1219089Spjd/* 2219089Spjd * CDDL HEADER START 3219089Spjd * 4219089Spjd * The contents of this file are subject to the terms of the 5219089Spjd * Common Development and Distribution License (the "License"). 6219089Spjd * You may not use this file except in compliance with the License. 7219089Spjd * 8219089Spjd * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9219089Spjd * or http://www.opensolaris.org/os/licensing. 10219089Spjd * See the License for the specific language governing permissions 11219089Spjd * and limitations under the License. 12219089Spjd * 13219089Spjd * When distributing Covered Code, include this CDDL HEADER in each 14219089Spjd * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15219089Spjd * If applicable, add the following below this CDDL HEADER, with the 16219089Spjd * fields enclosed by brackets "[]" replaced with your own identifying 17219089Spjd * information: Portions Copyright [yyyy] [name of copyright owner] 18219089Spjd * 19219089Spjd * CDDL HEADER END 20219089Spjd */ 21219089Spjd/* 22219089Spjd * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved. 23290765Smav * Copyright (c) 2014, 2015 by Delphix. All rights reserved. 24308246Savg * Copyright 2016 The MathWorks, Inc. All rights reserved. 25219089Spjd */ 26219089Spjd 27219089Spjd/* 28219089Spjd * A Zero Reference Lock (ZRL) is a reference count that can lock out new 29219089Spjd * references only when the count is zero and only without waiting if the count 30219089Spjd * is not already zero. It is similar to a read-write lock in that it allows 31219089Spjd * multiple readers and only a single writer, but it does not allow a writer to 32219089Spjd * block while waiting for readers to exit, and therefore the question of 33219089Spjd * reader/writer priority is moot (no WRWANT bit). Since the equivalent of 34219089Spjd * rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it 35219089Spjd * is perfectly safe for the same reader to acquire the same lock multiple 36219089Spjd * times. The fact that a ZRL is reentrant for readers (through multiple calls 37219089Spjd * to zrl_add()) makes it convenient for determining whether something is 38219089Spjd * actively referenced without the fuss of flagging lock ownership across 39219089Spjd * function calls. 40219089Spjd */ 41219089Spjd#include <sys/zrlock.h> 42219089Spjd 43219089Spjd/* 44219089Spjd * A ZRL can be locked only while there are zero references, so ZRL_LOCKED is 45219089Spjd * treated as zero references. 46219089Spjd */ 47288560Smav#define ZRL_LOCKED -1 48219089Spjd#define ZRL_DESTROYED -2 49219089Spjd 50219089Spjdvoid 51219089Spjdzrl_init(zrlock_t *zrl) 52219089Spjd{ 53219089Spjd mutex_init(&zrl->zr_mtx, NULL, MUTEX_DEFAULT, NULL); 54219089Spjd zrl->zr_refcount = 0; 55219089Spjd cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL); 56219089Spjd#ifdef ZFS_DEBUG 57219089Spjd zrl->zr_owner = NULL; 58219089Spjd zrl->zr_caller = NULL; 59219089Spjd#endif 60219089Spjd} 61219089Spjd 62219089Spjdvoid 63219089Spjdzrl_destroy(zrlock_t *zrl) 64219089Spjd{ 65288560Smav ASSERT0(zrl->zr_refcount); 66219089Spjd 67219089Spjd mutex_destroy(&zrl->zr_mtx); 68219089Spjd zrl->zr_refcount = ZRL_DESTROYED; 69219089Spjd cv_destroy(&zrl->zr_cv); 70219089Spjd} 71219089Spjd 72219089Spjdvoid 73290765Smavzrl_add_impl(zrlock_t *zrl, const char *zc) 74219089Spjd{ 75308246Savg for (;;) { 76308246Savg uint32_t n = (uint32_t)zrl->zr_refcount; 77308246Savg while (n != ZRL_LOCKED) { 78308246Savg uint32_t cas = atomic_cas_32( 79308246Savg (uint32_t *)&zrl->zr_refcount, n, n + 1); 80308246Savg if (cas == n) { 81308246Savg ASSERT3S((int32_t)n, >=, 0); 82219089Spjd#ifdef ZFS_DEBUG 83308246Savg if (zrl->zr_owner == curthread) { 84308246Savg DTRACE_PROBE2(zrlock__reentry, 85308246Savg zrlock_t *, zrl, uint32_t, n); 86308246Savg } 87308246Savg zrl->zr_owner = curthread; 88308246Savg zrl->zr_caller = zc; 89308246Savg#endif 90308246Savg return; 91219089Spjd } 92308246Savg n = cas; 93219089Spjd } 94219089Spjd 95308246Savg mutex_enter(&zrl->zr_mtx); 96308246Savg while (zrl->zr_refcount == ZRL_LOCKED) { 97308246Savg cv_wait(&zrl->zr_cv, &zrl->zr_mtx); 98308246Savg } 99308246Savg mutex_exit(&zrl->zr_mtx); 100219089Spjd } 101219089Spjd} 102219089Spjd 103219089Spjdvoid 104219089Spjdzrl_remove(zrlock_t *zrl) 105219089Spjd{ 106219089Spjd uint32_t n; 107219089Spjd 108219089Spjd#ifdef ZFS_DEBUG 109219089Spjd if (zrl->zr_owner == curthread) { 110219089Spjd zrl->zr_owner = NULL; 111219089Spjd zrl->zr_caller = NULL; 112219089Spjd } 113219089Spjd#endif 114288560Smav n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount); 115288560Smav ASSERT3S((int32_t)n, >=, 0); 116219089Spjd} 117219089Spjd 118219089Spjdint 119219089Spjdzrl_tryenter(zrlock_t *zrl) 120219089Spjd{ 121219089Spjd uint32_t n = (uint32_t)zrl->zr_refcount; 122219089Spjd 123219089Spjd if (n == 0) { 124219089Spjd uint32_t cas = atomic_cas_32( 125219089Spjd (uint32_t *)&zrl->zr_refcount, 0, ZRL_LOCKED); 126219089Spjd if (cas == 0) { 127219089Spjd#ifdef ZFS_DEBUG 128288560Smav ASSERT3P(zrl->zr_owner, ==, NULL); 129219089Spjd zrl->zr_owner = curthread; 130219089Spjd#endif 131219089Spjd return (1); 132219089Spjd } 133219089Spjd } 134219089Spjd 135288560Smav ASSERT3S((int32_t)n, >, ZRL_DESTROYED); 136219089Spjd 137219089Spjd return (0); 138219089Spjd} 139219089Spjd 140219089Spjdvoid 141219089Spjdzrl_exit(zrlock_t *zrl) 142219089Spjd{ 143288560Smav ASSERT3S(zrl->zr_refcount, ==, ZRL_LOCKED); 144219089Spjd 145219089Spjd mutex_enter(&zrl->zr_mtx); 146219089Spjd#ifdef ZFS_DEBUG 147288560Smav ASSERT3P(zrl->zr_owner, ==, curthread); 148219089Spjd zrl->zr_owner = NULL; 149219089Spjd membar_producer(); /* make sure the owner store happens first */ 150219089Spjd#endif 151219089Spjd zrl->zr_refcount = 0; 152219089Spjd cv_broadcast(&zrl->zr_cv); 153219089Spjd mutex_exit(&zrl->zr_mtx); 154219089Spjd} 155219089Spjd 156219089Spjdint 157219089Spjdzrl_refcount(zrlock_t *zrl) 158219089Spjd{ 159288560Smav ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED); 160219089Spjd 161219089Spjd int n = (int)zrl->zr_refcount; 162219089Spjd return (n <= 0 ? 0 : n); 163219089Spjd} 164219089Spjd 165219089Spjdint 166219089Spjdzrl_is_zero(zrlock_t *zrl) 167219089Spjd{ 168288560Smav ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED); 169219089Spjd 170219089Spjd return (zrl->zr_refcount <= 0); 171219089Spjd} 172219089Spjd 173219089Spjdint 174219089Spjdzrl_is_locked(zrlock_t *zrl) 175219089Spjd{ 176288560Smav ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED); 177219089Spjd 178219089Spjd return (zrl->zr_refcount == ZRL_LOCKED); 179219089Spjd} 180219089Spjd 181219089Spjd#ifdef ZFS_DEBUG 182219089Spjdkthread_t * 183219089Spjdzrl_owner(zrlock_t *zrl) 184219089Spjd{ 185219089Spjd return (zrl->zr_owner); 186219089Spjd} 187219089Spjd#endif 188