freebsd-dev/sys/kern/kern_sx.c
Julian Elischer b40ce4165d KSE Milestone 2
Note ALL MODULES MUST BE RECOMPILED
make the kernel aware that there are smaller units of scheduling than the
process. (but only allow one thread per process at this time).
This is functionally equivalent to teh previousl -current except
that there is a thread associated with each process.

Sorry john! (your next MFC will be a doosie!)

Reviewed by: peter@freebsd.org, dillon@freebsd.org

X-MFC after:    ha ha ha ha
2001-09-12 08:38:13 +00:00

293 lines
7.5 KiB
C

/*
* Copyright (C) 2001 Jason Evans <jasone@freebsd.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(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
*
* $FreeBSD$
*/
/*
* Shared/exclusive locks. This implementation assures deterministic lock
* granting behavior, so that slocks and xlocks are interleaved.
*
* Priority propagation will not generally raise the priority of lock holders,
* so should not be relied upon in combination with sx locks.
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/ktr.h>
#include <sys/condvar.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sx.h>
struct lock_class lock_class_sx = {
"sx",
LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE
};
void
sx_init(struct sx *sx, const char *description)
{
struct lock_object *lock;
bzero(sx, sizeof(*sx));
lock = &sx->sx_object;
lock->lo_class = &lock_class_sx;
lock->lo_name = description;
lock->lo_flags = LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE |
LO_UPGRADABLE;
mtx_init(&sx->sx_lock, "sx backing lock",
MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
sx->sx_cnt = 0;
cv_init(&sx->sx_shrd_cv, description);
sx->sx_shrd_wcnt = 0;
cv_init(&sx->sx_excl_cv, description);
sx->sx_excl_wcnt = 0;
sx->sx_xholder = NULL;
LOCK_LOG_INIT(lock, 0);
WITNESS_INIT(lock);
}
void
sx_destroy(struct sx *sx)
{
LOCK_LOG_DESTROY(&sx->sx_object, 0);
KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt ==
0), ("%s (%s): holders or waiters\n", __FUNCTION__,
sx->sx_object.lo_name));
mtx_destroy(&sx->sx_lock);
cv_destroy(&sx->sx_shrd_cv);
cv_destroy(&sx->sx_excl_cv);
WITNESS_DESTROY(&sx->sx_object);
}
void
_sx_slock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
KASSERT(sx->sx_xholder != curthread,
("%s (%s): slock while xlock is held @ %s:%d\n", __FUNCTION__,
sx->sx_object.lo_name, file, line));
/*
* Loop in case we lose the race for lock acquisition.
*/
while (sx->sx_cnt < 0) {
sx->sx_shrd_wcnt++;
cv_wait(&sx->sx_shrd_cv, &sx->sx_lock);
sx->sx_shrd_wcnt--;
}
/* Acquire a shared lock. */
sx->sx_cnt++;
LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line);
WITNESS_LOCK(&sx->sx_object, 0, file, line);
mtx_unlock(&sx->sx_lock);
}
int
_sx_try_slock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
if (sx->sx_cnt >= 0) {
sx->sx_cnt++;
LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line);
WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line);
mtx_unlock(&sx->sx_lock);
return (1);
} else {
LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
return (0);
}
}
void
_sx_xlock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
/*
* With sx locks, we're absolutely not permitted to recurse on
* xlocks, as it is fatal (deadlock). Normally, recursion is handled
* by WITNESS, but as it is not semantically correct to hold the
* xlock while in here, we consider it API abuse and put it under
* INVARIANTS.
*/
KASSERT(sx->sx_xholder != curthread,
("%s (%s): xlock already held @ %s:%d", __FUNCTION__,
sx->sx_object.lo_name, file, line));
/* Loop in case we lose the race for lock acquisition. */
while (sx->sx_cnt != 0) {
sx->sx_excl_wcnt++;
cv_wait(&sx->sx_excl_cv, &sx->sx_lock);
sx->sx_excl_wcnt--;
}
MPASS(sx->sx_cnt == 0);
/* Acquire an exclusive lock. */
sx->sx_cnt--;
sx->sx_xholder = curthread;
LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line);
WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
mtx_unlock(&sx->sx_lock);
}
int
_sx_try_xlock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
if (sx->sx_cnt == 0) {
sx->sx_cnt--;
sx->sx_xholder = curthread;
LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line);
WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file,
line);
mtx_unlock(&sx->sx_lock);
return (1);
} else {
LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
return (0);
}
}
void
_sx_sunlock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
_SX_ASSERT_SLOCKED(sx, file, line);
WITNESS_UNLOCK(&sx->sx_object, 0, file, line);
/* Release. */
sx->sx_cnt--;
/*
* If we just released the last shared lock, wake any waiters up, giving
* exclusive lockers precedence. In order to make sure that exclusive
* lockers won't be blocked forever, don't wake shared lock waiters if
* there are exclusive lock waiters.
*/
if (sx->sx_excl_wcnt > 0) {
if (sx->sx_cnt == 0)
cv_signal(&sx->sx_excl_cv);
} else if (sx->sx_shrd_wcnt > 0)
cv_broadcast(&sx->sx_shrd_cv);
LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
}
void
_sx_xunlock(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
_SX_ASSERT_XLOCKED(sx, file, line);
MPASS(sx->sx_cnt == -1);
WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
/* Release. */
sx->sx_cnt++;
sx->sx_xholder = NULL;
/*
* Wake up waiters if there are any. Give precedence to slock waiters.
*/
if (sx->sx_shrd_wcnt > 0)
cv_broadcast(&sx->sx_shrd_cv);
else if (sx->sx_excl_wcnt > 0)
cv_signal(&sx->sx_excl_cv);
LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
}
int
_sx_try_upgrade(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
_SX_ASSERT_SLOCKED(sx, file, line);
if (sx->sx_cnt == 1) {
sx->sx_cnt = -1;
sx->sx_xholder = curthread;
LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line);
WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
file, line);
mtx_unlock(&sx->sx_lock);
return (1);
} else {
LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
return (0);
}
}
void
_sx_downgrade(struct sx *sx, const char *file, int line)
{
mtx_lock(&sx->sx_lock);
_SX_ASSERT_XLOCKED(sx, file, line);
MPASS(sx->sx_cnt == -1);
WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line);
sx->sx_cnt = 1;
sx->sx_xholder = NULL;
if (sx->sx_shrd_wcnt > 0)
cv_broadcast(&sx->sx_shrd_cv);
LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line);
mtx_unlock(&sx->sx_lock);
}