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_kdtrace.h" 42 #include "opt_no_adaptive_sx.h" 43 44 #include <sys/cdefs.h> 45 __FBSDID("$FreeBSD$"); 46 47 #include <sys/param.h> 48 #include <sys/systm.h> 49 #include <sys/kdb.h> 50 #include <sys/ktr.h> 51 #include <sys/lock.h> 52 #include <sys/mutex.h> 53 #include <sys/proc.h> 54 #include <sys/sleepqueue.h> 55 #include <sys/sx.h> 56 #include <sys/sysctl.h> 57 58 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 59 #include <machine/cpu.h> 60 #endif 61 62 #ifdef DDB 63 #include <ddb/ddb.h> 64 #endif 65 66 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 67 #define ADAPTIVE_SX 68 #endif 69 70 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE); 71 72 #ifdef HWPMC_HOOKS 73 #include <sys/pmckern.h> 74 PMC_SOFT_DECLARE( , , lock, failed); 75 #endif 76 77 /* Handy macros for sleep queues. */ 78 #define SQ_EXCLUSIVE_QUEUE 0 79 #define SQ_SHARED_QUEUE 1 80 81 #ifdef ADAPTIVE_SX 82 #define ASX_RETRIES 10 83 #define ASX_LOOPS 10000 84 #endif 85 86 /* 87 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 88 * drop Giant anytime we have to sleep or if we adaptively spin. 89 */ 90 #define GIANT_DECLARE \ 91 int _giantcnt = 0; \ 92 WITNESS_SAVE_DECL(Giant) \ 93 94 #define GIANT_SAVE() do { \ 95 if (mtx_owned(&Giant)) { \ 96 WITNESS_SAVE(&Giant.lock_object, Giant); \ 97 while (mtx_owned(&Giant)) { \ 98 _giantcnt++; \ 99 mtx_unlock(&Giant); \ 100 } \ 101 } \ 102 } while (0) 103 104 #define GIANT_RESTORE() do { \ 105 if (_giantcnt > 0) { \ 106 mtx_assert(&Giant, MA_NOTOWNED); \ 107 while (_giantcnt--) \ 108 mtx_lock(&Giant); \ 109 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 110 } \ 111 } while (0) 112 113 /* 114 * Returns true if an exclusive lock is recursed. It assumes 115 * curthread currently has an exclusive lock. 116 */ 117 #define sx_recurse lock_object.lo_data 118 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 119 120 static void assert_sx(struct lock_object *lock, int what); 121 #ifdef DDB 122 static void db_show_sx(struct lock_object *lock); 123 #endif 124 static void lock_sx(struct lock_object *lock, int how); 125 #ifdef KDTRACE_HOOKS 126 static int owner_sx(struct lock_object *lock, struct thread **owner); 127 #endif 128 static int unlock_sx(struct lock_object *lock); 129 130 struct lock_class lock_class_sx = { 131 .lc_name = "sx", 132 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 133 .lc_assert = assert_sx, 134 #ifdef DDB 135 .lc_ddb_show = db_show_sx, 136 #endif 137 .lc_lock = lock_sx, 138 .lc_unlock = unlock_sx, 139 #ifdef KDTRACE_HOOKS 140 .lc_owner = owner_sx, 141 #endif 142 }; 143 144 #ifndef INVARIANTS 145 #define _sx_assert(sx, what, file, line) 146 #endif 147 148 void 149 assert_sx(struct lock_object *lock, int what) 150 { 151 152 sx_assert((struct sx *)lock, what); 153 } 154 155 void 156 lock_sx(struct lock_object *lock, int how) 157 { 158 struct sx *sx; 159 160 sx = (struct sx *)lock; 161 if (how) 162 sx_xlock(sx); 163 else 164 sx_slock(sx); 165 } 166 167 int 168 unlock_sx(struct lock_object *lock) 169 { 170 struct sx *sx; 171 172 sx = (struct sx *)lock; 173 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 174 if (sx_xlocked(sx)) { 175 sx_xunlock(sx); 176 return (1); 177 } else { 178 sx_sunlock(sx); 179 return (0); 180 } 181 } 182 183 #ifdef KDTRACE_HOOKS 184 int 185 owner_sx(struct lock_object *lock, struct thread **owner) 186 { 187 struct sx *sx = (struct sx *)lock; 188 uintptr_t x = sx->sx_lock; 189 190 *owner = (struct thread *)SX_OWNER(x); 191 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 192 (*owner != NULL)); 193 } 194 #endif 195 196 void 197 sx_sysinit(void *arg) 198 { 199 struct sx_args *sargs = arg; 200 201 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 202 } 203 204 void 205 sx_init_flags(struct sx *sx, const char *description, int opts) 206 { 207 int flags; 208 209 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 210 SX_NOPROFILE | SX_NOADAPTIVE)) == 0); 211 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 212 ("%s: sx_lock not aligned for %s: %p", __func__, description, 213 &sx->sx_lock)); 214 215 flags = LO_SLEEPABLE | LO_UPGRADABLE; 216 if (opts & SX_DUPOK) 217 flags |= LO_DUPOK; 218 if (opts & SX_NOPROFILE) 219 flags |= LO_NOPROFILE; 220 if (!(opts & SX_NOWITNESS)) 221 flags |= LO_WITNESS; 222 if (opts & SX_RECURSE) 223 flags |= LO_RECURSABLE; 224 if (opts & SX_QUIET) 225 flags |= LO_QUIET; 226 227 flags |= opts & SX_NOADAPTIVE; 228 sx->sx_lock = SX_LOCK_UNLOCKED; 229 sx->sx_recurse = 0; 230 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 231 } 232 233 void 234 sx_destroy(struct sx *sx) 235 { 236 237 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 238 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 239 sx->sx_lock = SX_LOCK_DESTROYED; 240 lock_destroy(&sx->lock_object); 241 } 242 243 int 244 _sx_slock(struct sx *sx, int opts, const char *file, int line) 245 { 246 int error = 0; 247 248 if (SCHEDULER_STOPPED()) 249 return (0); 250 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 251 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 252 curthread, sx->lock_object.lo_name, file, line)); 253 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 254 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 255 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 256 error = __sx_slock(sx, opts, file, line); 257 if (!error) { 258 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 259 WITNESS_LOCK(&sx->lock_object, 0, file, line); 260 curthread->td_locks++; 261 } 262 263 return (error); 264 } 265 266 int 267 _sx_try_slock(struct sx *sx, const char *file, int line) 268 { 269 uintptr_t x; 270 271 if (SCHEDULER_STOPPED()) 272 return (1); 273 274 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 275 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 276 curthread, sx->lock_object.lo_name, file, line)); 277 278 for (;;) { 279 x = sx->sx_lock; 280 KASSERT(x != SX_LOCK_DESTROYED, 281 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 282 if (!(x & SX_LOCK_SHARED)) 283 break; 284 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) { 285 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 286 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 287 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, 288 sx, 0, 0, file, line); 289 curthread->td_locks++; 290 return (1); 291 } 292 } 293 294 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 295 return (0); 296 } 297 298 int 299 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 300 { 301 int error = 0; 302 303 if (SCHEDULER_STOPPED()) 304 return (0); 305 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 306 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 307 curthread, sx->lock_object.lo_name, file, line)); 308 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 309 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 310 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 311 line, NULL); 312 error = __sx_xlock(sx, curthread, opts, file, line); 313 if (!error) { 314 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 315 file, line); 316 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 317 curthread->td_locks++; 318 } 319 320 return (error); 321 } 322 323 int 324 _sx_try_xlock(struct sx *sx, const char *file, int line) 325 { 326 int rval; 327 328 if (SCHEDULER_STOPPED()) 329 return (1); 330 331 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 332 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 333 curthread, sx->lock_object.lo_name, file, line)); 334 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 335 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 336 337 if (sx_xlocked(sx) && 338 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) { 339 sx->sx_recurse++; 340 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 341 rval = 1; 342 } else 343 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 344 (uintptr_t)curthread); 345 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 346 if (rval) { 347 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 348 file, line); 349 if (!sx_recursed(sx)) 350 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, 351 sx, 0, 0, file, line); 352 curthread->td_locks++; 353 } 354 355 return (rval); 356 } 357 358 void 359 _sx_sunlock(struct sx *sx, const char *file, int line) 360 { 361 362 if (SCHEDULER_STOPPED()) 363 return; 364 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 365 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 366 _sx_assert(sx, SA_SLOCKED, file, line); 367 curthread->td_locks--; 368 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 369 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 370 __sx_sunlock(sx, file, line); 371 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx); 372 } 373 374 void 375 _sx_xunlock(struct sx *sx, const char *file, int line) 376 { 377 378 if (SCHEDULER_STOPPED()) 379 return; 380 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 381 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 382 _sx_assert(sx, SA_XLOCKED, file, line); 383 curthread->td_locks--; 384 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 385 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 386 line); 387 if (!sx_recursed(sx)) 388 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx); 389 __sx_xunlock(sx, curthread, file, line); 390 } 391 392 /* 393 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 394 * This will only succeed if this thread holds a single shared lock. 395 * Return 1 if if the upgrade succeed, 0 otherwise. 396 */ 397 int 398 _sx_try_upgrade(struct sx *sx, const char *file, int line) 399 { 400 uintptr_t x; 401 int success; 402 403 if (SCHEDULER_STOPPED()) 404 return (1); 405 406 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 407 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 408 _sx_assert(sx, SA_SLOCKED, file, line); 409 410 /* 411 * Try to switch from one shared lock to an exclusive lock. We need 412 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 413 * we will wake up the exclusive waiters when we drop the lock. 414 */ 415 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 416 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 417 (uintptr_t)curthread | x); 418 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 419 if (success) { 420 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 421 file, line); 422 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx); 423 } 424 return (success); 425 } 426 427 /* 428 * Downgrade an unrecursed exclusive lock into a single shared lock. 429 */ 430 void 431 _sx_downgrade(struct sx *sx, const char *file, int line) 432 { 433 uintptr_t x; 434 int wakeup_swapper; 435 436 if (SCHEDULER_STOPPED()) 437 return; 438 439 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 440 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 441 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 442 #ifndef INVARIANTS 443 if (sx_recursed(sx)) 444 panic("downgrade of a recursed lock"); 445 #endif 446 447 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 448 449 /* 450 * Try to switch from an exclusive lock with no shared waiters 451 * to one sharer with no shared waiters. If there are 452 * exclusive waiters, we don't need to lock the sleep queue so 453 * long as we preserve the flag. We do one quick try and if 454 * that fails we grab the sleepq lock to keep the flags from 455 * changing and do it the slow way. 456 * 457 * We have to lock the sleep queue if there are shared waiters 458 * so we can wake them up. 459 */ 460 x = sx->sx_lock; 461 if (!(x & SX_LOCK_SHARED_WAITERS) && 462 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 463 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 464 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 465 return; 466 } 467 468 /* 469 * Lock the sleep queue so we can read the waiters bits 470 * without any races and wakeup any shared waiters. 471 */ 472 sleepq_lock(&sx->lock_object); 473 474 /* 475 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 476 * shared lock. If there are any shared waiters, wake them up. 477 */ 478 wakeup_swapper = 0; 479 x = sx->sx_lock; 480 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 481 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 482 if (x & SX_LOCK_SHARED_WAITERS) 483 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 484 0, SQ_SHARED_QUEUE); 485 sleepq_release(&sx->lock_object); 486 487 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 488 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx); 489 490 if (wakeup_swapper) 491 kick_proc0(); 492 } 493 494 /* 495 * This function represents the so-called 'hard case' for sx_xlock 496 * operation. All 'easy case' failures are redirected to this. Note 497 * that ideally this would be a static function, but it needs to be 498 * accessible from at least sx.h. 499 */ 500 int 501 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 502 int line) 503 { 504 GIANT_DECLARE; 505 #ifdef ADAPTIVE_SX 506 volatile struct thread *owner; 507 u_int i, spintries = 0; 508 #endif 509 uintptr_t x; 510 #ifdef LOCK_PROFILING 511 uint64_t waittime = 0; 512 int contested = 0; 513 #endif 514 int error = 0; 515 #ifdef KDTRACE_HOOKS 516 uintptr_t state; 517 uint64_t spin_cnt = 0; 518 uint64_t sleep_cnt = 0; 519 int64_t sleep_time = 0; 520 int64_t all_time = 0; 521 #endif 522 523 if (SCHEDULER_STOPPED()) 524 return (0); 525 526 /* If we already hold an exclusive lock, then recurse. */ 527 if (sx_xlocked(sx)) { 528 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 529 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 530 sx->lock_object.lo_name, file, line)); 531 sx->sx_recurse++; 532 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 533 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 534 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 535 return (0); 536 } 537 538 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 539 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 540 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 541 542 #ifdef KDTRACE_HOOKS 543 all_time -= lockstat_nsecs(&sx->lock_object); 544 state = sx->sx_lock; 545 #endif 546 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 547 #ifdef KDTRACE_HOOKS 548 spin_cnt++; 549 #endif 550 #ifdef HWPMC_HOOKS 551 PMC_SOFT_CALL( , , lock, failed); 552 #endif 553 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 554 &waittime); 555 #ifdef ADAPTIVE_SX 556 /* 557 * If the lock is write locked and the owner is 558 * running on another CPU, spin until the owner stops 559 * running or the state of the lock changes. 560 */ 561 x = sx->sx_lock; 562 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 563 if ((x & SX_LOCK_SHARED) == 0) { 564 x = SX_OWNER(x); 565 owner = (struct thread *)x; 566 if (TD_IS_RUNNING(owner)) { 567 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 568 CTR3(KTR_LOCK, 569 "%s: spinning on %p held by %p", 570 __func__, sx, owner); 571 GIANT_SAVE(); 572 while (SX_OWNER(sx->sx_lock) == x && 573 TD_IS_RUNNING(owner)) { 574 cpu_spinwait(); 575 #ifdef KDTRACE_HOOKS 576 spin_cnt++; 577 #endif 578 } 579 continue; 580 } 581 } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) { 582 GIANT_SAVE(); 583 spintries++; 584 for (i = 0; i < ASX_LOOPS; i++) { 585 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 586 CTR4(KTR_LOCK, 587 "%s: shared spinning on %p with %u and %u", 588 __func__, sx, spintries, i); 589 x = sx->sx_lock; 590 if ((x & SX_LOCK_SHARED) == 0 || 591 SX_SHARERS(x) == 0) 592 break; 593 cpu_spinwait(); 594 #ifdef KDTRACE_HOOKS 595 spin_cnt++; 596 #endif 597 } 598 if (i != ASX_LOOPS) 599 continue; 600 } 601 } 602 #endif 603 604 sleepq_lock(&sx->lock_object); 605 x = sx->sx_lock; 606 607 /* 608 * If the lock was released while spinning on the 609 * sleep queue chain lock, try again. 610 */ 611 if (x == SX_LOCK_UNLOCKED) { 612 sleepq_release(&sx->lock_object); 613 continue; 614 } 615 616 #ifdef ADAPTIVE_SX 617 /* 618 * The current lock owner might have started executing 619 * on another CPU (or the lock could have changed 620 * owners) while we were waiting on the sleep queue 621 * chain lock. If so, drop the sleep queue lock and try 622 * again. 623 */ 624 if (!(x & SX_LOCK_SHARED) && 625 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 626 owner = (struct thread *)SX_OWNER(x); 627 if (TD_IS_RUNNING(owner)) { 628 sleepq_release(&sx->lock_object); 629 continue; 630 } 631 } 632 #endif 633 634 /* 635 * If an exclusive lock was released with both shared 636 * and exclusive waiters and a shared waiter hasn't 637 * woken up and acquired the lock yet, sx_lock will be 638 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 639 * If we see that value, try to acquire it once. Note 640 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 641 * as there are other exclusive waiters still. If we 642 * fail, restart the loop. 643 */ 644 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 645 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 646 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 647 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 648 sleepq_release(&sx->lock_object); 649 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 650 __func__, sx); 651 break; 652 } 653 sleepq_release(&sx->lock_object); 654 continue; 655 } 656 657 /* 658 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 659 * than loop back and retry. 660 */ 661 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 662 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 663 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 664 sleepq_release(&sx->lock_object); 665 continue; 666 } 667 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 668 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 669 __func__, sx); 670 } 671 672 /* 673 * Since we have been unable to acquire the exclusive 674 * lock and the exclusive waiters flag is set, we have 675 * to sleep. 676 */ 677 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 678 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 679 __func__, sx); 680 681 #ifdef KDTRACE_HOOKS 682 sleep_time -= lockstat_nsecs(&sx->lock_object); 683 #endif 684 GIANT_SAVE(); 685 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 686 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 687 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 688 if (!(opts & SX_INTERRUPTIBLE)) 689 sleepq_wait(&sx->lock_object, 0); 690 else 691 error = sleepq_wait_sig(&sx->lock_object, 0); 692 #ifdef KDTRACE_HOOKS 693 sleep_time += lockstat_nsecs(&sx->lock_object); 694 sleep_cnt++; 695 #endif 696 if (error) { 697 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 698 CTR2(KTR_LOCK, 699 "%s: interruptible sleep by %p suspended by signal", 700 __func__, sx); 701 break; 702 } 703 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 704 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 705 __func__, sx); 706 } 707 #ifdef KDTRACE_HOOKS 708 all_time += lockstat_nsecs(&sx->lock_object); 709 if (sleep_time) 710 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time, 711 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 712 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 713 if (spin_cnt > sleep_cnt) 714 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time, 715 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 716 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 717 #endif 718 if (!error) 719 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx, 720 contested, waittime, file, line); 721 GIANT_RESTORE(); 722 return (error); 723 } 724 725 /* 726 * This function represents the so-called 'hard case' for sx_xunlock 727 * operation. All 'easy case' failures are redirected to this. Note 728 * that ideally this would be a static function, but it needs to be 729 * accessible from at least sx.h. 730 */ 731 void 732 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 733 { 734 uintptr_t x; 735 int queue, wakeup_swapper; 736 737 if (SCHEDULER_STOPPED()) 738 return; 739 740 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 741 742 /* If the lock is recursed, then unrecurse one level. */ 743 if (sx_xlocked(sx) && sx_recursed(sx)) { 744 if ((--sx->sx_recurse) == 0) 745 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 746 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 747 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 748 return; 749 } 750 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 751 SX_LOCK_EXCLUSIVE_WAITERS)); 752 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 753 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 754 755 sleepq_lock(&sx->lock_object); 756 x = SX_LOCK_UNLOCKED; 757 758 /* 759 * The wake up algorithm here is quite simple and probably not 760 * ideal. It gives precedence to shared waiters if they are 761 * present. For this condition, we have to preserve the 762 * state of the exclusive waiters flag. 763 * If interruptible sleeps left the shared queue empty avoid a 764 * starvation for the threads sleeping on the exclusive queue by giving 765 * them precedence and cleaning up the shared waiters bit anyway. 766 */ 767 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 && 768 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 769 queue = SQ_SHARED_QUEUE; 770 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 771 } else 772 queue = SQ_EXCLUSIVE_QUEUE; 773 774 /* Wake up all the waiters for the specific queue. */ 775 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 776 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 777 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 778 "exclusive"); 779 atomic_store_rel_ptr(&sx->sx_lock, x); 780 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 781 queue); 782 sleepq_release(&sx->lock_object); 783 if (wakeup_swapper) 784 kick_proc0(); 785 } 786 787 /* 788 * This function represents the so-called 'hard case' for sx_slock 789 * operation. All 'easy case' failures are redirected to this. Note 790 * that ideally this would be a static function, but it needs to be 791 * accessible from at least sx.h. 792 */ 793 int 794 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line) 795 { 796 GIANT_DECLARE; 797 #ifdef ADAPTIVE_SX 798 volatile struct thread *owner; 799 #endif 800 #ifdef LOCK_PROFILING 801 uint64_t waittime = 0; 802 int contested = 0; 803 #endif 804 uintptr_t x; 805 int error = 0; 806 #ifdef KDTRACE_HOOKS 807 uintptr_t state; 808 uint64_t spin_cnt = 0; 809 uint64_t sleep_cnt = 0; 810 int64_t sleep_time = 0; 811 int64_t all_time = 0; 812 #endif 813 814 if (SCHEDULER_STOPPED()) 815 return (0); 816 817 #ifdef KDTRACE_HOOKS 818 state = sx->sx_lock; 819 all_time -= lockstat_nsecs(&sx->lock_object); 820 #endif 821 822 /* 823 * As with rwlocks, we don't make any attempt to try to block 824 * shared locks once there is an exclusive waiter. 825 */ 826 for (;;) { 827 #ifdef KDTRACE_HOOKS 828 spin_cnt++; 829 #endif 830 x = sx->sx_lock; 831 832 /* 833 * If no other thread has an exclusive lock then try to bump up 834 * the count of sharers. Since we have to preserve the state 835 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 836 * shared lock loop back and retry. 837 */ 838 if (x & SX_LOCK_SHARED) { 839 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 840 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 841 x + SX_ONE_SHARER)) { 842 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 843 CTR4(KTR_LOCK, 844 "%s: %p succeed %p -> %p", __func__, 845 sx, (void *)x, 846 (void *)(x + SX_ONE_SHARER)); 847 break; 848 } 849 continue; 850 } 851 #ifdef HWPMC_HOOKS 852 PMC_SOFT_CALL( , , lock, failed); 853 #endif 854 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 855 &waittime); 856 857 #ifdef ADAPTIVE_SX 858 /* 859 * If the owner is running on another CPU, spin until 860 * the owner stops running or the state of the lock 861 * changes. 862 */ 863 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 864 x = SX_OWNER(x); 865 owner = (struct thread *)x; 866 if (TD_IS_RUNNING(owner)) { 867 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 868 CTR3(KTR_LOCK, 869 "%s: spinning on %p held by %p", 870 __func__, sx, owner); 871 GIANT_SAVE(); 872 while (SX_OWNER(sx->sx_lock) == x && 873 TD_IS_RUNNING(owner)) { 874 #ifdef KDTRACE_HOOKS 875 spin_cnt++; 876 #endif 877 cpu_spinwait(); 878 } 879 continue; 880 } 881 } 882 #endif 883 884 /* 885 * Some other thread already has an exclusive lock, so 886 * start the process of blocking. 887 */ 888 sleepq_lock(&sx->lock_object); 889 x = sx->sx_lock; 890 891 /* 892 * The lock could have been released while we spun. 893 * In this case loop back and retry. 894 */ 895 if (x & SX_LOCK_SHARED) { 896 sleepq_release(&sx->lock_object); 897 continue; 898 } 899 900 #ifdef ADAPTIVE_SX 901 /* 902 * If the owner is running on another CPU, spin until 903 * the owner stops running or the state of the lock 904 * changes. 905 */ 906 if (!(x & SX_LOCK_SHARED) && 907 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 908 owner = (struct thread *)SX_OWNER(x); 909 if (TD_IS_RUNNING(owner)) { 910 sleepq_release(&sx->lock_object); 911 continue; 912 } 913 } 914 #endif 915 916 /* 917 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 918 * fail to set it drop the sleep queue lock and loop 919 * back. 920 */ 921 if (!(x & SX_LOCK_SHARED_WAITERS)) { 922 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 923 x | SX_LOCK_SHARED_WAITERS)) { 924 sleepq_release(&sx->lock_object); 925 continue; 926 } 927 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 928 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 929 __func__, sx); 930 } 931 932 /* 933 * Since we have been unable to acquire the shared lock, 934 * we have to sleep. 935 */ 936 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 937 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 938 __func__, sx); 939 940 #ifdef KDTRACE_HOOKS 941 sleep_time -= lockstat_nsecs(&sx->lock_object); 942 #endif 943 GIANT_SAVE(); 944 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 945 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 946 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 947 if (!(opts & SX_INTERRUPTIBLE)) 948 sleepq_wait(&sx->lock_object, 0); 949 else 950 error = sleepq_wait_sig(&sx->lock_object, 0); 951 #ifdef KDTRACE_HOOKS 952 sleep_time += lockstat_nsecs(&sx->lock_object); 953 sleep_cnt++; 954 #endif 955 if (error) { 956 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 957 CTR2(KTR_LOCK, 958 "%s: interruptible sleep by %p suspended by signal", 959 __func__, sx); 960 break; 961 } 962 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 963 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 964 __func__, sx); 965 } 966 #ifdef KDTRACE_HOOKS 967 all_time += lockstat_nsecs(&sx->lock_object); 968 if (sleep_time) 969 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time, 970 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 971 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 972 if (spin_cnt > sleep_cnt) 973 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time, 974 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 975 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 976 #endif 977 if (error == 0) 978 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 979 contested, waittime, file, line); 980 GIANT_RESTORE(); 981 return (error); 982 } 983 984 /* 985 * This function represents the so-called 'hard case' for sx_sunlock 986 * operation. All 'easy case' failures are redirected to this. Note 987 * that ideally this would be a static function, but it needs to be 988 * accessible from at least sx.h. 989 */ 990 void 991 _sx_sunlock_hard(struct sx *sx, const char *file, int line) 992 { 993 uintptr_t x; 994 int wakeup_swapper; 995 996 if (SCHEDULER_STOPPED()) 997 return; 998 999 for (;;) { 1000 x = sx->sx_lock; 1001 1002 /* 1003 * We should never have sharers while at least one thread 1004 * holds a shared lock. 1005 */ 1006 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 1007 ("%s: waiting sharers", __func__)); 1008 1009 /* 1010 * See if there is more than one shared lock held. If 1011 * so, just drop one and return. 1012 */ 1013 if (SX_SHARERS(x) > 1) { 1014 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x, 1015 x - SX_ONE_SHARER)) { 1016 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1017 CTR4(KTR_LOCK, 1018 "%s: %p succeeded %p -> %p", 1019 __func__, sx, (void *)x, 1020 (void *)(x - SX_ONE_SHARER)); 1021 break; 1022 } 1023 continue; 1024 } 1025 1026 /* 1027 * If there aren't any waiters for an exclusive lock, 1028 * then try to drop it quickly. 1029 */ 1030 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 1031 MPASS(x == SX_SHARERS_LOCK(1)); 1032 if (atomic_cmpset_rel_ptr(&sx->sx_lock, 1033 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) { 1034 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1035 CTR2(KTR_LOCK, "%s: %p last succeeded", 1036 __func__, sx); 1037 break; 1038 } 1039 continue; 1040 } 1041 1042 /* 1043 * At this point, there should just be one sharer with 1044 * exclusive waiters. 1045 */ 1046 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1047 1048 sleepq_lock(&sx->lock_object); 1049 1050 /* 1051 * Wake up semantic here is quite simple: 1052 * Just wake up all the exclusive waiters. 1053 * Note that the state of the lock could have changed, 1054 * so if it fails loop back and retry. 1055 */ 1056 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, 1057 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 1058 SX_LOCK_UNLOCKED)) { 1059 sleepq_release(&sx->lock_object); 1060 continue; 1061 } 1062 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1063 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1064 "exclusive queue", __func__, sx); 1065 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1066 0, SQ_EXCLUSIVE_QUEUE); 1067 sleepq_release(&sx->lock_object); 1068 if (wakeup_swapper) 1069 kick_proc0(); 1070 break; 1071 } 1072 } 1073 1074 #ifdef INVARIANT_SUPPORT 1075 #ifndef INVARIANTS 1076 #undef _sx_assert 1077 #endif 1078 1079 /* 1080 * In the non-WITNESS case, sx_assert() can only detect that at least 1081 * *some* thread owns an slock, but it cannot guarantee that *this* 1082 * thread owns an slock. 1083 */ 1084 void 1085 _sx_assert(struct sx *sx, int what, const char *file, int line) 1086 { 1087 #ifndef WITNESS 1088 int slocked = 0; 1089 #endif 1090 1091 if (panicstr != NULL) 1092 return; 1093 switch (what) { 1094 case SA_SLOCKED: 1095 case SA_SLOCKED | SA_NOTRECURSED: 1096 case SA_SLOCKED | SA_RECURSED: 1097 #ifndef WITNESS 1098 slocked = 1; 1099 /* FALLTHROUGH */ 1100 #endif 1101 case SA_LOCKED: 1102 case SA_LOCKED | SA_NOTRECURSED: 1103 case SA_LOCKED | SA_RECURSED: 1104 #ifdef WITNESS 1105 witness_assert(&sx->lock_object, what, file, line); 1106 #else 1107 /* 1108 * If some other thread has an exclusive lock or we 1109 * have one and are asserting a shared lock, fail. 1110 * Also, if no one has a lock at all, fail. 1111 */ 1112 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1113 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1114 sx_xholder(sx) != curthread))) 1115 panic("Lock %s not %slocked @ %s:%d\n", 1116 sx->lock_object.lo_name, slocked ? "share " : "", 1117 file, line); 1118 1119 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1120 if (sx_recursed(sx)) { 1121 if (what & SA_NOTRECURSED) 1122 panic("Lock %s recursed @ %s:%d\n", 1123 sx->lock_object.lo_name, file, 1124 line); 1125 } else if (what & SA_RECURSED) 1126 panic("Lock %s not recursed @ %s:%d\n", 1127 sx->lock_object.lo_name, file, line); 1128 } 1129 #endif 1130 break; 1131 case SA_XLOCKED: 1132 case SA_XLOCKED | SA_NOTRECURSED: 1133 case SA_XLOCKED | SA_RECURSED: 1134 if (sx_xholder(sx) != curthread) 1135 panic("Lock %s not exclusively locked @ %s:%d\n", 1136 sx->lock_object.lo_name, file, line); 1137 if (sx_recursed(sx)) { 1138 if (what & SA_NOTRECURSED) 1139 panic("Lock %s recursed @ %s:%d\n", 1140 sx->lock_object.lo_name, file, line); 1141 } else if (what & SA_RECURSED) 1142 panic("Lock %s not recursed @ %s:%d\n", 1143 sx->lock_object.lo_name, file, line); 1144 break; 1145 case SA_UNLOCKED: 1146 #ifdef WITNESS 1147 witness_assert(&sx->lock_object, what, file, line); 1148 #else 1149 /* 1150 * If we hold an exclusve lock fail. We can't 1151 * reliably check to see if we hold a shared lock or 1152 * not. 1153 */ 1154 if (sx_xholder(sx) == curthread) 1155 panic("Lock %s exclusively locked @ %s:%d\n", 1156 sx->lock_object.lo_name, file, line); 1157 #endif 1158 break; 1159 default: 1160 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1161 line); 1162 } 1163 } 1164 #endif /* INVARIANT_SUPPORT */ 1165 1166 #ifdef DDB 1167 static void 1168 db_show_sx(struct lock_object *lock) 1169 { 1170 struct thread *td; 1171 struct sx *sx; 1172 1173 sx = (struct sx *)lock; 1174 1175 db_printf(" state: "); 1176 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1177 db_printf("UNLOCKED\n"); 1178 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1179 db_printf("DESTROYED\n"); 1180 return; 1181 } else if (sx->sx_lock & SX_LOCK_SHARED) 1182 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1183 else { 1184 td = sx_xholder(sx); 1185 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1186 td->td_tid, td->td_proc->p_pid, td->td_name); 1187 if (sx_recursed(sx)) 1188 db_printf(" recursed: %d\n", sx->sx_recurse); 1189 } 1190 1191 db_printf(" waiters: "); 1192 switch(sx->sx_lock & 1193 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1194 case SX_LOCK_SHARED_WAITERS: 1195 db_printf("shared\n"); 1196 break; 1197 case SX_LOCK_EXCLUSIVE_WAITERS: 1198 db_printf("exclusive\n"); 1199 break; 1200 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1201 db_printf("exclusive and shared\n"); 1202 break; 1203 default: 1204 db_printf("none\n"); 1205 } 1206 } 1207 1208 /* 1209 * Check to see if a thread that is blocked on a sleep queue is actually 1210 * blocked on an sx lock. If so, output some details and return true. 1211 * If the lock has an exclusive owner, return that in *ownerp. 1212 */ 1213 int 1214 sx_chain(struct thread *td, struct thread **ownerp) 1215 { 1216 struct sx *sx; 1217 1218 /* 1219 * Check to see if this thread is blocked on an sx lock. 1220 * First, we check the lock class. If that is ok, then we 1221 * compare the lock name against the wait message. 1222 */ 1223 sx = td->td_wchan; 1224 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1225 sx->lock_object.lo_name != td->td_wmesg) 1226 return (0); 1227 1228 /* We think we have an sx lock, so output some details. */ 1229 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1230 *ownerp = sx_xholder(sx); 1231 if (sx->sx_lock & SX_LOCK_SHARED) 1232 db_printf("SLOCK (count %ju)\n", 1233 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1234 else 1235 db_printf("XLOCK\n"); 1236 return (1); 1237 } 1238 #endif
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