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 int success; 417 418 if (SCHEDULER_STOPPED()) 419 return (1); 420 421 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 422 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 423 _sx_assert(sx, SA_SLOCKED, file, line); 424 425 /* 426 * Try to switch from one shared lock to an exclusive lock. We need 427 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 428 * we will wake up the exclusive waiters when we drop the lock. 429 */ 430 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 431 success = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 432 (uintptr_t)curthread | x); 433 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 434 if (success) { 435 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 436 file, line); 437 LOCKSTAT_RECORD0(sx__upgrade, sx); 438 } 439 return (success); 440 } 441 442 int 443 sx_try_upgrade_(struct sx *sx, const char *file, int line) 444 { 445 446 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 447 } 448 449 /* 450 * Downgrade an unrecursed exclusive lock into a single shared lock. 451 */ 452 void 453 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 454 { 455 uintptr_t x; 456 int wakeup_swapper; 457 458 if (SCHEDULER_STOPPED()) 459 return; 460 461 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 462 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 463 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 464 #ifndef INVARIANTS 465 if (sx_recursed(sx)) 466 panic("downgrade of a recursed lock"); 467 #endif 468 469 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 470 471 /* 472 * Try to switch from an exclusive lock with no shared waiters 473 * to one sharer with no shared waiters. If there are 474 * exclusive waiters, we don't need to lock the sleep queue so 475 * long as we preserve the flag. We do one quick try and if 476 * that fails we grab the sleepq lock to keep the flags from 477 * changing and do it the slow way. 478 * 479 * We have to lock the sleep queue if there are shared waiters 480 * so we can wake them up. 481 */ 482 x = sx->sx_lock; 483 if (!(x & SX_LOCK_SHARED_WAITERS) && 484 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 485 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 486 goto out; 487 488 /* 489 * Lock the sleep queue so we can read the waiters bits 490 * without any races and wakeup any shared waiters. 491 */ 492 sleepq_lock(&sx->lock_object); 493 494 /* 495 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 496 * shared lock. If there are any shared waiters, wake them up. 497 */ 498 wakeup_swapper = 0; 499 x = sx->sx_lock; 500 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 501 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 502 if (x & SX_LOCK_SHARED_WAITERS) 503 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 504 0, SQ_SHARED_QUEUE); 505 sleepq_release(&sx->lock_object); 506 507 if (wakeup_swapper) 508 kick_proc0(); 509 510 out: 511 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 512 LOCKSTAT_RECORD0(sx__downgrade, sx); 513 } 514 515 void 516 sx_downgrade_(struct sx *sx, const char *file, int line) 517 { 518 519 sx_downgrade_int(sx LOCK_FILE_LINE_ARG); 520 } 521 522 /* 523 * This function represents the so-called 'hard case' for sx_xlock 524 * operation. All 'easy case' failures are redirected to this. Note 525 * that ideally this would be a static function, but it needs to be 526 * accessible from at least sx.h. 527 */ 528 int 529 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 530 { 531 GIANT_DECLARE; 532 uintptr_t tid; 533 #ifdef ADAPTIVE_SX 534 volatile struct thread *owner; 535 u_int i, n, spintries = 0; 536 bool adaptive; 537 int sleep_reason = 0; 538 #endif 539 #ifdef LOCK_PROFILING 540 uint64_t waittime = 0; 541 int contested = 0; 542 #endif 543 int error = 0; 544 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 545 struct lock_delay_arg lda; 546 #endif 547 #ifdef KDTRACE_HOOKS 548 u_int sleep_cnt = 0; 549 int64_t sleep_time = 0; 550 int64_t all_time = 0; 551 #endif 552 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 553 uintptr_t state; 554 #endif 555 int extra_work = 0; 556 557 tid = (uintptr_t)curthread; 558 if (SCHEDULER_STOPPED()) 559 return (0); 560 561 #if defined(ADAPTIVE_SX) 562 lock_delay_arg_init(&lda, &sx_delay); 563 #elif defined(KDTRACE_HOOKS) 564 lock_delay_arg_init(&lda, NULL); 565 #endif 566 567 if (__predict_false(x == SX_LOCK_UNLOCKED)) 568 x = SX_READ_VALUE(sx); 569 570 /* If we already hold an exclusive lock, then recurse. */ 571 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 572 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 573 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 574 sx->lock_object.lo_name, file, line)); 575 sx->sx_recurse++; 576 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 577 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 578 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 579 return (0); 580 } 581 582 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 583 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 584 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 585 586 #ifdef ADAPTIVE_SX 587 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0); 588 #endif 589 590 #ifdef HWPMC_HOOKS 591 PMC_SOFT_CALL( , , lock, failed); 592 #endif 593 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 594 &waittime); 595 596 #ifdef LOCK_PROFILING 597 extra_work = 1; 598 state = x; 599 #elif defined(KDTRACE_HOOKS) 600 extra_work = lockstat_enabled; 601 if (__predict_false(extra_work)) { 602 all_time -= lockstat_nsecs(&sx->lock_object); 603 state = x; 604 } 605 #endif 606 #ifndef INVARIANTS 607 GIANT_SAVE(extra_work); 608 #endif 609 610 for (;;) { 611 if (x == SX_LOCK_UNLOCKED) { 612 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 613 break; 614 continue; 615 } 616 #ifdef INVARIANTS 617 GIANT_SAVE(extra_work); 618 #endif 619 #ifdef KDTRACE_HOOKS 620 lda.spin_cnt++; 621 #endif 622 #ifdef ADAPTIVE_SX 623 if (__predict_false(!adaptive)) 624 goto sleepq; 625 /* 626 * If the lock is write locked and the owner is 627 * running on another CPU, spin until the owner stops 628 * running or the state of the lock changes. 629 */ 630 if ((x & SX_LOCK_SHARED) == 0) { 631 owner = lv_sx_owner(x); 632 if (TD_IS_RUNNING(owner)) { 633 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 634 CTR3(KTR_LOCK, 635 "%s: spinning on %p held by %p", 636 __func__, sx, owner); 637 KTR_STATE1(KTR_SCHED, "thread", 638 sched_tdname(curthread), "spinning", 639 "lockname:\"%s\"", 640 sx->lock_object.lo_name); 641 do { 642 lock_delay(&lda); 643 x = SX_READ_VALUE(sx); 644 owner = lv_sx_owner(x); 645 } while (owner != NULL && 646 TD_IS_RUNNING(owner)); 647 KTR_STATE0(KTR_SCHED, "thread", 648 sched_tdname(curthread), "running"); 649 continue; 650 } 651 sleep_reason = 1; 652 } else if (SX_SHARERS(x) && spintries < asx_retries) { 653 KTR_STATE1(KTR_SCHED, "thread", 654 sched_tdname(curthread), "spinning", 655 "lockname:\"%s\"", sx->lock_object.lo_name); 656 spintries++; 657 for (i = 0; i < asx_loops; i += n) { 658 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 659 CTR4(KTR_LOCK, 660 "%s: shared spinning on %p with %u and %u", 661 __func__, sx, spintries, i); 662 n = SX_SHARERS(x); 663 lock_delay_spin(n); 664 x = SX_READ_VALUE(sx); 665 if ((x & SX_LOCK_SHARED) == 0 || 666 SX_SHARERS(x) == 0) 667 break; 668 } 669 #ifdef KDTRACE_HOOKS 670 lda.spin_cnt += i; 671 #endif 672 KTR_STATE0(KTR_SCHED, "thread", 673 sched_tdname(curthread), "running"); 674 if (i < asx_loops) 675 continue; 676 sleep_reason = 2; 677 } 678 sleepq: 679 #endif 680 sleepq_lock(&sx->lock_object); 681 x = SX_READ_VALUE(sx); 682 retry_sleepq: 683 684 /* 685 * If the lock was released while spinning on the 686 * sleep queue chain lock, try again. 687 */ 688 if (x == SX_LOCK_UNLOCKED) { 689 sleepq_release(&sx->lock_object); 690 continue; 691 } 692 693 #ifdef ADAPTIVE_SX 694 /* 695 * The current lock owner might have started executing 696 * on another CPU (or the lock could have changed 697 * owners) while we were waiting on the sleep queue 698 * chain lock. If so, drop the sleep queue lock and try 699 * again. 700 */ 701 if (adaptive) { 702 if (!(x & SX_LOCK_SHARED)) { 703 owner = (struct thread *)SX_OWNER(x); 704 if (TD_IS_RUNNING(owner)) { 705 sleepq_release(&sx->lock_object); 706 continue; 707 } 708 } else if (SX_SHARERS(x) > 0 && sleep_reason == 1) { 709 sleepq_release(&sx->lock_object); 710 continue; 711 } 712 } 713 #endif 714 715 /* 716 * If an exclusive lock was released with both shared 717 * and exclusive waiters and a shared waiter hasn't 718 * woken up and acquired the lock yet, sx_lock will be 719 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 720 * If we see that value, try to acquire it once. Note 721 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 722 * as there are other exclusive waiters still. If we 723 * fail, restart the loop. 724 */ 725 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 726 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 727 tid | SX_LOCK_EXCLUSIVE_WAITERS)) 728 goto retry_sleepq; 729 sleepq_release(&sx->lock_object); 730 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 731 __func__, sx); 732 break; 733 } 734 735 /* 736 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 737 * than loop back and retry. 738 */ 739 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 740 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 741 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 742 goto retry_sleepq; 743 } 744 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 745 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 746 __func__, sx); 747 } 748 749 /* 750 * Since we have been unable to acquire the exclusive 751 * lock and the exclusive waiters flag is set, we have 752 * to sleep. 753 */ 754 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 755 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 756 __func__, sx); 757 758 #ifdef KDTRACE_HOOKS 759 sleep_time -= lockstat_nsecs(&sx->lock_object); 760 #endif 761 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 762 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 763 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 764 if (!(opts & SX_INTERRUPTIBLE)) 765 sleepq_wait(&sx->lock_object, 0); 766 else 767 error = sleepq_wait_sig(&sx->lock_object, 0); 768 #ifdef KDTRACE_HOOKS 769 sleep_time += lockstat_nsecs(&sx->lock_object); 770 sleep_cnt++; 771 #endif 772 if (error) { 773 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 774 CTR2(KTR_LOCK, 775 "%s: interruptible sleep by %p suspended by signal", 776 __func__, sx); 777 break; 778 } 779 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 780 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 781 __func__, sx); 782 x = SX_READ_VALUE(sx); 783 } 784 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 785 if (__predict_true(!extra_work)) 786 return (error); 787 #endif 788 #ifdef KDTRACE_HOOKS 789 all_time += lockstat_nsecs(&sx->lock_object); 790 if (sleep_time) 791 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 792 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 793 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 794 if (lda.spin_cnt > sleep_cnt) 795 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 796 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 797 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 798 #endif 799 if (!error) 800 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 801 contested, waittime, file, line, LOCKSTAT_WRITER); 802 GIANT_RESTORE(); 803 return (error); 804 } 805 806 /* 807 * This function represents the so-called 'hard case' for sx_xunlock 808 * operation. All 'easy case' failures are redirected to this. Note 809 * that ideally this would be a static function, but it needs to be 810 * accessible from at least sx.h. 811 */ 812 void 813 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 814 { 815 uintptr_t tid, setx; 816 int queue, wakeup_swapper; 817 818 if (SCHEDULER_STOPPED()) 819 return; 820 821 tid = (uintptr_t)curthread; 822 823 if (__predict_false(x == tid)) 824 x = SX_READ_VALUE(sx); 825 826 MPASS(!(x & SX_LOCK_SHARED)); 827 828 if (__predict_false(x & SX_LOCK_RECURSED)) { 829 /* The lock is recursed, unrecurse one level. */ 830 if ((--sx->sx_recurse) == 0) 831 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 832 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 833 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 834 return; 835 } 836 837 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 838 if (x == tid && 839 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 840 return; 841 842 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 843 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 844 845 sleepq_lock(&sx->lock_object); 846 x = SX_READ_VALUE(sx); 847 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 848 849 /* 850 * The wake up algorithm here is quite simple and probably not 851 * ideal. It gives precedence to shared waiters if they are 852 * present. For this condition, we have to preserve the 853 * state of the exclusive waiters flag. 854 * If interruptible sleeps left the shared queue empty avoid a 855 * starvation for the threads sleeping on the exclusive queue by giving 856 * them precedence and cleaning up the shared waiters bit anyway. 857 */ 858 setx = SX_LOCK_UNLOCKED; 859 queue = SQ_EXCLUSIVE_QUEUE; 860 if ((x & SX_LOCK_SHARED_WAITERS) != 0 && 861 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 862 queue = SQ_SHARED_QUEUE; 863 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS); 864 } 865 atomic_store_rel_ptr(&sx->sx_lock, setx); 866 867 /* Wake up all the waiters for the specific queue. */ 868 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 869 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 870 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 871 "exclusive"); 872 873 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 874 queue); 875 sleepq_release(&sx->lock_object); 876 if (wakeup_swapper) 877 kick_proc0(); 878 } 879 880 static bool __always_inline 881 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF) 882 { 883 884 /* 885 * If no other thread has an exclusive lock then try to bump up 886 * the count of sharers. Since we have to preserve the state 887 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 888 * shared lock loop back and retry. 889 */ 890 while (*xp & SX_LOCK_SHARED) { 891 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 892 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 893 *xp + SX_ONE_SHARER)) { 894 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 895 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 896 __func__, sx, (void *)*xp, 897 (void *)(*xp + SX_ONE_SHARER)); 898 return (true); 899 } 900 } 901 return (false); 902 } 903 904 static int __noinline 905 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 906 { 907 GIANT_DECLARE; 908 #ifdef ADAPTIVE_SX 909 volatile struct thread *owner; 910 bool adaptive; 911 #endif 912 #ifdef LOCK_PROFILING 913 uint64_t waittime = 0; 914 int contested = 0; 915 #endif 916 int error = 0; 917 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 918 struct lock_delay_arg lda; 919 #endif 920 #ifdef KDTRACE_HOOKS 921 u_int sleep_cnt = 0; 922 int64_t sleep_time = 0; 923 int64_t all_time = 0; 924 #endif 925 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 926 uintptr_t state; 927 #endif 928 int extra_work = 0; 929 930 if (SCHEDULER_STOPPED()) 931 return (0); 932 933 #if defined(ADAPTIVE_SX) 934 lock_delay_arg_init(&lda, &sx_delay); 935 #elif defined(KDTRACE_HOOKS) 936 lock_delay_arg_init(&lda, NULL); 937 #endif 938 939 #ifdef ADAPTIVE_SX 940 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) != 0); 941 #endif 942 943 #ifdef HWPMC_HOOKS 944 PMC_SOFT_CALL( , , lock, failed); 945 #endif 946 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 947 &waittime); 948 949 #ifdef LOCK_PROFILING 950 extra_work = 1; 951 state = x; 952 #elif defined(KDTRACE_HOOKS) 953 extra_work = lockstat_enabled; 954 if (__predict_false(extra_work)) { 955 all_time -= lockstat_nsecs(&sx->lock_object); 956 state = x; 957 } 958 #endif 959 #ifndef INVARIANTS 960 GIANT_SAVE(extra_work); 961 #endif 962 963 /* 964 * As with rwlocks, we don't make any attempt to try to block 965 * shared locks once there is an exclusive waiter. 966 */ 967 for (;;) { 968 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 969 break; 970 #ifdef INVARIANTS 971 GIANT_SAVE(extra_work); 972 #endif 973 #ifdef KDTRACE_HOOKS 974 lda.spin_cnt++; 975 #endif 976 977 #ifdef ADAPTIVE_SX 978 if (__predict_false(!adaptive)) 979 goto sleepq; 980 /* 981 * If the owner is running on another CPU, spin until 982 * the owner stops running or the state of the lock 983 * changes. 984 */ 985 owner = lv_sx_owner(x); 986 if (TD_IS_RUNNING(owner)) { 987 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 988 CTR3(KTR_LOCK, 989 "%s: spinning on %p held by %p", 990 __func__, sx, owner); 991 KTR_STATE1(KTR_SCHED, "thread", 992 sched_tdname(curthread), "spinning", 993 "lockname:\"%s\"", sx->lock_object.lo_name); 994 do { 995 lock_delay(&lda); 996 x = SX_READ_VALUE(sx); 997 owner = lv_sx_owner(x); 998 } while (owner != NULL && TD_IS_RUNNING(owner)); 999 KTR_STATE0(KTR_SCHED, "thread", 1000 sched_tdname(curthread), "running"); 1001 continue; 1002 } 1003 sleepq: 1004 #endif 1005 1006 /* 1007 * Some other thread already has an exclusive lock, so 1008 * start the process of blocking. 1009 */ 1010 sleepq_lock(&sx->lock_object); 1011 x = SX_READ_VALUE(sx); 1012 retry_sleepq: 1013 /* 1014 * The lock could have been released while we spun. 1015 * In this case loop back and retry. 1016 */ 1017 if (x & SX_LOCK_SHARED) { 1018 sleepq_release(&sx->lock_object); 1019 continue; 1020 } 1021 1022 #ifdef ADAPTIVE_SX 1023 /* 1024 * If the owner is running on another CPU, spin until 1025 * the owner stops running or the state of the lock 1026 * changes. 1027 */ 1028 if (!(x & SX_LOCK_SHARED) && adaptive) { 1029 owner = (struct thread *)SX_OWNER(x); 1030 if (TD_IS_RUNNING(owner)) { 1031 sleepq_release(&sx->lock_object); 1032 x = SX_READ_VALUE(sx); 1033 continue; 1034 } 1035 } 1036 #endif 1037 1038 /* 1039 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1040 * fail to set it drop the sleep queue lock and loop 1041 * back. 1042 */ 1043 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1044 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1045 x | SX_LOCK_SHARED_WAITERS)) 1046 goto retry_sleepq; 1047 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1048 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1049 __func__, sx); 1050 } 1051 1052 /* 1053 * Since we have been unable to acquire the shared lock, 1054 * we have to sleep. 1055 */ 1056 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1057 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1058 __func__, sx); 1059 1060 #ifdef KDTRACE_HOOKS 1061 sleep_time -= lockstat_nsecs(&sx->lock_object); 1062 #endif 1063 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1064 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1065 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1066 if (!(opts & SX_INTERRUPTIBLE)) 1067 sleepq_wait(&sx->lock_object, 0); 1068 else 1069 error = sleepq_wait_sig(&sx->lock_object, 0); 1070 #ifdef KDTRACE_HOOKS 1071 sleep_time += lockstat_nsecs(&sx->lock_object); 1072 sleep_cnt++; 1073 #endif 1074 if (error) { 1075 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1076 CTR2(KTR_LOCK, 1077 "%s: interruptible sleep by %p suspended by signal", 1078 __func__, sx); 1079 break; 1080 } 1081 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1082 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1083 __func__, sx); 1084 x = SX_READ_VALUE(sx); 1085 } 1086 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1087 if (__predict_true(!extra_work)) 1088 return (error); 1089 #endif 1090 #ifdef KDTRACE_HOOKS 1091 all_time += lockstat_nsecs(&sx->lock_object); 1092 if (sleep_time) 1093 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1094 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1095 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1096 if (lda.spin_cnt > sleep_cnt) 1097 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1098 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1099 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1100 #endif 1101 if (error == 0) { 1102 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1103 contested, waittime, file, line, LOCKSTAT_READER); 1104 } 1105 GIANT_RESTORE(); 1106 return (error); 1107 } 1108 1109 int 1110 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1111 { 1112 uintptr_t x; 1113 int error; 1114 1115 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1116 !TD_IS_IDLETHREAD(curthread), 1117 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1118 curthread, sx->lock_object.lo_name, file, line)); 1119 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1120 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1121 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1122 1123 error = 0; 1124 x = SX_READ_VALUE(sx); 1125 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1126 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))) 1127 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1128 else 1129 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1130 file, line); 1131 if (error == 0) { 1132 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1133 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1134 TD_LOCKS_INC(curthread); 1135 } 1136 return (error); 1137 } 1138 1139 int 1140 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1141 { 1142 1143 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1144 } 1145 1146 static bool __always_inline 1147 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1148 { 1149 1150 for (;;) { 1151 /* 1152 * We should never have sharers while at least one thread 1153 * holds a shared lock. 1154 */ 1155 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1156 ("%s: waiting sharers", __func__)); 1157 1158 /* 1159 * See if there is more than one shared lock held. If 1160 * so, just drop one and return. 1161 */ 1162 if (SX_SHARERS(*xp) > 1) { 1163 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1164 *xp - SX_ONE_SHARER)) { 1165 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1166 CTR4(KTR_LOCK, 1167 "%s: %p succeeded %p -> %p", 1168 __func__, sx, (void *)*xp, 1169 (void *)(*xp - SX_ONE_SHARER)); 1170 return (true); 1171 } 1172 continue; 1173 } 1174 1175 /* 1176 * If there aren't any waiters for an exclusive lock, 1177 * then try to drop it quickly. 1178 */ 1179 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1180 MPASS(*xp == SX_SHARERS_LOCK(1)); 1181 *xp = SX_SHARERS_LOCK(1); 1182 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1183 xp, SX_LOCK_UNLOCKED)) { 1184 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1185 CTR2(KTR_LOCK, "%s: %p last succeeded", 1186 __func__, sx); 1187 return (true); 1188 } 1189 continue; 1190 } 1191 break; 1192 } 1193 return (false); 1194 } 1195 1196 static void __noinline 1197 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1198 { 1199 int wakeup_swapper = 0; 1200 uintptr_t setx; 1201 1202 if (SCHEDULER_STOPPED()) 1203 return; 1204 1205 if (_sx_sunlock_try(sx, &x)) 1206 goto out_lockstat; 1207 1208 /* 1209 * At this point, there should just be one sharer with 1210 * exclusive waiters. 1211 */ 1212 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1213 1214 sleepq_lock(&sx->lock_object); 1215 x = SX_READ_VALUE(sx); 1216 for (;;) { 1217 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS); 1218 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 1219 if (_sx_sunlock_try(sx, &x)) 1220 break; 1221 1222 /* 1223 * Wake up semantic here is quite simple: 1224 * Just wake up all the exclusive waiters. 1225 * Note that the state of the lock could have changed, 1226 * so if it fails loop back and retry. 1227 */ 1228 setx = x - SX_ONE_SHARER; 1229 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS; 1230 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1231 continue; 1232 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1233 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1234 "exclusive queue", __func__, sx); 1235 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1236 0, SQ_EXCLUSIVE_QUEUE); 1237 break; 1238 } 1239 sleepq_release(&sx->lock_object); 1240 if (wakeup_swapper) 1241 kick_proc0(); 1242 out_lockstat: 1243 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1244 } 1245 1246 void 1247 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1248 { 1249 uintptr_t x; 1250 1251 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1252 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1253 _sx_assert(sx, SA_SLOCKED, file, line); 1254 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1255 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1256 1257 x = SX_READ_VALUE(sx); 1258 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1259 !_sx_sunlock_try(sx, &x))) 1260 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG); 1261 else 1262 lock_profile_release_lock(&sx->lock_object); 1263 1264 TD_LOCKS_DEC(curthread); 1265 } 1266 1267 void 1268 _sx_sunlock(struct sx *sx, const char *file, int line) 1269 { 1270 1271 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1272 } 1273 1274 #ifdef INVARIANT_SUPPORT 1275 #ifndef INVARIANTS 1276 #undef _sx_assert 1277 #endif 1278 1279 /* 1280 * In the non-WITNESS case, sx_assert() can only detect that at least 1281 * *some* thread owns an slock, but it cannot guarantee that *this* 1282 * thread owns an slock. 1283 */ 1284 void 1285 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1286 { 1287 #ifndef WITNESS 1288 int slocked = 0; 1289 #endif 1290 1291 if (panicstr != NULL) 1292 return; 1293 switch (what) { 1294 case SA_SLOCKED: 1295 case SA_SLOCKED | SA_NOTRECURSED: 1296 case SA_SLOCKED | SA_RECURSED: 1297 #ifndef WITNESS 1298 slocked = 1; 1299 /* FALLTHROUGH */ 1300 #endif 1301 case SA_LOCKED: 1302 case SA_LOCKED | SA_NOTRECURSED: 1303 case SA_LOCKED | SA_RECURSED: 1304 #ifdef WITNESS 1305 witness_assert(&sx->lock_object, what, file, line); 1306 #else 1307 /* 1308 * If some other thread has an exclusive lock or we 1309 * have one and are asserting a shared lock, fail. 1310 * Also, if no one has a lock at all, fail. 1311 */ 1312 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1313 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1314 sx_xholder(sx) != curthread))) 1315 panic("Lock %s not %slocked @ %s:%d\n", 1316 sx->lock_object.lo_name, slocked ? "share " : "", 1317 file, line); 1318 1319 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1320 if (sx_recursed(sx)) { 1321 if (what & SA_NOTRECURSED) 1322 panic("Lock %s recursed @ %s:%d\n", 1323 sx->lock_object.lo_name, file, 1324 line); 1325 } else if (what & SA_RECURSED) 1326 panic("Lock %s not recursed @ %s:%d\n", 1327 sx->lock_object.lo_name, file, line); 1328 } 1329 #endif 1330 break; 1331 case SA_XLOCKED: 1332 case SA_XLOCKED | SA_NOTRECURSED: 1333 case SA_XLOCKED | SA_RECURSED: 1334 if (sx_xholder(sx) != curthread) 1335 panic("Lock %s not exclusively locked @ %s:%d\n", 1336 sx->lock_object.lo_name, file, line); 1337 if (sx_recursed(sx)) { 1338 if (what & SA_NOTRECURSED) 1339 panic("Lock %s recursed @ %s:%d\n", 1340 sx->lock_object.lo_name, file, line); 1341 } else if (what & SA_RECURSED) 1342 panic("Lock %s not recursed @ %s:%d\n", 1343 sx->lock_object.lo_name, file, line); 1344 break; 1345 case SA_UNLOCKED: 1346 #ifdef WITNESS 1347 witness_assert(&sx->lock_object, what, file, line); 1348 #else 1349 /* 1350 * If we hold an exclusve lock fail. We can't 1351 * reliably check to see if we hold a shared lock or 1352 * not. 1353 */ 1354 if (sx_xholder(sx) == curthread) 1355 panic("Lock %s exclusively locked @ %s:%d\n", 1356 sx->lock_object.lo_name, file, line); 1357 #endif 1358 break; 1359 default: 1360 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1361 line); 1362 } 1363 } 1364 #endif /* INVARIANT_SUPPORT */ 1365 1366 #ifdef DDB 1367 static void 1368 db_show_sx(const struct lock_object *lock) 1369 { 1370 struct thread *td; 1371 const struct sx *sx; 1372 1373 sx = (const struct sx *)lock; 1374 1375 db_printf(" state: "); 1376 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1377 db_printf("UNLOCKED\n"); 1378 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1379 db_printf("DESTROYED\n"); 1380 return; 1381 } else if (sx->sx_lock & SX_LOCK_SHARED) 1382 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1383 else { 1384 td = sx_xholder(sx); 1385 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1386 td->td_tid, td->td_proc->p_pid, td->td_name); 1387 if (sx_recursed(sx)) 1388 db_printf(" recursed: %d\n", sx->sx_recurse); 1389 } 1390 1391 db_printf(" waiters: "); 1392 switch(sx->sx_lock & 1393 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1394 case SX_LOCK_SHARED_WAITERS: 1395 db_printf("shared\n"); 1396 break; 1397 case SX_LOCK_EXCLUSIVE_WAITERS: 1398 db_printf("exclusive\n"); 1399 break; 1400 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1401 db_printf("exclusive and shared\n"); 1402 break; 1403 default: 1404 db_printf("none\n"); 1405 } 1406 } 1407 1408 /* 1409 * Check to see if a thread that is blocked on a sleep queue is actually 1410 * blocked on an sx lock. If so, output some details and return true. 1411 * If the lock has an exclusive owner, return that in *ownerp. 1412 */ 1413 int 1414 sx_chain(struct thread *td, struct thread **ownerp) 1415 { 1416 struct sx *sx; 1417 1418 /* 1419 * Check to see if this thread is blocked on an sx lock. 1420 * First, we check the lock class. If that is ok, then we 1421 * compare the lock name against the wait message. 1422 */ 1423 sx = td->td_wchan; 1424 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1425 sx->lock_object.lo_name != td->td_wmesg) 1426 return (0); 1427 1428 /* We think we have an sx lock, so output some details. */ 1429 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1430 *ownerp = sx_xholder(sx); 1431 if (sx->sx_lock & SX_LOCK_SHARED) 1432 db_printf("SLOCK (count %ju)\n", 1433 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1434 else 1435 db_printf("XLOCK\n"); 1436 return (1); 1437 } 1438 #endif 1439