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 /*
  24  * Simple, straightforward mutexes with strict semantics:
  25  *
  26  * - only one task can hold the mutex at a time
  27  * - only the owner can unlock the mutex
  28  * - multiple unlocks are not permitted
  29  * - recursive locking is not permitted
  30  * - a mutex object must be initialized via the API
  31  * - a mutex object must not be initialized via memset or copying
  32  * - task may not exit with mutex held
  33  * - memory areas where held locks reside must not be freed
  34  * - held mutexes must not be reinitialized
  35  * - mutexes may not be used in hardware or software interrupt
  36  *   contexts such as tasklets and timers
  37  *
  38  * These semantics are fully enforced when DEBUG_MUTEXES is
  39  * enabled. Furthermore, besides enforcing the above rules, the mutex
  40  * debugging code also implements a number of additional features
  41  * that make lock debugging easier and faster:
  42  *
  43  * - uses symbolic names of mutexes, whenever they are printed in debug output
  44  * - point-of-acquire tracking, symbolic lookup of function names
  45  * - list of all locks held in the system, printout of them
  46  * - owner tracking
  47  * - detects self-recursing locks and prints out all relevant info
  48  * - detects multi-task circular deadlocks and prints out all affected
  49  *   locks and tasks (and only those tasks)
  50  */
  51 struct mutex {
  52         atomic_long_t           owner;
  53         spinlock_t              wait_lock;
  54 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  55         struct optimistic_spin_queue osq; /* Spinner MCS lock */
  56 #endif
  57         struct list_head        wait_list;
  58 #ifdef CONFIG_DEBUG_MUTEXES
  59         void                    *magic;
  60 #endif
  61 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  62         struct lockdep_map      dep_map;
  63 #endif
  64 };
  65
  66 static inline struct task_struct *__mutex_owner(struct mutex *lock)
  67 {
  68         return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x03);
  69 }
  70
  71 /*
  72  * This is the control structure for tasks blocked on mutex,
  73  * which resides on the blocked task's kernel stack:
  74  */
  75 struct mutex_waiter {
  76         struct list_head        list;
  77         struct task_struct      *task;
  78 #ifdef CONFIG_DEBUG_MUTEXES
  79         void                    *magic;
  80 #endif
  81 };
  82
  83 #ifdef CONFIG_DEBUG_MUTEXES
  84
  85 #define __DEBUG_MUTEX_INITIALIZER(lockname)                             \
  86         , .magic = &lockname
  87
  88 extern void mutex_destroy(struct mutex *lock);
  89
  90 #else
  91
  92 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  93
  94 static inline void mutex_destroy(struct mutex *lock) {}
  95
  96 #endif
  97
  98 /**
  99  * mutex_init - initialize the mutex
 100  * @mutex: the mutex to be initialized
 101  *
 102  * Initialize the mutex to unlocked state.
 103  *
 104  * It is not allowed to initialize an already locked mutex.
 105  */
 106 #define mutex_init(mutex)                                               \
 107 do {                                                                    \
 108         static struct lock_class_key __key;                             \
 109                                                                         \
 110         __mutex_init((mutex), #mutex, &__key);                          \
 111 } while (0)
 112
 113 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 114 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 115                 , .dep_map = { .name = #lockname }
 116 #else
 117 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 118 #endif
 119
 120 #define __MUTEX_INITIALIZER(lockname) \
 121                 { .owner = ATOMIC_LONG_INIT(0) \
 122                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 123                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 124                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 125                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 126
 127 #define DEFINE_MUTEX(mutexname) \
 128         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 129
 130 extern void __mutex_init(struct mutex *lock, const char *name,
 131                          struct lock_class_key *key);
 132
 133 /**
 134  * mutex_is_locked - is the mutex locked
 135  * @lock: the mutex to be queried
 136  *
 137  * Returns 1 if the mutex is locked, 0 if unlocked.
 138  */
 139 static inline int mutex_is_locked(struct mutex *lock)
 140 {
 141         /*
 142          * XXX think about spin_is_locked
 143          */
 144         return __mutex_owner(lock) != NULL;
 145 }
 146
 147 /*
 148  * See kernel/locking/mutex.c for detailed documentation of these APIs.
 149  * Also see Documentation/locking/mutex-design.txt.
 150  */
 151 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 152 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 153 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 154
 155 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 156                                         unsigned int subclass);
 157 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 158                                         unsigned int subclass);
 159
 160 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 161 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 162 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 163
 164 #define mutex_lock_nest_lock(lock, nest_lock)                           \
 165 do {                                                                    \
 166         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 167         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 168 } while (0)
 169
 170 #else
 171 extern void mutex_lock(struct mutex *lock);
 172 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 173 extern int __must_check mutex_lock_killable(struct mutex *lock);
 174
 175 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 176 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 177 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 178 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 179 #endif
 180
 181 /*
 182  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 183  *       not the down_trylock() convention!
 184  *
 185  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 186  */
 187 extern int mutex_trylock(struct mutex *lock);
 188 extern void mutex_unlock(struct mutex *lock);
 189
 190 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 191
 192 /*
 193  * These values are chosen such that FAIL and SUCCESS match the
 194  * values of the regular mutex_trylock().
 195  */
 196 enum mutex_trylock_recursive_enum {
 197         MUTEX_TRYLOCK_FAILED    = 0,
 198         MUTEX_TRYLOCK_SUCCESS   = 1,
 199         MUTEX_TRYLOCK_RECURSIVE,
 200 };
 201
 202 /**
 203  * mutex_trylock_recursive - trylock variant that allows recursive locking
 204  * @lock: mutex to be locked
 205  *
 206  * This function should not be used, _ever_. It is purely for hysterical GEM
 207  * raisins, and once those are gone this will be removed.
 208  *
 209  * Returns:
 210  *  MUTEX_TRYLOCK_FAILED    - trylock failed,
 211  *  MUTEX_TRYLOCK_SUCCESS   - lock acquired,
 212  *  MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
 213  */
 214 static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
 215 mutex_trylock_recursive(struct mutex *lock)
 216 {
 217         if (unlikely(__mutex_owner(lock) == current))
 218                 return MUTEX_TRYLOCK_RECURSIVE;
 219
 220         return mutex_trylock(lock);
 221 }
 222
 223 #endif /* __LINUX_MUTEX_H */