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1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * Mutexes: blocking mutual exclusion locks
4 *
5 * started by Ingo Molnar:
6 *
7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 *
9 * This file contains the main data structure and API definitions.
10 */
11#ifndef __LINUX_MUTEX_H
12#define __LINUX_MUTEX_H
13
14#include <asm/current.h>
15#include <linux/list.h>
16#include <linux/spinlock_types.h>
17#include <linux/linkage.h>
18#include <linux/lockdep.h>
19#include <linux/atomic.h>
20#include <asm/processor.h>
21#include <linux/osq_lock.h>
22#include <linux/debug_locks.h>
23
24struct ww_acquire_ctx;
25
26/*
27 * Simple, straightforward mutexes with strict semantics:
28 *
29 * - only one task can hold the mutex at a time
30 * - only the owner can unlock the mutex
31 * - multiple unlocks are not permitted
32 * - recursive locking is not permitted
33 * - a mutex object must be initialized via the API
34 * - a mutex object must not be initialized via memset or copying
35 * - task may not exit with mutex held
36 * - memory areas where held locks reside must not be freed
37 * - held mutexes must not be reinitialized
38 * - mutexes may not be used in hardware or software interrupt
39 * contexts such as tasklets and timers
40 *
41 * These semantics are fully enforced when DEBUG_MUTEXES is
42 * enabled. Furthermore, besides enforcing the above rules, the mutex
43 * debugging code also implements a number of additional features
44 * that make lock debugging easier and faster:
45 *
46 * - uses symbolic names of mutexes, whenever they are printed in debug output
47 * - point-of-acquire tracking, symbolic lookup of function names
48 * - list of all locks held in the system, printout of them
49 * - owner tracking
50 * - detects self-recursing locks and prints out all relevant info
51 * - detects multi-task circular deadlocks and prints out all affected
52 * locks and tasks (and only those tasks)
53 */
54struct mutex {
55 atomic_long_t owner;
56 spinlock_t wait_lock;
57#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
58 struct optimistic_spin_queue osq; /* Spinner MCS lock */
59#endif
60 struct list_head wait_list;
61#ifdef CONFIG_DEBUG_MUTEXES
62 void *magic;
63#endif
64#ifdef CONFIG_DEBUG_LOCK_ALLOC
65 struct lockdep_map dep_map;
66#endif
67};
68
69/*
70 * Internal helper function; C doesn't allow us to hide it :/
71 *
72 * DO NOT USE (outside of mutex code).
73 */
74static inline struct task_struct *__mutex_owner(struct mutex *lock)
75{
76 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
77}
78
79/*
80 * This is the control structure for tasks blocked on mutex,
81 * which resides on the blocked task's kernel stack:
82 */
83struct mutex_waiter {
84 struct list_head list;
85 struct task_struct *task;
86 struct ww_acquire_ctx *ww_ctx;
87#ifdef CONFIG_DEBUG_MUTEXES
88 void *magic;
89#endif
90};
91
92#ifdef CONFIG_DEBUG_MUTEXES
93
94#define __DEBUG_MUTEX_INITIALIZER(lockname) \
95 , .magic = &lockname
96
97extern void mutex_destroy(struct mutex *lock);
98
99#else
100
101# define __DEBUG_MUTEX_INITIALIZER(lockname)
102
103static inline void mutex_destroy(struct mutex *lock) {}
104
105#endif
106
107/**
108 * mutex_init - initialize the mutex
109 * @mutex: the mutex to be initialized
110 *
111 * Initialize the mutex to unlocked state.
112 *
113 * It is not allowed to initialize an already locked mutex.
114 */
115#define mutex_init(mutex) \
116do { \
117 static struct lock_class_key __key; \
118 \
119 __mutex_init((mutex), #mutex, &__key); \
120} while (0)
121
122#ifdef CONFIG_DEBUG_LOCK_ALLOC
123# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
124 , .dep_map = { .name = #lockname }
125#else
126# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
127#endif
128
129#define __MUTEX_INITIALIZER(lockname) \
130 { .owner = ATOMIC_LONG_INIT(0) \
131 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
132 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
133 __DEBUG_MUTEX_INITIALIZER(lockname) \
134 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
135
136#define DEFINE_MUTEX(mutexname) \
137 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
138
139extern void __mutex_init(struct mutex *lock, const char *name,
140 struct lock_class_key *key);
141
142/**
143 * mutex_is_locked - is the mutex locked
144 * @lock: the mutex to be queried
145 *
146 * Returns true if the mutex is locked, false if unlocked.
147 */
148static inline bool mutex_is_locked(struct mutex *lock)
149{
150 /*
151 * XXX think about spin_is_locked
152 */
153 return __mutex_owner(lock) != NULL;
154}
155
156/*
157 * See kernel/locking/mutex.c for detailed documentation of these APIs.
158 * Also see Documentation/locking/mutex-design.txt.
159 */
160#ifdef CONFIG_DEBUG_LOCK_ALLOC
161extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
162extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
163
164extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
165 unsigned int subclass);
166extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
167 unsigned int subclass);
168extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
169
170#define mutex_lock(lock) mutex_lock_nested(lock, 0)
171#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
172#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
173#define mutex_lock_io(lock) mutex_lock_io_nested(lock, 0)
174
175#define mutex_lock_nest_lock(lock, nest_lock) \
176do { \
177 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
178 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
179} while (0)
180
181#else
182extern void mutex_lock(struct mutex *lock);
183extern int __must_check mutex_lock_interruptible(struct mutex *lock);
184extern int __must_check mutex_lock_killable(struct mutex *lock);
185extern void mutex_lock_io(struct mutex *lock);
186
187# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
188# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
189# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
190# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
191# define mutex_lock_io_nested(lock, subclass) mutex_lock(lock)
192#endif
193
194/*
195 * NOTE: mutex_trylock() follows the spin_trylock() convention,
196 * not the down_trylock() convention!
197 *
198 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
199 */
200extern int mutex_trylock(struct mutex *lock);
201extern void mutex_unlock(struct mutex *lock);
202
203extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
204
205/*
206 * These values are chosen such that FAIL and SUCCESS match the
207 * values of the regular mutex_trylock().
208 */
209enum mutex_trylock_recursive_enum {
210 MUTEX_TRYLOCK_FAILED = 0,
211 MUTEX_TRYLOCK_SUCCESS = 1,
212 MUTEX_TRYLOCK_RECURSIVE,
213};
214
215/**
216 * mutex_trylock_recursive - trylock variant that allows recursive locking
217 * @lock: mutex to be locked
218 *
219 * This function should not be used, _ever_. It is purely for hysterical GEM
220 * raisins, and once those are gone this will be removed.
221 *
222 * Returns:
223 * - MUTEX_TRYLOCK_FAILED - trylock failed,
224 * - MUTEX_TRYLOCK_SUCCESS - lock acquired,
225 * - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
226 */
227static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
228mutex_trylock_recursive(struct mutex *lock)
229{
230 if (unlikely(__mutex_owner(lock) == current))
231 return MUTEX_TRYLOCK_RECURSIVE;
232
233 return mutex_trylock(lock);
234}
235
236#endif /* __LINUX_MUTEX_H */