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
  22 /*
  23  * Simple, straightforward mutexes with strict semantics:
  24  *
  25  * - only one task can hold the mutex at a time
  26  * - only the owner can unlock the mutex
  27  * - multiple unlocks are not permitted
  28  * - recursive locking is not permitted
  29  * - a mutex object must be initialized via the API
  30  * - a mutex object must not be initialized via memset or copying
  31  * - task may not exit with mutex held
  32  * - memory areas where held locks reside must not be freed
  33  * - held mutexes must not be reinitialized
  34  * - mutexes may not be used in hardware or software interrupt
  35  *   contexts such as tasklets and timers
  36  *
  37  * These semantics are fully enforced when DEBUG_MUTEXES is
  38  * enabled. Furthermore, besides enforcing the above rules, the mutex
  39  * debugging code also implements a number of additional features
  40  * that make lock debugging easier and faster:
  41  *
  42  * - uses symbolic names of mutexes, whenever they are printed in debug output
  43  * - point-of-acquire tracking, symbolic lookup of function names
  44  * - list of all locks held in the system, printout of them
  45  * - owner tracking
  46  * - detects self-recursing locks and prints out all relevant info
  47  * - detects multi-task circular deadlocks and prints out all affected
  48  *   locks and tasks (and only those tasks)
  49  */
  50 struct mutex {
  51         /* 1: unlocked, 0: locked, negative: locked, possible waiters */
  52         atomic_t                count;
  53         spinlock_t              wait_lock;
  54         struct list_head        wait_list;
  55 #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
  56         struct task_struct      *owner;
  57 #endif
  58 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  59         struct optimistic_spin_queue osq; /* Spinner MCS lock */
  60 #endif
  61 #ifdef CONFIG_DEBUG_MUTEXES
  62         const char              *name;
  63         void                    *magic;
  64 #endif
  65 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  66         struct lockdep_map      dep_map;
  67 #endif
  68 };
  69
  70 /*
  71  * This is the control structure for tasks blocked on mutex,
  72  * which resides on the blocked task's kernel stack:
  73  */
  74 struct mutex_waiter {
  75         struct list_head        list;
  76         struct task_struct      *task;
  77 #ifdef CONFIG_DEBUG_MUTEXES
  78         void                    *magic;
  79 #endif
  80 };
  81
  82 #ifdef CONFIG_DEBUG_MUTEXES
  83 # include <linux/mutex-debug.h>
  84 #else
  85 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  86 /**
  87  * mutex_init - initialize the mutex
  88  * @mutex: the mutex to be initialized
  89  *
  90  * Initialize the mutex to unlocked state.
  91  *
  92  * It is not allowed to initialize an already locked mutex.
  93  */
  94 # define mutex_init(mutex) \
  95 do {                                                    \
  96         static struct lock_class_key __key;             \
  97                                                         \
  98         __mutex_init((mutex), #mutex, &__key);          \
  99 } while (0)
 100 static inline void mutex_destroy(struct mutex *lock) {}
 101 #endif
 102
 103 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 104 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 105                 , .dep_map = { .name = #lockname }
 106 #else
 107 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 108 #endif
 109
 110 #define __MUTEX_INITIALIZER(lockname) \
 111                 { .count = ATOMIC_INIT(1) \
 112                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 113                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 114                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 115                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 116
 117 #define DEFINE_MUTEX(mutexname) \
 118         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 119
 120 extern void __mutex_init(struct mutex *lock, const char *name,
 121                          struct lock_class_key *key);
 122
 123 /**
 124  * mutex_is_locked - is the mutex locked
 125  * @lock: the mutex to be queried
 126  *
 127  * Returns 1 if the mutex is locked, 0 if unlocked.
 128  */
 129 static inline int mutex_is_locked(struct mutex *lock)
 130 {
 131         return atomic_read(&lock->count) != 1;
 132 }
 133
 134 /*
 135  * See kernel/locking/mutex.c for detailed documentation of these APIs.
 136  * Also see Documentation/mutex-design.txt.
 137  */
 138 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 139 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 140 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 141
 142 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 143                                         unsigned int subclass);
 144 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 145                                         unsigned int subclass);
 146
 147 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 148 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 149 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 150
 151 #define mutex_lock_nest_lock(lock, nest_lock)                           \
 152 do {                                                                    \
 153         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 154         _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 155 } while (0)
 156
 157 #else
 158 extern void mutex_lock(struct mutex *lock);
 159 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 160 extern int __must_check mutex_lock_killable(struct mutex *lock);
 161
 162 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 163 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 164 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 165 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 166 #endif
 167
 168 /*
 169  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 170  *       not the down_trylock() convention!
 171  *
 172  * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 173  */
 174 extern int mutex_trylock(struct mutex *lock);
 175 extern void mutex_unlock(struct mutex *lock);
 176
 177 extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 178
 179 #endif /* __LINUX_MUTEX_H */