linux/include/linux/mutex.h
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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/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
  68/*
  69 * This is the control structure for tasks blocked on mutex,
  70 * which resides on the blocked task's kernel stack:
  71 */
  72struct mutex_waiter {
  73        struct list_head        list;
  74        struct task_struct      *task;
  75        struct ww_acquire_ctx   *ww_ctx;
  76#ifdef CONFIG_DEBUG_MUTEXES
  77        void                    *magic;
  78#endif
  79};
  80
  81#ifdef CONFIG_DEBUG_MUTEXES
  82
  83#define __DEBUG_MUTEX_INITIALIZER(lockname)                             \
  84        , .magic = &lockname
  85
  86extern void mutex_destroy(struct mutex *lock);
  87
  88#else
  89
  90# define __DEBUG_MUTEX_INITIALIZER(lockname)
  91
  92static inline void mutex_destroy(struct mutex *lock) {}
  93
  94#endif
  95
  96/**
  97 * mutex_init - initialize the mutex
  98 * @mutex: the mutex to be initialized
  99 *
 100 * Initialize the mutex to unlocked state.
 101 *
 102 * It is not allowed to initialize an already locked mutex.
 103 */
 104#define mutex_init(mutex)                                               \
 105do {                                                                    \
 106        static struct lock_class_key __key;                             \
 107                                                                        \
 108        __mutex_init((mutex), #mutex, &__key);                          \
 109} while (0)
 110
 111#ifdef CONFIG_DEBUG_LOCK_ALLOC
 112# define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
 113                , .dep_map = { .name = #lockname }
 114#else
 115# define __DEP_MAP_MUTEX_INITIALIZER(lockname)
 116#endif
 117
 118#define __MUTEX_INITIALIZER(lockname) \
 119                { .owner = ATOMIC_LONG_INIT(0) \
 120                , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
 121                , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
 122                __DEBUG_MUTEX_INITIALIZER(lockname) \
 123                __DEP_MAP_MUTEX_INITIALIZER(lockname) }
 124
 125#define DEFINE_MUTEX(mutexname) \
 126        struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
 127
 128extern void __mutex_init(struct mutex *lock, const char *name,
 129                         struct lock_class_key *key);
 130
 131/**
 132 * mutex_is_locked - is the mutex locked
 133 * @lock: the mutex to be queried
 134 *
 135 * Returns true if the mutex is locked, false if unlocked.
 136 */
 137extern bool mutex_is_locked(struct mutex *lock);
 138
 139/*
 140 * See kernel/locking/mutex.c for detailed documentation of these APIs.
 141 * Also see Documentation/locking/mutex-design.rst.
 142 */
 143#ifdef CONFIG_DEBUG_LOCK_ALLOC
 144extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 145extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 146
 147extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 148                                        unsigned int subclass);
 149extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 150                                        unsigned int subclass);
 151extern void mutex_lock_io_nested(struct mutex *lock, unsigned int subclass);
 152
 153#define mutex_lock(lock) mutex_lock_nested(lock, 0)
 154#define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
 155#define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
 156#define mutex_lock_io(lock) mutex_lock_io_nested(lock, 0)
 157
 158#define mutex_lock_nest_lock(lock, nest_lock)                           \
 159do {                                                                    \
 160        typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 161        _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map);             \
 162} while (0)
 163
 164#else
 165extern void mutex_lock(struct mutex *lock);
 166extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 167extern int __must_check mutex_lock_killable(struct mutex *lock);
 168extern void mutex_lock_io(struct mutex *lock);
 169
 170# define mutex_lock_nested(lock, subclass) mutex_lock(lock)
 171# define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
 172# define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
 173# define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
 174# define mutex_lock_io_nested(lock, subclass) mutex_lock(lock)
 175#endif
 176
 177/*
 178 * NOTE: mutex_trylock() follows the spin_trylock() convention,
 179 *       not the down_trylock() convention!
 180 *
 181 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 182 */
 183extern int mutex_trylock(struct mutex *lock);
 184extern void mutex_unlock(struct mutex *lock);
 185
 186extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);
 187
 188/*
 189 * These values are chosen such that FAIL and SUCCESS match the
 190 * values of the regular mutex_trylock().
 191 */
 192enum mutex_trylock_recursive_enum {
 193        MUTEX_TRYLOCK_FAILED    = 0,
 194        MUTEX_TRYLOCK_SUCCESS   = 1,
 195        MUTEX_TRYLOCK_RECURSIVE,
 196};
 197
 198/**
 199 * mutex_trylock_recursive - trylock variant that allows recursive locking
 200 * @lock: mutex to be locked
 201 *
 202 * This function should not be used, _ever_. It is purely for hysterical GEM
 203 * raisins, and once those are gone this will be removed.
 204 *
 205 * Returns:
 206 *  - MUTEX_TRYLOCK_FAILED    - trylock failed,
 207 *  - MUTEX_TRYLOCK_SUCCESS   - lock acquired,
 208 *  - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
 209 */
 210extern /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
 211mutex_trylock_recursive(struct mutex *lock);
 212
 213#endif /* __LINUX_MUTEX_H */
 214