7331c2a252
INVARIANTS case, define the actual KASSERT() in _SX_ASSERT_[SX]LOCKED macros that are used in the sx code itself and convert the SX_ASSERT_[SX]LOCKED macros to simple wrappers that grab the mutex for the duration of the check.
181 lines
4.9 KiB
C
181 lines
4.9 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.
|
|
*
|
|
* The witness code can not detect lock cycles (yet).
|
|
*
|
|
* XXX: When witness is made to function with sx locks, it will need to
|
|
* XXX: be taught to deal with these situations, as they are more involved:
|
|
* slock --> xlock (deadlock)
|
|
* slock --> slock (slock recursion, not fatal)
|
|
*/
|
|
|
|
#include <sys/param.h>
|
|
#include <sys/systm.h>
|
|
#include <sys/ktr.h>
|
|
#include <sys/condvar.h>
|
|
#include <sys/mutex.h>
|
|
#include <sys/sx.h>
|
|
|
|
void
|
|
sx_init(struct sx *sx, const char *description)
|
|
{
|
|
|
|
mtx_init(&sx->sx_lock, description, MTX_DEF);
|
|
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_descr = description;
|
|
sx->sx_excl_wcnt = 0;
|
|
sx->sx_xholder = NULL;
|
|
}
|
|
|
|
void
|
|
sx_destroy(struct sx *sx)
|
|
{
|
|
|
|
KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt ==
|
|
0), ("%s (%s): holders or waiters\n", __FUNCTION__, sx->sx_descr));
|
|
|
|
mtx_destroy(&sx->sx_lock);
|
|
cv_destroy(&sx->sx_shrd_cv);
|
|
cv_destroy(&sx->sx_excl_cv);
|
|
}
|
|
|
|
void
|
|
sx_slock(struct sx *sx)
|
|
{
|
|
|
|
mtx_lock(&sx->sx_lock);
|
|
KASSERT(sx->sx_xholder != curproc,
|
|
("%s (%s): trying to get slock while xlock is held\n", __FUNCTION__,
|
|
sx->sx_descr));
|
|
|
|
/*
|
|
* 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++;
|
|
|
|
mtx_unlock(&sx->sx_lock);
|
|
}
|
|
|
|
void
|
|
sx_xlock(struct sx *sx)
|
|
{
|
|
|
|
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 != curproc,
|
|
("%s (%s): xlock already held", __FUNCTION__, sx->sx_descr));
|
|
|
|
/* 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 = curproc;
|
|
|
|
mtx_unlock(&sx->sx_lock);
|
|
}
|
|
|
|
void
|
|
sx_sunlock(struct sx *sx)
|
|
{
|
|
|
|
mtx_lock(&sx->sx_lock);
|
|
_SX_ASSERT_SLOCKED(sx);
|
|
|
|
/* 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);
|
|
|
|
mtx_unlock(&sx->sx_lock);
|
|
}
|
|
|
|
void
|
|
sx_xunlock(struct sx *sx)
|
|
{
|
|
|
|
mtx_lock(&sx->sx_lock);
|
|
_SX_ASSERT_XLOCKED(sx);
|
|
MPASS(sx->sx_cnt == -1);
|
|
|
|
/* 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);
|
|
|
|
mtx_unlock(&sx->sx_lock);
|
|
}
|