blob: ab93b6eae6968e4eef4b29b2f1f134c4b21fe5d1 [file] [log] [blame]
/* SPDX-License-Identifier: GPL-2.0 */
/* rwsem.h: R/W semaphores, public interface
* Written by David Howells (
* Derived from asm-i386/semaphore.h
#ifndef _LINUX_RWSEM_H
#define _LINUX_RWSEM_H
#include <linux/linkage.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/atomic.h>
#include <linux/err.h>
#include <linux/osq_lock.h>
struct rw_semaphore;
#include <linux/rwsem-spinlock.h> /* use a generic implementation */
/* All arch specific implementations share the same struct */
struct rw_semaphore {
atomic_long_t count;
struct list_head wait_list;
raw_spinlock_t wait_lock;
struct optimistic_spin_queue osq; /* spinner MCS lock */
* Write owner. Used as a speculative check to see
* if the owner is running on the cpu.
struct task_struct *owner;
struct lockdep_map dep_map;
* Setting bit 0 of the owner field with other non-zero bits will indicate
* that the rwsem is writer-owned with an unknown owner.
#define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-1L)
extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
/* Include the arch specific part */
#include <asm/rwsem.h>
/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
return atomic_long_read(&sem->count) != 0;
/* Common initializer macros and functions */
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
# define __RWSEM_DEP_MAP_INIT(lockname)
#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
#define __RWSEM_OPT_INIT(lockname)
#define __RWSEM_INITIALIZER(name) \
{ __RWSEM_INIT_COUNT(name), \
.wait_list = LIST_HEAD_INIT((name).wait_list), \
.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
__RWSEM_OPT_INIT(name) \
#define DECLARE_RWSEM(name) \
struct rw_semaphore name = __RWSEM_INITIALIZER(name)
extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
struct lock_class_key *key);
#define init_rwsem(sem) \
do { \
static struct lock_class_key __key; \
__init_rwsem((sem), #sem, &__key); \
} while (0)
* This is the same regardless of which rwsem implementation that is being used.
* It is just a heuristic meant to be called by somebody alreadying holding the
* rwsem to see if somebody from an incompatible type is wanting access to the
* lock.
static inline int rwsem_is_contended(struct rw_semaphore *sem)
return !list_empty(&sem->wait_list);
* lock for reading
extern void down_read(struct rw_semaphore *sem);
extern int __must_check down_read_killable(struct rw_semaphore *sem);
* trylock for reading -- returns 1 if successful, 0 if contention
extern int down_read_trylock(struct rw_semaphore *sem);
* lock for writing
extern void down_write(struct rw_semaphore *sem);
extern int __must_check down_write_killable(struct rw_semaphore *sem);
* trylock for writing -- returns 1 if successful, 0 if contention
extern int down_write_trylock(struct rw_semaphore *sem);
* release a read lock
extern void up_read(struct rw_semaphore *sem);
* release a write lock
extern void up_write(struct rw_semaphore *sem);
* downgrade write lock to read lock
extern void downgrade_write(struct rw_semaphore *sem);
* nested locking. NOTE: rwsems are not allowed to recurse
* (which occurs if the same task tries to acquire the same
* lock instance multiple times), but multiple locks of the
* same lock class might be taken, if the order of the locks
* is always the same. This ordering rule can be expressed
* to lockdep via the _nested() APIs, but enumerating the
* subclasses that are used. (If the nesting relationship is
* static then another method for expressing nested locking is
* the explicit definition of lock class keys and the use of
* lockdep_set_class() at lock initialization time.
* See Documentation/locking/lockdep-design.txt for more details.)
extern void down_read_nested(struct rw_semaphore *sem, int subclass);
extern void down_write_nested(struct rw_semaphore *sem, int subclass);
extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
# define down_write_nest_lock(sem, nest_lock) \
do { \
typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
_down_write_nest_lock(sem, &(nest_lock)->dep_map); \
} while (0);
* Take/release a lock when not the owner will release it.
* [ This API should be avoided as much as possible - the
* proper abstraction for this case is completions. ]
extern void down_read_non_owner(struct rw_semaphore *sem);
extern void up_read_non_owner(struct rw_semaphore *sem);
# define down_read_nested(sem, subclass) down_read(sem)
# define down_write_nest_lock(sem, nest_lock) down_write(sem)
# define down_write_nested(sem, subclass) down_write(sem)
# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
# define down_read_non_owner(sem) down_read(sem)
# define up_read_non_owner(sem) up_read(sem)
#endif /* _LINUX_RWSEM_H */