freebsd-dev/sys/kern/kern_sx.c

472 lines
12 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.
*/
/*
* 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 "opt_ddb.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/ktr.h>
#include <sys/linker_set.h>
#include <sys/condvar.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sx.h>
#include <sys/lock_profile.h>
#ifdef DDB
#include <ddb/ddb.h>
static void db_show_sx(struct lock_object *lock);
#endif
struct lock_class lock_class_sx = {
"sx",
LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
#ifdef DDB
db_show_sx
#endif
};
#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)
{
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_profile_object_init(&sx->sx_object, &lock_class_sx, description);
lock_init(&sx->sx_object, &lock_class_sx, description, NULL,
LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE);
}
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", __func__,
sx->sx_object.lo_name));
sx->sx_lock = NULL;
cv_destroy(&sx->sx_shrd_cv);
cv_destroy(&sx->sx_excl_cv);
lock_profile_object_destroy(&sx->sx_object);
lock_destroy(&sx->sx_object);
}
void
_sx_slock(struct sx *sx, const char *file, int line)
{
uint64_t waittime = 0;
int contested;
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.
*/
if (sx->sx_cnt < 0)
lock_profile_waitstart(&waittime);
while (sx->sx_cnt < 0) {
sx->sx_shrd_wcnt++;
lock_profile_obtain_lock_failed(&sx->sx_object, &contested);
cv_wait(&sx->sx_shrd_cv, sx->sx_lock);
sx->sx_shrd_wcnt--;
}
/* Acquire a shared lock. */
sx->sx_cnt++;
if (sx->sx_cnt == 1)
lock_profile_obtain_lock_success(&sx->sx_object, waittime, file, line);
LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line);
WITNESS_LOCK(&sx->sx_object, 0, file, line);
curthread->td_locks++;
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);
curthread->td_locks++;
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)
{
int contested;
uint64_t waittime = 0;
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);
if (sx->sx_cnt)
lock_profile_waitstart(&waittime);
/* Loop in case we lose the race for lock acquisition. */
while (sx->sx_cnt != 0) {
sx->sx_excl_wcnt++;
lock_profile_obtain_lock_failed(&sx->sx_object, &contested);
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_profile_obtain_lock_success(&sx->sx_object, waittime, file, line);
LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line);
WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
curthread->td_locks++;
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);
curthread->td_locks++;
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);
curthread->td_locks--;
WITNESS_UNLOCK(&sx->sx_object, 0, file, line);
/* Release. */
sx->sx_cnt--;
if (sx->sx_cnt == 0)
lock_profile_release_lock(&sx->sx_object);
/*
* 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);
curthread->td_locks--;
WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
/* Release. */
sx->sx_cnt++;
sx->sx_xholder = NULL;
lock_profile_release_lock(&sx->sx_object);
/*
* 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 */
#ifdef DDB
void
db_show_sx(struct lock_object *lock)
{
struct thread *td;
struct sx *sx;
sx = (struct sx *)lock;
db_printf(" state: ");
if (sx->sx_cnt < 0) {
td = sx->sx_xholder;
db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm);
} else if (sx->sx_cnt > 0)
db_printf("SLOCK: %d locks\n", sx->sx_cnt);
else
db_printf("UNLOCKED\n");
db_printf(" waiters: %d shared, %d exclusive\n", sx->sx_shrd_wcnt,
sx->sx_excl_wcnt);
}
/*
* Check to see if a thread that is blocked on a sleep queue is actually
* blocked on an sx lock. If so, output some details and return true.
* If the lock has an exclusive owner, return that in *ownerp.
*/
int
sx_chain(struct thread *td, struct thread **ownerp)
{
struct sx *sx;
struct cv *cv;
/*
* First, see if it looks like td is blocked on a condition
* variable.
*/
cv = td->td_wchan;
if (cv->cv_description != td->td_wmesg)
return (0);
/*
* Ok, see if it looks like td is blocked on the exclusive
* condition variable.
*/
sx = (struct sx *)((char *)cv - offsetof(struct sx, sx_excl_cv));
if (LOCK_CLASS(&sx->sx_object) == &lock_class_sx &&
sx->sx_excl_wcnt > 0)
goto ok;
/*
* Second, see if it looks like td is blocked on the shared
* condition variable.
*/
sx = (struct sx *)((char *)cv - offsetof(struct sx, sx_shrd_cv));
if (LOCK_CLASS(&sx->sx_object) == &lock_class_sx &&
sx->sx_shrd_wcnt > 0)
goto ok;
/* Doesn't seem to be an sx lock. */
return (0);
ok:
/* We think we have an sx lock, so output some details. */
db_printf("blocked on sx \"%s\" ", td->td_wmesg);
if (sx->sx_cnt >= 0) {
db_printf("SLOCK (count %d)\n", sx->sx_cnt);
*ownerp = NULL;
} else {
db_printf("XLOCK\n");
*ownerp = sx->sx_xholder;
}
return (1);
}
#endif