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 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE); 75 76 #ifdef HWPMC_HOOKS 77 #include <sys/pmckern.h> 78 PMC_SOFT_DECLARE( , , lock, failed); 79 #endif 80 81 /* Handy macros for sleep queues. */ 82 #define SQ_EXCLUSIVE_QUEUE 0 83 #define SQ_SHARED_QUEUE 1 84 85 /* 86 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 87 * drop Giant anytime we have to sleep or if we adaptively spin. 88 */ 89 #define GIANT_DECLARE \ 90 int _giantcnt = 0; \ 91 WITNESS_SAVE_DECL(Giant) \ 92 93 #define GIANT_SAVE(work) do { \ 94 if (__predict_false(mtx_owned(&Giant))) { \ 95 work++; \ 96 WITNESS_SAVE(&Giant.lock_object, Giant); \ 97 while (mtx_owned(&Giant)) { \ 98 _giantcnt++; \ 99 mtx_unlock(&Giant); \ 100 } \ 101 } \ 102 } while (0) 103 104 #define GIANT_RESTORE() do { \ 105 if (_giantcnt > 0) { \ 106 mtx_assert(&Giant, MA_NOTOWNED); \ 107 while (_giantcnt--) \ 108 mtx_lock(&Giant); \ 109 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 110 } \ 111 } while (0) 112 113 /* 114 * Returns true if an exclusive lock is recursed. It assumes 115 * curthread currently has an exclusive lock. 116 */ 117 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 118 119 static void assert_sx(const struct lock_object *lock, int what); 120 #ifdef DDB 121 static void db_show_sx(const struct lock_object *lock); 122 #endif 123 static void lock_sx(struct lock_object *lock, uintptr_t how); 124 #ifdef KDTRACE_HOOKS 125 static int owner_sx(const struct lock_object *lock, struct thread **owner); 126 #endif 127 static uintptr_t unlock_sx(struct lock_object *lock); 128 129 struct lock_class lock_class_sx = { 130 .lc_name = "sx", 131 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 132 .lc_assert = assert_sx, 133 #ifdef DDB 134 .lc_ddb_show = db_show_sx, 135 #endif 136 .lc_lock = lock_sx, 137 .lc_unlock = unlock_sx, 138 #ifdef KDTRACE_HOOKS 139 .lc_owner = owner_sx, 140 #endif 141 }; 142 143 #ifndef INVARIANTS 144 #define _sx_assert(sx, what, file, line) 145 #endif 146 147 #ifdef ADAPTIVE_SX 148 static __read_frequently u_int asx_retries = 10; 149 static __read_frequently u_int asx_loops = 10000; 150 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging"); 151 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, ""); 152 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, ""); 153 154 static struct lock_delay_config __read_frequently sx_delay; 155 156 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base, 157 0, ""); 158 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max, 159 0, ""); 160 161 LOCK_DELAY_SYSINIT_DEFAULT(sx_delay); 162 #endif 163 164 void 165 assert_sx(const struct lock_object *lock, int what) 166 { 167 168 sx_assert((const struct sx *)lock, what); 169 } 170 171 void 172 lock_sx(struct lock_object *lock, uintptr_t how) 173 { 174 struct sx *sx; 175 176 sx = (struct sx *)lock; 177 if (how) 178 sx_slock(sx); 179 else 180 sx_xlock(sx); 181 } 182 183 uintptr_t 184 unlock_sx(struct lock_object *lock) 185 { 186 struct sx *sx; 187 188 sx = (struct sx *)lock; 189 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 190 if (sx_xlocked(sx)) { 191 sx_xunlock(sx); 192 return (0); 193 } else { 194 sx_sunlock(sx); 195 return (1); 196 } 197 } 198 199 #ifdef KDTRACE_HOOKS 200 int 201 owner_sx(const struct lock_object *lock, struct thread **owner) 202 { 203 const struct sx *sx; 204 uintptr_t x; 205 206 sx = (const struct sx *)lock; 207 x = sx->sx_lock; 208 *owner = NULL; 209 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 210 ((*owner = (struct thread *)SX_OWNER(x)) != NULL)); 211 } 212 #endif 213 214 void 215 sx_sysinit(void *arg) 216 { 217 struct sx_args *sargs = arg; 218 219 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 220 } 221 222 void 223 sx_init_flags(struct sx *sx, const char *description, int opts) 224 { 225 int flags; 226 227 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 228 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0); 229 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 230 ("%s: sx_lock not aligned for %s: %p", __func__, description, 231 &sx->sx_lock)); 232 233 flags = LO_SLEEPABLE | LO_UPGRADABLE; 234 if (opts & SX_DUPOK) 235 flags |= LO_DUPOK; 236 if (opts & SX_NOPROFILE) 237 flags |= LO_NOPROFILE; 238 if (!(opts & SX_NOWITNESS)) 239 flags |= LO_WITNESS; 240 if (opts & SX_RECURSE) 241 flags |= LO_RECURSABLE; 242 if (opts & SX_QUIET) 243 flags |= LO_QUIET; 244 if (opts & SX_NEW) 245 flags |= LO_NEW; 246 247 flags |= opts & SX_NOADAPTIVE; 248 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 249 sx->sx_lock = SX_LOCK_UNLOCKED; 250 sx->sx_recurse = 0; 251 } 252 253 void 254 sx_destroy(struct sx *sx) 255 { 256 257 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 258 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 259 sx->sx_lock = SX_LOCK_DESTROYED; 260 lock_destroy(&sx->lock_object); 261 } 262 263 int 264 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 265 { 266 uintptr_t x; 267 268 if (SCHEDULER_STOPPED()) 269 return (1); 270 271 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 272 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 273 curthread, sx->lock_object.lo_name, file, line)); 274 275 x = sx->sx_lock; 276 for (;;) { 277 KASSERT(x != SX_LOCK_DESTROYED, 278 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 279 if (!(x & SX_LOCK_SHARED)) 280 break; 281 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 282 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 283 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 284 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 285 sx, 0, 0, file, line, LOCKSTAT_READER); 286 TD_LOCKS_INC(curthread); 287 return (1); 288 } 289 } 290 291 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 292 return (0); 293 } 294 295 int 296 sx_try_slock_(struct sx *sx, const char *file, int line) 297 { 298 299 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG)); 300 } 301 302 int 303 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 304 { 305 uintptr_t tid, x; 306 int error = 0; 307 308 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 309 !TD_IS_IDLETHREAD(curthread), 310 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 311 curthread, sx->lock_object.lo_name, file, line)); 312 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 313 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 314 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 315 line, NULL); 316 tid = (uintptr_t)curthread; 317 x = SX_LOCK_UNLOCKED; 318 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 319 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG); 320 else 321 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 322 0, 0, file, line, LOCKSTAT_WRITER); 323 if (!error) { 324 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 325 file, line); 326 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 327 TD_LOCKS_INC(curthread); 328 } 329 330 return (error); 331 } 332 333 int 334 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 335 { 336 struct thread *td; 337 uintptr_t tid, x; 338 int rval; 339 bool recursed; 340 341 td = curthread; 342 tid = (uintptr_t)td; 343 if (SCHEDULER_STOPPED_TD(td)) 344 return (1); 345 346 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 347 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 348 curthread, sx->lock_object.lo_name, file, line)); 349 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 350 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 351 352 rval = 1; 353 recursed = false; 354 x = SX_LOCK_UNLOCKED; 355 for (;;) { 356 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 357 break; 358 if (x == SX_LOCK_UNLOCKED) 359 continue; 360 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 361 sx->sx_recurse++; 362 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 363 break; 364 } 365 rval = 0; 366 break; 367 } 368 369 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 370 if (rval) { 371 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 372 file, line); 373 if (!recursed) 374 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 375 sx, 0, 0, file, line, LOCKSTAT_WRITER); 376 TD_LOCKS_INC(curthread); 377 } 378 379 return (rval); 380 } 381 382 int 383 sx_try_xlock_(struct sx *sx, const char *file, int line) 384 { 385 386 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG)); 387 } 388 389 void 390 _sx_xunlock(struct sx *sx, const char *file, int line) 391 { 392 393 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 394 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 395 _sx_assert(sx, SA_XLOCKED, file, line); 396 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 397 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 398 line); 399 #if LOCK_DEBUG > 0 400 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 401 #else 402 __sx_xunlock(sx, curthread, file, line); 403 #endif 404 TD_LOCKS_DEC(curthread); 405 } 406 407 /* 408 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 409 * This will only succeed if this thread holds a single shared lock. 410 * Return 1 if if the upgrade succeed, 0 otherwise. 411 */ 412 int 413 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 414 { 415 uintptr_t x; 416 uintptr_t waiters; 417 int success; 418 419 if (SCHEDULER_STOPPED()) 420 return (1); 421 422 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 423 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 424 _sx_assert(sx, SA_SLOCKED, file, line); 425 426 /* 427 * Try to switch from one shared lock to an exclusive lock. We need 428 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 429 * we will wake up the exclusive waiters when we drop the lock. 430 */ 431 success = 0; 432 x = SX_READ_VALUE(sx); 433 for (;;) { 434 if (SX_SHARERS(x) > 1) 435 break; 436 waiters = (x & SX_LOCK_EXCLUSIVE_WAITERS); 437 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 438 (uintptr_t)curthread | waiters)) { 439 success = 1; 440 break; 441 } 442 } 443 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 444 if (success) { 445 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 446 file, line); 447 LOCKSTAT_RECORD0(sx__upgrade, sx); 448 } 449 return (success); 450 } 451 452 int 453 sx_try_upgrade_(struct sx *sx, const char *file, int line) 454 { 455 456 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 457 } 458 459 /* 460 * Downgrade an unrecursed exclusive lock into a single shared lock. 461 */ 462 void 463 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 464 { 465 uintptr_t x; 466 int wakeup_swapper; 467 468 if (SCHEDULER_STOPPED()) 469 return; 470 471 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 472 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 473 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 474 #ifndef INVARIANTS 475 if (sx_recursed(sx)) 476 panic("downgrade of a recursed lock"); 477 #endif 478 479 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 480 481 /* 482 * Try to switch from an exclusive lock with no shared waiters 483 * to one sharer with no shared waiters. If there are 484 * exclusive waiters, we don't need to lock the sleep queue so 485 * long as we preserve the flag. We do one quick try and if 486 * that fails we grab the sleepq lock to keep the flags from 487 * changing and do it the slow way. 488 * 489 * We have to lock the sleep queue if there are shared waiters 490 * so we can wake them up. 491 */ 492 x = sx->sx_lock; 493 if (!(x & SX_LOCK_SHARED_WAITERS) && 494 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 495 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 496 goto out; 497 498 /* 499 * Lock the sleep queue so we can read the waiters bits 500 * without any races and wakeup any shared waiters. 501 */ 502 sleepq_lock(&sx->lock_object); 503 504 /* 505 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 506 * shared lock. If there are any shared waiters, wake them up. 507 */ 508 wakeup_swapper = 0; 509 x = sx->sx_lock; 510 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 511 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 512 if (x & SX_LOCK_SHARED_WAITERS) 513 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 514 0, SQ_SHARED_QUEUE); 515 sleepq_release(&sx->lock_object); 516 517 if (wakeup_swapper) 518 kick_proc0(); 519 520 out: 521 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 522 LOCKSTAT_RECORD0(sx__downgrade, sx); 523 } 524 525 void 526 sx_downgrade_(struct sx *sx, const char *file, int line) 527 { 528 529 sx_downgrade_int(sx LOCK_FILE_LINE_ARG); 530 } 531 532 /* 533 * This function represents the so-called 'hard case' for sx_xlock 534 * operation. All 'easy case' failures are redirected to this. Note 535 * that ideally this would be a static function, but it needs to be 536 * accessible from at least sx.h. 537 */ 538 int 539 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 540 { 541 GIANT_DECLARE; 542 uintptr_t tid; 543 #ifdef ADAPTIVE_SX 544 volatile struct thread *owner; 545 u_int i, n, spintries = 0; 546 enum { READERS, WRITER } sleep_reason; 547 bool adaptive; 548 #endif 549 #ifdef LOCK_PROFILING 550 uint64_t waittime = 0; 551 int contested = 0; 552 #endif 553 int error = 0; 554 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 555 struct lock_delay_arg lda; 556 #endif 557 #ifdef KDTRACE_HOOKS 558 u_int sleep_cnt = 0; 559 int64_t sleep_time = 0; 560 int64_t all_time = 0; 561 #endif 562 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 563 uintptr_t state; 564 #endif 565 int extra_work = 0; 566 567 tid = (uintptr_t)curthread; 568 569 #ifdef KDTRACE_HOOKS 570 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 571 while (x == SX_LOCK_UNLOCKED) { 572 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 573 goto out_lockstat; 574 } 575 extra_work = 1; 576 all_time -= lockstat_nsecs(&sx->lock_object); 577 state = x; 578 } 579 #endif 580 #ifdef LOCK_PROFILING 581 extra_work = 1; 582 state = x; 583 #endif 584 585 if (SCHEDULER_STOPPED()) 586 return (0); 587 588 #if defined(ADAPTIVE_SX) 589 lock_delay_arg_init(&lda, &sx_delay); 590 #elif defined(KDTRACE_HOOKS) 591 lock_delay_arg_init(&lda, NULL); 592 #endif 593 594 if (__predict_false(x == SX_LOCK_UNLOCKED)) 595 x = SX_READ_VALUE(sx); 596 597 /* If we already hold an exclusive lock, then recurse. */ 598 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 599 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 600 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 601 sx->lock_object.lo_name, file, line)); 602 sx->sx_recurse++; 603 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 604 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 605 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 606 return (0); 607 } 608 609 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 610 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 611 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 612 613 #ifdef ADAPTIVE_SX 614 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 615 #endif 616 617 #ifdef HWPMC_HOOKS 618 PMC_SOFT_CALL( , , lock, failed); 619 #endif 620 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 621 &waittime); 622 623 #ifndef INVARIANTS 624 GIANT_SAVE(extra_work); 625 #endif 626 627 for (;;) { 628 if (x == SX_LOCK_UNLOCKED) { 629 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 630 break; 631 continue; 632 } 633 #ifdef INVARIANTS 634 GIANT_SAVE(extra_work); 635 #endif 636 #ifdef KDTRACE_HOOKS 637 lda.spin_cnt++; 638 #endif 639 #ifdef ADAPTIVE_SX 640 if (__predict_false(!adaptive)) 641 goto sleepq; 642 /* 643 * If the lock is write locked and the owner is 644 * running on another CPU, spin until the owner stops 645 * running or the state of the lock changes. 646 */ 647 if ((x & SX_LOCK_SHARED) == 0) { 648 sleep_reason = WRITER; 649 owner = lv_sx_owner(x); 650 if (!TD_IS_RUNNING(owner)) 651 goto sleepq; 652 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 653 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 654 __func__, sx, owner); 655 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 656 "spinning", "lockname:\"%s\"", 657 sx->lock_object.lo_name); 658 do { 659 lock_delay(&lda); 660 x = SX_READ_VALUE(sx); 661 owner = lv_sx_owner(x); 662 } while (owner != NULL && TD_IS_RUNNING(owner)); 663 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 664 "running"); 665 continue; 666 } else if (SX_SHARERS(x) > 0) { 667 sleep_reason = READERS; 668 if (spintries == asx_retries) 669 goto sleepq; 670 spintries++; 671 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 672 "spinning", "lockname:\"%s\"", 673 sx->lock_object.lo_name); 674 for (i = 0; i < asx_loops; i += n) { 675 n = SX_SHARERS(x); 676 lock_delay_spin(n); 677 x = SX_READ_VALUE(sx); 678 if ((x & SX_LOCK_SHARED) == 0 || 679 SX_SHARERS(x) == 0) 680 break; 681 } 682 #ifdef KDTRACE_HOOKS 683 lda.spin_cnt += i; 684 #endif 685 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 686 "running"); 687 if (i < asx_loops) 688 continue; 689 } 690 sleepq: 691 #endif 692 sleepq_lock(&sx->lock_object); 693 x = SX_READ_VALUE(sx); 694 retry_sleepq: 695 696 /* 697 * If the lock was released while spinning on the 698 * sleep queue chain lock, try again. 699 */ 700 if (x == SX_LOCK_UNLOCKED) { 701 sleepq_release(&sx->lock_object); 702 continue; 703 } 704 705 #ifdef ADAPTIVE_SX 706 /* 707 * The current lock owner might have started executing 708 * on another CPU (or the lock could have changed 709 * owners) while we were waiting on the sleep queue 710 * chain lock. If so, drop the sleep queue lock and try 711 * again. 712 */ 713 if (adaptive) { 714 if (!(x & SX_LOCK_SHARED)) { 715 owner = (struct thread *)SX_OWNER(x); 716 if (TD_IS_RUNNING(owner)) { 717 sleepq_release(&sx->lock_object); 718 continue; 719 } 720 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 721 sleepq_release(&sx->lock_object); 722 continue; 723 } 724 } 725 #endif 726 727 /* 728 * If an exclusive lock was released with both shared 729 * and exclusive waiters and a shared waiter hasn't 730 * woken up and acquired the lock yet, sx_lock will be 731 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 732 * If we see that value, try to acquire it once. Note 733 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 734 * as there are other exclusive waiters still. If we 735 * fail, restart the loop. 736 */ 737 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 738 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 739 tid | SX_LOCK_EXCLUSIVE_WAITERS)) 740 goto retry_sleepq; 741 sleepq_release(&sx->lock_object); 742 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 743 __func__, sx); 744 break; 745 } 746 747 /* 748 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 749 * than loop back and retry. 750 */ 751 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 752 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 753 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 754 goto retry_sleepq; 755 } 756 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 757 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 758 __func__, sx); 759 } 760 761 /* 762 * Since we have been unable to acquire the exclusive 763 * lock and the exclusive waiters flag is set, we have 764 * to sleep. 765 */ 766 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 767 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 768 __func__, sx); 769 770 #ifdef KDTRACE_HOOKS 771 sleep_time -= lockstat_nsecs(&sx->lock_object); 772 #endif 773 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 774 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 775 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 776 if (!(opts & SX_INTERRUPTIBLE)) 777 sleepq_wait(&sx->lock_object, 0); 778 else 779 error = sleepq_wait_sig(&sx->lock_object, 0); 780 #ifdef KDTRACE_HOOKS 781 sleep_time += lockstat_nsecs(&sx->lock_object); 782 sleep_cnt++; 783 #endif 784 if (error) { 785 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 786 CTR2(KTR_LOCK, 787 "%s: interruptible sleep by %p suspended by signal", 788 __func__, sx); 789 break; 790 } 791 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 792 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 793 __func__, sx); 794 x = SX_READ_VALUE(sx); 795 } 796 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 797 if (__predict_true(!extra_work)) 798 return (error); 799 #endif 800 #ifdef KDTRACE_HOOKS 801 all_time += lockstat_nsecs(&sx->lock_object); 802 if (sleep_time) 803 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 804 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 805 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 806 if (lda.spin_cnt > sleep_cnt) 807 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 808 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 809 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 810 out_lockstat: 811 #endif 812 if (!error) 813 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 814 contested, waittime, file, line, LOCKSTAT_WRITER); 815 GIANT_RESTORE(); 816 return (error); 817 } 818 819 /* 820 * This function represents the so-called 'hard case' for sx_xunlock 821 * operation. All 'easy case' failures are redirected to this. Note 822 * that ideally this would be a static function, but it needs to be 823 * accessible from at least sx.h. 824 */ 825 void 826 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 827 { 828 uintptr_t tid, setx; 829 int queue, wakeup_swapper; 830 831 if (SCHEDULER_STOPPED()) 832 return; 833 834 tid = (uintptr_t)curthread; 835 836 if (__predict_false(x == tid)) 837 x = SX_READ_VALUE(sx); 838 839 MPASS(!(x & SX_LOCK_SHARED)); 840 841 if (__predict_false(x & SX_LOCK_RECURSED)) { 842 /* The lock is recursed, unrecurse one level. */ 843 if ((--sx->sx_recurse) == 0) 844 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 845 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 846 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 847 return; 848 } 849 850 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 851 if (x == tid && 852 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 853 return; 854 855 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 856 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 857 858 sleepq_lock(&sx->lock_object); 859 x = SX_READ_VALUE(sx); 860 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 861 862 /* 863 * The wake up algorithm here is quite simple and probably not 864 * ideal. It gives precedence to shared waiters if they are 865 * present. For this condition, we have to preserve the 866 * state of the exclusive waiters flag. 867 * If interruptible sleeps left the shared queue empty avoid a 868 * starvation for the threads sleeping on the exclusive queue by giving 869 * them precedence and cleaning up the shared waiters bit anyway. 870 */ 871 setx = SX_LOCK_UNLOCKED; 872 queue = SQ_EXCLUSIVE_QUEUE; 873 if ((x & SX_LOCK_SHARED_WAITERS) != 0 && 874 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 875 queue = SQ_SHARED_QUEUE; 876 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS); 877 } 878 atomic_store_rel_ptr(&sx->sx_lock, setx); 879 880 /* Wake up all the waiters for the specific queue. */ 881 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 882 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 883 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 884 "exclusive"); 885 886 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 887 queue); 888 sleepq_release(&sx->lock_object); 889 if (wakeup_swapper) 890 kick_proc0(); 891 } 892 893 static bool __always_inline 894 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF) 895 { 896 897 /* 898 * If no other thread has an exclusive lock then try to bump up 899 * the count of sharers. Since we have to preserve the state 900 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 901 * shared lock loop back and retry. 902 */ 903 while (*xp & SX_LOCK_SHARED) { 904 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 905 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 906 *xp + SX_ONE_SHARER)) { 907 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 908 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 909 __func__, sx, (void *)*xp, 910 (void *)(*xp + SX_ONE_SHARER)); 911 return (true); 912 } 913 } 914 return (false); 915 } 916 917 static int __noinline 918 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 919 { 920 GIANT_DECLARE; 921 #ifdef ADAPTIVE_SX 922 volatile struct thread *owner; 923 bool adaptive; 924 #endif 925 #ifdef LOCK_PROFILING 926 uint64_t waittime = 0; 927 int contested = 0; 928 #endif 929 int error = 0; 930 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 931 struct lock_delay_arg lda; 932 #endif 933 #ifdef KDTRACE_HOOKS 934 u_int sleep_cnt = 0; 935 int64_t sleep_time = 0; 936 int64_t all_time = 0; 937 #endif 938 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 939 uintptr_t state; 940 #endif 941 int extra_work = 0; 942 943 #ifdef KDTRACE_HOOKS 944 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 945 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 946 goto out_lockstat; 947 extra_work = 1; 948 all_time -= lockstat_nsecs(&sx->lock_object); 949 state = x; 950 } 951 #endif 952 #ifdef LOCK_PROFILING 953 extra_work = 1; 954 state = x; 955 #endif 956 957 if (SCHEDULER_STOPPED()) 958 return (0); 959 960 #if defined(ADAPTIVE_SX) 961 lock_delay_arg_init(&lda, &sx_delay); 962 #elif defined(KDTRACE_HOOKS) 963 lock_delay_arg_init(&lda, NULL); 964 #endif 965 966 #ifdef ADAPTIVE_SX 967 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 968 #endif 969 970 #ifdef HWPMC_HOOKS 971 PMC_SOFT_CALL( , , lock, failed); 972 #endif 973 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 974 &waittime); 975 976 #ifndef INVARIANTS 977 GIANT_SAVE(extra_work); 978 #endif 979 980 /* 981 * As with rwlocks, we don't make any attempt to try to block 982 * shared locks once there is an exclusive waiter. 983 */ 984 for (;;) { 985 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 986 break; 987 #ifdef INVARIANTS 988 GIANT_SAVE(extra_work); 989 #endif 990 #ifdef KDTRACE_HOOKS 991 lda.spin_cnt++; 992 #endif 993 994 #ifdef ADAPTIVE_SX 995 if (__predict_false(!adaptive)) 996 goto sleepq; 997 /* 998 * If the owner is running on another CPU, spin until 999 * the owner stops running or the state of the lock 1000 * changes. 1001 */ 1002 owner = lv_sx_owner(x); 1003 if (TD_IS_RUNNING(owner)) { 1004 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1005 CTR3(KTR_LOCK, 1006 "%s: spinning on %p held by %p", 1007 __func__, sx, owner); 1008 KTR_STATE1(KTR_SCHED, "thread", 1009 sched_tdname(curthread), "spinning", 1010 "lockname:\"%s\"", sx->lock_object.lo_name); 1011 do { 1012 lock_delay(&lda); 1013 x = SX_READ_VALUE(sx); 1014 owner = lv_sx_owner(x); 1015 } while (owner != NULL && TD_IS_RUNNING(owner)); 1016 KTR_STATE0(KTR_SCHED, "thread", 1017 sched_tdname(curthread), "running"); 1018 continue; 1019 } 1020 sleepq: 1021 #endif 1022 1023 /* 1024 * Some other thread already has an exclusive lock, so 1025 * start the process of blocking. 1026 */ 1027 sleepq_lock(&sx->lock_object); 1028 x = SX_READ_VALUE(sx); 1029 retry_sleepq: 1030 /* 1031 * The lock could have been released while we spun. 1032 * In this case loop back and retry. 1033 */ 1034 if (x & SX_LOCK_SHARED) { 1035 sleepq_release(&sx->lock_object); 1036 continue; 1037 } 1038 1039 #ifdef ADAPTIVE_SX 1040 /* 1041 * If the owner is running on another CPU, spin until 1042 * the owner stops running or the state of the lock 1043 * changes. 1044 */ 1045 if (!(x & SX_LOCK_SHARED) && adaptive) { 1046 owner = (struct thread *)SX_OWNER(x); 1047 if (TD_IS_RUNNING(owner)) { 1048 sleepq_release(&sx->lock_object); 1049 x = SX_READ_VALUE(sx); 1050 continue; 1051 } 1052 } 1053 #endif 1054 1055 /* 1056 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1057 * fail to set it drop the sleep queue lock and loop 1058 * back. 1059 */ 1060 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1061 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1062 x | SX_LOCK_SHARED_WAITERS)) 1063 goto retry_sleepq; 1064 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1065 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1066 __func__, sx); 1067 } 1068 1069 /* 1070 * Since we have been unable to acquire the shared lock, 1071 * we have to sleep. 1072 */ 1073 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1074 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1075 __func__, sx); 1076 1077 #ifdef KDTRACE_HOOKS 1078 sleep_time -= lockstat_nsecs(&sx->lock_object); 1079 #endif 1080 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1081 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1082 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1083 if (!(opts & SX_INTERRUPTIBLE)) 1084 sleepq_wait(&sx->lock_object, 0); 1085 else 1086 error = sleepq_wait_sig(&sx->lock_object, 0); 1087 #ifdef KDTRACE_HOOKS 1088 sleep_time += lockstat_nsecs(&sx->lock_object); 1089 sleep_cnt++; 1090 #endif 1091 if (error) { 1092 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1093 CTR2(KTR_LOCK, 1094 "%s: interruptible sleep by %p suspended by signal", 1095 __func__, sx); 1096 break; 1097 } 1098 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1099 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1100 __func__, sx); 1101 x = SX_READ_VALUE(sx); 1102 } 1103 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1104 if (__predict_true(!extra_work)) 1105 return (error); 1106 #endif 1107 #ifdef KDTRACE_HOOKS 1108 all_time += lockstat_nsecs(&sx->lock_object); 1109 if (sleep_time) 1110 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1111 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1112 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1113 if (lda.spin_cnt > sleep_cnt) 1114 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1115 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1116 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1117 out_lockstat: 1118 #endif 1119 if (error == 0) { 1120 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1121 contested, waittime, file, line, LOCKSTAT_READER); 1122 } 1123 GIANT_RESTORE(); 1124 return (error); 1125 } 1126 1127 int 1128 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1129 { 1130 uintptr_t x; 1131 int error; 1132 1133 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1134 !TD_IS_IDLETHREAD(curthread), 1135 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1136 curthread, sx->lock_object.lo_name, file, line)); 1137 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1138 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1139 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1140 1141 error = 0; 1142 x = SX_READ_VALUE(sx); 1143 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1144 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))) 1145 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1146 else 1147 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1148 file, line); 1149 if (error == 0) { 1150 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1151 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1152 TD_LOCKS_INC(curthread); 1153 } 1154 return (error); 1155 } 1156 1157 int 1158 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1159 { 1160 1161 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1162 } 1163 1164 static bool __always_inline 1165 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1166 { 1167 1168 for (;;) { 1169 /* 1170 * We should never have sharers while at least one thread 1171 * holds a shared lock. 1172 */ 1173 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1174 ("%s: waiting sharers", __func__)); 1175 1176 /* 1177 * See if there is more than one shared lock held. If 1178 * so, just drop one and return. 1179 */ 1180 if (SX_SHARERS(*xp) > 1) { 1181 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1182 *xp - SX_ONE_SHARER)) { 1183 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1184 CTR4(KTR_LOCK, 1185 "%s: %p succeeded %p -> %p", 1186 __func__, sx, (void *)*xp, 1187 (void *)(*xp - SX_ONE_SHARER)); 1188 return (true); 1189 } 1190 continue; 1191 } 1192 1193 /* 1194 * If there aren't any waiters for an exclusive lock, 1195 * then try to drop it quickly. 1196 */ 1197 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1198 MPASS(*xp == SX_SHARERS_LOCK(1)); 1199 *xp = SX_SHARERS_LOCK(1); 1200 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1201 xp, SX_LOCK_UNLOCKED)) { 1202 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1203 CTR2(KTR_LOCK, "%s: %p last succeeded", 1204 __func__, sx); 1205 return (true); 1206 } 1207 continue; 1208 } 1209 break; 1210 } 1211 return (false); 1212 } 1213 1214 static void __noinline 1215 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1216 { 1217 int wakeup_swapper = 0; 1218 uintptr_t setx; 1219 1220 if (SCHEDULER_STOPPED()) 1221 return; 1222 1223 if (_sx_sunlock_try(sx, &x)) 1224 goto out_lockstat; 1225 1226 /* 1227 * At this point, there should just be one sharer with 1228 * exclusive waiters. 1229 */ 1230 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1231 1232 sleepq_lock(&sx->lock_object); 1233 x = SX_READ_VALUE(sx); 1234 for (;;) { 1235 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS); 1236 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 1237 if (_sx_sunlock_try(sx, &x)) 1238 break; 1239 1240 /* 1241 * Wake up semantic here is quite simple: 1242 * Just wake up all the exclusive waiters. 1243 * Note that the state of the lock could have changed, 1244 * so if it fails loop back and retry. 1245 */ 1246 setx = x - SX_ONE_SHARER; 1247 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS; 1248 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1249 continue; 1250 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1251 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1252 "exclusive queue", __func__, sx); 1253 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1254 0, SQ_EXCLUSIVE_QUEUE); 1255 break; 1256 } 1257 sleepq_release(&sx->lock_object); 1258 if (wakeup_swapper) 1259 kick_proc0(); 1260 out_lockstat: 1261 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1262 } 1263 1264 void 1265 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1266 { 1267 uintptr_t x; 1268 1269 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1270 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1271 _sx_assert(sx, SA_SLOCKED, file, line); 1272 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1273 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1274 1275 x = SX_READ_VALUE(sx); 1276 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1277 !_sx_sunlock_try(sx, &x))) 1278 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG); 1279 else 1280 lock_profile_release_lock(&sx->lock_object); 1281 1282 TD_LOCKS_DEC(curthread); 1283 } 1284 1285 void 1286 _sx_sunlock(struct sx *sx, const char *file, int line) 1287 { 1288 1289 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1290 } 1291 1292 #ifdef INVARIANT_SUPPORT 1293 #ifndef INVARIANTS 1294 #undef _sx_assert 1295 #endif 1296 1297 /* 1298 * In the non-WITNESS case, sx_assert() can only detect that at least 1299 * *some* thread owns an slock, but it cannot guarantee that *this* 1300 * thread owns an slock. 1301 */ 1302 void 1303 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1304 { 1305 #ifndef WITNESS 1306 int slocked = 0; 1307 #endif 1308 1309 if (panicstr != NULL) 1310 return; 1311 switch (what) { 1312 case SA_SLOCKED: 1313 case SA_SLOCKED | SA_NOTRECURSED: 1314 case SA_SLOCKED | SA_RECURSED: 1315 #ifndef WITNESS 1316 slocked = 1; 1317 /* FALLTHROUGH */ 1318 #endif 1319 case SA_LOCKED: 1320 case SA_LOCKED | SA_NOTRECURSED: 1321 case SA_LOCKED | SA_RECURSED: 1322 #ifdef WITNESS 1323 witness_assert(&sx->lock_object, what, file, line); 1324 #else 1325 /* 1326 * If some other thread has an exclusive lock or we 1327 * have one and are asserting a shared lock, fail. 1328 * Also, if no one has a lock at all, fail. 1329 */ 1330 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1331 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1332 sx_xholder(sx) != curthread))) 1333 panic("Lock %s not %slocked @ %s:%d\n", 1334 sx->lock_object.lo_name, slocked ? "share " : "", 1335 file, line); 1336 1337 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1338 if (sx_recursed(sx)) { 1339 if (what & SA_NOTRECURSED) 1340 panic("Lock %s recursed @ %s:%d\n", 1341 sx->lock_object.lo_name, file, 1342 line); 1343 } else if (what & SA_RECURSED) 1344 panic("Lock %s not recursed @ %s:%d\n", 1345 sx->lock_object.lo_name, file, line); 1346 } 1347 #endif 1348 break; 1349 case SA_XLOCKED: 1350 case SA_XLOCKED | SA_NOTRECURSED: 1351 case SA_XLOCKED | SA_RECURSED: 1352 if (sx_xholder(sx) != curthread) 1353 panic("Lock %s not exclusively locked @ %s:%d\n", 1354 sx->lock_object.lo_name, file, line); 1355 if (sx_recursed(sx)) { 1356 if (what & SA_NOTRECURSED) 1357 panic("Lock %s recursed @ %s:%d\n", 1358 sx->lock_object.lo_name, file, line); 1359 } else if (what & SA_RECURSED) 1360 panic("Lock %s not recursed @ %s:%d\n", 1361 sx->lock_object.lo_name, file, line); 1362 break; 1363 case SA_UNLOCKED: 1364 #ifdef WITNESS 1365 witness_assert(&sx->lock_object, what, file, line); 1366 #else 1367 /* 1368 * If we hold an exclusve lock fail. We can't 1369 * reliably check to see if we hold a shared lock or 1370 * not. 1371 */ 1372 if (sx_xholder(sx) == curthread) 1373 panic("Lock %s exclusively locked @ %s:%d\n", 1374 sx->lock_object.lo_name, file, line); 1375 #endif 1376 break; 1377 default: 1378 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1379 line); 1380 } 1381 } 1382 #endif /* INVARIANT_SUPPORT */ 1383 1384 #ifdef DDB 1385 static void 1386 db_show_sx(const struct lock_object *lock) 1387 { 1388 struct thread *td; 1389 const struct sx *sx; 1390 1391 sx = (const struct sx *)lock; 1392 1393 db_printf(" state: "); 1394 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1395 db_printf("UNLOCKED\n"); 1396 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1397 db_printf("DESTROYED\n"); 1398 return; 1399 } else if (sx->sx_lock & SX_LOCK_SHARED) 1400 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1401 else { 1402 td = sx_xholder(sx); 1403 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1404 td->td_tid, td->td_proc->p_pid, td->td_name); 1405 if (sx_recursed(sx)) 1406 db_printf(" recursed: %d\n", sx->sx_recurse); 1407 } 1408 1409 db_printf(" waiters: "); 1410 switch(sx->sx_lock & 1411 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1412 case SX_LOCK_SHARED_WAITERS: 1413 db_printf("shared\n"); 1414 break; 1415 case SX_LOCK_EXCLUSIVE_WAITERS: 1416 db_printf("exclusive\n"); 1417 break; 1418 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1419 db_printf("exclusive and shared\n"); 1420 break; 1421 default: 1422 db_printf("none\n"); 1423 } 1424 } 1425 1426 /* 1427 * Check to see if a thread that is blocked on a sleep queue is actually 1428 * blocked on an sx lock. If so, output some details and return true. 1429 * If the lock has an exclusive owner, return that in *ownerp. 1430 */ 1431 int 1432 sx_chain(struct thread *td, struct thread **ownerp) 1433 { 1434 struct sx *sx; 1435 1436 /* 1437 * Check to see if this thread is blocked on an sx lock. 1438 * First, we check the lock class. If that is ok, then we 1439 * compare the lock name against the wait message. 1440 */ 1441 sx = td->td_wchan; 1442 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1443 sx->lock_object.lo_name != td->td_wmesg) 1444 return (0); 1445 1446 /* We think we have an sx lock, so output some details. */ 1447 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1448 *ownerp = sx_xholder(sx); 1449 if (sx->sx_lock & SX_LOCK_SHARED) 1450 db_printf("SLOCK (count %ju)\n", 1451 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1452 else 1453 db_printf("XLOCK\n"); 1454 return (1); 1455 } 1456 #endif 1457