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); 131 132 mtx_unlock(sx->sx_lock); 133 } 134 135 int 136 _sx_try_slock(struct sx *sx, const char *file, int line) 137 { 138 139 mtx_lock(sx->sx_lock); 140 if (sx->sx_cnt >= 0) { 141 sx->sx_cnt++; 142 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line); 143 WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line); 144 mtx_unlock(sx->sx_lock); 145 return (1); 146 } else { 147 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line); 148 mtx_unlock(sx->sx_lock); 149 return (0); 150 } 151 } 152 153 void 154 _sx_xlock(struct sx *sx, const char *file, int line) 155 { 156 157 mtx_lock(sx->sx_lock); 158 159 /* 160 * With sx locks, we're absolutely not permitted to recurse on 161 * xlocks, as it is fatal (deadlock). Normally, recursion is handled 162 * by WITNESS, but as it is not semantically correct to hold the 163 * xlock while in here, we consider it API abuse and put it under 164 * INVARIANTS. 165 */ 166 KASSERT(sx->sx_xholder != curthread, 167 ("%s (%s): xlock already held @ %s:%d", __func__, 168 sx->sx_object.lo_name, file, line)); 169 WITNESS_CHECKORDER(&sx->sx_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 170 line); 171 172 /* Loop in case we lose the race for lock acquisition. */ 173 while (sx->sx_cnt != 0) { 174 sx->sx_excl_wcnt++; 175 cv_wait(&sx->sx_excl_cv, sx->sx_lock); 176 sx->sx_excl_wcnt--; 177 } 178 179 MPASS(sx->sx_cnt == 0); 180 181 /* Acquire an exclusive lock. */ 182 sx->sx_cnt--; 183 sx->sx_xholder = curthread; 184 185 LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line); 186 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 187 188 mtx_unlock(sx->sx_lock); 189 } 190 191 int 192 _sx_try_xlock(struct sx *sx, const char *file, int line) 193 { 194 195 mtx_lock(sx->sx_lock); 196 if (sx->sx_cnt == 0) { 197 sx->sx_cnt--; 198 sx->sx_xholder = curthread; 199 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line); 200 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file, 201 line); 202 mtx_unlock(sx->sx_lock); 203 return (1); 204 } else { 205 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line); 206 mtx_unlock(sx->sx_lock); 207 return (0); 208 } 209 } 210 211 void 212 _sx_sunlock(struct sx *sx, const char *file, int line) 213 { 214 215 _sx_assert(sx, SX_SLOCKED, file, line); 216 mtx_lock(sx->sx_lock); 217 218 WITNESS_UNLOCK(&sx->sx_object, 0, file, line); 219 220 /* Release. */ 221 sx->sx_cnt--; 222 223 /* 224 * If we just released the last shared lock, wake any waiters up, giving 225 * exclusive lockers precedence. In order to make sure that exclusive 226 * lockers won't be blocked forever, don't wake shared lock waiters if 227 * there are exclusive lock waiters. 228 */ 229 if (sx->sx_excl_wcnt > 0) { 230 if (sx->sx_cnt == 0) 231 cv_signal(&sx->sx_excl_cv); 232 } else if (sx->sx_shrd_wcnt > 0) 233 cv_broadcast(&sx->sx_shrd_cv); 234 235 LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line); 236 237 mtx_unlock(sx->sx_lock); 238 } 239 240 void 241 _sx_xunlock(struct sx *sx, const char *file, int line) 242 { 243 244 _sx_assert(sx, SX_XLOCKED, file, line); 245 mtx_lock(sx->sx_lock); 246 MPASS(sx->sx_cnt == -1); 247 248 WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line); 249 250 /* Release. */ 251 sx->sx_cnt++; 252 sx->sx_xholder = NULL; 253 254 /* 255 * Wake up waiters if there are any. Give precedence to slock waiters. 256 */ 257 if (sx->sx_shrd_wcnt > 0) 258 cv_broadcast(&sx->sx_shrd_cv); 259 else if (sx->sx_excl_wcnt > 0) 260 cv_signal(&sx->sx_excl_cv); 261 262 LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line); 263 264 mtx_unlock(sx->sx_lock); 265 } 266 267 int 268 _sx_try_upgrade(struct sx *sx, const char *file, int line) 269 { 270 271 _sx_assert(sx, SX_SLOCKED, file, line); 272 mtx_lock(sx->sx_lock); 273 274 if (sx->sx_cnt == 1) { 275 sx->sx_cnt = -1; 276 sx->sx_xholder = curthread; 277 278 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line); 279 WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 280 file, line); 281 282 mtx_unlock(sx->sx_lock); 283 return (1); 284 } else { 285 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line); 286 mtx_unlock(sx->sx_lock); 287 return (0); 288 } 289 } 290 291 void 292 _sx_downgrade(struct sx *sx, const char *file, int line) 293 { 294 295 _sx_assert(sx, SX_XLOCKED, file, line); 296 mtx_lock(sx->sx_lock); 297 MPASS(sx->sx_cnt == -1); 298 299 WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line); 300 301 sx->sx_cnt = 1; 302 sx->sx_xholder = NULL; 303 if (sx->sx_shrd_wcnt > 0) 304 cv_broadcast(&sx->sx_shrd_cv); 305 306 LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line); 307 308 mtx_unlock(sx->sx_lock); 309 } 310 311 #ifdef INVARIANT_SUPPORT 312 #ifndef INVARIANTS 313 #undef _sx_assert 314 #endif 315 316 /* 317 * In the non-WITNESS case, sx_assert() can only detect that at least 318 * *some* thread owns an slock, but it cannot guarantee that *this* 319 * thread owns an slock. 320 */ 321 void 322 _sx_assert(struct sx *sx, int what, const char *file, int line) 323 { 324 325 if (panicstr != NULL) 326 return; 327 switch (what) { 328 case SX_LOCKED: 329 case SX_SLOCKED: 330 #ifdef WITNESS 331 witness_assert(&sx->sx_object, what, file, line); 332 #else 333 mtx_lock(sx->sx_lock); 334 if (sx->sx_cnt <= 0 && 335 (what == SX_SLOCKED || sx->sx_xholder != curthread)) 336 panic("Lock %s not %slocked @ %s:%d\n", 337 sx->sx_object.lo_name, (what == SX_SLOCKED) ? 338 "share " : "", file, line); 339 mtx_unlock(sx->sx_lock); 340 #endif 341 break; 342 case SX_XLOCKED: 343 mtx_lock(sx->sx_lock); 344 if (sx->sx_xholder != curthread) 345 panic("Lock %s not exclusively locked @ %s:%d\n", 346 sx->sx_object.lo_name, file, line); 347 mtx_unlock(sx->sx_lock); 348 break; 349 case SX_UNLOCKED: 350 #ifdef WITNESS 351 witness_assert(&sx->sx_object, what, file, line); 352 #else 353 /* 354 * We are able to check only exclusive lock here, 355 * we cannot assert that *this* thread owns slock. 356 */ 357 mtx_lock(sx->sx_lock); 358 if (sx->sx_xholder == curthread) 359 panic("Lock %s exclusively locked @ %s:%d\n", 360 sx->sx_object.lo_name, file, line); 361 mtx_unlock(sx->sx_lock); 362 #endif 363 break; 364 default: 365 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 366 line); 367 } 368 } 369 #endif /* INVARIANT_SUPPORT */ 370 371 #ifdef DDB 372 void 373 db_show_sx(struct lock_object *lock) 374 { 375 struct thread *td; 376 struct sx *sx; 377 378 sx = (struct sx *)lock; 379 380 db_printf(" state: "); 381 if (sx->sx_cnt < 0) { 382 td = sx->sx_xholder; 383 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 384 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 385 } else if (sx->sx_cnt > 0) 386 db_printf("SLOCK: %d locks\n", sx->sx_cnt); 387 else 388 db_printf("UNLOCKED\n"); 389 db_printf(" waiters: %d shared, %d exclusive\n", sx->sx_shrd_wcnt, 390 sx->sx_excl_wcnt); 391 } 392 #endif 393