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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