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Diffstat (limited to 'module/zfs/zrlock.c')
| -rw-r--r-- | module/zfs/zrlock.c | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/module/zfs/zrlock.c b/module/zfs/zrlock.c new file mode 100644 index 000000000..ec94b0855 --- /dev/null +++ b/module/zfs/zrlock.c @@ -0,0 +1,194 @@ +/* + * 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. + */ + +/* + * 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> + +/* + * 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 |