1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org> 5 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org> 6 * All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice(s), this list of conditions and the following disclaimer as 13 * the first lines of this file unmodified other than the possible 14 * addition of one or more copyright notices. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice(s), this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 20 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 21 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 22 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 23 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 24 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 25 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 26 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 29 * DAMAGE. 30 */ 31 32 /* 33 * Shared/exclusive locks. This implementation attempts to ensure 34 * deterministic lock granting behavior, so that slocks and xlocks are 35 * interleaved. 36 * 37 * Priority propagation will not generally raise the priority of lock holders, 38 * so should not be relied upon in combination with sx locks. 39 */ 40 41 #include "opt_ddb.h" 42 #include "opt_hwpmc_hooks.h" 43 #include "opt_no_adaptive_sx.h" 44 45 #include <sys/param.h> 46 #include <sys/systm.h> 47 #include <sys/kdb.h> 48 #include <sys/kernel.h> 49 #include <sys/ktr.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/proc.h> 53 #include <sys/sched.h> 54 #include <sys/sleepqueue.h> 55 #include <sys/sx.h> 56 #include <sys/smp.h> 57 #include <sys/sysctl.h> 58 59 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 60 #include <machine/cpu.h> 61 #endif 62 63 #ifdef DDB 64 #include <ddb/ddb.h> 65 #endif 66 67 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 68 #define ADAPTIVE_SX 69 #endif 70 71 #ifdef HWPMC_HOOKS 72 #include <sys/pmckern.h> 73 PMC_SOFT_DECLARE( , , lock, failed); 74 #endif 75 76 /* Handy macros for sleep queues. */ 77 #define SQ_EXCLUSIVE_QUEUE 0 78 #define SQ_SHARED_QUEUE 1 79 80 /* 81 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 82 * drop Giant anytime we have to sleep or if we adaptively spin. 83 */ 84 #define GIANT_DECLARE \ 85 int _giantcnt = 0; \ 86 WITNESS_SAVE_DECL(Giant) \ 87 88 #define GIANT_SAVE(work) do { \ 89 if (__predict_false(mtx_owned(&Giant))) { \ 90 work++; \ 91 WITNESS_SAVE(&Giant.lock_object, Giant); \ 92 while (mtx_owned(&Giant)) { \ 93 _giantcnt++; \ 94 mtx_unlock(&Giant); \ 95 } \ 96 } \ 97 } while (0) 98 99 #define GIANT_RESTORE() do { \ 100 if (_giantcnt > 0) { \ 101 mtx_assert(&Giant, MA_NOTOWNED); \ 102 while (_giantcnt--) \ 103 mtx_lock(&Giant); \ 104 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 105 } \ 106 } while (0) 107 108 /* 109 * Returns true if an exclusive lock is recursed. It assumes 110 * curthread currently has an exclusive lock. 111 */ 112 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 113 114 static void assert_sx(const struct lock_object *lock, int what); 115 #ifdef DDB 116 static void db_show_sx(const struct lock_object *lock); 117 #endif 118 static void lock_sx(struct lock_object *lock, uintptr_t how); 119 #ifdef KDTRACE_HOOKS 120 static int owner_sx(const struct lock_object *lock, struct thread **owner); 121 #endif 122 static uintptr_t unlock_sx(struct lock_object *lock); 123 124 struct lock_class lock_class_sx = { 125 .lc_name = "sx", 126 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 127 .lc_assert = assert_sx, 128 #ifdef DDB 129 .lc_ddb_show = db_show_sx, 130 #endif 131 .lc_lock = lock_sx, 132 .lc_unlock = unlock_sx, 133 #ifdef KDTRACE_HOOKS 134 .lc_owner = owner_sx, 135 #endif 136 }; 137 138 #ifndef INVARIANTS 139 #define _sx_assert(sx, what, file, line) 140 #endif 141 142 #ifdef ADAPTIVE_SX 143 #ifdef SX_CUSTOM_BACKOFF 144 static u_short __read_frequently asx_retries; 145 static u_short __read_frequently asx_loops; 146 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 147 "sxlock debugging"); 148 SYSCTL_U16(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, ""); 149 SYSCTL_U16(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, ""); 150 151 static struct lock_delay_config __read_frequently sx_delay; 152 153 SYSCTL_U16(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base, 154 0, ""); 155 SYSCTL_U16(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max, 156 0, ""); 157 158 static void 159 sx_lock_delay_init(void *arg __unused) 160 { 161 162 lock_delay_default_init(&sx_delay); 163 asx_retries = 10; 164 asx_loops = max(10000, sx_delay.max); 165 } 166 LOCK_DELAY_SYSINIT(sx_lock_delay_init); 167 #else 168 #define sx_delay locks_delay 169 #define asx_retries locks_delay_retries 170 #define asx_loops locks_delay_loops 171 #endif 172 #endif 173 174 void 175 assert_sx(const struct lock_object *lock, int what) 176 { 177 178 sx_assert((const struct sx *)lock, what); 179 } 180 181 void 182 lock_sx(struct lock_object *lock, uintptr_t how) 183 { 184 struct sx *sx; 185 186 sx = (struct sx *)lock; 187 if (how) 188 sx_slock(sx); 189 else 190 sx_xlock(sx); 191 } 192 193 uintptr_t 194 unlock_sx(struct lock_object *lock) 195 { 196 struct sx *sx; 197 198 sx = (struct sx *)lock; 199 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 200 if (sx_xlocked(sx)) { 201 sx_xunlock(sx); 202 return (0); 203 } else { 204 sx_sunlock(sx); 205 return (1); 206 } 207 } 208 209 #ifdef KDTRACE_HOOKS 210 int 211 owner_sx(const struct lock_object *lock, struct thread **owner) 212 { 213 const struct sx *sx; 214 uintptr_t x; 215 216 sx = (const struct sx *)lock; 217 x = sx->sx_lock; 218 *owner = NULL; 219 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 220 ((*owner = (struct thread *)SX_OWNER(x)) != NULL)); 221 } 222 #endif 223 224 void 225 sx_sysinit(void *arg) 226 { 227 struct sx_args *sargs = arg; 228 229 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 230 } 231 232 void 233 sx_init_flags(struct sx *sx, const char *description, int opts) 234 { 235 int flags; 236 237 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 238 SX_NOPROFILE | SX_NEW)) == 0); 239 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 240 ("%s: sx_lock not aligned for %s: %p", __func__, description, 241 &sx->sx_lock)); 242 243 flags = LO_SLEEPABLE | LO_UPGRADABLE; 244 if (opts & SX_DUPOK) 245 flags |= LO_DUPOK; 246 if (opts & SX_NOPROFILE) 247 flags |= LO_NOPROFILE; 248 if (!(opts & SX_NOWITNESS)) 249 flags |= LO_WITNESS; 250 if (opts & SX_RECURSE) 251 flags |= LO_RECURSABLE; 252 if (opts & SX_QUIET) 253 flags |= LO_QUIET; 254 if (opts & SX_NEW) 255 flags |= LO_NEW; 256 257 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 258 sx->sx_lock = SX_LOCK_UNLOCKED; 259 sx->sx_recurse = 0; 260 } 261 262 void 263 sx_destroy(struct sx *sx) 264 { 265 266 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 267 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 268 sx->sx_lock = SX_LOCK_DESTROYED; 269 lock_destroy(&sx->lock_object); 270 } 271 272 int 273 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 274 { 275 uintptr_t x; 276 277 if (SCHEDULER_STOPPED()) 278 return (1); 279 280 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 281 ("sx_try_slock() by idle thread %p on sx %p @ %s:%d", 282 curthread, sx, file, line)); 283 284 x = sx->sx_lock; 285 for (;;) { 286 KASSERT(x != SX_LOCK_DESTROYED, 287 ("sx_try_slock() of destroyed sx %p @ %s:%d", sx, file, 288 line)); 289 if (!(x & SX_LOCK_SHARED)) 290 break; 291 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 292 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 293 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 294 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 295 sx, 0, 0, file, line, LOCKSTAT_READER); 296 TD_LOCKS_INC(curthread); 297 curthread->td_sx_slocks++; 298 return (1); 299 } 300 } 301 302 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 303 return (0); 304 } 305 306 int 307 sx_try_slock_(struct sx *sx, const char *file, int line) 308 { 309 310 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG)); 311 } 312 313 int 314 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 315 { 316 uintptr_t tid, x; 317 int error = 0; 318 319 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 320 !TD_IS_IDLETHREAD(curthread), 321 ("sx_xlock() by idle thread %p on sx %p @ %s:%d", 322 curthread, sx, file, line)); 323 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 324 ("sx_xlock() of destroyed sx %p @ %s:%d", sx, file, line)); 325 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 326 line, NULL); 327 tid = (uintptr_t)curthread; 328 x = SX_LOCK_UNLOCKED; 329 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 330 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG); 331 else 332 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 333 0, 0, file, line, LOCKSTAT_WRITER); 334 if (!error) { 335 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 336 file, line); 337 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 338 TD_LOCKS_INC(curthread); 339 } 340 341 return (error); 342 } 343 344 int 345 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 346 { 347 struct thread *td; 348 uintptr_t tid, x; 349 int rval; 350 bool recursed; 351 352 td = curthread; 353 tid = (uintptr_t)td; 354 if (SCHEDULER_STOPPED()) 355 return (1); 356 357 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 358 ("sx_try_xlock() by idle thread %p on sx %p @ %s:%d", 359 curthread, sx, file, line)); 360 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 361 ("sx_try_xlock() of destroyed sx %p @ %s:%d", sx, file, line)); 362 363 rval = 1; 364 recursed = false; 365 x = SX_LOCK_UNLOCKED; 366 for (;;) { 367 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 368 break; 369 if (x == SX_LOCK_UNLOCKED) 370 continue; 371 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 372 sx->sx_recurse++; 373 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 374 break; 375 } 376 rval = 0; 377 break; 378 } 379 380 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 381 if (rval) { 382 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 383 file, line); 384 if (!recursed) 385 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 386 sx, 0, 0, file, line, LOCKSTAT_WRITER); 387 TD_LOCKS_INC(curthread); 388 } 389 390 return (rval); 391 } 392 393 int 394 sx_try_xlock_(struct sx *sx, const char *file, int line) 395 { 396 397 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG)); 398 } 399 400 void 401 _sx_xunlock(struct sx *sx, const char *file, int line) 402 { 403 404 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 405 ("sx_xunlock() of destroyed sx %p @ %s:%d", sx, file, line)); 406 _sx_assert(sx, SA_XLOCKED, file, line); 407 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 408 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 409 line); 410 #if LOCK_DEBUG > 0 411 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 412 #else 413 __sx_xunlock(sx, curthread, file, line); 414 #endif 415 TD_LOCKS_DEC(curthread); 416 } 417 418 /* 419 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 420 * This will only succeed if this thread holds a single shared lock. 421 * Return 1 if if the upgrade succeed, 0 otherwise. 422 */ 423 int 424 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 425 { 426 uintptr_t x; 427 uintptr_t waiters; 428 int success; 429 430 if (SCHEDULER_STOPPED()) 431 return (1); 432 433 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 434 ("sx_try_upgrade() of destroyed sx %p @ %s:%d", sx, file, line)); 435 _sx_assert(sx, SA_SLOCKED, file, line); 436 437 /* 438 * Try to switch from one shared lock to an exclusive lock. We need 439 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 440 * we will wake up the exclusive waiters when we drop the lock. 441 */ 442 success = 0; 443 x = SX_READ_VALUE(sx); 444 for (;;) { 445 if (SX_SHARERS(x) > 1) 446 break; 447 waiters = (x & SX_LOCK_WAITERS); 448 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 449 (uintptr_t)curthread | waiters)) { 450 success = 1; 451 break; 452 } 453 } 454 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 455 if (success) { 456 curthread->td_sx_slocks--; 457 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 458 file, line); 459 LOCKSTAT_RECORD0(sx__upgrade, sx); 460 } 461 return (success); 462 } 463 464 int 465 sx_try_upgrade_(struct sx *sx, const char *file, int line) 466 { 467 468 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 469 } 470 471 /* 472 * Downgrade an unrecursed exclusive lock into a single shared lock. 473 */ 474 void 475 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 476 { 477 uintptr_t x; 478 479 if (SCHEDULER_STOPPED()) 480 return; 481 482 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 483 ("sx_downgrade() of destroyed sx %p @ %s:%d", sx, file, line)); 484 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 485 #ifndef INVARIANTS 486 if (sx_recursed(sx)) 487 panic("downgrade of a recursed lock"); 488 #endif 489 490 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 491 492 /* 493 * Try to switch from an exclusive lock with no shared waiters 494 * to one sharer with no shared waiters. If there are 495 * exclusive waiters, we don't need to lock the sleep queue so 496 * long as we preserve the flag. We do one quick try and if 497 * that fails we grab the sleepq lock to keep the flags from 498 * changing and do it the slow way. 499 * 500 * We have to lock the sleep queue if there are shared waiters 501 * so we can wake them up. 502 */ 503 x = sx->sx_lock; 504 if (!(x & SX_LOCK_SHARED_WAITERS) && 505 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 506 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 507 goto out; 508 509 /* 510 * Lock the sleep queue so we can read the waiters bits 511 * without any races and wakeup any shared waiters. 512 */ 513 sleepq_lock(&sx->lock_object); 514 515 /* 516 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 517 * shared lock. If there are any shared waiters, wake them up. 518 */ 519 x = sx->sx_lock; 520 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 521 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 522 if (x & SX_LOCK_SHARED_WAITERS) 523 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 524 SQ_SHARED_QUEUE); 525 sleepq_release(&sx->lock_object); 526 527 out: 528 curthread->td_sx_slocks++; 529 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 530 LOCKSTAT_RECORD0(sx__downgrade, sx); 531 } 532 533 void 534 sx_downgrade_(struct sx *sx, const char *file, int line) 535 { 536 537 sx_downgrade_int(sx LOCK_FILE_LINE_ARG); 538 } 539 540 #ifdef ADAPTIVE_SX 541 static inline void 542 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work) 543 { 544 545 if (x & SX_LOCK_WRITE_SPINNER) 546 return; 547 if (*in_critical) { 548 critical_exit(); 549 *in_critical = false; 550 (*extra_work)--; 551 } 552 } 553 #else 554 #define sx_drop_critical(x, in_critical, extra_work) do { } while (0) 555 #endif 556 557 /* 558 * This function represents the so-called 'hard case' for sx_xlock 559 * operation. All 'easy case' failures are redirected to this. Note 560 * that ideally this would be a static function, but it needs to be 561 * accessible from at least sx.h. 562 */ 563 int 564 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 565 { 566 GIANT_DECLARE; 567 uintptr_t tid, setx; 568 #ifdef ADAPTIVE_SX 569 struct thread *owner; 570 u_int i, n, spintries = 0; 571 enum { READERS, WRITER } sleep_reason = READERS; 572 bool in_critical = false; 573 #endif 574 #ifdef LOCK_PROFILING 575 uint64_t waittime = 0; 576 int contested = 0; 577 #endif 578 int error = 0; 579 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 580 struct lock_delay_arg lda; 581 #endif 582 #ifdef KDTRACE_HOOKS 583 u_int sleep_cnt = 0; 584 int64_t sleep_time = 0; 585 int64_t all_time = 0; 586 uintptr_t state = 0; 587 #endif 588 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 589 int doing_lockprof = 0; 590 #endif 591 int extra_work = 0; 592 593 tid = (uintptr_t)curthread; 594 595 #ifdef KDTRACE_HOOKS 596 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 597 while (x == SX_LOCK_UNLOCKED) { 598 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 599 goto out_lockstat; 600 } 601 extra_work = 1; 602 doing_lockprof = 1; 603 all_time -= lockstat_nsecs(&sx->lock_object); 604 } 605 state = x; 606 #endif 607 #ifdef LOCK_PROFILING 608 extra_work = 1; 609 doing_lockprof = 1; 610 #endif 611 612 if (SCHEDULER_STOPPED()) 613 return (0); 614 615 if (__predict_false(x == SX_LOCK_UNLOCKED)) 616 x = SX_READ_VALUE(sx); 617 618 /* If we already hold an exclusive lock, then recurse. */ 619 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 620 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 621 ("_sx_xlock_hard: recursed on non-recursive sx %p @ %s:%d\n", 622 sx, file, line)); 623 sx->sx_recurse++; 624 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 625 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 626 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 627 return (0); 628 } 629 630 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 631 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 632 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 633 634 #if defined(ADAPTIVE_SX) 635 lock_delay_arg_init(&lda, &sx_delay); 636 #elif defined(KDTRACE_HOOKS) 637 lock_delay_arg_init_noadapt(&lda); 638 #endif 639 640 #ifdef HWPMC_HOOKS 641 PMC_SOFT_CALL( , , lock, failed); 642 #endif 643 lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested, 644 &waittime); 645 646 #ifndef INVARIANTS 647 GIANT_SAVE(extra_work); 648 #endif 649 650 THREAD_CONTENDS_ON_LOCK(&sx->lock_object); 651 652 for (;;) { 653 if (x == SX_LOCK_UNLOCKED) { 654 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 655 break; 656 continue; 657 } 658 #ifdef INVARIANTS 659 GIANT_SAVE(extra_work); 660 #endif 661 #ifdef KDTRACE_HOOKS 662 lda.spin_cnt++; 663 #endif 664 #ifdef ADAPTIVE_SX 665 if (x == (SX_LOCK_SHARED | SX_LOCK_WRITE_SPINNER)) { 666 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 667 break; 668 continue; 669 } 670 671 /* 672 * If the lock is write locked and the owner is 673 * running on another CPU, spin until the owner stops 674 * running or the state of the lock changes. 675 */ 676 if ((x & SX_LOCK_SHARED) == 0) { 677 sx_drop_critical(x, &in_critical, &extra_work); 678 sleep_reason = WRITER; 679 owner = lv_sx_owner(x); 680 if (!TD_IS_RUNNING(owner)) 681 goto sleepq; 682 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 683 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 684 __func__, sx, owner); 685 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 686 "spinning", "lockname:\"%s\"", 687 sx->lock_object.lo_name); 688 do { 689 lock_delay(&lda); 690 x = SX_READ_VALUE(sx); 691 owner = lv_sx_owner(x); 692 } while (owner != NULL && TD_IS_RUNNING(owner)); 693 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 694 "running"); 695 continue; 696 } else if (SX_SHARERS(x) > 0) { 697 sleep_reason = READERS; 698 if (spintries == asx_retries) 699 goto sleepq; 700 if (!(x & SX_LOCK_WRITE_SPINNER)) { 701 if (!in_critical) { 702 critical_enter(); 703 in_critical = true; 704 extra_work++; 705 } 706 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 707 x | SX_LOCK_WRITE_SPINNER)) { 708 critical_exit(); 709 in_critical = false; 710 extra_work--; 711 continue; 712 } 713 } 714 spintries++; 715 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 716 "spinning", "lockname:\"%s\"", 717 sx->lock_object.lo_name); 718 n = SX_SHARERS(x); 719 for (i = 0; i < asx_loops; i += n) { 720 lock_delay_spin(n); 721 x = SX_READ_VALUE(sx); 722 if (!(x & SX_LOCK_WRITE_SPINNER)) 723 break; 724 if (!(x & SX_LOCK_SHARED)) 725 break; 726 n = SX_SHARERS(x); 727 if (n == 0) 728 break; 729 } 730 #ifdef KDTRACE_HOOKS 731 lda.spin_cnt += i; 732 #endif 733 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 734 "running"); 735 if (i < asx_loops) 736 continue; 737 } 738 sleepq: 739 #endif 740 sleepq_lock(&sx->lock_object); 741 x = SX_READ_VALUE(sx); 742 retry_sleepq: 743 744 /* 745 * If the lock was released while spinning on the 746 * sleep queue chain lock, try again. 747 */ 748 if (x == SX_LOCK_UNLOCKED) { 749 sleepq_release(&sx->lock_object); 750 sx_drop_critical(x, &in_critical, &extra_work); 751 continue; 752 } 753 754 #ifdef ADAPTIVE_SX 755 /* 756 * The current lock owner might have started executing 757 * on another CPU (or the lock could have changed 758 * owners) while we were waiting on the sleep queue 759 * chain lock. If so, drop the sleep queue lock and try 760 * again. 761 */ 762 if (!(x & SX_LOCK_SHARED)) { 763 owner = (struct thread *)SX_OWNER(x); 764 if (TD_IS_RUNNING(owner)) { 765 sleepq_release(&sx->lock_object); 766 sx_drop_critical(x, &in_critical, 767 &extra_work); 768 continue; 769 } 770 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 771 sleepq_release(&sx->lock_object); 772 sx_drop_critical(x, &in_critical, &extra_work); 773 continue; 774 } 775 #endif 776 777 /* 778 * If an exclusive lock was released with both shared 779 * and exclusive waiters and a shared waiter hasn't 780 * woken up and acquired the lock yet, sx_lock will be 781 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 782 * If we see that value, try to acquire it once. Note 783 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 784 * as there are other exclusive waiters still. If we 785 * fail, restart the loop. 786 */ 787 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER); 788 if ((x & ~setx) == SX_LOCK_SHARED) { 789 setx &= ~SX_LOCK_WRITE_SPINNER; 790 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx)) 791 goto retry_sleepq; 792 sleepq_release(&sx->lock_object); 793 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 794 __func__, sx); 795 break; 796 } 797 798 #ifdef ADAPTIVE_SX 799 /* 800 * It is possible we set the SX_LOCK_WRITE_SPINNER bit. 801 * It is an invariant that when the bit is set, there is 802 * a writer ready to grab the lock. Thus clear the bit since 803 * we are going to sleep. 804 */ 805 if (in_critical) { 806 if ((x & SX_LOCK_WRITE_SPINNER) || 807 !((x & SX_LOCK_EXCLUSIVE_WAITERS))) { 808 setx = x & ~SX_LOCK_WRITE_SPINNER; 809 setx |= SX_LOCK_EXCLUSIVE_WAITERS; 810 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 811 setx)) { 812 goto retry_sleepq; 813 } 814 } 815 critical_exit(); 816 in_critical = false; 817 } else { 818 #endif 819 /* 820 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 821 * than loop back and retry. 822 */ 823 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 824 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 825 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 826 goto retry_sleepq; 827 } 828 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 829 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 830 __func__, sx); 831 } 832 #ifdef ADAPTIVE_SX 833 } 834 #endif 835 836 /* 837 * Since we have been unable to acquire the exclusive 838 * lock and the exclusive waiters flag is set, we have 839 * to sleep. 840 */ 841 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 842 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 843 __func__, sx); 844 845 #ifdef KDTRACE_HOOKS 846 sleep_time -= lockstat_nsecs(&sx->lock_object); 847 #endif 848 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 849 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 850 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 851 /* 852 * Hack: this can land in thread_suspend_check which will 853 * conditionally take a mutex, tripping over an assert if a 854 * lock we are waiting for is set. 855 */ 856 THREAD_CONTENTION_DONE(&sx->lock_object); 857 if (!(opts & SX_INTERRUPTIBLE)) 858 sleepq_wait(&sx->lock_object, 0); 859 else 860 error = sleepq_wait_sig(&sx->lock_object, 0); 861 THREAD_CONTENDS_ON_LOCK(&sx->lock_object); 862 #ifdef KDTRACE_HOOKS 863 sleep_time += lockstat_nsecs(&sx->lock_object); 864 sleep_cnt++; 865 #endif 866 if (error) { 867 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 868 CTR2(KTR_LOCK, 869 "%s: interruptible sleep by %p suspended by signal", 870 __func__, sx); 871 break; 872 } 873 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 874 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 875 __func__, sx); 876 x = SX_READ_VALUE(sx); 877 } 878 THREAD_CONTENTION_DONE(&sx->lock_object); 879 if (__predict_true(!extra_work)) 880 return (error); 881 #ifdef ADAPTIVE_SX 882 if (in_critical) 883 critical_exit(); 884 #endif 885 GIANT_RESTORE(); 886 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 887 if (__predict_true(!doing_lockprof)) 888 return (error); 889 #endif 890 #ifdef KDTRACE_HOOKS 891 all_time += lockstat_nsecs(&sx->lock_object); 892 if (sleep_time) 893 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 894 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 895 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 896 if (lda.spin_cnt > sleep_cnt) 897 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 898 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 899 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 900 out_lockstat: 901 #endif 902 if (!error) 903 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 904 contested, waittime, file, line, LOCKSTAT_WRITER); 905 return (error); 906 } 907 908 /* 909 * This function represents the so-called 'hard case' for sx_xunlock 910 * operation. All 'easy case' failures are redirected to this. Note 911 * that ideally this would be a static function, but it needs to be 912 * accessible from at least sx.h. 913 */ 914 void 915 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 916 { 917 uintptr_t tid, setx; 918 int queue; 919 920 if (SCHEDULER_STOPPED()) 921 return; 922 923 tid = (uintptr_t)curthread; 924 925 if (__predict_false(x == tid)) 926 x = SX_READ_VALUE(sx); 927 928 MPASS(!(x & SX_LOCK_SHARED)); 929 930 if (__predict_false(x & SX_LOCK_RECURSED)) { 931 /* The lock is recursed, unrecurse one level. */ 932 if ((--sx->sx_recurse) == 0) 933 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 934 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 935 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 936 return; 937 } 938 939 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 940 if (x == tid && 941 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 942 return; 943 944 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 945 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 946 947 sleepq_lock(&sx->lock_object); 948 x = SX_READ_VALUE(sx); 949 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 950 951 /* 952 * The wake up algorithm here is quite simple and probably not 953 * ideal. It gives precedence to shared waiters if they are 954 * present. For this condition, we have to preserve the 955 * state of the exclusive waiters flag. 956 * If interruptible sleeps left the shared queue empty avoid a 957 * starvation for the threads sleeping on the exclusive queue by giving 958 * them precedence and cleaning up the shared waiters bit anyway. 959 */ 960 setx = SX_LOCK_UNLOCKED; 961 queue = SQ_SHARED_QUEUE; 962 if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 && 963 sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) { 964 queue = SQ_EXCLUSIVE_QUEUE; 965 setx |= (x & SX_LOCK_SHARED_WAITERS); 966 } 967 atomic_store_rel_ptr(&sx->sx_lock, setx); 968 969 /* Wake up all the waiters for the specific queue. */ 970 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 971 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 972 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 973 "exclusive"); 974 975 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, queue); 976 sleepq_release(&sx->lock_object); 977 } 978 979 static __always_inline bool 980 __sx_can_read(struct thread *td, uintptr_t x, bool fp) 981 { 982 983 if ((x & (SX_LOCK_SHARED | SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_WRITE_SPINNER)) 984 == SX_LOCK_SHARED) 985 return (true); 986 if (!fp && td->td_sx_slocks && (x & SX_LOCK_SHARED)) 987 return (true); 988 return (false); 989 } 990 991 static __always_inline bool 992 __sx_slock_try(struct sx *sx, struct thread *td, uintptr_t *xp, bool fp 993 LOCK_FILE_LINE_ARG_DEF) 994 { 995 996 /* 997 * If no other thread has an exclusive lock then try to bump up 998 * the count of sharers. Since we have to preserve the state 999 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 1000 * shared lock loop back and retry. 1001 */ 1002 while (__sx_can_read(td, *xp, fp)) { 1003 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 1004 *xp + SX_ONE_SHARER)) { 1005 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1006 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 1007 __func__, sx, (void *)*xp, 1008 (void *)(*xp + SX_ONE_SHARER)); 1009 td->td_sx_slocks++; 1010 return (true); 1011 } 1012 } 1013 return (false); 1014 } 1015 1016 static int __noinline 1017 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1018 { 1019 GIANT_DECLARE; 1020 struct thread *td; 1021 #ifdef ADAPTIVE_SX 1022 struct thread *owner; 1023 u_int i, n, spintries = 0; 1024 #endif 1025 #ifdef LOCK_PROFILING 1026 uint64_t waittime = 0; 1027 int contested = 0; 1028 #endif 1029 int error = 0; 1030 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 1031 struct lock_delay_arg lda; 1032 #endif 1033 #ifdef KDTRACE_HOOKS 1034 u_int sleep_cnt = 0; 1035 int64_t sleep_time = 0; 1036 int64_t all_time = 0; 1037 uintptr_t state = 0; 1038 #endif 1039 int extra_work __sdt_used = 0; 1040 1041 td = curthread; 1042 1043 #ifdef KDTRACE_HOOKS 1044 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 1045 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG)) 1046 goto out_lockstat; 1047 extra_work = 1; 1048 all_time -= lockstat_nsecs(&sx->lock_object); 1049 } 1050 state = x; 1051 #endif 1052 #ifdef LOCK_PROFILING 1053 extra_work = 1; 1054 #endif 1055 1056 if (SCHEDULER_STOPPED()) 1057 return (0); 1058 1059 #if defined(ADAPTIVE_SX) 1060 lock_delay_arg_init(&lda, &sx_delay); 1061 #elif defined(KDTRACE_HOOKS) 1062 lock_delay_arg_init_noadapt(&lda); 1063 #endif 1064 1065 #ifdef HWPMC_HOOKS 1066 PMC_SOFT_CALL( , , lock, failed); 1067 #endif 1068 lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested, 1069 &waittime); 1070 1071 #ifndef INVARIANTS 1072 GIANT_SAVE(extra_work); 1073 #endif 1074 1075 THREAD_CONTENDS_ON_LOCK(&sx->lock_object); 1076 1077 /* 1078 * As with rwlocks, we don't make any attempt to try to block 1079 * shared locks once there is an exclusive waiter. 1080 */ 1081 for (;;) { 1082 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG)) 1083 break; 1084 #ifdef INVARIANTS 1085 GIANT_SAVE(extra_work); 1086 #endif 1087 #ifdef KDTRACE_HOOKS 1088 lda.spin_cnt++; 1089 #endif 1090 1091 #ifdef ADAPTIVE_SX 1092 /* 1093 * If the owner is running on another CPU, spin until 1094 * the owner stops running or the state of the lock 1095 * changes. 1096 */ 1097 if ((x & SX_LOCK_SHARED) == 0) { 1098 owner = lv_sx_owner(x); 1099 if (TD_IS_RUNNING(owner)) { 1100 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1101 CTR3(KTR_LOCK, 1102 "%s: spinning on %p held by %p", 1103 __func__, sx, owner); 1104 KTR_STATE1(KTR_SCHED, "thread", 1105 sched_tdname(curthread), "spinning", 1106 "lockname:\"%s\"", sx->lock_object.lo_name); 1107 do { 1108 lock_delay(&lda); 1109 x = SX_READ_VALUE(sx); 1110 owner = lv_sx_owner(x); 1111 } while (owner != NULL && TD_IS_RUNNING(owner)); 1112 KTR_STATE0(KTR_SCHED, "thread", 1113 sched_tdname(curthread), "running"); 1114 continue; 1115 } 1116 } else { 1117 if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) { 1118 MPASS(!__sx_can_read(td, x, false)); 1119 lock_delay_spin(2); 1120 x = SX_READ_VALUE(sx); 1121 continue; 1122 } 1123 if (spintries < asx_retries) { 1124 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 1125 "spinning", "lockname:\"%s\"", 1126 sx->lock_object.lo_name); 1127 n = SX_SHARERS(x); 1128 for (i = 0; i < asx_loops; i += n) { 1129 lock_delay_spin(n); 1130 x = SX_READ_VALUE(sx); 1131 if (!(x & SX_LOCK_SHARED)) 1132 break; 1133 n = SX_SHARERS(x); 1134 if (n == 0) 1135 break; 1136 if (__sx_can_read(td, x, false)) 1137 break; 1138 } 1139 #ifdef KDTRACE_HOOKS 1140 lda.spin_cnt += i; 1141 #endif 1142 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 1143 "running"); 1144 if (i < asx_loops) 1145 continue; 1146 } 1147 } 1148 #endif 1149 1150 /* 1151 * Some other thread already has an exclusive lock, so 1152 * start the process of blocking. 1153 */ 1154 sleepq_lock(&sx->lock_object); 1155 x = SX_READ_VALUE(sx); 1156 retry_sleepq: 1157 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) || 1158 __sx_can_read(td, x, false)) { 1159 sleepq_release(&sx->lock_object); 1160 continue; 1161 } 1162 1163 #ifdef ADAPTIVE_SX 1164 /* 1165 * If the owner is running on another CPU, spin until 1166 * the owner stops running or the state of the lock 1167 * changes. 1168 */ 1169 if (!(x & SX_LOCK_SHARED)) { 1170 owner = (struct thread *)SX_OWNER(x); 1171 if (TD_IS_RUNNING(owner)) { 1172 sleepq_release(&sx->lock_object); 1173 x = SX_READ_VALUE(sx); 1174 continue; 1175 } 1176 } 1177 #endif 1178 1179 /* 1180 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1181 * fail to set it drop the sleep queue lock and loop 1182 * back. 1183 */ 1184 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1185 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1186 x | SX_LOCK_SHARED_WAITERS)) 1187 goto retry_sleepq; 1188 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1189 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1190 __func__, sx); 1191 } 1192 1193 /* 1194 * Since we have been unable to acquire the shared lock, 1195 * we have to sleep. 1196 */ 1197 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1198 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1199 __func__, sx); 1200 1201 #ifdef KDTRACE_HOOKS 1202 sleep_time -= lockstat_nsecs(&sx->lock_object); 1203 #endif 1204 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1205 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1206 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1207 /* 1208 * Hack: this can land in thread_suspend_check which will 1209 * conditionally take a mutex, tripping over an assert if a 1210 * lock we are waiting for is set. 1211 */ 1212 THREAD_CONTENTION_DONE(&sx->lock_object); 1213 if (!(opts & SX_INTERRUPTIBLE)) 1214 sleepq_wait(&sx->lock_object, 0); 1215 else 1216 error = sleepq_wait_sig(&sx->lock_object, 0); 1217 THREAD_CONTENDS_ON_LOCK(&sx->lock_object); 1218 #ifdef KDTRACE_HOOKS 1219 sleep_time += lockstat_nsecs(&sx->lock_object); 1220 sleep_cnt++; 1221 #endif 1222 if (error) { 1223 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1224 CTR2(KTR_LOCK, 1225 "%s: interruptible sleep by %p suspended by signal", 1226 __func__, sx); 1227 break; 1228 } 1229 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1230 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1231 __func__, sx); 1232 x = SX_READ_VALUE(sx); 1233 } 1234 THREAD_CONTENTION_DONE(&sx->lock_object); 1235 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1236 if (__predict_true(!extra_work)) 1237 return (error); 1238 #endif 1239 #ifdef KDTRACE_HOOKS 1240 all_time += lockstat_nsecs(&sx->lock_object); 1241 if (sleep_time) 1242 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1243 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1244 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1245 if (lda.spin_cnt > sleep_cnt) 1246 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1247 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1248 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1249 out_lockstat: 1250 #endif 1251 if (error == 0) { 1252 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1253 contested, waittime, file, line, LOCKSTAT_READER); 1254 } 1255 GIANT_RESTORE(); 1256 return (error); 1257 } 1258 1259 int 1260 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1261 { 1262 struct thread *td; 1263 uintptr_t x; 1264 int error; 1265 1266 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1267 !TD_IS_IDLETHREAD(curthread), 1268 ("sx_slock() by idle thread %p on sx %p @ %s:%d", 1269 curthread, sx, file, line)); 1270 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1271 ("sx_slock() of destroyed sx %p @ %s:%d", sx, file, line)); 1272 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1273 1274 error = 0; 1275 td = curthread; 1276 x = SX_READ_VALUE(sx); 1277 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1278 !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG))) 1279 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1280 else 1281 lock_profile_obtain_lock_success(&sx->lock_object, false, 0, 0, 1282 file, line); 1283 if (error == 0) { 1284 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1285 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1286 TD_LOCKS_INC(curthread); 1287 } 1288 return (error); 1289 } 1290 1291 int 1292 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1293 { 1294 1295 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1296 } 1297 1298 static __always_inline bool 1299 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp) 1300 { 1301 1302 for (;;) { 1303 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) { 1304 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1305 *xp - SX_ONE_SHARER)) { 1306 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1307 CTR4(KTR_LOCK, 1308 "%s: %p succeeded %p -> %p", 1309 __func__, sx, (void *)*xp, 1310 (void *)(*xp - SX_ONE_SHARER)); 1311 td->td_sx_slocks--; 1312 return (true); 1313 } 1314 continue; 1315 } 1316 break; 1317 } 1318 return (false); 1319 } 1320 1321 static void __noinline 1322 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x 1323 LOCK_FILE_LINE_ARG_DEF) 1324 { 1325 uintptr_t setx, queue; 1326 1327 if (SCHEDULER_STOPPED()) 1328 return; 1329 1330 if (_sx_sunlock_try(sx, td, &x)) 1331 goto out_lockstat; 1332 1333 sleepq_lock(&sx->lock_object); 1334 x = SX_READ_VALUE(sx); 1335 for (;;) { 1336 if (_sx_sunlock_try(sx, td, &x)) 1337 break; 1338 1339 /* 1340 * Wake up semantic here is quite simple: 1341 * Just wake up all the exclusive waiters. 1342 * Note that the state of the lock could have changed, 1343 * so if it fails loop back and retry. 1344 */ 1345 setx = SX_LOCK_UNLOCKED; 1346 queue = SQ_SHARED_QUEUE; 1347 if (x & SX_LOCK_EXCLUSIVE_WAITERS) { 1348 setx |= (x & SX_LOCK_SHARED_WAITERS); 1349 queue = SQ_EXCLUSIVE_QUEUE; 1350 } 1351 setx |= (x & SX_LOCK_WRITE_SPINNER); 1352 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1353 continue; 1354 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1355 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1356 "exclusive queue", __func__, sx); 1357 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, queue); 1358 td->td_sx_slocks--; 1359 break; 1360 } 1361 sleepq_release(&sx->lock_object); 1362 out_lockstat: 1363 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1364 } 1365 1366 void 1367 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1368 { 1369 struct thread *td; 1370 uintptr_t x; 1371 1372 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1373 ("sx_sunlock() of destroyed sx %p @ %s:%d", sx, file, line)); 1374 _sx_assert(sx, SA_SLOCKED, file, line); 1375 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1376 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1377 1378 td = curthread; 1379 x = SX_READ_VALUE(sx); 1380 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1381 !_sx_sunlock_try(sx, td, &x))) 1382 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG); 1383 else 1384 lock_profile_release_lock(&sx->lock_object, false); 1385 1386 TD_LOCKS_DEC(curthread); 1387 } 1388 1389 void 1390 _sx_sunlock(struct sx *sx, const char *file, int line) 1391 { 1392 1393 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1394 } 1395 1396 #ifdef INVARIANT_SUPPORT 1397 #ifndef INVARIANTS 1398 #undef _sx_assert 1399 #endif 1400 1401 /* 1402 * In the non-WITNESS case, sx_assert() can only detect that at least 1403 * *some* thread owns an slock, but it cannot guarantee that *this* 1404 * thread owns an slock. 1405 */ 1406 void 1407 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1408 { 1409 #ifndef WITNESS 1410 int slocked = 0; 1411 #endif 1412 1413 if (SCHEDULER_STOPPED()) 1414 return; 1415 switch (what) { 1416 case SA_SLOCKED: 1417 case SA_SLOCKED | SA_NOTRECURSED: 1418 case SA_SLOCKED | SA_RECURSED: 1419 #ifndef WITNESS 1420 slocked = 1; 1421 /* FALLTHROUGH */ 1422 #endif 1423 case SA_LOCKED: 1424 case SA_LOCKED | SA_NOTRECURSED: 1425 case SA_LOCKED | SA_RECURSED: 1426 #ifdef WITNESS 1427 witness_assert(&sx->lock_object, what, file, line); 1428 #else 1429 /* 1430 * If some other thread has an exclusive lock or we 1431 * have one and are asserting a shared lock, fail. 1432 * Also, if no one has a lock at all, fail. 1433 */ 1434 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1435 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1436 sx_xholder(sx) != curthread))) 1437 panic("Lock %s not %slocked @ %s:%d\n", 1438 sx->lock_object.lo_name, slocked ? "share " : "", 1439 file, line); 1440 1441 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1442 if (sx_recursed(sx)) { 1443 if (what & SA_NOTRECURSED) 1444 panic("Lock %s recursed @ %s:%d\n", 1445 sx->lock_object.lo_name, file, 1446 line); 1447 } else if (what & SA_RECURSED) 1448 panic("Lock %s not recursed @ %s:%d\n", 1449 sx->lock_object.lo_name, file, line); 1450 } 1451 #endif 1452 break; 1453 case SA_XLOCKED: 1454 case SA_XLOCKED | SA_NOTRECURSED: 1455 case SA_XLOCKED | SA_RECURSED: 1456 if (sx_xholder(sx) != curthread) 1457 panic("Lock %s not exclusively locked @ %s:%d\n", 1458 sx->lock_object.lo_name, file, line); 1459 if (sx_recursed(sx)) { 1460 if (what & SA_NOTRECURSED) 1461 panic("Lock %s recursed @ %s:%d\n", 1462 sx->lock_object.lo_name, file, line); 1463 } else if (what & SA_RECURSED) 1464 panic("Lock %s not recursed @ %s:%d\n", 1465 sx->lock_object.lo_name, file, line); 1466 break; 1467 case SA_UNLOCKED: 1468 #ifdef WITNESS 1469 witness_assert(&sx->lock_object, what, file, line); 1470 #else 1471 /* 1472 * If we hold an exclusve lock fail. We can't 1473 * reliably check to see if we hold a shared lock or 1474 * not. 1475 */ 1476 if (sx_xholder(sx) == curthread) 1477 panic("Lock %s exclusively locked @ %s:%d\n", 1478 sx->lock_object.lo_name, file, line); 1479 #endif 1480 break; 1481 default: 1482 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1483 line); 1484 } 1485 } 1486 #endif /* INVARIANT_SUPPORT */ 1487 1488 #ifdef DDB 1489 static void 1490 db_show_sx(const struct lock_object *lock) 1491 { 1492 struct thread *td; 1493 const struct sx *sx; 1494 1495 sx = (const struct sx *)lock; 1496 1497 db_printf(" state: "); 1498 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1499 db_printf("UNLOCKED\n"); 1500 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1501 db_printf("DESTROYED\n"); 1502 return; 1503 } else if (sx->sx_lock & SX_LOCK_SHARED) 1504 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1505 else { 1506 td = sx_xholder(sx); 1507 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1508 td->td_tid, td->td_proc->p_pid, td->td_name); 1509 if (sx_recursed(sx)) 1510 db_printf(" recursed: %d\n", sx->sx_recurse); 1511 } 1512 1513 db_printf(" waiters: "); 1514 switch(sx->sx_lock & 1515 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1516 case SX_LOCK_SHARED_WAITERS: 1517 db_printf("shared\n"); 1518 break; 1519 case SX_LOCK_EXCLUSIVE_WAITERS: 1520 db_printf("exclusive\n"); 1521 break; 1522 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1523 db_printf("exclusive and shared\n"); 1524 break; 1525 default: 1526 db_printf("none\n"); 1527 } 1528 } 1529 1530 /* 1531 * Check to see if a thread that is blocked on a sleep queue is actually 1532 * blocked on an sx lock. If so, output some details and return true. 1533 * If the lock has an exclusive owner, return that in *ownerp. 1534 */ 1535 int 1536 sx_chain(struct thread *td, struct thread **ownerp) 1537 { 1538 const struct sx *sx; 1539 1540 /* 1541 * Check to see if this thread is blocked on an sx lock. 1542 * First, we check the lock class. If that is ok, then we 1543 * compare the lock name against the wait message. 1544 */ 1545 sx = td->td_wchan; 1546 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1547 sx->lock_object.lo_name != td->td_wmesg) 1548 return (0); 1549 1550 /* We think we have an sx lock, so output some details. */ 1551 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1552 *ownerp = sx_xholder(sx); 1553 if (sx->sx_lock & SX_LOCK_SHARED) 1554 db_printf("SLOCK (count %ju)\n", 1555 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1556 else 1557 db_printf("XLOCK\n"); 1558 return (1); 1559 } 1560 #endif 1561