zrlock.c

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/*
 * 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.
 */

#include <sys/zrlock.h>

/*
 * A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
 * treated as zero references.
 */
#define ZRL_LOCKED      ((uint32_t)-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)
{
        ASSERT(zrl->zr_refcount == 0);

        mutex_destroy(&zrl->zr_mtx);
        zrl->zr_refcount = ZRL_DESTROYED;
        cv_destroy(&zrl->zr_cv);
}

void
#ifdef  ZFS_DEBUG
zrl_add_debug(zrlock_t *zrl, const char *zc)
#else
zrl_add(zrlock_t *zrl)
#endif
{
        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) {
                        ASSERT((int32_t)n >= 0);
#ifdef  ZFS_DEBUG
                        if (zrl->zr_owner == curthread) {
                                DTRACE_PROBE2(zrlock__reentry,
                                    zrlock_t *, zrl, 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);
        }
        ASSERT(zrl->zr_refcount >= 0);
        zrl->zr_refcount++;
#ifdef  ZFS_DEBUG
        zrl->zr_owner = curthread;
        zrl->zr_caller = zc;
#endif
        mutex_exit(&zrl->zr_mtx);
}

void
zrl_remove(zrlock_t *zrl)
{
        uint32_t n;

        n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
        ASSERT((int32_t)n >= 0);
#ifdef  ZFS_DEBUG
        if (zrl->zr_owner == curthread) {
                zrl->zr_owner = NULL;
                zrl->zr_caller = NULL;
        }
#endif
}

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
                        ASSERT(zrl->zr_owner == NULL);
                        zrl->zr_owner = curthread;
#endif
                        return (1);
                }
        }

        ASSERT((int32_t)n > ZRL_DESTROYED);

        return (0);
}

void
zrl_exit(zrlock_t *zrl)
{
        ASSERT(zrl->zr_refcount == ZRL_LOCKED);

        mutex_enter(&zrl->zr_mtx);
#ifdef  ZFS_DEBUG
        ASSERT(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_refcount(zrlock_t *zrl)
{
        ASSERT(zrl->zr_refcount > ZRL_DESTROYED);

        int n = (int)zrl->zr_refcount;
        return (n <= 0 ? 0 : n);
}

int
zrl_is_zero(zrlock_t *zrl)
{
        ASSERT(zrl->zr_refcount > ZRL_DESTROYED);

        return (zrl->zr_refcount <= 0);
}

int
zrl_is_locked(zrlock_t *zrl)
{
        ASSERT(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