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 <linux/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 task_struct	*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 /**
82  * mutex_init - initialize the mutex
83  * @mutex: the mutex to be initialized
84  *
85  * Initialize the mutex to unlocked state.
86  *
87  * It is not allowed to initialize an already locked mutex.
88  */
89 # define mutex_init(mutex) \
90 do {							\
91 	static struct lock_class_key __key;		\
92 							\
93 	__mutex_init((mutex), #mutex, &__key);		\
94 } while (0)
mutex_destroy(struct mutex * lock)95 static inline void mutex_destroy(struct mutex *lock) {}
96 #endif
97 
98 #ifdef CONFIG_DEBUG_LOCK_ALLOC
99 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
100 		, .dep_map = { .name = #lockname }
101 #else
102 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
103 #endif
104 
105 #define __MUTEX_INITIALIZER(lockname) \
106 		{ .count = ATOMIC_INIT(1) \
107 		, .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
108 		, .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
109 		__DEBUG_MUTEX_INITIALIZER(lockname) \
110 		__DEP_MAP_MUTEX_INITIALIZER(lockname) }
111 
112 #define DEFINE_MUTEX(mutexname) \
113 	struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
114 
115 extern void __mutex_init(struct mutex *lock, const char *name,
116 			 struct lock_class_key *key);
117 
118 /**
119  * mutex_is_locked - is the mutex locked
120  * @lock: the mutex to be queried
121  *
122  * Returns 1 if the mutex is locked, 0 if unlocked.
123  */
mutex_is_locked(struct mutex * lock)124 static inline int mutex_is_locked(struct mutex *lock)
125 {
126 	return atomic_read(&lock->count) != 1;
127 }
128 
129 /*
130  * See kernel/mutex.c for detailed documentation of these APIs.
131  * Also see Documentation/mutex-design.txt.
132  */
133 #ifdef CONFIG_DEBUG_LOCK_ALLOC
134 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
135 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
136 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
137 					unsigned int subclass);
138 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
139 					unsigned int subclass);
140 
141 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
142 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
143 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
144 
145 #define mutex_lock_nest_lock(lock, nest_lock)				\
146 do {									\
147 	typecheck(struct lockdep_map *, &(nest_lock)->dep_map);		\
148 	_mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);		\
149 } while (0)
150 
151 #else
152 extern void mutex_lock(struct mutex *lock);
153 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
154 extern int __must_check mutex_lock_killable(struct mutex *lock);
155 
156 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
157 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
158 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
159 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
160 #endif
161 
162 /*
163  * NOTE: mutex_trylock() follows the spin_trylock() convention,
164  *       not the down_trylock() convention!
165  *
166  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
167  */
168 extern int mutex_trylock(struct mutex *lock);
169 extern void mutex_unlock(struct mutex *lock);
170 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
171 
172 #ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
173 #define arch_mutex_cpu_relax()	cpu_relax()
174 #endif
175 
176 #endif
177