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 #ifdef CONFIG_MT_DEBUG_MUTEXES
  78     struct task_struct  *task_wait_on;
  79 #endif
  80 #endif
  81 };
  82
  83 #ifdef CONFIG_DEBUG_MUTEXES
  84 # include <linux/mutex-debug.h>
  85 #else
  86 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  87 /**
  88  * mutex_init - initialize the mutex
  89  * @mutex: the mutex to be initialized
  90  *
  91  * Initialize the mutex to unlocked state.
  92  *
  93  * It is not allowed to initialize an already locked mutex.
  94  */
  95 # define mutex_init(mutex) \
  96 do {                                                    \
  97         static struct lock_class_key __key;             \
  98                                                         \
  99         __mutex_init((mutex), #mutex, &__key);          \
 100 } while (0)
 101 static inline void mutex_destroy(struct mutex *lock) {}
 102 #endif
 103
 104 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 105 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 106                 , .dep_map = { .name = #lockname }
 107 #else
 108 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 109 #endif
 110
 111 #ifdef CONFIG_DEBUG_MUTEXES
 112 #define __MUTEX_NAME_INITIALIZER(lockname) \
 113     , .name = #lockname
 114 #else
 115 #define __MUTEX_NAME_INITIALIZER(lockname)
 116 #endif
 117
 118 #define __MUTEX_INITIALIZER(lockname) \
 119                 { .count = ATOMIC_INIT(1) \
 120                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 121                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 122                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 123         __MUTEX_NAME_INITIALIZER(lockname) \
 124                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 125
 126 #define DEFINE_MUTEX(mutexname) \
 127         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 128
 129 extern void __mutex_init(struct mutex *lock, const char *name,
 130                          struct lock_class_key *key);
 131
 132 /**
 133  * mutex_is_locked - is the mutex locked
 134  * @lock: the mutex to be queried
 135  *
 136  * Returns 1 if the mutex is locked, 0 if unlocked.
 137  */
 138 static inline int mutex_is_locked(struct mutex *lock)
 139 {
 140         return atomic_read(&lock->count) != 1;
 141 }
 142
 143 /*
 144  * See kernel/mutex.c for detailed documentation of these APIs.
 145  * Also see Documentation/mutex-design.txt.
 146  */
 147 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 148 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 149 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 150 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 151                                         unsigned int subclass);
 152 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 153                                         unsigned int subclass);
 154
 155 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 156 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 157 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 158
 159 #define mutex_lock_nest_lock(lock, nest_lock)                           \
 160 do {                                                                    \
 161         typecheck(struct lockdep_map *, &(nest_lock)->dep_map);         \
 162         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 163 } while (0)
 164
 165 #else
 166 extern void mutex_lock(struct mutex *lock);
 167 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 168 extern int __must_check mutex_lock_killable(struct mutex *lock);
 169
 170 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 171 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 172 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 173 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 174 #endif
 175
 176 /*
 177  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 178  *       not the down_trylock() convention!
 179  *
 180  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 181  */
 182 extern int mutex_trylock(struct mutex *lock);
 183 extern void mutex_unlock(struct mutex *lock);
 184 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 185
 186 #ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
 187 #define arch_mutex_cpu_relax()  cpu_relax()
 188 #endif
 189
 190 #endif