1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 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/cdefs.h> 46 __FBSDID("$FreeBSD$"); 47 48 #include <sys/param.h> 49 #include <sys/systm.h> 50 #include <sys/kdb.h> 51 #include <sys/kernel.h> 52 #include <sys/ktr.h> 53 #include <sys/lock.h> 54 #include <sys/mutex.h> 55 #include <sys/proc.h> 56 #include <sys/sched.h> 57 #include <sys/sleepqueue.h> 58 #include <sys/sx.h> 59 #include <sys/smp.h> 60 #include <sys/sysctl.h> 61 62 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 63 #include <machine/cpu.h> 64 #endif 65 66 #ifdef DDB 67 #include <ddb/ddb.h> 68 #endif 69 70 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 71 #define ADAPTIVE_SX 72 #endif 73 74 #ifdef HWPMC_HOOKS 75 #include <sys/pmckern.h> 76 PMC_SOFT_DECLARE( , , lock, failed); 77 #endif 78 79 /* Handy macros for sleep queues. */ 80 #define SQ_EXCLUSIVE_QUEUE 0 81 #define SQ_SHARED_QUEUE 1 82 83 /* 84 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 85 * drop Giant anytime we have to sleep or if we adaptively spin. 86 */ 87 #define GIANT_DECLARE \ 88 int _giantcnt = 0; \ 89 WITNESS_SAVE_DECL(Giant) \ 90 91 #define GIANT_SAVE(work) do { \ 92 if (__predict_false(mtx_owned(&Giant))) { \ 93 work++; \ 94 WITNESS_SAVE(&Giant.lock_object, Giant); \ 95 while (mtx_owned(&Giant)) { \ 96 _giantcnt++; \ 97 mtx_unlock(&Giant); \ 98 } \ 99 } \ 100 } while (0) 101 102 #define GIANT_RESTORE() do { \ 103 if (_giantcnt > 0) { \ 104 mtx_assert(&Giant, MA_NOTOWNED); \ 105 while (_giantcnt--) \ 106 mtx_lock(&Giant); \ 107 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 108 } \ 109 } while (0) 110 111 /* 112 * Returns true if an exclusive lock is recursed. It assumes 113 * curthread currently has an exclusive lock. 114 */ 115 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 116 117 static void assert_sx(const struct lock_object *lock, int what); 118 #ifdef DDB 119 static void db_show_sx(const struct lock_object *lock); 120 #endif 121 static void lock_sx(struct lock_object *lock, uintptr_t how); 122 #ifdef KDTRACE_HOOKS 123 static int owner_sx(const struct lock_object *lock, struct thread **owner); 124 #endif 125 static uintptr_t unlock_sx(struct lock_object *lock); 126 127 struct lock_class lock_class_sx = { 128 .lc_name = "sx", 129 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 130 .lc_assert = assert_sx, 131 #ifdef DDB 132 .lc_ddb_show = db_show_sx, 133 #endif 134 .lc_lock = lock_sx, 135 .lc_unlock = unlock_sx, 136 #ifdef KDTRACE_HOOKS 137 .lc_owner = owner_sx, 138 #endif 139 }; 140 141 #ifndef INVARIANTS 142 #define _sx_assert(sx, what, file, line) 143 #endif 144 145 #ifdef ADAPTIVE_SX 146 #ifdef SX_CUSTOM_BACKOFF 147 static u_short __read_frequently asx_retries; 148 static u_short __read_frequently asx_loops; 149 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging"); 150 SYSCTL_U16(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, ""); 151 SYSCTL_U16(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, ""); 152 153 static struct lock_delay_config __read_frequently sx_delay; 154 155 SYSCTL_U16(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base, 156 0, ""); 157 SYSCTL_U16(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max, 158 0, ""); 159 160 static void 161 sx_lock_delay_init(void *arg __unused) 162 { 163 164 lock_delay_default_init(&sx_delay); 165 asx_retries = 10; 166 asx_loops = max(10000, sx_delay.max); 167 } 168 LOCK_DELAY_SYSINIT(sx_lock_delay_init); 169 #else 170 #define sx_delay locks_delay 171 #define asx_retries locks_delay_retries 172 #define asx_loops locks_delay_loops 173 #endif 174 #endif 175 176 void 177 assert_sx(const struct lock_object *lock, int what) 178 { 179 180 sx_assert((const struct sx *)lock, what); 181 } 182 183 void 184 lock_sx(struct lock_object *lock, uintptr_t how) 185 { 186 struct sx *sx; 187 188 sx = (struct sx *)lock; 189 if (how) 190 sx_slock(sx); 191 else 192 sx_xlock(sx); 193 } 194 195 uintptr_t 196 unlock_sx(struct lock_object *lock) 197 { 198 struct sx *sx; 199 200 sx = (struct sx *)lock; 201 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 202 if (sx_xlocked(sx)) { 203 sx_xunlock(sx); 204 return (0); 205 } else { 206 sx_sunlock(sx); 207 return (1); 208 } 209 } 210 211 #ifdef KDTRACE_HOOKS 212 int 213 owner_sx(const struct lock_object *lock, struct thread **owner) 214 { 215 const struct sx *sx; 216 uintptr_t x; 217 218 sx = (const struct sx *)lock; 219 x = sx->sx_lock; 220 *owner = NULL; 221 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 222 ((*owner = (struct thread *)SX_OWNER(x)) != NULL)); 223 } 224 #endif 225 226 void 227 sx_sysinit(void *arg) 228 { 229 struct sx_args *sargs = arg; 230 231 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 232 } 233 234 void 235 sx_init_flags(struct sx *sx, const char *description, int opts) 236 { 237 int flags; 238 239 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 240 SX_NOPROFILE | SX_NEW)) == 0); 241 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 242 ("%s: sx_lock not aligned for %s: %p", __func__, description, 243 &sx->sx_lock)); 244 245 flags = LO_SLEEPABLE | LO_UPGRADABLE; 246 if (opts & SX_DUPOK) 247 flags |= LO_DUPOK; 248 if (opts & SX_NOPROFILE) 249 flags |= LO_NOPROFILE; 250 if (!(opts & SX_NOWITNESS)) 251 flags |= LO_WITNESS; 252 if (opts & SX_RECURSE) 253 flags |= LO_RECURSABLE; 254 if (opts & SX_QUIET) 255 flags |= LO_QUIET; 256 if (opts & SX_NEW) 257 flags |= LO_NEW; 258 259 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 260 sx->sx_lock = SX_LOCK_UNLOCKED; 261 sx->sx_recurse = 0; 262 } 263 264 void 265 sx_destroy(struct sx *sx) 266 { 267 268 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 269 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 270 sx->sx_lock = SX_LOCK_DESTROYED; 271 lock_destroy(&sx->lock_object); 272 } 273 274 int 275 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 276 { 277 uintptr_t x; 278 279 if (SCHEDULER_STOPPED()) 280 return (1); 281 282 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 283 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 284 curthread, sx->lock_object.lo_name, file, line)); 285 286 x = sx->sx_lock; 287 for (;;) { 288 KASSERT(x != SX_LOCK_DESTROYED, 289 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 290 if (!(x & SX_LOCK_SHARED)) 291 break; 292 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 293 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 294 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 295 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 296 sx, 0, 0, file, line, LOCKSTAT_READER); 297 TD_LOCKS_INC(curthread); 298 curthread->td_sx_slocks++; 299 return (1); 300 } 301 } 302 303 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 304 return (0); 305 } 306 307 int 308 sx_try_slock_(struct sx *sx, const char *file, int line) 309 { 310 311 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG)); 312 } 313 314 int 315 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 316 { 317 uintptr_t tid, x; 318 int error = 0; 319 320 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 321 !TD_IS_IDLETHREAD(curthread), 322 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 323 curthread, sx->lock_object.lo_name, file, line)); 324 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 325 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 326 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 327 line, NULL); 328 tid = (uintptr_t)curthread; 329 x = SX_LOCK_UNLOCKED; 330 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 331 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG); 332 else 333 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 334 0, 0, file, line, LOCKSTAT_WRITER); 335 if (!error) { 336 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 337 file, line); 338 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 339 TD_LOCKS_INC(curthread); 340 } 341 342 return (error); 343 } 344 345 int 346 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 347 { 348 struct thread *td; 349 uintptr_t tid, x; 350 int rval; 351 bool recursed; 352 353 td = curthread; 354 tid = (uintptr_t)td; 355 if (SCHEDULER_STOPPED_TD(td)) 356 return (1); 357 358 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 359 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 360 curthread, sx->lock_object.lo_name, file, line)); 361 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 362 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 363 364 rval = 1; 365 recursed = false; 366 x = SX_LOCK_UNLOCKED; 367 for (;;) { 368 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 369 break; 370 if (x == SX_LOCK_UNLOCKED) 371 continue; 372 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 373 sx->sx_recurse++; 374 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 375 break; 376 } 377 rval = 0; 378 break; 379 } 380 381 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 382 if (rval) { 383 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 384 file, line); 385 if (!recursed) 386 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 387 sx, 0, 0, file, line, LOCKSTAT_WRITER); 388 TD_LOCKS_INC(curthread); 389 } 390 391 return (rval); 392 } 393 394 int 395 sx_try_xlock_(struct sx *sx, const char *file, int line) 396 { 397 398 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG)); 399 } 400 401 void 402 _sx_xunlock(struct sx *sx, const char *file, int line) 403 { 404 405 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 406 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 407 _sx_assert(sx, SA_XLOCKED, file, line); 408 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 409 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 410 line); 411 #if LOCK_DEBUG > 0 412 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 413 #else 414 __sx_xunlock(sx, curthread, file, line); 415 #endif 416 TD_LOCKS_DEC(curthread); 417 } 418 419 /* 420 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 421 * This will only succeed if this thread holds a single shared lock. 422 * Return 1 if if the upgrade succeed, 0 otherwise. 423 */ 424 int 425 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 426 { 427 uintptr_t x; 428 uintptr_t waiters; 429 int success; 430 431 if (SCHEDULER_STOPPED()) 432 return (1); 433 434 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 435 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 436 _sx_assert(sx, SA_SLOCKED, file, line); 437 438 /* 439 * Try to switch from one shared lock to an exclusive lock. We need 440 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 441 * we will wake up the exclusive waiters when we drop the lock. 442 */ 443 success = 0; 444 x = SX_READ_VALUE(sx); 445 for (;;) { 446 if (SX_SHARERS(x) > 1) 447 break; 448 waiters = (x & SX_LOCK_WAITERS); 449 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 450 (uintptr_t)curthread | waiters)) { 451 success = 1; 452 break; 453 } 454 } 455 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 456 if (success) { 457 curthread->td_sx_slocks--; 458 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 459 file, line); 460 LOCKSTAT_RECORD0(sx__upgrade, sx); 461 } 462 return (success); 463 } 464 465 int 466 sx_try_upgrade_(struct sx *sx, const char *file, int line) 467 { 468 469 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 470 } 471 472 /* 473 * Downgrade an unrecursed exclusive lock into a single shared lock. 474 */ 475 void 476 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 477 { 478 uintptr_t x; 479 int wakeup_swapper; 480 481 if (SCHEDULER_STOPPED()) 482 return; 483 484 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 485 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 486 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 487 #ifndef INVARIANTS 488 if (sx_recursed(sx)) 489 panic("downgrade of a recursed lock"); 490 #endif 491 492 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 493 494 /* 495 * Try to switch from an exclusive lock with no shared waiters 496 * to one sharer with no shared waiters. If there are 497 * exclusive waiters, we don't need to lock the sleep queue so 498 * long as we preserve the flag. We do one quick try and if 499 * that fails we grab the sleepq lock to keep the flags from 500 * changing and do it the slow way. 501 * 502 * We have to lock the sleep queue if there are shared waiters 503 * so we can wake them up. 504 */ 505 x = sx->sx_lock; 506 if (!(x & SX_LOCK_SHARED_WAITERS) && 507 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 508 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 509 goto out; 510 511 /* 512 * Lock the sleep queue so we can read the waiters bits 513 * without any races and wakeup any shared waiters. 514 */ 515 sleepq_lock(&sx->lock_object); 516 517 /* 518 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 519 * shared lock. If there are any shared waiters, wake them up. 520 */ 521 wakeup_swapper = 0; 522 x = sx->sx_lock; 523 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 524 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 525 if (x & SX_LOCK_SHARED_WAITERS) 526 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 527 0, SQ_SHARED_QUEUE); 528 sleepq_release(&sx->lock_object); 529 530 if (wakeup_swapper) 531 kick_proc0(); 532 533 out: 534 curthread->td_sx_slocks++; 535 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 536 LOCKSTAT_RECORD0(sx__downgrade, sx); 537 } 538 539 void 540 sx_downgrade_(struct sx *sx, const char *file, int line) 541 { 542 543 sx_downgrade_int(sx LOCK_FILE_LINE_ARG); 544 } 545 546 #ifdef ADAPTIVE_SX 547 static inline void 548 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work) 549 { 550 551 if (x & SX_LOCK_WRITE_SPINNER) 552 return; 553 if (*in_critical) { 554 critical_exit(); 555 *in_critical = false; 556 (*extra_work)--; 557 } 558 } 559 #else 560 #define sx_drop_critical(x, in_critical, extra_work) do { } while(0) 561 #endif 562 563 /* 564 * This function represents the so-called 'hard case' for sx_xlock 565 * operation. All 'easy case' failures are redirected to this. Note 566 * that ideally this would be a static function, but it needs to be 567 * accessible from at least sx.h. 568 */ 569 int 570 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 571 { 572 GIANT_DECLARE; 573 uintptr_t tid, setx; 574 #ifdef ADAPTIVE_SX 575 volatile struct thread *owner; 576 u_int i, n, spintries = 0; 577 enum { READERS, WRITER } sleep_reason = READERS; 578 bool in_critical = false; 579 #endif 580 #ifdef LOCK_PROFILING 581 uint64_t waittime = 0; 582 int contested = 0; 583 #endif 584 int error = 0; 585 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 586 struct lock_delay_arg lda; 587 #endif 588 #ifdef KDTRACE_HOOKS 589 u_int sleep_cnt = 0; 590 int64_t sleep_time = 0; 591 int64_t all_time = 0; 592 #endif 593 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 594 uintptr_t state = 0; 595 int doing_lockprof = 0; 596 #endif 597 int extra_work = 0; 598 599 tid = (uintptr_t)curthread; 600 601 #ifdef KDTRACE_HOOKS 602 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 603 while (x == SX_LOCK_UNLOCKED) { 604 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 605 goto out_lockstat; 606 } 607 extra_work = 1; 608 doing_lockprof = 1; 609 all_time -= lockstat_nsecs(&sx->lock_object); 610 state = x; 611 } 612 #endif 613 #ifdef LOCK_PROFILING 614 extra_work = 1; 615 doing_lockprof = 1; 616 state = x; 617 #endif 618 619 if (SCHEDULER_STOPPED()) 620 return (0); 621 622 #if defined(ADAPTIVE_SX) 623 lock_delay_arg_init(&lda, &sx_delay); 624 #elif defined(KDTRACE_HOOKS) 625 lock_delay_arg_init(&lda, NULL); 626 #endif 627 628 if (__predict_false(x == SX_LOCK_UNLOCKED)) 629 x = SX_READ_VALUE(sx); 630 631 /* If we already hold an exclusive lock, then recurse. */ 632 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 633 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 634 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 635 sx->lock_object.lo_name, file, line)); 636 sx->sx_recurse++; 637 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 638 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 639 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 640 return (0); 641 } 642 643 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 644 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 645 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 646 647 #ifdef HWPMC_HOOKS 648 PMC_SOFT_CALL( , , lock, failed); 649 #endif 650 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 651 &waittime); 652 653 #ifndef INVARIANTS 654 GIANT_SAVE(extra_work); 655 #endif 656 657 for (;;) { 658 if (x == SX_LOCK_UNLOCKED) { 659 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 660 break; 661 continue; 662 } 663 #ifdef INVARIANTS 664 GIANT_SAVE(extra_work); 665 #endif 666 #ifdef KDTRACE_HOOKS 667 lda.spin_cnt++; 668 #endif 669 #ifdef ADAPTIVE_SX 670 if (x == (SX_LOCK_SHARED | SX_LOCK_WRITE_SPINNER)) { 671 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 672 break; 673 continue; 674 } 675 676 /* 677 * If the lock is write locked and the owner is 678 * running on another CPU, spin until the owner stops 679 * running or the state of the lock changes. 680 */ 681 if ((x & SX_LOCK_SHARED) == 0) { 682 sx_drop_critical(x, &in_critical, &extra_work); 683 sleep_reason = WRITER; 684 owner = lv_sx_owner(x); 685 if (!TD_IS_RUNNING(owner)) 686 goto sleepq; 687 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 688 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 689 __func__, sx, owner); 690 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 691 "spinning", "lockname:\"%s\"", 692 sx->lock_object.lo_name); 693 do { 694 lock_delay(&lda); 695 x = SX_READ_VALUE(sx); 696 owner = lv_sx_owner(x); 697 } while (owner != NULL && TD_IS_RUNNING(owner)); 698 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 699 "running"); 700 continue; 701 } else if (SX_SHARERS(x) > 0) { 702 sleep_reason = READERS; 703 if (spintries == asx_retries) 704 goto sleepq; 705 if (!(x & SX_LOCK_WRITE_SPINNER)) { 706 if (!in_critical) { 707 critical_enter(); 708 in_critical = true; 709 extra_work++; 710 } 711 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 712 x | SX_LOCK_WRITE_SPINNER)) { 713 critical_exit(); 714 in_critical = false; 715 extra_work--; 716 continue; 717 } 718 } 719 spintries++; 720 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 721 "spinning", "lockname:\"%s\"", 722 sx->lock_object.lo_name); 723 n = SX_SHARERS(x); 724 for (i = 0; i < asx_loops; i += n) { 725 lock_delay_spin(n); 726 x = SX_READ_VALUE(sx); 727 if (!(x & SX_LOCK_WRITE_SPINNER)) 728 break; 729 if (!(x & SX_LOCK_SHARED)) 730 break; 731 n = SX_SHARERS(x); 732 if (n == 0) 733 break; 734 } 735 #ifdef KDTRACE_HOOKS 736 lda.spin_cnt += i; 737 #endif 738 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 739 "running"); 740 if (i < asx_loops) 741 continue; 742 } 743 sleepq: 744 #endif 745 sleepq_lock(&sx->lock_object); 746 x = SX_READ_VALUE(sx); 747 retry_sleepq: 748 749 /* 750 * If the lock was released while spinning on the 751 * sleep queue chain lock, try again. 752 */ 753 if (x == SX_LOCK_UNLOCKED) { 754 sleepq_release(&sx->lock_object); 755 sx_drop_critical(x, &in_critical, &extra_work); 756 continue; 757 } 758 759 #ifdef ADAPTIVE_SX 760 /* 761 * The current lock owner might have started executing 762 * on another CPU (or the lock could have changed 763 * owners) while we were waiting on the sleep queue 764 * chain lock. If so, drop the sleep queue lock and try 765 * again. 766 */ 767 if (!(x & SX_LOCK_SHARED)) { 768 owner = (struct thread *)SX_OWNER(x); 769 if (TD_IS_RUNNING(owner)) { 770 sleepq_release(&sx->lock_object); 771 sx_drop_critical(x, &in_critical, 772 &extra_work); 773 continue; 774 } 775 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 776 sleepq_release(&sx->lock_object); 777 sx_drop_critical(x, &in_critical, &extra_work); 778 continue; 779 } 780 #endif 781 782 /* 783 * If an exclusive lock was released with both shared 784 * and exclusive waiters and a shared waiter hasn't 785 * woken up and acquired the lock yet, sx_lock will be 786 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 787 * If we see that value, try to acquire it once. Note 788 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 789 * as there are other exclusive waiters still. If we 790 * fail, restart the loop. 791 */ 792 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER); 793 if ((x & ~setx) == SX_LOCK_SHARED) { 794 setx &= ~SX_LOCK_WRITE_SPINNER; 795 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx)) 796 goto retry_sleepq; 797 sleepq_release(&sx->lock_object); 798 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 799 __func__, sx); 800 break; 801 } 802 803 #ifdef ADAPTIVE_SX 804 /* 805 * It is possible we set the SX_LOCK_WRITE_SPINNER bit. 806 * It is an invariant that when the bit is set, there is 807 * a writer ready to grab the lock. Thus clear the bit since 808 * we are going to sleep. 809 */ 810 if (in_critical) { 811 if ((x & SX_LOCK_WRITE_SPINNER) || 812 !((x & SX_LOCK_EXCLUSIVE_WAITERS))) { 813 setx = x & ~SX_LOCK_WRITE_SPINNER; 814 setx |= SX_LOCK_EXCLUSIVE_WAITERS; 815 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 816 setx)) { 817 goto retry_sleepq; 818 } 819 } 820 critical_exit(); 821 in_critical = false; 822 } else { 823 #endif 824 /* 825 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 826 * than loop back and retry. 827 */ 828 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 829 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 830 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 831 goto retry_sleepq; 832 } 833 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 834 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 835 __func__, sx); 836 } 837 #ifdef ADAPTIVE_SX 838 } 839 #endif 840 841 /* 842 * Since we have been unable to acquire the exclusive 843 * lock and the exclusive waiters flag is set, we have 844 * to sleep. 845 */ 846 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 847 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 848 __func__, sx); 849 850 #ifdef KDTRACE_HOOKS 851 sleep_time -= lockstat_nsecs(&sx->lock_object); 852 #endif 853 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 854 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 855 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 856 if (!(opts & SX_INTERRUPTIBLE)) 857 sleepq_wait(&sx->lock_object, 0); 858 else 859 error = sleepq_wait_sig(&sx->lock_object, 0); 860 #ifdef KDTRACE_HOOKS 861 sleep_time += lockstat_nsecs(&sx->lock_object); 862 sleep_cnt++; 863 #endif 864 if (error) { 865 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 866 CTR2(KTR_LOCK, 867 "%s: interruptible sleep by %p suspended by signal", 868 __func__, sx); 869 break; 870 } 871 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 872 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 873 __func__, sx); 874 x = SX_READ_VALUE(sx); 875 } 876 if (__predict_true(!extra_work)) 877 return (error); 878 #ifdef ADAPTIVE_SX 879 if (in_critical) 880 critical_exit(); 881 #endif 882 GIANT_RESTORE(); 883 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 884 if (__predict_true(!doing_lockprof)) 885 return (error); 886 #endif 887 #ifdef KDTRACE_HOOKS 888 all_time += lockstat_nsecs(&sx->lock_object); 889 if (sleep_time) 890 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 891 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 892 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 893 if (lda.spin_cnt > sleep_cnt) 894 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 895 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 896 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 897 out_lockstat: 898 #endif 899 if (!error) 900 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 901 contested, waittime, file, line, LOCKSTAT_WRITER); 902 return (error); 903 } 904 905 /* 906 * This function represents the so-called 'hard case' for sx_xunlock 907 * operation. All 'easy case' failures are redirected to this. Note 908 * that ideally this would be a static function, but it needs to be 909 * accessible from at least sx.h. 910 */ 911 void 912 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 913 { 914 uintptr_t tid, setx; 915 int queue, wakeup_swapper; 916 917 if (SCHEDULER_STOPPED()) 918 return; 919 920 tid = (uintptr_t)curthread; 921 922 if (__predict_false(x == tid)) 923 x = SX_READ_VALUE(sx); 924 925 MPASS(!(x & SX_LOCK_SHARED)); 926 927 if (__predict_false(x & SX_LOCK_RECURSED)) { 928 /* The lock is recursed, unrecurse one level. */ 929 if ((--sx->sx_recurse) == 0) 930 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 931 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 932 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 933 return; 934 } 935 936 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 937 if (x == tid && 938 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 939 return; 940 941 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 942 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 943 944 sleepq_lock(&sx->lock_object); 945 x = SX_READ_VALUE(sx); 946 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 947 948 /* 949 * The wake up algorithm here is quite simple and probably not 950 * ideal. It gives precedence to shared waiters if they are 951 * present. For this condition, we have to preserve the 952 * state of the exclusive waiters flag. 953 * If interruptible sleeps left the shared queue empty avoid a 954 * starvation for the threads sleeping on the exclusive queue by giving 955 * them precedence and cleaning up the shared waiters bit anyway. 956 */ 957 setx = SX_LOCK_UNLOCKED; 958 queue = SQ_SHARED_QUEUE; 959 if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 && 960 sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) { 961 queue = SQ_EXCLUSIVE_QUEUE; 962 setx |= (x & SX_LOCK_SHARED_WAITERS); 963 } 964 atomic_store_rel_ptr(&sx->sx_lock, setx); 965 966 /* Wake up all the waiters for the specific queue. */ 967 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 968 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 969 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 970 "exclusive"); 971 972 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 973 queue); 974 sleepq_release(&sx->lock_object); 975 if (wakeup_swapper) 976 kick_proc0(); 977 } 978 979 static bool __always_inline 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 bool __always_inline 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 volatile 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 #endif 1038 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1039 uintptr_t state = 0; 1040 #endif 1041 int extra_work = 0; 1042 1043 td = curthread; 1044 1045 #ifdef KDTRACE_HOOKS 1046 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 1047 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG)) 1048 goto out_lockstat; 1049 extra_work = 1; 1050 all_time -= lockstat_nsecs(&sx->lock_object); 1051 state = x; 1052 } 1053 #endif 1054 #ifdef LOCK_PROFILING 1055 extra_work = 1; 1056 state = x; 1057 #endif 1058 1059 if (SCHEDULER_STOPPED()) 1060 return (0); 1061 1062 #if defined(ADAPTIVE_SX) 1063 lock_delay_arg_init(&lda, &sx_delay); 1064 #elif defined(KDTRACE_HOOKS) 1065 lock_delay_arg_init(&lda, NULL); 1066 #endif 1067 1068 #ifdef HWPMC_HOOKS 1069 PMC_SOFT_CALL( , , lock, failed); 1070 #endif 1071 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 1072 &waittime); 1073 1074 #ifndef INVARIANTS 1075 GIANT_SAVE(extra_work); 1076 #endif 1077 1078 /* 1079 * As with rwlocks, we don't make any attempt to try to block 1080 * shared locks once there is an exclusive waiter. 1081 */ 1082 for (;;) { 1083 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG)) 1084 break; 1085 #ifdef INVARIANTS 1086 GIANT_SAVE(extra_work); 1087 #endif 1088 #ifdef KDTRACE_HOOKS 1089 lda.spin_cnt++; 1090 #endif 1091 1092 #ifdef ADAPTIVE_SX 1093 /* 1094 * If the owner is running on another CPU, spin until 1095 * the owner stops running or the state of the lock 1096 * changes. 1097 */ 1098 if ((x & SX_LOCK_SHARED) == 0) { 1099 owner = lv_sx_owner(x); 1100 if (TD_IS_RUNNING(owner)) { 1101 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1102 CTR3(KTR_LOCK, 1103 "%s: spinning on %p held by %p", 1104 __func__, sx, owner); 1105 KTR_STATE1(KTR_SCHED, "thread", 1106 sched_tdname(curthread), "spinning", 1107 "lockname:\"%s\"", sx->lock_object.lo_name); 1108 do { 1109 lock_delay(&lda); 1110 x = SX_READ_VALUE(sx); 1111 owner = lv_sx_owner(x); 1112 } while (owner != NULL && TD_IS_RUNNING(owner)); 1113 KTR_STATE0(KTR_SCHED, "thread", 1114 sched_tdname(curthread), "running"); 1115 continue; 1116 } 1117 } else { 1118 if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) { 1119 MPASS(!__sx_can_read(td, x, false)); 1120 lock_delay_spin(2); 1121 x = SX_READ_VALUE(sx); 1122 continue; 1123 } 1124 if (spintries < asx_retries) { 1125 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 1126 "spinning", "lockname:\"%s\"", 1127 sx->lock_object.lo_name); 1128 n = SX_SHARERS(x); 1129 for (i = 0; i < asx_loops; i += n) { 1130 lock_delay_spin(n); 1131 x = SX_READ_VALUE(sx); 1132 if (!(x & SX_LOCK_SHARED)) 1133 break; 1134 n = SX_SHARERS(x); 1135 if (n == 0) 1136 break; 1137 if (__sx_can_read(td, x, false)) 1138 break; 1139 } 1140 #ifdef KDTRACE_HOOKS 1141 lda.spin_cnt += i; 1142 #endif 1143 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 1144 "running"); 1145 if (i < asx_loops) 1146 continue; 1147 } 1148 } 1149 #endif 1150 1151 /* 1152 * Some other thread already has an exclusive lock, so 1153 * start the process of blocking. 1154 */ 1155 sleepq_lock(&sx->lock_object); 1156 x = SX_READ_VALUE(sx); 1157 retry_sleepq: 1158 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) || 1159 __sx_can_read(td, x, false)) { 1160 sleepq_release(&sx->lock_object); 1161 continue; 1162 } 1163 1164 #ifdef ADAPTIVE_SX 1165 /* 1166 * If the owner is running on another CPU, spin until 1167 * the owner stops running or the state of the lock 1168 * changes. 1169 */ 1170 if (!(x & SX_LOCK_SHARED)) { 1171 owner = (struct thread *)SX_OWNER(x); 1172 if (TD_IS_RUNNING(owner)) { 1173 sleepq_release(&sx->lock_object); 1174 x = SX_READ_VALUE(sx); 1175 continue; 1176 } 1177 } 1178 #endif 1179 1180 /* 1181 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1182 * fail to set it drop the sleep queue lock and loop 1183 * back. 1184 */ 1185 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1186 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1187 x | SX_LOCK_SHARED_WAITERS)) 1188 goto retry_sleepq; 1189 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1190 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1191 __func__, sx); 1192 } 1193 1194 /* 1195 * Since we have been unable to acquire the shared lock, 1196 * we have to sleep. 1197 */ 1198 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1199 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1200 __func__, sx); 1201 1202 #ifdef KDTRACE_HOOKS 1203 sleep_time -= lockstat_nsecs(&sx->lock_object); 1204 #endif 1205 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1206 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1207 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1208 if (!(opts & SX_INTERRUPTIBLE)) 1209 sleepq_wait(&sx->lock_object, 0); 1210 else 1211 error = sleepq_wait_sig(&sx->lock_object, 0); 1212 #ifdef KDTRACE_HOOKS 1213 sleep_time += lockstat_nsecs(&sx->lock_object); 1214 sleep_cnt++; 1215 #endif 1216 if (error) { 1217 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1218 CTR2(KTR_LOCK, 1219 "%s: interruptible sleep by %p suspended by signal", 1220 __func__, sx); 1221 break; 1222 } 1223 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1224 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1225 __func__, sx); 1226 x = SX_READ_VALUE(sx); 1227 } 1228 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1229 if (__predict_true(!extra_work)) 1230 return (error); 1231 #endif 1232 #ifdef KDTRACE_HOOKS 1233 all_time += lockstat_nsecs(&sx->lock_object); 1234 if (sleep_time) 1235 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1236 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1237 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1238 if (lda.spin_cnt > sleep_cnt) 1239 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1240 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1241 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1242 out_lockstat: 1243 #endif 1244 if (error == 0) { 1245 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1246 contested, waittime, file, line, LOCKSTAT_READER); 1247 } 1248 GIANT_RESTORE(); 1249 return (error); 1250 } 1251 1252 int 1253 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1254 { 1255 struct thread *td; 1256 uintptr_t x; 1257 int error; 1258 1259 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1260 !TD_IS_IDLETHREAD(curthread), 1261 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1262 curthread, sx->lock_object.lo_name, file, line)); 1263 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1264 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1265 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1266 1267 error = 0; 1268 td = curthread; 1269 x = SX_READ_VALUE(sx); 1270 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1271 !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG))) 1272 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1273 else 1274 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1275 file, line); 1276 if (error == 0) { 1277 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1278 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1279 TD_LOCKS_INC(curthread); 1280 } 1281 return (error); 1282 } 1283 1284 int 1285 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1286 { 1287 1288 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1289 } 1290 1291 static bool __always_inline 1292 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp) 1293 { 1294 1295 for (;;) { 1296 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) { 1297 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1298 *xp - SX_ONE_SHARER)) { 1299 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1300 CTR4(KTR_LOCK, 1301 "%s: %p succeeded %p -> %p", 1302 __func__, sx, (void *)*xp, 1303 (void *)(*xp - SX_ONE_SHARER)); 1304 td->td_sx_slocks--; 1305 return (true); 1306 } 1307 continue; 1308 } 1309 break; 1310 } 1311 return (false); 1312 } 1313 1314 static void __noinline 1315 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x 1316 LOCK_FILE_LINE_ARG_DEF) 1317 { 1318 int wakeup_swapper = 0; 1319 uintptr_t setx, queue; 1320 1321 if (SCHEDULER_STOPPED()) 1322 return; 1323 1324 if (_sx_sunlock_try(sx, td, &x)) 1325 goto out_lockstat; 1326 1327 sleepq_lock(&sx->lock_object); 1328 x = SX_READ_VALUE(sx); 1329 for (;;) { 1330 if (_sx_sunlock_try(sx, td, &x)) 1331 break; 1332 1333 /* 1334 * Wake up semantic here is quite simple: 1335 * Just wake up all the exclusive waiters. 1336 * Note that the state of the lock could have changed, 1337 * so if it fails loop back and retry. 1338 */ 1339 setx = SX_LOCK_UNLOCKED; 1340 queue = SQ_SHARED_QUEUE; 1341 if (x & SX_LOCK_EXCLUSIVE_WAITERS) { 1342 setx |= (x & SX_LOCK_SHARED_WAITERS); 1343 queue = SQ_EXCLUSIVE_QUEUE; 1344 } 1345 setx |= (x & SX_LOCK_WRITE_SPINNER); 1346 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1347 continue; 1348 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1349 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1350 "exclusive queue", __func__, sx); 1351 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1352 0, queue); 1353 td->td_sx_slocks--; 1354 break; 1355 } 1356 sleepq_release(&sx->lock_object); 1357 if (wakeup_swapper) 1358 kick_proc0(); 1359 out_lockstat: 1360 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1361 } 1362 1363 void 1364 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1365 { 1366 struct thread *td; 1367 uintptr_t x; 1368 1369 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1370 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1371 _sx_assert(sx, SA_SLOCKED, file, line); 1372 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1373 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1374 1375 td = curthread; 1376 x = SX_READ_VALUE(sx); 1377 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1378 !_sx_sunlock_try(sx, td, &x))) 1379 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG); 1380 else 1381 lock_profile_release_lock(&sx->lock_object); 1382 1383 TD_LOCKS_DEC(curthread); 1384 } 1385 1386 void 1387 _sx_sunlock(struct sx *sx, const char *file, int line) 1388 { 1389 1390 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1391 } 1392 1393 #ifdef INVARIANT_SUPPORT 1394 #ifndef INVARIANTS 1395 #undef _sx_assert 1396 #endif 1397 1398 /* 1399 * In the non-WITNESS case, sx_assert() can only detect that at least 1400 * *some* thread owns an slock, but it cannot guarantee that *this* 1401 * thread owns an slock. 1402 */ 1403 void 1404 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1405 { 1406 #ifndef WITNESS 1407 int slocked = 0; 1408 #endif 1409 1410 if (SCHEDULER_STOPPED()) 1411 return; 1412 switch (what) { 1413 case SA_SLOCKED: 1414 case SA_SLOCKED | SA_NOTRECURSED: 1415 case SA_SLOCKED | SA_RECURSED: 1416 #ifndef WITNESS 1417 slocked = 1; 1418 /* FALLTHROUGH */ 1419 #endif 1420 case SA_LOCKED: 1421 case SA_LOCKED | SA_NOTRECURSED: 1422 case SA_LOCKED | SA_RECURSED: 1423 #ifdef WITNESS 1424 witness_assert(&sx->lock_object, what, file, line); 1425 #else 1426 /* 1427 * If some other thread has an exclusive lock or we 1428 * have one and are asserting a shared lock, fail. 1429 * Also, if no one has a lock at all, fail. 1430 */ 1431 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1432 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1433 sx_xholder(sx) != curthread))) 1434 panic("Lock %s not %slocked @ %s:%d\n", 1435 sx->lock_object.lo_name, slocked ? "share " : "", 1436 file, line); 1437 1438 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1439 if (sx_recursed(sx)) { 1440 if (what & SA_NOTRECURSED) 1441 panic("Lock %s recursed @ %s:%d\n", 1442 sx->lock_object.lo_name, file, 1443 line); 1444 } else if (what & SA_RECURSED) 1445 panic("Lock %s not recursed @ %s:%d\n", 1446 sx->lock_object.lo_name, file, line); 1447 } 1448 #endif 1449 break; 1450 case SA_XLOCKED: 1451 case SA_XLOCKED | SA_NOTRECURSED: 1452 case SA_XLOCKED | SA_RECURSED: 1453 if (sx_xholder(sx) != curthread) 1454 panic("Lock %s not exclusively locked @ %s:%d\n", 1455 sx->lock_object.lo_name, file, line); 1456 if (sx_recursed(sx)) { 1457 if (what & SA_NOTRECURSED) 1458 panic("Lock %s recursed @ %s:%d\n", 1459 sx->lock_object.lo_name, file, line); 1460 } else if (what & SA_RECURSED) 1461 panic("Lock %s not recursed @ %s:%d\n", 1462 sx->lock_object.lo_name, file, line); 1463 break; 1464 case SA_UNLOCKED: 1465 #ifdef WITNESS 1466 witness_assert(&sx->lock_object, what, file, line); 1467 #else 1468 /* 1469 * If we hold an exclusve lock fail. We can't 1470 * reliably check to see if we hold a shared lock or 1471 * not. 1472 */ 1473 if (sx_xholder(sx) == curthread) 1474 panic("Lock %s exclusively locked @ %s:%d\n", 1475 sx->lock_object.lo_name, file, line); 1476 #endif 1477 break; 1478 default: 1479 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1480 line); 1481 } 1482 } 1483 #endif /* INVARIANT_SUPPORT */ 1484 1485 #ifdef DDB 1486 static void 1487 db_show_sx(const struct lock_object *lock) 1488 { 1489 struct thread *td; 1490 const struct sx *sx; 1491 1492 sx = (const struct sx *)lock; 1493 1494 db_printf(" state: "); 1495 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1496 db_printf("UNLOCKED\n"); 1497 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1498 db_printf("DESTROYED\n"); 1499 return; 1500 } else if (sx->sx_lock & SX_LOCK_SHARED) 1501 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1502 else { 1503 td = sx_xholder(sx); 1504 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1505 td->td_tid, td->td_proc->p_pid, td->td_name); 1506 if (sx_recursed(sx)) 1507 db_printf(" recursed: %d\n", sx->sx_recurse); 1508 } 1509 1510 db_printf(" waiters: "); 1511 switch(sx->sx_lock & 1512 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1513 case SX_LOCK_SHARED_WAITERS: 1514 db_printf("shared\n"); 1515 break; 1516 case SX_LOCK_EXCLUSIVE_WAITERS: 1517 db_printf("exclusive\n"); 1518 break; 1519 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1520 db_printf("exclusive and shared\n"); 1521 break; 1522 default: 1523 db_printf("none\n"); 1524 } 1525 } 1526 1527 /* 1528 * Check to see if a thread that is blocked on a sleep queue is actually 1529 * blocked on an sx lock. If so, output some details and return true. 1530 * If the lock has an exclusive owner, return that in *ownerp. 1531 */ 1532 int 1533 sx_chain(struct thread *td, struct thread **ownerp) 1534 { 1535 const struct sx *sx; 1536 1537 /* 1538 * Check to see if this thread is blocked on an sx lock. 1539 * First, we check the lock class. If that is ok, then we 1540 * compare the lock name against the wait message. 1541 */ 1542 sx = td->td_wchan; 1543 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1544 sx->lock_object.lo_name != td->td_wmesg) 1545 return (0); 1546 1547 /* We think we have an sx lock, so output some details. */ 1548 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1549 *ownerp = sx_xholder(sx); 1550 if (sx->sx_lock & SX_LOCK_SHARED) 1551 db_printf("SLOCK (count %ju)\n", 1552 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1553 else 1554 db_printf("XLOCK\n"); 1555 return (1); 1556 } 1557 #endif 1558