188 lines
4.5 KiB
C
188 lines
4.5 KiB
C
/*
|
|
* CDDL HEADER START
|
|
*
|
|
* The contents of this file are subject to the terms of the
|
|
* Common Development and Distribution License (the "License").
|
|
* You may not use this file except in compliance with the License.
|
|
*
|
|
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
|
|
* or http://www.opensolaris.org/os/licensing.
|
|
* See the License for the specific language governing permissions
|
|
* and limitations under the License.
|
|
*
|
|
* When distributing Covered Code, include this CDDL HEADER in each
|
|
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
|
|
* If applicable, add the following below this CDDL HEADER, with the
|
|
* fields enclosed by brackets "[]" replaced with your own identifying
|
|
* information: Portions Copyright [yyyy] [name of copyright owner]
|
|
*
|
|
* CDDL HEADER END
|
|
*/
|
|
/*
|
|
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
|
|
* Copyright (c) 2014, 2015 by Delphix. All rights reserved.
|
|
* Copyright 2016 The MathWorks, Inc. All rights reserved.
|
|
*/
|
|
|
|
/*
|
|
* A Zero Reference Lock (ZRL) is a reference count that can lock out new
|
|
* references only when the count is zero and only without waiting if the count
|
|
* is not already zero. It is similar to a read-write lock in that it allows
|
|
* multiple readers and only a single writer, but it does not allow a writer to
|
|
* block while waiting for readers to exit, and therefore the question of
|
|
* reader/writer priority is moot (no WRWANT bit). Since the equivalent of
|
|
* rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
|
|
* is perfectly safe for the same reader to acquire the same lock multiple
|
|
* times. The fact that a ZRL is reentrant for readers (through multiple calls
|
|
* to zrl_add()) makes it convenient for determining whether something is
|
|
* actively referenced without the fuss of flagging lock ownership across
|
|
* function calls.
|
|
*/
|
|
#include <sys/zrlock.h>
|
|
#include <sys/trace_zfs.h>
|
|
|
|
/*
|
|
* A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
|
|
* treated as zero references.
|
|
*/
|
|
#define ZRL_LOCKED -1
|
|
#define ZRL_DESTROYED -2
|
|
|
|
void
|
|
zrl_init(zrlock_t *zrl)
|
|
{
|
|
mutex_init(&zrl->zr_mtx, NULL, MUTEX_DEFAULT, NULL);
|
|
zrl->zr_refcount = 0;
|
|
cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
|
|
#ifdef ZFS_DEBUG
|
|
zrl->zr_owner = NULL;
|
|
zrl->zr_caller = NULL;
|
|
#endif
|
|
}
|
|
|
|
void
|
|
zrl_destroy(zrlock_t *zrl)
|
|
{
|
|
ASSERT0(zrl->zr_refcount);
|
|
|
|
mutex_destroy(&zrl->zr_mtx);
|
|
zrl->zr_refcount = ZRL_DESTROYED;
|
|
cv_destroy(&zrl->zr_cv);
|
|
}
|
|
|
|
void
|
|
zrl_add_impl(zrlock_t *zrl, const char *zc)
|
|
{
|
|
for (;;) {
|
|
uint32_t n = (uint32_t)zrl->zr_refcount;
|
|
while (n != ZRL_LOCKED) {
|
|
uint32_t cas = atomic_cas_32(
|
|
(uint32_t *)&zrl->zr_refcount, n, n + 1);
|
|
if (cas == n) {
|
|
ASSERT3S((int32_t)n, >=, 0);
|
|
#ifdef ZFS_DEBUG
|
|
if (zrl->zr_owner == curthread) {
|
|
DTRACE_PROBE3(zrlock__reentry,
|
|
zrlock_t *, zrl,
|
|
kthread_t *, curthread,
|
|
uint32_t, n);
|
|
}
|
|
zrl->zr_owner = curthread;
|
|
zrl->zr_caller = zc;
|
|
#endif
|
|
return;
|
|
}
|
|
n = cas;
|
|
}
|
|
|
|
mutex_enter(&zrl->zr_mtx);
|
|
while (zrl->zr_refcount == ZRL_LOCKED) {
|
|
cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
|
|
}
|
|
mutex_exit(&zrl->zr_mtx);
|
|
}
|
|
}
|
|
|
|
void
|
|
zrl_remove(zrlock_t *zrl)
|
|
{
|
|
uint32_t n;
|
|
|
|
#ifdef ZFS_DEBUG
|
|
if (zrl->zr_owner == curthread) {
|
|
zrl->zr_owner = NULL;
|
|
zrl->zr_caller = NULL;
|
|
}
|
|
#endif
|
|
n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
|
|
ASSERT3S((int32_t)n, >=, 0);
|
|
}
|
|
|
|
int
|
|
zrl_tryenter(zrlock_t *zrl)
|
|
{
|
|
uint32_t n = (uint32_t)zrl->zr_refcount;
|
|
|
|
if (n == 0) {
|
|
uint32_t cas = atomic_cas_32(
|
|
(uint32_t *)&zrl->zr_refcount, 0, ZRL_LOCKED);
|
|
if (cas == 0) {
|
|
#ifdef ZFS_DEBUG
|
|
ASSERT3P(zrl->zr_owner, ==, NULL);
|
|
zrl->zr_owner = curthread;
|
|
#endif
|
|
return (1);
|
|
}
|
|
}
|
|
|
|
ASSERT3S((int32_t)n, >, ZRL_DESTROYED);
|
|
|
|
return (0);
|
|
}
|
|
|
|
void
|
|
zrl_exit(zrlock_t *zrl)
|
|
{
|
|
ASSERT3S(zrl->zr_refcount, ==, ZRL_LOCKED);
|
|
|
|
mutex_enter(&zrl->zr_mtx);
|
|
#ifdef ZFS_DEBUG
|
|
ASSERT3P(zrl->zr_owner, ==, curthread);
|
|
zrl->zr_owner = NULL;
|
|
membar_producer(); /* make sure the owner store happens first */
|
|
#endif
|
|
zrl->zr_refcount = 0;
|
|
cv_broadcast(&zrl->zr_cv);
|
|
mutex_exit(&zrl->zr_mtx);
|
|
}
|
|
|
|
int
|
|
zrl_is_zero(zrlock_t *zrl)
|
|
{
|
|
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
|
|
|
|
return (zrl->zr_refcount <= 0);
|
|
}
|
|
|
|
int
|
|
zrl_is_locked(zrlock_t *zrl)
|
|
{
|
|
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
|
|
|
|
return (zrl->zr_refcount == ZRL_LOCKED);
|
|
}
|
|
|
|
#ifdef ZFS_DEBUG
|
|
kthread_t *
|
|
zrl_owner(zrlock_t *zrl)
|
|
{
|
|
return (zrl->zr_owner);
|
|
}
|
|
#endif
|
|
|
|
#if defined(_KERNEL)
|
|
|
|
EXPORT_SYMBOL(zrl_add_impl);
|
|
EXPORT_SYMBOL(zrl_remove);
|
|
|
|
#endif
|