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 */
48 struct 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 */
69 struct 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 # define mutex_init(mutex) \
82 do { \
83 static struct lock_class_key __key; \
84 \
85 __mutex_init((mutex), #mutex, &__key); \
86 } while (0)
87 # define mutex_destroy(mutex) do { } while (0)
88 #endif
89
90 #ifdef CONFIG_DEBUG_LOCK_ALLOC
91 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
92 , .dep_map = { .name = #lockname }
93 #else
94 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
95 #endif
96
97 #define __MUTEX_INITIALIZER(lockname) \
98 { .count = ATOMIC_INIT(1) \
99 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
100 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
101 __DEBUG_MUTEX_INITIALIZER(lockname) \
102 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
103
104 #define DEFINE_MUTEX(mutexname) \
105 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
106
107 extern void __mutex_init(struct mutex *lock, const char *name,
108 struct lock_class_key *key);
109
110 /**
111 * mutex_is_locked - is the mutex locked
112 * @lock: the mutex to be queried
113 *
114 * Returns 1 if the mutex is locked, 0 if unlocked.
115 */
116 static inline int mutex_is_locked(struct mutex *lock)
117 {
118 return atomic_read(&lock->count) != 1;
119 }
120
121 /*
122 * See kernel/mutex.c for detailed documentation of these APIs.
123 * Also see Documentation/mutex-design.txt.
124 */
125 #ifdef CONFIG_DEBUG_LOCK_ALLOC
126 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
127 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
128 unsigned int subclass);
129 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
130 unsigned int subclass);
131
132 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
133 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
134 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
135 #else
136 extern void mutex_lock(struct mutex *lock);
137 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
138 extern int __must_check mutex_lock_killable(struct mutex *lock);
139
140 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
141 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
142 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
143 #endif
144
145 /*
146 * NOTE: mutex_trylock() follows the spin_trylock() convention,
147 * not the down_trylock() convention!
148 *
149 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
150 */
151 extern int mutex_trylock(struct mutex *lock);
152 extern void mutex_unlock(struct mutex *lock);
153 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
154
155 #endif
156
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