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