539fc86f2e
illumos/illumos-gate@260af64db7
260af64db7
https://www.illumos.org/issues/3746
From the original change log:
It was possible for a reference to be added even with the lock held, and
for references added just after a lock release to be lost.
This bug was also independently found and reported in wesunsolve.net
issues 6985013 6995524.
In zrl_add(), always use an atomic operation to update the refcount.
The mutex in the ZRL only guarantees that wakeups occur for waiters on the
lock. It offers no protection against concurrent updates of the refcount.
The only refcount transition that is safe to perform without an atomic
operation is from ZRL_LOCKED back to 0, since this can only be performed
by the thread which has the ZRL locked.
Authored by: Will Andrews <will@freebsd.org>
Reviewed by: Boris Protopopov <bprotopopov@hotmail.com>
Reviewed by: Pavel Zakharov <pavel.zakha@gmail.com>
Reviewed by: Yuri Pankov <yuri.pankov@gmail.com>
Reviewed by: Justin T. Gibbs <gibbs@scsiguy.com>
Approved by: Matt Ahrens <mahrens@delphix.com>
Author: Youzhong Yang <yyang@mathworks.com>
PR: 204037
MFC after: 1 week
188 lines
4.4 KiB
C
188 lines
4.4 KiB
C
/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License (the "License").
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* You may not use this file except in compliance with the License.
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*
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* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
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* or http://www.opensolaris.org/os/licensing.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information: Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*/
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/*
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* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
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* Copyright (c) 2014, 2015 by Delphix. All rights reserved.
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* Copyright 2016 The MathWorks, Inc. All rights reserved.
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*/
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/*
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* A Zero Reference Lock (ZRL) is a reference count that can lock out new
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* references only when the count is zero and only without waiting if the count
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* is not already zero. It is similar to a read-write lock in that it allows
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* multiple readers and only a single writer, but it does not allow a writer to
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* block while waiting for readers to exit, and therefore the question of
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* reader/writer priority is moot (no WRWANT bit). Since the equivalent of
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* rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
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* is perfectly safe for the same reader to acquire the same lock multiple
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* times. The fact that a ZRL is reentrant for readers (through multiple calls
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* to zrl_add()) makes it convenient for determining whether something is
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* actively referenced without the fuss of flagging lock ownership across
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* function calls.
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*/
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#include <sys/zrlock.h>
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/*
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* A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
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* treated as zero references.
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*/
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#define ZRL_LOCKED -1
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#define ZRL_DESTROYED -2
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void
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zrl_init(zrlock_t *zrl)
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{
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mutex_init(&zrl->zr_mtx, NULL, MUTEX_DEFAULT, NULL);
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zrl->zr_refcount = 0;
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cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
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#ifdef ZFS_DEBUG
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zrl->zr_owner = NULL;
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zrl->zr_caller = NULL;
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#endif
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}
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void
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zrl_destroy(zrlock_t *zrl)
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{
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ASSERT0(zrl->zr_refcount);
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mutex_destroy(&zrl->zr_mtx);
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zrl->zr_refcount = ZRL_DESTROYED;
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cv_destroy(&zrl->zr_cv);
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}
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void
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zrl_add_impl(zrlock_t *zrl, const char *zc)
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{
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for (;;) {
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uint32_t n = (uint32_t)zrl->zr_refcount;
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while (n != ZRL_LOCKED) {
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uint32_t cas = atomic_cas_32(
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(uint32_t *)&zrl->zr_refcount, n, n + 1);
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if (cas == n) {
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ASSERT3S((int32_t)n, >=, 0);
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#ifdef ZFS_DEBUG
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if (zrl->zr_owner == curthread) {
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DTRACE_PROBE2(zrlock__reentry,
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zrlock_t *, zrl, uint32_t, n);
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}
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zrl->zr_owner = curthread;
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zrl->zr_caller = zc;
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#endif
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return;
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}
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n = cas;
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}
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mutex_enter(&zrl->zr_mtx);
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while (zrl->zr_refcount == ZRL_LOCKED) {
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cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
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}
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mutex_exit(&zrl->zr_mtx);
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}
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}
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void
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zrl_remove(zrlock_t *zrl)
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{
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uint32_t n;
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#ifdef ZFS_DEBUG
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if (zrl->zr_owner == curthread) {
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zrl->zr_owner = NULL;
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zrl->zr_caller = NULL;
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}
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#endif
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n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
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ASSERT3S((int32_t)n, >=, 0);
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}
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int
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zrl_tryenter(zrlock_t *zrl)
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{
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uint32_t n = (uint32_t)zrl->zr_refcount;
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if (n == 0) {
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uint32_t cas = atomic_cas_32(
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(uint32_t *)&zrl->zr_refcount, 0, ZRL_LOCKED);
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if (cas == 0) {
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#ifdef ZFS_DEBUG
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ASSERT3P(zrl->zr_owner, ==, NULL);
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zrl->zr_owner = curthread;
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#endif
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return (1);
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}
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}
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ASSERT3S((int32_t)n, >, ZRL_DESTROYED);
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return (0);
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}
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void
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zrl_exit(zrlock_t *zrl)
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{
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ASSERT3S(zrl->zr_refcount, ==, ZRL_LOCKED);
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mutex_enter(&zrl->zr_mtx);
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#ifdef ZFS_DEBUG
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ASSERT3P(zrl->zr_owner, ==, curthread);
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zrl->zr_owner = NULL;
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membar_producer(); /* make sure the owner store happens first */
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#endif
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zrl->zr_refcount = 0;
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cv_broadcast(&zrl->zr_cv);
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mutex_exit(&zrl->zr_mtx);
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}
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int
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zrl_refcount(zrlock_t *zrl)
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{
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ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
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int n = (int)zrl->zr_refcount;
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return (n <= 0 ? 0 : n);
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}
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int
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zrl_is_zero(zrlock_t *zrl)
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{
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ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
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return (zrl->zr_refcount <= 0);
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}
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int
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zrl_is_locked(zrlock_t *zrl)
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{
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ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
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return (zrl->zr_refcount == ZRL_LOCKED);
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}
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#ifdef ZFS_DEBUG
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kthread_t *
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zrl_owner(zrlock_t *zrl)
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{
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return (zrl->zr_owner);
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}
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#endif
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