kern_sx.c revision 169774
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 42#include <sys/cdefs.h> 43__FBSDID("$FreeBSD: head/sys/kern/kern_sx.c 169774 2007-05-19 18:34:24Z jhb $"); 44 45#include <sys/param.h> 46#include <sys/ktr.h> 47#include <sys/lock.h> 48#include <sys/lock_profile.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 67/* Handy macros for sleep queues. */ 68#define SQ_EXCLUSIVE_QUEUE 0 69#define SQ_SHARED_QUEUE 1 70 71/* 72 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 73 * drop Giant anytime we have to sleep or if we adaptively spin. 74 */ 75#define GIANT_DECLARE \ 76 int _giantcnt = 0; \ 77 WITNESS_SAVE_DECL(Giant) \ 78 79#define GIANT_SAVE() do { \ 80 if (mtx_owned(&Giant)) { \ 81 WITNESS_SAVE(&Giant.lock_object, Giant); \ 82 while (mtx_owned(&Giant)) { \ 83 _giantcnt++; \ 84 mtx_unlock(&Giant); \ 85 } \ 86 } \ 87} while (0) 88 89#define GIANT_RESTORE() do { \ 90 if (_giantcnt > 0) { \ 91 mtx_assert(&Giant, MA_NOTOWNED); \ 92 while (_giantcnt--) \ 93 mtx_lock(&Giant); \ 94 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 95 } \ 96} while (0) 97 98/* 99 * Returns true if an exclusive lock is recursed. It assumes 100 * curthread currently has an exclusive lock. 101 */ 102#define sx_recursed(sx) ((sx)->sx_recurse != 0) 103 104/* 105 * Return a pointer to the owning thread if the lock is exclusively 106 * locked. 107 */ 108#define sx_xholder(sx) \ 109 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \ 110 (struct thread *)SX_OWNER((sx)->sx_lock)) 111 112#ifdef DDB 113static void db_show_sx(struct lock_object *lock); 114#endif 115static void lock_sx(struct lock_object *lock, int how); 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#ifdef DDB 122 .lc_ddb_show = db_show_sx, 123#endif 124 .lc_lock = lock_sx, 125 .lc_unlock = unlock_sx, 126}; 127 128#ifndef INVARIANTS 129#define _sx_assert(sx, what, file, line) 130#endif 131 132void 133lock_sx(struct lock_object *lock, int how) 134{ 135 struct sx *sx; 136 137 sx = (struct sx *)lock; 138 if (how) 139 sx_xlock(sx); 140 else 141 sx_slock(sx); 142} 143 144int 145unlock_sx(struct lock_object *lock) 146{ 147 struct sx *sx; 148 149 sx = (struct sx *)lock; 150 sx_assert(sx, SX_LOCKED | SX_NOTRECURSED); 151 if (sx_xlocked(sx)) { 152 sx_xunlock(sx); 153 return (1); 154 } else { 155 sx_sunlock(sx); 156 return (0); 157 } 158} 159 160void 161sx_sysinit(void *arg) 162{ 163 struct sx_args *sargs = arg; 164 165 sx_init(sargs->sa_sx, sargs->sa_desc); 166} 167 168void 169sx_init_flags(struct sx *sx, const char *description, int opts) 170{ 171 int flags; 172 173 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 174 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0); 175 176 flags = LO_SLEEPABLE | LO_UPGRADABLE | LO_RECURSABLE; 177 if (opts & SX_DUPOK) 178 flags |= LO_DUPOK; 179 if (opts & SX_NOPROFILE) 180 flags |= LO_NOPROFILE; 181 if (!(opts & SX_NOWITNESS)) 182 flags |= LO_WITNESS; 183 if (opts & SX_QUIET) 184 flags |= LO_QUIET; 185 186 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE); 187 sx->sx_lock = SX_LOCK_UNLOCKED; 188 sx->sx_recurse = 0; 189 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 190} 191 192void 193sx_destroy(struct sx *sx) 194{ 195 196 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 197 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 198 sx->sx_lock = SX_LOCK_DESTROYED; 199 lock_destroy(&sx->lock_object); 200} 201 202void 203_sx_slock(struct sx *sx, const char *file, int line) 204{ 205 206 MPASS(curthread != NULL); 207 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 208 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 209 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line); 210 __sx_slock(sx, file, line); 211 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 212 WITNESS_LOCK(&sx->lock_object, 0, file, line); 213 curthread->td_locks++; 214} 215 216int 217_sx_try_slock(struct sx *sx, const char *file, int line) 218{ 219 uintptr_t x; 220 221 x = sx->sx_lock; 222 KASSERT(x != SX_LOCK_DESTROYED, 223 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 224 if ((x & SX_LOCK_SHARED) && atomic_cmpset_acq_ptr(&sx->sx_lock, x, 225 x + SX_ONE_SHARER)) { 226 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 227 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 228 curthread->td_locks++; 229 return (1); 230 } 231 232 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 233 return (0); 234} 235 236void 237_sx_xlock(struct sx *sx, const char *file, int line) 238{ 239 240 MPASS(curthread != NULL); 241 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 242 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 243 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 244 line); 245 __sx_xlock(sx, curthread, file, line); 246 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, file, line); 247 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 248 curthread->td_locks++; 249} 250 251int 252_sx_try_xlock(struct sx *sx, const char *file, int line) 253{ 254 int rval; 255 256 MPASS(curthread != NULL); 257 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 258 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 259 260 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) { 261 sx->sx_recurse++; 262 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 263 rval = 1; 264 } else 265 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 266 (uintptr_t)curthread); 267 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 268 if (rval) { 269 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 270 file, line); 271 curthread->td_locks++; 272 } 273 274 return (rval); 275} 276 277void 278_sx_sunlock(struct sx *sx, const char *file, int line) 279{ 280 281 MPASS(curthread != NULL); 282 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 283 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 284 _sx_assert(sx, SX_SLOCKED, file, line); 285 curthread->td_locks--; 286 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 287 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 288 if (SX_SHARERS(sx->sx_lock) == 0) 289 lock_profile_release_lock(&sx->lock_object); 290 __sx_sunlock(sx, file, line); 291} 292 293void 294_sx_xunlock(struct sx *sx, const char *file, int line) 295{ 296 297 MPASS(curthread != NULL); 298 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 299 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 300 _sx_assert(sx, SX_XLOCKED, file, line); 301 curthread->td_locks--; 302 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 303 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 304 line); 305 if (!sx_recursed(sx)) 306 lock_profile_release_lock(&sx->lock_object); 307 __sx_xunlock(sx, curthread, file, line); 308} 309 310/* 311 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 312 * This will only succeed if this thread holds a single shared lock. 313 * Return 1 if if the upgrade succeed, 0 otherwise. 314 */ 315int 316_sx_try_upgrade(struct sx *sx, const char *file, int line) 317{ 318 uintptr_t x; 319 int success; 320 321 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 322 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 323 _sx_assert(sx, SX_SLOCKED, file, line); 324 325 /* 326 * Try to switch from one shared lock to an exclusive lock. We need 327 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 328 * we will wake up the exclusive waiters when we drop the lock. 329 */ 330 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 331 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 332 (uintptr_t)curthread | x); 333 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 334 if (success) 335 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 336 file, line); 337 return (success); 338} 339 340/* 341 * Downgrade an unrecursed exclusive lock into a single shared lock. 342 */ 343void 344_sx_downgrade(struct sx *sx, const char *file, int line) 345{ 346 uintptr_t x; 347 348 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 349 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 350 _sx_assert(sx, SX_XLOCKED | SX_NOTRECURSED, file, line); 351#ifndef INVARIANTS 352 if (sx_recursed(sx)) 353 panic("downgrade of a recursed lock"); 354#endif 355 356 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 357 358 /* 359 * Try to switch from an exclusive lock with no shared waiters 360 * to one sharer with no shared waiters. If there are 361 * exclusive waiters, we don't need to lock the sleep queue so 362 * long as we preserve the flag. We do one quick try and if 363 * that fails we grab the sleepq lock to keep the flags from 364 * changing and do it the slow way. 365 * 366 * We have to lock the sleep queue if there are shared waiters 367 * so we can wake them up. 368 */ 369 x = sx->sx_lock; 370 if (!(x & SX_LOCK_SHARED_WAITERS) && 371 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 372 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 373 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 374 return; 375 } 376 377 /* 378 * Lock the sleep queue so we can read the waiters bits 379 * without any races and wakeup any shared waiters. 380 */ 381 sleepq_lock(&sx->lock_object); 382 383 /* 384 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 385 * shared lock. If there are any shared waiters, wake them up. 386 */ 387 x = sx->sx_lock; 388 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 389 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 390 if (x & SX_LOCK_SHARED_WAITERS) 391 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 392 SQ_SHARED_QUEUE); 393 else 394 sleepq_release(&sx->lock_object); 395 396 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 397} 398 399/* 400 * This function represents the so-called 'hard case' for sx_xlock 401 * operation. All 'easy case' failures are redirected to this. Note 402 * that ideally this would be a static function, but it needs to be 403 * accessible from at least sx.h. 404 */ 405void 406_sx_xlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 407{ 408 GIANT_DECLARE; 409#ifdef ADAPTIVE_SX 410 volatile struct thread *owner; 411#endif 412 uintptr_t x; 413 int contested = 0; 414 uint64_t waitstart = 0; 415 416 /* If we already hold an exclusive lock, then recurse. */ 417 if (sx_xlocked(sx)) { 418 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0, 419 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 420 sx->lock_object.lo_name, file, line)); 421 sx->sx_recurse++; 422 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 423 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 424 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 425 return; 426 } 427 lock_profile_obtain_lock_failed(&(sx)->lock_object, 428 &contested, &waitstart); 429 430 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 431 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 432 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 433 434 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 435#ifdef ADAPTIVE_SX 436 /* 437 * If the lock is write locked and the owner is 438 * running on another CPU, spin until the owner stops 439 * running or the state of the lock changes. 440 */ 441 x = sx->sx_lock; 442 if (!(x & SX_LOCK_SHARED) && 443 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 444 x = SX_OWNER(x); 445 owner = (struct thread *)x; 446 if (TD_IS_RUNNING(owner)) { 447 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 448 CTR3(KTR_LOCK, 449 "%s: spinning on %p held by %p", 450 __func__, sx, owner); 451 GIANT_SAVE(); 452 while (SX_OWNER(sx->sx_lock) == x && 453 TD_IS_RUNNING(owner)) 454 cpu_spinwait(); 455 continue; 456 } 457 } 458#endif 459 460 sleepq_lock(&sx->lock_object); 461 x = sx->sx_lock; 462 463 /* 464 * If the lock was released while spinning on the 465 * sleep queue chain lock, try again. 466 */ 467 if (x == SX_LOCK_UNLOCKED) { 468 sleepq_release(&sx->lock_object); 469 continue; 470 } 471 472#ifdef ADAPTIVE_SX 473 /* 474 * The current lock owner might have started executing 475 * on another CPU (or the lock could have changed 476 * owners) while we were waiting on the sleep queue 477 * chain lock. If so, drop the sleep queue lock and try 478 * again. 479 */ 480 if (!(x & SX_LOCK_SHARED) && 481 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 482 owner = (struct thread *)SX_OWNER(x); 483 if (TD_IS_RUNNING(owner)) { 484 sleepq_release(&sx->lock_object); 485 continue; 486 } 487 } 488#endif 489 490 /* 491 * If an exclusive lock was released with both shared 492 * and exclusive waiters and a shared waiter hasn't 493 * woken up and acquired the lock yet, sx_lock will be 494 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 495 * If we see that value, try to acquire it once. Note 496 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 497 * as there are other exclusive waiters still. If we 498 * fail, restart the loop. 499 */ 500 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 501 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 502 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 503 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 504 sleepq_release(&sx->lock_object); 505 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 506 __func__, sx); 507 break; 508 } 509 sleepq_release(&sx->lock_object); 510 continue; 511 } 512 513 /* 514 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 515 * than loop back and retry. 516 */ 517 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 518 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 519 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 520 sleepq_release(&sx->lock_object); 521 continue; 522 } 523 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 524 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 525 __func__, sx); 526 } 527 528 /* 529 * Since we have been unable to acquire the exclusive 530 * lock and the exclusive waiters flag is set, we have 531 * to sleep. 532 */ 533 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 534 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 535 __func__, sx); 536 537 GIANT_SAVE(); 538 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 539 SLEEPQ_SX, SQ_EXCLUSIVE_QUEUE); 540 sleepq_wait(&sx->lock_object); 541 542 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 543 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 544 __func__, sx); 545 } 546 547 GIANT_RESTORE(); 548 lock_profile_obtain_lock_success(&(sx)->lock_object, contested, 549 waitstart, file, line); 550} 551 552/* 553 * This function represents the so-called 'hard case' for sx_xunlock 554 * operation. All 'easy case' failures are redirected to this. Note 555 * that ideally this would be a static function, but it needs to be 556 * accessible from at least sx.h. 557 */ 558void 559_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 560{ 561 uintptr_t x; 562 int queue; 563 564 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 565 566 /* If the lock is recursed, then unrecurse one level. */ 567 if (sx_xlocked(sx) && sx_recursed(sx)) { 568 if ((--sx->sx_recurse) == 0) 569 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 570 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 571 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 572 return; 573 } 574 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 575 SX_LOCK_EXCLUSIVE_WAITERS)); 576 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 577 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 578 579 sleepq_lock(&sx->lock_object); 580 x = SX_LOCK_UNLOCKED; 581 582 /* 583 * The wake up algorithm here is quite simple and probably not 584 * ideal. It gives precedence to shared waiters if they are 585 * present. For this condition, we have to preserve the 586 * state of the exclusive waiters flag. 587 */ 588 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) { 589 queue = SQ_SHARED_QUEUE; 590 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 591 } else 592 queue = SQ_EXCLUSIVE_QUEUE; 593 594 /* Wake up all the waiters for the specific queue. */ 595 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 596 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 597 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 598 "exclusive"); 599 atomic_store_rel_ptr(&sx->sx_lock, x); 600 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, queue); 601} 602 603/* 604 * This function represents the so-called 'hard case' for sx_slock 605 * operation. All 'easy case' failures are redirected to this. Note 606 * that ideally this would be a static function, but it needs to be 607 * accessible from at least sx.h. 608 */ 609void 610_sx_slock_hard(struct sx *sx, const char *file, int line) 611{ 612 GIANT_DECLARE; 613#ifdef ADAPTIVE_SX 614 volatile struct thread *owner; 615#endif 616 uintptr_t x; 617 uint64_t waitstart = 0; 618 int contested = 0; 619 /* 620 * As with rwlocks, we don't make any attempt to try to block 621 * shared locks once there is an exclusive waiter. 622 */ 623 624 for (;;) { 625 x = sx->sx_lock; 626 627 /* 628 * If no other thread has an exclusive lock then try to bump up 629 * the count of sharers. Since we have to preserve the state 630 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 631 * shared lock loop back and retry. 632 */ 633 if (x & SX_LOCK_SHARED) { 634 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 635 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 636 x + SX_ONE_SHARER)) { 637 if (SX_SHARERS(x) == 0) 638 lock_profile_obtain_lock_success( 639 &sx->lock_object, contested, 640 waitstart, file, line); 641 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 642 CTR4(KTR_LOCK, 643 "%s: %p succeed %p -> %p", __func__, 644 sx, (void *)x, 645 (void *)(x + SX_ONE_SHARER)); 646 break; 647 } 648 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 649 &waitstart); 650 651 continue; 652 } 653 654#ifdef ADAPTIVE_SX 655 /* 656 * If the owner is running on another CPU, spin until 657 * the owner stops running or the state of the lock 658 * changes. 659 */ 660 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) { 661 x = SX_OWNER(x); 662 owner = (struct thread *)x; 663 if (TD_IS_RUNNING(owner)) { 664 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 665 &waitstart); 666 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 667 CTR3(KTR_LOCK, 668 "%s: spinning on %p held by %p", 669 __func__, sx, owner); 670 GIANT_SAVE(); 671 while (SX_OWNER(sx->sx_lock) == x && 672 TD_IS_RUNNING(owner)) 673 cpu_spinwait(); 674 continue; 675 } 676 } 677#endif 678 else 679 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 680 &waitstart); 681 682 /* 683 * Some other thread already has an exclusive lock, so 684 * start the process of blocking. 685 */ 686 sleepq_lock(&sx->lock_object); 687 x = sx->sx_lock; 688 689 /* 690 * The lock could have been released while we spun. 691 * In this case loop back and retry. 692 */ 693 if (x & SX_LOCK_SHARED) { 694 sleepq_release(&sx->lock_object); 695 continue; 696 } 697 698#ifdef ADAPTIVE_SX 699 /* 700 * If the owner is running on another CPU, spin until 701 * the owner stops running or the state of the lock 702 * changes. 703 */ 704 if (!(x & SX_LOCK_SHARED) && 705 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 706 owner = (struct thread *)SX_OWNER(x); 707 if (TD_IS_RUNNING(owner)) { 708 sleepq_release(&sx->lock_object); 709 continue; 710 } 711 } 712#endif 713 714 /* 715 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 716 * fail to set it drop the sleep queue lock and loop 717 * back. 718 */ 719 if (!(x & SX_LOCK_SHARED_WAITERS)) { 720 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 721 x | SX_LOCK_SHARED_WAITERS)) { 722 sleepq_release(&sx->lock_object); 723 continue; 724 } 725 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 726 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 727 __func__, sx); 728 } 729 730 /* 731 * Since we have been unable to acquire the shared lock, 732 * we have to sleep. 733 */ 734 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 735 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 736 __func__, sx); 737 738 GIANT_SAVE(); 739 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 740 SLEEPQ_SX, SQ_SHARED_QUEUE); 741 sleepq_wait(&sx->lock_object); 742 743 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 744 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 745 __func__, sx); 746 } 747 748 GIANT_RESTORE(); 749} 750 751/* 752 * This function represents the so-called 'hard case' for sx_sunlock 753 * operation. All 'easy case' failures are redirected to this. Note 754 * that ideally this would be a static function, but it needs to be 755 * accessible from at least sx.h. 756 */ 757void 758_sx_sunlock_hard(struct sx *sx, const char *file, int line) 759{ 760 uintptr_t x; 761 762 for (;;) { 763 x = sx->sx_lock; 764 765 /* 766 * We should never have sharers while at least one thread 767 * holds a shared lock. 768 */ 769 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 770 ("%s: waiting sharers", __func__)); 771 772 /* 773 * See if there is more than one shared lock held. If 774 * so, just drop one and return. 775 */ 776 if (SX_SHARERS(x) > 1) { 777 if (atomic_cmpset_ptr(&sx->sx_lock, x, 778 x - SX_ONE_SHARER)) { 779 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 780 CTR4(KTR_LOCK, 781 "%s: %p succeeded %p -> %p", 782 __func__, sx, (void *)x, 783 (void *)(x - SX_ONE_SHARER)); 784 break; 785 } 786 continue; 787 } 788 789 /* 790 * If there aren't any waiters for an exclusive lock, 791 * then try to drop it quickly. 792 */ 793 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 794 MPASS(x == SX_SHARERS_LOCK(1)); 795 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1), 796 SX_LOCK_UNLOCKED)) { 797 lock_profile_release_lock(&sx->lock_object); 798 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 799 CTR2(KTR_LOCK, "%s: %p last succeeded", 800 __func__, sx); 801 break; 802 } 803 continue; 804 } 805 806 /* 807 * At this point, there should just be one sharer with 808 * exclusive waiters. 809 */ 810 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 811 812 lock_profile_release_lock(&sx->lock_object); 813 sleepq_lock(&sx->lock_object); 814 815 /* 816 * Wake up semantic here is quite simple: 817 * Just wake up all the exclusive waiters. 818 * Note that the state of the lock could have changed, 819 * so if it fails loop back and retry. 820 */ 821 if (!atomic_cmpset_ptr(&sx->sx_lock, 822 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 823 SX_LOCK_UNLOCKED)) { 824 sleepq_release(&sx->lock_object); 825 continue; 826 } 827 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 828 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 829 "exclusive queue", __func__, sx); 830 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 831 SQ_EXCLUSIVE_QUEUE); 832 break; 833 } 834} 835 836#ifdef INVARIANT_SUPPORT 837#ifndef INVARIANTS 838#undef _sx_assert 839#endif 840 841/* 842 * In the non-WITNESS case, sx_assert() can only detect that at least 843 * *some* thread owns an slock, but it cannot guarantee that *this* 844 * thread owns an slock. 845 */ 846void 847_sx_assert(struct sx *sx, int what, const char *file, int line) 848{ 849#ifndef WITNESS 850 int slocked = 0; 851#endif 852 853 if (panicstr != NULL) 854 return; 855 switch (what) { 856 case SX_SLOCKED: 857 case SX_SLOCKED | SX_NOTRECURSED: 858 case SX_SLOCKED | SX_RECURSED: 859#ifndef WITNESS 860 slocked = 1; 861 /* FALLTHROUGH */ 862#endif 863 case SX_LOCKED: 864 case SX_LOCKED | SX_NOTRECURSED: 865 case SX_LOCKED | SX_RECURSED: 866#ifdef WITNESS 867 witness_assert(&sx->lock_object, what, file, line); 868#else 869 /* 870 * If some other thread has an exclusive lock or we 871 * have one and are asserting a shared lock, fail. 872 * Also, if no one has a lock at all, fail. 873 */ 874 if (sx->sx_lock == SX_LOCK_UNLOCKED || 875 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 876 sx_xholder(sx) != curthread))) 877 panic("Lock %s not %slocked @ %s:%d\n", 878 sx->lock_object.lo_name, slocked ? "share " : "", 879 file, line); 880 881 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 882 if (sx_recursed(sx)) { 883 if (what & SX_NOTRECURSED) 884 panic("Lock %s recursed @ %s:%d\n", 885 sx->lock_object.lo_name, file, 886 line); 887 } else if (what & SX_RECURSED) 888 panic("Lock %s not recursed @ %s:%d\n", 889 sx->lock_object.lo_name, file, line); 890 } 891#endif 892 break; 893 case SX_XLOCKED: 894 case SX_XLOCKED | SX_NOTRECURSED: 895 case SX_XLOCKED | SX_RECURSED: 896 if (sx_xholder(sx) != curthread) 897 panic("Lock %s not exclusively locked @ %s:%d\n", 898 sx->lock_object.lo_name, file, line); 899 if (sx_recursed(sx)) { 900 if (what & SX_NOTRECURSED) 901 panic("Lock %s recursed @ %s:%d\n", 902 sx->lock_object.lo_name, file, line); 903 } else if (what & SX_RECURSED) 904 panic("Lock %s not recursed @ %s:%d\n", 905 sx->lock_object.lo_name, file, line); 906 break; 907 case SX_UNLOCKED: 908#ifdef WITNESS 909 witness_assert(&sx->lock_object, what, file, line); 910#else 911 /* 912 * If we hold an exclusve lock fail. We can't 913 * reliably check to see if we hold a shared lock or 914 * not. 915 */ 916 if (sx_xholder(sx) == curthread) 917 panic("Lock %s exclusively locked @ %s:%d\n", 918 sx->lock_object.lo_name, file, line); 919#endif 920 break; 921 default: 922 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 923 line); 924 } 925} 926#endif /* INVARIANT_SUPPORT */ 927 928#ifdef DDB 929static void 930db_show_sx(struct lock_object *lock) 931{ 932 struct thread *td; 933 struct sx *sx; 934 935 sx = (struct sx *)lock; 936 937 db_printf(" state: "); 938 if (sx->sx_lock == SX_LOCK_UNLOCKED) 939 db_printf("UNLOCKED\n"); 940 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 941 db_printf("DESTROYED\n"); 942 return; 943 } else if (sx->sx_lock & SX_LOCK_SHARED) 944 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 945 else { 946 td = sx_xholder(sx); 947 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 948 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 949 if (sx_recursed(sx)) 950 db_printf(" recursed: %d\n", sx->sx_recurse); 951 } 952 953 db_printf(" waiters: "); 954 switch(sx->sx_lock & 955 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 956 case SX_LOCK_SHARED_WAITERS: 957 db_printf("shared\n"); 958 break; 959 case SX_LOCK_EXCLUSIVE_WAITERS: 960 db_printf("exclusive\n"); 961 break; 962 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 963 db_printf("exclusive and shared\n"); 964 break; 965 default: 966 db_printf("none\n"); 967 } 968} 969 970/* 971 * Check to see if a thread that is blocked on a sleep queue is actually 972 * blocked on an sx lock. If so, output some details and return true. 973 * If the lock has an exclusive owner, return that in *ownerp. 974 */ 975int 976sx_chain(struct thread *td, struct thread **ownerp) 977{ 978 struct sx *sx; 979 980 /* 981 * Check to see if this thread is blocked on an sx lock. 982 * First, we check the lock class. If that is ok, then we 983 * compare the lock name against the wait message. 984 */ 985 sx = td->td_wchan; 986 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 987 sx->lock_object.lo_name != td->td_wmesg) 988 return (0); 989 990 /* We think we have an sx lock, so output some details. */ 991 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 992 *ownerp = sx_xholder(sx); 993 if (sx->sx_lock & SX_LOCK_SHARED) 994 db_printf("SLOCK (count %ju)\n", 995 (uintmax_t)SX_SHARERS(sx->sx_lock)); 996 else 997 db_printf("XLOCK\n"); 998 return (1); 999} 1000#endif 1001