freebsd-dev/sys/kern/kern_sx.c
John Baldwin 5f36700a32 - Add trylock variants of shared and exclusive locks.
- The sx assertions don't actually need the internal sx mutex lock, so
  don't bother doing so.
- Add a new assertion SX_ASSERT_LOCKED() that asserts that either a
  shared or exclusive lock should be held.  This assertion should be used
  instead of SX_ASSERT_SLOCKED() in almost all cases.
- Adjust some KASSERT()'s to include file and line information.
- Use the new witness_assert() function in the WITNESS case for sx slock
  asserts to verify that the current thread actually owns a slock.
2001-06-27 06:39:37 +00:00

248 lines
6.5 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
};
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;
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 != curproc,
("%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 != curproc,
("%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 = curproc;
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 = curproc;
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);
}