kern_rwlock.c revision 157846
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 * 3. Neither the name of the author nor the names of any co-contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 */ 29 30/* 31 * Machine independent bits of reader/writer lock implementation. 32 */ 33 34#include <sys/cdefs.h> 35__FBSDID("$FreeBSD: head/sys/kern/kern_rwlock.c 157846 2006-04-18 18:27:54Z jhb $"); 36 37#include "opt_ddb.h" 38 39#include <sys/param.h> 40#include <sys/ktr.h> 41#include <sys/lock.h> 42#include <sys/mutex.h> 43#include <sys/proc.h> 44#include <sys/rwlock.h> 45#include <sys/systm.h> 46#include <sys/turnstile.h> 47 48#include <machine/cpu.h> 49 50#ifdef DDB 51#include <ddb/ddb.h> 52 53static void db_show_rwlock(struct lock_object *lock); 54#endif 55 56struct lock_class lock_class_rw = { 57 "rw", 58 LC_SLEEPLOCK | LC_RECURSABLE /* | LC_UPGRADABLE */, 59#ifdef DDB 60 db_show_rwlock 61#endif 62}; 63 64/* 65 * Return a pointer to the owning thread if the lock is write-locked or 66 * NULL if the lock is unlocked or read-locked. 67 */ 68#define rw_wowner(rw) \ 69 ((rw)->rw_lock & RW_LOCK_READ ? NULL : \ 70 (struct thread *)RW_OWNER((rw)->rw_lock)) 71 72/* 73 * Return a pointer to the owning thread for this lock who should receive 74 * any priority lent by threads that block on this lock. Currently this 75 * is identical to rw_wowner(). 76 */ 77#define rw_owner(rw) rw_wowner(rw) 78 79#ifndef INVARIANTS 80#define _rw_assert(rw, what, file, line) 81#endif 82 83void 84rw_init(struct rwlock *rw, const char *name) 85{ 86 87 rw->rw_lock = RW_UNLOCKED; 88 89 lock_init(&rw->rw_object, &lock_class_rw, name, NULL, LO_WITNESS | 90 LO_RECURSABLE /* | LO_UPGRADABLE */); 91} 92 93void 94rw_destroy(struct rwlock *rw) 95{ 96 97 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock not unlocked")); 98 lock_destroy(&rw->rw_object); 99} 100 101void 102rw_sysinit(void *arg) 103{ 104 struct rw_args *args = arg; 105 106 rw_init(args->ra_rw, args->ra_desc); 107} 108 109void 110_rw_wlock(struct rwlock *rw, const char *file, int line) 111{ 112 113 MPASS(curthread != NULL); 114 KASSERT(rw_wowner(rw) != curthread, 115 ("%s (%s): wlock already held @ %s:%d", __func__, 116 rw->rw_object.lo_name, file, line)); 117 WITNESS_CHECKORDER(&rw->rw_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 118 line); 119 __rw_wlock(rw, curthread, file, line); 120 LOCK_LOG_LOCK("WLOCK", &rw->rw_object, 0, 0, file, line); 121 WITNESS_LOCK(&rw->rw_object, LOP_EXCLUSIVE, file, line); 122} 123 124void 125_rw_wunlock(struct rwlock *rw, const char *file, int line) 126{ 127 128 MPASS(curthread != NULL); 129 _rw_assert(rw, RA_WLOCKED, file, line); 130 WITNESS_UNLOCK(&rw->rw_object, LOP_EXCLUSIVE, file, line); 131 LOCK_LOG_LOCK("WUNLOCK", &rw->rw_object, 0, 0, file, line); 132 __rw_wunlock(rw, curthread, file, line); 133} 134 135void 136_rw_rlock(struct rwlock *rw, const char *file, int line) 137{ 138 volatile struct thread *owner; 139 uintptr_t x; 140 141 KASSERT(rw_wowner(rw) != curthread, 142 ("%s (%s): wlock already held @ %s:%d", __func__, 143 rw->rw_object.lo_name, file, line)); 144 WITNESS_CHECKORDER(&rw->rw_object, LOP_NEWORDER, file, line); 145 146 /* 147 * Note that we don't make any attempt to try to block read 148 * locks once a writer has blocked on the lock. The reason is 149 * that we currently allow for read locks to recurse and we 150 * don't keep track of all the holders of read locks. Thus, if 151 * we were to block readers once a writer blocked and a reader 152 * tried to recurse on their reader lock after a writer had 153 * blocked we would end up in a deadlock since the reader would 154 * be blocked on the writer, and the writer would be blocked 155 * waiting for the reader to release its original read lock. 156 */ 157 for (;;) { 158 /* 159 * Handle the easy case. If no other thread has a write 160 * lock, then try to bump up the count of read locks. Note 161 * that we have to preserve the current state of the 162 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a 163 * read lock, then rw_lock must have changed, so restart 164 * the loop. Note that this handles the case of a 165 * completely unlocked rwlock since such a lock is encoded 166 * as a read lock with no waiters. 167 */ 168 x = rw->rw_lock; 169 if (x & RW_LOCK_READ) { 170 171 /* 172 * The RW_LOCK_READ_WAITERS flag should only be set 173 * if another thread currently holds a write lock, 174 * and in that case RW_LOCK_READ should be clear. 175 */ 176 MPASS((x & RW_LOCK_READ_WAITERS) == 0); 177 if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, 178 x + RW_ONE_READER)) { 179 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 180 CTR4(KTR_LOCK, 181 "%s: %p succeed %p -> %p", __func__, 182 rw, (void *)x, 183 (void *)(x + RW_ONE_READER)); 184 break; 185 } 186 cpu_spinwait(); 187 continue; 188 } 189 190 /* 191 * Okay, now it's the hard case. Some other thread already 192 * has a write lock, so acquire the turnstile lock so we can 193 * begin the process of blocking. 194 */ 195 turnstile_lock(&rw->rw_object); 196 197 /* 198 * The lock might have been released while we spun, so 199 * recheck its state and restart the loop if there is no 200 * longer a write lock. 201 */ 202 x = rw->rw_lock; 203 if (x & RW_LOCK_READ) { 204 turnstile_release(&rw->rw_object); 205 cpu_spinwait(); 206 continue; 207 } 208 209 /* 210 * Ok, it's still a write lock. If the RW_LOCK_READ_WAITERS 211 * flag is already set, then we can go ahead and block. If 212 * it is not set then try to set it. If we fail to set it 213 * drop the turnstile lock and restart the loop. 214 */ 215 if (!(x & RW_LOCK_READ_WAITERS)) { 216 if (!atomic_cmpset_ptr(&rw->rw_lock, x, 217 x | RW_LOCK_READ_WAITERS)) { 218 turnstile_release(&rw->rw_object); 219 cpu_spinwait(); 220 continue; 221 } 222 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 223 CTR2(KTR_LOCK, "%s: %p set read waiters flag", 224 __func__, rw); 225 } 226 227#ifdef SMP 228 /* 229 * If the owner is running on another CPU, spin until 230 * the owner stops running or the state of the lock 231 * changes. 232 */ 233 owner = (struct thread *)RW_OWNER(x); 234 if (TD_IS_RUNNING(owner)) { 235 turnstile_release(&rw->rw_object); 236 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 237 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 238 __func__, rw, owner); 239 while ((struct thread*)RW_OWNER(rw->rw_lock)== owner && 240 TD_IS_RUNNING(owner)) 241 cpu_spinwait(); 242 continue; 243 } 244#endif 245 246 /* 247 * We were unable to acquire the lock and the read waiters 248 * flag is set, so we must block on the turnstile. 249 */ 250 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 251 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 252 rw); 253 turnstile_wait(&rw->rw_object, rw_owner(rw), TS_SHARED_QUEUE); 254 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 255 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 256 __func__, rw); 257 } 258 259 /* 260 * TODO: acquire "owner of record" here. Here be turnstile dragons 261 * however. turnstiles don't like owners changing between calls to 262 * turnstile_wait() currently. 263 */ 264 265 LOCK_LOG_LOCK("RLOCK", &rw->rw_object, 0, 0, file, line); 266 WITNESS_LOCK(&rw->rw_object, 0, file, line); 267} 268 269void 270_rw_runlock(struct rwlock *rw, const char *file, int line) 271{ 272 struct turnstile *ts; 273 uintptr_t x; 274 275 _rw_assert(rw, RA_RLOCKED, file, line); 276 WITNESS_UNLOCK(&rw->rw_object, 0, file, line); 277 LOCK_LOG_LOCK("RUNLOCK", &rw->rw_object, 0, 0, file, line); 278 279 /* TODO: drop "owner of record" here. */ 280 281 for (;;) { 282 /* 283 * See if there is more than one read lock held. If so, 284 * just drop one and return. 285 */ 286 x = rw->rw_lock; 287 if (RW_READERS(x) > 1) { 288 if (atomic_cmpset_ptr(&rw->rw_lock, x, 289 x - RW_ONE_READER)) { 290 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 291 CTR4(KTR_LOCK, 292 "%s: %p succeeded %p -> %p", 293 __func__, rw, (void *)x, 294 (void *)(x - RW_ONE_READER)); 295 break; 296 } 297 continue; 298 } 299 300 /* 301 * We should never have read waiters while at least one 302 * thread holds a read lock. (See note above) 303 */ 304 KASSERT(!(x & RW_LOCK_READ_WAITERS), 305 ("%s: waiting readers", __func__)); 306 307 /* 308 * If there aren't any waiters for a write lock, then try 309 * to drop it quickly. 310 */ 311 if (!(x & RW_LOCK_WRITE_WAITERS)) { 312 313 /* 314 * There shouldn't be any flags set and we should 315 * be the only read lock. If we fail to release 316 * the single read lock, then another thread might 317 * have just acquired a read lock, so go back up 318 * to the multiple read locks case. 319 */ 320 MPASS(x == RW_READERS_LOCK(1)); 321 if (atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1), 322 RW_UNLOCKED)) { 323 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 324 CTR2(KTR_LOCK, "%s: %p last succeeded", 325 __func__, rw); 326 break; 327 } 328 continue; 329 } 330 331 /* 332 * There should just be one reader with one or more 333 * writers waiting. 334 */ 335 MPASS(x == (RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS)); 336 337 /* 338 * Ok, we know we have a waiting writer and we think we 339 * are the last reader, so grab the turnstile lock. 340 */ 341 turnstile_lock(&rw->rw_object); 342 343 /* 344 * Try to drop our lock leaving the lock in a unlocked 345 * state. 346 * 347 * If you wanted to do explicit lock handoff you'd have to 348 * do it here. You'd also want to use turnstile_signal() 349 * and you'd have to handle the race where a higher 350 * priority thread blocks on the write lock before the 351 * thread you wakeup actually runs and have the new thread 352 * "steal" the lock. For now it's a lot simpler to just 353 * wakeup all of the waiters. 354 * 355 * As above, if we fail, then another thread might have 356 * acquired a read lock, so drop the turnstile lock and 357 * restart. 358 */ 359 if (!atomic_cmpset_ptr(&rw->rw_lock, 360 RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS, RW_UNLOCKED)) { 361 turnstile_release(&rw->rw_object); 362 continue; 363 } 364 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 365 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", 366 __func__, rw); 367 368 /* 369 * Ok. The lock is released and all that's left is to 370 * wake up the waiters. Note that the lock might not be 371 * free anymore, but in that case the writers will just 372 * block again if they run before the new lock holder(s) 373 * release the lock. 374 */ 375 ts = turnstile_lookup(&rw->rw_object); 376 MPASS(ts != NULL); 377 turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); 378 turnstile_unpend(ts, TS_SHARED_LOCK); 379 break; 380 } 381} 382 383/* 384 * This function is called when we are unable to obtain a write lock on the 385 * first try. This means that at least one other thread holds either a 386 * read or write lock. 387 */ 388void 389_rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 390{ 391 volatile struct thread *owner; 392 uintptr_t v; 393 394 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 395 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 396 rw->rw_object.lo_name, (void *)rw->rw_lock, file, line); 397 398 while (!_rw_write_lock(rw, tid)) { 399 turnstile_lock(&rw->rw_object); 400 v = rw->rw_lock; 401 402 /* 403 * If the lock was released while spinning on the 404 * turnstile chain lock, try again. 405 */ 406 if (v == RW_UNLOCKED) { 407 turnstile_release(&rw->rw_object); 408 cpu_spinwait(); 409 continue; 410 } 411 412 /* 413 * If the lock was released by a writer with both readers 414 * and writers waiting and a reader hasn't woken up and 415 * acquired the lock yet, rw_lock will be set to the 416 * value RW_UNLOCKED | RW_LOCK_WRITE_WAITERS. If we see 417 * that value, try to acquire it once. Note that we have 418 * to preserve the RW_LOCK_WRITE_WAITERS flag as there are 419 * other writers waiting still. If we fail, restart the 420 * loop. 421 */ 422 if (v == (RW_UNLOCKED | RW_LOCK_WRITE_WAITERS)) { 423 if (atomic_cmpset_acq_ptr(&rw->rw_lock, 424 RW_UNLOCKED | RW_LOCK_WRITE_WAITERS, 425 tid | RW_LOCK_WRITE_WAITERS)) { 426 turnstile_claim(&rw->rw_object); 427 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 428 __func__, rw); 429 break; 430 } 431 turnstile_release(&rw->rw_object); 432 cpu_spinwait(); 433 continue; 434 } 435 436 /* 437 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to 438 * set it. If we fail to set it, then loop back and try 439 * again. 440 */ 441 if (!(v & RW_LOCK_WRITE_WAITERS)) { 442 if (!atomic_cmpset_ptr(&rw->rw_lock, v, 443 v | RW_LOCK_WRITE_WAITERS)) { 444 turnstile_release(&rw->rw_object); 445 cpu_spinwait(); 446 continue; 447 } 448 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 449 CTR2(KTR_LOCK, "%s: %p set write waiters flag", 450 __func__, rw); 451 } 452 453#ifdef SMP 454 /* 455 * If the lock is write locked and the owner is 456 * running on another CPU, spin until the owner stops 457 * running or the state of the lock changes. 458 */ 459 owner = (struct thread *)RW_OWNER(v); 460 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) { 461 turnstile_release(&rw->rw_object); 462 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 463 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 464 __func__, rw, owner); 465 while ((struct thread*)RW_OWNER(rw->rw_lock)== owner && 466 TD_IS_RUNNING(owner)) 467 cpu_spinwait(); 468 continue; 469 } 470#endif 471 472 /* 473 * We were unable to acquire the lock and the write waiters 474 * flag is set, so we must block on the turnstile. 475 */ 476 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 477 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 478 rw); 479 turnstile_wait(&rw->rw_object, rw_owner(rw), 480 TS_EXCLUSIVE_QUEUE); 481 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 482 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 483 __func__, rw); 484 } 485} 486 487/* 488 * This function is called if the first try at releasing a write lock failed. 489 * This means that one of the 2 waiter bits must be set indicating that at 490 * least one thread is waiting on this lock. 491 */ 492void 493_rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 494{ 495 struct turnstile *ts; 496 uintptr_t v; 497 int queue; 498 499 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), 500 ("%s: neither of the waiter flags are set", __func__)); 501 502 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 503 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); 504 505 turnstile_lock(&rw->rw_object); 506 ts = turnstile_lookup(&rw->rw_object); 507 508#ifdef SMP 509 /* 510 * There might not be a turnstile for this lock if all of 511 * the waiters are adaptively spinning. In that case, just 512 * reset the lock to the unlocked state and return. 513 */ 514 if (ts == NULL) { 515 atomic_store_rel_ptr(&rw->rw_lock, RW_UNLOCKED); 516 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 517 CTR2(KTR_LOCK, "%s: %p no sleepers", __func__, rw); 518 turnstile_release(&rw->rw_object); 519 return; 520 } 521#else 522 MPASS(ts != NULL); 523#endif 524 525 /* 526 * Use the same algo as sx locks for now. Prefer waking up shared 527 * waiters if we have any over writers. This is probably not ideal. 528 * 529 * 'v' is the value we are going to write back to rw_lock. If we 530 * have waiters on both queues, we need to preserve the state of 531 * the waiter flag for the queue we don't wake up. For now this is 532 * hardcoded for the algorithm mentioned above. 533 * 534 * In the case of both readers and writers waiting we wakeup the 535 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a 536 * new writer comes in before a reader it will claim the lock up 537 * above. There is probably a potential priority inversion in 538 * there that could be worked around either by waking both queues 539 * of waiters or doing some complicated lock handoff gymnastics. 540 * 541 * Note that in the SMP case, if both flags are set, there might 542 * not be any actual writers on the turnstile as they might all 543 * be spinning. In that case, we don't want to preserve the 544 * RW_LOCK_WRITE_WAITERS flag as the turnstile is going to go 545 * away once we wakeup all the readers. 546 */ 547 v = RW_UNLOCKED; 548 if (rw->rw_lock & RW_LOCK_READ_WAITERS) { 549 queue = TS_SHARED_QUEUE; 550#ifdef SMP 551 if (rw->rw_lock & RW_LOCK_WRITE_WAITERS && 552 !turnstile_empty(ts, TS_EXCLUSIVE_QUEUE)) 553 v |= RW_LOCK_WRITE_WAITERS; 554#else 555 v |= (rw->rw_lock & RW_LOCK_WRITE_WAITERS); 556#endif 557 } else 558 queue = TS_EXCLUSIVE_QUEUE; 559 560#ifdef SMP 561 /* 562 * We have to make sure that we actually have waiters to 563 * wakeup. If they are all spinning, then we just need to 564 * disown the turnstile and return. 565 */ 566 if (turnstile_empty(ts, queue)) { 567 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 568 CTR2(KTR_LOCK, "%s: %p no sleepers 2", __func__, rw); 569 atomic_store_rel_ptr(&rw->rw_lock, v); 570 turnstile_disown(ts); 571 return; 572 } 573#endif 574 575 /* Wake up all waiters for the specific queue. */ 576 if (LOCK_LOG_TEST(&rw->rw_object, 0)) 577 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, 578 queue == TS_SHARED_QUEUE ? "read" : "write"); 579 turnstile_broadcast(ts, queue); 580 atomic_store_rel_ptr(&rw->rw_lock, v); 581 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 582} 583 584#ifdef INVARIANT_SUPPORT 585#ifndef INVARIANTS 586#undef _rw_assert 587#endif 588 589/* 590 * In the non-WITNESS case, rw_assert() can only detect that at least 591 * *some* thread owns an rlock, but it cannot guarantee that *this* 592 * thread owns an rlock. 593 */ 594void 595_rw_assert(struct rwlock *rw, int what, const char *file, int line) 596{ 597 598 if (panicstr != NULL) 599 return; 600 switch (what) { 601 case RA_LOCKED: 602 case RA_RLOCKED: 603#ifdef WITNESS 604 witness_assert(&rw->rw_object, what, file, line); 605#else 606 /* 607 * If some other thread has a write lock or we have one 608 * and are asserting a read lock, fail. Also, if no one 609 * has a lock at all, fail. 610 */ 611 if (rw->rw_lock == RW_UNLOCKED || 612 (!(rw->rw_lock & RW_LOCK_READ) && (what == RA_RLOCKED || 613 rw_wowner(rw) != curthread))) 614 panic("Lock %s not %slocked @ %s:%d\n", 615 rw->rw_object.lo_name, (what == RA_RLOCKED) ? 616 "read " : "", file, line); 617#endif 618 break; 619 case RA_WLOCKED: 620 if (rw_wowner(rw) != curthread) 621 panic("Lock %s not exclusively locked @ %s:%d\n", 622 rw->rw_object.lo_name, file, line); 623 break; 624 case RA_UNLOCKED: 625#ifdef WITNESS 626 witness_assert(&rw->rw_object, what, file, line); 627#else 628 /* 629 * If we hold a write lock fail. We can't reliably check 630 * to see if we hold a read lock or not. 631 */ 632 if (rw_wowner(rw) == curthread) 633 panic("Lock %s exclusively locked @ %s:%d\n", 634 rw->rw_object.lo_name, file, line); 635#endif 636 break; 637 default: 638 panic("Unknown rw lock assertion: %d @ %s:%d", what, file, 639 line); 640 } 641} 642#endif /* INVARIANT_SUPPORT */ 643 644#ifdef DDB 645void 646db_show_rwlock(struct lock_object *lock) 647{ 648 struct rwlock *rw; 649 struct thread *td; 650 651 rw = (struct rwlock *)lock; 652 653 db_printf(" state: "); 654 if (rw->rw_lock == RW_UNLOCKED) 655 db_printf("UNLOCKED\n"); 656 else if (rw->rw_lock & RW_LOCK_READ) 657 db_printf("RLOCK: %jd locks\n", 658 (intmax_t)(RW_READERS(rw->rw_lock))); 659 else { 660 td = rw_wowner(rw); 661 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 662 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 663 } 664 db_printf(" waiters: "); 665 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { 666 case RW_LOCK_READ_WAITERS: 667 db_printf("readers\n"); 668 break; 669 case RW_LOCK_WRITE_WAITERS: 670 db_printf("writers\n"); 671 break; 672 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: 673 db_printf("readers and waiters\n"); 674 break; 675 default: 676 db_printf("none\n"); 677 break; 678 } 679} 680 681#endif 682