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