[linux-2.6-block.git] / include / asm-i386 / rwsem.h

/* rwsem.h: R/W semaphores implemented using XADD/CMPXCHG for i486+
 *
 * Written by David Howells (dhowells@redhat.com).
 *
 * Derived from asm-i386/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>

struct rwsem_waiter;

extern struct rw_semaphore *FASTCALL(rwsem_down_read_failed(struct rw_semaphore *sem));
extern struct rw_semaphore *FASTCALL(rwsem_down_write_failed(struct rw_semaphore *sem));
extern struct rw_semaphore *FASTCALL(rwsem_wake(struct rw_semaphore *));
extern struct rw_semaphore *FASTCALL(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;
};

#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
	}

#define DECLARE_RWSEM(name) \
	struct rw_semaphore name = __RWSEM_INITIALIZER(name)

static inline void init_rwsem(struct rw_semaphore *sem)
{
	sem->count = RWSEM_UNLOCKED_VALUE;
	spin_lock_init(&sem->wait_lock);
	INIT_LIST_HEAD(&sem->wait_list);
}

/*
 * 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 */
		"  js        2f\n\t" /* jump if we weren't granted the lock */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  pushl     %%ecx\n\t"
		"  pushl     %%edx\n\t"
		"  call      rwsem_down_read_failed\n\t"
		"  popl      %%edx\n\t"
		"  popl      %%ecx\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending down_read\n\t"
		: "=m"(sem->count)
		: "a"(sem), "m"(sem->count)
		: "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(struct rw_semaphore *sem)
{
	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? */
		"  jnz       2f\n\t" /* jump if we weren't granted the lock */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  pushl     %%ecx\n\t"
		"  call      rwsem_down_write_failed\n\t"
		"  popl      %%ecx\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending down_write"
		: "=m"(sem->count), "=d"(tmp)
		: "a"(sem), "1"(tmp), "m"(sem->count)
		: "memory", "cc");
}

/*
 * 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 */
		"  js        2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  decw      %%dx\n\t" /* do nothing if still outstanding active readers */
		"  jnz       1b\n\t"
		"  pushl     %%ecx\n\t"
		"  call      rwsem_wake\n\t"
		"  popl      %%ecx\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __up_read\n"
		: "=m"(sem->count), "=d"(tmp)
		: "a"(sem), "1"(tmp), "m"(sem->count)
		: "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 */
		"  jnz       2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  decw      %%dx\n\t" /* did the active count reduce to 0? */
		"  jnz       1b\n\t" /* jump back if not */
		"  pushl     %%ecx\n\t"
		"  call      rwsem_wake\n\t"
		"  popl      %%ecx\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __up_write\n"
		: "=m"(sem->count)
		: "a"(sem), "i"(-RWSEM_ACTIVE_WRITE_BIAS), "m"(sem->count)
		: "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 */
		"  js        2f\n\t" /* jump if the lock is being waited upon */
		"1:\n\t"
		LOCK_SECTION_START("")
		"2:\n\t"
		"  pushl     %%ecx\n\t"
		"  pushl     %%edx\n\t"
		"  call      rwsem_downgrade_wake\n\t"
		"  popl      %%edx\n\t"
		"  popl      %%ecx\n\t"
		"  jmp       1b\n"
		LOCK_SECTION_END
		"# ending __downgrade_write\n"
		: "=m"(sem->count)
		: "a"(sem), "i"(-RWSEM_WAITING_BIAS), "m"(sem->count)
		: "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), "m"(sem->count));
}

/*
 * 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,(%2)"
		: "+r"(tmp), "=m"(sem->count)
		: "r"(sem), "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	*
	5	* Derived from asm-i386/semaphore.h
	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>
	43
	44	struct rwsem_waiter;
	45
	46	extern struct rw_semaphore FASTCALL(rwsem_down_read_failed(struct rw_semaphore sem));
	47	extern struct rw_semaphore FASTCALL(rwsem_down_write_failed(struct rw_semaphore sem));
	48	extern struct rw_semaphore FASTCALL(rwsem_wake(struct rw_semaphore ));
	49	extern struct rw_semaphore FASTCALL(rwsem_downgrade_wake(struct rw_semaphore sem));
	50
	51	/*
	52	* the semaphore definition
	53	*/
	54	struct rw_semaphore {
	55	signed long count;
	56	#define RWSEM_UNLOCKED_VALUE 0x00000000
	57	#define RWSEM_ACTIVE_BIAS 0x00000001
	58	#define RWSEM_ACTIVE_MASK 0x0000ffff
	59	#define RWSEM_WAITING_BIAS (-0x00010000)
	60	#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
	61	#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
	62	spinlock_t wait_lock;
	63	struct list_head wait_list;
1da177e4 LT	64	};
1da177e4 LT	65
1da177e4 LT	66	#define __RWSEM_INITIALIZER(name) \
1da177e4 LT	67	{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) \
c4e05116	68	}
1da177e4 LT	69
	70	#define DECLARE_RWSEM(name) \
	71	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
	72
	73	static inline void init_rwsem(struct rw_semaphore *sem)
	74	{
	75	sem->count = RWSEM_UNLOCKED_VALUE;
	76	spin_lock_init(&sem->wait_lock);
	77	INIT_LIST_HEAD(&sem->wait_list);
1da177e4 LT	78	}
	79
	80	/*
	81	* lock for reading
	82	*/
	83	static inline void __down_read(struct rw_semaphore *sem)
	84	{
	85	__asm__ __volatile__(
	86	"# beginning down_read\n\t"
	87	LOCK_PREFIX " incl (%%eax)\n\t" /* adds 0x00000001, returns the old value */
	88	" js 2f\n\t" /* jump if we weren't granted the lock */
	89	"1:\n\t"
	90	LOCK_SECTION_START("")
	91	"2:\n\t"
	92	" pushl %%ecx\n\t"
	93	" pushl %%edx\n\t"
	94	" call rwsem_down_read_failed\n\t"
	95	" popl %%edx\n\t"
	96	" popl %%ecx\n\t"
	97	" jmp 1b\n"
	98	LOCK_SECTION_END
	99	"# ending down_read\n\t"
	100	: "=m"(sem->count)
	101	: "a"(sem), "m"(sem->count)
	102	: "memory", "cc");
	103	}
	104
	105	/*
	106	* trylock for reading -- returns 1 if successful, 0 if contention
	107	*/
	108	static inline int __down_read_trylock(struct rw_semaphore *sem)
	109	{
	110	__s32 result, tmp;
	111	__asm__ __volatile__(
	112	"# beginning __down_read_trylock\n\t"
	113	" movl %0,%1\n\t"
	114	"1:\n\t"
	115	" movl %1,%2\n\t"
	116	" addl %3,%2\n\t"
	117	" jle 2f\n\t"
	118	LOCK_PREFIX " cmpxchgl %2,%0\n\t"
	119	" jnz 1b\n\t"
	120	"2:\n\t"
	121	"# ending __down_read_trylock\n\t"
	122	: "+m"(sem->count), "=&a"(result), "=&r"(tmp)
	123	: "i"(RWSEM_ACTIVE_READ_BIAS)
	124	: "memory", "cc");
	125	return result>=0 ? 1 : 0;
	126	}
	127
	128	/*
	129	* lock for writing
	130	*/
	131	static inline void __down_write(struct rw_semaphore *sem)
	132	{
	133	int tmp;
	134
	135	tmp = RWSEM_ACTIVE_WRITE_BIAS;
	136	__asm__ __volatile__(
	137	"# beginning down_write\n\t"
	138	LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtract 0x0000ffff, returns the old value */
	139	" testl %%edx,%%edx\n\t" /* was the count 0 before? */
	140	" jnz 2f\n\t" /* jump if we weren't granted the lock */
	141	"1:\n\t"
142	LOCK_SECTION_START("")
143	"2:\n\t"
144	" pushl %%ecx\n\t"
145	" call rwsem_down_write_failed\n\t"
146	" popl %%ecx\n\t"
147	" jmp 1b\n"
148	LOCK_SECTION_END
149	"# ending down_write"
150	: "=m"(sem->count), "=d"(tmp)
151	: "a"(sem), "1"(tmp), "m"(sem->count)
152	: "memory", "cc");
153	}
154
155	/*
156	* trylock for writing -- returns 1 if successful, 0 if contention
157	*/
158	static inline int __down_write_trylock(struct rw_semaphore *sem)
159	{
160	signed long ret = cmpxchg(&sem->count,
161	RWSEM_UNLOCKED_VALUE,
162	RWSEM_ACTIVE_WRITE_BIAS);
163	if (ret == RWSEM_UNLOCKED_VALUE)
164	return 1;
165	return 0;
166	}
167
168	/*
169	* unlock after reading
170	*/
171	static inline void __up_read(struct rw_semaphore *sem)
172	{
173	__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
174	__asm__ __volatile__(
175	"# beginning __up_read\n\t"
176	LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtracts 1, returns the old value */
177	" js 2f\n\t" /* jump if the lock is being waited upon */
178	"1:\n\t"
179	LOCK_SECTION_START("")
180	"2:\n\t"
181	" decw %%dx\n\t" /* do nothing if still outstanding active readers */
182	" jnz 1b\n\t"
183	" pushl %%ecx\n\t"
184	" call rwsem_wake\n\t"
185	" popl %%ecx\n\t"
186	" jmp 1b\n"
187	LOCK_SECTION_END
188	"# ending __up_read\n"
189	: "=m"(sem->count), "=d"(tmp)
190	: "a"(sem), "1"(tmp), "m"(sem->count)
191	: "memory", "cc");
192	}
193
194	/*
195	* unlock after writing
196	*/
197	static inline void __up_write(struct rw_semaphore *sem)
198	{
199	__asm__ __volatile__(
200	"# beginning __up_write\n\t"
201	" movl %2,%%edx\n\t"
202	LOCK_PREFIX " xaddl %%edx,(%%eax)\n\t" /* tries to transition 0xffff0001 -> 0x00000000 */
203	" jnz 2f\n\t" /* jump if the lock is being waited upon */
204	"1:\n\t"
205	LOCK_SECTION_START("")
206	"2:\n\t"
207	" decw %%dx\n\t" /* did the active count reduce to 0? */
208	" jnz 1b\n\t" /* jump back if not */
209	" pushl %%ecx\n\t"
210	" call rwsem_wake\n\t"
211	" popl %%ecx\n\t"
212	" jmp 1b\n"
213	LOCK_SECTION_END
214	"# ending __up_write\n"
215	: "=m"(sem->count)
216	: "a"(sem), "i"(-RWSEM_ACTIVE_WRITE_BIAS), "m"(sem->count)
217	: "memory", "cc", "edx");
218	}
219
220	/*
221	* downgrade write lock to read lock
222	*/
223	static inline void __downgrade_write(struct rw_semaphore *sem)
224	{
225	__asm__ __volatile__(
226	"# beginning __downgrade_write\n\t"
227	LOCK_PREFIX " addl %2,(%%eax)\n\t" /* transitions 0xZZZZ0001 -> 0xYYYY0001 */
228	" js 2f\n\t" /* jump if the lock is being waited upon */
229	"1:\n\t"
230	LOCK_SECTION_START("")
231	"2:\n\t"
232	" pushl %%ecx\n\t"
233	" pushl %%edx\n\t"
234	" call rwsem_downgrade_wake\n\t"
235	" popl %%edx\n\t"
236	" popl %%ecx\n\t"
237	" jmp 1b\n"
238	LOCK_SECTION_END
239	"# ending __downgrade_write\n"
240	: "=m"(sem->count)
241	: "a"(sem), "i"(-RWSEM_WAITING_BIAS), "m"(sem->count)
242	: "memory", "cc");
243	}
244
245	/*
246	* implement atomic add functionality
247	*/
248	static inline void rwsem_atomic_add(int delta, struct rw_semaphore *sem)
249	{
250	__asm__ __volatile__(
251	LOCK_PREFIX "addl %1,%0"
252	: "=m"(sem->count)
253	: "ir"(delta), "m"(sem->count));
254	}
255
256	/*
257	* implement exchange and add functionality
258	*/
259	static inline int rwsem_atomic_update(int delta, struct rw_semaphore *sem)
260	{
261	int tmp = delta;
262
263	__asm__ __volatile__(
264	LOCK_PREFIX "xadd %0,(%2)"
265	: "+r"(tmp), "=m"(sem->count)
266	: "r"(sem), "m"(sem->count)
267	: "memory");
268
269	return tmp+delta;
270	}
271
eb92f4ef RVR	272	static inline int rwsem_is_locked(struct rw_semaphore *sem)
	273	{
	274	return (sem->count != 0);
	275	}
	276
1da177e4 LT	277	#endif /* __KERNEL__ */
1da177e4 LT	278	#endif /* _I386_RWSEM_H */