LXR linux/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 */
  46struct 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 */
  64struct 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
  94extern 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 */
 102static 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 */
 111extern void fastcall mutex_lock(struct mutex *lock);
 112extern 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 */
 117extern int fastcall mutex_trylock(struct mutex *lock);
 118extern void fastcall mutex_unlock(struct mutex *lock);
 119
 120#endif
 121