197 lines
4.6 KiB
C
197 lines
4.6 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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#include <sys/trace_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_PROBE3(zrlock__reentry,
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zrlock_t *, zrl,
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kthread_t *, curthread,
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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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#if defined(_KERNEL)
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EXPORT_SYMBOL(zrl_add_impl);
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EXPORT_SYMBOL(zrl_remove);
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#endif
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