};
67
68/*
69 * This is the control structure for tasks blocked on mutex,
70 * which resides on the blocked task's kernel stack:
71 */
72struct mutex_waiter {
73 struct list_head list;
74 struct task_struct *task;
75#ifdef CONFIG_DEBUG_MUTEXES
76 void *magic;
77#endif
78};
79
80#ifdef CONFIG_DEBUG_MUTEXES
81# include <linux/mutex-debug.h>
82#else
83# define __DEBUG_MUTEX_INITIALIZER(lockname)
84/**
85 * mutex_init - initialize the mutex
86 * @mutex: the mutex to be initialized
87 *
88 * Initialize the mutex to unlocked state.
89 *
90 * It is not allowed to initialize an already locked mutex.
91 */
92# define mutex_init(mutex) \
93do { \
94 static struct lock_class_key __key; \
95 \
96 __mutex_init((mutex), #mutex, &__key); \
97} while (0)
98static inline void mutex_destroy(struct mutex *lock) {}
99#endif
100
101#ifdef CONFIG_DEBUG_LOCK_ALLOC
102# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
103 , .dep_map = { .name = #lockname }
104#else
105# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
106#endif
107
108#define __MUTEX_INITIALIZER(lockname) \
109 { .count = ATOMIC_INIT(1) \
110 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
111 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
112 __DEBUG_MUTEX_INITIALIZER(lockname) \
113 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
114
115#define DEFINE_MUTEX(mutexname) \
116 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
117
118extern void __mutex_init(struct mutex *lock, const char *name,
119 struct lock_class_key *key);
120
121/**
122 * mutex_is_locked - is the mutex locked
123 * @lock: the mutex to be queried
124 *
125 * Returns 1 if the mutex is locked, 0 if unlocked.
126 */
127static inline int mutex_is_locked(struct mutex *lock)
128{
129 return atomic_read(&lock->count) != 1;
130}
131
132/*
133 * See kernel/mutex.c for detailed documentation of these APIs.
134 * Also see Documentation/mutex-design.txt.
135 */
136#ifdef CONFIG_DEBUG_LOCK_ALLOC
137extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
138extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
139extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
140 unsigned int subclass);
141extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
142 unsigned int subclass);
143
144#define mutex_lock(lock) mutex_lock_nested(lock, 0)
145#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
146#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
147
148#define mutex_lock_nest_lock(lock, nest_lock) \
149do { \
150 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
151 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
152} while (0)
153
154#else
155extern void mutex_lock(struct mutex *lock);
156extern int __must_check mutex_lock_interruptible(struct mutex *lock);
157extern int __must_check mutex_lock_killable(struct mutex *lock);
158
159# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
160# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
161# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
162# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
163#endif
164
165/*
166 * NOTE: mutex_trylock() follows the spin_trylock() convention,
167 * not the down_trylock() convention!
168 *
169 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
170 */
171extern int mutex_trylock(struct mutex *lock);
172extern void mutex_unlock(struct mutex *lock);
173extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
174
175#ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
176#define arch_mutex_cpu_relax() cpu_relax()
177#endif
178
179#endif