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         struct list_head        held_list;
  54         unsigned long           acquire_ip;
  55         const char              *name;
  56         void                    *magic;
  57 #endif
  58 };
  59
  60 /*
  61  * This is the control structure for tasks blocked on mutex,
  62  * which resides on the blocked task's kernel stack:
  63  */
  64 struct mutex_waiter {
  65         struct list_head        list;
  66         struct task_struct      *task;
  67 #ifdef CONFIG_DEBUG_MUTEXES
  68         struct mutex            *lock;
  69         void                    *magic;
  70 #endif
  71 };
  72
  73 #ifdef CONFIG_DEBUG_MUTEXES
  74 # include <linux/mutex-debug.h>
  75 #else
  76 # define __DEBUG_MUTEX_INITIALIZER(lockname)
  77 # define mutex_init(mutex)                      __mutex_init(mutex, NULL)
  78 # define mutex_destroy(mutex)                           do { } while (0)
  79 # define mutex_debug_show_all_locks()                   do { } while (0)
  80 # define mutex_debug_show_held_locks(p)                 do { } while (0)
  81 # define mutex_debug_check_no_locks_held(task)          do { } while (0)
  82 # define mutex_debug_check_no_locks_freed(from, len)    do { } while (0)
  83 #endif
  84
  85 #define __MUTEX_INITIALIZER(lockname) \
  86                 { .count = ATOMIC_INIT(1) \
  87                 , .wait_lock = SPIN_LOCK_UNLOCKED \
  88                 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
  89                 __DEBUG_MUTEX_INITIALIZER(lockname) }
  90
  91 #define DEFINE_MUTEX(mutexname) \
  92         struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
  93
  94 extern void fastcall __mutex_init(struct mutex *lock, const char *name);
  95
  96 /***
  97  * mutex_is_locked - is the mutex locked
  98  * @lock: the mutex to be queried
  99  *
 100  * Returns 1 if the mutex is locked, 0 if unlocked.
 101  */
 102 static inline int fastcall mutex_is_locked(struct mutex *lock)
 103 {
 104         return atomic_read(&lock->count) != 1;
 105 }
 106
 107 /*
 108  * See kernel/mutex.c for detailed documentation of these APIs.
 109  * Also see Documentation/mutex-design.txt.
 110  */
 111 extern void fastcall mutex_lock(struct mutex *lock);
 112 extern int fastcall mutex_lock_interruptible(struct mutex *lock);
 113 /*
 114  * NOTE: mutex_trylock() follows the spin_trylock() convention,
 115  *       not the down_trylock() convention!
 116  */
 117 extern int fastcall mutex_trylock(struct mutex *lock);
 118 extern void fastcall mutex_unlock(struct mutex *lock);
 119
 120 #endif