60ad130f46
These functions are intended to be used to drop a lock and then reacquire it when doing an sleep such as msleep(9). Both functions accept a 'struct lock_object *' as their first parameter. The 'lc_unlock' function returns an integer that is then passed as the second paramter to the subsequent 'lc_lock' function. This can be used to communicate state. For example, sx locks and rwlocks use this to indicate if the lock was share/read locked vs exclusive/write locked. Currently, spin mutexes and lockmgr locks do not provide working lc_lock and lc_unlock functions.
501 lines
12 KiB
C
501 lines
12 KiB
C
/*-
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* Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice(s), this list of conditions and the following disclaimer as
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* the first lines of this file unmodified other than the possible
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* addition of one or more copyright notices.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice(s), this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*/
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/*
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* Shared/exclusive locks. This implementation assures deterministic lock
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* granting behavior, so that slocks and xlocks are interleaved.
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*
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* Priority propagation will not generally raise the priority of lock holders,
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* so should not be relied upon in combination with sx locks.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include "opt_ddb.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/ktr.h>
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#include <sys/linker_set.h>
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#include <sys/condvar.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/proc.h>
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#include <sys/sx.h>
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#include <sys/lock_profile.h>
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#ifdef DDB
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#include <ddb/ddb.h>
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static void db_show_sx(struct lock_object *lock);
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#endif
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static void lock_sx(struct lock_object *lock, int how);
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static int unlock_sx(struct lock_object *lock);
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struct lock_class lock_class_sx = {
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.lc_name = "sx",
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.lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
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#ifdef DDB
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.lc_ddb_show = db_show_sx,
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#endif
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.lc_lock = lock_sx,
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.lc_unlock = unlock_sx,
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};
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#ifndef INVARIANTS
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#define _sx_assert(sx, what, file, line)
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#endif
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void
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lock_sx(struct lock_object *lock, int how)
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{
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struct sx *sx;
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sx = (struct sx *)lock;
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if (how)
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sx_xlock(sx);
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else
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sx_slock(sx);
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}
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int
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unlock_sx(struct lock_object *lock)
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{
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struct sx *sx;
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sx = (struct sx *)lock;
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sx_assert(sx, SX_LOCKED | LA_NOTRECURSED);
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if (sx_xlocked(sx)) {
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sx_xunlock(sx);
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return (1);
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} else {
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sx_sunlock(sx);
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return (0);
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}
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}
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void
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sx_sysinit(void *arg)
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{
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struct sx_args *sargs = arg;
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sx_init(sargs->sa_sx, sargs->sa_desc);
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}
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void
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sx_init(struct sx *sx, const char *description)
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{
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sx->sx_lock = mtx_pool_find(mtxpool_lockbuilder, sx);
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sx->sx_cnt = 0;
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cv_init(&sx->sx_shrd_cv, description);
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sx->sx_shrd_wcnt = 0;
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cv_init(&sx->sx_excl_cv, description);
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sx->sx_excl_wcnt = 0;
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sx->sx_xholder = NULL;
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lock_profile_object_init(&sx->sx_object, &lock_class_sx, description);
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lock_init(&sx->sx_object, &lock_class_sx, description, NULL,
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LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE);
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}
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void
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sx_destroy(struct sx *sx)
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{
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KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt ==
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0), ("%s (%s): holders or waiters\n", __func__,
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sx->sx_object.lo_name));
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sx->sx_lock = NULL;
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cv_destroy(&sx->sx_shrd_cv);
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cv_destroy(&sx->sx_excl_cv);
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lock_profile_object_destroy(&sx->sx_object);
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lock_destroy(&sx->sx_object);
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}
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void
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_sx_slock(struct sx *sx, const char *file, int line)
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{
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uint64_t waittime = 0;
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int contested = 0;
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mtx_lock(sx->sx_lock);
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KASSERT(sx->sx_xholder != curthread,
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("%s (%s): slock while xlock is held @ %s:%d\n", __func__,
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sx->sx_object.lo_name, file, line));
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WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER, file, line);
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/*
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* Loop in case we lose the race for lock acquisition.
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*/
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while (sx->sx_cnt < 0) {
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sx->sx_shrd_wcnt++;
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lock_profile_obtain_lock_failed(&sx->sx_object, &contested, &waittime);
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cv_wait(&sx->sx_shrd_cv, sx->sx_lock);
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sx->sx_shrd_wcnt--;
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}
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/* Acquire a shared lock. */
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sx->sx_cnt++;
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if (sx->sx_cnt == 1)
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lock_profile_obtain_lock_success(&sx->sx_object, contested, waittime, file, line);
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LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line);
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WITNESS_LOCK(&sx->sx_object, 0, file, line);
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curthread->td_locks++;
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mtx_unlock(sx->sx_lock);
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}
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int
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_sx_try_slock(struct sx *sx, const char *file, int line)
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{
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mtx_lock(sx->sx_lock);
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if (sx->sx_cnt >= 0) {
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sx->sx_cnt++;
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LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line);
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WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line);
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curthread->td_locks++;
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mtx_unlock(sx->sx_lock);
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return (1);
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} else {
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LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line);
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mtx_unlock(sx->sx_lock);
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return (0);
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}
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}
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void
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_sx_xlock(struct sx *sx, const char *file, int line)
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{
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int contested = 0;
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uint64_t waittime = 0;
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mtx_lock(sx->sx_lock);
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/*
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* With sx locks, we're absolutely not permitted to recurse on
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* xlocks, as it is fatal (deadlock). Normally, recursion is handled
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* by WITNESS, but as it is not semantically correct to hold the
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* xlock while in here, we consider it API abuse and put it under
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* INVARIANTS.
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*/
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KASSERT(sx->sx_xholder != curthread,
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("%s (%s): xlock already held @ %s:%d", __func__,
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sx->sx_object.lo_name, file, line));
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WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
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line);
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/* Loop in case we lose the race for lock acquisition. */
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while (sx->sx_cnt != 0) {
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sx->sx_excl_wcnt++;
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lock_profile_obtain_lock_failed(&sx->sx_object, &contested, &waittime);
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cv_wait(&sx->sx_excl_cv, sx->sx_lock);
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sx->sx_excl_wcnt--;
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}
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MPASS(sx->sx_cnt == 0);
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/* Acquire an exclusive lock. */
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sx->sx_cnt--;
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sx->sx_xholder = curthread;
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lock_profile_obtain_lock_success(&sx->sx_object, contested, waittime, file, line);
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LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line);
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WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
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curthread->td_locks++;
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mtx_unlock(sx->sx_lock);
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}
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int
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_sx_try_xlock(struct sx *sx, const char *file, int line)
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{
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mtx_lock(sx->sx_lock);
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if (sx->sx_cnt == 0) {
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sx->sx_cnt--;
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sx->sx_xholder = curthread;
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LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line);
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WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file,
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line);
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curthread->td_locks++;
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mtx_unlock(sx->sx_lock);
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return (1);
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} else {
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LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line);
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mtx_unlock(sx->sx_lock);
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return (0);
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}
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}
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void
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_sx_sunlock(struct sx *sx, const char *file, int line)
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{
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_sx_assert(sx, SX_SLOCKED, file, line);
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mtx_lock(sx->sx_lock);
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curthread->td_locks--;
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WITNESS_UNLOCK(&sx->sx_object, 0, file, line);
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/* Release. */
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sx->sx_cnt--;
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if (sx->sx_cnt == 0) {
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lock_profile_release_lock(&sx->sx_object);
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}
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/*
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* If we just released the last shared lock, wake any waiters up, giving
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* exclusive lockers precedence. In order to make sure that exclusive
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* lockers won't be blocked forever, don't wake shared lock waiters if
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* there are exclusive lock waiters.
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*/
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if (sx->sx_excl_wcnt > 0) {
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if (sx->sx_cnt == 0)
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cv_signal(&sx->sx_excl_cv);
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} else if (sx->sx_shrd_wcnt > 0)
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cv_broadcast(&sx->sx_shrd_cv);
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LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line);
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mtx_unlock(sx->sx_lock);
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}
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void
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_sx_xunlock(struct sx *sx, const char *file, int line)
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{
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_sx_assert(sx, SX_XLOCKED, file, line);
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mtx_lock(sx->sx_lock);
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MPASS(sx->sx_cnt == -1);
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curthread->td_locks--;
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WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
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/* Release. */
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sx->sx_cnt++;
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sx->sx_xholder = NULL;
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/*
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* Wake up waiters if there are any. Give precedence to slock waiters.
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*/
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if (sx->sx_shrd_wcnt > 0)
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cv_broadcast(&sx->sx_shrd_cv);
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else if (sx->sx_excl_wcnt > 0)
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cv_signal(&sx->sx_excl_cv);
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LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line);
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lock_profile_release_lock(&sx->sx_object);
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mtx_unlock(sx->sx_lock);
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}
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int
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_sx_try_upgrade(struct sx *sx, const char *file, int line)
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{
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_sx_assert(sx, SX_SLOCKED, file, line);
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mtx_lock(sx->sx_lock);
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if (sx->sx_cnt == 1) {
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sx->sx_cnt = -1;
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sx->sx_xholder = curthread;
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LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line);
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WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
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file, line);
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mtx_unlock(sx->sx_lock);
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return (1);
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} else {
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LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line);
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mtx_unlock(sx->sx_lock);
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return (0);
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}
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}
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void
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_sx_downgrade(struct sx *sx, const char *file, int line)
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{
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_sx_assert(sx, SX_XLOCKED, file, line);
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mtx_lock(sx->sx_lock);
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MPASS(sx->sx_cnt == -1);
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WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line);
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sx->sx_cnt = 1;
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sx->sx_xholder = NULL;
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if (sx->sx_shrd_wcnt > 0)
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cv_broadcast(&sx->sx_shrd_cv);
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LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line);
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mtx_unlock(sx->sx_lock);
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}
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#ifdef INVARIANT_SUPPORT
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#ifndef INVARIANTS
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#undef _sx_assert
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#endif
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/*
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* In the non-WITNESS case, sx_assert() can only detect that at least
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* *some* thread owns an slock, but it cannot guarantee that *this*
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* thread owns an slock.
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*/
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void
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_sx_assert(struct sx *sx, int what, const char *file, int line)
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{
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if (panicstr != NULL)
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return;
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switch (what) {
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case SX_LOCKED:
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case SX_LOCKED | LA_NOTRECURSED:
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case SX_SLOCKED:
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#ifdef WITNESS
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witness_assert(&sx->sx_object, what, file, line);
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#else
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mtx_lock(sx->sx_lock);
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if (sx->sx_cnt <= 0 &&
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(what == SX_SLOCKED || sx->sx_xholder != curthread))
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panic("Lock %s not %slocked @ %s:%d\n",
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sx->sx_object.lo_name, (what == SX_SLOCKED) ?
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"share " : "", file, line);
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mtx_unlock(sx->sx_lock);
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#endif
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break;
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case SX_XLOCKED:
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mtx_lock(sx->sx_lock);
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if (sx->sx_xholder != curthread)
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panic("Lock %s not exclusively locked @ %s:%d\n",
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sx->sx_object.lo_name, file, line);
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mtx_unlock(sx->sx_lock);
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break;
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case SX_UNLOCKED:
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#ifdef WITNESS
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witness_assert(&sx->sx_object, what, file, line);
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#else
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/*
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* We are able to check only exclusive lock here,
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* we cannot assert that *this* thread owns slock.
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*/
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mtx_lock(sx->sx_lock);
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if (sx->sx_xholder == curthread)
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panic("Lock %s exclusively locked @ %s:%d\n",
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sx->sx_object.lo_name, file, line);
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mtx_unlock(sx->sx_lock);
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#endif
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break;
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default:
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panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
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line);
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}
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}
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#endif /* INVARIANT_SUPPORT */
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|
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#ifdef DDB
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void
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db_show_sx(struct lock_object *lock)
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{
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struct thread *td;
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struct sx *sx;
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sx = (struct sx *)lock;
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db_printf(" state: ");
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if (sx->sx_cnt < 0) {
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td = sx->sx_xholder;
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db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
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td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm);
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} else if (sx->sx_cnt > 0)
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db_printf("SLOCK: %d locks\n", sx->sx_cnt);
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else
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db_printf("UNLOCKED\n");
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db_printf(" waiters: %d shared, %d exclusive\n", sx->sx_shrd_wcnt,
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sx->sx_excl_wcnt);
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}
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|
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/*
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* Check to see if a thread that is blocked on a sleep queue is actually
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* blocked on an sx lock. If so, output some details and return true.
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* If the lock has an exclusive owner, return that in *ownerp.
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*/
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int
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sx_chain(struct thread *td, struct thread **ownerp)
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{
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struct sx *sx;
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struct cv *cv;
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/*
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* First, see if it looks like td is blocked on a condition
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* variable.
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*/
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cv = td->td_wchan;
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if (cv->cv_description != td->td_wmesg)
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return (0);
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/*
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* Ok, see if it looks like td is blocked on the exclusive
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* condition variable.
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*/
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sx = (struct sx *)((char *)cv - offsetof(struct sx, sx_excl_cv));
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if (LOCK_CLASS(&sx->sx_object) == &lock_class_sx &&
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sx->sx_excl_wcnt > 0)
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goto ok;
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/*
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* Second, see if it looks like td is blocked on the shared
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* condition variable.
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*/
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sx = (struct sx *)((char *)cv - offsetof(struct sx, sx_shrd_cv));
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if (LOCK_CLASS(&sx->sx_object) == &lock_class_sx &&
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sx->sx_shrd_wcnt > 0)
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goto ok;
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/* Doesn't seem to be an sx lock. */
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return (0);
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ok:
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/* We think we have an sx lock, so output some details. */
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db_printf("blocked on sx \"%s\" ", td->td_wmesg);
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if (sx->sx_cnt >= 0) {
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db_printf("SLOCK (count %d)\n", sx->sx_cnt);
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*ownerp = NULL;
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} else {
|
|
db_printf("XLOCK\n");
|
|
*ownerp = sx->sx_xholder;
|
|
}
|
|
return (1);
|
|
}
|
|
#endif
|