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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 <asm/current.h>
14#include <linux/list.h>
15#include <linux/spinlock_types.h>
16#include <linux/linkage.h>
17#include <linux/lockdep.h>
18#include <linux/atomic.h>
19#include <asm/processor.h>
20#include <linux/osq_lock.h>
21#include <linux/debug_locks.h>
22
23/*
24 * Simple, straightforward mutexes with strict semantics:
25 *
26 * - only one task can hold the mutex at a time
27 * - only the owner can unlock the mutex
28 * - multiple unlocks are not permitted
29 * - recursive locking is not permitted
30 * - a mutex object must be initialized via the API
31 * - a mutex object must not be initialized via memset or copying
32 * - task may not exit with mutex held
33 * - memory areas where held locks reside must not be freed
34 * - held mutexes must not be reinitialized
35 * - mutexes may not be used in hardware or software interrupt
36 * contexts such as tasklets and timers
37 *
38 * These semantics are fully enforced when DEBUG_MUTEXES is
39 * enabled. Furthermore, besides enforcing the above rules, the mutex
40 * debugging code also implements a number of additional features
41 * that make lock debugging easier and faster:
42 *
43 * - uses symbolic names of mutexes, whenever they are printed in debug output
44 * - point-of-acquire tracking, symbolic lookup of function names
45 * - list of all locks held in the system, printout of them
46 * - owner tracking
47 * - detects self-recursing locks and prints out all relevant info
48 * - detects multi-task circular deadlocks and prints out all affected
49 * locks and tasks (and only those tasks)
50 */
51struct mutex {
52 atomic_long_t owner;
53 spinlock_t wait_lock;
54#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
55 struct optimistic_spin_queue osq; /* Spinner MCS lock */
56#endif
57 struct list_head wait_list;
58#ifdef CONFIG_DEBUG_MUTEXES
59 void *magic;
60#endif
61#ifdef CONFIG_DEBUG_LOCK_ALLOC
62 struct lockdep_map dep_map;
63#endif
64};
65
66static inline struct task_struct *__mutex_owner(struct mutex *lock)
67{
68 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x03);
69}
70
71/*
72 * This is the control structure for tasks blocked on mutex,
73 * which resides on the blocked task's kernel stack:
74 */
75struct mutex_waiter {
76 struct list_head list;
77 struct task_struct *task;
78#ifdef CONFIG_DEBUG_MUTEXES
79 void *magic;
80#endif
81};
82
83#ifdef CONFIG_DEBUG_MUTEXES
84
85#define __DEBUG_MUTEX_INITIALIZER(lockname) \
86 , .magic = &lockname
87
88extern void mutex_destroy(struct mutex *lock);
89
90#else
91
92# define __DEBUG_MUTEX_INITIALIZER(lockname)
93
94static inline void mutex_destroy(struct mutex *lock) {}
95
96#endif
97
98/**
99 * mutex_init - initialize the mutex
100 * @mutex: the mutex to be initialized
101 *
102 * Initialize the mutex to unlocked state.
103 *
104 * It is not allowed to initialize an already locked mutex.
105 */
106#define mutex_init(mutex) \
107do { \
108 static struct lock_class_key __key; \
109 \
110 __mutex_init((mutex), #mutex, &__key); \
111} while (0)
112
113#ifdef CONFIG_DEBUG_LOCK_ALLOC
114# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
115 , .dep_map = { .name = #lockname }
116#else
117# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
118#endif
119
120#define __MUTEX_INITIALIZER(lockname) \
121 { .owner = ATOMIC_LONG_INIT(0) \
122 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
123 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
124 __DEBUG_MUTEX_INITIALIZER(lockname) \
125 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
126
127#define DEFINE_MUTEX(mutexname) \
128 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
129
130extern void __mutex_init(struct mutex *lock, const char *name,
131 struct lock_class_key *key);
132
133/**
134 * mutex_is_locked - is the mutex locked
135 * @lock: the mutex to be queried
136 *
137 * Returns 1 if the mutex is locked, 0 if unlocked.
138 */
139static inline int mutex_is_locked(struct mutex *lock)
140{
141 /*
142 * XXX think about spin_is_locked
143 */
144 return __mutex_owner(lock) != NULL;
145}
146
147/*
148 * See kernel/locking/mutex.c for detailed documentation of these APIs.
149 * Also see Documentation/locking/mutex-design.txt.
150 */
151#ifdef CONFIG_DEBUG_LOCK_ALLOC
152extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
153extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
154
155extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
156 unsigned int subclass);
157extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
158 unsigned int subclass);
159
160#define mutex_lock(lock) mutex_lock_nested(lock, 0)
161#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
162#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
163
164#define mutex_lock_nest_lock(lock, nest_lock) \
165do { \
166 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
167 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
168} while (0)
169
170#else
171extern void mutex_lock(struct mutex *lock);
172extern int __must_check mutex_lock_interruptible(struct mutex *lock);
173extern int __must_check mutex_lock_killable(struct mutex *lock);
174
175# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
176# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
177# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
178# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
179#endif
180
181/*
182 * NOTE: mutex_trylock() follows the spin_trylock() convention,
183 * not the down_trylock() convention!
184 *
185 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
186 */
187extern int mutex_trylock(struct mutex *lock);
188extern void mutex_unlock(struct mutex *lock);
189
190extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
191
192/*
193 * These values are chosen such that FAIL and SUCCESS match the
194 * values of the regular mutex_trylock().
195 */
196enum mutex_trylock_recursive_enum {
197 MUTEX_TRYLOCK_FAILED = 0,
198 MUTEX_TRYLOCK_SUCCESS = 1,
199 MUTEX_TRYLOCK_RECURSIVE,
200};
201
202/**
203 * mutex_trylock_recursive - trylock variant that allows recursive locking
204 * @lock: mutex to be locked
205 *
206 * This function should not be used, _ever_. It is purely for hysterical GEM
207 * raisins, and once those are gone this will be removed.
208 *
209 * Returns:
210 * MUTEX_TRYLOCK_FAILED - trylock failed,
211 * MUTEX_TRYLOCK_SUCCESS - lock acquired,
212 * MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
213 */
214static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
215mutex_trylock_recursive(struct mutex *lock)
216{
217 if (unlikely(__mutex_owner(lock) == current))
218 return MUTEX_TRYLOCK_RECURSIVE;
219
220 return mutex_trylock(lock);
221}
222
223#endif /* __LINUX_MUTEX_H */