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 irq contexts
33 *
34 * These semantics are fully enforced when DEBUG_MUTEXES is
35 * enabled. Furthermore, besides enforcing the above rules, the mutex
36 * debugging code also implements a number of additional features
37 * that make lock debugging easier and faster:
38 *
39 * - uses symbolic names of mutexes, whenever they are printed in debug output
40 * - point-of-acquire tracking, symbolic lookup of function names
41 * - list of all locks held in the system, printout of them
42 * - owner tracking
43 * - detects self-recursing locks and prints out all relevant info
44 * - detects multi-task circular deadlocks and prints out all affected
45 * locks and tasks (and only those tasks)
46 */
47 struct mutex {
48 /* 1: unlocked, 0: locked, negative: locked, possible waiters */
49 atomic_t count;
50 spinlock_t wait_lock;
51 struct list_head wait_list;
52 #ifdef CONFIG_DEBUG_MUTEXES
53 struct thread_info *owner;
54 const char *name;
55 void *magic;
56 #endif
57 #ifdef CONFIG_DEBUG_LOCK_ALLOC
58 struct lockdep_map dep_map;
59 #endif
60 };
61
62 /*
63 * This is the control structure for tasks blocked on mutex,
64 * which resides on the blocked task's kernel stack:
65 */
66 struct mutex_waiter {
67 struct list_head list;
68 struct task_struct *task;
69 #ifdef CONFIG_DEBUG_MUTEXES
70 struct mutex *lock;
71 void *magic;
72 #endif
73 };
74
75 #ifdef CONFIG_DEBUG_MUTEXES
76 # include <linux/mutex-debug.h>
77 #else
78 # define __DEBUG_MUTEX_INITIALIZER(lockname)
79 # define mutex_init(mutex) \
80 do { \
81 static struct lock_class_key __key; \
82 \
83 __mutex_init((mutex), #mutex, &__key); \
84 } while (0)
85 # define mutex_destroy(mutex) do { } while (0)
86 #endif
87
88 #ifdef CONFIG_DEBUG_LOCK_ALLOC
89 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
90 , .dep_map = { .name = #lockname }
91 #else
92 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
93 #endif
94
95 #define __MUTEX_INITIALIZER(lockname) \
96 { .count = ATOMIC_INIT(1) \
97 , .wait_lock = SPIN_LOCK_UNLOCKED \
98 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
99 __DEBUG_MUTEX_INITIALIZER(lockname) \
100 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
101
102 #define DEFINE_MUTEX(mutexname) \
103 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
104
105 extern void __mutex_init(struct mutex *lock, const char *name,
106 struct lock_class_key *key);
107
108 /***
109 * mutex_is_locked - is the mutex locked
110 * @lock: the mutex to be queried
111 *
112 * Returns 1 if the mutex is locked, 0 if unlocked.
113 */
mutex_is_locked(struct mutex * lock)114 static inline int fastcall mutex_is_locked(struct mutex *lock)
115 {
116 return atomic_read(&lock->count) != 1;
117 }
118
119 /*
120 * See kernel/mutex.c for detailed documentation of these APIs.
121 * Also see Documentation/mutex-design.txt.
122 */
123 extern void fastcall mutex_lock(struct mutex *lock);
124 extern int fastcall mutex_lock_interruptible(struct mutex *lock);
125
126 #ifdef CONFIG_DEBUG_LOCK_ALLOC
127 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
128 #else
129 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
130 #endif
131
132 /*
133 * NOTE: mutex_trylock() follows the spin_trylock() convention,
134 * not the down_trylock() convention!
135 */
136 extern int fastcall mutex_trylock(struct mutex *lock);
137 extern void fastcall mutex_unlock(struct mutex *lock);
138
139 #endif
140