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 if (SCHEDULER_STOPPED()) 569 return (0); 570 571 #if defined(ADAPTIVE_SX) 572 lock_delay_arg_init(&lda, &sx_delay); 573 #elif defined(KDTRACE_HOOKS) 574 lock_delay_arg_init(&lda, NULL); 575 #endif 576 577 if (__predict_false(x == SX_LOCK_UNLOCKED)) 578 x = SX_READ_VALUE(sx); 579 580 /* If we already hold an exclusive lock, then recurse. */ 581 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 582 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 583 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 584 sx->lock_object.lo_name, file, line)); 585 sx->sx_recurse++; 586 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 587 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 588 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 589 return (0); 590 } 591 592 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 593 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 594 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 595 596 #ifdef ADAPTIVE_SX 597 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 598 #endif 599 600 #ifdef HWPMC_HOOKS 601 PMC_SOFT_CALL( , , lock, failed); 602 #endif 603 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 604 &waittime); 605 606 #ifdef LOCK_PROFILING 607 extra_work = 1; 608 state = x; 609 #elif defined(KDTRACE_HOOKS) 610 extra_work = lockstat_enabled; 611 if (__predict_false(extra_work)) { 612 all_time -= lockstat_nsecs(&sx->lock_object); 613 state = x; 614 } 615 #endif 616 #ifndef INVARIANTS 617 GIANT_SAVE(extra_work); 618 #endif 619 620 for (;;) { 621 if (x == SX_LOCK_UNLOCKED) { 622 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 623 break; 624 continue; 625 } 626 #ifdef INVARIANTS 627 GIANT_SAVE(extra_work); 628 #endif 629 #ifdef KDTRACE_HOOKS 630 lda.spin_cnt++; 631 #endif 632 #ifdef ADAPTIVE_SX 633 if (__predict_false(!adaptive)) 634 goto sleepq; 635 /* 636 * If the lock is write locked and the owner is 637 * running on another CPU, spin until the owner stops 638 * running or the state of the lock changes. 639 */ 640 if ((x & SX_LOCK_SHARED) == 0) { 641 sleep_reason = WRITER; 642 owner = lv_sx_owner(x); 643 if (!TD_IS_RUNNING(owner)) 644 goto sleepq; 645 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 646 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 647 __func__, sx, owner); 648 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 649 "spinning", "lockname:\"%s\"", 650 sx->lock_object.lo_name); 651 do { 652 lock_delay(&lda); 653 x = SX_READ_VALUE(sx); 654 owner = lv_sx_owner(x); 655 } while (owner != NULL && TD_IS_RUNNING(owner)); 656 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 657 "running"); 658 continue; 659 } else if (SX_SHARERS(x) > 0) { 660 sleep_reason = READERS; 661 if (spintries == asx_retries) 662 goto sleepq; 663 spintries++; 664 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 665 "spinning", "lockname:\"%s\"", 666 sx->lock_object.lo_name); 667 for (i = 0; i < asx_loops; i += n) { 668 n = SX_SHARERS(x); 669 lock_delay_spin(n); 670 x = SX_READ_VALUE(sx); 671 if ((x & SX_LOCK_SHARED) == 0 || 672 SX_SHARERS(x) == 0) 673 break; 674 } 675 #ifdef KDTRACE_HOOKS 676 lda.spin_cnt += i; 677 #endif 678 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 679 "running"); 680 if (i < asx_loops) 681 continue; 682 } 683 sleepq: 684 #endif 685 sleepq_lock(&sx->lock_object); 686 x = SX_READ_VALUE(sx); 687 retry_sleepq: 688 689 /* 690 * If the lock was released while spinning on the 691 * sleep queue chain lock, try again. 692 */ 693 if (x == SX_LOCK_UNLOCKED) { 694 sleepq_release(&sx->lock_object); 695 continue; 696 } 697 698 #ifdef ADAPTIVE_SX 699 /* 700 * The current lock owner might have started executing 701 * on another CPU (or the lock could have changed 702 * owners) while we were waiting on the sleep queue 703 * chain lock. If so, drop the sleep queue lock and try 704 * again. 705 */ 706 if (adaptive) { 707 if (!(x & SX_LOCK_SHARED)) { 708 owner = (struct thread *)SX_OWNER(x); 709 if (TD_IS_RUNNING(owner)) { 710 sleepq_release(&sx->lock_object); 711 continue; 712 } 713 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 714 sleepq_release(&sx->lock_object); 715 continue; 716 } 717 } 718 #endif 719 720 /* 721 * If an exclusive lock was released with both shared 722 * and exclusive waiters and a shared waiter hasn't 723 * woken up and acquired the lock yet, sx_lock will be 724 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 725 * If we see that value, try to acquire it once. Note 726 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 727 * as there are other exclusive waiters still. If we 728 * fail, restart the loop. 729 */ 730 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 731 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 732 tid | SX_LOCK_EXCLUSIVE_WAITERS)) 733 goto retry_sleepq; 734 sleepq_release(&sx->lock_object); 735 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 736 __func__, sx); 737 break; 738 } 739 740 /* 741 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 742 * than loop back and retry. 743 */ 744 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 745 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 746 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 747 goto retry_sleepq; 748 } 749 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 750 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 751 __func__, sx); 752 } 753 754 /* 755 * Since we have been unable to acquire the exclusive 756 * lock and the exclusive waiters flag is set, we have 757 * to sleep. 758 */ 759 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 760 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 761 __func__, sx); 762 763 #ifdef KDTRACE_HOOKS 764 sleep_time -= lockstat_nsecs(&sx->lock_object); 765 #endif 766 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 767 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 768 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 769 if (!(opts & SX_INTERRUPTIBLE)) 770 sleepq_wait(&sx->lock_object, 0); 771 else 772 error = sleepq_wait_sig(&sx->lock_object, 0); 773 #ifdef KDTRACE_HOOKS 774 sleep_time += lockstat_nsecs(&sx->lock_object); 775 sleep_cnt++; 776 #endif 777 if (error) { 778 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 779 CTR2(KTR_LOCK, 780 "%s: interruptible sleep by %p suspended by signal", 781 __func__, sx); 782 break; 783 } 784 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 785 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 786 __func__, sx); 787 x = SX_READ_VALUE(sx); 788 } 789 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 790 if (__predict_true(!extra_work)) 791 return (error); 792 #endif 793 #ifdef KDTRACE_HOOKS 794 all_time += lockstat_nsecs(&sx->lock_object); 795 if (sleep_time) 796 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 797 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 798 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 799 if (lda.spin_cnt > sleep_cnt) 800 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 801 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 802 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 803 #endif 804 if (!error) 805 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 806 contested, waittime, file, line, LOCKSTAT_WRITER); 807 GIANT_RESTORE(); 808 return (error); 809 } 810 811 /* 812 * This function represents the so-called 'hard case' for sx_xunlock 813 * operation. All 'easy case' failures are redirected to this. Note 814 * that ideally this would be a static function, but it needs to be 815 * accessible from at least sx.h. 816 */ 817 void 818 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 819 { 820 uintptr_t tid, setx; 821 int queue, wakeup_swapper; 822 823 if (SCHEDULER_STOPPED()) 824 return; 825 826 tid = (uintptr_t)curthread; 827 828 if (__predict_false(x == tid)) 829 x = SX_READ_VALUE(sx); 830 831 MPASS(!(x & SX_LOCK_SHARED)); 832 833 if (__predict_false(x & SX_LOCK_RECURSED)) { 834 /* The lock is recursed, unrecurse one level. */ 835 if ((--sx->sx_recurse) == 0) 836 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 837 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 838 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 839 return; 840 } 841 842 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 843 if (x == tid && 844 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 845 return; 846 847 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 848 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 849 850 sleepq_lock(&sx->lock_object); 851 x = SX_READ_VALUE(sx); 852 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 853 854 /* 855 * The wake up algorithm here is quite simple and probably not 856 * ideal. It gives precedence to shared waiters if they are 857 * present. For this condition, we have to preserve the 858 * state of the exclusive waiters flag. 859 * If interruptible sleeps left the shared queue empty avoid a 860 * starvation for the threads sleeping on the exclusive queue by giving 861 * them precedence and cleaning up the shared waiters bit anyway. 862 */ 863 setx = SX_LOCK_UNLOCKED; 864 queue = SQ_EXCLUSIVE_QUEUE; 865 if ((x & SX_LOCK_SHARED_WAITERS) != 0 && 866 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 867 queue = SQ_SHARED_QUEUE; 868 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS); 869 } 870 atomic_store_rel_ptr(&sx->sx_lock, setx); 871 872 /* Wake up all the waiters for the specific queue. */ 873 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 874 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 875 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 876 "exclusive"); 877 878 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 879 queue); 880 sleepq_release(&sx->lock_object); 881 if (wakeup_swapper) 882 kick_proc0(); 883 } 884 885 static bool __always_inline 886 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF) 887 { 888 889 /* 890 * If no other thread has an exclusive lock then try to bump up 891 * the count of sharers. Since we have to preserve the state 892 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 893 * shared lock loop back and retry. 894 */ 895 while (*xp & SX_LOCK_SHARED) { 896 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 897 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 898 *xp + SX_ONE_SHARER)) { 899 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 900 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 901 __func__, sx, (void *)*xp, 902 (void *)(*xp + SX_ONE_SHARER)); 903 return (true); 904 } 905 } 906 return (false); 907 } 908 909 static int __noinline 910 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 911 { 912 GIANT_DECLARE; 913 #ifdef ADAPTIVE_SX 914 volatile struct thread *owner; 915 bool adaptive; 916 #endif 917 #ifdef LOCK_PROFILING 918 uint64_t waittime = 0; 919 int contested = 0; 920 #endif 921 int error = 0; 922 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 923 struct lock_delay_arg lda; 924 #endif 925 #ifdef KDTRACE_HOOKS 926 u_int sleep_cnt = 0; 927 int64_t sleep_time = 0; 928 int64_t all_time = 0; 929 #endif 930 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 931 uintptr_t state; 932 #endif 933 int extra_work = 0; 934 935 if (SCHEDULER_STOPPED()) 936 return (0); 937 938 #if defined(ADAPTIVE_SX) 939 lock_delay_arg_init(&lda, &sx_delay); 940 #elif defined(KDTRACE_HOOKS) 941 lock_delay_arg_init(&lda, NULL); 942 #endif 943 944 #ifdef ADAPTIVE_SX 945 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 946 #endif 947 948 #ifdef HWPMC_HOOKS 949 PMC_SOFT_CALL( , , lock, failed); 950 #endif 951 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 952 &waittime); 953 954 #ifdef LOCK_PROFILING 955 extra_work = 1; 956 state = x; 957 #elif defined(KDTRACE_HOOKS) 958 extra_work = lockstat_enabled; 959 if (__predict_false(extra_work)) { 960 all_time -= lockstat_nsecs(&sx->lock_object); 961 state = x; 962 } 963 #endif 964 #ifndef INVARIANTS 965 GIANT_SAVE(extra_work); 966 #endif 967 968 /* 969 * As with rwlocks, we don't make any attempt to try to block 970 * shared locks once there is an exclusive waiter. 971 */ 972 for (;;) { 973 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 974 break; 975 #ifdef INVARIANTS 976 GIANT_SAVE(extra_work); 977 #endif 978 #ifdef KDTRACE_HOOKS 979 lda.spin_cnt++; 980 #endif 981 982 #ifdef ADAPTIVE_SX 983 if (__predict_false(!adaptive)) 984 goto sleepq; 985 /* 986 * If the owner is running on another CPU, spin until 987 * the owner stops running or the state of the lock 988 * changes. 989 */ 990 owner = lv_sx_owner(x); 991 if (TD_IS_RUNNING(owner)) { 992 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 993 CTR3(KTR_LOCK, 994 "%s: spinning on %p held by %p", 995 __func__, sx, owner); 996 KTR_STATE1(KTR_SCHED, "thread", 997 sched_tdname(curthread), "spinning", 998 "lockname:\"%s\"", sx->lock_object.lo_name); 999 do { 1000 lock_delay(&lda); 1001 x = SX_READ_VALUE(sx); 1002 owner = lv_sx_owner(x); 1003 } while (owner != NULL && TD_IS_RUNNING(owner)); 1004 KTR_STATE0(KTR_SCHED, "thread", 1005 sched_tdname(curthread), "running"); 1006 continue; 1007 } 1008 sleepq: 1009 #endif 1010 1011 /* 1012 * Some other thread already has an exclusive lock, so 1013 * start the process of blocking. 1014 */ 1015 sleepq_lock(&sx->lock_object); 1016 x = SX_READ_VALUE(sx); 1017 retry_sleepq: 1018 /* 1019 * The lock could have been released while we spun. 1020 * In this case loop back and retry. 1021 */ 1022 if (x & SX_LOCK_SHARED) { 1023 sleepq_release(&sx->lock_object); 1024 continue; 1025 } 1026 1027 #ifdef ADAPTIVE_SX 1028 /* 1029 * If the owner is running on another CPU, spin until 1030 * the owner stops running or the state of the lock 1031 * changes. 1032 */ 1033 if (!(x & SX_LOCK_SHARED) && adaptive) { 1034 owner = (struct thread *)SX_OWNER(x); 1035 if (TD_IS_RUNNING(owner)) { 1036 sleepq_release(&sx->lock_object); 1037 x = SX_READ_VALUE(sx); 1038 continue; 1039 } 1040 } 1041 #endif 1042 1043 /* 1044 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1045 * fail to set it drop the sleep queue lock and loop 1046 * back. 1047 */ 1048 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1049 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1050 x | SX_LOCK_SHARED_WAITERS)) 1051 goto retry_sleepq; 1052 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1053 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1054 __func__, sx); 1055 } 1056 1057 /* 1058 * Since we have been unable to acquire the shared lock, 1059 * we have to sleep. 1060 */ 1061 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1062 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1063 __func__, sx); 1064 1065 #ifdef KDTRACE_HOOKS 1066 sleep_time -= lockstat_nsecs(&sx->lock_object); 1067 #endif 1068 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1069 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1070 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1071 if (!(opts & SX_INTERRUPTIBLE)) 1072 sleepq_wait(&sx->lock_object, 0); 1073 else 1074 error = sleepq_wait_sig(&sx->lock_object, 0); 1075 #ifdef KDTRACE_HOOKS 1076 sleep_time += lockstat_nsecs(&sx->lock_object); 1077 sleep_cnt++; 1078 #endif 1079 if (error) { 1080 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1081 CTR2(KTR_LOCK, 1082 "%s: interruptible sleep by %p suspended by signal", 1083 __func__, sx); 1084 break; 1085 } 1086 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1087 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1088 __func__, sx); 1089 x = SX_READ_VALUE(sx); 1090 } 1091 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1092 if (__predict_true(!extra_work)) 1093 return (error); 1094 #endif 1095 #ifdef KDTRACE_HOOKS 1096 all_time += lockstat_nsecs(&sx->lock_object); 1097 if (sleep_time) 1098 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1099 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1100 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1101 if (lda.spin_cnt > sleep_cnt) 1102 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1103 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1104 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1105 #endif 1106 if (error == 0) { 1107 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1108 contested, waittime, file, line, LOCKSTAT_READER); 1109 } 1110 GIANT_RESTORE(); 1111 return (error); 1112 } 1113 1114 int 1115 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1116 { 1117 uintptr_t x; 1118 int error; 1119 1120 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1121 !TD_IS_IDLETHREAD(curthread), 1122 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1123 curthread, sx->lock_object.lo_name, file, line)); 1124 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1125 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1126 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1127 1128 error = 0; 1129 x = SX_READ_VALUE(sx); 1130 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1131 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))) 1132 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1133 else 1134 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1135 file, line); 1136 if (error == 0) { 1137 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1138 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1139 TD_LOCKS_INC(curthread); 1140 } 1141 return (error); 1142 } 1143 1144 int 1145 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1146 { 1147 1148 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1149 } 1150 1151 static bool __always_inline 1152 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1153 { 1154 1155 for (;;) { 1156 /* 1157 * We should never have sharers while at least one thread 1158 * holds a shared lock. 1159 */ 1160 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1161 ("%s: waiting sharers", __func__)); 1162 1163 /* 1164 * See if there is more than one shared lock held. If 1165 * so, just drop one and return. 1166 */ 1167 if (SX_SHARERS(*xp) > 1) { 1168 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1169 *xp - SX_ONE_SHARER)) { 1170 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1171 CTR4(KTR_LOCK, 1172 "%s: %p succeeded %p -> %p", 1173 __func__, sx, (void *)*xp, 1174 (void *)(*xp - SX_ONE_SHARER)); 1175 return (true); 1176 } 1177 continue; 1178 } 1179 1180 /* 1181 * If there aren't any waiters for an exclusive lock, 1182 * then try to drop it quickly. 1183 */ 1184 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1185 MPASS(*xp == SX_SHARERS_LOCK(1)); 1186 *xp = SX_SHARERS_LOCK(1); 1187 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1188 xp, SX_LOCK_UNLOCKED)) { 1189 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1190 CTR2(KTR_LOCK, "%s: %p last succeeded", 1191 __func__, sx); 1192 return (true); 1193 } 1194 continue; 1195 } 1196 break; 1197 } 1198 return (false); 1199 } 1200 1201 static void __noinline 1202 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1203 { 1204 int wakeup_swapper = 0; 1205 uintptr_t setx; 1206 1207 if (SCHEDULER_STOPPED()) 1208 return; 1209 1210 if (_sx_sunlock_try(sx, &x)) 1211 goto out_lockstat; 1212 1213 /* 1214 * At this point, there should just be one sharer with 1215 * exclusive waiters. 1216 */ 1217 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1218 1219 sleepq_lock(&sx->lock_object); 1220 x = SX_READ_VALUE(sx); 1221 for (;;) { 1222 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS); 1223 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 1224 if (_sx_sunlock_try(sx, &x)) 1225 break; 1226 1227 /* 1228 * Wake up semantic here is quite simple: 1229 * Just wake up all the exclusive waiters. 1230 * Note that the state of the lock could have changed, 1231 * so if it fails loop back and retry. 1232 */ 1233 setx = x - SX_ONE_SHARER; 1234 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS; 1235 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1236 continue; 1237 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1238 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1239 "exclusive queue", __func__, sx); 1240 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1241 0, SQ_EXCLUSIVE_QUEUE); 1242 break; 1243 } 1244 sleepq_release(&sx->lock_object); 1245 if (wakeup_swapper) 1246 kick_proc0(); 1247 out_lockstat: 1248 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1249 } 1250 1251 void 1252 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1253 { 1254 uintptr_t x; 1255 1256 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1257 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1258 _sx_assert(sx, SA_SLOCKED, file, line); 1259 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1260 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1261 1262 x = SX_READ_VALUE(sx); 1263 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1264 !_sx_sunlock_try(sx, &x))) 1265 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG); 1266 else 1267 lock_profile_release_lock(&sx->lock_object); 1268 1269 TD_LOCKS_DEC(curthread); 1270 } 1271 1272 void 1273 _sx_sunlock(struct sx *sx, const char *file, int line) 1274 { 1275 1276 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1277 } 1278 1279 #ifdef INVARIANT_SUPPORT 1280 #ifndef INVARIANTS 1281 #undef _sx_assert 1282 #endif 1283 1284 /* 1285 * In the non-WITNESS case, sx_assert() can only detect that at least 1286 * *some* thread owns an slock, but it cannot guarantee that *this* 1287 * thread owns an slock. 1288 */ 1289 void 1290 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1291 { 1292 #ifndef WITNESS 1293 int slocked = 0; 1294 #endif 1295 1296 if (panicstr != NULL) 1297 return; 1298 switch (what) { 1299 case SA_SLOCKED: 1300 case SA_SLOCKED | SA_NOTRECURSED: 1301 case SA_SLOCKED | SA_RECURSED: 1302 #ifndef WITNESS 1303 slocked = 1; 1304 /* FALLTHROUGH */ 1305 #endif 1306 case SA_LOCKED: 1307 case SA_LOCKED | SA_NOTRECURSED: 1308 case SA_LOCKED | SA_RECURSED: 1309 #ifdef WITNESS 1310 witness_assert(&sx->lock_object, what, file, line); 1311 #else 1312 /* 1313 * If some other thread has an exclusive lock or we 1314 * have one and are asserting a shared lock, fail. 1315 * Also, if no one has a lock at all, fail. 1316 */ 1317 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1318 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1319 sx_xholder(sx) != curthread))) 1320 panic("Lock %s not %slocked @ %s:%d\n", 1321 sx->lock_object.lo_name, slocked ? "share " : "", 1322 file, line); 1323 1324 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1325 if (sx_recursed(sx)) { 1326 if (what & SA_NOTRECURSED) 1327 panic("Lock %s recursed @ %s:%d\n", 1328 sx->lock_object.lo_name, file, 1329 line); 1330 } else if (what & SA_RECURSED) 1331 panic("Lock %s not recursed @ %s:%d\n", 1332 sx->lock_object.lo_name, file, line); 1333 } 1334 #endif 1335 break; 1336 case SA_XLOCKED: 1337 case SA_XLOCKED | SA_NOTRECURSED: 1338 case SA_XLOCKED | SA_RECURSED: 1339 if (sx_xholder(sx) != curthread) 1340 panic("Lock %s not exclusively locked @ %s:%d\n", 1341 sx->lock_object.lo_name, file, line); 1342 if (sx_recursed(sx)) { 1343 if (what & SA_NOTRECURSED) 1344 panic("Lock %s recursed @ %s:%d\n", 1345 sx->lock_object.lo_name, file, line); 1346 } else if (what & SA_RECURSED) 1347 panic("Lock %s not recursed @ %s:%d\n", 1348 sx->lock_object.lo_name, file, line); 1349 break; 1350 case SA_UNLOCKED: 1351 #ifdef WITNESS 1352 witness_assert(&sx->lock_object, what, file, line); 1353 #else 1354 /* 1355 * If we hold an exclusve lock fail. We can't 1356 * reliably check to see if we hold a shared lock or 1357 * not. 1358 */ 1359 if (sx_xholder(sx) == curthread) 1360 panic("Lock %s exclusively locked @ %s:%d\n", 1361 sx->lock_object.lo_name, file, line); 1362 #endif 1363 break; 1364 default: 1365 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1366 line); 1367 } 1368 } 1369 #endif /* INVARIANT_SUPPORT */ 1370 1371 #ifdef DDB 1372 static void 1373 db_show_sx(const struct lock_object *lock) 1374 { 1375 struct thread *td; 1376 const struct sx *sx; 1377 1378 sx = (const struct sx *)lock; 1379 1380 db_printf(" state: "); 1381 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1382 db_printf("UNLOCKED\n"); 1383 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1384 db_printf("DESTROYED\n"); 1385 return; 1386 } else if (sx->sx_lock & SX_LOCK_SHARED) 1387 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1388 else { 1389 td = sx_xholder(sx); 1390 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1391 td->td_tid, td->td_proc->p_pid, td->td_name); 1392 if (sx_recursed(sx)) 1393 db_printf(" recursed: %d\n", sx->sx_recurse); 1394 } 1395 1396 db_printf(" waiters: "); 1397 switch(sx->sx_lock & 1398 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1399 case SX_LOCK_SHARED_WAITERS: 1400 db_printf("shared\n"); 1401 break; 1402 case SX_LOCK_EXCLUSIVE_WAITERS: 1403 db_printf("exclusive\n"); 1404 break; 1405 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1406 db_printf("exclusive and shared\n"); 1407 break; 1408 default: 1409 db_printf("none\n"); 1410 } 1411 } 1412 1413 /* 1414 * Check to see if a thread that is blocked on a sleep queue is actually 1415 * blocked on an sx lock. If so, output some details and return true. 1416 * If the lock has an exclusive owner, return that in *ownerp. 1417 */ 1418 int 1419 sx_chain(struct thread *td, struct thread **ownerp) 1420 { 1421 struct sx *sx; 1422 1423 /* 1424 * Check to see if this thread is blocked on an sx lock. 1425 * First, we check the lock class. If that is ok, then we 1426 * compare the lock name against the wait message. 1427 */ 1428 sx = td->td_wchan; 1429 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1430 sx->lock_object.lo_name != td->td_wmesg) 1431 return (0); 1432 1433 /* We think we have an sx lock, so output some details. */ 1434 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1435 *ownerp = sx_xholder(sx); 1436 if (sx->sx_lock & SX_LOCK_SHARED) 1437 db_printf("SLOCK (count %ju)\n", 1438 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1439 else 1440 db_printf("XLOCK\n"); 1441 return (1); 1442 } 1443 #endif 1444