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) 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 */ 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