1 /* 2 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions 6 * are met: 7 * 1. Redistributions of source code must retain the above copyright 8 * notice(s), this list of conditions and the following disclaimer as 9 * the first lines of this file unmodified other than the possible 10 * addition of one or more copyright notices. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice(s), this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 16 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 18 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25 * DAMAGE. 26 * 27 * $FreeBSD$ 28 */ 29 30 /* 31 * Shared/exclusive locks. This implementation assures deterministic lock 32 * granting behavior, so that slocks and xlocks are interleaved. 33 * 34 * Priority propagation will not generally raise the priority of lock holders, 35 * so should not be relied upon in combination with sx locks. 36 */ 37 38 #include <sys/param.h> 39 #include <sys/systm.h> 40 #include <sys/ktr.h> 41 #include <sys/condvar.h> 42 #include <sys/lock.h> 43 #include <sys/mutex.h> 44 #include <sys/sx.h> 45 46 struct lock_class lock_class_sx = { 47 "sx", 48 LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE 49 }; 50 51 void 52 sx_init(struct sx *sx, const char *description) 53 { 54 struct lock_object *lock; 55 56 bzero(sx, sizeof(*sx)); 57 lock = &sx->sx_object; 58 lock->lo_class = &lock_class_sx; 59 lock->lo_name = description; 60 lock->lo_flags = LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE; 61 mtx_init(&sx->sx_lock, "sx backing lock", 62 MTX_DEF | MTX_NOWITNESS | MTX_QUIET); 63 sx->sx_cnt = 0; 64 cv_init(&sx->sx_shrd_cv, description); 65 sx->sx_shrd_wcnt = 0; 66 cv_init(&sx->sx_excl_cv, description); 67 sx->sx_excl_wcnt = 0; 68 sx->sx_xholder = NULL; 69 70 LOCK_LOG_INIT(lock, 0); 71 72 WITNESS_INIT(lock); 73 } 74 75 void 76 sx_destroy(struct sx *sx) 77 { 78 79 LOCK_LOG_DESTROY(&sx->sx_object, 0); 80 81 KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt == 82 0), ("%s (%s): holders or waiters\n", __FUNCTION__, 83 sx->sx_object.lo_name)); 84 85 mtx_destroy(&sx->sx_lock); 86 cv_destroy(&sx->sx_shrd_cv); 87 cv_destroy(&sx->sx_excl_cv); 88 89 WITNESS_DESTROY(&sx->sx_object); 90 } 91 92 void 93 _sx_slock(struct sx *sx, const char *file, int line) 94 { 95 96 mtx_lock(&sx->sx_lock); 97 KASSERT(sx->sx_xholder != curproc, 98 ("%s (%s): trying to get slock while xlock is held\n", __FUNCTION__, 99 sx->sx_object.lo_name)); 100 101 /* 102 * Loop in case we lose the race for lock acquisition. 103 */ 104 while (sx->sx_cnt < 0) { 105 sx->sx_shrd_wcnt++; 106 cv_wait(&sx->sx_shrd_cv, &sx->sx_lock); 107 sx->sx_shrd_wcnt--; 108 } 109 110 /* Acquire a shared lock. */ 111 sx->sx_cnt++; 112 113 LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line); 114 WITNESS_LOCK(&sx->sx_object, 0, file, line); 115 116 mtx_unlock(&sx->sx_lock); 117 } 118 119 void 120 _sx_xlock(struct sx *sx, const char *file, int line) 121 { 122 123 mtx_lock(&sx->sx_lock); 124 125 /* 126 * With sx locks, we're absolutely not permitted to recurse on 127 * xlocks, as it is fatal (deadlock). Normally, recursion is handled 128 * by WITNESS, but as it is not semantically correct to hold the 129 * xlock while in here, we consider it API abuse and put it under 130 * INVARIANTS. 131 */ 132 KASSERT(sx->sx_xholder != curproc, 133 ("%s (%s): xlock already held @ %s:%d", __FUNCTION__, 134 sx->sx_object.lo_name, file, line)); 135 136 /* Loop in case we lose the race for lock acquisition. */ 137 while (sx->sx_cnt != 0) { 138 sx->sx_excl_wcnt++; 139 cv_wait(&sx->sx_excl_cv, &sx->sx_lock); 140 sx->sx_excl_wcnt--; 141 } 142 143 MPASS(sx->sx_cnt == 0); 144 145 /* Acquire an exclusive lock. */ 146 sx->sx_cnt--; 147 sx->sx_xholder = curproc; 148 149 LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line); 150 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 151 152 mtx_unlock(&sx->sx_lock); 153 } 154 155 void 156 _sx_sunlock(struct sx *sx, const char *file, int line) 157 { 158 159 mtx_lock(&sx->sx_lock); 160 _SX_ASSERT_SLOCKED(sx); 161 162 WITNESS_UNLOCK(&sx->sx_object, 0, file, line); 163 164 /* Release. */ 165 sx->sx_cnt--; 166 167 /* 168 * If we just released the last shared lock, wake any waiters up, giving 169 * exclusive lockers precedence. In order to make sure that exclusive 170 * lockers won't be blocked forever, don't wake shared lock waiters if 171 * there are exclusive lock waiters. 172 */ 173 if (sx->sx_excl_wcnt > 0) { 174 if (sx->sx_cnt == 0) 175 cv_signal(&sx->sx_excl_cv); 176 } else if (sx->sx_shrd_wcnt > 0) 177 cv_broadcast(&sx->sx_shrd_cv); 178 179 LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line); 180 181 mtx_unlock(&sx->sx_lock); 182 } 183 184 void 185 _sx_xunlock(struct sx *sx, const char *file, int line) 186 { 187 188 mtx_lock(&sx->sx_lock); 189 _SX_ASSERT_XLOCKED(sx); 190 MPASS(sx->sx_cnt == -1); 191 192 WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 193 194 /* Release. */ 195 sx->sx_cnt++; 196 sx->sx_xholder = NULL; 197 198 /* 199 * Wake up waiters if there are any. Give precedence to slock waiters. 200 */ 201 if (sx->sx_shrd_wcnt > 0) 202 cv_broadcast(&sx->sx_shrd_cv); 203 else if (sx->sx_excl_wcnt > 0) 204 cv_signal(&sx->sx_excl_cv); 205 206 LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line); 207 208 mtx_unlock(&sx->sx_lock); 209 } 210