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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
69static inline struct task_struct *__mutex_owner(struct mutex *lock)
70{
71 return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
72}
73
74/*
75 * This is the control structure for tasks blocked on mutex,
76 * which resides on the blocked task's kernel stack:
77 */
78struct mutex_waiter {
79 struct list_head list;
80 struct task_struct *task;
81 struct ww_acquire_ctx *ww_ctx;
82#ifdef CONFIG_DEBUG_MUTEXES
83 void *magic;
84#endif
85};
86
87#ifdef CONFIG_DEBUG_MUTEXES
88
89#define __DEBUG_MUTEX_INITIALIZER(lockname) \
90 , .magic = &lockname
91
92extern void mutex_destroy(struct mutex *lock);
93
94#else
95
96# define __DEBUG_MUTEX_INITIALIZER(lockname)
97
98static inline void mutex_destroy(struct mutex *lock) {}
99
100#endif
101
102/**
103 * mutex_init - initialize the mutex
104 * @mutex: the mutex to be initialized
105 *
106 * Initialize the mutex to unlocked state.
107 *
108 * It is not allowed to initialize an already locked mutex.
109 */
110#define mutex_init(mutex) \
111do { \
112 static struct lock_class_key __key; \
113 \
114 __mutex_init((mutex), #mutex, &__key); \
115} while (0)
116
117#ifdef CONFIG_DEBUG_LOCK_ALLOC
118# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
119 , .dep_map = { .name = #lockname }
120#else
121# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
122#endif
123
124#define __MUTEX_INITIALIZER(lockname) \
125 { .owner = ATOMIC_LONG_INIT(0) \
126 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
127 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
128 __DEBUG_MUTEX_INITIALIZER(lockname) \
129 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
130
131#define DEFINE_MUTEX(mutexname) \
132 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
133
134extern void __mutex_init(struct mutex *lock, const char *name,
135 struct lock_class_key *key);
136
137/**
138 * mutex_is_locked - is the mutex locked
139 * @lock: the mutex to be queried
140 *
141 * Returns 1 if the mutex is locked, 0 if unlocked.
142 */
143static inline int mutex_is_locked(struct mutex *lock)
144{
145 /*
146 * XXX think about spin_is_locked
147 */
148 return __mutex_owner(lock) != NULL;
149}
150
151/*
152 * See kernel/locking/mutex.c for detailed documentation of these APIs.
153 * Also see Documentation/locking/mutex-design.txt.
154 */
155#ifdef CONFIG_DEBUG_LOCK_ALLOC
156extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
157extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
158
159extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
160 unsigned int subclass);
161extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
162 unsigned int subclass);
163extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
164
165#define mutex_lock(lock) mutex_lock_nested(lock, 0)
166#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
167#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
168#define mutex_lock_io(lock) mutex_lock_io_nested(lock, 0)
169
170#define mutex_lock_nest_lock(lock, nest_lock) \
171do { \
172 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
173 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
174} while (0)
175
176#else
177extern void mutex_lock(struct mutex *lock);
178extern int __must_check mutex_lock_interruptible(struct mutex *lock);
179extern int __must_check mutex_lock_killable(struct mutex *lock);
180extern void mutex_lock_io(struct mutex *lock);
181
182# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
183# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
184# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
185# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
186# define mutex_lock_io_nested(lock, subclass) mutex_lock(lock)
187#endif
188
189/*
190 * NOTE: mutex_trylock() follows the spin_trylock() convention,
191 * not the down_trylock() convention!
192 *
193 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
194 */
195extern int mutex_trylock(struct mutex *lock);
196extern void mutex_unlock(struct mutex *lock);
197
198extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
199
200/*
201 * These values are chosen such that FAIL and SUCCESS match the
202 * values of the regular mutex_trylock().
203 */
204enum mutex_trylock_recursive_enum {
205 MUTEX_TRYLOCK_FAILED = 0,
206 MUTEX_TRYLOCK_SUCCESS = 1,
207 MUTEX_TRYLOCK_RECURSIVE,
208};
209
210/**
211 * mutex_trylock_recursive - trylock variant that allows recursive locking
212 * @lock: mutex to be locked
213 *
214 * This function should not be used, _ever_. It is purely for hysterical GEM
215 * raisins, and once those are gone this will be removed.
216 *
217 * Returns:
218 * - MUTEX_TRYLOCK_FAILED - trylock failed,
219 * - MUTEX_TRYLOCK_SUCCESS - lock acquired,
220 * - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
221 */
222static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
223mutex_trylock_recursive(struct mutex *lock)
224{
225 if (unlikely(__mutex_owner(lock) == current))
226 return MUTEX_TRYLOCK_RECURSIVE;
227
228 return mutex_trylock(lock);
229}
230
231#endif /* __LINUX_MUTEX_H */