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