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; 149 static __read_frequently u_int asx_loops; 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 static void 162 sx_lock_delay_init(void *arg __unused) 163 { 164 165 lock_delay_default_init(&sx_delay); 166 asx_retries = 10; 167 asx_loops = max(10000, sx_delay.max); 168 } 169 LOCK_DELAY_SYSINIT(sx_lock_delay_init); 170 #endif 171 172 void 173 assert_sx(const struct lock_object *lock, int what) 174 { 175 176 sx_assert((const struct sx *)lock, what); 177 } 178 179 void 180 lock_sx(struct lock_object *lock, uintptr_t how) 181 { 182 struct sx *sx; 183 184 sx = (struct sx *)lock; 185 if (how) 186 sx_slock(sx); 187 else 188 sx_xlock(sx); 189 } 190 191 uintptr_t 192 unlock_sx(struct lock_object *lock) 193 { 194 struct sx *sx; 195 196 sx = (struct sx *)lock; 197 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 198 if (sx_xlocked(sx)) { 199 sx_xunlock(sx); 200 return (0); 201 } else { 202 sx_sunlock(sx); 203 return (1); 204 } 205 } 206 207 #ifdef KDTRACE_HOOKS 208 int 209 owner_sx(const struct lock_object *lock, struct thread **owner) 210 { 211 const struct sx *sx; 212 uintptr_t x; 213 214 sx = (const struct sx *)lock; 215 x = sx->sx_lock; 216 *owner = NULL; 217 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 218 ((*owner = (struct thread *)SX_OWNER(x)) != NULL)); 219 } 220 #endif 221 222 void 223 sx_sysinit(void *arg) 224 { 225 struct sx_args *sargs = arg; 226 227 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 228 } 229 230 void 231 sx_init_flags(struct sx *sx, const char *description, int opts) 232 { 233 int flags; 234 235 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 236 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0); 237 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 238 ("%s: sx_lock not aligned for %s: %p", __func__, description, 239 &sx->sx_lock)); 240 241 flags = LO_SLEEPABLE | LO_UPGRADABLE; 242 if (opts & SX_DUPOK) 243 flags |= LO_DUPOK; 244 if (opts & SX_NOPROFILE) 245 flags |= LO_NOPROFILE; 246 if (!(opts & SX_NOWITNESS)) 247 flags |= LO_WITNESS; 248 if (opts & SX_RECURSE) 249 flags |= LO_RECURSABLE; 250 if (opts & SX_QUIET) 251 flags |= LO_QUIET; 252 if (opts & SX_NEW) 253 flags |= LO_NEW; 254 255 flags |= opts & SX_NOADAPTIVE; 256 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 257 sx->sx_lock = SX_LOCK_UNLOCKED; 258 sx->sx_recurse = 0; 259 } 260 261 void 262 sx_destroy(struct sx *sx) 263 { 264 265 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 266 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 267 sx->sx_lock = SX_LOCK_DESTROYED; 268 lock_destroy(&sx->lock_object); 269 } 270 271 int 272 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 273 { 274 uintptr_t x; 275 276 if (SCHEDULER_STOPPED()) 277 return (1); 278 279 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 280 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 281 curthread, sx->lock_object.lo_name, file, line)); 282 283 x = sx->sx_lock; 284 for (;;) { 285 KASSERT(x != SX_LOCK_DESTROYED, 286 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 287 if (!(x & SX_LOCK_SHARED)) 288 break; 289 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 290 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 291 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 292 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 293 sx, 0, 0, file, line, LOCKSTAT_READER); 294 TD_LOCKS_INC(curthread); 295 return (1); 296 } 297 } 298 299 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 300 return (0); 301 } 302 303 int 304 sx_try_slock_(struct sx *sx, const char *file, int line) 305 { 306 307 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG)); 308 } 309 310 int 311 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 312 { 313 uintptr_t tid, x; 314 int error = 0; 315 316 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 317 !TD_IS_IDLETHREAD(curthread), 318 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 319 curthread, sx->lock_object.lo_name, file, line)); 320 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 321 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 322 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 323 line, NULL); 324 tid = (uintptr_t)curthread; 325 x = SX_LOCK_UNLOCKED; 326 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 327 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG); 328 else 329 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 330 0, 0, file, line, LOCKSTAT_WRITER); 331 if (!error) { 332 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 333 file, line); 334 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 335 TD_LOCKS_INC(curthread); 336 } 337 338 return (error); 339 } 340 341 int 342 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 343 { 344 struct thread *td; 345 uintptr_t tid, x; 346 int rval; 347 bool recursed; 348 349 td = curthread; 350 tid = (uintptr_t)td; 351 if (SCHEDULER_STOPPED_TD(td)) 352 return (1); 353 354 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 355 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 356 curthread, sx->lock_object.lo_name, file, line)); 357 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 358 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 359 360 rval = 1; 361 recursed = false; 362 x = SX_LOCK_UNLOCKED; 363 for (;;) { 364 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 365 break; 366 if (x == SX_LOCK_UNLOCKED) 367 continue; 368 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 369 sx->sx_recurse++; 370 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 371 break; 372 } 373 rval = 0; 374 break; 375 } 376 377 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 378 if (rval) { 379 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 380 file, line); 381 if (!recursed) 382 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 383 sx, 0, 0, file, line, LOCKSTAT_WRITER); 384 TD_LOCKS_INC(curthread); 385 } 386 387 return (rval); 388 } 389 390 int 391 sx_try_xlock_(struct sx *sx, const char *file, int line) 392 { 393 394 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG)); 395 } 396 397 void 398 _sx_xunlock(struct sx *sx, const char *file, int line) 399 { 400 401 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 402 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 403 _sx_assert(sx, SA_XLOCKED, file, line); 404 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 405 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 406 line); 407 #if LOCK_DEBUG > 0 408 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 409 #else 410 __sx_xunlock(sx, curthread, file, line); 411 #endif 412 TD_LOCKS_DEC(curthread); 413 } 414 415 /* 416 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 417 * This will only succeed if this thread holds a single shared lock. 418 * Return 1 if if the upgrade succeed, 0 otherwise. 419 */ 420 int 421 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 422 { 423 uintptr_t x; 424 uintptr_t waiters; 425 int success; 426 427 if (SCHEDULER_STOPPED()) 428 return (1); 429 430 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 431 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 432 _sx_assert(sx, SA_SLOCKED, file, line); 433 434 /* 435 * Try to switch from one shared lock to an exclusive lock. We need 436 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 437 * we will wake up the exclusive waiters when we drop the lock. 438 */ 439 success = 0; 440 x = SX_READ_VALUE(sx); 441 for (;;) { 442 if (SX_SHARERS(x) > 1) 443 break; 444 waiters = (x & SX_LOCK_EXCLUSIVE_WAITERS); 445 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 446 (uintptr_t)curthread | waiters)) { 447 success = 1; 448 break; 449 } 450 } 451 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 452 if (success) { 453 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 454 file, line); 455 LOCKSTAT_RECORD0(sx__upgrade, sx); 456 } 457 return (success); 458 } 459 460 int 461 sx_try_upgrade_(struct sx *sx, const char *file, int line) 462 { 463 464 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 465 } 466 467 /* 468 * Downgrade an unrecursed exclusive lock into a single shared lock. 469 */ 470 void 471 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 472 { 473 uintptr_t x; 474 int wakeup_swapper; 475 476 if (SCHEDULER_STOPPED()) 477 return; 478 479 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 480 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 481 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 482 #ifndef INVARIANTS 483 if (sx_recursed(sx)) 484 panic("downgrade of a recursed lock"); 485 #endif 486 487 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 488 489 /* 490 * Try to switch from an exclusive lock with no shared waiters 491 * to one sharer with no shared waiters. If there are 492 * exclusive waiters, we don't need to lock the sleep queue so 493 * long as we preserve the flag. We do one quick try and if 494 * that fails we grab the sleepq lock to keep the flags from 495 * changing and do it the slow way. 496 * 497 * We have to lock the sleep queue if there are shared waiters 498 * so we can wake them up. 499 */ 500 x = sx->sx_lock; 501 if (!(x & SX_LOCK_SHARED_WAITERS) && 502 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 503 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 504 goto out; 505 506 /* 507 * Lock the sleep queue so we can read the waiters bits 508 * without any races and wakeup any shared waiters. 509 */ 510 sleepq_lock(&sx->lock_object); 511 512 /* 513 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 514 * shared lock. If there are any shared waiters, wake them up. 515 */ 516 wakeup_swapper = 0; 517 x = sx->sx_lock; 518 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 519 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 520 if (x & SX_LOCK_SHARED_WAITERS) 521 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 522 0, SQ_SHARED_QUEUE); 523 sleepq_release(&sx->lock_object); 524 525 if (wakeup_swapper) 526 kick_proc0(); 527 528 out: 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 /* 541 * This function represents the so-called 'hard case' for sx_xlock 542 * operation. All 'easy case' failures are redirected to this. Note 543 * that ideally this would be a static function, but it needs to be 544 * accessible from at least sx.h. 545 */ 546 int 547 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 548 { 549 GIANT_DECLARE; 550 uintptr_t tid; 551 #ifdef ADAPTIVE_SX 552 volatile struct thread *owner; 553 u_int i, n, spintries = 0; 554 enum { READERS, WRITER } sleep_reason = READERS; 555 bool adaptive; 556 #endif 557 #ifdef LOCK_PROFILING 558 uint64_t waittime = 0; 559 int contested = 0; 560 #endif 561 int error = 0; 562 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 563 struct lock_delay_arg lda; 564 #endif 565 #ifdef KDTRACE_HOOKS 566 u_int sleep_cnt = 0; 567 int64_t sleep_time = 0; 568 int64_t all_time = 0; 569 #endif 570 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 571 uintptr_t state = 0; 572 #endif 573 int extra_work = 0; 574 575 tid = (uintptr_t)curthread; 576 577 #ifdef KDTRACE_HOOKS 578 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 579 while (x == SX_LOCK_UNLOCKED) { 580 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 581 goto out_lockstat; 582 } 583 extra_work = 1; 584 all_time -= lockstat_nsecs(&sx->lock_object); 585 state = x; 586 } 587 #endif 588 #ifdef LOCK_PROFILING 589 extra_work = 1; 590 state = x; 591 #endif 592 593 if (SCHEDULER_STOPPED()) 594 return (0); 595 596 #if defined(ADAPTIVE_SX) 597 lock_delay_arg_init(&lda, &sx_delay); 598 #elif defined(KDTRACE_HOOKS) 599 lock_delay_arg_init(&lda, NULL); 600 #endif 601 602 if (__predict_false(x == SX_LOCK_UNLOCKED)) 603 x = SX_READ_VALUE(sx); 604 605 /* If we already hold an exclusive lock, then recurse. */ 606 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 607 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 608 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 609 sx->lock_object.lo_name, file, line)); 610 sx->sx_recurse++; 611 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 612 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 613 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 614 return (0); 615 } 616 617 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 618 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 619 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 620 621 #ifdef ADAPTIVE_SX 622 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 623 #endif 624 625 #ifdef HWPMC_HOOKS 626 PMC_SOFT_CALL( , , lock, failed); 627 #endif 628 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 629 &waittime); 630 631 #ifndef INVARIANTS 632 GIANT_SAVE(extra_work); 633 #endif 634 635 for (;;) { 636 if (x == SX_LOCK_UNLOCKED) { 637 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 638 break; 639 continue; 640 } 641 #ifdef INVARIANTS 642 GIANT_SAVE(extra_work); 643 #endif 644 #ifdef KDTRACE_HOOKS 645 lda.spin_cnt++; 646 #endif 647 #ifdef ADAPTIVE_SX 648 if (__predict_false(!adaptive)) 649 goto sleepq; 650 /* 651 * If the lock is write locked and the owner is 652 * running on another CPU, spin until the owner stops 653 * running or the state of the lock changes. 654 */ 655 if ((x & SX_LOCK_SHARED) == 0) { 656 sleep_reason = WRITER; 657 owner = lv_sx_owner(x); 658 if (!TD_IS_RUNNING(owner)) 659 goto sleepq; 660 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 661 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 662 __func__, sx, owner); 663 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 664 "spinning", "lockname:\"%s\"", 665 sx->lock_object.lo_name); 666 do { 667 lock_delay(&lda); 668 x = SX_READ_VALUE(sx); 669 owner = lv_sx_owner(x); 670 } while (owner != NULL && TD_IS_RUNNING(owner)); 671 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 672 "running"); 673 continue; 674 } else if (SX_SHARERS(x) > 0) { 675 sleep_reason = READERS; 676 if (spintries == asx_retries) 677 goto sleepq; 678 spintries++; 679 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 680 "spinning", "lockname:\"%s\"", 681 sx->lock_object.lo_name); 682 for (i = 0; i < asx_loops; i += n) { 683 n = SX_SHARERS(x); 684 lock_delay_spin(n); 685 x = SX_READ_VALUE(sx); 686 if ((x & SX_LOCK_SHARED) == 0 || 687 SX_SHARERS(x) == 0) 688 break; 689 } 690 #ifdef KDTRACE_HOOKS 691 lda.spin_cnt += i; 692 #endif 693 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 694 "running"); 695 if (i < asx_loops) 696 continue; 697 } 698 sleepq: 699 #endif 700 sleepq_lock(&sx->lock_object); 701 x = SX_READ_VALUE(sx); 702 retry_sleepq: 703 704 /* 705 * If the lock was released while spinning on the 706 * sleep queue chain lock, try again. 707 */ 708 if (x == SX_LOCK_UNLOCKED) { 709 sleepq_release(&sx->lock_object); 710 continue; 711 } 712 713 #ifdef ADAPTIVE_SX 714 /* 715 * The current lock owner might have started executing 716 * on another CPU (or the lock could have changed 717 * owners) while we were waiting on the sleep queue 718 * chain lock. If so, drop the sleep queue lock and try 719 * again. 720 */ 721 if (adaptive) { 722 if (!(x & SX_LOCK_SHARED)) { 723 owner = (struct thread *)SX_OWNER(x); 724 if (TD_IS_RUNNING(owner)) { 725 sleepq_release(&sx->lock_object); 726 continue; 727 } 728 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 729 sleepq_release(&sx->lock_object); 730 continue; 731 } 732 } 733 #endif 734 735 /* 736 * If an exclusive lock was released with both shared 737 * and exclusive waiters and a shared waiter hasn't 738 * woken up and acquired the lock yet, sx_lock will be 739 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 740 * If we see that value, try to acquire it once. Note 741 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 742 * as there are other exclusive waiters still. If we 743 * fail, restart the loop. 744 */ 745 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 746 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 747 tid | SX_LOCK_EXCLUSIVE_WAITERS)) 748 goto retry_sleepq; 749 sleepq_release(&sx->lock_object); 750 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 751 __func__, sx); 752 break; 753 } 754 755 /* 756 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 757 * than loop back and retry. 758 */ 759 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 760 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 761 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 762 goto retry_sleepq; 763 } 764 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 765 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 766 __func__, sx); 767 } 768 769 /* 770 * Since we have been unable to acquire the exclusive 771 * lock and the exclusive waiters flag is set, we have 772 * to sleep. 773 */ 774 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 775 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 776 __func__, sx); 777 778 #ifdef KDTRACE_HOOKS 779 sleep_time -= lockstat_nsecs(&sx->lock_object); 780 #endif 781 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 782 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 783 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 784 if (!(opts & SX_INTERRUPTIBLE)) 785 sleepq_wait(&sx->lock_object, 0); 786 else 787 error = sleepq_wait_sig(&sx->lock_object, 0); 788 #ifdef KDTRACE_HOOKS 789 sleep_time += lockstat_nsecs(&sx->lock_object); 790 sleep_cnt++; 791 #endif 792 if (error) { 793 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 794 CTR2(KTR_LOCK, 795 "%s: interruptible sleep by %p suspended by signal", 796 __func__, sx); 797 break; 798 } 799 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 800 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 801 __func__, sx); 802 x = SX_READ_VALUE(sx); 803 } 804 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 805 if (__predict_true(!extra_work)) 806 return (error); 807 #endif 808 #ifdef KDTRACE_HOOKS 809 all_time += lockstat_nsecs(&sx->lock_object); 810 if (sleep_time) 811 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 812 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 813 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 814 if (lda.spin_cnt > sleep_cnt) 815 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 816 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 817 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 818 out_lockstat: 819 #endif 820 if (!error) 821 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 822 contested, waittime, file, line, LOCKSTAT_WRITER); 823 GIANT_RESTORE(); 824 return (error); 825 } 826 827 /* 828 * This function represents the so-called 'hard case' for sx_xunlock 829 * operation. All 'easy case' failures are redirected to this. Note 830 * that ideally this would be a static function, but it needs to be 831 * accessible from at least sx.h. 832 */ 833 void 834 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 835 { 836 uintptr_t tid, setx; 837 int queue, wakeup_swapper; 838 839 if (SCHEDULER_STOPPED()) 840 return; 841 842 tid = (uintptr_t)curthread; 843 844 if (__predict_false(x == tid)) 845 x = SX_READ_VALUE(sx); 846 847 MPASS(!(x & SX_LOCK_SHARED)); 848 849 if (__predict_false(x & SX_LOCK_RECURSED)) { 850 /* The lock is recursed, unrecurse one level. */ 851 if ((--sx->sx_recurse) == 0) 852 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 853 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 854 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 855 return; 856 } 857 858 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 859 if (x == tid && 860 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 861 return; 862 863 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 864 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 865 866 sleepq_lock(&sx->lock_object); 867 x = SX_READ_VALUE(sx); 868 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 869 870 /* 871 * The wake up algorithm here is quite simple and probably not 872 * ideal. It gives precedence to shared waiters if they are 873 * present. For this condition, we have to preserve the 874 * state of the exclusive waiters flag. 875 * If interruptible sleeps left the shared queue empty avoid a 876 * starvation for the threads sleeping on the exclusive queue by giving 877 * them precedence and cleaning up the shared waiters bit anyway. 878 */ 879 setx = SX_LOCK_UNLOCKED; 880 queue = SQ_EXCLUSIVE_QUEUE; 881 if ((x & SX_LOCK_SHARED_WAITERS) != 0 && 882 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 883 queue = SQ_SHARED_QUEUE; 884 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS); 885 } 886 atomic_store_rel_ptr(&sx->sx_lock, setx); 887 888 /* Wake up all the waiters for the specific queue. */ 889 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 890 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 891 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 892 "exclusive"); 893 894 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 895 queue); 896 sleepq_release(&sx->lock_object); 897 if (wakeup_swapper) 898 kick_proc0(); 899 } 900 901 static bool __always_inline 902 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF) 903 { 904 905 /* 906 * If no other thread has an exclusive lock then try to bump up 907 * the count of sharers. Since we have to preserve the state 908 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 909 * shared lock loop back and retry. 910 */ 911 while (*xp & SX_LOCK_SHARED) { 912 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 913 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 914 *xp + SX_ONE_SHARER)) { 915 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 916 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 917 __func__, sx, (void *)*xp, 918 (void *)(*xp + SX_ONE_SHARER)); 919 return (true); 920 } 921 } 922 return (false); 923 } 924 925 static int __noinline 926 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 927 { 928 GIANT_DECLARE; 929 #ifdef ADAPTIVE_SX 930 volatile struct thread *owner; 931 bool adaptive; 932 #endif 933 #ifdef LOCK_PROFILING 934 uint64_t waittime = 0; 935 int contested = 0; 936 #endif 937 int error = 0; 938 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 939 struct lock_delay_arg lda; 940 #endif 941 #ifdef KDTRACE_HOOKS 942 u_int sleep_cnt = 0; 943 int64_t sleep_time = 0; 944 int64_t all_time = 0; 945 #endif 946 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 947 uintptr_t state = 0; 948 #endif 949 int extra_work = 0; 950 951 #ifdef KDTRACE_HOOKS 952 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 953 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 954 goto out_lockstat; 955 extra_work = 1; 956 all_time -= lockstat_nsecs(&sx->lock_object); 957 state = x; 958 } 959 #endif 960 #ifdef LOCK_PROFILING 961 extra_work = 1; 962 state = x; 963 #endif 964 965 if (SCHEDULER_STOPPED()) 966 return (0); 967 968 #if defined(ADAPTIVE_SX) 969 lock_delay_arg_init(&lda, &sx_delay); 970 #elif defined(KDTRACE_HOOKS) 971 lock_delay_arg_init(&lda, NULL); 972 #endif 973 974 #ifdef ADAPTIVE_SX 975 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 976 #endif 977 978 #ifdef HWPMC_HOOKS 979 PMC_SOFT_CALL( , , lock, failed); 980 #endif 981 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 982 &waittime); 983 984 #ifndef INVARIANTS 985 GIANT_SAVE(extra_work); 986 #endif 987 988 /* 989 * As with rwlocks, we don't make any attempt to try to block 990 * shared locks once there is an exclusive waiter. 991 */ 992 for (;;) { 993 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 994 break; 995 #ifdef INVARIANTS 996 GIANT_SAVE(extra_work); 997 #endif 998 #ifdef KDTRACE_HOOKS 999 lda.spin_cnt++; 1000 #endif 1001 1002 #ifdef ADAPTIVE_SX 1003 if (__predict_false(!adaptive)) 1004 goto sleepq; 1005 /* 1006 * If the owner is running on another CPU, spin until 1007 * the owner stops running or the state of the lock 1008 * changes. 1009 */ 1010 owner = lv_sx_owner(x); 1011 if (TD_IS_RUNNING(owner)) { 1012 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1013 CTR3(KTR_LOCK, 1014 "%s: spinning on %p held by %p", 1015 __func__, sx, owner); 1016 KTR_STATE1(KTR_SCHED, "thread", 1017 sched_tdname(curthread), "spinning", 1018 "lockname:\"%s\"", sx->lock_object.lo_name); 1019 do { 1020 lock_delay(&lda); 1021 x = SX_READ_VALUE(sx); 1022 owner = lv_sx_owner(x); 1023 } while (owner != NULL && TD_IS_RUNNING(owner)); 1024 KTR_STATE0(KTR_SCHED, "thread", 1025 sched_tdname(curthread), "running"); 1026 continue; 1027 } 1028 sleepq: 1029 #endif 1030 1031 /* 1032 * Some other thread already has an exclusive lock, so 1033 * start the process of blocking. 1034 */ 1035 sleepq_lock(&sx->lock_object); 1036 x = SX_READ_VALUE(sx); 1037 retry_sleepq: 1038 /* 1039 * The lock could have been released while we spun. 1040 * In this case loop back and retry. 1041 */ 1042 if (x & SX_LOCK_SHARED) { 1043 sleepq_release(&sx->lock_object); 1044 continue; 1045 } 1046 1047 #ifdef ADAPTIVE_SX 1048 /* 1049 * If the owner is running on another CPU, spin until 1050 * the owner stops running or the state of the lock 1051 * changes. 1052 */ 1053 if (!(x & SX_LOCK_SHARED) && adaptive) { 1054 owner = (struct thread *)SX_OWNER(x); 1055 if (TD_IS_RUNNING(owner)) { 1056 sleepq_release(&sx->lock_object); 1057 x = SX_READ_VALUE(sx); 1058 continue; 1059 } 1060 } 1061 #endif 1062 1063 /* 1064 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1065 * fail to set it drop the sleep queue lock and loop 1066 * back. 1067 */ 1068 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1069 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1070 x | SX_LOCK_SHARED_WAITERS)) 1071 goto retry_sleepq; 1072 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1073 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1074 __func__, sx); 1075 } 1076 1077 /* 1078 * Since we have been unable to acquire the shared lock, 1079 * we have to sleep. 1080 */ 1081 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1082 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1083 __func__, sx); 1084 1085 #ifdef KDTRACE_HOOKS 1086 sleep_time -= lockstat_nsecs(&sx->lock_object); 1087 #endif 1088 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1089 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1090 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1091 if (!(opts & SX_INTERRUPTIBLE)) 1092 sleepq_wait(&sx->lock_object, 0); 1093 else 1094 error = sleepq_wait_sig(&sx->lock_object, 0); 1095 #ifdef KDTRACE_HOOKS 1096 sleep_time += lockstat_nsecs(&sx->lock_object); 1097 sleep_cnt++; 1098 #endif 1099 if (error) { 1100 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1101 CTR2(KTR_LOCK, 1102 "%s: interruptible sleep by %p suspended by signal", 1103 __func__, sx); 1104 break; 1105 } 1106 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1107 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1108 __func__, sx); 1109 x = SX_READ_VALUE(sx); 1110 } 1111 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1112 if (__predict_true(!extra_work)) 1113 return (error); 1114 #endif 1115 #ifdef KDTRACE_HOOKS 1116 all_time += lockstat_nsecs(&sx->lock_object); 1117 if (sleep_time) 1118 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1119 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1120 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1121 if (lda.spin_cnt > sleep_cnt) 1122 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1123 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1124 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1125 out_lockstat: 1126 #endif 1127 if (error == 0) { 1128 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1129 contested, waittime, file, line, LOCKSTAT_READER); 1130 } 1131 GIANT_RESTORE(); 1132 return (error); 1133 } 1134 1135 int 1136 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1137 { 1138 uintptr_t x; 1139 int error; 1140 1141 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1142 !TD_IS_IDLETHREAD(curthread), 1143 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1144 curthread, sx->lock_object.lo_name, file, line)); 1145 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1146 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1147 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1148 1149 error = 0; 1150 x = SX_READ_VALUE(sx); 1151 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1152 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))) 1153 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1154 else 1155 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1156 file, line); 1157 if (error == 0) { 1158 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1159 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1160 TD_LOCKS_INC(curthread); 1161 } 1162 return (error); 1163 } 1164 1165 int 1166 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1167 { 1168 1169 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1170 } 1171 1172 static bool __always_inline 1173 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1174 { 1175 1176 for (;;) { 1177 /* 1178 * We should never have sharers while at least one thread 1179 * holds a shared lock. 1180 */ 1181 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1182 ("%s: waiting sharers", __func__)); 1183 1184 /* 1185 * See if there is more than one shared lock held. If 1186 * so, just drop one and return. 1187 */ 1188 if (SX_SHARERS(*xp) > 1) { 1189 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1190 *xp - SX_ONE_SHARER)) { 1191 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1192 CTR4(KTR_LOCK, 1193 "%s: %p succeeded %p -> %p", 1194 __func__, sx, (void *)*xp, 1195 (void *)(*xp - SX_ONE_SHARER)); 1196 return (true); 1197 } 1198 continue; 1199 } 1200 1201 /* 1202 * If there aren't any waiters for an exclusive lock, 1203 * then try to drop it quickly. 1204 */ 1205 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1206 MPASS(*xp == SX_SHARERS_LOCK(1)); 1207 *xp = SX_SHARERS_LOCK(1); 1208 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1209 xp, SX_LOCK_UNLOCKED)) { 1210 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1211 CTR2(KTR_LOCK, "%s: %p last succeeded", 1212 __func__, sx); 1213 return (true); 1214 } 1215 continue; 1216 } 1217 break; 1218 } 1219 return (false); 1220 } 1221 1222 static void __noinline 1223 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1224 { 1225 int wakeup_swapper = 0; 1226 uintptr_t setx; 1227 1228 if (SCHEDULER_STOPPED()) 1229 return; 1230 1231 if (_sx_sunlock_try(sx, &x)) 1232 goto out_lockstat; 1233 1234 /* 1235 * At this point, there should just be one sharer with 1236 * exclusive waiters. 1237 */ 1238 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1239 1240 sleepq_lock(&sx->lock_object); 1241 x = SX_READ_VALUE(sx); 1242 for (;;) { 1243 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS); 1244 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 1245 if (_sx_sunlock_try(sx, &x)) 1246 break; 1247 1248 /* 1249 * Wake up semantic here is quite simple: 1250 * Just wake up all the exclusive waiters. 1251 * Note that the state of the lock could have changed, 1252 * so if it fails loop back and retry. 1253 */ 1254 setx = x - SX_ONE_SHARER; 1255 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS; 1256 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1257 continue; 1258 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1259 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1260 "exclusive queue", __func__, sx); 1261 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1262 0, SQ_EXCLUSIVE_QUEUE); 1263 break; 1264 } 1265 sleepq_release(&sx->lock_object); 1266 if (wakeup_swapper) 1267 kick_proc0(); 1268 out_lockstat: 1269 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1270 } 1271 1272 void 1273 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1274 { 1275 uintptr_t x; 1276 1277 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1278 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1279 _sx_assert(sx, SA_SLOCKED, file, line); 1280 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1281 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1282 1283 x = SX_READ_VALUE(sx); 1284 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1285 !_sx_sunlock_try(sx, &x))) 1286 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG); 1287 else 1288 lock_profile_release_lock(&sx->lock_object); 1289 1290 TD_LOCKS_DEC(curthread); 1291 } 1292 1293 void 1294 _sx_sunlock(struct sx *sx, const char *file, int line) 1295 { 1296 1297 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1298 } 1299 1300 #ifdef INVARIANT_SUPPORT 1301 #ifndef INVARIANTS 1302 #undef _sx_assert 1303 #endif 1304 1305 /* 1306 * In the non-WITNESS case, sx_assert() can only detect that at least 1307 * *some* thread owns an slock, but it cannot guarantee that *this* 1308 * thread owns an slock. 1309 */ 1310 void 1311 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1312 { 1313 #ifndef WITNESS 1314 int slocked = 0; 1315 #endif 1316 1317 if (panicstr != NULL) 1318 return; 1319 switch (what) { 1320 case SA_SLOCKED: 1321 case SA_SLOCKED | SA_NOTRECURSED: 1322 case SA_SLOCKED | SA_RECURSED: 1323 #ifndef WITNESS 1324 slocked = 1; 1325 /* FALLTHROUGH */ 1326 #endif 1327 case SA_LOCKED: 1328 case SA_LOCKED | SA_NOTRECURSED: 1329 case SA_LOCKED | SA_RECURSED: 1330 #ifdef WITNESS 1331 witness_assert(&sx->lock_object, what, file, line); 1332 #else 1333 /* 1334 * If some other thread has an exclusive lock or we 1335 * have one and are asserting a shared lock, fail. 1336 * Also, if no one has a lock at all, fail. 1337 */ 1338 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1339 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1340 sx_xholder(sx) != curthread))) 1341 panic("Lock %s not %slocked @ %s:%d\n", 1342 sx->lock_object.lo_name, slocked ? "share " : "", 1343 file, line); 1344 1345 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1346 if (sx_recursed(sx)) { 1347 if (what & SA_NOTRECURSED) 1348 panic("Lock %s recursed @ %s:%d\n", 1349 sx->lock_object.lo_name, file, 1350 line); 1351 } else if (what & SA_RECURSED) 1352 panic("Lock %s not recursed @ %s:%d\n", 1353 sx->lock_object.lo_name, file, line); 1354 } 1355 #endif 1356 break; 1357 case SA_XLOCKED: 1358 case SA_XLOCKED | SA_NOTRECURSED: 1359 case SA_XLOCKED | SA_RECURSED: 1360 if (sx_xholder(sx) != curthread) 1361 panic("Lock %s not exclusively locked @ %s:%d\n", 1362 sx->lock_object.lo_name, file, line); 1363 if (sx_recursed(sx)) { 1364 if (what & SA_NOTRECURSED) 1365 panic("Lock %s recursed @ %s:%d\n", 1366 sx->lock_object.lo_name, file, line); 1367 } else if (what & SA_RECURSED) 1368 panic("Lock %s not recursed @ %s:%d\n", 1369 sx->lock_object.lo_name, file, line); 1370 break; 1371 case SA_UNLOCKED: 1372 #ifdef WITNESS 1373 witness_assert(&sx->lock_object, what, file, line); 1374 #else 1375 /* 1376 * If we hold an exclusve lock fail. We can't 1377 * reliably check to see if we hold a shared lock or 1378 * not. 1379 */ 1380 if (sx_xholder(sx) == curthread) 1381 panic("Lock %s exclusively locked @ %s:%d\n", 1382 sx->lock_object.lo_name, file, line); 1383 #endif 1384 break; 1385 default: 1386 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1387 line); 1388 } 1389 } 1390 #endif /* INVARIANT_SUPPORT */ 1391 1392 #ifdef DDB 1393 static void 1394 db_show_sx(const struct lock_object *lock) 1395 { 1396 struct thread *td; 1397 const struct sx *sx; 1398 1399 sx = (const struct sx *)lock; 1400 1401 db_printf(" state: "); 1402 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1403 db_printf("UNLOCKED\n"); 1404 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1405 db_printf("DESTROYED\n"); 1406 return; 1407 } else if (sx->sx_lock & SX_LOCK_SHARED) 1408 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1409 else { 1410 td = sx_xholder(sx); 1411 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1412 td->td_tid, td->td_proc->p_pid, td->td_name); 1413 if (sx_recursed(sx)) 1414 db_printf(" recursed: %d\n", sx->sx_recurse); 1415 } 1416 1417 db_printf(" waiters: "); 1418 switch(sx->sx_lock & 1419 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1420 case SX_LOCK_SHARED_WAITERS: 1421 db_printf("shared\n"); 1422 break; 1423 case SX_LOCK_EXCLUSIVE_WAITERS: 1424 db_printf("exclusive\n"); 1425 break; 1426 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1427 db_printf("exclusive and shared\n"); 1428 break; 1429 default: 1430 db_printf("none\n"); 1431 } 1432 } 1433 1434 /* 1435 * Check to see if a thread that is blocked on a sleep queue is actually 1436 * blocked on an sx lock. If so, output some details and return true. 1437 * If the lock has an exclusive owner, return that in *ownerp. 1438 */ 1439 int 1440 sx_chain(struct thread *td, struct thread **ownerp) 1441 { 1442 struct sx *sx; 1443 1444 /* 1445 * Check to see if this thread is blocked on an sx lock. 1446 * First, we check the lock class. If that is ok, then we 1447 * compare the lock name against the wait message. 1448 */ 1449 sx = td->td_wchan; 1450 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1451 sx->lock_object.lo_name != td->td_wmesg) 1452 return (0); 1453 1454 /* We think we have an sx lock, so output some details. */ 1455 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1456 *ownerp = sx_xholder(sx); 1457 if (sx->sx_lock & SX_LOCK_SHARED) 1458 db_printf("SLOCK (count %ju)\n", 1459 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1460 else 1461 db_printf("XLOCK\n"); 1462 return (1); 1463 } 1464 #endif 1465