[deliverable/linux.git] / include / linux / rwsem.h

/* rwsem.h: R/W semaphores, public interface
 *
 * Written by David Howells (dhowells@redhat.com).
 * 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>
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
#include <linux/osq_lock.h>
#endif

struct rw_semaphore;

#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
#include <linux/rwsem-spinlock.h> /* use a generic implementation */
#else
/* All arch specific implementations share the same struct */
struct rw_semaphore {
	long count;
	struct list_head wait_list;
	raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
	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;
#endif
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map	dep_map;
#endif
};

extern struct rw_semaphore *rwsem_down_read_failed(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 sem->count != 0;
}

#endif

/* Common initializer macros and functions */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif

#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
#else
#define __RWSEM_OPT_INIT(lockname)
#endif

#define __RWSEM_INITIALIZER(name)				\
	{ .count = RWSEM_UNLOCKED_VALUE,			\
	  .wait_list = LIST_HEAD_INIT((name).wait_list),	\
	  .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock)	\
	  __RWSEM_OPT_INIT(name)				\
	  __RWSEM_DEP_MAP_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);

/*
 * 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);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
 * 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 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);
#else
# 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_read_non_owner(sem)		down_read(sem)
# define up_read_non_owner(sem)			up_read(sem)
#endif

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