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 irq contexts
  33  *
  34  * These semantics are fully enforced when DEBUG_MUTEXES is
  35  * enabled. Furthermore, besides enforcing the above rules, the mutex
  36  * debugging code also implements a number of additional features
  37  * that make lock debugging easier and faster:
  38  *
  39  * - uses symbolic names of mutexes, whenever they are printed in debug output
  40  * - point-of-acquire tracking, symbolic lookup of function names
  41  * - list of all locks held in the system, printout of them
  42  * - owner tracking
  43  * - detects self-recursing locks and prints out all relevant info
  44  * - detects multi-task circular deadlocks and prints out all affected
  45  *   locks and tasks (and only those tasks)
  46  */
  47 struct mutex {
  48         /* 1: unlocked, 0: locked, negative: locked, possible waiters */
  49         atomic_t                count;
  50         spinlock_t              wait_lock;
  51         struct list_head        wait_list;
  52 #ifdef CONFIG_DEBUG_MUTEXES
  53         struct thread_info      *owner;
  54         const char              *name;
  55         void                    *magic;
  56 #endif
  57 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  58         struct lockdep_map      dep_map;
  59 #endif
  60 };
  61
  62 /*
  63  * This is the control structure for tasks blocked on mutex,
  64  * which resides on the blocked task's kernel stack:
  65  */
  66 struct mutex_waiter {
  67         struct list_head        list;
  68         struct task_struct      *task;
  69 #ifdef CONFIG_DEBUG_MUTEXES
  70         struct mutex            *lock;
  71         void                    *magic;
  72 #endif
  73 };
  74
  75 #ifdef CONFIG_DEBUG_MUTEXES
  76 # include <linux/mutex-debug.h>
  77 #else
  78 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  79 # define mutex_init(mutex) \
  80 do {                                                    \
  81         static struct lock_class_key __key;             \
  82                                                         \
  83         __mutex_init((mutex), #mutex, &__key);          \
  84 } while (0)
  85 # define mutex_destroy(mutex)                           do { } while (0)
  86 #endif
  87
  88 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  89 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
  90                 , .dep_map = { .name = #lockname }
  91 #else
  92 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
  93 #endif
  94
  95 #define __MUTEX_INITIALIZER(lockname) \
  96                 { .count = ATOMIC_INIT(1) \
  97                 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
  98                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
  99                 __DEBUG_MUTEX_INITIALIZER(lockname) \
 100                 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 101
 102 #define DEFINE_MUTEX(mutexname) \
 103         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 104
 105 extern void __mutex_init(struct mutex *lock, const char *name,
 106                          struct lock_class_key *key);
 107
 108 /**
 109  * mutex_is_locked - is the mutex locked
 110  * @lock: the mutex to be queried
 111  *
 112  * Returns 1 if the mutex is locked, 0 if unlocked.
 113  */
 114 static inline int fastcall mutex_is_locked(struct mutex *lock)
 115 {
 116         return atomic_read(&lock->count) != 1;
 117 }
 118
 119 /*
 120  * See kernel/mutex.c for detailed documentation of these APIs.
 121  * Also see Documentation/mutex-design.txt.
 122  */
 123 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 124 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 125 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 126                                         unsigned int subclass);
 127
 128 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
 129 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 130 #else
 131 extern void fastcall mutex_lock(struct mutex *lock);
 132 extern int __must_check fastcall mutex_lock_interruptible(struct mutex *lock);
 133
 134 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 135 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 136 #endif
 137
 138 /*
 139  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 140  *       not the down_trylock() convention!
 141  */
 142 extern int fastcall mutex_trylock(struct mutex *lock);
 143 extern void fastcall mutex_unlock(struct mutex *lock);
 144
 145 #endif