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
  17 #include <asm/atomic.h>
  18
  19 /*
  20  * Simple, straightforward mutexes with strict semantics:
  21  *
  22  * - only one task can hold the mutex at a time
  23  * - only the owner can unlock the mutex
  24  * - multiple unlocks are not permitted
  25  * - recursive locking is not permitted
  26  * - a mutex object must be initialized via the API
  27  * - a mutex object must not be initialized via memset or copying
  28  * - task may not exit with mutex held
  29  * - memory areas where held locks reside must not be freed
  30  * - held mutexes must not be reinitialized
  31  * - mutexes may not be used in irq contexts
  32  *
  33  * These semantics are fully enforced when DEBUG_MUTEXES is
  34  * enabled. Furthermore, besides enforcing the above rules, the mutex
  35  * debugging code also implements a number of additional features
  36  * that make lock debugging easier and faster:
  37  *
  38  * - uses symbolic names of mutexes, whenever they are printed in debug output
  39  * - point-of-acquire tracking, symbolic lookup of function names
  40  * - list of all locks held in the system, printout of them
  41  * - owner tracking
  42  * - detects self-recursing locks and prints out all relevant info
  43  * - detects multi-task circular deadlocks and prints out all affected
  44  *   locks and tasks (and only those tasks)
  45  */
  46 struct mutex {
  47         /* 1: unlocked, 0: locked, negative: locked, possible waiters */
  48         atomic_t                count;
  49         spinlock_t              wait_lock;
  50         struct list_head        wait_list;
  51 #ifdef CONFIG_DEBUG_MUTEXES
  52         struct thread_info      *owner;
  53         const char              *name;
  54         void                    *magic;
  55 #endif
  56 };
  57
  58 /*
  59  * This is the control structure for tasks blocked on mutex,
  60  * which resides on the blocked task's kernel stack:
  61  */
  62 struct mutex_waiter {
  63         struct list_head        list;
  64         struct task_struct      *task;
  65 #ifdef CONFIG_DEBUG_MUTEXES
  66         struct mutex            *lock;
  67         void                    *magic;
  68 #endif
  69 };
  70
  71 #ifdef CONFIG_DEBUG_MUTEXES
  72 # include <linux/mutex-debug.h>
  73 #else
  74 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  75 # define mutex_init(mutex)                      __mutex_init(mutex, NULL)
  76 # define mutex_destroy(mutex)                           do { } while (0)
  77 #endif
  78
  79 #define __MUTEX_INITIALIZER(lockname) \
  80                 { .count = ATOMIC_INIT(1) \
  81                 , .wait_lock = SPIN_LOCK_UNLOCKED \
  82                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
  83                 __DEBUG_MUTEX_INITIALIZER(lockname) }
  84
  85 #define DEFINE_MUTEX(mutexname) \
  86         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
  87
  88 extern void fastcall __mutex_init(struct mutex *lock, const char *name);
  89
  90 /***
  91  * mutex_is_locked - is the mutex locked
  92  * @lock: the mutex to be queried
  93  *
  94  * Returns 1 if the mutex is locked, 0 if unlocked.
  95  */
  96 static inline int fastcall mutex_is_locked(struct mutex *lock)
  97 {
  98         return atomic_read(&lock->count) != 1;
  99 }
 100
 101 /*
 102  * See kernel/mutex.c for detailed documentation of these APIs.
 103  * Also see Documentation/mutex-design.txt.
 104  */
 105 extern void fastcall mutex_lock(struct mutex *lock);
 106 extern int fastcall mutex_lock_interruptible(struct mutex *lock);
 107 /*
 108  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 109  *       not the down_trylock() convention!
 110  */
 111 extern int fastcall mutex_trylock(struct mutex *lock);
 112 extern void fastcall mutex_unlock(struct mutex *lock);
 113
 114 #endif