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 | LC_UPGRADABLE 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 LO_UPGRADABLE; 62 mtx_init(&sx->sx_lock, "sx backing lock", 63 MTX_DEF | MTX_NOWITNESS | MTX_QUIET); 64 sx->sx_cnt = 0; 65 cv_init(&sx->sx_shrd_cv, description); 66 sx->sx_shrd_wcnt = 0; 67 cv_init(&sx->sx_excl_cv, description); 68 sx->sx_excl_wcnt = 0; 69 sx->sx_xholder = NULL; 70 71 LOCK_LOG_INIT(lock, 0); 72 73 WITNESS_INIT(lock); 74 } 75 76 void 77 sx_destroy(struct sx *sx) 78 { 79 80 LOCK_LOG_DESTROY(&sx->sx_object, 0); 81 82 KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt == 83 0), ("%s (%s): holders or waiters\n", __FUNCTION__, 84 sx->sx_object.lo_name)); 85 86 mtx_destroy(&sx->sx_lock); 87 cv_destroy(&sx->sx_shrd_cv); 88 cv_destroy(&sx->sx_excl_cv); 89 90 WITNESS_DESTROY(&sx->sx_object); 91 } 92 93 void 94 _sx_slock(struct sx *sx, const char *file, int line) 95 { 96 97 mtx_lock(&sx->sx_lock); 98 KASSERT(sx->sx_xholder != curthread, 99 ("%s (%s): slock while xlock is held @ %s:%d\n", __FUNCTION__, 100 sx->sx_object.lo_name, file, line)); 101 102 /* 103 * Loop in case we lose the race for lock acquisition. 104 */ 105 while (sx->sx_cnt < 0) { 106 sx->sx_shrd_wcnt++; 107 cv_wait(&sx->sx_shrd_cv, &sx->sx_lock); 108 sx->sx_shrd_wcnt--; 109 } 110 111 /* Acquire a shared lock. */ 112 sx->sx_cnt++; 113 114 LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line); 115 WITNESS_LOCK(&sx->sx_object, 0, file, line); 116 117 mtx_unlock(&sx->sx_lock); 118 } 119 120 int 121 _sx_try_slock(struct sx *sx, const char *file, int line) 122 { 123 124 mtx_lock(&sx->sx_lock); 125 if (sx->sx_cnt >= 0) { 126 sx->sx_cnt++; 127 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line); 128 WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line); 129 mtx_unlock(&sx->sx_lock); 130 return (1); 131 } else { 132 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line); 133 mtx_unlock(&sx->sx_lock); 134 return (0); 135 } 136 } 137 138 void 139 _sx_xlock(struct sx *sx, const char *file, int line) 140 { 141 142 mtx_lock(&sx->sx_lock); 143 144 /* 145 * With sx locks, we're absolutely not permitted to recurse on 146 * xlocks, as it is fatal (deadlock). Normally, recursion is handled 147 * by WITNESS, but as it is not semantically correct to hold the 148 * xlock while in here, we consider it API abuse and put it under 149 * INVARIANTS. 150 */ 151 KASSERT(sx->sx_xholder != curthread, 152 ("%s (%s): xlock already held @ %s:%d", __FUNCTION__, 153 sx->sx_object.lo_name, file, line)); 154 155 /* Loop in case we lose the race for lock acquisition. */ 156 while (sx->sx_cnt != 0) { 157 sx->sx_excl_wcnt++; 158 cv_wait(&sx->sx_excl_cv, &sx->sx_lock); 159 sx->sx_excl_wcnt--; 160 } 161 162 MPASS(sx->sx_cnt == 0); 163 164 /* Acquire an exclusive lock. */ 165 sx->sx_cnt--; 166 sx->sx_xholder = curthread; 167 168 LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line); 169 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 170 171 mtx_unlock(&sx->sx_lock); 172 } 173 174 int 175 _sx_try_xlock(struct sx *sx, const char *file, int line) 176 { 177 178 mtx_lock(&sx->sx_lock); 179 if (sx->sx_cnt == 0) { 180 sx->sx_cnt--; 181 sx->sx_xholder = curthread; 182 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line); 183 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file, 184 line); 185 mtx_unlock(&sx->sx_lock); 186 return (1); 187 } else { 188 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line); 189 mtx_unlock(&sx->sx_lock); 190 return (0); 191 } 192 } 193 194 void 195 _sx_sunlock(struct sx *sx, const char *file, int line) 196 { 197 198 mtx_lock(&sx->sx_lock); 199 _SX_ASSERT_SLOCKED(sx, file, line); 200 201 WITNESS_UNLOCK(&sx->sx_object, 0, file, line); 202 203 /* Release. */ 204 sx->sx_cnt--; 205 206 /* 207 * If we just released the last shared lock, wake any waiters up, giving 208 * exclusive lockers precedence. In order to make sure that exclusive 209 * lockers won't be blocked forever, don't wake shared lock waiters if 210 * there are exclusive lock waiters. 211 */ 212 if (sx->sx_excl_wcnt > 0) { 213 if (sx->sx_cnt == 0) 214 cv_signal(&sx->sx_excl_cv); 215 } else if (sx->sx_shrd_wcnt > 0) 216 cv_broadcast(&sx->sx_shrd_cv); 217 218 LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line); 219 220 mtx_unlock(&sx->sx_lock); 221 } 222 223 void 224 _sx_xunlock(struct sx *sx, const char *file, int line) 225 { 226 227 mtx_lock(&sx->sx_lock); 228 _SX_ASSERT_XLOCKED(sx, file, line); 229 MPASS(sx->sx_cnt == -1); 230 231 WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 232 233 /* Release. */ 234 sx->sx_cnt++; 235 sx->sx_xholder = NULL; 236 237 /* 238 * Wake up waiters if there are any. Give precedence to slock waiters. 239 */ 240 if (sx->sx_shrd_wcnt > 0) 241 cv_broadcast(&sx->sx_shrd_cv); 242 else if (sx->sx_excl_wcnt > 0) 243 cv_signal(&sx->sx_excl_cv); 244 245 LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line); 246 247 mtx_unlock(&sx->sx_lock); 248 } 249 250 int 251 _sx_try_upgrade(struct sx *sx, const char *file, int line) 252 { 253 254 mtx_lock(&sx->sx_lock); 255 _SX_ASSERT_SLOCKED(sx, file, line); 256 257 if (sx->sx_cnt == 1) { 258 sx->sx_cnt = -1; 259 sx->sx_xholder = curthread; 260 261 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line); 262 WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 263 file, line); 264 265 mtx_unlock(&sx->sx_lock); 266 return (1); 267 } else { 268 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line); 269 mtx_unlock(&sx->sx_lock); 270 return (0); 271 } 272 } 273 274 void 275 _sx_downgrade(struct sx *sx, const char *file, int line) 276 { 277 278 mtx_lock(&sx->sx_lock); 279 _SX_ASSERT_XLOCKED(sx, file, line); 280 MPASS(sx->sx_cnt == -1); 281 282 WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line); 283 284 sx->sx_cnt = 1; 285 sx->sx_xholder = NULL; 286 if (sx->sx_shrd_wcnt > 0) 287 cv_broadcast(&sx->sx_shrd_cv); 288 289 LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line); 290 291 mtx_unlock(&sx->sx_lock); 292 } 293