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/* $OpenBSD: kern_rwlock.c,v 1.3 2004/07/21 12:10:20 art Exp $ */
/*
* Copyright (c) 2002, 2003 Artur Grabowski <art@openbsd.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
* THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/rwlock.h>
/* XXX - temporary measure until proc0 is properly aligned */
#define RW_PROC(p) (((unsigned long)p) & ~RWLOCK_MASK)
#ifndef __HAVE_MD_RWLOCK
/*
* Simple cases that should be in MD code and atomic.
*/
void
rw_enter_read(struct rwlock *rwl)
{
while (__predict_false(rwl->rwl_owner & RWLOCK_WRLOCK)) {
/*
* Not the simple case, go to slow path.
*/
rw_enter_wait(rwl, curproc, RW_READ);
}
rwl->rwl_owner += RWLOCK_READ_INCR;
}
void
rw_enter_write(struct rwlock *rwl)
{
struct proc *p = curproc;
while (__predict_false(rwl->rwl_owner != 0)) {
/*
* Not the simple case, go to slow path.
*/
rw_enter_wait(rwl, p, RW_WRITE);
}
rwl->rwl_owner = RW_PROC(p) | RWLOCK_WRLOCK;
}
void
rw_exit_read(struct rwlock *rwl)
{
unsigned long owner = rwl->rwl_owner;
unsigned long decr = (owner & (RWLOCK_WAIT|RWLOCK_WRWANT)) |
RWLOCK_READ_INCR;
rwl->rwl_owner -= decr;
/*
* Potential MP race here. If the owner had WRWANT set we cleared
* it and a reader can sneak in before a writer. Do we care?
*/
if (__predict_false(owner & RWLOCK_WAIT))
rw_exit_waiters(rwl, owner);
}
void
rw_exit_write(struct rwlock *rwl)
{
unsigned long owner = rwl->rwl_owner;
rwl->rwl_owner = 0;
/*
* Potential MP race here. If the owner had WRWANT set we cleared
* it and a reader can sneak in before a writer. Do we care?
*/
if (__predict_false(owner & RWLOCK_WAIT))
rw_exit_waiters(rwl, owner);
}
#endif
void
rw_init(struct rwlock *rwl)
{
rwl->rwl_owner = 0;
}
void
rw_enter_wait(struct rwlock *rwl, struct proc *p, int how)
{
unsigned long need_wait, set_wait;
int wait_prio;
#ifdef DIAGNOSTIC
if (p == NULL)
panic("rw_enter_wait: NULL proc");
#endif
/*
* XXX - this function needs a lot of help to become MP safe.
*/
switch (how) {
case RW_READ:
/*
* Let writers through before obtaining read lock.
*/
need_wait = RWLOCK_WRLOCK | RWLOCK_WRWANT;
set_wait = RWLOCK_WAIT;
wait_prio = PLOCK;
break;
case RW_WRITE:
need_wait = ~0UL;
set_wait = RWLOCK_WAIT | RWLOCK_WRWANT;
wait_prio = PLOCK - 4;
if (RW_PROC(RWLOCK_OWNER(rwl)) == RW_PROC(p)) {
panic("rw_enter: locking against myself");
}
break;
}
while (rwl->rwl_owner & need_wait) {
rwl->rwl_owner |= set_wait;
tsleep(rwl, wait_prio, "rwlock", 0);
}
}
void
rw_exit_waiters(struct rwlock *rwl, unsigned long owner)
{
#ifdef DIAGNOSTIC
if ((owner & RWLOCK_WAIT) == 0)
panic("rw_exit_waiters: no waiter");
#endif
/* We wake up all waiters because we can't know how many they are. */
wakeup(rwl);
}
#ifdef RWLOCK_TEST
#include <sys/kthread.h>
void rwlock_test(void);
void rwlock_testp1(void *);
void rwlock_testp2(void *);
void rwlock_testp3(void *);
struct rwlock rw_test = RWLOCK_INITIALIZER;
void
rwlock_test(void)
{
kthread_create(rwlock_testp1, NULL, NULL, "rw1");
kthread_create(rwlock_testp2, NULL, NULL, "rw2");
kthread_create(rwlock_testp3, NULL, NULL, "rw3");
}
void
rwlock_testp1(void *a)
{
int local;
printf("rwlock test1 start\n");
rw_enter_read(&rw_test);
printf("rwlock test1 obtained\n");
tsleep(&local, PWAIT, "rw1", 4);
rw_exit_read(&rw_test);
printf("rwlock test1 released\n");
tsleep(&local, PWAIT, "rw1/2", 3);
rw_enter_read(&rw_test);
printf("rwlock test1 obtained\n");
rw_exit_read(&rw_test);
printf("rwlock test1 released\n");
kthread_exit(0);
}
void
rwlock_testp2(void *a)
{
int local;
printf("rwlock test2 start\n");
rw_enter_read(&rw_test);
printf("rwlock test2 obtained\n");
tsleep(&local, PWAIT, "rw2", 4);
rw_exit_read(&rw_test);
printf("rwlock test2 released\n");
kthread_exit(0);
}
void
rwlock_testp3(void *a)
{
int local;
printf("rwlock test3 start\n");
tsleep(&local, PWAIT, "rw3", 2);
printf("rwlock test3 exited waiting\n");
rw_enter_write(&rw_test);
printf("rwlock test3 obtained\n");
tsleep(&local, PWAIT, "rw3/2", 4);
rw_exit_write(&rw_test);
printf("rwlock test3 released\n");
kthread_exit(0);
}
#endif
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