| /* |
| * 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_zrlock.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_refcount(zrlock_t *zrl) |
| { |
| ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED); |
| |
| int n = (int)zrl->zr_refcount; |
| return (n <= 0 ? 0 : n); |
| } |
| |
| 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 |