include/linux/mutex.h

   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
  24 struct 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  */
  54 struct 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  */
  74 static 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  */
  83 struct 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
  97 extern void mutex_destroy(struct mutex *lock);
  98
  99 #else
 100
 101 # define __DEBUG_MUTEX_INITIALIZER(lockname)
 102
 103 static 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)                                               \
 116 do {                                                                    \
 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
 139 extern 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  */
 148 static 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
 161 extern void mutex_lock_nested(struct mutex *lock, unsigned int subclass);
 162 extern void _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest_lock);
 163
 164 extern int __must_check mutex_lock_interruptible_nested(struct mutex *lock,
 165                                         unsigned int subclass);
 166 extern int __must_check mutex_lock_killable_nested(struct mutex *lock,
 167                                         unsigned int subclass);
 168 extern 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)                           \
 176 do {                                                                    \
 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
 182 extern void mutex_lock(struct mutex *lock);
 183 extern int __must_check mutex_lock_interruptible(struct mutex *lock);
 184 extern int __must_check mutex_lock_killable(struct mutex *lock);
 185 extern 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  */
 200 extern int mutex_trylock(struct mutex *lock);
 201 extern void mutex_unlock(struct mutex *lock);
 202
 203 extern 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  */
 209 enum 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  */
 227 static inline /* __deprecated */ __must_check enum mutex_trylock_recursive_enum
 228 mutex_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 */