[mirror_ubuntu-artful-kernel.git] / include / asm-x86 / rwsem.h

/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
 *
 * Written by David Howells (dhowells@redhat.com).
 *
 * Derived from asm-x86/semaphore.h
 *
 *
 * The MSW of the count is the negated number of active writers and waiting
 * lockers, and the LSW is the total number of active locks
 *
 * The lock count is initialized to 0 (no active and no waiting lockers).
 *
 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
 * uncontended lock. This can be determined because XADD returns the old value.
 * Readers increment by 1 and see a positive value when uncontended, negative
 * if there are writers (and maybe) readers waiting (in which case it goes to
 * sleep).
 *
 * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
 * be extended to 65534 by manually checking the whole MSW rather than relying
 * on the S flag.
 *
 * The value of ACTIVE_BIAS supports up to 65535 active processes.
 *
 * This should be totally fair - if anything is waiting, a process that wants a
 * lock will go to the back of the queue. When the currently active lock is
 * released, if there's a writer at the front of the queue, then that and only
 * that will be woken up; if there's a bunch of consequtive readers at the
 * front, then they'll all be woken up, but no other readers will be.
 */

#ifndef _I386_RWSEM_H
#define _I386_RWSEM_H

#ifndef _LINUX_RWSEM_H
#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
#endif

#ifdef __KERNEL__

#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/lockdep.h>

struct rwsem_waiter;

extern asmregparm struct rw_semaphore *
 rwsem_down_read_failed(struct rw_semaphore *sem);
extern asmregparm struct rw_semaphore *
 rwsem_down_write_failed(struct rw_semaphore *sem);
extern asmregparm struct rw_semaphore *
 rwsem_wake(struct rw_semaphore *);
extern asmregparm struct rw_semaphore *
 rwsem_downgrade_wake(struct rw_semaphore *sem);

/*
 * the semaphore definition
 */
struct rw_semaphore {
	signed long		count;
#define RWSEM_UNLOCKED_VALUE		0x00000000
#define RWSEM_ACTIVE_BIAS		0x00000001
#define RWSEM_ACTIVE_MASK		0x0000ffff
#define RWSEM_WAITING_BIAS		(-0x00010000)
#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
	spinlock_t		wait_lock;
	struct list_head	wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
#endif
};

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


#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
  LIST_HEAD_INIT((name).wait_list) __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)

/*
 * lock for reading
 */
static inline void __down_read(struct rw_semaphore *sem)
{
	__asm__ __volatile__(
		"# beginning down_read\n\t"
LOCK_PREFIX	"  incl      (%%eax)\n\t" /* adds 0x00000001, returns the old value */
		"  jns        1f\n"
		"  call call_rwsem_down_read_failed\n"
		"1:\n\t"
		"# ending down_read\n\t"
		: "+m" (sem->count)
		: "a" (sem)
		: "memory", "cc");
}

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
	__s32 result, tmp;
	__asm__ __volatile__(
		"# beginning __down_read_trylock\n\t"
		"  movl      %0,%1\n\t"
		"1:\n\t"
		"  movl	     %1,%2\n\t"
		"  addl      %3,%2\n\t"
		"  jle	     2f\n\t"
LOCK_PREFIX	"  cmpxchgl  %2,%0\n\t"
		"  jnz	     1b\n\t"
		"2:\n\t"
		"# ending __down_read_trylock\n\t"
		: "+m" (sem->count), "=&a" (result), "=&r" (tmp)
		: "i" (RWSEM_ACTIVE_READ_BIAS)
		: "memory", "cc");
	return result>=0 ? 1 : 0;
}

/*
 * lock for writing
 */
static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
{
	int tmp;

	tmp = RWSEM_ACTIVE_WRITE_BIAS;
	__asm__ __volatile__(
		"# beginning down_write\n\t"
LOCK_PREFIX	"  xadd      %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */
		"  testl     %%edx,%%edx\n\t" /* was the count 0 before? */
		"  jz        1f\n"
		"  call call_rwsem_down_write_failed\n"
		"1:\n"
		"# ending down_write"
		: "+m" (sem->count), "=d" (tmp)
		: "a" (sem), "1" (tmp)
		: "memory", "cc");
}

static inline void __down_write(struct rw_semaphore *sem)
{
	__down_write_nested(sem, 0);
}

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
	signed long ret = cmpxchg(&sem->count,
				  RWSEM_UNLOCKED_VALUE, 
				  RWSEM_ACTIVE_WRITE_BIAS);
	if (ret == RWSEM_UNLOCKED_VALUE)
		return 1;
	return 0;
}

/*
 * unlock after reading
 */
static inline void __up_read(struct rw_semaphore *sem)
{
	__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
	__asm__ __volatile__(
		"# beginning __up_read\n\t"
LOCK_PREFIX	"  xadd      %%edx,(%%eax)\n\t" /* subtracts 1, returns the old value */
		"  jns        1f\n\t"
		"  call call_rwsem_wake\n"
		"1:\n"
		"# ending __up_read\n"
		: "+m" (sem->count), "=d" (tmp)
		: "a" (sem), "1" (tmp)
		: "memory", "cc");
}

/*
 * unlock after writing
 */
static inline void __up_write(struct rw_semaphore *sem)
{
	__asm__ __volatile__(
		"# beginning __up_write\n\t"
		"  movl      %2,%%edx\n\t"
LOCK_PREFIX	"  xaddl     %%edx,(%%eax)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
		"  jz       1f\n"
		"  call call_rwsem_wake\n"
		"1:\n\t"
		"# ending __up_write\n"
		: "+m" (sem->count)
		: "a" (sem), "i" (-RWSEM_ACTIVE_WRITE_BIAS)
		: "memory", "cc", "edx");
}

/*
 * downgrade write lock to read lock
 */
static inline void __downgrade_write(struct rw_semaphore *sem)
{
	__asm__ __volatile__(
		"# beginning __downgrade_write\n\t"
LOCK_PREFIX	"  addl      %2,(%%eax)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
		"  jns       1f\n\t"
		"  call call_rwsem_downgrade_wake\n"
		"1:\n\t"
		"# ending __downgrade_write\n"
		: "+m" (sem->count)
		: "a" (sem), "i" (-RWSEM_WAITING_BIAS)
		: "memory", "cc");
}

/*
 * implement atomic add functionality
 */
static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
{
	__asm__ __volatile__(
LOCK_PREFIX	"addl %1,%0"
		: "+m" (sem->count)
		: "ir" (delta));
}

/*
 * implement exchange and add functionality
 */
static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
{
	int tmp = delta;

	__asm__ __volatile__(
LOCK_PREFIX	"xadd %0,%1"
		: "+r" (tmp), "+m" (sem->count)
		: : "memory");

	return tmp+delta;
}

static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
	return (sem->count != 0);
}

#endif /* __KERNEL__ */
#endif /* _I386_RWSEM_H */
Commit	Line	Data
1da177e4 LT	1	/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
	2	*
	3	* Written by David Howells (dhowells@redhat.com).
	4	*
99122a3f	5	* Derived from asm-x86/semaphore.h
1da177e4 LT	6	*
	7	*
	8	* The MSW of the count is the negated number of active writers and waiting
	9	* lockers, and the LSW is the total number of active locks
	10	*
	11	* The lock count is initialized to 0 (no active and no waiting lockers).
	12	*
	13	* When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
	14	* uncontended lock. This can be determined because XADD returns the old value.
	15	* Readers increment by 1 and see a positive value when uncontended, negative
	16	* if there are writers (and maybe) readers waiting (in which case it goes to
	17	* sleep).
	18	*
	19	* The value of WAITING_BIAS supports up to 32766 waiting processes. This can
	20	* be extended to 65534 by manually checking the whole MSW rather than relying
	21	* on the S flag.
	22	*
	23	* The value of ACTIVE_BIAS supports up to 65535 active processes.
	24	*
	25	* This should be totally fair - if anything is waiting, a process that wants a
	26	* lock will go to the back of the queue. When the currently active lock is
	27	* released, if there's a writer at the front of the queue, then that and only
	28	* that will be woken up; if there's a bunch of consequtive readers at the
	29	* front, then they'll all be woken up, but no other readers will be.
	30	*/
	31
	32	#ifndef _I386_RWSEM_H
	33	#define _I386_RWSEM_H
	34
	35	#ifndef _LINUX_RWSEM_H
	36	#error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
	37	#endif
	38
	39	#ifdef __KERNEL__
	40
	41	#include <linux/list.h>
	42	#include <linux/spinlock.h>
4ea2176d	43	#include <linux/lockdep.h>
1da177e4 LT	44
	45	struct rwsem_waiter;
	46
d50efc6c IM	47	extern asmregparm struct rw_semaphore *
	48	rwsem_down_read_failed(struct rw_semaphore *sem);
	49	extern asmregparm struct rw_semaphore *
	50	rwsem_down_write_failed(struct rw_semaphore *sem);
	51	extern asmregparm struct rw_semaphore *
	52	rwsem_wake(struct rw_semaphore *);
	53	extern asmregparm struct rw_semaphore *
	54	rwsem_downgrade_wake(struct rw_semaphore *sem);
1da177e4 LT	55
	56	/*
	57	* the semaphore definition
	58	*/
	59	struct rw_semaphore {
	60	signed long count;
	61	#define RWSEM_UNLOCKED_VALUE 0x00000000
	62	#define RWSEM_ACTIVE_BIAS 0x00000001
	63	#define RWSEM_ACTIVE_MASK 0x0000ffff
	64	#define RWSEM_WAITING_BIAS (-0x00010000)
	65	#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
	66	#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
	67	spinlock_t wait_lock;
	68	struct list_head wait_list;
4ea2176d IM	69	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	70	struct lockdep_map dep_map;
	71	#endif
1da177e4 LT	72	};
1da177e4 LT	73
4ea2176d IM	74	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	75	# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
	76	#else
	77	# define __RWSEM_DEP_MAP_INIT(lockname)
	78	#endif
	79
	80
1da177e4	81	#define __RWSEM_INITIALIZER(name) \
6cfd76a2 PZ	82	{ RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED((name).wait_lock), \
6cfd76a2 PZ	83	LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }
1da177e4 LT	84
	85	#define DECLARE_RWSEM(name) \
	86	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
	87
4ea2176d IM	88	extern void __init_rwsem(struct rw_semaphore sem, const char name,
	89	struct lock_class_key *key);
	90
	91	#define init_rwsem(sem) \
	92	do { \
	93	static struct lock_class_key __key; \
	94	\
	95	__init_rwsem((sem), #sem, &__key); \
	96	} while (0)
1da177e4 LT	97
	98	/*
	99	* lock for reading
	100	*/
	101	static inline void __down_read(struct rw_semaphore *sem)
	102	{
	103	__asm__ __volatile__(
	104	"# beginning down_read\n\t"
	105	LOCK_PREFIX " incl (%%eax)\n\t" /* adds 0x00000001, returns the old value */
add659bf AK	106	" jns 1f\n"
add659bf AK	107	" call call_rwsem_down_read_failed\n"
1da177e4	108	"1:\n\t"
1da177e4	109	"# ending down_read\n\t"
b862f3b0 LT	110	: "+m" (sem->count)
b862f3b0 LT	111	: "a" (sem)
1da177e4 LT	112	: "memory", "cc");
	113	}
	114
	115	/*
	116	* trylock for reading -- returns 1 if successful, 0 if contention
	117	*/
	118	static inline int __down_read_trylock(struct rw_semaphore *sem)
	119	{
	120	__s32 result, tmp;
	121	__asm__ __volatile__(
	122	"# beginning __down_read_trylock\n\t"
	123	" movl %0,%1\n\t"
	124	"1:\n\t"
	125	" movl %1,%2\n\t"
	126	" addl %3,%2\n\t"
	127	" jle 2f\n\t"
	128	LOCK_PREFIX " cmpxchgl %2,%0\n\t"
	129	" jnz 1b\n\t"
	130	"2:\n\t"
	131	"# ending __down_read_trylock\n\t"
b862f3b0 LT	132	: "+m" (sem->count), "=&a" (result), "=&r" (tmp)
b862f3b0 LT	133	: "i" (RWSEM_ACTIVE_READ_BIAS)
1da177e4 LT	134	: "memory", "cc");
	135	return result>=0 ? 1 : 0;
	136	}
	137
	138	/*
	139	* lock for writing
	140	*/
4ea2176d	141	static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
1da177e4 LT	142	{
	143	int tmp;
	144
	145	tmp = RWSEM_ACTIVE_WRITE_BIAS;
	146	__asm__ __volatile__(
	147	"# beginning down_write\n\t"
	148	LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */
	149	" testl %%edx,%%edx\n\t" /* was the count 0 before? */
add659bf AK	150	" jz 1f\n"
	151	" call call_rwsem_down_write_failed\n"
	152	"1:\n"
1da177e4	153	"# ending down_write"
b862f3b0 LT	154	: "+m" (sem->count), "=d" (tmp)
b862f3b0 LT	155	: "a" (sem), "1" (tmp)
1da177e4 LT	156	: "memory", "cc");
	157	}
	158
4ea2176d IM	159	static inline void __down_write(struct rw_semaphore *sem)
	160	{
	161	__down_write_nested(sem, 0);
	162	}
	163
1da177e4 LT	164	/*
	165	* trylock for writing -- returns 1 if successful, 0 if contention
	166	*/
	167	static inline int __down_write_trylock(struct rw_semaphore *sem)
	168	{
	169	signed long ret = cmpxchg(&sem->count,
	170	RWSEM_UNLOCKED_VALUE,
	171	RWSEM_ACTIVE_WRITE_BIAS);
	172	if (ret == RWSEM_UNLOCKED_VALUE)
	173	return 1;
	174	return 0;
	175	}
	176
	177	/*
	178	* unlock after reading
	179	*/
	180	static inline void __up_read(struct rw_semaphore *sem)
	181	{
	182	__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
	183	__asm__ __volatile__(
	184	"# beginning __up_read\n\t"
	185	LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtracts 1, returns the old value */
add659bf AK	186	" jns 1f\n\t"
	187	" call call_rwsem_wake\n"
	188	"1:\n"
1da177e4	189	"# ending __up_read\n"
b862f3b0 LT	190	: "+m" (sem->count), "=d" (tmp)
b862f3b0 LT	191	: "a" (sem), "1" (tmp)
1da177e4 LT	192	: "memory", "cc");
	193	}
	194
	195	/*
	196	* unlock after writing
	197	*/
	198	static inline void __up_write(struct rw_semaphore *sem)
	199	{
	200	__asm__ __volatile__(
	201	"# beginning __up_write\n\t"
	202	" movl %2,%%edx\n\t"
	203	LOCK_PREFIX " xaddl %%edx,(%%eax)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
add659bf AK	204	" jz 1f\n"
add659bf AK	205	" call call_rwsem_wake\n"
1da177e4	206	"1:\n\t"
1da177e4	207	"# ending __up_write\n"
b862f3b0 LT	208	: "+m" (sem->count)
b862f3b0 LT	209	: "a" (sem), "i" (-RWSEM_ACTIVE_WRITE_BIAS)
1da177e4 LT	210	: "memory", "cc", "edx");
	211	}
	212
	213	/*
	214	* downgrade write lock to read lock
	215	*/
	216	static inline void __downgrade_write(struct rw_semaphore *sem)
	217	{
	218	__asm__ __volatile__(
	219	"# beginning __downgrade_write\n\t"
	220	LOCK_PREFIX " addl %2,(%%eax)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
add659bf AK	221	" jns 1f\n\t"
add659bf AK	222	" call call_rwsem_downgrade_wake\n"
1da177e4	223	"1:\n\t"
1da177e4	224	"# ending __downgrade_write\n"
b862f3b0 LT	225	: "+m" (sem->count)
b862f3b0 LT	226	: "a" (sem), "i" (-RWSEM_WAITING_BIAS)
1da177e4 LT	227	: "memory", "cc");
	228	}
	229
	230	/*
	231	* implement atomic add functionality
	232	*/
	233	static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
	234	{
	235	__asm__ __volatile__(
	236	LOCK_PREFIX "addl %1,%0"
b862f3b0 LT	237	: "+m" (sem->count)
b862f3b0 LT	238	: "ir" (delta));
1da177e4 LT	239	}
	240
	241	/*
	242	* implement exchange and add functionality
	243	*/
	244	static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
	245	{
	246	int tmp = delta;
	247
	248	__asm__ __volatile__(
b862f3b0 LT	249	LOCK_PREFIX "xadd %0,%1"
	250	: "+r" (tmp), "+m" (sem->count)
	251	: : "memory");
1da177e4 LT	252
	253	return tmp+delta;
	254	}
	255
eb92f4ef RVR	256	static inline int rwsem_is_locked(struct rw_semaphore *sem)
	257	{
	258	return (sem->count != 0);
	259	}
	260
1da177e4 LT	261	#endif /* __KERNEL__ */
1da177e4 LT	262	#endif /* _I386_RWSEM_H */