da7bbd2c08
routine wakes up proc0 so that proc0 can swap the thread back in. Historically, this has been done by waking up proc0 directly from setrunnable() itself via a wakeup(). When waking up a sleeping thread that was swapped out (the usual case when waking proc0 since only sleeping threads are eligible to be swapped out), this resulted in a bit of recursion (e.g. wakeup() -> setrunnable() -> wakeup()). With sleep queues having separate locks in 6.x and later, this caused a spin lock LOR (sleepq lock -> sched_lock/thread lock -> sleepq lock). An attempt was made to fix this in 7.0 by making the proc0 wakeup use the ithread mechanism for doing the wakeup. However, this required grabbing proc0's thread lock to perform the wakeup. If proc0 was asleep elsewhere in the kernel (e.g. waiting for disk I/O), then this degenerated into the same LOR since the thread lock would be some other sleepq lock. Fix this by deferring the wakeup of the swapper until after the sleepq lock held by the upper layer has been locked. The setrunnable() routine now returns a boolean value to indicate whether or not proc0 needs to be woken up. The end result is that consumers of the sleepq API such as *sleep/wakeup, condition variables, sx locks, and lockmgr, have to wakeup proc0 if they get a non-zero return value from sleepq_abort(), sleepq_broadcast(), or sleepq_signal(). Discussed with: jeff Glanced at by: sam Tested by: Jurgen Weber jurgen - ish com au MFC after: 2 weeks
1048 lines
28 KiB
C
1048 lines
28 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_adaptive_sx.h"
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#include "opt_ddb.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/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/sleepqueue.h>
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#include <sys/sx.h>
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#include <sys/systm.h>
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#ifdef 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(ADAPTIVE_SX)
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#error "You must have SMP to enable the ADAPTIVE_SX option"
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#endif
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CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) ==
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(SX_ADAPTIVESPIN | SX_RECURSE));
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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_recurse lock_object.lo_data
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#define sx_recursed(sx) ((sx)->sx_recurse != 0)
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static void assert_sx(struct lock_object *lock, int what);
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#ifdef DDB
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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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.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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};
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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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assert_sx(struct lock_object *lock, int what)
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{
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sx_assert((struct sx *)lock, what);
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}
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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, SA_LOCKED | SA_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_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_ADAPTIVESPIN)) == 0);
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flags = LO_RECURSABLE | 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_QUIET)
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flags |= LO_QUIET;
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flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE);
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sx->sx_lock = SX_LOCK_UNLOCKED;
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sx->sx_recurse = 0;
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lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
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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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MPASS(curthread != NULL);
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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);
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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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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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MPASS(curthread != NULL);
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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);
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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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MPASS(curthread != NULL);
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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) && (sx->lock_object.lo_flags & SX_RECURSE) != 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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MPASS(curthread != NULL);
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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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curthread->td_locks--;
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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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lock_profile_release_lock(&sx->lock_object);
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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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|
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|
MPASS(curthread != NULL);
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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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curthread->td_locks--;
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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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if (!sx_recursed(sx))
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lock_profile_release_lock(&sx->lock_object);
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__sx_xunlock(sx, curthread, file, line);
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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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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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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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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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|
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WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
|
|
|
|
/*
|
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* Try to switch from an exclusive lock with no shared waiters
|
|
* to one sharer with no shared waiters. If there are
|
|
* exclusive waiters, we don't need to lock the sleep queue so
|
|
* 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.
|
|
*
|
|
* We have to lock the sleep queue if there are shared waiters
|
|
* so we can wake them up.
|
|
*/
|
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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;
|
|
}
|
|
|
|
/*
|
|
* Lock the sleep queue so we can read the waiters bits
|
|
* without any races and wakeup any shared waiters.
|
|
*/
|
|
sleepq_lock(&sx->lock_object);
|
|
|
|
/*
|
|
* Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
|
|
* shared lock. If there are any shared waiters, wake them up.
|
|
*/
|
|
wakeup_swapper = 0;
|
|
x = sx->sx_lock;
|
|
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);
|
|
|
|
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;
|
|
#endif
|
|
uint64_t waittime = 0;
|
|
uintptr_t x;
|
|
int contested = 0, error = 0;
|
|
|
|
/* If we already hold an exclusive lock, then recurse. */
|
|
if (sx_xlocked(sx)) {
|
|
KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 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)) {
|
|
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 (!(x & SX_LOCK_SHARED) &&
|
|
(sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
|
|
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);
|
|
GIANT_SAVE();
|
|
while (SX_OWNER(sx->sx_lock) == x &&
|
|
TD_IS_RUNNING(owner))
|
|
cpu_spinwait();
|
|
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_ADAPTIVESPIN)) {
|
|
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);
|
|
|
|
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);
|
|
|
|
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)
|
|
lock_profile_obtain_lock_success(&sx->lock_object, contested,
|
|
waittime, file, line);
|
|
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;
|
|
|
|
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 (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
|
|
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
|
|
uint64_t waittime = 0;
|
|
int contested = 0;
|
|
uintptr_t x;
|
|
int error = 0;
|
|
|
|
/*
|
|
* As with rwlocks, we don't make any attempt to try to block
|
|
* shared locks once there is an exclusive waiter.
|
|
*/
|
|
for (;;) {
|
|
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;
|
|
}
|
|
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_ADAPTIVESPIN) {
|
|
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);
|
|
GIANT_SAVE();
|
|
while (SX_OWNER(sx->sx_lock) == x &&
|
|
TD_IS_RUNNING(owner))
|
|
cpu_spinwait();
|
|
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_ADAPTIVESPIN)) {
|
|
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);
|
|
|
|
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);
|
|
|
|
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)
|
|
lock_profile_obtain_lock_success(&sx->lock_object, contested,
|
|
waittime, file, line);
|
|
|
|
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;
|
|
|
|
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_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_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_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(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(struct lock_object *lock)
|
|
{
|
|
struct thread *td;
|
|
struct sx *sx;
|
|
|
|
sx = (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
|