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 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 */ 27 28 /* 29 * Machine independent bits of reader/writer lock implementation. 30 */ 31 32 #include <sys/cdefs.h> 33 __FBSDID("$FreeBSD$"); 34 35 #include "opt_ddb.h" 36 #include "opt_hwpmc_hooks.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 __read_frequently rowner_retries; 98 static int __read_frequently rowner_loops; 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 __read_frequently rw_delay; 105 106 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base, 107 0, ""); 108 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max, 109 0, ""); 110 111 static void 112 rw_lock_delay_init(void *arg __unused) 113 { 114 115 lock_delay_default_init(&rw_delay); 116 rowner_retries = 10; 117 rowner_loops = max(10000, rw_delay.max); 118 } 119 LOCK_DELAY_SYSINIT(rw_lock_delay_init); 120 #endif 121 122 /* 123 * Return a pointer to the owning thread if the lock is write-locked or 124 * NULL if the lock is unlocked or read-locked. 125 */ 126 127 #define lv_rw_wowner(v) \ 128 ((v) & RW_LOCK_READ ? NULL : \ 129 (struct thread *)RW_OWNER((v))) 130 131 #define rw_wowner(rw) lv_rw_wowner(RW_READ_VALUE(rw)) 132 133 /* 134 * Returns if a write owner is recursed. Write ownership is not assured 135 * here and should be previously checked. 136 */ 137 #define rw_recursed(rw) ((rw)->rw_recurse != 0) 138 139 /* 140 * Return true if curthread helds the lock. 141 */ 142 #define rw_wlocked(rw) (rw_wowner((rw)) == curthread) 143 144 /* 145 * Return a pointer to the owning thread for this lock who should receive 146 * any priority lent by threads that block on this lock. Currently this 147 * is identical to rw_wowner(). 148 */ 149 #define rw_owner(rw) rw_wowner(rw) 150 151 #ifndef INVARIANTS 152 #define __rw_assert(c, what, file, line) 153 #endif 154 155 void 156 assert_rw(const struct lock_object *lock, int what) 157 { 158 159 rw_assert((const struct rwlock *)lock, what); 160 } 161 162 void 163 lock_rw(struct lock_object *lock, uintptr_t how) 164 { 165 struct rwlock *rw; 166 167 rw = (struct rwlock *)lock; 168 if (how) 169 rw_rlock(rw); 170 else 171 rw_wlock(rw); 172 } 173 174 uintptr_t 175 unlock_rw(struct lock_object *lock) 176 { 177 struct rwlock *rw; 178 179 rw = (struct rwlock *)lock; 180 rw_assert(rw, RA_LOCKED | LA_NOTRECURSED); 181 if (rw->rw_lock & RW_LOCK_READ) { 182 rw_runlock(rw); 183 return (1); 184 } else { 185 rw_wunlock(rw); 186 return (0); 187 } 188 } 189 190 #ifdef KDTRACE_HOOKS 191 int 192 owner_rw(const struct lock_object *lock, struct thread **owner) 193 { 194 const struct rwlock *rw = (const struct rwlock *)lock; 195 uintptr_t x = rw->rw_lock; 196 197 *owner = rw_wowner(rw); 198 return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) : 199 (*owner != NULL)); 200 } 201 #endif 202 203 void 204 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts) 205 { 206 struct rwlock *rw; 207 int flags; 208 209 rw = rwlock2rw(c); 210 211 MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | 212 RW_RECURSE | RW_NEW)) == 0); 213 ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock, 214 ("%s: rw_lock not aligned for %s: %p", __func__, name, 215 &rw->rw_lock)); 216 217 flags = LO_UPGRADABLE; 218 if (opts & RW_DUPOK) 219 flags |= LO_DUPOK; 220 if (opts & RW_NOPROFILE) 221 flags |= LO_NOPROFILE; 222 if (!(opts & RW_NOWITNESS)) 223 flags |= LO_WITNESS; 224 if (opts & RW_RECURSE) 225 flags |= LO_RECURSABLE; 226 if (opts & RW_QUIET) 227 flags |= LO_QUIET; 228 if (opts & RW_NEW) 229 flags |= LO_NEW; 230 231 lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); 232 rw->rw_lock = RW_UNLOCKED; 233 rw->rw_recurse = 0; 234 } 235 236 void 237 _rw_destroy(volatile uintptr_t *c) 238 { 239 struct rwlock *rw; 240 241 rw = rwlock2rw(c); 242 243 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw)); 244 KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw)); 245 rw->rw_lock = RW_DESTROYED; 246 lock_destroy(&rw->lock_object); 247 } 248 249 void 250 rw_sysinit(void *arg) 251 { 252 struct rw_args *args; 253 254 args = arg; 255 rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc, 256 args->ra_flags); 257 } 258 259 int 260 _rw_wowned(const volatile uintptr_t *c) 261 { 262 263 return (rw_wowner(rwlock2rw(c)) == curthread); 264 } 265 266 void 267 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line) 268 { 269 struct rwlock *rw; 270 uintptr_t tid, v; 271 272 rw = rwlock2rw(c); 273 274 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 275 !TD_IS_IDLETHREAD(curthread), 276 ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d", 277 curthread, rw->lock_object.lo_name, file, line)); 278 KASSERT(rw->rw_lock != RW_DESTROYED, 279 ("rw_wlock() of destroyed rwlock @ %s:%d", file, line)); 280 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 281 line, NULL); 282 tid = (uintptr_t)curthread; 283 v = RW_UNLOCKED; 284 if (!_rw_write_lock_fetch(rw, &v, tid)) 285 _rw_wlock_hard(rw, v, file, line); 286 else 287 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, 288 0, 0, file, line, LOCKSTAT_WRITER); 289 290 LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line); 291 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 292 TD_LOCKS_INC(curthread); 293 } 294 295 int 296 __rw_try_wlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 297 { 298 struct thread *td; 299 uintptr_t tid, v; 300 int rval; 301 bool recursed; 302 303 td = curthread; 304 tid = (uintptr_t)td; 305 if (SCHEDULER_STOPPED_TD(td)) 306 return (1); 307 308 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 309 ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d", 310 curthread, rw->lock_object.lo_name, file, line)); 311 KASSERT(rw->rw_lock != RW_DESTROYED, 312 ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line)); 313 314 rval = 1; 315 recursed = false; 316 v = RW_UNLOCKED; 317 for (;;) { 318 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid)) 319 break; 320 if (v == RW_UNLOCKED) 321 continue; 322 if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) { 323 rw->rw_recurse++; 324 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED); 325 break; 326 } 327 rval = 0; 328 break; 329 } 330 331 LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line); 332 if (rval) { 333 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 334 file, line); 335 if (!recursed) 336 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, 337 rw, 0, 0, file, line, LOCKSTAT_WRITER); 338 TD_LOCKS_INC(curthread); 339 } 340 return (rval); 341 } 342 343 int 344 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line) 345 { 346 struct rwlock *rw; 347 348 rw = rwlock2rw(c); 349 return (__rw_try_wlock_int(rw LOCK_FILE_LINE_ARG)); 350 } 351 352 void 353 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line) 354 { 355 struct rwlock *rw; 356 357 rw = rwlock2rw(c); 358 359 KASSERT(rw->rw_lock != RW_DESTROYED, 360 ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); 361 __rw_assert(c, RA_WLOCKED, file, line); 362 WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 363 LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file, 364 line); 365 366 #ifdef LOCK_PROFILING 367 _rw_wunlock_hard(rw, (uintptr_t)curthread, file, line); 368 #else 369 __rw_wunlock(rw, curthread, file, line); 370 #endif 371 372 TD_LOCKS_DEC(curthread); 373 } 374 375 /* 376 * Determines whether a new reader can acquire a lock. Succeeds if the 377 * reader already owns a read lock and the lock is locked for read to 378 * prevent deadlock from reader recursion. Also succeeds if the lock 379 * is unlocked and has no writer waiters or spinners. Failing otherwise 380 * prioritizes writers before readers. 381 */ 382 static bool __always_inline 383 __rw_can_read(struct thread *td, uintptr_t v, bool fp) 384 { 385 386 if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) 387 == RW_LOCK_READ) 388 return (true); 389 if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ)) 390 return (true); 391 return (false); 392 } 393 394 static bool __always_inline 395 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp 396 LOCK_FILE_LINE_ARG_DEF) 397 { 398 399 /* 400 * Handle the easy case. If no other thread has a write 401 * lock, then try to bump up the count of read locks. Note 402 * that we have to preserve the current state of the 403 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a 404 * read lock, then rw_lock must have changed, so restart 405 * the loop. Note that this handles the case of a 406 * completely unlocked rwlock since such a lock is encoded 407 * as a read lock with no waiters. 408 */ 409 while (__rw_can_read(td, *vp, fp)) { 410 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp, 411 *vp + RW_ONE_READER)) { 412 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 413 CTR4(KTR_LOCK, 414 "%s: %p succeed %p -> %p", __func__, 415 rw, (void *)*vp, 416 (void *)(*vp + RW_ONE_READER)); 417 td->td_rw_rlocks++; 418 return (true); 419 } 420 } 421 return (false); 422 } 423 424 static void __noinline 425 __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v 426 LOCK_FILE_LINE_ARG_DEF) 427 { 428 struct turnstile *ts; 429 struct thread *owner; 430 #ifdef ADAPTIVE_RWLOCKS 431 int spintries = 0; 432 int i, n; 433 #endif 434 #ifdef LOCK_PROFILING 435 uint64_t waittime = 0; 436 int contested = 0; 437 #endif 438 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS) 439 struct lock_delay_arg lda; 440 #endif 441 #ifdef KDTRACE_HOOKS 442 u_int sleep_cnt = 0; 443 int64_t sleep_time = 0; 444 int64_t all_time = 0; 445 #endif 446 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 447 uintptr_t state = 0; 448 int doing_lockprof = 0; 449 #endif 450 451 #ifdef KDTRACE_HOOKS 452 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) { 453 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG)) 454 goto out_lockstat; 455 doing_lockprof = 1; 456 all_time -= lockstat_nsecs(&rw->lock_object); 457 state = v; 458 } 459 #endif 460 #ifdef LOCK_PROFILING 461 doing_lockprof = 1; 462 state = v; 463 #endif 464 465 if (SCHEDULER_STOPPED()) 466 return; 467 468 #if defined(ADAPTIVE_RWLOCKS) 469 lock_delay_arg_init(&lda, &rw_delay); 470 #elif defined(KDTRACE_HOOKS) 471 lock_delay_arg_init(&lda, NULL); 472 #endif 473 474 #ifdef HWPMC_HOOKS 475 PMC_SOFT_CALL( , , lock, failed); 476 #endif 477 lock_profile_obtain_lock_failed(&rw->lock_object, 478 &contested, &waittime); 479 480 for (;;) { 481 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG)) 482 break; 483 #ifdef KDTRACE_HOOKS 484 lda.spin_cnt++; 485 #endif 486 487 #ifdef ADAPTIVE_RWLOCKS 488 /* 489 * If the owner is running on another CPU, spin until 490 * the owner stops running or the state of the lock 491 * changes. 492 */ 493 if ((v & RW_LOCK_READ) == 0) { 494 owner = (struct thread *)RW_OWNER(v); 495 if (TD_IS_RUNNING(owner)) { 496 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 497 CTR3(KTR_LOCK, 498 "%s: spinning on %p held by %p", 499 __func__, rw, owner); 500 KTR_STATE1(KTR_SCHED, "thread", 501 sched_tdname(curthread), "spinning", 502 "lockname:\"%s\"", rw->lock_object.lo_name); 503 do { 504 lock_delay(&lda); 505 v = RW_READ_VALUE(rw); 506 owner = lv_rw_wowner(v); 507 } while (owner != NULL && TD_IS_RUNNING(owner)); 508 KTR_STATE0(KTR_SCHED, "thread", 509 sched_tdname(curthread), "running"); 510 continue; 511 } 512 } else { 513 if ((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) { 514 MPASS(!__rw_can_read(td, v, false)); 515 lock_delay_spin(2); 516 v = RW_READ_VALUE(rw); 517 continue; 518 } 519 if (spintries < rowner_retries) { 520 spintries++; 521 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 522 "spinning", "lockname:\"%s\"", 523 rw->lock_object.lo_name); 524 n = RW_READERS(v); 525 for (i = 0; i < rowner_loops; i += n) { 526 lock_delay_spin(n); 527 v = RW_READ_VALUE(rw); 528 if (!(v & RW_LOCK_READ)) 529 break; 530 n = RW_READERS(v); 531 if (n == 0) 532 break; 533 if (__rw_can_read(td, v, false)) 534 break; 535 } 536 #ifdef KDTRACE_HOOKS 537 lda.spin_cnt += rowner_loops - i; 538 #endif 539 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 540 "running"); 541 if (i < rowner_loops) 542 continue; 543 } 544 } 545 #endif 546 547 /* 548 * Okay, now it's the hard case. Some other thread already 549 * has a write lock or there are write waiters present, 550 * acquire the turnstile lock so we can begin the process 551 * of blocking. 552 */ 553 ts = turnstile_trywait(&rw->lock_object); 554 555 /* 556 * The lock might have been released while we spun, so 557 * recheck its state and restart the loop if needed. 558 */ 559 v = RW_READ_VALUE(rw); 560 retry_ts: 561 if (((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) || 562 __rw_can_read(td, v, false)) { 563 turnstile_cancel(ts); 564 continue; 565 } 566 567 owner = lv_rw_wowner(v); 568 569 #ifdef ADAPTIVE_RWLOCKS 570 /* 571 * The current lock owner might have started executing 572 * on another CPU (or the lock could have changed 573 * owners) while we were waiting on the turnstile 574 * chain lock. If so, drop the turnstile lock and try 575 * again. 576 */ 577 if (owner != NULL) { 578 if (TD_IS_RUNNING(owner)) { 579 turnstile_cancel(ts); 580 continue; 581 } 582 } 583 #endif 584 585 /* 586 * The lock is held in write mode or it already has waiters. 587 */ 588 MPASS(!__rw_can_read(td, v, false)); 589 590 /* 591 * If the RW_LOCK_READ_WAITERS flag is already set, then 592 * we can go ahead and block. If it is not set then try 593 * to set it. If we fail to set it drop the turnstile 594 * lock and restart the loop. 595 */ 596 if (!(v & RW_LOCK_READ_WAITERS)) { 597 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, 598 v | RW_LOCK_READ_WAITERS)) 599 goto retry_ts; 600 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 601 CTR2(KTR_LOCK, "%s: %p set read waiters flag", 602 __func__, rw); 603 } 604 605 /* 606 * We were unable to acquire the lock and the read waiters 607 * flag is set, so we must block on the turnstile. 608 */ 609 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 610 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 611 rw); 612 #ifdef KDTRACE_HOOKS 613 sleep_time -= lockstat_nsecs(&rw->lock_object); 614 #endif 615 MPASS(owner == rw_owner(rw)); 616 turnstile_wait(ts, owner, TS_SHARED_QUEUE); 617 #ifdef KDTRACE_HOOKS 618 sleep_time += lockstat_nsecs(&rw->lock_object); 619 sleep_cnt++; 620 #endif 621 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 622 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 623 __func__, rw); 624 v = RW_READ_VALUE(rw); 625 } 626 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 627 if (__predict_true(!doing_lockprof)) 628 return; 629 #endif 630 #ifdef KDTRACE_HOOKS 631 all_time += lockstat_nsecs(&rw->lock_object); 632 if (sleep_time) 633 LOCKSTAT_RECORD4(rw__block, rw, sleep_time, 634 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0, 635 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 636 637 /* Record only the loops spinning and not sleeping. */ 638 if (lda.spin_cnt > sleep_cnt) 639 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time, 640 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0, 641 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 642 out_lockstat: 643 #endif 644 /* 645 * TODO: acquire "owner of record" here. Here be turnstile dragons 646 * however. turnstiles don't like owners changing between calls to 647 * turnstile_wait() currently. 648 */ 649 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested, 650 waittime, file, line, LOCKSTAT_READER); 651 } 652 653 void 654 __rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 655 { 656 struct thread *td; 657 uintptr_t v; 658 659 td = curthread; 660 661 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) || 662 !TD_IS_IDLETHREAD(td), 663 ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d", 664 td, rw->lock_object.lo_name, file, line)); 665 KASSERT(rw->rw_lock != RW_DESTROYED, 666 ("rw_rlock() of destroyed rwlock @ %s:%d", file, line)); 667 KASSERT(rw_wowner(rw) != td, 668 ("rw_rlock: wlock already held for %s @ %s:%d", 669 rw->lock_object.lo_name, file, line)); 670 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL); 671 672 v = RW_READ_VALUE(rw); 673 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__acquire) || 674 !__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG))) 675 __rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG); 676 else 677 lock_profile_obtain_lock_success(&rw->lock_object, 0, 0, 678 file, line); 679 680 LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line); 681 WITNESS_LOCK(&rw->lock_object, 0, file, line); 682 TD_LOCKS_INC(curthread); 683 } 684 685 void 686 __rw_rlock(volatile uintptr_t *c, const char *file, int line) 687 { 688 struct rwlock *rw; 689 690 rw = rwlock2rw(c); 691 __rw_rlock_int(rw LOCK_FILE_LINE_ARG); 692 } 693 694 int 695 __rw_try_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 696 { 697 uintptr_t x; 698 699 if (SCHEDULER_STOPPED()) 700 return (1); 701 702 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 703 ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d", 704 curthread, rw->lock_object.lo_name, file, line)); 705 706 x = rw->rw_lock; 707 for (;;) { 708 KASSERT(rw->rw_lock != RW_DESTROYED, 709 ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line)); 710 if (!(x & RW_LOCK_READ)) 711 break; 712 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) { 713 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file, 714 line); 715 WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line); 716 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, 717 rw, 0, 0, file, line, LOCKSTAT_READER); 718 TD_LOCKS_INC(curthread); 719 curthread->td_rw_rlocks++; 720 return (1); 721 } 722 } 723 724 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line); 725 return (0); 726 } 727 728 int 729 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line) 730 { 731 struct rwlock *rw; 732 733 rw = rwlock2rw(c); 734 return (__rw_try_rlock_int(rw LOCK_FILE_LINE_ARG)); 735 } 736 737 static bool __always_inline 738 __rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp) 739 { 740 741 for (;;) { 742 if (RW_READERS(*vp) > 1 || !(*vp & RW_LOCK_WAITERS)) { 743 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp, 744 *vp - RW_ONE_READER)) { 745 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 746 CTR4(KTR_LOCK, 747 "%s: %p succeeded %p -> %p", 748 __func__, rw, (void *)*vp, 749 (void *)(*vp - RW_ONE_READER)); 750 td->td_rw_rlocks--; 751 return (true); 752 } 753 continue; 754 } 755 break; 756 } 757 return (false); 758 } 759 760 static void __noinline 761 __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v 762 LOCK_FILE_LINE_ARG_DEF) 763 { 764 struct turnstile *ts; 765 uintptr_t setv, queue; 766 767 if (SCHEDULER_STOPPED()) 768 return; 769 770 if (__rw_runlock_try(rw, td, &v)) 771 goto out_lockstat; 772 773 /* 774 * Ok, we know we have waiters and we think we are the 775 * last reader, so grab the turnstile lock. 776 */ 777 turnstile_chain_lock(&rw->lock_object); 778 v = RW_READ_VALUE(rw); 779 for (;;) { 780 if (__rw_runlock_try(rw, td, &v)) 781 break; 782 783 MPASS(v & RW_LOCK_WAITERS); 784 785 /* 786 * Try to drop our lock leaving the lock in a unlocked 787 * state. 788 * 789 * If you wanted to do explicit lock handoff you'd have to 790 * do it here. You'd also want to use turnstile_signal() 791 * and you'd have to handle the race where a higher 792 * priority thread blocks on the write lock before the 793 * thread you wakeup actually runs and have the new thread 794 * "steal" the lock. For now it's a lot simpler to just 795 * wakeup all of the waiters. 796 * 797 * As above, if we fail, then another thread might have 798 * acquired a read lock, so drop the turnstile lock and 799 * restart. 800 */ 801 setv = RW_UNLOCKED; 802 queue = TS_SHARED_QUEUE; 803 if (v & RW_LOCK_WRITE_WAITERS) { 804 queue = TS_EXCLUSIVE_QUEUE; 805 setv |= (v & RW_LOCK_READ_WAITERS); 806 } 807 setv |= (v & RW_LOCK_WRITE_SPINNER); 808 if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv)) 809 continue; 810 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 811 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", 812 __func__, rw); 813 814 /* 815 * Ok. The lock is released and all that's left is to 816 * wake up the waiters. Note that the lock might not be 817 * free anymore, but in that case the writers will just 818 * block again if they run before the new lock holder(s) 819 * release the lock. 820 */ 821 ts = turnstile_lookup(&rw->lock_object); 822 MPASS(ts != NULL); 823 turnstile_broadcast(ts, queue); 824 turnstile_unpend(ts); 825 td->td_rw_rlocks--; 826 break; 827 } 828 turnstile_chain_unlock(&rw->lock_object); 829 out_lockstat: 830 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER); 831 } 832 833 void 834 _rw_runlock_cookie_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 835 { 836 struct thread *td; 837 uintptr_t v; 838 839 KASSERT(rw->rw_lock != RW_DESTROYED, 840 ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); 841 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line); 842 WITNESS_UNLOCK(&rw->lock_object, 0, file, line); 843 LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line); 844 845 td = curthread; 846 v = RW_READ_VALUE(rw); 847 848 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__release) || 849 !__rw_runlock_try(rw, td, &v))) 850 __rw_runlock_hard(rw, td, v LOCK_FILE_LINE_ARG); 851 else 852 lock_profile_release_lock(&rw->lock_object); 853 854 TD_LOCKS_DEC(curthread); 855 } 856 857 void 858 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line) 859 { 860 struct rwlock *rw; 861 862 rw = rwlock2rw(c); 863 _rw_runlock_cookie_int(rw LOCK_FILE_LINE_ARG); 864 } 865 866 #ifdef ADAPTIVE_RWLOCKS 867 static inline void 868 rw_drop_critical(uintptr_t v, bool *in_critical, int *extra_work) 869 { 870 871 if (v & RW_LOCK_WRITE_SPINNER) 872 return; 873 if (*in_critical) { 874 critical_exit(); 875 *in_critical = false; 876 (*extra_work)--; 877 } 878 } 879 #else 880 #define rw_drop_critical(v, in_critical, extra_work) do { } while (0) 881 #endif 882 883 /* 884 * This function is called when we are unable to obtain a write lock on the 885 * first try. This means that at least one other thread holds either a 886 * read or write lock. 887 */ 888 void 889 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF) 890 { 891 uintptr_t tid; 892 struct rwlock *rw; 893 struct turnstile *ts; 894 struct thread *owner; 895 #ifdef ADAPTIVE_RWLOCKS 896 int spintries = 0; 897 int i, n; 898 enum { READERS, WRITER } sleep_reason = READERS; 899 bool in_critical = false; 900 #endif 901 uintptr_t setv; 902 #ifdef LOCK_PROFILING 903 uint64_t waittime = 0; 904 int contested = 0; 905 #endif 906 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS) 907 struct lock_delay_arg lda; 908 #endif 909 #ifdef KDTRACE_HOOKS 910 u_int sleep_cnt = 0; 911 int64_t sleep_time = 0; 912 int64_t all_time = 0; 913 #endif 914 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 915 uintptr_t state = 0; 916 int doing_lockprof = 0; 917 #endif 918 int extra_work = 0; 919 920 tid = (uintptr_t)curthread; 921 rw = rwlock2rw(c); 922 923 #ifdef KDTRACE_HOOKS 924 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) { 925 while (v == RW_UNLOCKED) { 926 if (_rw_write_lock_fetch(rw, &v, tid)) 927 goto out_lockstat; 928 } 929 extra_work = 1; 930 doing_lockprof = 1; 931 all_time -= lockstat_nsecs(&rw->lock_object); 932 state = v; 933 } 934 #endif 935 #ifdef LOCK_PROFILING 936 extra_work = 1; 937 doing_lockprof = 1; 938 state = v; 939 #endif 940 941 if (SCHEDULER_STOPPED()) 942 return; 943 944 #if defined(ADAPTIVE_RWLOCKS) 945 lock_delay_arg_init(&lda, &rw_delay); 946 #elif defined(KDTRACE_HOOKS) 947 lock_delay_arg_init(&lda, NULL); 948 #endif 949 if (__predict_false(v == RW_UNLOCKED)) 950 v = RW_READ_VALUE(rw); 951 952 if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) { 953 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE, 954 ("%s: recursing but non-recursive rw %s @ %s:%d\n", 955 __func__, rw->lock_object.lo_name, file, line)); 956 rw->rw_recurse++; 957 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED); 958 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 959 CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw); 960 return; 961 } 962 963 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 964 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 965 rw->lock_object.lo_name, (void *)rw->rw_lock, file, line); 966 967 #ifdef HWPMC_HOOKS 968 PMC_SOFT_CALL( , , lock, failed); 969 #endif 970 lock_profile_obtain_lock_failed(&rw->lock_object, 971 &contested, &waittime); 972 973 for (;;) { 974 if (v == RW_UNLOCKED) { 975 if (_rw_write_lock_fetch(rw, &v, tid)) 976 break; 977 continue; 978 } 979 #ifdef KDTRACE_HOOKS 980 lda.spin_cnt++; 981 #endif 982 983 #ifdef ADAPTIVE_RWLOCKS 984 if (v == (RW_LOCK_READ | RW_LOCK_WRITE_SPINNER)) { 985 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid)) 986 break; 987 continue; 988 } 989 990 /* 991 * If the lock is write locked and the owner is 992 * running on another CPU, spin until the owner stops 993 * running or the state of the lock changes. 994 */ 995 if (!(v & RW_LOCK_READ)) { 996 rw_drop_critical(v, &in_critical, &extra_work); 997 sleep_reason = WRITER; 998 owner = lv_rw_wowner(v); 999 if (!TD_IS_RUNNING(owner)) 1000 goto ts; 1001 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1002 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 1003 __func__, rw, owner); 1004 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 1005 "spinning", "lockname:\"%s\"", 1006 rw->lock_object.lo_name); 1007 do { 1008 lock_delay(&lda); 1009 v = RW_READ_VALUE(rw); 1010 owner = lv_rw_wowner(v); 1011 } while (owner != NULL && TD_IS_RUNNING(owner)); 1012 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 1013 "running"); 1014 continue; 1015 } else if (RW_READERS(v) > 0) { 1016 sleep_reason = READERS; 1017 if (spintries == rowner_retries) 1018 goto ts; 1019 if (!(v & RW_LOCK_WRITE_SPINNER)) { 1020 if (!in_critical) { 1021 critical_enter(); 1022 in_critical = true; 1023 extra_work++; 1024 } 1025 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, 1026 v | RW_LOCK_WRITE_SPINNER)) { 1027 critical_exit(); 1028 in_critical = false; 1029 extra_work--; 1030 continue; 1031 } 1032 } 1033 spintries++; 1034 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 1035 "spinning", "lockname:\"%s\"", 1036 rw->lock_object.lo_name); 1037 n = RW_READERS(v); 1038 for (i = 0; i < rowner_loops; i += n) { 1039 lock_delay_spin(n); 1040 v = RW_READ_VALUE(rw); 1041 if (!(v & RW_LOCK_WRITE_SPINNER)) 1042 break; 1043 if (!(v & RW_LOCK_READ)) 1044 break; 1045 n = RW_READERS(v); 1046 if (n == 0) 1047 break; 1048 } 1049 #ifdef KDTRACE_HOOKS 1050 lda.spin_cnt += i; 1051 #endif 1052 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 1053 "running"); 1054 if (i < rowner_loops) 1055 continue; 1056 } 1057 ts: 1058 #endif 1059 ts = turnstile_trywait(&rw->lock_object); 1060 v = RW_READ_VALUE(rw); 1061 retry_ts: 1062 owner = lv_rw_wowner(v); 1063 1064 #ifdef ADAPTIVE_RWLOCKS 1065 /* 1066 * The current lock owner might have started executing 1067 * on another CPU (or the lock could have changed 1068 * owners) while we were waiting on the turnstile 1069 * chain lock. If so, drop the turnstile lock and try 1070 * again. 1071 */ 1072 if (owner != NULL) { 1073 if (TD_IS_RUNNING(owner)) { 1074 turnstile_cancel(ts); 1075 rw_drop_critical(v, &in_critical, &extra_work); 1076 continue; 1077 } 1078 } else if (RW_READERS(v) > 0 && sleep_reason == WRITER) { 1079 turnstile_cancel(ts); 1080 rw_drop_critical(v, &in_critical, &extra_work); 1081 continue; 1082 } 1083 #endif 1084 /* 1085 * Check for the waiters flags about this rwlock. 1086 * If the lock was released, without maintain any pending 1087 * waiters queue, simply try to acquire it. 1088 * If a pending waiters queue is present, claim the lock 1089 * ownership and maintain the pending queue. 1090 */ 1091 setv = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER); 1092 if ((v & ~setv) == RW_UNLOCKED) { 1093 setv &= ~RW_LOCK_WRITE_SPINNER; 1094 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | setv)) { 1095 if (setv) 1096 turnstile_claim(ts); 1097 else 1098 turnstile_cancel(ts); 1099 break; 1100 } 1101 goto retry_ts; 1102 } 1103 1104 #ifdef ADAPTIVE_RWLOCKS 1105 if (in_critical) { 1106 if ((v & RW_LOCK_WRITE_SPINNER) || 1107 !((v & RW_LOCK_WRITE_WAITERS))) { 1108 setv = v & ~RW_LOCK_WRITE_SPINNER; 1109 setv |= RW_LOCK_WRITE_WAITERS; 1110 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, setv)) 1111 goto retry_ts; 1112 } 1113 critical_exit(); 1114 in_critical = false; 1115 extra_work--; 1116 } else { 1117 #endif 1118 /* 1119 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to 1120 * set it. If we fail to set it, then loop back and try 1121 * again. 1122 */ 1123 if (!(v & RW_LOCK_WRITE_WAITERS)) { 1124 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, 1125 v | RW_LOCK_WRITE_WAITERS)) 1126 goto retry_ts; 1127 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1128 CTR2(KTR_LOCK, "%s: %p set write waiters flag", 1129 __func__, rw); 1130 } 1131 #ifdef ADAPTIVE_RWLOCKS 1132 } 1133 #endif 1134 /* 1135 * We were unable to acquire the lock and the write waiters 1136 * flag is set, so we must block on the turnstile. 1137 */ 1138 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1139 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 1140 rw); 1141 #ifdef KDTRACE_HOOKS 1142 sleep_time -= lockstat_nsecs(&rw->lock_object); 1143 #endif 1144 MPASS(owner == rw_owner(rw)); 1145 turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE); 1146 #ifdef KDTRACE_HOOKS 1147 sleep_time += lockstat_nsecs(&rw->lock_object); 1148 sleep_cnt++; 1149 #endif 1150 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1151 CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 1152 __func__, rw); 1153 #ifdef ADAPTIVE_RWLOCKS 1154 spintries = 0; 1155 #endif 1156 v = RW_READ_VALUE(rw); 1157 } 1158 if (__predict_true(!extra_work)) 1159 return; 1160 #ifdef ADAPTIVE_RWLOCKS 1161 if (in_critical) 1162 critical_exit(); 1163 #endif 1164 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1165 if (__predict_true(!doing_lockprof)) 1166 return; 1167 #endif 1168 #ifdef KDTRACE_HOOKS 1169 all_time += lockstat_nsecs(&rw->lock_object); 1170 if (sleep_time) 1171 LOCKSTAT_RECORD4(rw__block, rw, sleep_time, 1172 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0, 1173 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 1174 1175 /* Record only the loops spinning and not sleeping. */ 1176 if (lda.spin_cnt > sleep_cnt) 1177 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time, 1178 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0, 1179 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state)); 1180 out_lockstat: 1181 #endif 1182 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested, 1183 waittime, file, line, LOCKSTAT_WRITER); 1184 } 1185 1186 /* 1187 * This function is called if lockstat is active or the first try at releasing 1188 * a write lock failed. The latter means that the lock is recursed or one of 1189 * the 2 waiter bits must be set indicating that at least one thread is waiting 1190 * on this lock. 1191 */ 1192 void 1193 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF) 1194 { 1195 struct rwlock *rw; 1196 struct turnstile *ts; 1197 uintptr_t tid, setv; 1198 int queue; 1199 1200 tid = (uintptr_t)curthread; 1201 if (SCHEDULER_STOPPED()) 1202 return; 1203 1204 rw = rwlock2rw(c); 1205 if (__predict_false(v == tid)) 1206 v = RW_READ_VALUE(rw); 1207 1208 if (v & RW_LOCK_WRITER_RECURSED) { 1209 if (--(rw->rw_recurse) == 0) 1210 atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED); 1211 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1212 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw); 1213 return; 1214 } 1215 1216 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER); 1217 if (v == tid && _rw_write_unlock(rw, tid)) 1218 return; 1219 1220 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), 1221 ("%s: neither of the waiter flags are set", __func__)); 1222 1223 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1224 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); 1225 1226 turnstile_chain_lock(&rw->lock_object); 1227 1228 /* 1229 * Use the same algo as sx locks for now. Prefer waking up shared 1230 * waiters if we have any over writers. This is probably not ideal. 1231 * 1232 * 'v' is the value we are going to write back to rw_lock. If we 1233 * have waiters on both queues, we need to preserve the state of 1234 * the waiter flag for the queue we don't wake up. For now this is 1235 * hardcoded for the algorithm mentioned above. 1236 * 1237 * In the case of both readers and writers waiting we wakeup the 1238 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a 1239 * new writer comes in before a reader it will claim the lock up 1240 * above. There is probably a potential priority inversion in 1241 * there that could be worked around either by waking both queues 1242 * of waiters or doing some complicated lock handoff gymnastics. 1243 */ 1244 setv = RW_UNLOCKED; 1245 v = RW_READ_VALUE(rw); 1246 queue = TS_SHARED_QUEUE; 1247 if (v & RW_LOCK_WRITE_WAITERS) { 1248 queue = TS_EXCLUSIVE_QUEUE; 1249 setv |= (v & RW_LOCK_READ_WAITERS); 1250 } 1251 atomic_store_rel_ptr(&rw->rw_lock, setv); 1252 1253 /* Wake up all waiters for the specific queue. */ 1254 if (LOCK_LOG_TEST(&rw->lock_object, 0)) 1255 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, 1256 queue == TS_SHARED_QUEUE ? "read" : "write"); 1257 1258 ts = turnstile_lookup(&rw->lock_object); 1259 MPASS(ts != NULL); 1260 turnstile_broadcast(ts, queue); 1261 turnstile_unpend(ts); 1262 turnstile_chain_unlock(&rw->lock_object); 1263 } 1264 1265 /* 1266 * Attempt to do a non-blocking upgrade from a read lock to a write 1267 * lock. This will only succeed if this thread holds a single read 1268 * lock. Returns true if the upgrade succeeded and false otherwise. 1269 */ 1270 int 1271 __rw_try_upgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 1272 { 1273 uintptr_t v, setv, tid; 1274 struct turnstile *ts; 1275 int success; 1276 1277 if (SCHEDULER_STOPPED()) 1278 return (1); 1279 1280 KASSERT(rw->rw_lock != RW_DESTROYED, 1281 ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); 1282 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line); 1283 1284 /* 1285 * Attempt to switch from one reader to a writer. If there 1286 * are any write waiters, then we will have to lock the 1287 * turnstile first to prevent races with another writer 1288 * calling turnstile_wait() before we have claimed this 1289 * turnstile. So, do the simple case of no waiters first. 1290 */ 1291 tid = (uintptr_t)curthread; 1292 success = 0; 1293 v = RW_READ_VALUE(rw); 1294 for (;;) { 1295 if (RW_READERS(v) > 1) 1296 break; 1297 if (!(v & RW_LOCK_WAITERS)) { 1298 success = atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid); 1299 if (!success) 1300 continue; 1301 break; 1302 } 1303 1304 /* 1305 * Ok, we think we have waiters, so lock the turnstile. 1306 */ 1307 ts = turnstile_trywait(&rw->lock_object); 1308 v = RW_READ_VALUE(rw); 1309 retry_ts: 1310 if (RW_READERS(v) > 1) { 1311 turnstile_cancel(ts); 1312 break; 1313 } 1314 /* 1315 * Try to switch from one reader to a writer again. This time 1316 * we honor the current state of the waiters flags. 1317 * If we obtain the lock with the flags set, then claim 1318 * ownership of the turnstile. 1319 */ 1320 setv = tid | (v & RW_LOCK_WAITERS); 1321 success = atomic_fcmpset_ptr(&rw->rw_lock, &v, setv); 1322 if (success) { 1323 if (v & RW_LOCK_WAITERS) 1324 turnstile_claim(ts); 1325 else 1326 turnstile_cancel(ts); 1327 break; 1328 } 1329 goto retry_ts; 1330 } 1331 LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line); 1332 if (success) { 1333 curthread->td_rw_rlocks--; 1334 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 1335 file, line); 1336 LOCKSTAT_RECORD0(rw__upgrade, rw); 1337 } 1338 return (success); 1339 } 1340 1341 int 1342 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line) 1343 { 1344 struct rwlock *rw; 1345 1346 rw = rwlock2rw(c); 1347 return (__rw_try_upgrade_int(rw LOCK_FILE_LINE_ARG)); 1348 } 1349 1350 /* 1351 * Downgrade a write lock into a single read lock. 1352 */ 1353 void 1354 __rw_downgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF) 1355 { 1356 struct turnstile *ts; 1357 uintptr_t tid, v; 1358 int rwait, wwait; 1359 1360 if (SCHEDULER_STOPPED()) 1361 return; 1362 1363 KASSERT(rw->rw_lock != RW_DESTROYED, 1364 ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); 1365 __rw_assert(&rw->rw_lock, RA_WLOCKED | RA_NOTRECURSED, file, line); 1366 #ifndef INVARIANTS 1367 if (rw_recursed(rw)) 1368 panic("downgrade of a recursed lock"); 1369 #endif 1370 1371 WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line); 1372 1373 /* 1374 * Convert from a writer to a single reader. First we handle 1375 * the easy case with no waiters. If there are any waiters, we 1376 * lock the turnstile and "disown" the lock. 1377 */ 1378 tid = (uintptr_t)curthread; 1379 if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1))) 1380 goto out; 1381 1382 /* 1383 * Ok, we think we have waiters, so lock the turnstile so we can 1384 * read the waiter flags without any races. 1385 */ 1386 turnstile_chain_lock(&rw->lock_object); 1387 v = rw->rw_lock & RW_LOCK_WAITERS; 1388 rwait = v & RW_LOCK_READ_WAITERS; 1389 wwait = v & RW_LOCK_WRITE_WAITERS; 1390 MPASS(rwait | wwait); 1391 1392 /* 1393 * Downgrade from a write lock while preserving waiters flag 1394 * and give up ownership of the turnstile. 1395 */ 1396 ts = turnstile_lookup(&rw->lock_object); 1397 MPASS(ts != NULL); 1398 if (!wwait) 1399 v &= ~RW_LOCK_READ_WAITERS; 1400 atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v); 1401 /* 1402 * Wake other readers if there are no writers pending. Otherwise they 1403 * won't be able to acquire the lock anyway. 1404 */ 1405 if (rwait && !wwait) { 1406 turnstile_broadcast(ts, TS_SHARED_QUEUE); 1407 turnstile_unpend(ts); 1408 } else 1409 turnstile_disown(ts); 1410 turnstile_chain_unlock(&rw->lock_object); 1411 out: 1412 curthread->td_rw_rlocks++; 1413 LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line); 1414 LOCKSTAT_RECORD0(rw__downgrade, rw); 1415 } 1416 1417 void 1418 __rw_downgrade(volatile uintptr_t *c, const char *file, int line) 1419 { 1420 struct rwlock *rw; 1421 1422 rw = rwlock2rw(c); 1423 __rw_downgrade_int(rw LOCK_FILE_LINE_ARG); 1424 } 1425 1426 #ifdef INVARIANT_SUPPORT 1427 #ifndef INVARIANTS 1428 #undef __rw_assert 1429 #endif 1430 1431 /* 1432 * In the non-WITNESS case, rw_assert() can only detect that at least 1433 * *some* thread owns an rlock, but it cannot guarantee that *this* 1434 * thread owns an rlock. 1435 */ 1436 void 1437 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line) 1438 { 1439 const struct rwlock *rw; 1440 1441 if (SCHEDULER_STOPPED()) 1442 return; 1443 1444 rw = rwlock2rw(c); 1445 1446 switch (what) { 1447 case RA_LOCKED: 1448 case RA_LOCKED | RA_RECURSED: 1449 case RA_LOCKED | RA_NOTRECURSED: 1450 case RA_RLOCKED: 1451 case RA_RLOCKED | RA_RECURSED: 1452 case RA_RLOCKED | RA_NOTRECURSED: 1453 #ifdef WITNESS 1454 witness_assert(&rw->lock_object, what, file, line); 1455 #else 1456 /* 1457 * If some other thread has a write lock or we have one 1458 * and are asserting a read lock, fail. Also, if no one 1459 * has a lock at all, fail. 1460 */ 1461 if (rw->rw_lock == RW_UNLOCKED || 1462 (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED || 1463 rw_wowner(rw) != curthread))) 1464 panic("Lock %s not %slocked @ %s:%d\n", 1465 rw->lock_object.lo_name, (what & RA_RLOCKED) ? 1466 "read " : "", file, line); 1467 1468 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) { 1469 if (rw_recursed(rw)) { 1470 if (what & RA_NOTRECURSED) 1471 panic("Lock %s recursed @ %s:%d\n", 1472 rw->lock_object.lo_name, file, 1473 line); 1474 } else if (what & RA_RECURSED) 1475 panic("Lock %s not recursed @ %s:%d\n", 1476 rw->lock_object.lo_name, file, line); 1477 } 1478 #endif 1479 break; 1480 case RA_WLOCKED: 1481 case RA_WLOCKED | RA_RECURSED: 1482 case RA_WLOCKED | RA_NOTRECURSED: 1483 if (rw_wowner(rw) != curthread) 1484 panic("Lock %s not exclusively locked @ %s:%d\n", 1485 rw->lock_object.lo_name, file, line); 1486 if (rw_recursed(rw)) { 1487 if (what & RA_NOTRECURSED) 1488 panic("Lock %s recursed @ %s:%d\n", 1489 rw->lock_object.lo_name, file, line); 1490 } else if (what & RA_RECURSED) 1491 panic("Lock %s not recursed @ %s:%d\n", 1492 rw->lock_object.lo_name, file, line); 1493 break; 1494 case RA_UNLOCKED: 1495 #ifdef WITNESS 1496 witness_assert(&rw->lock_object, what, file, line); 1497 #else 1498 /* 1499 * If we hold a write lock fail. We can't reliably check 1500 * to see if we hold a read lock or not. 1501 */ 1502 if (rw_wowner(rw) == curthread) 1503 panic("Lock %s exclusively locked @ %s:%d\n", 1504 rw->lock_object.lo_name, file, line); 1505 #endif 1506 break; 1507 default: 1508 panic("Unknown rw lock assertion: %d @ %s:%d", what, file, 1509 line); 1510 } 1511 } 1512 #endif /* INVARIANT_SUPPORT */ 1513 1514 #ifdef DDB 1515 void 1516 db_show_rwlock(const struct lock_object *lock) 1517 { 1518 const struct rwlock *rw; 1519 struct thread *td; 1520 1521 rw = (const struct rwlock *)lock; 1522 1523 db_printf(" state: "); 1524 if (rw->rw_lock == RW_UNLOCKED) 1525 db_printf("UNLOCKED\n"); 1526 else if (rw->rw_lock == RW_DESTROYED) { 1527 db_printf("DESTROYED\n"); 1528 return; 1529 } else if (rw->rw_lock & RW_LOCK_READ) 1530 db_printf("RLOCK: %ju locks\n", 1531 (uintmax_t)(RW_READERS(rw->rw_lock))); 1532 else { 1533 td = rw_wowner(rw); 1534 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1535 td->td_tid, td->td_proc->p_pid, td->td_name); 1536 if (rw_recursed(rw)) 1537 db_printf(" recursed: %u\n", rw->rw_recurse); 1538 } 1539 db_printf(" waiters: "); 1540 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { 1541 case RW_LOCK_READ_WAITERS: 1542 db_printf("readers\n"); 1543 break; 1544 case RW_LOCK_WRITE_WAITERS: 1545 db_printf("writers\n"); 1546 break; 1547 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: 1548 db_printf("readers and writers\n"); 1549 break; 1550 default: 1551 db_printf("none\n"); 1552 break; 1553 } 1554 } 1555 1556 #endif
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