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 #include <linux/osq_lock.h>
  21 #include <linux/debug_locks.h>
  22
  23 struct ww_acquire_ctx;
  24
  25 /*
  26  * Simple, straightforward mutexes with strict semantics:
  27  *
  28  * - only one task can hold the mutex at a time
  29  * - only the owner can unlock the mutex
  30  * - multiple unlocks are not permitted
  31  * - recursive locking is not permitted
  32  * - a mutex object must be initialized via the API
  33  * - a mutex object must not be initialized via memset or copying
  34  * - task may not exit with mutex held
  35  * - memory areas where held locks reside must not be freed
  36  * - held mutexes must not be reinitialized
  37  * - mutexes may not be used in hardware or software interrupt
  38  *   contexts such as tasklets and timers
  39  *
  40  * These semantics are fully enforced when DEBUG_MUTEXES is
  41  * enabled. Furthermore, besides enforcing the above rules, the mutex
  42  * debugging code also implements a number of additional features
  43  * that make lock debugging easier and faster:
  44  *
  45  * - uses symbolic names of mutexes, whenever they are printed in debug output
  46  * - point-of-acquire tracking, symbolic lookup of function names
  47  * - list of all locks held in the system, printout of them
  48  * - owner tracking
  49  * - detects self-recursing locks and prints out all relevant info
  50  * - detects multi-task circular deadlocks and prints out all affected
  51  *   locks and tasks (and only those tasks)
  52  */
  53 struct mutex {
  54         atomic_long_t           owner;
  55         spinlock_t              wait_lock;
  56 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  57         struct optimistic_spin_queue osq; /* Spinner MCS lock */
  58 #endif
  59         struct list_head        wait_list;
  60 #ifdef CONFIG_DEBUG_MUTEXES
  61         void                    *magic;
  62 #endif
  63 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  64         struct lockdep_map      dep_map;
  65 #endif
  66 };
  67
  68 static inline struct task_struct *__mutex_owner(struct mutex *lock)
  69 {
  70         return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
  71 }
  72
  73 /*
  74  * This is the control structure for tasks blocked on mutex,
  75  * which resides on the blocked task's kernel stack:
  76  */
  77 struct mutex_waiter {
  78         struct list_head        list;
  79         struct task_struct      *task;
  80         struct ww_acquire_ctx   *ww_ctx;
  81 #ifdef CONFIG_DEBUG_MUTEXES
  82         void                    *magic;
  83 #endif
  84 };
  85
  86 #ifdef CONFIG_DEBUG_MUTEXES
  87
  88 #define __DEBUG_MUTEX_INITIALIZER(lockname)                             \
  89         , .magic = &lockname
  90
  91 extern void mutex_destroy(struct mutex *lock);
  92
  93 #else
  94
  95 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  96
  97 static inline void mutex_destroy(struct mutex *lock) {}
  98
  99 #endif
 100
 101 /**
 102  * mutex_init - initialize the mutex
 103  * @mutex: the mutex to be initialized
 104  *
 105  * Initialize the mutex to unlocked state.
 106  *
 107  * It is not allowed to initialize an already locked mutex.
 108  */
 109 #define mutex_init(mutex)                                               \
 110 do {                                                                    \
 111         static struct lock_class_key __key;                             \
 112                                                                         \
 113         __mutex_init((mutex), #mutex, &__key);                          \
 114 } while (0)
 115
 116 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 117 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 118                 , .dep_map = { .name = #lockname }
 119 #else
 120 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 121 #endif
 122
 123 #define __MUTEX_INITIALIZER(lockname) \
 124                 { .owner = ATOMIC_LONG_INIT(0) \
 125                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 126                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 127                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 128                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 129
 130 #define DEFINE_MUTEX(mutexname) \
 131         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 132
 133 extern void __mutex_init(struct mutex *lock, const char *name,
 134                          struct lock_class_key *key);
 135
 136 /**
 137  * mutex_is_locked - is the mutex locked
 138  * @lock: the mutex to be queried
 139  *
 140  * Returns 1 if the mutex is locked, 0 if unlocked.
 141  */
 142 static inline int mutex_is_locked(struct mutex *lock)
 143 {
 144         /*
 145          * XXX think about spin_is_locked
 146          */
 147         return __mutex_owner(lock) != NULL;
 148 }
 149
 150 /*
 151  * See kernel/locking/mutex.c for detailed documentation of these APIs.
 152  * Also see Documentation/locking/mutex-design.txt.
 153  */
 154 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 155 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 156 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 157
 158 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 159                                         unsigned int subclass);
 160 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 161                                         unsigned int subclass);
 162 extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
 163
 164 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 165 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 166 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 167 #define mutex_lock_io(lock) mutex_lock_io_nested(lock, 0)
 168
 169 #define mutex_lock_nest_lock(lock, nest_lock)                           \
 170 do {                                                                    \
 171         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 172         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 173 } while (0)
 174
 175 #else
 176 extern void mutex_lock(struct mutex *lock);
 177 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 178 extern int __must_check mutex_lock_killable(struct mutex *lock);
 179 extern void mutex_lock_io(struct mutex *lock);
 180
 181 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 182 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 183 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 184 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 185 # define mutex_lock_io_nested(lock, subclass) mutex_lock(lock)
 186 #endif
 187
 188 /*
 189  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 190  *       not the down_trylock() convention!
 191  *
 192  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 193  */
 194 extern int mutex_trylock(struct mutex *lock);
 195 extern void mutex_unlock(struct mutex *lock);
 196
 197 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 198
 199 /*
 200  * These values are chosen such that FAIL and SUCCESS match the
 201  * values of the regular mutex_trylock().
 202  */
 203 enum mutex_trylock_recursive_enum {
 204         MUTEX_TRYLOCK_FAILED    = 0,
 205         MUTEX_TRYLOCK_SUCCESS   = 1,
 206         MUTEX_TRYLOCK_RECURSIVE,
 207 };
 208
 209 /**
 210  * mutex_trylock_recursive - trylock variant that allows recursive locking
 211  * @lock: mutex to be locked
 212  *
 213  * This function should not be used, _ever_. It is purely for hysterical GEM
 214  * raisins, and once those are gone this will be removed.
 215  *
 216  * Returns:
 217  *  - MUTEX_TRYLOCK_FAILED    - trylock failed,
 218  *  - MUTEX_TRYLOCK_SUCCESS   - lock acquired,
 219  *  - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
 220  */
 221 static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
 222 mutex_trylock_recursive(struct mutex *lock)
 223 {
 224         if (unlikely(__mutex_owner(lock) == current))
 225                 return MUTEX_TRYLOCK_RECURSIVE;
 226
 227         return mutex_trylock(lock);
 228 }
 229
 230 #endif /* __LINUX_MUTEX_H */