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