Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/kern/kern_rwlock.c
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1 /*- 2 * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 /* 28 * Machine independent bits of reader/writer lock implementation. 29 */ 30 31 #include <sys/cdefs.h> 32 __FBSDID("$FreeBSD: releng/10.4/sys/kern/kern_rwlock.c 323872 2017-09-21 20:13:03Z marius $"); 33 34 #include "opt_ddb.h" 35 #include "opt_hwpmc_hooks.h" 36 #include "opt_kdtrace.h" 37 #include "opt_no_adaptive_rwlocks.h" 38 39 #include <sys/param.h> 40 #include <sys/kdb.h> 41 #include <sys/ktr.h> 42 #include <sys/kernel.h> 43 #include <sys/lock.h> 44 #include <sys/mutex.h> 45 #include <sys/proc.h> 46 #include <sys/rwlock.h> 47 #include <sys/sched.h> 48 #include <sys/smp.h> 49 #include <sys/sysctl.h> 50 #include <sys/systm.h> 51 #include <sys/turnstile.h> 52 53 #include <machine/cpu.h> 54 55 #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS) 56 #define ADAPTIVE_RWLOCKS 57 #endif 58 59 #ifdef HWPMC_HOOKS 60 #include <sys/pmckern.h> 61 PMC_SOFT_DECLARE( , , lock, failed); 62 #endif 63 64 /* 65 * Return the rwlock address when the lock cookie address is provided. 66 * This functionality assumes that struct rwlock* have a member named rw_lock. 67 */ 68 #define rwlock2rw(c) (__containerof(c, struct rwlock, rw_lock)) 69 70 #ifdef DDB 71 #include <ddb/ddb.h> 72 73 static void db_show_rwlock(const struct lock_object *lock); 74 #endif 75 static void assert_rw(const struct lock_object *lock, int what); 76 static void lock_rw(struct lock_object *lock, uintptr_t how); 77 #ifdef KDTRACE_HOOKS 78 static int owner_rw(const struct lock_object *lock, struct thread **owner); 79 #endif 80 static uintptr_t unlock_rw(struct lock_object *lock); 81 82 struct lock_class lock_class_rw = { 83 .lc_name = "rw", 84 .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE, 85 .lc_assert = assert_rw, 86 #ifdef DDB 87 .lc_ddb_show = db_show_rwlock, 88 #endif 89 .lc_lock = lock_rw, 90 .lc_unlock = unlock_rw, 91 #ifdef KDTRACE_HOOKS 92 .lc_owner = owner_rw, 93 #endif 94 }; 95 96 #ifdef ADAPTIVE_RWLOCKS 97 static int rowner_retries = 10; 98 static int rowner_loops = 10000; 99 static SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL, 100 "rwlock debugging"); 101 SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, ""); 102 SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, ""); 103 104 static struct lock_delay_config rw_delay = { 105 .initial = 1000, 106 .step = 500, 107 .min = 100, 108 .max = 5000, 109 }; 110 111 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_initial, CTLFLAG_RW, &rw_delay.initial, 112 0, ""); 113 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_step, CTLFLAG_RW, &rw_delay.step, 114 0, ""); 115 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_min, CTLFLAG_RW, &rw_delay.min, 116 0, ""); 117 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max, 118 0, ""); 119 120 static void 121 rw_delay_sysinit(void *dummy) 122 { 123 124 rw_delay.initial = mp_ncpus * 25; 125 rw_delay.step = (mp_ncpus * 25) / 2; 126 rw_delay.min = mp_ncpus * 5; 127 rw_delay.max = mp_ncpus * 25 * 10; 128 } 129 LOCK_DELAY_SYSINIT(rw_delay_sysinit); 130 #endif 131 132 /* 133 * Return a pointer to the owning thread if the lock is write-locked or 134 * NULL if the lock is unlocked or read-locked. 135 */ 136 #define rw_wowner(rw) \ 137 ((rw)->rw_lock & RW_LOCK_READ ? NULL : \ 138 (struct thread *)RW_OWNER((rw)->rw_lock)) 139 140 /* 141 * Returns if a write owner is recursed. Write ownership is not assured 142 * here and should be previously checked. 143 */ 144 #define rw_recursed(rw) ((rw)->rw_recurse != 0) 145 146 /* 147 * Return true if curthread helds the lock. 148 */ 149 #define rw_wlocked(rw) (rw_wowner((rw)) == curthread) 150 151 /* 152 * Return a pointer to the owning thread for this lock who should receive 153 * any priority lent by threads that block on this lock. Currently this 154 * is identical to rw_wowner(). 155 */ 156 #define rw_owner(rw) rw_wowner(rw) 157 158 #ifndef INVARIANTS 159 #define __rw_assert(c, what, file, line) 160 #endif 161 162 void 163 assert_rw(const struct lock_object *lock, int what) 164 { 165 166 rw_assert((const struct rwlock *)lock, what); 167 } 168 169 void 170 lock_rw(struct lock_object *lock, uintptr_t how) 171 { 172 struct rwlock *rw; 173 174 rw = (struct rwlock *)lock; 175 if (how) 176 rw_rlock(rw); 177 else 178 rw_wlock(rw); 179 } 180 181 uintptr_t 182 unlock_rw(struct lock_object *lock) 183 { 184 struct rwlock *rw; 185 186 rw = (struct rwlock *)lock; 187 rw_assert(rw, RA_LOCKED | LA_NOTRECURSED); 188 if (rw->rw_lock & RW_LOCK_READ) { 189 rw_runlock(rw); 190 return (1); 191 } else { 192 rw_wunlock(rw); 193 return (0); 194 } 195 } 196 197 #ifdef KDTRACE_HOOKS 198 int 199 owner_rw(const struct lock_object *lock, struct thread **owner) 200 { 201 const struct rwlock *rw = (const struct rwlock *)lock; 202 uintptr_t x = rw->rw_lock; 203 204 *owner = rw_wowner(rw); 205 return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) : 206 (*owner != NULL)); 207 } 208 #endif 209 210 void 211 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts) 212 { 213 struct rwlock *rw; 214 int flags; 215 216 rw = rwlock2rw(c); 217 218 MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | 219 RW_RECURSE | RW_NEW)) == 0); 220 ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock, 221 ("%s: rw_lock not aligned for %s: %p", __func__, name, 222 &rw->rw_lock)); 223 224 flags = LO_UPGRADABLE; 225 if (opts & RW_DUPOK) 226 flags |= LO_DUPOK; 227 if (opts & RW_NOPROFILE) 228 flags |= LO_NOPROFILE; 229 if (!(opts & RW_NOWITNESS)) 230 flags |= LO_WITNESS; 231 if (opts & RW_RECURSE) 232 flags |= LO_RECURSABLE; 233 if (opts & RW_QUIET) 234 flags |= LO_QUIET; 235 if (opts & RW_NEW) 236 flags |= LO_NEW; 237 238 lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); 239 rw->rw_lock = RW_UNLOCKED; 240 rw->rw_recurse = 0; 241 } 242 243 void 244 _rw_destroy(volatile uintptr_t *c) 245 { 246 struct rwlock *rw; 247 248 rw = rwlock2rw(c); 249 250 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw)); 251 KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw)); 252 rw->rw_lock = RW_DESTROYED; 253 lock_destroy(&rw->lock_object); 254 } 255 256 void 257 rw_sysinit(void *arg) 258 { 259 struct rw_args *args = arg; 260 261 rw_init((struct rwlock *)args->ra_rw, args->ra_desc); 262 } 263 264 void 265 rw_sysinit_flags(void *arg) 266 { 267 struct rw_args_flags *args = arg; 268 269 rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc, 270 args->ra_flags); 271 } 272 273 int 274 _rw_wowned(const volatile uintptr_t *c) 275 { 276 277 return (rw_wowner(rwlock2rw(c)) == curthread); 278 } 279 280 void 281 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line) 282 { 283 struct rwlock *rw; 284 285 if (SCHEDULER_STOPPED()) 286 return; 287 288 rw = rwlock2rw(c); 289 290 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 291 ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d", 292 curthread, rw->lock_object.lo_name, file, line)); 293 KASSERT(rw->rw_lock != RW_DESTROYED, 294 ("rw_wlock() of destroyed rwlock @ %s:%d", file, line)); 295 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 296 line, NULL); 297 __rw_wlock(rw, curthread, file, line); 298 LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line); 299 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 300 curthread->td_locks++; 301 } 302 303 int 304 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line) 305 { 306 struct rwlock *rw; 307 int rval; 308 309 if (SCHEDULER_STOPPED()) 310 return (1); 311 312 rw = rwlock2rw(c); 313 314 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 315 ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d", 316 curthread, rw->lock_object.lo_name, file, line)); 317 KASSERT(rw->rw_lock != RW_DESTROYED, 318 ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line)); 319 320 if (rw_wlocked(rw) && 321 (rw->lock_object.lo_flags & LO_RECURSABLE) != 0) { 322 rw->rw_recurse++; 323 rval = 1; 324 } else 325 rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED, 326 (uintptr_t)curthread); 327 328 LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line); 329 if (rval) { 330 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 331 file, line); 332 if (!rw_recursed(rw)) 333 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE, 334 rw, 0, 0, file, line); 335 curthread->td_locks++; 336 } 337 return (rval); 338 } 339 340 void 341 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line) 342 { 343 struct rwlock *rw; 344 345 if (SCHEDULER_STOPPED()) 346 return; 347 348 rw = rwlock2rw(c); 349 350 KASSERT(rw->rw_lock != RW_DESTROYED, 351 ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); 352 __rw_assert(c, RA_WLOCKED, file, line); 353 WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 354 LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file, 355 line); 356 if (!rw_recursed(rw)) 357 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_WUNLOCK_RELEASE, rw); 358 __rw_wunlock(rw, curthread, file, line); 359 curthread->td_locks--; 360 } 361 /* 362 * Determines whether a new reader can acquire a lock. Succeeds if the 363 * reader already owns a read lock and the lock is locked for read to 364 * prevent deadlock from reader recursion. Also succeeds if the lock 365 * is unlocked and has no writer waiters or spinners. Failing otherwise 366 * prioritizes writers before readers. 367 */ 368 #define RW_CAN_READ(_rw) \ 369 ((curthread->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) & \ 370 (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) == \ 371 RW_LOCK_READ) 372 373 void 374 __rw_rlock(volatile uintptr_t *c, const char *file, int line) 375 { 376 struct rwlock *rw; 377 struct turnstile *ts; 378 #ifdef ADAPTIVE_RWLOCKS 379 volatile struct thread *owner; 380 int spintries = 0; 381 int i; 382 #endif 383 #ifdef LOCK_PROFILING 384 uint64_t waittime = 0; 385 int contested = 0; 386 #endif 387 uintptr_t v; 388 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS) 389 struct lock_delay_arg lda; 390 #endif 391 #ifdef KDTRACE_HOOKS 392 uintptr_t state; 393 u_int sleep_cnt = 0; 394 int64_t sleep_time = 0; 395 int64_t all_time = 0; 396 #endif 397 398 if (SCHEDULER_STOPPED()) 399 return; 400 401 #if defined(ADAPTIVE_RWLOCKS) 402 lock_delay_arg_init(&lda, &rw_delay); 403 #elif defined(KDTRACE_HOOKS) 404 lock_delay_arg_init(&lda, NULL); 405 #endif 406 rw = rwlock2rw(c); 407 408 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 409 ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d", 410 curthread, rw->lock_object.lo_name, file, line)); 411 KASSERT(rw->rw_lock != RW_DESTROYED, 412 ("rw_rlock() of destroyed rwlock @ %s:%d", file, line)); 413 KASSERT(rw_wowner(rw) != curthread, 414 ("rw_rlock: wlock already held for %s @ %s:%d", 415 rw->lock_object.lo_name, file, line)); 416 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL); 417 418 #ifdef KDTRACE_HOOKS 419 all_time -= lockstat_nsecs(&rw->lock_object); 420 state = rw->rw_lock; 421 #endif 422 for (;;) { 423 /* 424 * Handle the easy case. If no other thread has a write 425 * lock, then try to bump up the count of read locks. Note 426 * that we have to preserve the current state of the 427 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a 428 * read lock, then rw_lock must have changed, so restart 429 * the loop. Note that this handles the case of a 430 * completely unlocked rwlock since such a lock is encoded 431 * as a read lock with no waiters. 432 */ 433 v = rw->rw_lock; 434 if (RW_CAN_READ(v)) { 435 /* 436 * The RW_LOCK_READ_WAITERS flag should only be set 437 * if the lock has been unlocked and write waiters 438 * were present. 439 */ 440 if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, 441 v + RW_ONE_READER)) { 442 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 443 CTR4(KTR_LOCK, 444 "%s: %p succeed %p -> %p", __func__, 445 rw, (void *)v, 446 (void *)(v + RW_ONE_READER)); 447 break; 448 } 449 continue; 450 } 451 #ifdef KDTRACE_HOOKS 452 lda.spin_cnt++; 453 #endif 454 #ifdef HWPMC_HOOKS 455 PMC_SOFT_CALL( , , lock, failed); 456 #endif 457 lock_profile_obtain_lock_failed(&rw->lock_object, 458 &contested, &waittime); 459 460 #ifdef ADAPTIVE_RWLOCKS 461 /* 462 * If the owner is running on another CPU, spin until 463 * the owner stops running or the state of the lock 464 * changes. 465 */ 466 if ((v & RW_LOCK_READ) == 0) { 467 owner = (struct thread *)RW_OWNER(v); 468 if (TD_IS_RUNNING(owner)) { 469 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 470 CTR3(KTR_LOCK, 471 "%s: spinning on %p held by %p", 472 __func__, rw, owner); 473 KTR_STATE1(KTR_SCHED, "thread", 474 sched_tdname(curthread), "spinning", 475 "lockname:\"%s\"", rw->lock_object.lo_name); 476 while ((struct thread*)RW_OWNER(rw->rw_lock) == 477 owner && TD_IS_RUNNING(owner)) 478 lock_delay(&lda); 479 KTR_STATE0(KTR_SCHED, "thread", 480 sched_tdname(curthread), "running"); 481 continue; 482 } 483 } else if (spintries < rowner_retries) { 484 spintries++; 485 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 486 "spinning", "lockname:\"%s\"", 487 rw->lock_object.lo_name); 488 for (i = 0; i < rowner_loops; i++) { 489 v = rw->rw_lock; 490 if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v)) 491 break; 492 cpu_spinwait(); 493 } 494 #ifdef KDTRACE_HOOKS 495 lda.spin_cnt += rowner_loops - i; 496 #endif 497 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 498 "running"); 499 if (i != rowner_loops) 500 continue; 501 } 502 #endif 503 504 /* 505 * Okay, now it's the hard case. Some other thread already 506 * has a write lock or there are write waiters present, 507 * acquire the turnstile lock so we can begin the process 508 * of blocking. 509 */ 510 ts = turnstile_trywait(&rw->lock_object); 511 512 /* 513 * The lock might have been released while we spun, so 514 * recheck its state and restart the loop if needed. 515 */ 516 v = rw->rw_lock; 517 if (RW_CAN_READ(v)) { 518 turnstile_cancel(ts); 519 continue; 520 } 521 522 #ifdef ADAPTIVE_RWLOCKS 523 /* 524 * The current lock owner might have started executing 525 * on another CPU (or the lock could have changed 526 * owners) while we were waiting on the turnstile 527 * chain lock. If so, drop the turnstile lock and try 528 * again. 529 */ 530 if ((v & RW_LOCK_READ) == 0) { 531 owner = (struct thread *)RW_OWNER(v); 532 if (TD_IS_RUNNING(owner)) { 533 turnstile_cancel(ts); 534 continue; 535 } 536 } 537 #endif 538 539 /* 540 * The lock is held in write mode or it already has waiters. 541 */ 542 MPASS(!RW_CAN_READ(v)); 543 544 /* 545 * If the RW_LOCK_READ_WAITERS flag is already set, then 546 * we can go ahead and block. If it is not set then try 547 * to set it. If we fail to set it drop the turnstile 548 * lock and restart the loop. 549 */ 550 if (!(v & RW_LOCK_READ_WAITERS)) { 551 if (!atomic_cmpset_ptr(&rw->rw_lock, v, 552 v | RW_LOCK_READ_WAITERS)) { 553 turnstile_cancel(ts); 554 continue; 555 } 556 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 557 CTR2(KTR_LOCK, "%s: %p set read waiters flag", 558 __func__, rw); 559 } 560 561 /* 562 * We were unable to acquire the lock and the read waiters 563 * flag is set, so we must block on the turnstile. 564 */ 565 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 566 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 567 rw); 568 #ifdef KDTRACE_HOOKS 569 sleep_time -= lockstat_nsecs(&rw->lock_object); 570 #endif 571 turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE); 572 #ifdef KDTRACE_HOOKS 573 sleep_time += lockstat_nsecs(&rw->lock_object); 574 sleep_cnt++; 575 #endif 576 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 577 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 578 __func__, rw); 579 } 580 #ifdef KDTRACE_HOOKS 581 all_time += lockstat_nsecs(&rw->lock_object); 582 if (sleep_time) 583 LOCKSTAT_RECORD4(LS_RW_RLOCK_BLOCK, rw, sleep_time, 584 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0, 585 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 586 587 /* Record only the loops spinning and not sleeping. */ 588 if (lda.spin_cnt > sleep_cnt) 589 LOCKSTAT_RECORD4(LS_RW_RLOCK_SPIN, rw, all_time - sleep_time, 590 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0, 591 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 592 #endif 593 /* 594 * TODO: acquire "owner of record" here. Here be turnstile dragons 595 * however. turnstiles don't like owners changing between calls to 596 * turnstile_wait() currently. 597 */ 598 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, rw, contested, 599 waittime, file, line); 600 LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line); 601 WITNESS_LOCK(&rw->lock_object, 0, file, line); 602 curthread->td_locks++; 603 curthread->td_rw_rlocks++; 604 } 605 606 int 607 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line) 608 { 609 struct rwlock *rw; 610 uintptr_t x; 611 612 if (SCHEDULER_STOPPED()) 613 return (1); 614 615 rw = rwlock2rw(c); 616 617 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 618 ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d", 619 curthread, rw->lock_object.lo_name, file, line)); 620 621 for (;;) { 622 x = rw->rw_lock; 623 KASSERT(rw->rw_lock != RW_DESTROYED, 624 ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line)); 625 if (!(x & RW_LOCK_READ)) 626 break; 627 if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, x + RW_ONE_READER)) { 628 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file, 629 line); 630 WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line); 631 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, 632 rw, 0, 0, file, line); 633 curthread->td_locks++; 634 curthread->td_rw_rlocks++; 635 return (1); 636 } 637 } 638 639 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line); 640 return (0); 641 } 642 643 void 644 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line) 645 { 646 struct rwlock *rw; 647 struct turnstile *ts; 648 uintptr_t x, v, queue; 649 650 if (SCHEDULER_STOPPED()) 651 return; 652 653 rw = rwlock2rw(c); 654 655 KASSERT(rw->rw_lock != RW_DESTROYED, 656 ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); 657 __rw_assert(c, RA_RLOCKED, file, line); 658 WITNESS_UNLOCK(&rw->lock_object, 0, file, line); 659 LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line); 660 661 /* TODO: drop "owner of record" here. */ 662 663 for (;;) { 664 /* 665 * See if there is more than one read lock held. If so, 666 * just drop one and return. 667 */ 668 x = rw->rw_lock; 669 if (RW_READERS(x) > 1) { 670 if (atomic_cmpset_rel_ptr(&rw->rw_lock, x, 671 x - RW_ONE_READER)) { 672 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 673 CTR4(KTR_LOCK, 674 "%s: %p succeeded %p -> %p", 675 __func__, rw, (void *)x, 676 (void *)(x - RW_ONE_READER)); 677 break; 678 } 679 continue; 680 } 681 /* 682 * If there aren't any waiters for a write lock, then try 683 * to drop it quickly. 684 */ 685 if (!(x & RW_LOCK_WAITERS)) { 686 MPASS((x & ~RW_LOCK_WRITE_SPINNER) == 687 RW_READERS_LOCK(1)); 688 if (atomic_cmpset_rel_ptr(&rw->rw_lock, x, 689 RW_UNLOCKED)) { 690 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 691 CTR2(KTR_LOCK, "%s: %p last succeeded", 692 __func__, rw); 693 break; 694 } 695 continue; 696 } 697 /* 698 * Ok, we know we have waiters and we think we are the 699 * last reader, so grab the turnstile lock. 700 */ 701 turnstile_chain_lock(&rw->lock_object); 702 v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER); 703 MPASS(v & RW_LOCK_WAITERS); 704 705 /* 706 * Try to drop our lock leaving the lock in a unlocked 707 * state. 708 * 709 * If you wanted to do explicit lock handoff you'd have to 710 * do it here. You'd also want to use turnstile_signal() 711 * and you'd have to handle the race where a higher 712 * priority thread blocks on the write lock before the 713 * thread you wakeup actually runs and have the new thread 714 * "steal" the lock. For now it's a lot simpler to just 715 * wakeup all of the waiters. 716 * 717 * As above, if we fail, then another thread might have 718 * acquired a read lock, so drop the turnstile lock and 719 * restart. 720 */ 721 x = RW_UNLOCKED; 722 if (v & RW_LOCK_WRITE_WAITERS) { 723 queue = TS_EXCLUSIVE_QUEUE; 724 x |= (v & RW_LOCK_READ_WAITERS); 725 } else 726 queue = TS_SHARED_QUEUE; 727 if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, 728 x)) { 729 turnstile_chain_unlock(&rw->lock_object); 730 continue; 731 } 732 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 733 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", 734 __func__, rw); 735 736 /* 737 * Ok. The lock is released and all that's left is to 738 * wake up the waiters. Note that the lock might not be 739 * free anymore, but in that case the writers will just 740 * block again if they run before the new lock holder(s) 741 * release the lock. 742 */ 743 ts = turnstile_lookup(&rw->lock_object); 744 MPASS(ts != NULL); 745 turnstile_broadcast(ts, queue); 746 turnstile_unpend(ts, TS_SHARED_LOCK); 747 turnstile_chain_unlock(&rw->lock_object); 748 break; 749 } 750 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_RUNLOCK_RELEASE, rw); 751 curthread->td_locks--; 752 curthread->td_rw_rlocks--; 753 } 754 755 /* 756 * This function is called when we are unable to obtain a write lock on the 757 * first try. This means that at least one other thread holds either a 758 * read or write lock. 759 */ 760 void 761 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file, 762 int line) 763 { 764 struct rwlock *rw; 765 struct turnstile *ts; 766 #ifdef ADAPTIVE_RWLOCKS 767 volatile struct thread *owner; 768 int spintries = 0; 769 int i; 770 #endif 771 uintptr_t v, x; 772 #ifdef LOCK_PROFILING 773 uint64_t waittime = 0; 774 int contested = 0; 775 #endif 776 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS) 777 struct lock_delay_arg lda; 778 #endif 779 #ifdef KDTRACE_HOOKS 780 uintptr_t state; 781 u_int sleep_cnt = 0; 782 int64_t sleep_time = 0; 783 int64_t all_time = 0; 784 #endif 785 786 if (SCHEDULER_STOPPED()) 787 return; 788 789 #if defined(ADAPTIVE_RWLOCKS) 790 lock_delay_arg_init(&lda, &rw_delay); 791 #elif defined(KDTRACE_HOOKS) 792 lock_delay_arg_init(&lda, NULL); 793 #endif 794 rw = rwlock2rw(c); 795 796 if (rw_wlocked(rw)) { 797 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE, 798 ("%s: recursing but non-recursive rw %s @ %s:%d\n", 799 __func__, rw->lock_object.lo_name, file, line)); 800 rw->rw_recurse++; 801 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 802 CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw); 803 return; 804 } 805 806 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 807 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 808 rw->lock_object.lo_name, (void *)rw->rw_lock, file, line); 809 810 #ifdef KDTRACE_HOOKS 811 all_time -= lockstat_nsecs(&rw->lock_object); 812 state = rw->rw_lock; 813 #endif 814 for (;;) { 815 if (rw->rw_lock == RW_UNLOCKED && _rw_write_lock(rw, tid)) 816 break; 817 #ifdef KDTRACE_HOOKS 818 lda.spin_cnt++; 819 #endif 820 #ifdef HWPMC_HOOKS 821 PMC_SOFT_CALL( , , lock, failed); 822 #endif 823 lock_profile_obtain_lock_failed(&rw->lock_object, 824 &contested, &waittime); 825 #ifdef ADAPTIVE_RWLOCKS 826 /* 827 * If the lock is write locked and the owner is 828 * running on another CPU, spin until the owner stops 829 * running or the state of the lock changes. 830 */ 831 v = rw->rw_lock; 832 owner = (struct thread *)RW_OWNER(v); 833 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) { 834 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 835 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 836 __func__, rw, owner); 837 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 838 "spinning", "lockname:\"%s\"", 839 rw->lock_object.lo_name); 840 while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && 841 TD_IS_RUNNING(owner)) 842 lock_delay(&lda); 843 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 844 "running"); 845 continue; 846 } 847 if ((v & RW_LOCK_READ) && RW_READERS(v) && 848 spintries < rowner_retries) { 849 if (!(v & RW_LOCK_WRITE_SPINNER)) { 850 if (!atomic_cmpset_ptr(&rw->rw_lock, v, 851 v | RW_LOCK_WRITE_SPINNER)) { 852 continue; 853 } 854 } 855 spintries++; 856 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 857 "spinning", "lockname:\"%s\"", 858 rw->lock_object.lo_name); 859 for (i = 0; i < rowner_loops; i++) { 860 if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0) 861 break; 862 cpu_spinwait(); 863 } 864 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 865 "running"); 866 #ifdef KDTRACE_HOOKS 867 lda.spin_cnt += rowner_loops - i; 868 #endif 869 if (i != rowner_loops) 870 continue; 871 } 872 #endif 873 ts = turnstile_trywait(&rw->lock_object); 874 v = rw->rw_lock; 875 876 #ifdef ADAPTIVE_RWLOCKS 877 /* 878 * The current lock owner might have started executing 879 * on another CPU (or the lock could have changed 880 * owners) while we were waiting on the turnstile 881 * chain lock. If so, drop the turnstile lock and try 882 * again. 883 */ 884 if (!(v & RW_LOCK_READ)) { 885 owner = (struct thread *)RW_OWNER(v); 886 if (TD_IS_RUNNING(owner)) { 887 turnstile_cancel(ts); 888 continue; 889 } 890 } 891 #endif 892 /* 893 * Check for the waiters flags about this rwlock. 894 * If the lock was released, without maintain any pending 895 * waiters queue, simply try to acquire it. 896 * If a pending waiters queue is present, claim the lock 897 * ownership and maintain the pending queue. 898 */ 899 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER); 900 if ((v & ~x) == RW_UNLOCKED) { 901 x &= ~RW_LOCK_WRITE_SPINNER; 902 if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) { 903 if (x) 904 turnstile_claim(ts); 905 else 906 turnstile_cancel(ts); 907 break; 908 } 909 turnstile_cancel(ts); 910 continue; 911 } 912 /* 913 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to 914 * set it. If we fail to set it, then loop back and try 915 * again. 916 */ 917 if (!(v & RW_LOCK_WRITE_WAITERS)) { 918 if (!atomic_cmpset_ptr(&rw->rw_lock, v, 919 v | RW_LOCK_WRITE_WAITERS)) { 920 turnstile_cancel(ts); 921 continue; 922 } 923 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 924 CTR2(KTR_LOCK, "%s: %p set write waiters flag", 925 __func__, rw); 926 } 927 /* 928 * We were unable to acquire the lock and the write waiters 929 * flag is set, so we must block on the turnstile. 930 */ 931 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 932 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 933 rw); 934 #ifdef KDTRACE_HOOKS 935 sleep_time -= lockstat_nsecs(&rw->lock_object); 936 #endif 937 turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE); 938 #ifdef KDTRACE_HOOKS 939 sleep_time += lockstat_nsecs(&rw->lock_object); 940 sleep_cnt++; 941 #endif 942 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 943 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 944 __func__, rw); 945 #ifdef ADAPTIVE_RWLOCKS 946 spintries = 0; 947 #endif 948 } 949 #ifdef KDTRACE_HOOKS 950 all_time += lockstat_nsecs(&rw->lock_object); 951 if (sleep_time) 952 LOCKSTAT_RECORD4(LS_RW_WLOCK_BLOCK, rw, sleep_time, 953 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0, 954 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 955 956 /* Record only the loops spinning and not sleeping. */ 957 if (lda.spin_cnt > sleep_cnt) 958 LOCKSTAT_RECORD4(LS_RW_WLOCK_SPIN, rw, all_time - sleep_time, 959 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0, 960 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 961 #endif 962 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE, rw, contested, 963 waittime, file, line); 964 } 965 966 /* 967 * This function is called if the first try at releasing a write lock failed. 968 * This means that one of the 2 waiter bits must be set indicating that at 969 * least one thread is waiting on this lock. 970 */ 971 void 972 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file, 973 int line) 974 { 975 struct rwlock *rw; 976 struct turnstile *ts; 977 uintptr_t v; 978 int queue; 979 980 if (SCHEDULER_STOPPED()) 981 return; 982 983 rw = rwlock2rw(c); 984 985 if (rw_wlocked(rw) && rw_recursed(rw)) { 986 rw->rw_recurse--; 987 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 988 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw); 989 return; 990 } 991 992 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), 993 ("%s: neither of the waiter flags are set", __func__)); 994 995 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 996 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); 997 998 turnstile_chain_lock(&rw->lock_object); 999 ts = turnstile_lookup(&rw->lock_object); 1000 MPASS(ts != NULL); 1001 1002 /* 1003 * Use the same algo as sx locks for now. Prefer waking up shared 1004 * waiters if we have any over writers. This is probably not ideal. 1005 * 1006 * 'v' is the value we are going to write back to rw_lock. If we 1007 * have waiters on both queues, we need to preserve the state of 1008 * the waiter flag for the queue we don't wake up. For now this is 1009 * hardcoded for the algorithm mentioned above. 1010 * 1011 * In the case of both readers and writers waiting we wakeup the 1012 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a 1013 * new writer comes in before a reader it will claim the lock up 1014 * above. There is probably a potential priority inversion in 1015 * there that could be worked around either by waking both queues 1016 * of waiters or doing some complicated lock handoff gymnastics. 1017 */ 1018 v = RW_UNLOCKED; 1019 if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) { 1020 queue = TS_EXCLUSIVE_QUEUE; 1021 v |= (rw->rw_lock & RW_LOCK_READ_WAITERS); 1022 } else 1023 queue = TS_SHARED_QUEUE; 1024 1025 /* Wake up all waiters for the specific queue. */ 1026 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1027 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, 1028 queue == TS_SHARED_QUEUE ? "read" : "write"); 1029 turnstile_broadcast(ts, queue); 1030 atomic_store_rel_ptr(&rw->rw_lock, v); 1031 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 1032 turnstile_chain_unlock(&rw->lock_object); 1033 } 1034 1035 /* 1036 * Attempt to do a non-blocking upgrade from a read lock to a write 1037 * lock. This will only succeed if this thread holds a single read 1038 * lock. Returns true if the upgrade succeeded and false otherwise. 1039 */ 1040 int 1041 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line) 1042 { 1043 struct rwlock *rw; 1044 uintptr_t v, x, tid; 1045 struct turnstile *ts; 1046 int success; 1047 1048 if (SCHEDULER_STOPPED()) 1049 return (1); 1050 1051 rw = rwlock2rw(c); 1052 1053 KASSERT(rw->rw_lock != RW_DESTROYED, 1054 ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); 1055 __rw_assert(c, RA_RLOCKED, file, line); 1056 1057 /* 1058 * Attempt to switch from one reader to a writer. If there 1059 * are any write waiters, then we will have to lock the 1060 * turnstile first to prevent races with another writer 1061 * calling turnstile_wait() before we have claimed this 1062 * turnstile. So, do the simple case of no waiters first. 1063 */ 1064 tid = (uintptr_t)curthread; 1065 success = 0; 1066 for (;;) { 1067 v = rw->rw_lock; 1068 if (RW_READERS(v) > 1) 1069 break; 1070 if (!(v & RW_LOCK_WAITERS)) { 1071 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid); 1072 if (!success) 1073 continue; 1074 break; 1075 } 1076 1077 /* 1078 * Ok, we think we have waiters, so lock the turnstile. 1079 */ 1080 ts = turnstile_trywait(&rw->lock_object); 1081 v = rw->rw_lock; 1082 if (RW_READERS(v) > 1) { 1083 turnstile_cancel(ts); 1084 break; 1085 } 1086 /* 1087 * Try to switch from one reader to a writer again. This time 1088 * we honor the current state of the waiters flags. 1089 * If we obtain the lock with the flags set, then claim 1090 * ownership of the turnstile. 1091 */ 1092 x = rw->rw_lock & RW_LOCK_WAITERS; 1093 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x); 1094 if (success) { 1095 if (x) 1096 turnstile_claim(ts); 1097 else 1098 turnstile_cancel(ts); 1099 break; 1100 } 1101 turnstile_cancel(ts); 1102 } 1103 LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line); 1104 if (success) { 1105 curthread->td_rw_rlocks--; 1106 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 1107 file, line); 1108 LOCKSTAT_RECORD0(LS_RW_TRYUPGRADE_UPGRADE, rw); 1109 } 1110 return (success); 1111 } 1112 1113 /* 1114 * Downgrade a write lock into a single read lock. 1115 */ 1116 void 1117 __rw_downgrade(volatile uintptr_t *c, const char *file, int line) 1118 { 1119 struct rwlock *rw; 1120 struct turnstile *ts; 1121 uintptr_t tid, v; 1122 int rwait, wwait; 1123 1124 if (SCHEDULER_STOPPED()) 1125 return; 1126 1127 rw = rwlock2rw(c); 1128 1129 KASSERT(rw->rw_lock != RW_DESTROYED, 1130 ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); 1131 __rw_assert(c, RA_WLOCKED | RA_NOTRECURSED, file, line); 1132 #ifndef INVARIANTS 1133 if (rw_recursed(rw)) 1134 panic("downgrade of a recursed lock"); 1135 #endif 1136 1137 WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line); 1138 1139 /* 1140 * Convert from a writer to a single reader. First we handle 1141 * the easy case with no waiters. If there are any waiters, we 1142 * lock the turnstile and "disown" the lock. 1143 */ 1144 tid = (uintptr_t)curthread; 1145 if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1))) 1146 goto out; 1147 1148 /* 1149 * Ok, we think we have waiters, so lock the turnstile so we can 1150 * read the waiter flags without any races. 1151 */ 1152 turnstile_chain_lock(&rw->lock_object); 1153 v = rw->rw_lock & RW_LOCK_WAITERS; 1154 rwait = v & RW_LOCK_READ_WAITERS; 1155 wwait = v & RW_LOCK_WRITE_WAITERS; 1156 MPASS(rwait | wwait); 1157 1158 /* 1159 * Downgrade from a write lock while preserving waiters flag 1160 * and give up ownership of the turnstile. 1161 */ 1162 ts = turnstile_lookup(&rw->lock_object); 1163 MPASS(ts != NULL); 1164 if (!wwait) 1165 v &= ~RW_LOCK_READ_WAITERS; 1166 atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v); 1167 /* 1168 * Wake other readers if there are no writers pending. Otherwise they 1169 * won't be able to acquire the lock anyway. 1170 */ 1171 if (rwait && !wwait) { 1172 turnstile_broadcast(ts, TS_SHARED_QUEUE); 1173 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 1174 } else 1175 turnstile_disown(ts); 1176 turnstile_chain_unlock(&rw->lock_object); 1177 out: 1178 curthread->td_rw_rlocks++; 1179 LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line); 1180 LOCKSTAT_RECORD0(LS_RW_DOWNGRADE_DOWNGRADE, rw); 1181 } 1182 1183 #ifdef INVARIANT_SUPPORT 1184 #ifndef INVARIANTS 1185 #undef __rw_assert 1186 #endif 1187 1188 /* 1189 * In the non-WITNESS case, rw_assert() can only detect that at least 1190 * *some* thread owns an rlock, but it cannot guarantee that *this* 1191 * thread owns an rlock. 1192 */ 1193 void 1194 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line) 1195 { 1196 const struct rwlock *rw; 1197 1198 if (panicstr != NULL) 1199 return; 1200 1201 rw = rwlock2rw(c); 1202 1203 switch (what) { 1204 case RA_LOCKED: 1205 case RA_LOCKED | RA_RECURSED: 1206 case RA_LOCKED | RA_NOTRECURSED: 1207 case RA_RLOCKED: 1208 case RA_RLOCKED | RA_RECURSED: 1209 case RA_RLOCKED | RA_NOTRECURSED: 1210 #ifdef WITNESS 1211 witness_assert(&rw->lock_object, what, file, line); 1212 #else 1213 /* 1214 * If some other thread has a write lock or we have one 1215 * and are asserting a read lock, fail. Also, if no one 1216 * has a lock at all, fail. 1217 */ 1218 if (rw->rw_lock == RW_UNLOCKED || 1219 (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED || 1220 rw_wowner(rw) != curthread))) 1221 panic("Lock %s not %slocked @ %s:%d\n", 1222 rw->lock_object.lo_name, (what & RA_RLOCKED) ? 1223 "read " : "", file, line); 1224 1225 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) { 1226 if (rw_recursed(rw)) { 1227 if (what & RA_NOTRECURSED) 1228 panic("Lock %s recursed @ %s:%d\n", 1229 rw->lock_object.lo_name, file, 1230 line); 1231 } else if (what & RA_RECURSED) 1232 panic("Lock %s not recursed @ %s:%d\n", 1233 rw->lock_object.lo_name, file, line); 1234 } 1235 #endif 1236 break; 1237 case RA_WLOCKED: 1238 case RA_WLOCKED | RA_RECURSED: 1239 case RA_WLOCKED | RA_NOTRECURSED: 1240 if (rw_wowner(rw) != curthread) 1241 panic("Lock %s not exclusively locked @ %s:%d\n", 1242 rw->lock_object.lo_name, file, line); 1243 if (rw_recursed(rw)) { 1244 if (what & RA_NOTRECURSED) 1245 panic("Lock %s recursed @ %s:%d\n", 1246 rw->lock_object.lo_name, file, line); 1247 } else if (what & RA_RECURSED) 1248 panic("Lock %s not recursed @ %s:%d\n", 1249 rw->lock_object.lo_name, file, line); 1250 break; 1251 case RA_UNLOCKED: 1252 #ifdef WITNESS 1253 witness_assert(&rw->lock_object, what, file, line); 1254 #else 1255 /* 1256 * If we hold a write lock fail. We can't reliably check 1257 * to see if we hold a read lock or not. 1258 */ 1259 if (rw_wowner(rw) == curthread) 1260 panic("Lock %s exclusively locked @ %s:%d\n", 1261 rw->lock_object.lo_name, file, line); 1262 #endif 1263 break; 1264 default: 1265 panic("Unknown rw lock assertion: %d @ %s:%d", what, file, 1266 line); 1267 } 1268 } 1269 #endif /* INVARIANT_SUPPORT */ 1270 1271 #ifdef DDB 1272 void 1273 db_show_rwlock(const struct lock_object *lock) 1274 { 1275 const struct rwlock *rw; 1276 struct thread *td; 1277 1278 rw = (const struct rwlock *)lock; 1279 1280 db_printf(" state: "); 1281 if (rw->rw_lock == RW_UNLOCKED) 1282 db_printf("UNLOCKED\n"); 1283 else if (rw->rw_lock == RW_DESTROYED) { 1284 db_printf("DESTROYED\n"); 1285 return; 1286 } else if (rw->rw_lock & RW_LOCK_READ) 1287 db_printf("RLOCK: %ju locks\n", 1288 (uintmax_t)(RW_READERS(rw->rw_lock))); 1289 else { 1290 td = rw_wowner(rw); 1291 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1292 td->td_tid, td->td_proc->p_pid, td->td_name); 1293 if (rw_recursed(rw)) 1294 db_printf(" recursed: %u\n", rw->rw_recurse); 1295 } 1296 db_printf(" waiters: "); 1297 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { 1298 case RW_LOCK_READ_WAITERS: 1299 db_printf("readers\n"); 1300 break; 1301 case RW_LOCK_WRITE_WAITERS: 1302 db_printf("writers\n"); 1303 break; 1304 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: 1305 db_printf("readers and writers\n"); 1306 break; 1307 default: 1308 db_printf("none\n"); 1309 break; 1310 } 1311 } 1312 1313 #endif
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