Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/kern/kern_sx.c
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1 /*- 2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org> 3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org> 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice(s), this list of conditions and the following disclaimer as 11 * the first lines of this file unmodified other than the possible 12 * addition of one or more copyright notices. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice(s), this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 27 * DAMAGE. 28 */ 29 30 /* 31 * Shared/exclusive locks. This implementation attempts to ensure 32 * deterministic lock granting behavior, so that slocks and xlocks are 33 * interleaved. 34 * 35 * Priority propagation will not generally raise the priority of lock holders, 36 * so should not be relied upon in combination with sx locks. 37 */ 38 39 #include "opt_ddb.h" 40 #include "opt_hwpmc_hooks.h" 41 #include "opt_no_adaptive_sx.h" 42 43 #include <sys/cdefs.h> 44 __FBSDID("$FreeBSD$"); 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/kdb.h> 49 #include <sys/kernel.h> 50 #include <sys/ktr.h> 51 #include <sys/lock.h> 52 #include <sys/mutex.h> 53 #include <sys/proc.h> 54 #include <sys/sched.h> 55 #include <sys/sleepqueue.h> 56 #include <sys/sx.h> 57 #include <sys/smp.h> 58 #include <sys/sysctl.h> 59 60 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 61 #include <machine/cpu.h> 62 #endif 63 64 #ifdef DDB 65 #include <ddb/ddb.h> 66 #endif 67 68 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 69 #define ADAPTIVE_SX 70 #endif 71 72 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE); 73 74 #ifdef HWPMC_HOOKS 75 #include <sys/pmckern.h> 76 PMC_SOFT_DECLARE( , , lock, failed); 77 #endif 78 79 /* Handy macros for sleep queues. */ 80 #define SQ_EXCLUSIVE_QUEUE 0 81 #define SQ_SHARED_QUEUE 1 82 83 /* 84 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 85 * drop Giant anytime we have to sleep or if we adaptively spin. 86 */ 87 #define GIANT_DECLARE \ 88 int _giantcnt = 0; \ 89 WITNESS_SAVE_DECL(Giant) \ 90 91 #define GIANT_SAVE(work) do { \ 92 if (__predict_false(mtx_owned(&Giant))) { \ 93 work++; \ 94 WITNESS_SAVE(&Giant.lock_object, Giant); \ 95 while (mtx_owned(&Giant)) { \ 96 _giantcnt++; \ 97 mtx_unlock(&Giant); \ 98 } \ 99 } \ 100 } while (0) 101 102 #define GIANT_RESTORE() do { \ 103 if (_giantcnt > 0) { \ 104 mtx_assert(&Giant, MA_NOTOWNED); \ 105 while (_giantcnt--) \ 106 mtx_lock(&Giant); \ 107 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 108 } \ 109 } while (0) 110 111 /* 112 * Returns true if an exclusive lock is recursed. It assumes 113 * curthread currently has an exclusive lock. 114 */ 115 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 116 117 static void assert_sx(const struct lock_object *lock, int what); 118 #ifdef DDB 119 static void db_show_sx(const struct lock_object *lock); 120 #endif 121 static void lock_sx(struct lock_object *lock, uintptr_t how); 122 #ifdef KDTRACE_HOOKS 123 static int owner_sx(const struct lock_object *lock, struct thread **owner); 124 #endif 125 static uintptr_t unlock_sx(struct lock_object *lock); 126 127 struct lock_class lock_class_sx = { 128 .lc_name = "sx", 129 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 130 .lc_assert = assert_sx, 131 #ifdef DDB 132 .lc_ddb_show = db_show_sx, 133 #endif 134 .lc_lock = lock_sx, 135 .lc_unlock = unlock_sx, 136 #ifdef KDTRACE_HOOKS 137 .lc_owner = owner_sx, 138 #endif 139 }; 140 141 #ifndef INVARIANTS 142 #define _sx_assert(sx, what, file, line) 143 #endif 144 145 #ifdef ADAPTIVE_SX 146 static __read_frequently u_int asx_retries; 147 static __read_frequently u_int asx_loops; 148 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging"); 149 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, ""); 150 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, ""); 151 152 static struct lock_delay_config __read_frequently sx_delay; 153 154 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base, 155 0, ""); 156 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max, 157 0, ""); 158 159 static void 160 sx_lock_delay_init(void *arg __unused) 161 { 162 163 lock_delay_default_init(&sx_delay); 164 asx_retries = 10; 165 asx_loops = max(10000, sx_delay.max); 166 } 167 LOCK_DELAY_SYSINIT(sx_lock_delay_init); 168 #endif 169 170 void 171 assert_sx(const struct lock_object *lock, int what) 172 { 173 174 sx_assert((const struct sx *)lock, what); 175 } 176 177 void 178 lock_sx(struct lock_object *lock, uintptr_t how) 179 { 180 struct sx *sx; 181 182 sx = (struct sx *)lock; 183 if (how) 184 sx_slock(sx); 185 else 186 sx_xlock(sx); 187 } 188 189 uintptr_t 190 unlock_sx(struct lock_object *lock) 191 { 192 struct sx *sx; 193 194 sx = (struct sx *)lock; 195 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 196 if (sx_xlocked(sx)) { 197 sx_xunlock(sx); 198 return (0); 199 } else { 200 sx_sunlock(sx); 201 return (1); 202 } 203 } 204 205 #ifdef KDTRACE_HOOKS 206 int 207 owner_sx(const struct lock_object *lock, struct thread **owner) 208 { 209 const struct sx *sx; 210 uintptr_t x; 211 212 sx = (const struct sx *)lock; 213 x = sx->sx_lock; 214 *owner = NULL; 215 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 216 ((*owner = (struct thread *)SX_OWNER(x)) != NULL)); 217 } 218 #endif 219 220 void 221 sx_sysinit(void *arg) 222 { 223 struct sx_args *sargs = arg; 224 225 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 226 } 227 228 void 229 sx_init_flags(struct sx *sx, const char *description, int opts) 230 { 231 int flags; 232 233 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 234 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0); 235 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 236 ("%s: sx_lock not aligned for %s: %p", __func__, description, 237 &sx->sx_lock)); 238 239 flags = LO_SLEEPABLE | LO_UPGRADABLE; 240 if (opts & SX_DUPOK) 241 flags |= LO_DUPOK; 242 if (opts & SX_NOPROFILE) 243 flags |= LO_NOPROFILE; 244 if (!(opts & SX_NOWITNESS)) 245 flags |= LO_WITNESS; 246 if (opts & SX_RECURSE) 247 flags |= LO_RECURSABLE; 248 if (opts & SX_QUIET) 249 flags |= LO_QUIET; 250 if (opts & SX_NEW) 251 flags |= LO_NEW; 252 253 flags |= opts & SX_NOADAPTIVE; 254 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 255 sx->sx_lock = SX_LOCK_UNLOCKED; 256 sx->sx_recurse = 0; 257 } 258 259 void 260 sx_destroy(struct sx *sx) 261 { 262 263 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 264 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 265 sx->sx_lock = SX_LOCK_DESTROYED; 266 lock_destroy(&sx->lock_object); 267 } 268 269 int 270 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 271 { 272 uintptr_t x; 273 274 if (SCHEDULER_STOPPED()) 275 return (1); 276 277 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 278 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 279 curthread, sx->lock_object.lo_name, file, line)); 280 281 x = sx->sx_lock; 282 for (;;) { 283 KASSERT(x != SX_LOCK_DESTROYED, 284 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 285 if (!(x & SX_LOCK_SHARED)) 286 break; 287 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 288 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 289 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 290 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 291 sx, 0, 0, file, line, LOCKSTAT_READER); 292 TD_LOCKS_INC(curthread); 293 return (1); 294 } 295 } 296 297 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 298 return (0); 299 } 300 301 int 302 sx_try_slock_(struct sx *sx, const char *file, int line) 303 { 304 305 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG)); 306 } 307 308 int 309 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 310 { 311 uintptr_t tid, x; 312 int error = 0; 313 314 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 315 !TD_IS_IDLETHREAD(curthread), 316 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 317 curthread, sx->lock_object.lo_name, file, line)); 318 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 319 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 320 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 321 line, NULL); 322 tid = (uintptr_t)curthread; 323 x = SX_LOCK_UNLOCKED; 324 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 325 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG); 326 else 327 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 328 0, 0, file, line, LOCKSTAT_WRITER); 329 if (!error) { 330 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 331 file, line); 332 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 333 TD_LOCKS_INC(curthread); 334 } 335 336 return (error); 337 } 338 339 int 340 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 341 { 342 struct thread *td; 343 uintptr_t tid, x; 344 int rval; 345 bool recursed; 346 347 td = curthread; 348 tid = (uintptr_t)td; 349 if (SCHEDULER_STOPPED_TD(td)) 350 return (1); 351 352 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 353 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 354 curthread, sx->lock_object.lo_name, file, line)); 355 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 356 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 357 358 rval = 1; 359 recursed = false; 360 x = SX_LOCK_UNLOCKED; 361 for (;;) { 362 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 363 break; 364 if (x == SX_LOCK_UNLOCKED) 365 continue; 366 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 367 sx->sx_recurse++; 368 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 369 break; 370 } 371 rval = 0; 372 break; 373 } 374 375 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 376 if (rval) { 377 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 378 file, line); 379 if (!recursed) 380 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 381 sx, 0, 0, file, line, LOCKSTAT_WRITER); 382 TD_LOCKS_INC(curthread); 383 } 384 385 return (rval); 386 } 387 388 int 389 sx_try_xlock_(struct sx *sx, const char *file, int line) 390 { 391 392 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG)); 393 } 394 395 void 396 _sx_xunlock(struct sx *sx, const char *file, int line) 397 { 398 399 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 400 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 401 _sx_assert(sx, SA_XLOCKED, file, line); 402 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 403 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 404 line); 405 #if LOCK_DEBUG > 0 406 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 407 #else 408 __sx_xunlock(sx, curthread, file, line); 409 #endif 410 TD_LOCKS_DEC(curthread); 411 } 412 413 /* 414 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 415 * This will only succeed if this thread holds a single shared lock. 416 * Return 1 if if the upgrade succeed, 0 otherwise. 417 */ 418 int 419 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 420 { 421 uintptr_t x; 422 uintptr_t waiters; 423 int success; 424 425 if (SCHEDULER_STOPPED()) 426 return (1); 427 428 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 429 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 430 _sx_assert(sx, SA_SLOCKED, file, line); 431 432 /* 433 * Try to switch from one shared lock to an exclusive lock. We need 434 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 435 * we will wake up the exclusive waiters when we drop the lock. 436 */ 437 success = 0; 438 x = SX_READ_VALUE(sx); 439 for (;;) { 440 if (SX_SHARERS(x) > 1) 441 break; 442 waiters = (x & SX_LOCK_EXCLUSIVE_WAITERS); 443 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 444 (uintptr_t)curthread | waiters)) { 445 success = 1; 446 break; 447 } 448 } 449 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 450 if (success) { 451 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 452 file, line); 453 LOCKSTAT_RECORD0(sx__upgrade, sx); 454 } 455 return (success); 456 } 457 458 int 459 sx_try_upgrade_(struct sx *sx, const char *file, int line) 460 { 461 462 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG)); 463 } 464 465 /* 466 * Downgrade an unrecursed exclusive lock into a single shared lock. 467 */ 468 void 469 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 470 { 471 uintptr_t x; 472 int wakeup_swapper; 473 474 if (SCHEDULER_STOPPED()) 475 return; 476 477 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 478 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 479 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 480 #ifndef INVARIANTS 481 if (sx_recursed(sx)) 482 panic("downgrade of a recursed lock"); 483 #endif 484 485 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 486 487 /* 488 * Try to switch from an exclusive lock with no shared waiters 489 * to one sharer with no shared waiters. If there are 490 * exclusive waiters, we don't need to lock the sleep queue so 491 * long as we preserve the flag. We do one quick try and if 492 * that fails we grab the sleepq lock to keep the flags from 493 * changing and do it the slow way. 494 * 495 * We have to lock the sleep queue if there are shared waiters 496 * so we can wake them up. 497 */ 498 x = sx->sx_lock; 499 if (!(x & SX_LOCK_SHARED_WAITERS) && 500 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 501 (x & SX_LOCK_EXCLUSIVE_WAITERS))) 502 goto out; 503 504 /* 505 * Lock the sleep queue so we can read the waiters bits 506 * without any races and wakeup any shared waiters. 507 */ 508 sleepq_lock(&sx->lock_object); 509 510 /* 511 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 512 * shared lock. If there are any shared waiters, wake them up. 513 */ 514 wakeup_swapper = 0; 515 x = sx->sx_lock; 516 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 517 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 518 if (x & SX_LOCK_SHARED_WAITERS) 519 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 520 0, SQ_SHARED_QUEUE); 521 sleepq_release(&sx->lock_object); 522 523 if (wakeup_swapper) 524 kick_proc0(); 525 526 out: 527 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 528 LOCKSTAT_RECORD0(sx__downgrade, sx); 529 } 530 531 void 532 sx_downgrade_(struct sx *sx, const char *file, int line) 533 { 534 535 sx_downgrade_int(sx LOCK_FILE_LINE_ARG); 536 } 537 538 /* 539 * This function represents the so-called 'hard case' for sx_xlock 540 * operation. All 'easy case' failures are redirected to this. Note 541 * that ideally this would be a static function, but it needs to be 542 * accessible from at least sx.h. 543 */ 544 int 545 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF) 546 { 547 GIANT_DECLARE; 548 uintptr_t tid; 549 #ifdef ADAPTIVE_SX 550 volatile struct thread *owner; 551 u_int i, n, spintries = 0; 552 enum { READERS, WRITER } sleep_reason = READERS; 553 bool adaptive; 554 #endif 555 #ifdef LOCK_PROFILING 556 uint64_t waittime = 0; 557 int contested = 0; 558 #endif 559 int error = 0; 560 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 561 struct lock_delay_arg lda; 562 #endif 563 #ifdef KDTRACE_HOOKS 564 u_int sleep_cnt = 0; 565 int64_t sleep_time = 0; 566 int64_t all_time = 0; 567 #endif 568 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 569 uintptr_t state = 0; 570 #endif 571 int extra_work = 0; 572 573 tid = (uintptr_t)curthread; 574 575 #ifdef KDTRACE_HOOKS 576 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 577 while (x == SX_LOCK_UNLOCKED) { 578 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 579 goto out_lockstat; 580 } 581 extra_work = 1; 582 all_time -= lockstat_nsecs(&sx->lock_object); 583 state = x; 584 } 585 #endif 586 #ifdef LOCK_PROFILING 587 extra_work = 1; 588 state = x; 589 #endif 590 591 if (SCHEDULER_STOPPED()) 592 return (0); 593 594 #if defined(ADAPTIVE_SX) 595 lock_delay_arg_init(&lda, &sx_delay); 596 #elif defined(KDTRACE_HOOKS) 597 lock_delay_arg_init(&lda, NULL); 598 #endif 599 600 if (__predict_false(x == SX_LOCK_UNLOCKED)) 601 x = SX_READ_VALUE(sx); 602 603 /* If we already hold an exclusive lock, then recurse. */ 604 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 605 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 606 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 607 sx->lock_object.lo_name, file, line)); 608 sx->sx_recurse++; 609 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 610 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 611 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 612 return (0); 613 } 614 615 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 616 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 617 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 618 619 #ifdef ADAPTIVE_SX 620 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 621 #endif 622 623 #ifdef HWPMC_HOOKS 624 PMC_SOFT_CALL( , , lock, failed); 625 #endif 626 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 627 &waittime); 628 629 #ifndef INVARIANTS 630 GIANT_SAVE(extra_work); 631 #endif 632 633 for (;;) { 634 if (x == SX_LOCK_UNLOCKED) { 635 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 636 break; 637 continue; 638 } 639 #ifdef INVARIANTS 640 GIANT_SAVE(extra_work); 641 #endif 642 #ifdef KDTRACE_HOOKS 643 lda.spin_cnt++; 644 #endif 645 #ifdef ADAPTIVE_SX 646 if (__predict_false(!adaptive)) 647 goto sleepq; 648 /* 649 * If the lock is write locked and the owner is 650 * running on another CPU, spin until the owner stops 651 * running or the state of the lock changes. 652 */ 653 if ((x & SX_LOCK_SHARED) == 0) { 654 sleep_reason = WRITER; 655 owner = lv_sx_owner(x); 656 if (!TD_IS_RUNNING(owner)) 657 goto sleepq; 658 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 659 CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 660 __func__, sx, owner); 661 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 662 "spinning", "lockname:\"%s\"", 663 sx->lock_object.lo_name); 664 do { 665 lock_delay(&lda); 666 x = SX_READ_VALUE(sx); 667 owner = lv_sx_owner(x); 668 } while (owner != NULL && TD_IS_RUNNING(owner)); 669 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 670 "running"); 671 continue; 672 } else if (SX_SHARERS(x) > 0) { 673 sleep_reason = READERS; 674 if (spintries == asx_retries) 675 goto sleepq; 676 spintries++; 677 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), 678 "spinning", "lockname:\"%s\"", 679 sx->lock_object.lo_name); 680 for (i = 0; i < asx_loops; i += n) { 681 n = SX_SHARERS(x); 682 lock_delay_spin(n); 683 x = SX_READ_VALUE(sx); 684 if ((x & SX_LOCK_SHARED) == 0 || 685 SX_SHARERS(x) == 0) 686 break; 687 } 688 #ifdef KDTRACE_HOOKS 689 lda.spin_cnt += i; 690 #endif 691 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread), 692 "running"); 693 if (i < asx_loops) 694 continue; 695 } 696 sleepq: 697 #endif 698 sleepq_lock(&sx->lock_object); 699 x = SX_READ_VALUE(sx); 700 retry_sleepq: 701 702 /* 703 * If the lock was released while spinning on the 704 * sleep queue chain lock, try again. 705 */ 706 if (x == SX_LOCK_UNLOCKED) { 707 sleepq_release(&sx->lock_object); 708 continue; 709 } 710 711 #ifdef ADAPTIVE_SX 712 /* 713 * The current lock owner might have started executing 714 * on another CPU (or the lock could have changed 715 * owners) while we were waiting on the sleep queue 716 * chain lock. If so, drop the sleep queue lock and try 717 * again. 718 */ 719 if (adaptive) { 720 if (!(x & SX_LOCK_SHARED)) { 721 owner = (struct thread *)SX_OWNER(x); 722 if (TD_IS_RUNNING(owner)) { 723 sleepq_release(&sx->lock_object); 724 continue; 725 } 726 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) { 727 sleepq_release(&sx->lock_object); 728 continue; 729 } 730 } 731 #endif 732 733 /* 734 * If an exclusive lock was released with both shared 735 * and exclusive waiters and a shared waiter hasn't 736 * woken up and acquired the lock yet, sx_lock will be 737 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 738 * If we see that value, try to acquire it once. Note 739 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 740 * as there are other exclusive waiters still. If we 741 * fail, restart the loop. 742 */ 743 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 744 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, 745 tid | SX_LOCK_EXCLUSIVE_WAITERS)) 746 goto retry_sleepq; 747 sleepq_release(&sx->lock_object); 748 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 749 __func__, sx); 750 break; 751 } 752 753 /* 754 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 755 * than loop back and retry. 756 */ 757 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 758 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 759 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 760 goto retry_sleepq; 761 } 762 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 763 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 764 __func__, sx); 765 } 766 767 /* 768 * Since we have been unable to acquire the exclusive 769 * lock and the exclusive waiters flag is set, we have 770 * to sleep. 771 */ 772 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 773 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 774 __func__, sx); 775 776 #ifdef KDTRACE_HOOKS 777 sleep_time -= lockstat_nsecs(&sx->lock_object); 778 #endif 779 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 780 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 781 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 782 if (!(opts & SX_INTERRUPTIBLE)) 783 sleepq_wait(&sx->lock_object, 0); 784 else 785 error = sleepq_wait_sig(&sx->lock_object, 0); 786 #ifdef KDTRACE_HOOKS 787 sleep_time += lockstat_nsecs(&sx->lock_object); 788 sleep_cnt++; 789 #endif 790 if (error) { 791 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 792 CTR2(KTR_LOCK, 793 "%s: interruptible sleep by %p suspended by signal", 794 __func__, sx); 795 break; 796 } 797 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 798 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 799 __func__, sx); 800 x = SX_READ_VALUE(sx); 801 } 802 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 803 if (__predict_true(!extra_work)) 804 return (error); 805 #endif 806 #ifdef KDTRACE_HOOKS 807 all_time += lockstat_nsecs(&sx->lock_object); 808 if (sleep_time) 809 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 810 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 811 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 812 if (lda.spin_cnt > sleep_cnt) 813 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 814 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 815 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 816 out_lockstat: 817 #endif 818 if (!error) 819 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 820 contested, waittime, file, line, LOCKSTAT_WRITER); 821 GIANT_RESTORE(); 822 return (error); 823 } 824 825 /* 826 * This function represents the so-called 'hard case' for sx_xunlock 827 * operation. All 'easy case' failures are redirected to this. Note 828 * that ideally this would be a static function, but it needs to be 829 * accessible from at least sx.h. 830 */ 831 void 832 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 833 { 834 uintptr_t tid, setx; 835 int queue, wakeup_swapper; 836 837 if (SCHEDULER_STOPPED()) 838 return; 839 840 tid = (uintptr_t)curthread; 841 842 if (__predict_false(x == tid)) 843 x = SX_READ_VALUE(sx); 844 845 MPASS(!(x & SX_LOCK_SHARED)); 846 847 if (__predict_false(x & SX_LOCK_RECURSED)) { 848 /* The lock is recursed, unrecurse one level. */ 849 if ((--sx->sx_recurse) == 0) 850 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 851 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 852 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 853 return; 854 } 855 856 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 857 if (x == tid && 858 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 859 return; 860 861 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 862 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 863 864 sleepq_lock(&sx->lock_object); 865 x = SX_READ_VALUE(sx); 866 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)); 867 868 /* 869 * The wake up algorithm here is quite simple and probably not 870 * ideal. It gives precedence to shared waiters if they are 871 * present. For this condition, we have to preserve the 872 * state of the exclusive waiters flag. 873 * If interruptible sleeps left the shared queue empty avoid a 874 * starvation for the threads sleeping on the exclusive queue by giving 875 * them precedence and cleaning up the shared waiters bit anyway. 876 */ 877 setx = SX_LOCK_UNLOCKED; 878 queue = SQ_EXCLUSIVE_QUEUE; 879 if ((x & SX_LOCK_SHARED_WAITERS) != 0 && 880 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 881 queue = SQ_SHARED_QUEUE; 882 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS); 883 } 884 atomic_store_rel_ptr(&sx->sx_lock, setx); 885 886 /* Wake up all the waiters for the specific queue. */ 887 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 888 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 889 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 890 "exclusive"); 891 892 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 893 queue); 894 sleepq_release(&sx->lock_object); 895 if (wakeup_swapper) 896 kick_proc0(); 897 } 898 899 static bool __always_inline 900 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF) 901 { 902 903 /* 904 * If no other thread has an exclusive lock then try to bump up 905 * the count of sharers. Since we have to preserve the state 906 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 907 * shared lock loop back and retry. 908 */ 909 while (*xp & SX_LOCK_SHARED) { 910 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 911 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 912 *xp + SX_ONE_SHARER)) { 913 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 914 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 915 __func__, sx, (void *)*xp, 916 (void *)(*xp + SX_ONE_SHARER)); 917 return (true); 918 } 919 } 920 return (false); 921 } 922 923 static int __noinline 924 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 925 { 926 GIANT_DECLARE; 927 #ifdef ADAPTIVE_SX 928 volatile struct thread *owner; 929 bool adaptive; 930 #endif 931 #ifdef LOCK_PROFILING 932 uint64_t waittime = 0; 933 int contested = 0; 934 #endif 935 int error = 0; 936 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 937 struct lock_delay_arg lda; 938 #endif 939 #ifdef KDTRACE_HOOKS 940 u_int sleep_cnt = 0; 941 int64_t sleep_time = 0; 942 int64_t all_time = 0; 943 #endif 944 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 945 uintptr_t state = 0; 946 #endif 947 int extra_work = 0; 948 949 #ifdef KDTRACE_HOOKS 950 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) { 951 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 952 goto out_lockstat; 953 extra_work = 1; 954 all_time -= lockstat_nsecs(&sx->lock_object); 955 state = x; 956 } 957 #endif 958 #ifdef LOCK_PROFILING 959 extra_work = 1; 960 state = x; 961 #endif 962 963 if (SCHEDULER_STOPPED()) 964 return (0); 965 966 #if defined(ADAPTIVE_SX) 967 lock_delay_arg_init(&lda, &sx_delay); 968 #elif defined(KDTRACE_HOOKS) 969 lock_delay_arg_init(&lda, NULL); 970 #endif 971 972 #ifdef ADAPTIVE_SX 973 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0); 974 #endif 975 976 #ifdef HWPMC_HOOKS 977 PMC_SOFT_CALL( , , lock, failed); 978 #endif 979 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 980 &waittime); 981 982 #ifndef INVARIANTS 983 GIANT_SAVE(extra_work); 984 #endif 985 986 /* 987 * As with rwlocks, we don't make any attempt to try to block 988 * shared locks once there is an exclusive waiter. 989 */ 990 for (;;) { 991 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)) 992 break; 993 #ifdef INVARIANTS 994 GIANT_SAVE(extra_work); 995 #endif 996 #ifdef KDTRACE_HOOKS 997 lda.spin_cnt++; 998 #endif 999 1000 #ifdef ADAPTIVE_SX 1001 if (__predict_false(!adaptive)) 1002 goto sleepq; 1003 /* 1004 * If the owner is running on another CPU, spin until 1005 * the owner stops running or the state of the lock 1006 * changes. 1007 */ 1008 owner = lv_sx_owner(x); 1009 if (TD_IS_RUNNING(owner)) { 1010 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1011 CTR3(KTR_LOCK, 1012 "%s: spinning on %p held by %p", 1013 __func__, sx, owner); 1014 KTR_STATE1(KTR_SCHED, "thread", 1015 sched_tdname(curthread), "spinning", 1016 "lockname:\"%s\"", sx->lock_object.lo_name); 1017 do { 1018 lock_delay(&lda); 1019 x = SX_READ_VALUE(sx); 1020 owner = lv_sx_owner(x); 1021 } while (owner != NULL && TD_IS_RUNNING(owner)); 1022 KTR_STATE0(KTR_SCHED, "thread", 1023 sched_tdname(curthread), "running"); 1024 continue; 1025 } 1026 sleepq: 1027 #endif 1028 1029 /* 1030 * Some other thread already has an exclusive lock, so 1031 * start the process of blocking. 1032 */ 1033 sleepq_lock(&sx->lock_object); 1034 x = SX_READ_VALUE(sx); 1035 retry_sleepq: 1036 /* 1037 * The lock could have been released while we spun. 1038 * In this case loop back and retry. 1039 */ 1040 if (x & SX_LOCK_SHARED) { 1041 sleepq_release(&sx->lock_object); 1042 continue; 1043 } 1044 1045 #ifdef ADAPTIVE_SX 1046 /* 1047 * If the owner is running on another CPU, spin until 1048 * the owner stops running or the state of the lock 1049 * changes. 1050 */ 1051 if (!(x & SX_LOCK_SHARED) && adaptive) { 1052 owner = (struct thread *)SX_OWNER(x); 1053 if (TD_IS_RUNNING(owner)) { 1054 sleepq_release(&sx->lock_object); 1055 x = SX_READ_VALUE(sx); 1056 continue; 1057 } 1058 } 1059 #endif 1060 1061 /* 1062 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 1063 * fail to set it drop the sleep queue lock and loop 1064 * back. 1065 */ 1066 if (!(x & SX_LOCK_SHARED_WAITERS)) { 1067 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x, 1068 x | SX_LOCK_SHARED_WAITERS)) 1069 goto retry_sleepq; 1070 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1071 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 1072 __func__, sx); 1073 } 1074 1075 /* 1076 * Since we have been unable to acquire the shared lock, 1077 * we have to sleep. 1078 */ 1079 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1080 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 1081 __func__, sx); 1082 1083 #ifdef KDTRACE_HOOKS 1084 sleep_time -= lockstat_nsecs(&sx->lock_object); 1085 #endif 1086 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 1087 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 1088 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 1089 if (!(opts & SX_INTERRUPTIBLE)) 1090 sleepq_wait(&sx->lock_object, 0); 1091 else 1092 error = sleepq_wait_sig(&sx->lock_object, 0); 1093 #ifdef KDTRACE_HOOKS 1094 sleep_time += lockstat_nsecs(&sx->lock_object); 1095 sleep_cnt++; 1096 #endif 1097 if (error) { 1098 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1099 CTR2(KTR_LOCK, 1100 "%s: interruptible sleep by %p suspended by signal", 1101 __func__, sx); 1102 break; 1103 } 1104 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1105 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1106 __func__, sx); 1107 x = SX_READ_VALUE(sx); 1108 } 1109 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING) 1110 if (__predict_true(!extra_work)) 1111 return (error); 1112 #endif 1113 #ifdef KDTRACE_HOOKS 1114 all_time += lockstat_nsecs(&sx->lock_object); 1115 if (sleep_time) 1116 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1117 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1118 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1119 if (lda.spin_cnt > sleep_cnt) 1120 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1121 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1122 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1123 out_lockstat: 1124 #endif 1125 if (error == 0) { 1126 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1127 contested, waittime, file, line, LOCKSTAT_READER); 1128 } 1129 GIANT_RESTORE(); 1130 return (error); 1131 } 1132 1133 int 1134 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF) 1135 { 1136 uintptr_t x; 1137 int error; 1138 1139 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1140 !TD_IS_IDLETHREAD(curthread), 1141 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1142 curthread, sx->lock_object.lo_name, file, line)); 1143 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1144 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1145 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1146 1147 error = 0; 1148 x = SX_READ_VALUE(sx); 1149 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) || 1150 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))) 1151 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG); 1152 else 1153 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, 1154 file, line); 1155 if (error == 0) { 1156 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1157 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1158 TD_LOCKS_INC(curthread); 1159 } 1160 return (error); 1161 } 1162 1163 int 1164 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1165 { 1166 1167 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG)); 1168 } 1169 1170 static bool __always_inline 1171 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1172 { 1173 1174 for (;;) { 1175 /* 1176 * We should never have sharers while at least one thread 1177 * holds a shared lock. 1178 */ 1179 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1180 ("%s: waiting sharers", __func__)); 1181 1182 /* 1183 * See if there is more than one shared lock held. If 1184 * so, just drop one and return. 1185 */ 1186 if (SX_SHARERS(*xp) > 1) { 1187 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1188 *xp - SX_ONE_SHARER)) { 1189 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1190 CTR4(KTR_LOCK, 1191 "%s: %p succeeded %p -> %p", 1192 __func__, sx, (void *)*xp, 1193 (void *)(*xp - SX_ONE_SHARER)); 1194 return (true); 1195 } 1196 continue; 1197 } 1198 1199 /* 1200 * If there aren't any waiters for an exclusive lock, 1201 * then try to drop it quickly. 1202 */ 1203 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1204 MPASS(*xp == SX_SHARERS_LOCK(1)); 1205 *xp = SX_SHARERS_LOCK(1); 1206 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1207 xp, SX_LOCK_UNLOCKED)) { 1208 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1209 CTR2(KTR_LOCK, "%s: %p last succeeded", 1210 __func__, sx); 1211 return (true); 1212 } 1213 continue; 1214 } 1215 break; 1216 } 1217 return (false); 1218 } 1219 1220 static void __noinline 1221 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF) 1222 { 1223 int wakeup_swapper = 0; 1224 uintptr_t setx; 1225 1226 if (SCHEDULER_STOPPED()) 1227 return; 1228 1229 if (_sx_sunlock_try(sx, &x)) 1230 goto out_lockstat; 1231 1232 /* 1233 * At this point, there should just be one sharer with 1234 * exclusive waiters. 1235 */ 1236 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1237 1238 sleepq_lock(&sx->lock_object); 1239 x = SX_READ_VALUE(sx); 1240 for (;;) { 1241 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS); 1242 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 1243 if (_sx_sunlock_try(sx, &x)) 1244 break; 1245 1246 /* 1247 * Wake up semantic here is quite simple: 1248 * Just wake up all the exclusive waiters. 1249 * Note that the state of the lock could have changed, 1250 * so if it fails loop back and retry. 1251 */ 1252 setx = x - SX_ONE_SHARER; 1253 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS; 1254 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx)) 1255 continue; 1256 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1257 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1258 "exclusive queue", __func__, sx); 1259 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1260 0, SQ_EXCLUSIVE_QUEUE); 1261 break; 1262 } 1263 sleepq_release(&sx->lock_object); 1264 if (wakeup_swapper) 1265 kick_proc0(); 1266 out_lockstat: 1267 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1268 } 1269 1270 void 1271 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF) 1272 { 1273 uintptr_t x; 1274 1275 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1276 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1277 _sx_assert(sx, SA_SLOCKED, file, line); 1278 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1279 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1280 1281 x = SX_READ_VALUE(sx); 1282 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) || 1283 !_sx_sunlock_try(sx, &x))) 1284 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG); 1285 else 1286 lock_profile_release_lock(&sx->lock_object); 1287 1288 TD_LOCKS_DEC(curthread); 1289 } 1290 1291 void 1292 _sx_sunlock(struct sx *sx, const char *file, int line) 1293 { 1294 1295 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG); 1296 } 1297 1298 #ifdef INVARIANT_SUPPORT 1299 #ifndef INVARIANTS 1300 #undef _sx_assert 1301 #endif 1302 1303 /* 1304 * In the non-WITNESS case, sx_assert() can only detect that at least 1305 * *some* thread owns an slock, but it cannot guarantee that *this* 1306 * thread owns an slock. 1307 */ 1308 void 1309 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1310 { 1311 #ifndef WITNESS 1312 int slocked = 0; 1313 #endif 1314 1315 if (SCHEDULER_STOPPED()) 1316 return; 1317 switch (what) { 1318 case SA_SLOCKED: 1319 case SA_SLOCKED | SA_NOTRECURSED: 1320 case SA_SLOCKED | SA_RECURSED: 1321 #ifndef WITNESS 1322 slocked = 1; 1323 /* FALLTHROUGH */ 1324 #endif 1325 case SA_LOCKED: 1326 case SA_LOCKED | SA_NOTRECURSED: 1327 case SA_LOCKED | SA_RECURSED: 1328 #ifdef WITNESS 1329 witness_assert(&sx->lock_object, what, file, line); 1330 #else 1331 /* 1332 * If some other thread has an exclusive lock or we 1333 * have one and are asserting a shared lock, fail. 1334 * Also, if no one has a lock at all, fail. 1335 */ 1336 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1337 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1338 sx_xholder(sx) != curthread))) 1339 panic("Lock %s not %slocked @ %s:%d\n", 1340 sx->lock_object.lo_name, slocked ? "share " : "", 1341 file, line); 1342 1343 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1344 if (sx_recursed(sx)) { 1345 if (what & SA_NOTRECURSED) 1346 panic("Lock %s recursed @ %s:%d\n", 1347 sx->lock_object.lo_name, file, 1348 line); 1349 } else if (what & SA_RECURSED) 1350 panic("Lock %s not recursed @ %s:%d\n", 1351 sx->lock_object.lo_name, file, line); 1352 } 1353 #endif 1354 break; 1355 case SA_XLOCKED: 1356 case SA_XLOCKED | SA_NOTRECURSED: 1357 case SA_XLOCKED | SA_RECURSED: 1358 if (sx_xholder(sx) != curthread) 1359 panic("Lock %s not exclusively locked @ %s:%d\n", 1360 sx->lock_object.lo_name, file, line); 1361 if (sx_recursed(sx)) { 1362 if (what & SA_NOTRECURSED) 1363 panic("Lock %s recursed @ %s:%d\n", 1364 sx->lock_object.lo_name, file, line); 1365 } else if (what & SA_RECURSED) 1366 panic("Lock %s not recursed @ %s:%d\n", 1367 sx->lock_object.lo_name, file, line); 1368 break; 1369 case SA_UNLOCKED: 1370 #ifdef WITNESS 1371 witness_assert(&sx->lock_object, what, file, line); 1372 #else 1373 /* 1374 * If we hold an exclusve lock fail. We can't 1375 * reliably check to see if we hold a shared lock or 1376 * not. 1377 */ 1378 if (sx_xholder(sx) == curthread) 1379 panic("Lock %s exclusively locked @ %s:%d\n", 1380 sx->lock_object.lo_name, file, line); 1381 #endif 1382 break; 1383 default: 1384 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1385 line); 1386 } 1387 } 1388 #endif /* INVARIANT_SUPPORT */ 1389 1390 #ifdef DDB 1391 static void 1392 db_show_sx(const struct lock_object *lock) 1393 { 1394 struct thread *td; 1395 const struct sx *sx; 1396 1397 sx = (const struct sx *)lock; 1398 1399 db_printf(" state: "); 1400 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1401 db_printf("UNLOCKED\n"); 1402 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1403 db_printf("DESTROYED\n"); 1404 return; 1405 } else if (sx->sx_lock & SX_LOCK_SHARED) 1406 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1407 else { 1408 td = sx_xholder(sx); 1409 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1410 td->td_tid, td->td_proc->p_pid, td->td_name); 1411 if (sx_recursed(sx)) 1412 db_printf(" recursed: %d\n", sx->sx_recurse); 1413 } 1414 1415 db_printf(" waiters: "); 1416 switch(sx->sx_lock & 1417 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1418 case SX_LOCK_SHARED_WAITERS: 1419 db_printf("shared\n"); 1420 break; 1421 case SX_LOCK_EXCLUSIVE_WAITERS: 1422 db_printf("exclusive\n"); 1423 break; 1424 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1425 db_printf("exclusive and shared\n"); 1426 break; 1427 default: 1428 db_printf("none\n"); 1429 } 1430 } 1431 1432 /* 1433 * Check to see if a thread that is blocked on a sleep queue is actually 1434 * blocked on an sx lock. If so, output some details and return true. 1435 * If the lock has an exclusive owner, return that in *ownerp. 1436 */ 1437 int 1438 sx_chain(struct thread *td, struct thread **ownerp) 1439 { 1440 struct sx *sx; 1441 1442 /* 1443 * Check to see if this thread is blocked on an sx lock. 1444 * First, we check the lock class. If that is ok, then we 1445 * compare the lock name against the wait message. 1446 */ 1447 sx = td->td_wchan; 1448 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1449 sx->lock_object.lo_name != td->td_wmesg) 1450 return (0); 1451 1452 /* We think we have an sx lock, so output some details. */ 1453 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1454 *ownerp = sx_xholder(sx); 1455 if (sx->sx_lock & SX_LOCK_SHARED) 1456 db_printf("SLOCK (count %ju)\n", 1457 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1458 else 1459 db_printf("XLOCK\n"); 1460 return (1); 1461 } 1462 #endif
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