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 #ifdef CONFIG_DEBUG_MUTEXES
54 struct thread_info *owner;
55 const char *name;
56 void *magic;
57 #endif
58 #ifdef CONFIG_DEBUG_LOCK_ALLOC
59 struct lockdep_map dep_map;
60 #endif
61 };
62
63 /*
64 * This is the control structure for tasks blocked on mutex,
65 * which resides on the blocked task's kernel stack:
66 */
67 struct mutex_waiter {
68 struct list_head list;
69 struct task_struct *task;
70 #ifdef CONFIG_DEBUG_MUTEXES
71 struct mutex *lock;
72 void *magic;
73 #endif
74 };
75
76 #ifdef CONFIG_DEBUG_MUTEXES
77 # include <linux/mutex-debug.h>
78 #else
79 # define __DEBUG_MUTEX_INITIALIZER(lockname)
80 # define mutex_init(mutex) \
81 do { \
82 static struct lock_class_key __key; \
83 \
84 __mutex_init((mutex), #mutex, &__key); \
85 } while (0)
86 # define mutex_destroy(mutex) do { } while (0)
87 #endif
88
89 #ifdef CONFIG_DEBUG_LOCK_ALLOC
90 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
91 , .dep_map = { .name = #lockname }
92 #else
93 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
94 #endif
95
96 #define __MUTEX_INITIALIZER(lockname) \
97 { .count = ATOMIC_INIT(1) \
98 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
99 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
100 __DEBUG_MUTEX_INITIALIZER(lockname) \
101 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
102
103 #define DEFINE_MUTEX(mutexname) \
104 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
105
106 extern void __mutex_init(struct mutex *lock, const char *name,
107 struct lock_class_key *key);
108
109 /**
110 * mutex_is_locked - is the mutex locked
111 * @lock: the mutex to be queried
112 *
113 * Returns 1 if the mutex is locked, 0 if unlocked.
114 */
115 static inline int mutex_is_locked(struct mutex *lock)
116 {
117 return atomic_read(&lock->count) != 1;
118 }
119
120 /*
121 * See kernel/mutex.c for detailed documentation of these APIs.
122 * Also see Documentation/mutex-design.txt.
123 */
124 #ifdef CONFIG_DEBUG_LOCK_ALLOC
125 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
126 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
127 unsigned int subclass);
128 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
129 unsigned int subclass);
130
131 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
132 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
133 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
134 #else
135 extern void mutex_lock(struct mutex *lock);
136 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
137 extern int __must_check mutex_lock_killable(struct mutex *lock);
138
139 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
140 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
141 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
142 #endif
143
144 /*
145 * NOTE: mutex_trylock() follows the spin_trylock() convention,
146 * not the down_trylock() convention!
147 */
148 extern int mutex_trylock(struct mutex *lock);
149 extern void mutex_unlock(struct mutex *lock);
150
151 #endif
152
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