6f2b57128c
A _NEW flag passed to _init_flags() to avoid check for double-init. Differential Revision: https://reviews.freebsd.org/D1208 Reviewed by: jhb, wblock MFC after: 1 Month
1229 lines
33 KiB
C
1229 lines
33 KiB
C
/*-
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* Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
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* Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
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* 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 attempts to ensure
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* deterministic lock granting behavior, so that slocks and xlocks are
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* 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 "opt_ddb.h"
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#include "opt_hwpmc_hooks.h"
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#include "opt_no_adaptive_sx.h"
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/kdb.h>
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#include <sys/ktr.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/sched.h>
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#include <sys/sleepqueue.h>
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#include <sys/sx.h>
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#include <sys/sysctl.h>
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#if defined(SMP) && !defined(NO_ADAPTIVE_SX)
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#include <machine/cpu.h>
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#endif
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#ifdef DDB
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#include <ddb/ddb.h>
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#endif
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#if defined(SMP) && !defined(NO_ADAPTIVE_SX)
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#define ADAPTIVE_SX
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#endif
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CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
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#ifdef HWPMC_HOOKS
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#include <sys/pmckern.h>
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PMC_SOFT_DECLARE( , , lock, failed);
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#endif
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/* Handy macros for sleep queues. */
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#define SQ_EXCLUSIVE_QUEUE 0
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#define SQ_SHARED_QUEUE 1
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/*
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* Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
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* drop Giant anytime we have to sleep or if we adaptively spin.
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*/
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#define GIANT_DECLARE \
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int _giantcnt = 0; \
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WITNESS_SAVE_DECL(Giant) \
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#define GIANT_SAVE() do { \
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if (mtx_owned(&Giant)) { \
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WITNESS_SAVE(&Giant.lock_object, Giant); \
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while (mtx_owned(&Giant)) { \
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_giantcnt++; \
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mtx_unlock(&Giant); \
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} \
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} \
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} while (0)
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#define GIANT_RESTORE() do { \
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if (_giantcnt > 0) { \
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mtx_assert(&Giant, MA_NOTOWNED); \
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while (_giantcnt--) \
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mtx_lock(&Giant); \
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WITNESS_RESTORE(&Giant.lock_object, Giant); \
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} \
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} while (0)
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/*
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* Returns true if an exclusive lock is recursed. It assumes
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* curthread currently has an exclusive lock.
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*/
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#define sx_recursed(sx) ((sx)->sx_recurse != 0)
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static void assert_sx(const struct lock_object *lock, int what);
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#ifdef DDB
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static void db_show_sx(const struct lock_object *lock);
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#endif
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static void lock_sx(struct lock_object *lock, uintptr_t how);
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#ifdef KDTRACE_HOOKS
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static int owner_sx(const struct lock_object *lock, struct thread **owner);
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#endif
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static uintptr_t 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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.lc_assert = assert_sx,
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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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#ifdef KDTRACE_HOOKS
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.lc_owner = owner_sx,
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#endif
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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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#ifdef ADAPTIVE_SX
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static u_int asx_retries = 10;
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static u_int asx_loops = 10000;
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static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
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SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
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SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
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#endif
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void
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assert_sx(const struct lock_object *lock, int what)
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{
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sx_assert((const struct sx *)lock, what);
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}
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void
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lock_sx(struct lock_object *lock, uintptr_t 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_slock(sx);
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else
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sx_xlock(sx);
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}
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uintptr_t
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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, SA_LOCKED | SA_NOTRECURSED);
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if (sx_xlocked(sx)) {
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sx_xunlock(sx);
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return (0);
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} else {
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sx_sunlock(sx);
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return (1);
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}
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}
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#ifdef KDTRACE_HOOKS
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int
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owner_sx(const struct lock_object *lock, struct thread **owner)
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{
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const struct sx *sx = (const struct sx *)lock;
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uintptr_t x = sx->sx_lock;
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*owner = (struct thread *)SX_OWNER(x);
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return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
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(*owner != NULL));
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}
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#endif
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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_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
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}
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void
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sx_init_flags(struct sx *sx, const char *description, int opts)
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{
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int flags;
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MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
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SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
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ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
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("%s: sx_lock not aligned for %s: %p", __func__, description,
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&sx->sx_lock));
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flags = LO_SLEEPABLE | LO_UPGRADABLE;
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if (opts & SX_DUPOK)
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flags |= LO_DUPOK;
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if (opts & SX_NOPROFILE)
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flags |= LO_NOPROFILE;
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if (!(opts & SX_NOWITNESS))
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flags |= LO_WITNESS;
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if (opts & SX_RECURSE)
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flags |= LO_RECURSABLE;
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if (opts & SX_QUIET)
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flags |= LO_QUIET;
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if (opts & SX_NEW)
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flags |= LO_NEW;
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flags |= opts & SX_NOADAPTIVE;
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lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
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sx->sx_lock = SX_LOCK_UNLOCKED;
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sx->sx_recurse = 0;
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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_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
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KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
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sx->sx_lock = SX_LOCK_DESTROYED;
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lock_destroy(&sx->lock_object);
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}
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int
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_sx_slock(struct sx *sx, int opts, const char *file, int line)
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{
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int error = 0;
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if (SCHEDULER_STOPPED())
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return (0);
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KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
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("sx_slock() by idle thread %p on sx %s @ %s:%d",
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curthread, sx->lock_object.lo_name, file, line));
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_slock() of destroyed sx @ %s:%d", file, line));
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WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
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error = __sx_slock(sx, opts, file, line);
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if (!error) {
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LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
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WITNESS_LOCK(&sx->lock_object, 0, file, line);
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curthread->td_locks++;
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}
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return (error);
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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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uintptr_t x;
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if (SCHEDULER_STOPPED())
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return (1);
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KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
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("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
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curthread, sx->lock_object.lo_name, file, line));
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for (;;) {
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x = sx->sx_lock;
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KASSERT(x != SX_LOCK_DESTROYED,
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("sx_try_slock() of destroyed sx @ %s:%d", file, line));
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if (!(x & SX_LOCK_SHARED))
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break;
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if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
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LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
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WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
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curthread->td_locks++;
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return (1);
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}
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}
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LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
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return (0);
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}
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int
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_sx_xlock(struct sx *sx, int opts, const char *file, int line)
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{
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int error = 0;
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if (SCHEDULER_STOPPED())
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return (0);
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KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
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("sx_xlock() by idle thread %p on sx %s @ %s:%d",
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curthread, sx->lock_object.lo_name, file, line));
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_xlock() of destroyed sx @ %s:%d", file, line));
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WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
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line, NULL);
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error = __sx_xlock(sx, curthread, opts, file, line);
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if (!error) {
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LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
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file, line);
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WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
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curthread->td_locks++;
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}
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return (error);
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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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int rval;
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if (SCHEDULER_STOPPED())
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return (1);
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KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
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("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
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curthread, sx->lock_object.lo_name, file, line));
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
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if (sx_xlocked(sx) &&
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(sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
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sx->sx_recurse++;
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atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
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rval = 1;
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} else
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rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
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(uintptr_t)curthread);
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LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
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if (rval) {
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WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
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file, line);
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curthread->td_locks++;
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}
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return (rval);
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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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if (SCHEDULER_STOPPED())
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return;
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_sunlock() of destroyed sx @ %s:%d", file, line));
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_sx_assert(sx, SA_SLOCKED, file, line);
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WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
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LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
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__sx_sunlock(sx, file, line);
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curthread->td_locks--;
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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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if (SCHEDULER_STOPPED())
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return;
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_xunlock() of destroyed sx @ %s:%d", file, line));
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_sx_assert(sx, SA_XLOCKED, file, line);
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WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
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LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
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line);
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__sx_xunlock(sx, curthread, file, line);
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curthread->td_locks--;
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}
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/*
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* Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
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* This will only succeed if this thread holds a single shared lock.
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* Return 1 if if the upgrade succeed, 0 otherwise.
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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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uintptr_t x;
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int success;
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if (SCHEDULER_STOPPED())
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return (1);
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
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_sx_assert(sx, SA_SLOCKED, file, line);
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/*
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* Try to switch from one shared lock to an exclusive lock. We need
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* to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
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* we will wake up the exclusive waiters when we drop the lock.
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*/
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x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
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success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
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(uintptr_t)curthread | x);
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LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
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if (success) {
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WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
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file, line);
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LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
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}
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return (success);
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}
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/*
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* Downgrade an unrecursed exclusive lock into a single shared lock.
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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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uintptr_t x;
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int wakeup_swapper;
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if (SCHEDULER_STOPPED())
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return;
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KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
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("sx_downgrade() of destroyed sx @ %s:%d", file, line));
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_sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
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#ifndef INVARIANTS
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if (sx_recursed(sx))
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panic("downgrade of a recursed lock");
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#endif
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WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
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/*
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* Try to switch from an exclusive lock with no shared waiters
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* to one sharer with no shared waiters. If there are
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* exclusive waiters, we don't need to lock the sleep queue so
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* long as we preserve the flag. We do one quick try and if
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* that fails we grab the sleepq lock to keep the flags from
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* changing and do it the slow way.
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*
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* We have to lock the sleep queue if there are shared waiters
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* so we can wake them up.
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*/
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x = sx->sx_lock;
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if (!(x & SX_LOCK_SHARED_WAITERS) &&
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atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
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(x & SX_LOCK_EXCLUSIVE_WAITERS))) {
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LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
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return;
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}
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/*
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* Lock the sleep queue so we can read the waiters bits
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* without any races and wakeup any shared waiters.
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*/
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sleepq_lock(&sx->lock_object);
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/*
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* Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
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* shared lock. If there are any shared waiters, wake them up.
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*/
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wakeup_swapper = 0;
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x = sx->sx_lock;
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|
atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
|
|
(x & SX_LOCK_EXCLUSIVE_WAITERS));
|
|
if (x & SX_LOCK_SHARED_WAITERS)
|
|
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
|
|
0, SQ_SHARED_QUEUE);
|
|
sleepq_release(&sx->lock_object);
|
|
|
|
LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
|
|
LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
|
|
|
|
if (wakeup_swapper)
|
|
kick_proc0();
|
|
}
|
|
|
|
/*
|
|
* This function represents the so-called 'hard case' for sx_xlock
|
|
* operation. All 'easy case' failures are redirected to this. Note
|
|
* that ideally this would be a static function, but it needs to be
|
|
* accessible from at least sx.h.
|
|
*/
|
|
int
|
|
_sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
|
|
int line)
|
|
{
|
|
GIANT_DECLARE;
|
|
#ifdef ADAPTIVE_SX
|
|
volatile struct thread *owner;
|
|
u_int i, spintries = 0;
|
|
#endif
|
|
uintptr_t x;
|
|
#ifdef LOCK_PROFILING
|
|
uint64_t waittime = 0;
|
|
int contested = 0;
|
|
#endif
|
|
int error = 0;
|
|
#ifdef KDTRACE_HOOKS
|
|
uint64_t spin_cnt = 0;
|
|
uint64_t sleep_cnt = 0;
|
|
int64_t sleep_time = 0;
|
|
#endif
|
|
|
|
if (SCHEDULER_STOPPED())
|
|
return (0);
|
|
|
|
/* If we already hold an exclusive lock, then recurse. */
|
|
if (sx_xlocked(sx)) {
|
|
KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
|
|
("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line));
|
|
sx->sx_recurse++;
|
|
atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
|
|
return (0);
|
|
}
|
|
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
|
|
sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
|
|
|
|
while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
|
|
#ifdef KDTRACE_HOOKS
|
|
spin_cnt++;
|
|
#endif
|
|
#ifdef HWPMC_HOOKS
|
|
PMC_SOFT_CALL( , , lock, failed);
|
|
#endif
|
|
lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
|
|
&waittime);
|
|
#ifdef ADAPTIVE_SX
|
|
/*
|
|
* If the lock is write locked and the owner is
|
|
* running on another CPU, spin until the owner stops
|
|
* running or the state of the lock changes.
|
|
*/
|
|
x = sx->sx_lock;
|
|
if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
|
|
if ((x & SX_LOCK_SHARED) == 0) {
|
|
x = SX_OWNER(x);
|
|
owner = (struct thread *)x;
|
|
if (TD_IS_RUNNING(owner)) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR3(KTR_LOCK,
|
|
"%s: spinning on %p held by %p",
|
|
__func__, sx, owner);
|
|
KTR_STATE1(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "spinning",
|
|
"lockname:\"%s\"",
|
|
sx->lock_object.lo_name);
|
|
GIANT_SAVE();
|
|
while (SX_OWNER(sx->sx_lock) == x &&
|
|
TD_IS_RUNNING(owner)) {
|
|
cpu_spinwait();
|
|
#ifdef KDTRACE_HOOKS
|
|
spin_cnt++;
|
|
#endif
|
|
}
|
|
KTR_STATE0(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "running");
|
|
continue;
|
|
}
|
|
} else if (SX_SHARERS(x) && spintries < asx_retries) {
|
|
KTR_STATE1(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "spinning",
|
|
"lockname:\"%s\"", sx->lock_object.lo_name);
|
|
GIANT_SAVE();
|
|
spintries++;
|
|
for (i = 0; i < asx_loops; i++) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR4(KTR_LOCK,
|
|
"%s: shared spinning on %p with %u and %u",
|
|
__func__, sx, spintries, i);
|
|
x = sx->sx_lock;
|
|
if ((x & SX_LOCK_SHARED) == 0 ||
|
|
SX_SHARERS(x) == 0)
|
|
break;
|
|
cpu_spinwait();
|
|
#ifdef KDTRACE_HOOKS
|
|
spin_cnt++;
|
|
#endif
|
|
}
|
|
KTR_STATE0(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "running");
|
|
if (i != asx_loops)
|
|
continue;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
sleepq_lock(&sx->lock_object);
|
|
x = sx->sx_lock;
|
|
|
|
/*
|
|
* If the lock was released while spinning on the
|
|
* sleep queue chain lock, try again.
|
|
*/
|
|
if (x == SX_LOCK_UNLOCKED) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
|
|
#ifdef ADAPTIVE_SX
|
|
/*
|
|
* The current lock owner might have started executing
|
|
* on another CPU (or the lock could have changed
|
|
* owners) while we were waiting on the sleep queue
|
|
* chain lock. If so, drop the sleep queue lock and try
|
|
* again.
|
|
*/
|
|
if (!(x & SX_LOCK_SHARED) &&
|
|
(sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
|
|
owner = (struct thread *)SX_OWNER(x);
|
|
if (TD_IS_RUNNING(owner)) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* If an exclusive lock was released with both shared
|
|
* and exclusive waiters and a shared waiter hasn't
|
|
* woken up and acquired the lock yet, sx_lock will be
|
|
* set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
|
|
* If we see that value, try to acquire it once. Note
|
|
* that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
|
|
* as there are other exclusive waiters still. If we
|
|
* fail, restart the loop.
|
|
*/
|
|
if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
if (atomic_cmpset_acq_ptr(&sx->sx_lock,
|
|
SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
|
|
tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
sleepq_release(&sx->lock_object);
|
|
CTR2(KTR_LOCK, "%s: %p claimed by new writer",
|
|
__func__, sx);
|
|
break;
|
|
}
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
|
|
* than loop back and retry.
|
|
*/
|
|
if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
if (!atomic_cmpset_ptr(&sx->sx_lock, x,
|
|
x | SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
|
|
__func__, sx);
|
|
}
|
|
|
|
/*
|
|
* Since we have been unable to acquire the exclusive
|
|
* lock and the exclusive waiters flag is set, we have
|
|
* to sleep.
|
|
*/
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
|
|
__func__, sx);
|
|
|
|
#ifdef KDTRACE_HOOKS
|
|
sleep_time -= lockstat_nsecs();
|
|
#endif
|
|
GIANT_SAVE();
|
|
sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
|
|
SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
|
|
SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
|
|
if (!(opts & SX_INTERRUPTIBLE))
|
|
sleepq_wait(&sx->lock_object, 0);
|
|
else
|
|
error = sleepq_wait_sig(&sx->lock_object, 0);
|
|
#ifdef KDTRACE_HOOKS
|
|
sleep_time += lockstat_nsecs();
|
|
sleep_cnt++;
|
|
#endif
|
|
if (error) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK,
|
|
"%s: interruptible sleep by %p suspended by signal",
|
|
__func__, sx);
|
|
break;
|
|
}
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
|
|
__func__, sx);
|
|
}
|
|
|
|
GIANT_RESTORE();
|
|
if (!error)
|
|
LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
|
|
contested, waittime, file, line);
|
|
#ifdef KDTRACE_HOOKS
|
|
if (sleep_time)
|
|
LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
|
|
if (spin_cnt > sleep_cnt)
|
|
LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
|
|
#endif
|
|
return (error);
|
|
}
|
|
|
|
/*
|
|
* This function represents the so-called 'hard case' for sx_xunlock
|
|
* operation. All 'easy case' failures are redirected to this. Note
|
|
* that ideally this would be a static function, but it needs to be
|
|
* accessible from at least sx.h.
|
|
*/
|
|
void
|
|
_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
|
|
{
|
|
uintptr_t x;
|
|
int queue, wakeup_swapper;
|
|
|
|
if (SCHEDULER_STOPPED())
|
|
return;
|
|
|
|
MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
|
|
|
|
/* If the lock is recursed, then unrecurse one level. */
|
|
if (sx_xlocked(sx) && sx_recursed(sx)) {
|
|
if ((--sx->sx_recurse) == 0)
|
|
atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
|
|
return;
|
|
}
|
|
MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
|
|
SX_LOCK_EXCLUSIVE_WAITERS));
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
|
|
|
|
sleepq_lock(&sx->lock_object);
|
|
x = SX_LOCK_UNLOCKED;
|
|
|
|
/*
|
|
* The wake up algorithm here is quite simple and probably not
|
|
* ideal. It gives precedence to shared waiters if they are
|
|
* present. For this condition, we have to preserve the
|
|
* state of the exclusive waiters flag.
|
|
* If interruptible sleeps left the shared queue empty avoid a
|
|
* starvation for the threads sleeping on the exclusive queue by giving
|
|
* them precedence and cleaning up the shared waiters bit anyway.
|
|
*/
|
|
if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
|
|
sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
|
|
queue = SQ_SHARED_QUEUE;
|
|
x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
|
|
} else
|
|
queue = SQ_EXCLUSIVE_QUEUE;
|
|
|
|
/* Wake up all the waiters for the specific queue. */
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
|
|
__func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
|
|
"exclusive");
|
|
atomic_store_rel_ptr(&sx->sx_lock, x);
|
|
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
|
|
queue);
|
|
sleepq_release(&sx->lock_object);
|
|
if (wakeup_swapper)
|
|
kick_proc0();
|
|
}
|
|
|
|
/*
|
|
* This function represents the so-called 'hard case' for sx_slock
|
|
* operation. All 'easy case' failures are redirected to this. Note
|
|
* that ideally this would be a static function, but it needs to be
|
|
* accessible from at least sx.h.
|
|
*/
|
|
int
|
|
_sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
|
|
{
|
|
GIANT_DECLARE;
|
|
#ifdef ADAPTIVE_SX
|
|
volatile struct thread *owner;
|
|
#endif
|
|
#ifdef LOCK_PROFILING
|
|
uint64_t waittime = 0;
|
|
int contested = 0;
|
|
#endif
|
|
uintptr_t x;
|
|
int error = 0;
|
|
#ifdef KDTRACE_HOOKS
|
|
uint64_t spin_cnt = 0;
|
|
uint64_t sleep_cnt = 0;
|
|
int64_t sleep_time = 0;
|
|
#endif
|
|
|
|
if (SCHEDULER_STOPPED())
|
|
return (0);
|
|
|
|
/*
|
|
* As with rwlocks, we don't make any attempt to try to block
|
|
* shared locks once there is an exclusive waiter.
|
|
*/
|
|
for (;;) {
|
|
#ifdef KDTRACE_HOOKS
|
|
spin_cnt++;
|
|
#endif
|
|
x = sx->sx_lock;
|
|
|
|
/*
|
|
* If no other thread has an exclusive lock then try to bump up
|
|
* the count of sharers. Since we have to preserve the state
|
|
* of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
|
|
* shared lock loop back and retry.
|
|
*/
|
|
if (x & SX_LOCK_SHARED) {
|
|
MPASS(!(x & SX_LOCK_SHARED_WAITERS));
|
|
if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
|
|
x + SX_ONE_SHARER)) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR4(KTR_LOCK,
|
|
"%s: %p succeed %p -> %p", __func__,
|
|
sx, (void *)x,
|
|
(void *)(x + SX_ONE_SHARER));
|
|
break;
|
|
}
|
|
continue;
|
|
}
|
|
#ifdef HWPMC_HOOKS
|
|
PMC_SOFT_CALL( , , lock, failed);
|
|
#endif
|
|
lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
|
|
&waittime);
|
|
|
|
#ifdef ADAPTIVE_SX
|
|
/*
|
|
* If the owner is running on another CPU, spin until
|
|
* the owner stops running or the state of the lock
|
|
* changes.
|
|
*/
|
|
if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
|
|
x = SX_OWNER(x);
|
|
owner = (struct thread *)x;
|
|
if (TD_IS_RUNNING(owner)) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR3(KTR_LOCK,
|
|
"%s: spinning on %p held by %p",
|
|
__func__, sx, owner);
|
|
KTR_STATE1(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "spinning",
|
|
"lockname:\"%s\"", sx->lock_object.lo_name);
|
|
GIANT_SAVE();
|
|
while (SX_OWNER(sx->sx_lock) == x &&
|
|
TD_IS_RUNNING(owner)) {
|
|
#ifdef KDTRACE_HOOKS
|
|
spin_cnt++;
|
|
#endif
|
|
cpu_spinwait();
|
|
}
|
|
KTR_STATE0(KTR_SCHED, "thread",
|
|
sched_tdname(curthread), "running");
|
|
continue;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* Some other thread already has an exclusive lock, so
|
|
* start the process of blocking.
|
|
*/
|
|
sleepq_lock(&sx->lock_object);
|
|
x = sx->sx_lock;
|
|
|
|
/*
|
|
* The lock could have been released while we spun.
|
|
* In this case loop back and retry.
|
|
*/
|
|
if (x & SX_LOCK_SHARED) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
|
|
#ifdef ADAPTIVE_SX
|
|
/*
|
|
* If the owner is running on another CPU, spin until
|
|
* the owner stops running or the state of the lock
|
|
* changes.
|
|
*/
|
|
if (!(x & SX_LOCK_SHARED) &&
|
|
(sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
|
|
owner = (struct thread *)SX_OWNER(x);
|
|
if (TD_IS_RUNNING(owner)) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
/*
|
|
* Try to set the SX_LOCK_SHARED_WAITERS flag. If we
|
|
* fail to set it drop the sleep queue lock and loop
|
|
* back.
|
|
*/
|
|
if (!(x & SX_LOCK_SHARED_WAITERS)) {
|
|
if (!atomic_cmpset_ptr(&sx->sx_lock, x,
|
|
x | SX_LOCK_SHARED_WAITERS)) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
|
|
__func__, sx);
|
|
}
|
|
|
|
/*
|
|
* Since we have been unable to acquire the shared lock,
|
|
* we have to sleep.
|
|
*/
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
|
|
__func__, sx);
|
|
|
|
#ifdef KDTRACE_HOOKS
|
|
sleep_time -= lockstat_nsecs();
|
|
#endif
|
|
GIANT_SAVE();
|
|
sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
|
|
SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
|
|
SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
|
|
if (!(opts & SX_INTERRUPTIBLE))
|
|
sleepq_wait(&sx->lock_object, 0);
|
|
else
|
|
error = sleepq_wait_sig(&sx->lock_object, 0);
|
|
#ifdef KDTRACE_HOOKS
|
|
sleep_time += lockstat_nsecs();
|
|
sleep_cnt++;
|
|
#endif
|
|
if (error) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK,
|
|
"%s: interruptible sleep by %p suspended by signal",
|
|
__func__, sx);
|
|
break;
|
|
}
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
|
|
__func__, sx);
|
|
}
|
|
if (error == 0)
|
|
LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
|
|
contested, waittime, file, line);
|
|
#ifdef KDTRACE_HOOKS
|
|
if (sleep_time)
|
|
LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
|
|
if (spin_cnt > sleep_cnt)
|
|
LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
|
|
#endif
|
|
GIANT_RESTORE();
|
|
return (error);
|
|
}
|
|
|
|
/*
|
|
* This function represents the so-called 'hard case' for sx_sunlock
|
|
* operation. All 'easy case' failures are redirected to this. Note
|
|
* that ideally this would be a static function, but it needs to be
|
|
* accessible from at least sx.h.
|
|
*/
|
|
void
|
|
_sx_sunlock_hard(struct sx *sx, const char *file, int line)
|
|
{
|
|
uintptr_t x;
|
|
int wakeup_swapper;
|
|
|
|
if (SCHEDULER_STOPPED())
|
|
return;
|
|
|
|
for (;;) {
|
|
x = sx->sx_lock;
|
|
|
|
/*
|
|
* We should never have sharers while at least one thread
|
|
* holds a shared lock.
|
|
*/
|
|
KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
|
|
("%s: waiting sharers", __func__));
|
|
|
|
/*
|
|
* See if there is more than one shared lock held. If
|
|
* so, just drop one and return.
|
|
*/
|
|
if (SX_SHARERS(x) > 1) {
|
|
if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
|
|
x - SX_ONE_SHARER)) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR4(KTR_LOCK,
|
|
"%s: %p succeeded %p -> %p",
|
|
__func__, sx, (void *)x,
|
|
(void *)(x - SX_ONE_SHARER));
|
|
break;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* If there aren't any waiters for an exclusive lock,
|
|
* then try to drop it quickly.
|
|
*/
|
|
if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
MPASS(x == SX_SHARERS_LOCK(1));
|
|
if (atomic_cmpset_rel_ptr(&sx->sx_lock,
|
|
SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p last succeeded",
|
|
__func__, sx);
|
|
break;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* At this point, there should just be one sharer with
|
|
* exclusive waiters.
|
|
*/
|
|
MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
|
|
|
|
sleepq_lock(&sx->lock_object);
|
|
|
|
/*
|
|
* Wake up semantic here is quite simple:
|
|
* Just wake up all the exclusive waiters.
|
|
* Note that the state of the lock could have changed,
|
|
* so if it fails loop back and retry.
|
|
*/
|
|
if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
|
|
SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
|
|
SX_LOCK_UNLOCKED)) {
|
|
sleepq_release(&sx->lock_object);
|
|
continue;
|
|
}
|
|
if (LOCK_LOG_TEST(&sx->lock_object, 0))
|
|
CTR2(KTR_LOCK, "%s: %p waking up all thread on"
|
|
"exclusive queue", __func__, sx);
|
|
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
|
|
0, SQ_EXCLUSIVE_QUEUE);
|
|
sleepq_release(&sx->lock_object);
|
|
if (wakeup_swapper)
|
|
kick_proc0();
|
|
break;
|
|
}
|
|
}
|
|
|
|
#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(const struct sx *sx, int what, const char *file, int line)
|
|
{
|
|
#ifndef WITNESS
|
|
int slocked = 0;
|
|
#endif
|
|
|
|
if (panicstr != NULL)
|
|
return;
|
|
switch (what) {
|
|
case SA_SLOCKED:
|
|
case SA_SLOCKED | SA_NOTRECURSED:
|
|
case SA_SLOCKED | SA_RECURSED:
|
|
#ifndef WITNESS
|
|
slocked = 1;
|
|
/* FALLTHROUGH */
|
|
#endif
|
|
case SA_LOCKED:
|
|
case SA_LOCKED | SA_NOTRECURSED:
|
|
case SA_LOCKED | SA_RECURSED:
|
|
#ifdef WITNESS
|
|
witness_assert(&sx->lock_object, what, file, line);
|
|
#else
|
|
/*
|
|
* If some other thread has an exclusive lock or we
|
|
* have one and are asserting a shared lock, fail.
|
|
* Also, if no one has a lock at all, fail.
|
|
*/
|
|
if (sx->sx_lock == SX_LOCK_UNLOCKED ||
|
|
(!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
|
|
sx_xholder(sx) != curthread)))
|
|
panic("Lock %s not %slocked @ %s:%d\n",
|
|
sx->lock_object.lo_name, slocked ? "share " : "",
|
|
file, line);
|
|
|
|
if (!(sx->sx_lock & SX_LOCK_SHARED)) {
|
|
if (sx_recursed(sx)) {
|
|
if (what & SA_NOTRECURSED)
|
|
panic("Lock %s recursed @ %s:%d\n",
|
|
sx->lock_object.lo_name, file,
|
|
line);
|
|
} else if (what & SA_RECURSED)
|
|
panic("Lock %s not recursed @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line);
|
|
}
|
|
#endif
|
|
break;
|
|
case SA_XLOCKED:
|
|
case SA_XLOCKED | SA_NOTRECURSED:
|
|
case SA_XLOCKED | SA_RECURSED:
|
|
if (sx_xholder(sx) != curthread)
|
|
panic("Lock %s not exclusively locked @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line);
|
|
if (sx_recursed(sx)) {
|
|
if (what & SA_NOTRECURSED)
|
|
panic("Lock %s recursed @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line);
|
|
} else if (what & SA_RECURSED)
|
|
panic("Lock %s not recursed @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line);
|
|
break;
|
|
case SA_UNLOCKED:
|
|
#ifdef WITNESS
|
|
witness_assert(&sx->lock_object, what, file, line);
|
|
#else
|
|
/*
|
|
* If we hold an exclusve lock fail. We can't
|
|
* reliably check to see if we hold a shared lock or
|
|
* not.
|
|
*/
|
|
if (sx_xholder(sx) == curthread)
|
|
panic("Lock %s exclusively locked @ %s:%d\n",
|
|
sx->lock_object.lo_name, file, line);
|
|
#endif
|
|
break;
|
|
default:
|
|
panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
|
|
line);
|
|
}
|
|
}
|
|
#endif /* INVARIANT_SUPPORT */
|
|
|
|
#ifdef DDB
|
|
static void
|
|
db_show_sx(const struct lock_object *lock)
|
|
{
|
|
struct thread *td;
|
|
const struct sx *sx;
|
|
|
|
sx = (const struct sx *)lock;
|
|
|
|
db_printf(" state: ");
|
|
if (sx->sx_lock == SX_LOCK_UNLOCKED)
|
|
db_printf("UNLOCKED\n");
|
|
else if (sx->sx_lock == SX_LOCK_DESTROYED) {
|
|
db_printf("DESTROYED\n");
|
|
return;
|
|
} else if (sx->sx_lock & SX_LOCK_SHARED)
|
|
db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
|
|
else {
|
|
td = sx_xholder(sx);
|
|
db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
|
|
td->td_tid, td->td_proc->p_pid, td->td_name);
|
|
if (sx_recursed(sx))
|
|
db_printf(" recursed: %d\n", sx->sx_recurse);
|
|
}
|
|
|
|
db_printf(" waiters: ");
|
|
switch(sx->sx_lock &
|
|
(SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
|
|
case SX_LOCK_SHARED_WAITERS:
|
|
db_printf("shared\n");
|
|
break;
|
|
case SX_LOCK_EXCLUSIVE_WAITERS:
|
|
db_printf("exclusive\n");
|
|
break;
|
|
case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
|
|
db_printf("exclusive and shared\n");
|
|
break;
|
|
default:
|
|
db_printf("none\n");
|
|
}
|
|
}
|
|
|
|
/*
|
|
* 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;
|
|
|
|
/*
|
|
* Check to see if this thread is blocked on an sx lock.
|
|
* First, we check the lock class. If that is ok, then we
|
|
* compare the lock name against the wait message.
|
|
*/
|
|
sx = td->td_wchan;
|
|
if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
|
|
sx->lock_object.lo_name != td->td_wmesg)
|
|
return (0);
|
|
|
|
/* We think we have an sx lock, so output some details. */
|
|
db_printf("blocked on sx \"%s\" ", td->td_wmesg);
|
|
*ownerp = sx_xholder(sx);
|
|
if (sx->sx_lock & SX_LOCK_SHARED)
|
|
db_printf("SLOCK (count %ju)\n",
|
|
(uintmax_t)SX_SHARERS(sx->sx_lock));
|
|
else
|
|
db_printf("XLOCK\n");
|
|
return (1);
|
|
}
|
|
#endif
|