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linux/include/asm-s390/rwsem.h
Rik Van Riel eb92f4ef32 [PATCH] add sem_is_read/write_locked() 
Add sem_is_read/write_locked functions to the read/write semaphores, along the
same lines of the *_is_locked spinlock functions.  The swap token tuning patch
uses sem_is_read_locked; sem_is_write_locked is added for completeness.

Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2005-10-29 21:40:35 -07:00

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#ifndef _S390_RWSEM_H
#define _S390_RWSEM_H
/*
* include/asm-s390/rwsem.h
*
* S390 version
* Copyright (C) 2002 IBM Deutschland Entwicklung GmbH, IBM Corporation
* Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
*
* Based on asm-alpha/semaphore.h and asm-i386/rwsem.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 _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 *rwsem_down_read_failed(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_write(struct rw_semaphore *);
/*
* the semaphore definition
*/
struct rw_semaphore {
signed long count;
spinlock_t wait_lock;
struct list_head wait_list;
};
#ifndef __s390x__
#define RWSEM_UNLOCKED_VALUE 0x00000000
#define RWSEM_ACTIVE_BIAS 0x00000001
#define RWSEM_ACTIVE_MASK 0x0000ffff
#define RWSEM_WAITING_BIAS (-0x00010000)
#else /* __s390x__ */
#define RWSEM_UNLOCKED_VALUE 0x0000000000000000L
#define RWSEM_ACTIVE_BIAS 0x0000000000000001L
#define RWSEM_ACTIVE_MASK 0x00000000ffffffffL
#define RWSEM_WAITING_BIAS (-0x0000000100000000L)
#endif /* __s390x__ */
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
/*
* initialisation
*/
#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)
{
signed long old, new;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" ahi %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" aghi %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count),
"i" (RWSEM_ACTIVE_READ_BIAS) : "cc", "memory" );
if (old < 0)
rwsem_down_read_failed(sem);
}
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
static inline int __down_read_trylock(struct rw_semaphore *sem)
{
signed long old, new;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: ltr %1,%0\n"
" jm 1f\n"
" ahi %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b\n"
"1:"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: ltgr %1,%0\n"
" jm 1f\n"
" aghi %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b\n"
"1:"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count),
"i" (RWSEM_ACTIVE_READ_BIAS) : "cc", "memory" );
return old >= 0 ? 1 : 0;
}
/*
* lock for writing
*/
static inline void __down_write(struct rw_semaphore *sem)
{
signed long old, new, tmp;
tmp = RWSEM_ACTIVE_WRITE_BIAS;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" a %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" ag %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count), "m" (tmp)
: "cc", "memory" );
if (old != 0)
rwsem_down_write_failed(sem);
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
signed long old;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%2)\n"
"0: ltr %0,%0\n"
" jnz 1f\n"
" cs %0,%4,0(%2)\n"
" jl 0b\n"
#else /* __s390x__ */
" lg %0,0(%2)\n"
"0: ltgr %0,%0\n"
" jnz 1f\n"
" csg %0,%4,0(%2)\n"
" jl 0b\n"
#endif /* __s390x__ */
"1:"
: "=&d" (old), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count),
"d" (RWSEM_ACTIVE_WRITE_BIAS) : "cc", "memory" );
return (old == RWSEM_UNLOCKED_VALUE) ? 1 : 0;
}
/*
* unlock after reading
*/
static inline void __up_read(struct rw_semaphore *sem)
{
signed long old, new;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" ahi %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" aghi %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count),
"i" (-RWSEM_ACTIVE_READ_BIAS)
: "cc", "memory" );
if (new < 0)
if ((new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* unlock after writing
*/
static inline void __up_write(struct rw_semaphore *sem)
{
signed long old, new, tmp;
tmp = -RWSEM_ACTIVE_WRITE_BIAS;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" a %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" ag %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count), "m" (tmp)
: "cc", "memory" );
if (new < 0)
if ((new & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}
/*
* downgrade write lock to read lock
*/
static inline void __downgrade_write(struct rw_semaphore *sem)
{
signed long old, new, tmp;
tmp = -RWSEM_WAITING_BIAS;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" a %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" ag %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count), "m" (tmp)
: "cc", "memory" );
if (new > 1)
rwsem_downgrade_wake(sem);
}
/*
* implement atomic add functionality
*/
static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
{
signed long old, new;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" ar %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" agr %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count), "d" (delta)
: "cc", "memory" );
}
/*
* implement exchange and add functionality
*/
static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
{
signed long old, new;
__asm__ __volatile__(
#ifndef __s390x__
" l %0,0(%3)\n"
"0: lr %1,%0\n"
" ar %1,%5\n"
" cs %0,%1,0(%3)\n"
" jl 0b"
#else /* __s390x__ */
" lg %0,0(%3)\n"
"0: lgr %1,%0\n"
" agr %1,%5\n"
" csg %0,%1,0(%3)\n"
" jl 0b"
#endif /* __s390x__ */
: "=&d" (old), "=&d" (new), "=m" (sem->count)
: "a" (&sem->count), "m" (sem->count), "d" (delta)
: "cc", "memory" );
return new;
}
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
return (sem->count != 0);
}
#endif /* __KERNEL__ */
#endif /* _S390_RWSEM_H */
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