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
  16 #include <asm/atomic.h>
  17
  18 /*
  19  * Simple, straightforward mutexes with strict semantics:
  20  *
  21  * - only one task can hold the mutex at a time
  22  * - only the owner can unlock the mutex
  23  * - multiple unlocks are not permitted
  24  * - recursive locking is not permitted
  25  * - a mutex object must be initialized via the API
  26  * - a mutex object must not be initialized via memset or copying
  27  * - task may not exit with mutex held
  28  * - memory areas where held locks reside must not be freed
  29  * - held mutexes must not be reinitialized
  30  * - mutexes may not be used in irq contexts
  31  *
  32  * These semantics are fully enforced when DEBUG_MUTEXES is
  33  * enabled. Furthermore, besides enforcing the above rules, the mutex
  34  * debugging code also implements a number of additional features
  35  * that make lock debugging easier and faster:
  36  *
  37  * - uses symbolic names of mutexes, whenever they are printed in debug output
  38  * - point-of-acquire tracking, symbolic lookup of function names
  39  * - list of all locks held in the system, printout of them
  40  * - owner tracking
  41  * - detects self-recursing locks and prints out all relevant info
  42  * - detects multi-task circular deadlocks and prints out all affected
  43  *   locks and tasks (and only those tasks)
  44  */
  45 struct mutex {
  46         /* 1: unlocked, 0: locked, negative: locked, possible waiters */
  47         atomic_t                count;
  48         spinlock_t              wait_lock;
  49         struct list_head        wait_list;
  50 #ifdef CONFIG_DEBUG_MUTEXES
  51         struct thread_info      *owner;
  52         struct list_head        held_list;
  53         unsigned long           acquire_ip;
  54         const char              *name;
  55         void                    *magic;
  56 #endif
  57 };
  58
  59 /*
  60  * This is the control structure for tasks blocked on mutex,
  61  * which resides on the blocked task's kernel stack:
  62  */
  63 struct mutex_waiter {
  64         struct list_head        list;
  65         struct task_struct      *task;
  66 #ifdef CONFIG_DEBUG_MUTEXES
  67         struct mutex            *lock;
  68         void                    *magic;
  69 #endif
  70 };
  71
  72 #ifdef CONFIG_DEBUG_MUTEXES
  73 # include <linux/mutex-debug.h>
  74 #else
  75 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  76 # define mutex_init(mutex)                      __mutex_init(mutex, NULL)
  77 # define mutex_destroy(mutex)                           do { } while (0)
  78 # define mutex_debug_show_all_locks()                   do { } while (0)
  79 # define mutex_debug_show_held_locks(p)                 do { } while (0)
  80 # define mutex_debug_check_no_locks_held(task)          do { } while (0)
  81 # define mutex_debug_check_no_locks_freed(from, to)     do { } while (0)
  82 #endif
  83
  84 #define __MUTEX_INITIALIZER(lockname) \
  85                 { .count = ATOMIC_INIT(1) \
  86                 , .wait_lock = SPIN_LOCK_UNLOCKED \
  87                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
  88                 __DEBUG_MUTEX_INITIALIZER(lockname) }
  89
  90 #define DEFINE_MUTEX(mutexname) \
  91         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
  92
  93 extern void fastcall __mutex_init(struct mutex *lock, const char *name);
  94
  95 /***
  96  * mutex_is_locked - is the mutex locked
  97  * @lock: the mutex to be queried
  98  *
  99  * Returns 1 if the mutex is locked, 0 if unlocked.
 100  */
 101 static inline int fastcall mutex_is_locked(struct mutex *lock)
 102 {
 103         return atomic_read(&lock->count) != 1;
 104 }
 105
 106 /*
 107  * See kernel/mutex.c for detailed documentation of these APIs.
 108  * Also see Documentation/mutex-design.txt.
 109  */
 110 extern void fastcall mutex_lock(struct mutex *lock);
 111 extern int fastcall mutex_lock_interruptible(struct mutex *lock);
 112 /*
 113  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 114  *       not the down_trylock() convention!
 115  */
 116 extern int fastcall mutex_trylock(struct mutex *lock);
 117 extern void fastcall mutex_unlock(struct mutex *lock);
 118
 119 #endif