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