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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
23struct ww_acquire_ctx;
24
25/*
26 * Simple, straightforward mutexes with strict semantics:
27 *
28 * - only one task can hold the mutex at a time
29 * - only the owner can unlock the mutex
30 * - multiple unlocks are not permitted
31 * - recursive locking is not permitted
32 * - a mutex object must be initialized via the API
33 * - a mutex object must not be initialized via memset or copying
34 * - task may not exit with mutex held
35 * - memory areas where held locks reside must not be freed
36 * - held mutexes must not be reinitialized
37 * - mutexes may not be used in hardware or software interrupt
38 * contexts such as tasklets and timers
39 *
40 * These semantics are fully enforced when DEBUG_MUTEXES is
41 * enabled. Furthermore, besides enforcing the above rules, the mutex
42 * debugging code also implements a number of additional features
43 * that make lock debugging easier and faster:
44 *
45 * - uses symbolic names of mutexes, whenever they are printed in debug output
46 * - point-of-acquire tracking, symbolic lookup of function names
47 * - list of all locks held in the system, printout of them
48 * - owner tracking
49 * - detects self-recursing locks and prints out all relevant info
50 * - detects multi-task circular deadlocks and prints out all affected
51 * locks and tasks (and only those tasks)
52 */
53struct mutex {
54 atomic_long_t owner;
55 spinlock_t wait_lock;
56#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
57 struct optimistic_spin_queue osq; /* Spinner MCS lock */
58#endif
59 struct list_head wait_list;
60#ifdef CONFIG_DEBUG_MUTEXES
61 void *magic;
62#endif
63#ifdef CONFIG_DEBUG_LOCK_ALLOC
64 struct lockdep_map dep_map;
65#endif
66};
67
68static inline struct task_struct *__mutex_owner(struct mutex *lock)
69{
70 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
71}
72
73/*
74 * This is the control structure for tasks blocked on mutex,
75 * which resides on the blocked task's kernel stack:
76 */
77struct mutex_waiter {
78 struct list_head list;
79 struct task_struct *task;
80 struct ww_acquire_ctx *ww_ctx;
81#ifdef CONFIG_DEBUG_MUTEXES
82 void *magic;
83#endif
84};
85
86#ifdef CONFIG_DEBUG_MUTEXES
87
88#define __DEBUG_MUTEX_INITIALIZER(lockname) \
89 , .magic = &lockname
90
91extern void mutex_destroy(struct mutex *lock);
92
93#else
94
95# define __DEBUG_MUTEX_INITIALIZER(lockname)
96
97static inline void mutex_destroy(struct mutex *lock) {}
98
99#endif
100
101/**
102 * mutex_init - initialize the mutex
103 * @mutex: the mutex to be initialized
104 *
105 * Initialize the mutex to unlocked state.
106 *
107 * It is not allowed to initialize an already locked mutex.
108 */
109#define mutex_init(mutex) \
110do { \
111 static struct lock_class_key __key; \
112 \
113 __mutex_init((mutex), #mutex, &__key); \
114} while (0)
115
116#ifdef CONFIG_DEBUG_LOCK_ALLOC
117# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
118 , .dep_map = { .name = #lockname }
119#else
120# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
121#endif
122
123#define __MUTEX_INITIALIZER(lockname) \
124 { .owner = ATOMIC_LONG_INIT(0) \
125 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
126 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
127 __DEBUG_MUTEX_INITIALIZER(lockname) \
128 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
129
130#define DEFINE_MUTEX(mutexname) \
131 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
132
133extern void __mutex_init(struct mutex *lock, const char *name,
134 struct lock_class_key *key);
135
136/**
137 * mutex_is_locked - is the mutex locked
138 * @lock: the mutex to be queried
139 *
140 * Returns 1 if the mutex is locked, 0 if unlocked.
141 */
142static inline int mutex_is_locked(struct mutex *lock)
143{
144 /*
145 * XXX think about spin_is_locked
146 */
147 return __mutex_owner(lock) != NULL;
148}
149
150/*
151 * See kernel/locking/mutex.c for detailed documentation of these APIs.
152 * Also see Documentation/locking/mutex-design.txt.
153 */
154#ifdef CONFIG_DEBUG_LOCK_ALLOC
155extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
156extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
157
158extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
159 unsigned int subclass);
160extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
161 unsigned int subclass);
162extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
163
164#define mutex_lock(lock) mutex_lock_nested(lock, 0)
165#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
166#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
167#define mutex_lock_io(lock) mutex_lock_io_nested(lock, 0)
168
169#define mutex_lock_nest_lock(lock, nest_lock) \
170do { \
171 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
172 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
173} while (0)
174
175#else
176extern void mutex_lock(struct mutex *lock);
177extern int __must_check mutex_lock_interruptible(struct mutex *lock);
178extern int __must_check mutex_lock_killable(struct mutex *lock);
179extern void mutex_lock_io(struct mutex *lock);
180
181# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
182# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
183# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
184# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
185# define mutex_lock_io_nested(lock, subclass) mutex_lock(lock)
186#endif
187
188/*
189 * NOTE: mutex_trylock() follows the spin_trylock() convention,
190 * not the down_trylock() convention!
191 *
192 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
193 */
194extern int mutex_trylock(struct mutex *lock);
195extern void mutex_unlock(struct mutex *lock);
196
197extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
198
199/*
200 * These values are chosen such that FAIL and SUCCESS match the
201 * values of the regular mutex_trylock().
202 */
203enum mutex_trylock_recursive_enum {
204 MUTEX_TRYLOCK_FAILED = 0,
205 MUTEX_TRYLOCK_SUCCESS = 1,
206 MUTEX_TRYLOCK_RECURSIVE,
207};
208
209/**
210 * mutex_trylock_recursive - trylock variant that allows recursive locking
211 * @lock: mutex to be locked
212 *
213 * This function should not be used, _ever_. It is purely for hysterical GEM
214 * raisins, and once those are gone this will be removed.
215 *
216 * Returns:
217 * MUTEX_TRYLOCK_FAILED - trylock failed,
218 * MUTEX_TRYLOCK_SUCCESS - lock acquired,
219 * MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
220 */
221static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
222mutex_trylock_recursive(struct mutex *lock)
223{
224 if (unlikely(__mutex_owner(lock) == current))
225 return MUTEX_TRYLOCK_RECURSIVE;
226
227 return mutex_trylock(lock);
228}
229
230#endif /* __LINUX_MUTEX_H */