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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 <asm/current.h>
14#include <linux/list.h>
15#include <linux/spinlock_types.h>
16#include <linux/linkage.h>
17#include <linux/lockdep.h>
18#include <linux/atomic.h>
19#include <asm/processor.h>
20
21/*
22 * Simple, straightforward mutexes with strict semantics:
23 *
24 * - only one task can hold the mutex at a time
25 * - only the owner can unlock the mutex
26 * - multiple unlocks are not permitted
27 * - recursive locking is not permitted
28 * - a mutex object must be initialized via the API
29 * - a mutex object must not be initialized via memset or copying
30 * - task may not exit with mutex held
31 * - memory areas where held locks reside must not be freed
32 * - held mutexes must not be reinitialized
33 * - mutexes may not be used in hardware or software interrupt
34 * contexts such as tasklets and timers
35 *
36 * These semantics are fully enforced when DEBUG_MUTEXES is
37 * enabled. Furthermore, besides enforcing the above rules, the mutex
38 * debugging code also implements a number of additional features
39 * that make lock debugging easier and faster:
40 *
41 * - uses symbolic names of mutexes, whenever they are printed in debug output
42 * - point-of-acquire tracking, symbolic lookup of function names
43 * - list of all locks held in the system, printout of them
44 * - owner tracking
45 * - detects self-recursing locks and prints out all relevant info
46 * - detects multi-task circular deadlocks and prints out all affected
47 * locks and tasks (and only those tasks)
48 */
49struct mutex {
50 /* 1: unlocked, 0: locked, negative: locked, possible waiters */
51 atomic_t count;
52 spinlock_t wait_lock;
53 struct list_head wait_list;
54#if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
55 struct task_struct *owner;
56#endif
57#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
58 void *spin_mlock; /* Spinner MCS lock */
59#endif
60#ifdef CONFIG_DEBUG_MUTEXES
61 const char *name;
62 void *magic;
63#endif
64#ifdef CONFIG_DEBUG_LOCK_ALLOC
65 struct lockdep_map dep_map;
66#endif
67};
68
69/*
70 * This is the control structure for tasks blocked on mutex,
71 * which resides on the blocked task's kernel stack:
72 */
73struct mutex_waiter {
74 struct list_head list;
75 struct task_struct *task;
76#ifdef CONFIG_DEBUG_MUTEXES
77 void *magic;
78#endif
79};
80
81#ifdef CONFIG_DEBUG_MUTEXES
82# include <linux/mutex-debug.h>
83#else
84# define __DEBUG_MUTEX_INITIALIZER(lockname)
85/**
86 * mutex_init - initialize the mutex
87 * @mutex: the mutex to be initialized
88 *
89 * Initialize the mutex to unlocked state.
90 *
91 * It is not allowed to initialize an already locked mutex.
92 */
93# define mutex_init(mutex) \
94do { \
95 static struct lock_class_key __key; \
96 \
97 __mutex_init((mutex), #mutex, &__key); \
98} while (0)
99static inline void mutex_destroy(struct mutex *lock) {}
100#endif
101
102#ifdef CONFIG_DEBUG_LOCK_ALLOC
103# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
104 , .dep_map = { .name = #lockname }
105#else
106# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
107#endif
108
109#define __MUTEX_INITIALIZER(lockname) \
110 { .count = ATOMIC_INIT(1) \
111 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
112 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
113 __DEBUG_MUTEX_INITIALIZER(lockname) \
114 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
115
116#define DEFINE_MUTEX(mutexname) \
117 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
118
119extern void __mutex_init(struct mutex *lock, const char *name,
120 struct lock_class_key *key);
121
122/**
123 * mutex_is_locked - is the mutex locked
124 * @lock: the mutex to be queried
125 *
126 * Returns 1 if the mutex is locked, 0 if unlocked.
127 */
128static inline int mutex_is_locked(struct mutex *lock)
129{
130 return atomic_read(&lock->count) != 1;
131}
132
133/*
134 * See kernel/mutex.c for detailed documentation of these APIs.
135 * Also see Documentation/mutex-design.txt.
136 */
137#ifdef CONFIG_DEBUG_LOCK_ALLOC
138extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
139extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
140
141extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
142 unsigned int subclass);
143extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
144 unsigned int subclass);
145
146#define mutex_lock(lock) mutex_lock_nested(lock, 0)
147#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
148#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
149
150#define mutex_lock_nest_lock(lock, nest_lock) \
151do { \
152 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
153 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
154} while (0)
155
156#else
157extern void mutex_lock(struct mutex *lock);
158extern int __must_check mutex_lock_interruptible(struct mutex *lock);
159extern int __must_check mutex_lock_killable(struct mutex *lock);
160
161# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
162# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
163# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
164# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
165#endif
166
167/*
168 * NOTE: mutex_trylock() follows the spin_trylock() convention,
169 * not the down_trylock() convention!
170 *
171 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
172 */
173extern int mutex_trylock(struct mutex *lock);
174extern void mutex_unlock(struct mutex *lock);
175
176extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
177
178#ifndef arch_mutex_cpu_relax
179# define arch_mutex_cpu_relax() cpu_relax()
180#endif
181
182#endif