/*-
* 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.
*/
/*
* 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/cdefs.h>
__FBSDID("$FreeBSD$");
#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
};
#ifndef INVARIANTS
#define _sx_assert(sx, what, file, line)
#endif
void
sx_sysinit(void *arg)
{
struct sx_args *sargs = arg;
sx_init(sargs->sa_sx, sargs->sa_desc);
}
void
sx_init(struct sx *sx, const char *description)
{
struct lock_object *lock;
lock = &sx->sx_object;
KASSERT((lock->lo_flags & LO_INITIALIZED) == 0,
("sx lock %s %p already initialized", description, sx));
bzero(sx, sizeof(*sx));
lock->lo_class = &lock_class_sx;
lock->lo_type = lock->lo_name = description;
lock->lo_flags = LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE |
LO_UPGRADABLE;
sx->sx_lock = mtx_pool_find(mtxpool_lockbuilder, sx);
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", __func__,
sx->sx_object.lo_name));
sx->sx_lock = NULL;
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", __func__,
sx->sx_object.lo_name, file, line));
WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER, 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", __func__,
sx->sx_object.lo_name, file, line));
WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER | LOP_EXCLUSIVE, 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)
{
_sx_assert(sx, SX_SLOCKED, file, line);
mtx_lock(sx->sx_lock);
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)
{
_sx_assert(sx, SX_XLOCKED, file, line);
mtx_lock(sx->sx_lock);
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)
{
_sx_assert(sx, SX_SLOCKED, file, line);
mtx_lock(sx->sx_lock);
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)
{
_sx_assert(sx, SX_XLOCKED, file, line);
mtx_lock(sx->sx_lock);
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);
}
#ifdef INVARIANT_SUPPORT
#ifndef INVARIANTS
#undef _sx_assert
#endif
/*
* In the non-WITNESS case, sx_assert() can only detect that at least
* *some* thread owns an slock, but it cannot guarantee that *this*
* thread owns an slock.
*/
void
_sx_assert(struct sx *sx, int what, const char *file, int line)
{
if (panicstr != NULL)
return;
switch (what) {
case SX_LOCKED:
case SX_SLOCKED:
#ifdef WITNESS
witness_assert(&sx->sx_object, what, file, line);
#else
mtx_lock(sx->sx_lock);
if (sx->sx_cnt <= 0 &&
(what == SX_SLOCKED || sx->sx_xholder != curthread))
panic("Lock %s not %slocked @ %s:%d\n",
sx->sx_object.lo_name, (what == SX_SLOCKED) ?
"share " : "", file, line);
mtx_unlock(sx->sx_lock);
#endif
break;
case SX_XLOCKED:
mtx_lock(sx->sx_lock);
if (sx->sx_xholder != curthread)
panic("Lock %s not exclusively locked @ %s:%d\n",
sx->sx_object.lo_name, file, line);
mtx_unlock(sx->sx_lock);
break;
case SX_UNLOCKED:
#ifdef WITNESS
witness_assert(&sx->sx_object, what, file, line);
#else
/*
* We are able to check only exclusive lock here,
* we cannot assert that *this* thread owns slock.
*/
mtx_lock(sx->sx_lock);
if (sx->sx_xholder == curthread)
panic("Lock %s exclusively locked @ %s:%d\n",
sx->sx_object.lo_name, file, line);
mtx_unlock(sx->sx_lock);
#endif
break;
default:
panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
line);
}
}
#endif /* INVARIANT_SUPPORT */
