LXR linux/include/linux/rwsem.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2/* rwsem.h: R/W semaphores, public interface
   3 *
   4 * Written by David Howells (dhowells@redhat.com).
   5 * Derived from asm-i386/semaphore.h
   6 */
   7
   8#ifndef _LINUX_RWSEM_H
   9#define _LINUX_RWSEM_H
  10
  11#include <linux/linkage.h>
  12
  13#include <linux/types.h>
  14#include <linux/kernel.h>
  15#include <linux/list.h>
  16#include <linux/spinlock.h>
  17#include <linux/atomic.h>
  18#include <linux/err.h>
  19#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  20#include <linux/osq_lock.h>
  21#endif
  22
  23struct rw_semaphore;
  24
  25#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  26#include <linux/rwsem-spinlock.h> /* use a generic implementation */
  27#define __RWSEM_INIT_COUNT(name)        .count = RWSEM_UNLOCKED_VALUE
  28#else
  29/* All arch specific implementations share the same struct */
  30struct rw_semaphore {
  31        atomic_long_t count;
  32        struct list_head wait_list;
  33        raw_spinlock_t wait_lock;
  34#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  35        struct optimistic_spin_queue osq; /* spinner MCS lock */
  36        /*
  37         * Write owner. Used as a speculative check to see
  38         * if the owner is running on the cpu.
  39         */
  40        struct task_struct *owner;
  41#endif
  42#ifdef CONFIG_DEBUG_LOCK_ALLOC
  43        struct lockdep_map      dep_map;
  44#endif
  45};
  46
  47extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  48extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
  49extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  50extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
  51extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  52extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  53
  54/* Include the arch specific part */
  55#include <asm/rwsem.h>
  56
  57/* In all implementations count != 0 means locked */
  58static inline int rwsem_is_locked(struct rw_semaphore *sem)
  59{
  60        return atomic_long_read(&sem->count) != 0;
  61}
  62
  63#define __RWSEM_INIT_COUNT(name)        .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
  64#endif
  65
  66/* Common initializer macros and functions */
  67
  68#ifdef CONFIG_DEBUG_LOCK_ALLOC
  69# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  70#else
  71# define __RWSEM_DEP_MAP_INIT(lockname)
  72#endif
  73
  74#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  75#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
  76#else
  77#define __RWSEM_OPT_INIT(lockname)
  78#endif
  79
  80#define __RWSEM_INITIALIZER(name)                               \
  81        { __RWSEM_INIT_COUNT(name),                             \
  82          .wait_list = LIST_HEAD_INIT((name).wait_list),        \
  83          .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
  84          __RWSEM_OPT_INIT(name)                                \
  85          __RWSEM_DEP_MAP_INIT(name) }
  86
  87#define DECLARE_RWSEM(name) \
  88        struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  89
  90extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  91                         struct lock_class_key *key);
  92
  93#define init_rwsem(sem)                                         \
  94do {                                                            \
  95        static struct lock_class_key __key;                     \
  96                                                                \
  97        __init_rwsem((sem), #sem, &__key);                      \
  98} while (0)
  99
 100/*
 101 * This is the same regardless of which rwsem implementation that is being used.
 102 * It is just a heuristic meant to be called by somebody alreadying holding the
 103 * rwsem to see if somebody from an incompatible type is wanting access to the
 104 * lock.
 105 */
 106static inline int rwsem_is_contended(struct rw_semaphore *sem)
 107{
 108        return !list_empty(&sem->wait_list);
 109}
 110
 111/*
 112 * lock for reading
 113 */
 114extern void down_read(struct rw_semaphore *sem);
 115extern int __must_check down_read_killable(struct rw_semaphore *sem);
 116
 117/*
 118 * trylock for reading -- returns 1 if successful, 0 if contention
 119 */
 120extern int down_read_trylock(struct rw_semaphore *sem);
 121
 122/*
 123 * lock for writing
 124 */
 125extern void down_write(struct rw_semaphore *sem);
 126extern int __must_check down_write_killable(struct rw_semaphore *sem);
 127
 128/*
 129 * trylock for writing -- returns 1 if successful, 0 if contention
 130 */
 131extern int down_write_trylock(struct rw_semaphore *sem);
 132
 133/*
 134 * release a read lock
 135 */
 136extern void up_read(struct rw_semaphore *sem);
 137
 138/*
 139 * release a write lock
 140 */
 141extern void up_write(struct rw_semaphore *sem);
 142
 143/*
 144 * downgrade write lock to read lock
 145 */
 146extern void downgrade_write(struct rw_semaphore *sem);
 147
 148#ifdef CONFIG_DEBUG_LOCK_ALLOC
 149/*
 150 * nested locking. NOTE: rwsems are not allowed to recurse
 151 * (which occurs if the same task tries to acquire the same
 152 * lock instance multiple times), but multiple locks of the
 153 * same lock class might be taken, if the order of the locks
 154 * is always the same. This ordering rule can be expressed
 155 * to lockdep via the _nested() APIs, but enumerating the
 156 * subclasses that are used. (If the nesting relationship is
 157 * static then another method for expressing nested locking is
 158 * the explicit definition of lock class keys and the use of
 159 * lockdep_set_class() at lock initialization time.
 160 * See Documentation/locking/lockdep-design.txt for more details.)
 161 */
 162extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 163extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 164extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
 165extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
 166
 167# define down_write_nest_lock(sem, nest_lock)                   \
 168do {                                                            \
 169        typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 170        _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
 171} while (0);
 172
 173/*
 174 * Take/release a lock when not the owner will release it.
 175 *
 176 * [ This API should be avoided as much as possible - the
 177 *   proper abstraction for this case is completions. ]
 178 */
 179extern void down_read_non_owner(struct rw_semaphore *sem);
 180extern void up_read_non_owner(struct rw_semaphore *sem);
 181#else
 182# define down_read_nested(sem, subclass)                down_read(sem)
 183# define down_write_nest_lock(sem, nest_lock)   down_write(sem)
 184# define down_write_nested(sem, subclass)       down_write(sem)
 185# define down_write_killable_nested(sem, subclass)      down_write_killable(sem)
 186# define down_read_non_owner(sem)               down_read(sem)
 187# define up_read_non_owner(sem)                 up_read(sem)
 188#endif
 189
 190#endif /* _LINUX_RWSEM_H */
 191