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 <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_MUTEX_SPIN_ON_OWNER
  57         void                    *spin_mlock;    /* Spinner MCS lock */
  58 #endif
  59 #ifdef CONFIG_DEBUG_MUTEXES
  60         const char              *name;
  61         void                    *magic;
  62 #endif
  63 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  64         struct lockdep_map      dep_map;
  65 #endif
  66 };
  67
  68 /*
  69  * This is the control structure for tasks blocked on mutex,
  70  * which resides on the blocked task's kernel stack:
  71  */
  72 struct mutex_waiter {
  73         struct list_head        list;
  74         struct task_struct      *task;
  75 #ifdef CONFIG_DEBUG_MUTEXES
  76         void                    *magic;
  77 #endif
  78 };
  79
  80 #ifdef CONFIG_DEBUG_MUTEXES
  81 # include <linux/mutex-debug.h>
  82 #else
  83 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  84 /**
  85  * mutex_init - initialize the mutex
  86  * @mutex: the mutex to be initialized
  87  *
  88  * Initialize the mutex to unlocked state.
  89  *
  90  * It is not allowed to initialize an already locked mutex.
  91  */
  92 # define mutex_init(mutex) \
  93 do {                                                    \
  94         static struct lock_class_key __key;             \
  95                                                         \
  96         __mutex_init((mutex), #mutex, &__key);          \
  97 } while (0)
  98 static inline void mutex_destroy(struct mutex *lock) {}
  99 #endif
 100
 101 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 102 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 103                 , .dep_map = { .name = #lockname }
 104 #else
 105 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 106 #endif
 107
 108 #define __MUTEX_INITIALIZER(lockname) \
 109                 { .count = ATOMIC_INIT(1) \
 110                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 111                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 112                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 113                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 114
 115 #define DEFINE_MUTEX(mutexname) \
 116         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 117
 118 extern void __mutex_init(struct mutex *lock, const char *name,
 119                          struct lock_class_key *key);
 120
 121 /**
 122  * mutex_is_locked - is the mutex locked
 123  * @lock: the mutex to be queried
 124  *
 125  * Returns 1 if the mutex is locked, 0 if unlocked.
 126  */
 127 static inline int mutex_is_locked(struct mutex *lock)
 128 {
 129         return atomic_read(&lock->count) != 1;
 130 }
 131
 132 /*
 133  * See kernel/mutex.c for detailed documentation of these APIs.
 134  * Also see Documentation/mutex-design.txt.
 135  */
 136 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 137 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 138 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 139 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 140                                         unsigned int subclass);
 141 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 142                                         unsigned int subclass);
 143
 144 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 145 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 146 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 147
 148 #define mutex_lock_nest_lock(lock, nest_lock)                           \
 149 do {                                                                    \
 150         typecheck(struct lockdep_map *, &(nest_lock)->dep_map);         \
 151         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 152 } while (0)
 153
 154 #else
 155 extern void mutex_lock(struct mutex *lock);
 156 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 157 extern int __must_check mutex_lock_killable(struct mutex *lock);
 158
 159 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 160 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 161 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 162 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 163 #endif
 164
 165 /*
 166  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 167  *       not the down_trylock() convention!
 168  *
 169  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 170  */
 171 extern int mutex_trylock(struct mutex *lock);
 172 extern void mutex_unlock(struct mutex *lock);
 173 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 174
 175 #ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
 176 #define arch_mutex_cpu_relax()  cpu_relax()
 177 #endif
 178
 179 #endif