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Linux/include/linux/mutex.h

  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 
 21 /*
 22  * Simple, straightforward mutexes with strict semantics:
 23  *
 24  * - only one task can hold the mutex at a time
 25  * - only the owner can unlock the mutex
 26  * - multiple unlocks are not permitted
 27  * - recursive locking is not permitted
 28  * - a mutex object must be initialized via the API
 29  * - a mutex object must not be initialized via memset or copying
 30  * - task may not exit with mutex held
 31  * - memory areas where held locks reside must not be freed
 32  * - held mutexes must not be reinitialized
 33  * - mutexes may not be used in hardware or software interrupt
 34  *   contexts such as tasklets and timers
 35  *
 36  * These semantics are fully enforced when DEBUG_MUTEXES is
 37  * enabled. Furthermore, besides enforcing the above rules, the mutex
 38  * debugging code also implements a number of additional features
 39  * that make lock debugging easier and faster:
 40  *
 41  * - uses symbolic names of mutexes, whenever they are printed in debug output
 42  * - point-of-acquire tracking, symbolic lookup of function names
 43  * - list of all locks held in the system, printout of them
 44  * - owner tracking
 45  * - detects self-recursing locks and prints out all relevant info
 46  * - detects multi-task circular deadlocks and prints out all affected
 47  *   locks and tasks (and only those tasks)
 48  */
 49 struct mutex {
 50         /* 1: unlocked, 0: locked, negative: locked, possible waiters */
 51         atomic_t                count;
 52         spinlock_t              wait_lock;
 53         struct list_head        wait_list;
 54 #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
 55         struct task_struct      *owner;
 56 #endif
 57 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 58         void                    *spin_mlock;    /* Spinner MCS lock */
 59 #endif
 60 #ifdef CONFIG_DEBUG_MUTEXES
 61         const char              *name;
 62         void                    *magic;
 63 #endif
 64 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 65         struct lockdep_map      dep_map;
 66 #endif
 67 };
 68 
 69 /*
 70  * This is the control structure for tasks blocked on mutex,
 71  * which resides on the blocked task's kernel stack:
 72  */
 73 struct mutex_waiter {
 74         struct list_head        list;
 75         struct task_struct      *task;
 76 #ifdef CONFIG_DEBUG_MUTEXES
 77         void                    *magic;
 78 #endif
 79 };
 80 
 81 #ifdef CONFIG_DEBUG_MUTEXES
 82 # include <linux/mutex-debug.h>
 83 #else
 84 # define __DEBUG_MUTEX_INITIALIZER(lockname)
 85 /**
 86  * mutex_init - initialize the mutex
 87  * @mutex: the mutex to be initialized
 88  *
 89  * Initialize the mutex to unlocked state.
 90  *
 91  * It is not allowed to initialize an already locked mutex.
 92  */
 93 # define mutex_init(mutex) \
 94 do {                                                    \
 95         static struct lock_class_key __key;             \
 96                                                         \
 97         __mutex_init((mutex), #mutex, &__key);          \
 98 } while (0)
 99 static inline void mutex_destroy(struct mutex *lock) {}
100 #endif
101 
102 #ifdef CONFIG_DEBUG_LOCK_ALLOC
103 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
104                 , .dep_map = { .name = #lockname }
105 #else
106 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
107 #endif
108 
109 #define __MUTEX_INITIALIZER(lockname) \
110                 { .count = ATOMIC_INIT(1) \
111                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
112                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
113                 __DEBUG_MUTEX_INITIALIZER(lockname) \
114                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
115 
116 #define DEFINE_MUTEX(mutexname) \
117         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
118 
119 extern void __mutex_init(struct mutex *lock, const char *name,
120                          struct lock_class_key *key);
121 
122 /**
123  * mutex_is_locked - is the mutex locked
124  * @lock: the mutex to be queried
125  *
126  * Returns 1 if the mutex is locked, 0 if unlocked.
127  */
128 static inline int mutex_is_locked(struct mutex *lock)
129 {
130         return atomic_read(&lock->count) != 1;
131 }
132 
133 /*
134  * See kernel/locking/mutex.c for detailed documentation of these APIs.
135  * Also see Documentation/mutex-design.txt.
136  */
137 #ifdef CONFIG_DEBUG_LOCK_ALLOC
138 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
139 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
140 
141 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
142                                         unsigned int subclass);
143 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
144                                         unsigned int subclass);
145 
146 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
147 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
148 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
149 
150 #define mutex_lock_nest_lock(lock, nest_lock)                           \
151 do {                                                                    \
152         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
153         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
154 } while (0)
155 
156 #else
157 extern void mutex_lock(struct mutex *lock);
158 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
159 extern int __must_check mutex_lock_killable(struct mutex *lock);
160 
161 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
162 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
163 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
164 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
165 #endif
166 
167 /*
168  * NOTE: mutex_trylock() follows the spin_trylock() convention,
169  *       not the down_trylock() convention!
170  *
171  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
172  */
173 extern int mutex_trylock(struct mutex *lock);
174 extern void mutex_unlock(struct mutex *lock);
175 
176 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
177 
178 #ifndef arch_mutex_cpu_relax
179 # define arch_mutex_cpu_relax() cpu_relax()
180 #endif
181 
182 #endif
183 

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