kern_sx.c revision 192853
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_adaptive_sx.h" 40#include "opt_ddb.h" 41#include "opt_kdtrace.h" 42 43#include <sys/cdefs.h> 44__FBSDID("$FreeBSD: head/sys/kern/kern_sx.c 192853 2009-05-26 20:28:22Z sson $"); 45 46#include <sys/param.h> 47#include <sys/ktr.h> 48#include <sys/lock.h> 49#include <sys/mutex.h> 50#include <sys/proc.h> 51#include <sys/sleepqueue.h> 52#include <sys/sx.h> 53#include <sys/systm.h> 54 55#ifdef ADAPTIVE_SX 56#include <machine/cpu.h> 57#endif 58 59#ifdef DDB 60#include <ddb/ddb.h> 61#endif 62 63#if !defined(SMP) && defined(ADAPTIVE_SX) 64#error "You must have SMP to enable the ADAPTIVE_SX option" 65#endif 66 67CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) == 68 (SX_ADAPTIVESPIN | SX_RECURSE)); 69 70/* Handy macros for sleep queues. */ 71#define SQ_EXCLUSIVE_QUEUE 0 72#define SQ_SHARED_QUEUE 1 73 74/* 75 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 76 * drop Giant anytime we have to sleep or if we adaptively spin. 77 */ 78#define GIANT_DECLARE \ 79 int _giantcnt = 0; \ 80 WITNESS_SAVE_DECL(Giant) \ 81 82#define GIANT_SAVE() do { \ 83 if (mtx_owned(&Giant)) { \ 84 WITNESS_SAVE(&Giant.lock_object, Giant); \ 85 while (mtx_owned(&Giant)) { \ 86 _giantcnt++; \ 87 mtx_unlock(&Giant); \ 88 } \ 89 } \ 90} while (0) 91 92#define GIANT_RESTORE() do { \ 93 if (_giantcnt > 0) { \ 94 mtx_assert(&Giant, MA_NOTOWNED); \ 95 while (_giantcnt--) \ 96 mtx_lock(&Giant); \ 97 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 98 } \ 99} while (0) 100 101/* 102 * Returns true if an exclusive lock is recursed. It assumes 103 * curthread currently has an exclusive lock. 104 */ 105#define sx_recurse lock_object.lo_data 106#define sx_recursed(sx) ((sx)->sx_recurse != 0) 107 108static void assert_sx(struct lock_object *lock, int what); 109#ifdef DDB 110static void db_show_sx(struct lock_object *lock); 111#endif 112static void lock_sx(struct lock_object *lock, int how); 113#ifdef KDTRACE_HOOKS 114static int owner_sx(struct lock_object *lock, struct thread **owner); 115#endif 116static int unlock_sx(struct lock_object *lock); 117 118struct lock_class lock_class_sx = { 119 .lc_name = "sx", 120 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 121 .lc_assert = assert_sx, 122#ifdef DDB 123 .lc_ddb_show = db_show_sx, 124#endif 125 .lc_lock = lock_sx, 126 .lc_unlock = unlock_sx, 127#ifdef KDTRACE_HOOKS 128 .lc_owner = owner_sx, 129#endif 130}; 131 132#ifndef INVARIANTS 133#define _sx_assert(sx, what, file, line) 134#endif 135 136void 137assert_sx(struct lock_object *lock, int what) 138{ 139 140 sx_assert((struct sx *)lock, what); 141} 142 143void 144lock_sx(struct lock_object *lock, int how) 145{ 146 struct sx *sx; 147 148 sx = (struct sx *)lock; 149 if (how) 150 sx_xlock(sx); 151 else 152 sx_slock(sx); 153} 154 155int 156unlock_sx(struct lock_object *lock) 157{ 158 struct sx *sx; 159 160 sx = (struct sx *)lock; 161 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 162 if (sx_xlocked(sx)) { 163 sx_xunlock(sx); 164 return (1); 165 } else { 166 sx_sunlock(sx); 167 return (0); 168 } 169} 170 171#ifdef KDTRACE_HOOKS 172int 173owner_sx(struct lock_object *lock, struct thread **owner) 174{ 175 struct sx *sx = (struct sx *)lock; 176 uintptr_t x = sx->sx_lock; 177 178 *owner = (struct thread *)SX_OWNER(x); 179 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 180 (*owner != NULL)); 181} 182#endif 183 184void 185sx_sysinit(void *arg) 186{ 187 struct sx_args *sargs = arg; 188 189 sx_init(sargs->sa_sx, sargs->sa_desc); 190} 191 192void 193sx_init_flags(struct sx *sx, const char *description, int opts) 194{ 195 int flags; 196 197 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 198 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0); 199 200 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE; 201 if (opts & SX_DUPOK) 202 flags |= LO_DUPOK; 203 if (opts & SX_NOPROFILE) 204 flags |= LO_NOPROFILE; 205 if (!(opts & SX_NOWITNESS)) 206 flags |= LO_WITNESS; 207 if (opts & SX_QUIET) 208 flags |= LO_QUIET; 209 210 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE); 211 sx->sx_lock = SX_LOCK_UNLOCKED; 212 sx->sx_recurse = 0; 213 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 214} 215 216void 217sx_destroy(struct sx *sx) 218{ 219 220 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 221 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 222 sx->sx_lock = SX_LOCK_DESTROYED; 223 lock_destroy(&sx->lock_object); 224} 225 226int 227_sx_slock(struct sx *sx, int opts, const char *file, int line) 228{ 229 int error = 0; 230 231 MPASS(curthread != NULL); 232 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 233 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 234 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 235 error = __sx_slock(sx, opts, file, line); 236 if (!error) { 237 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 238 WITNESS_LOCK(&sx->lock_object, 0, file, line); 239 curthread->td_locks++; 240 } 241 242 return (error); 243} 244 245int 246_sx_try_slock(struct sx *sx, const char *file, int line) 247{ 248 uintptr_t x; 249 250 for (;;) { 251 x = sx->sx_lock; 252 KASSERT(x != SX_LOCK_DESTROYED, 253 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 254 if (!(x & SX_LOCK_SHARED)) 255 break; 256 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) { 257 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 258 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 259 curthread->td_locks++; 260 return (1); 261 } 262 } 263 264 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 265 return (0); 266} 267 268int 269_sx_xlock(struct sx *sx, int opts, const char *file, int line) 270{ 271 int error = 0; 272 273 MPASS(curthread != NULL); 274 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 275 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 276 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 277 line, NULL); 278 error = __sx_xlock(sx, curthread, opts, file, line); 279 if (!error) { 280 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 281 file, line); 282 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 283 curthread->td_locks++; 284 } 285 286 return (error); 287} 288 289int 290_sx_try_xlock(struct sx *sx, const char *file, int line) 291{ 292 int rval; 293 294 MPASS(curthread != NULL); 295 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 296 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 297 298 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) { 299 sx->sx_recurse++; 300 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 301 rval = 1; 302 } else 303 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 304 (uintptr_t)curthread); 305 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 306 if (rval) { 307 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 308 file, line); 309 curthread->td_locks++; 310 } 311 312 return (rval); 313} 314 315void 316_sx_sunlock(struct sx *sx, const char *file, int line) 317{ 318 319 MPASS(curthread != NULL); 320 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 321 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 322 _sx_assert(sx, SA_SLOCKED, file, line); 323 curthread->td_locks--; 324 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 325 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 326 __sx_sunlock(sx, file, line); 327 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx); 328} 329 330void 331_sx_xunlock(struct sx *sx, const char *file, int line) 332{ 333 334 MPASS(curthread != NULL); 335 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 336 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 337 _sx_assert(sx, SA_XLOCKED, file, line); 338 curthread->td_locks--; 339 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 340 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 341 line); 342 if (!sx_recursed(sx)) 343 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx); 344 __sx_xunlock(sx, curthread, file, line); 345} 346 347/* 348 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 349 * This will only succeed if this thread holds a single shared lock. 350 * Return 1 if if the upgrade succeed, 0 otherwise. 351 */ 352int 353_sx_try_upgrade(struct sx *sx, const char *file, int line) 354{ 355 uintptr_t x; 356 int success; 357 358 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 359 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 360 _sx_assert(sx, SA_SLOCKED, file, line); 361 362 /* 363 * Try to switch from one shared lock to an exclusive lock. We need 364 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 365 * we will wake up the exclusive waiters when we drop the lock. 366 */ 367 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 368 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 369 (uintptr_t)curthread | x); 370 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 371 if (success) { 372 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 373 file, line); 374 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx); 375 } 376 return (success); 377} 378 379/* 380 * Downgrade an unrecursed exclusive lock into a single shared lock. 381 */ 382void 383_sx_downgrade(struct sx *sx, const char *file, int line) 384{ 385 uintptr_t x; 386 int wakeup_swapper; 387 388 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 389 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 390 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 391#ifndef INVARIANTS 392 if (sx_recursed(sx)) 393 panic("downgrade of a recursed lock"); 394#endif 395 396 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 397 398 /* 399 * Try to switch from an exclusive lock with no shared waiters 400 * to one sharer with no shared waiters. If there are 401 * exclusive waiters, we don't need to lock the sleep queue so 402 * long as we preserve the flag. We do one quick try and if 403 * that fails we grab the sleepq lock to keep the flags from 404 * changing and do it the slow way. 405 * 406 * We have to lock the sleep queue if there are shared waiters 407 * so we can wake them up. 408 */ 409 x = sx->sx_lock; 410 if (!(x & SX_LOCK_SHARED_WAITERS) && 411 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 412 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 413 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 414 return; 415 } 416 417 /* 418 * Lock the sleep queue so we can read the waiters bits 419 * without any races and wakeup any shared waiters. 420 */ 421 sleepq_lock(&sx->lock_object); 422 423 /* 424 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 425 * shared lock. If there are any shared waiters, wake them up. 426 */ 427 wakeup_swapper = 0; 428 x = sx->sx_lock; 429 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 430 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 431 if (x & SX_LOCK_SHARED_WAITERS) 432 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 433 0, SQ_SHARED_QUEUE); 434 sleepq_release(&sx->lock_object); 435 436 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 437 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx); 438 439 if (wakeup_swapper) 440 kick_proc0(); 441} 442 443/* 444 * This function represents the so-called 'hard case' for sx_xlock 445 * operation. All 'easy case' failures are redirected to this. Note 446 * that ideally this would be a static function, but it needs to be 447 * accessible from at least sx.h. 448 */ 449int 450_sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 451 int line) 452{ 453 GIANT_DECLARE; 454#ifdef ADAPTIVE_SX 455 volatile struct thread *owner; 456#endif 457 uintptr_t x; 458#ifdef LOCK_PROFILING 459 uint64_t waittime = 0; 460 int contested = 0; 461#endif 462 int error = 0; 463#ifdef KDTRACE_HOOKS 464 uint64_t spin_cnt = 0; 465 uint64_t sleep_cnt = 0; 466 int64_t sleep_time = 0; 467#endif 468 469 /* If we already hold an exclusive lock, then recurse. */ 470 if (sx_xlocked(sx)) { 471 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0, 472 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 473 sx->lock_object.lo_name, file, line)); 474 sx->sx_recurse++; 475 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 476 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 477 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 478 return (0); 479 } 480 481 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 482 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 483 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 484 485 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 486#ifdef KDTRACE_HOOKS 487 spin_cnt++; 488#endif 489 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 490 &waittime); 491#ifdef ADAPTIVE_SX 492 /* 493 * If the lock is write locked and the owner is 494 * running on another CPU, spin until the owner stops 495 * running or the state of the lock changes. 496 */ 497 x = sx->sx_lock; 498 if (!(x & SX_LOCK_SHARED) && 499 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 500 x = SX_OWNER(x); 501 owner = (struct thread *)x; 502 if (TD_IS_RUNNING(owner)) { 503 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 504 CTR3(KTR_LOCK, 505 "%s: spinning on %p held by %p", 506 __func__, sx, owner); 507 GIANT_SAVE(); 508 while (SX_OWNER(sx->sx_lock) == x && 509 TD_IS_RUNNING(owner)) { 510 cpu_spinwait(); 511#ifdef KDTRACE_HOOKS 512 spin_cnt++; 513#endif 514 } 515 continue; 516 } 517 } 518#endif 519 520 sleepq_lock(&sx->lock_object); 521 x = sx->sx_lock; 522 523 /* 524 * If the lock was released while spinning on the 525 * sleep queue chain lock, try again. 526 */ 527 if (x == SX_LOCK_UNLOCKED) { 528 sleepq_release(&sx->lock_object); 529 continue; 530 } 531 532#ifdef ADAPTIVE_SX 533 /* 534 * The current lock owner might have started executing 535 * on another CPU (or the lock could have changed 536 * owners) while we were waiting on the sleep queue 537 * chain lock. If so, drop the sleep queue lock and try 538 * again. 539 */ 540 if (!(x & SX_LOCK_SHARED) && 541 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 542 owner = (struct thread *)SX_OWNER(x); 543 if (TD_IS_RUNNING(owner)) { 544 sleepq_release(&sx->lock_object); 545 continue; 546 } 547 } 548#endif 549 550 /* 551 * If an exclusive lock was released with both shared 552 * and exclusive waiters and a shared waiter hasn't 553 * woken up and acquired the lock yet, sx_lock will be 554 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 555 * If we see that value, try to acquire it once. Note 556 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 557 * as there are other exclusive waiters still. If we 558 * fail, restart the loop. 559 */ 560 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 561 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 562 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 563 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 564 sleepq_release(&sx->lock_object); 565 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 566 __func__, sx); 567 break; 568 } 569 sleepq_release(&sx->lock_object); 570 continue; 571 } 572 573 /* 574 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 575 * than loop back and retry. 576 */ 577 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 578 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 579 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 580 sleepq_release(&sx->lock_object); 581 continue; 582 } 583 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 584 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 585 __func__, sx); 586 } 587 588 /* 589 * Since we have been unable to acquire the exclusive 590 * lock and the exclusive waiters flag is set, we have 591 * to sleep. 592 */ 593 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 594 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 595 __func__, sx); 596 597#ifdef KDTRACE_HOOKS 598 sleep_time -= lockstat_nsecs(); 599#endif 600 GIANT_SAVE(); 601 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 602 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 603 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 604 if (!(opts & SX_INTERRUPTIBLE)) 605 sleepq_wait(&sx->lock_object, 0); 606 else 607 error = sleepq_wait_sig(&sx->lock_object, 0); 608#ifdef KDTRACE_HOOKS 609 sleep_time += lockstat_nsecs(); 610 sleep_cnt++; 611#endif 612 if (error) { 613 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 614 CTR2(KTR_LOCK, 615 "%s: interruptible sleep by %p suspended by signal", 616 __func__, sx); 617 break; 618 } 619 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 620 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 621 __func__, sx); 622 } 623 624 GIANT_RESTORE(); 625 if (!error) 626 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx, 627 contested, waittime, file, line); 628#ifdef KDTRACE_HOOKS 629 if (sleep_time) 630 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time); 631 if (spin_cnt > sleep_cnt) 632 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt)); 633#endif 634 return (error); 635} 636 637/* 638 * This function represents the so-called 'hard case' for sx_xunlock 639 * operation. All 'easy case' failures are redirected to this. Note 640 * that ideally this would be a static function, but it needs to be 641 * accessible from at least sx.h. 642 */ 643void 644_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 645{ 646 uintptr_t x; 647 int queue, wakeup_swapper; 648 649 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 650 651 /* If the lock is recursed, then unrecurse one level. */ 652 if (sx_xlocked(sx) && sx_recursed(sx)) { 653 if ((--sx->sx_recurse) == 0) 654 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 655 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 656 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 657 return; 658 } 659 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 660 SX_LOCK_EXCLUSIVE_WAITERS)); 661 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 662 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 663 664 sleepq_lock(&sx->lock_object); 665 x = SX_LOCK_UNLOCKED; 666 667 /* 668 * The wake up algorithm here is quite simple and probably not 669 * ideal. It gives precedence to shared waiters if they are 670 * present. For this condition, we have to preserve the 671 * state of the exclusive waiters flag. 672 */ 673 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) { 674 queue = SQ_SHARED_QUEUE; 675 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 676 } else 677 queue = SQ_EXCLUSIVE_QUEUE; 678 679 /* Wake up all the waiters for the specific queue. */ 680 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 681 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 682 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 683 "exclusive"); 684 atomic_store_rel_ptr(&sx->sx_lock, x); 685 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 686 queue); 687 sleepq_release(&sx->lock_object); 688 if (wakeup_swapper) 689 kick_proc0(); 690} 691 692/* 693 * This function represents the so-called 'hard case' for sx_slock 694 * operation. All 'easy case' failures are redirected to this. Note 695 * that ideally this would be a static function, but it needs to be 696 * accessible from at least sx.h. 697 */ 698int 699_sx_slock_hard(struct sx *sx, int opts, const char *file, int line) 700{ 701 GIANT_DECLARE; 702#ifdef ADAPTIVE_SX 703 volatile struct thread *owner; 704#endif 705#ifdef LOCK_PROFILING 706 uint64_t waittime = 0; 707 int contested = 0; 708#endif 709 uintptr_t x; 710 int error = 0; 711#ifdef KDTRACE_HOOKS 712 uint64_t spin_cnt = 0; 713 uint64_t sleep_cnt = 0; 714 int64_t sleep_time = 0; 715#endif 716 717 /* 718 * As with rwlocks, we don't make any attempt to try to block 719 * shared locks once there is an exclusive waiter. 720 */ 721 for (;;) { 722#ifdef KDTRACE_HOOKS 723 spin_cnt++; 724#endif 725 x = sx->sx_lock; 726 727 /* 728 * If no other thread has an exclusive lock then try to bump up 729 * the count of sharers. Since we have to preserve the state 730 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 731 * shared lock loop back and retry. 732 */ 733 if (x & SX_LOCK_SHARED) { 734 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 735 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 736 x + SX_ONE_SHARER)) { 737 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 738 CTR4(KTR_LOCK, 739 "%s: %p succeed %p -> %p", __func__, 740 sx, (void *)x, 741 (void *)(x + SX_ONE_SHARER)); 742 break; 743 } 744 continue; 745 } 746 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 747 &waittime); 748 749#ifdef ADAPTIVE_SX 750 /* 751 * If the owner is running on another CPU, spin until 752 * the owner stops running or the state of the lock 753 * changes. 754 */ 755 if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) { 756 x = SX_OWNER(x); 757 owner = (struct thread *)x; 758 if (TD_IS_RUNNING(owner)) { 759 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 760 CTR3(KTR_LOCK, 761 "%s: spinning on %p held by %p", 762 __func__, sx, owner); 763 GIANT_SAVE(); 764 while (SX_OWNER(sx->sx_lock) == x && 765 TD_IS_RUNNING(owner)) { 766#ifdef KDTRACE_HOOKS 767 spin_cnt++; 768#endif 769 cpu_spinwait(); 770 } 771 continue; 772 } 773 } 774#endif 775 776 /* 777 * Some other thread already has an exclusive lock, so 778 * start the process of blocking. 779 */ 780 sleepq_lock(&sx->lock_object); 781 x = sx->sx_lock; 782 783 /* 784 * The lock could have been released while we spun. 785 * In this case loop back and retry. 786 */ 787 if (x & SX_LOCK_SHARED) { 788 sleepq_release(&sx->lock_object); 789 continue; 790 } 791 792#ifdef ADAPTIVE_SX 793 /* 794 * If the owner is running on another CPU, spin until 795 * the owner stops running or the state of the lock 796 * changes. 797 */ 798 if (!(x & SX_LOCK_SHARED) && 799 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 800 owner = (struct thread *)SX_OWNER(x); 801 if (TD_IS_RUNNING(owner)) { 802 sleepq_release(&sx->lock_object); 803 continue; 804 } 805 } 806#endif 807 808 /* 809 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 810 * fail to set it drop the sleep queue lock and loop 811 * back. 812 */ 813 if (!(x & SX_LOCK_SHARED_WAITERS)) { 814 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 815 x | SX_LOCK_SHARED_WAITERS)) { 816 sleepq_release(&sx->lock_object); 817 continue; 818 } 819 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 820 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 821 __func__, sx); 822 } 823 824 /* 825 * Since we have been unable to acquire the shared lock, 826 * we have to sleep. 827 */ 828 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 829 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 830 __func__, sx); 831 832#ifdef KDTRACE_HOOKS 833 sleep_time -= lockstat_nsecs(); 834#endif 835 GIANT_SAVE(); 836 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 837 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 838 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 839 if (!(opts & SX_INTERRUPTIBLE)) 840 sleepq_wait(&sx->lock_object, 0); 841 else 842 error = sleepq_wait_sig(&sx->lock_object, 0); 843#ifdef KDTRACE_HOOKS 844 sleep_time += lockstat_nsecs(); 845 sleep_cnt++; 846#endif 847 if (error) { 848 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 849 CTR2(KTR_LOCK, 850 "%s: interruptible sleep by %p suspended by signal", 851 __func__, sx); 852 break; 853 } 854 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 855 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 856 __func__, sx); 857 } 858 if (error == 0) 859 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 860 contested, waittime, file, line); 861#ifdef KDTRACE_HOOKS 862 if (sleep_time) 863 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time); 864 if (spin_cnt > sleep_cnt) 865 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt)); 866#endif 867 GIANT_RESTORE(); 868 return (error); 869} 870 871/* 872 * This function represents the so-called 'hard case' for sx_sunlock 873 * operation. All 'easy case' failures are redirected to this. Note 874 * that ideally this would be a static function, but it needs to be 875 * accessible from at least sx.h. 876 */ 877void 878_sx_sunlock_hard(struct sx *sx, const char *file, int line) 879{ 880 uintptr_t x; 881 int wakeup_swapper; 882 883 for (;;) { 884 x = sx->sx_lock; 885 886 /* 887 * We should never have sharers while at least one thread 888 * holds a shared lock. 889 */ 890 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 891 ("%s: waiting sharers", __func__)); 892 893 /* 894 * See if there is more than one shared lock held. If 895 * so, just drop one and return. 896 */ 897 if (SX_SHARERS(x) > 1) { 898 if (atomic_cmpset_ptr(&sx->sx_lock, x, 899 x - SX_ONE_SHARER)) { 900 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 901 CTR4(KTR_LOCK, 902 "%s: %p succeeded %p -> %p", 903 __func__, sx, (void *)x, 904 (void *)(x - SX_ONE_SHARER)); 905 break; 906 } 907 continue; 908 } 909 910 /* 911 * If there aren't any waiters for an exclusive lock, 912 * then try to drop it quickly. 913 */ 914 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 915 MPASS(x == SX_SHARERS_LOCK(1)); 916 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1), 917 SX_LOCK_UNLOCKED)) { 918 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 919 CTR2(KTR_LOCK, "%s: %p last succeeded", 920 __func__, sx); 921 break; 922 } 923 continue; 924 } 925 926 /* 927 * At this point, there should just be one sharer with 928 * exclusive waiters. 929 */ 930 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 931 932 sleepq_lock(&sx->lock_object); 933 934 /* 935 * Wake up semantic here is quite simple: 936 * Just wake up all the exclusive waiters. 937 * Note that the state of the lock could have changed, 938 * so if it fails loop back and retry. 939 */ 940 if (!atomic_cmpset_ptr(&sx->sx_lock, 941 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 942 SX_LOCK_UNLOCKED)) { 943 sleepq_release(&sx->lock_object); 944 continue; 945 } 946 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 947 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 948 "exclusive queue", __func__, sx); 949 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 950 0, SQ_EXCLUSIVE_QUEUE); 951 sleepq_release(&sx->lock_object); 952 if (wakeup_swapper) 953 kick_proc0(); 954 break; 955 } 956} 957 958#ifdef INVARIANT_SUPPORT 959#ifndef INVARIANTS 960#undef _sx_assert 961#endif 962 963/* 964 * In the non-WITNESS case, sx_assert() can only detect that at least 965 * *some* thread owns an slock, but it cannot guarantee that *this* 966 * thread owns an slock. 967 */ 968void 969_sx_assert(struct sx *sx, int what, const char *file, int line) 970{ 971#ifndef WITNESS 972 int slocked = 0; 973#endif 974 975 if (panicstr != NULL) 976 return; 977 switch (what) { 978 case SA_SLOCKED: 979 case SA_SLOCKED | SA_NOTRECURSED: 980 case SA_SLOCKED | SA_RECURSED: 981#ifndef WITNESS 982 slocked = 1; 983 /* FALLTHROUGH */ 984#endif 985 case SA_LOCKED: 986 case SA_LOCKED | SA_NOTRECURSED: 987 case SA_LOCKED | SA_RECURSED: 988#ifdef WITNESS 989 witness_assert(&sx->lock_object, what, file, line); 990#else 991 /* 992 * If some other thread has an exclusive lock or we 993 * have one and are asserting a shared lock, fail. 994 * Also, if no one has a lock at all, fail. 995 */ 996 if (sx->sx_lock == SX_LOCK_UNLOCKED || 997 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 998 sx_xholder(sx) != curthread))) 999 panic("Lock %s not %slocked @ %s:%d\n", 1000 sx->lock_object.lo_name, slocked ? "share " : "", 1001 file, line); 1002 1003 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1004 if (sx_recursed(sx)) { 1005 if (what & SA_NOTRECURSED) 1006 panic("Lock %s recursed @ %s:%d\n", 1007 sx->lock_object.lo_name, file, 1008 line); 1009 } else if (what & SA_RECURSED) 1010 panic("Lock %s not recursed @ %s:%d\n", 1011 sx->lock_object.lo_name, file, line); 1012 } 1013#endif 1014 break; 1015 case SA_XLOCKED: 1016 case SA_XLOCKED | SA_NOTRECURSED: 1017 case SA_XLOCKED | SA_RECURSED: 1018 if (sx_xholder(sx) != curthread) 1019 panic("Lock %s not exclusively locked @ %s:%d\n", 1020 sx->lock_object.lo_name, file, line); 1021 if (sx_recursed(sx)) { 1022 if (what & SA_NOTRECURSED) 1023 panic("Lock %s recursed @ %s:%d\n", 1024 sx->lock_object.lo_name, file, line); 1025 } else if (what & SA_RECURSED) 1026 panic("Lock %s not recursed @ %s:%d\n", 1027 sx->lock_object.lo_name, file, line); 1028 break; 1029 case SA_UNLOCKED: 1030#ifdef WITNESS 1031 witness_assert(&sx->lock_object, what, file, line); 1032#else 1033 /* 1034 * If we hold an exclusve lock fail. We can't 1035 * reliably check to see if we hold a shared lock or 1036 * not. 1037 */ 1038 if (sx_xholder(sx) == curthread) 1039 panic("Lock %s exclusively locked @ %s:%d\n", 1040 sx->lock_object.lo_name, file, line); 1041#endif 1042 break; 1043 default: 1044 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1045 line); 1046 } 1047} 1048#endif /* INVARIANT_SUPPORT */ 1049 1050#ifdef DDB 1051static void 1052db_show_sx(struct lock_object *lock) 1053{ 1054 struct thread *td; 1055 struct sx *sx; 1056 1057 sx = (struct sx *)lock; 1058 1059 db_printf(" state: "); 1060 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1061 db_printf("UNLOCKED\n"); 1062 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1063 db_printf("DESTROYED\n"); 1064 return; 1065 } else if (sx->sx_lock & SX_LOCK_SHARED) 1066 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1067 else { 1068 td = sx_xholder(sx); 1069 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1070 td->td_tid, td->td_proc->p_pid, td->td_name); 1071 if (sx_recursed(sx)) 1072 db_printf(" recursed: %d\n", sx->sx_recurse); 1073 } 1074 1075 db_printf(" waiters: "); 1076 switch(sx->sx_lock & 1077 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1078 case SX_LOCK_SHARED_WAITERS: 1079 db_printf("shared\n"); 1080 break; 1081 case SX_LOCK_EXCLUSIVE_WAITERS: 1082 db_printf("exclusive\n"); 1083 break; 1084 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1085 db_printf("exclusive and shared\n"); 1086 break; 1087 default: 1088 db_printf("none\n"); 1089 } 1090} 1091 1092/* 1093 * Check to see if a thread that is blocked on a sleep queue is actually 1094 * blocked on an sx lock. If so, output some details and return true. 1095 * If the lock has an exclusive owner, return that in *ownerp. 1096 */ 1097int 1098sx_chain(struct thread *td, struct thread **ownerp) 1099{ 1100 struct sx *sx; 1101 1102 /* 1103 * Check to see if this thread is blocked on an sx lock. 1104 * First, we check the lock class. If that is ok, then we 1105 * compare the lock name against the wait message. 1106 */ 1107 sx = td->td_wchan; 1108 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1109 sx->lock_object.lo_name != td->td_wmesg) 1110 return (0); 1111 1112 /* We think we have an sx lock, so output some details. */ 1113 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1114 *ownerp = sx_xholder(sx); 1115 if (sx->sx_lock & SX_LOCK_SHARED) 1116 db_printf("SLOCK (count %ju)\n", 1117 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1118 else 1119 db_printf("XLOCK\n"); 1120 return (1); 1121} 1122#endif 1123