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