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 28 /* 29 * Shared/exclusive locks. This implementation assures deterministic lock 30 * granting behavior, so that slocks and xlocks are interleaved. 31 * 32 * Priority propagation will not generally raise the priority of lock holders, 33 * so should not be relied upon in combination with sx locks. 34 */ 35 36 #include <sys/cdefs.h> 37 __FBSDID("$FreeBSD$"); 38 39 #include "opt_ddb.h" 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/ktr.h> 44 #include <sys/linker_set.h> 45 #include <sys/condvar.h> 46 #include <sys/lock.h> 47 #include <sys/mutex.h> 48 #include <sys/proc.h> 49 #include <sys/sx.h> 50 51 #include <ddb/ddb.h> 52 53 #ifdef DDB 54 static void db_show_sx(struct lock_object *lock); 55 #endif 56 57 struct lock_class lock_class_sx = { 58 "sx", 59 LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 60 #ifdef DDB 61 db_show_sx 62 #endif 63 }; 64 65 #ifndef INVARIANTS 66 #define _sx_assert(sx, what, file, line) 67 #endif 68 69 void 70 sx_sysinit(void *arg) 71 { 72 struct sx_args *sargs = arg; 73 74 sx_init(sargs->sa_sx, sargs->sa_desc); 75 } 76 77 void 78 sx_init(struct sx *sx, const char *description) 79 { 80 81 sx->sx_lock = mtx_pool_find(mtxpool_lockbuilder, sx); 82 sx->sx_cnt = 0; 83 cv_init(&sx->sx_shrd_cv, description); 84 sx->sx_shrd_wcnt = 0; 85 cv_init(&sx->sx_excl_cv, description); 86 sx->sx_excl_wcnt = 0; 87 sx->sx_xholder = NULL; 88 lock_init(&sx->sx_object, &lock_class_sx, description, NULL, 89 LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE); 90 } 91 92 void 93 sx_destroy(struct sx *sx) 94 { 95 96 KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt == 97 0), ("%s (%s): holders or waiters\n", __func__, 98 sx->sx_object.lo_name)); 99 100 sx->sx_lock = NULL; 101 cv_destroy(&sx->sx_shrd_cv); 102 cv_destroy(&sx->sx_excl_cv); 103 104 lock_destroy(&sx->sx_object); 105 } 106 107 void 108 _sx_slock(struct sx *sx, const char *file, int line) 109 { 110 111 mtx_lock(sx->sx_lock); 112 KASSERT(sx->sx_xholder != curthread, 113 ("%s (%s): slock while xlock is held @ %s:%d\n", __func__, 114 sx->sx_object.lo_name, file, line)); 115 WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER, file, line); 116 117 /* 118 * Loop in case we lose the race for lock acquisition. 119 */ 120 while (sx->sx_cnt < 0) { 121 sx->sx_shrd_wcnt++; 122 cv_wait(&sx->sx_shrd_cv, sx->sx_lock); 123 sx->sx_shrd_wcnt--; 124 } 125 126 /* Acquire a shared lock. */ 127 sx->sx_cnt++; 128 129 LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line); 130 WITNESS_LOCK(&sx->sx_object, 0, file, line); 131 curthread->td_locks++; 132 133 mtx_unlock(sx->sx_lock); 134 } 135 136 int 137 _sx_try_slock(struct sx *sx, const char *file, int line) 138 { 139 140 mtx_lock(sx->sx_lock); 141 if (sx->sx_cnt >= 0) { 142 sx->sx_cnt++; 143 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line); 144 WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line); 145 curthread->td_locks++; 146 mtx_unlock(sx->sx_lock); 147 return (1); 148 } else { 149 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line); 150 mtx_unlock(sx->sx_lock); 151 return (0); 152 } 153 } 154 155 void 156 _sx_xlock(struct sx *sx, const char *file, int line) 157 { 158 159 mtx_lock(sx->sx_lock); 160 161 /* 162 * With sx locks, we're absolutely not permitted to recurse on 163 * xlocks, as it is fatal (deadlock). Normally, recursion is handled 164 * by WITNESS, but as it is not semantically correct to hold the 165 * xlock while in here, we consider it API abuse and put it under 166 * INVARIANTS. 167 */ 168 KASSERT(sx->sx_xholder != curthread, 169 ("%s (%s): xlock already held @ %s:%d", __func__, 170 sx->sx_object.lo_name, file, line)); 171 WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 172 line); 173 174 /* Loop in case we lose the race for lock acquisition. */ 175 while (sx->sx_cnt != 0) { 176 sx->sx_excl_wcnt++; 177 cv_wait(&sx->sx_excl_cv, sx->sx_lock); 178 sx->sx_excl_wcnt--; 179 } 180 181 MPASS(sx->sx_cnt == 0); 182 183 /* Acquire an exclusive lock. */ 184 sx->sx_cnt--; 185 sx->sx_xholder = curthread; 186 187 LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line); 188 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 189 curthread->td_locks++; 190 191 mtx_unlock(sx->sx_lock); 192 } 193 194 int 195 _sx_try_xlock(struct sx *sx, const char *file, int line) 196 { 197 198 mtx_lock(sx->sx_lock); 199 if (sx->sx_cnt == 0) { 200 sx->sx_cnt--; 201 sx->sx_xholder = curthread; 202 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line); 203 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file, 204 line); 205 curthread->td_locks++; 206 mtx_unlock(sx->sx_lock); 207 return (1); 208 } else { 209 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line); 210 mtx_unlock(sx->sx_lock); 211 return (0); 212 } 213 } 214 215 void 216 _sx_sunlock(struct sx *sx, const char *file, int line) 217 { 218 219 _sx_assert(sx, SX_SLOCKED, file, line); 220 mtx_lock(sx->sx_lock); 221 222 curthread->td_locks--; 223 WITNESS_UNLOCK(&sx->sx_object, 0, file, line); 224 225 /* Release. */ 226 sx->sx_cnt--; 227 228 /* 229 * If we just released the last shared lock, wake any waiters up, giving 230 * exclusive lockers precedence. In order to make sure that exclusive 231 * lockers won't be blocked forever, don't wake shared lock waiters if 232 * there are exclusive lock waiters. 233 */ 234 if (sx->sx_excl_wcnt > 0) { 235 if (sx->sx_cnt == 0) 236 cv_signal(&sx->sx_excl_cv); 237 } else if (sx->sx_shrd_wcnt > 0) 238 cv_broadcast(&sx->sx_shrd_cv); 239 240 LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line); 241 242 mtx_unlock(sx->sx_lock); 243 } 244 245 void 246 _sx_xunlock(struct sx *sx, const char *file, int line) 247 { 248 249 _sx_assert(sx, SX_XLOCKED, file, line); 250 mtx_lock(sx->sx_lock); 251 MPASS(sx->sx_cnt == -1); 252 253 curthread->td_locks--; 254 WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 255 256 /* Release. */ 257 sx->sx_cnt++; 258 sx->sx_xholder = NULL; 259 260 /* 261 * Wake up waiters if there are any. Give precedence to slock waiters. 262 */ 263 if (sx->sx_shrd_wcnt > 0) 264 cv_broadcast(&sx->sx_shrd_cv); 265 else if (sx->sx_excl_wcnt > 0) 266 cv_signal(&sx->sx_excl_cv); 267 268 LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line); 269 270 mtx_unlock(sx->sx_lock); 271 } 272 273 int 274 _sx_try_upgrade(struct sx *sx, const char *file, int line) 275 { 276 277 _sx_assert(sx, SX_SLOCKED, file, line); 278 mtx_lock(sx->sx_lock); 279 280 if (sx->sx_cnt == 1) { 281 sx->sx_cnt = -1; 282 sx->sx_xholder = curthread; 283 284 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line); 285 WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 286 file, line); 287 288 mtx_unlock(sx->sx_lock); 289 return (1); 290 } else { 291 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line); 292 mtx_unlock(sx->sx_lock); 293 return (0); 294 } 295 } 296 297 void 298 _sx_downgrade(struct sx *sx, const char *file, int line) 299 { 300 301 _sx_assert(sx, SX_XLOCKED, file, line); 302 mtx_lock(sx->sx_lock); 303 MPASS(sx->sx_cnt == -1); 304 305 WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line); 306 307 sx->sx_cnt = 1; 308 sx->sx_xholder = NULL; 309 if (sx->sx_shrd_wcnt > 0) 310 cv_broadcast(&sx->sx_shrd_cv); 311 312 LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line); 313 314 mtx_unlock(sx->sx_lock); 315 } 316 317 #ifdef INVARIANT_SUPPORT 318 #ifndef INVARIANTS 319 #undef _sx_assert 320 #endif 321 322 /* 323 * In the non-WITNESS case, sx_assert() can only detect that at least 324 * *some* thread owns an slock, but it cannot guarantee that *this* 325 * thread owns an slock. 326 */ 327 void 328 _sx_assert(struct sx *sx, int what, const char *file, int line) 329 { 330 331 if (panicstr != NULL) 332 return; 333 switch (what) { 334 case SX_LOCKED: 335 case SX_SLOCKED: 336 #ifdef WITNESS 337 witness_assert(&sx->sx_object, what, file, line); 338 #else 339 mtx_lock(sx->sx_lock); 340 if (sx->sx_cnt <= 0 && 341 (what == SX_SLOCKED || sx->sx_xholder != curthread)) 342 panic("Lock %s not %slocked @ %s:%d\n", 343 sx->sx_object.lo_name, (what == SX_SLOCKED) ? 344 "share " : "", file, line); 345 mtx_unlock(sx->sx_lock); 346 #endif 347 break; 348 case SX_XLOCKED: 349 mtx_lock(sx->sx_lock); 350 if (sx->sx_xholder != curthread) 351 panic("Lock %s not exclusively locked @ %s:%d\n", 352 sx->sx_object.lo_name, file, line); 353 mtx_unlock(sx->sx_lock); 354 break; 355 case SX_UNLOCKED: 356 #ifdef WITNESS 357 witness_assert(&sx->sx_object, what, file, line); 358 #else 359 /* 360 * We are able to check only exclusive lock here, 361 * we cannot assert that *this* thread owns slock. 362 */ 363 mtx_lock(sx->sx_lock); 364 if (sx->sx_xholder == curthread) 365 panic("Lock %s exclusively locked @ %s:%d\n", 366 sx->sx_object.lo_name, file, line); 367 mtx_unlock(sx->sx_lock); 368 #endif 369 break; 370 default: 371 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 372 line); 373 } 374 } 375 #endif /* INVARIANT_SUPPORT */ 376 377 #ifdef DDB 378 void 379 db_show_sx(struct lock_object *lock) 380 { 381 struct thread *td; 382 struct sx *sx; 383 384 sx = (struct sx *)lock; 385 386 db_printf(" state: "); 387 if (sx->sx_cnt < 0) { 388 td = sx->sx_xholder; 389 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 390 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 391 } else if (sx->sx_cnt > 0) 392 db_printf("SLOCK: %d locks\n", sx->sx_cnt); 393 else 394 db_printf("UNLOCKED\n"); 395 db_printf(" waiters: %d shared, %d exclusive\n", sx->sx_shrd_wcnt, 396 sx->sx_excl_wcnt); 397 } 398 #endif 399