Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/kern/kern_sx.c
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1 /*- 2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org> 3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org> 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice(s), this list of conditions and the following disclaimer as 11 * the first lines of this file unmodified other than the possible 12 * addition of one or more copyright notices. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice(s), this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 27 * DAMAGE. 28 */ 29 30 /* 31 * Shared/exclusive locks. This implementation attempts to ensure 32 * deterministic lock granting behavior, so that slocks and xlocks are 33 * interleaved. 34 * 35 * Priority propagation will not generally raise the priority of lock holders, 36 * so should not be relied upon in combination with sx locks. 37 */ 38 39 #include "opt_ddb.h" 40 #include "opt_hwpmc_hooks.h" 41 #include "opt_no_adaptive_sx.h" 42 43 #include <sys/cdefs.h> 44 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_sx.c 320241 2017-06-22 18:40:34Z markj $"); 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/kdb.h> 49 #include <sys/kernel.h> 50 #include <sys/ktr.h> 51 #include <sys/lock.h> 52 #include <sys/mutex.h> 53 #include <sys/proc.h> 54 #include <sys/sched.h> 55 #include <sys/sleepqueue.h> 56 #include <sys/sx.h> 57 #include <sys/smp.h> 58 #include <sys/sysctl.h> 59 60 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 61 #include <machine/cpu.h> 62 #endif 63 64 #ifdef DDB 65 #include <ddb/ddb.h> 66 #endif 67 68 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 69 #define ADAPTIVE_SX 70 #endif 71 72 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE); 73 74 #ifdef HWPMC_HOOKS 75 #include <sys/pmckern.h> 76 PMC_SOFT_DECLARE( , , lock, failed); 77 #endif 78 79 /* Handy macros for sleep queues. */ 80 #define SQ_EXCLUSIVE_QUEUE 0 81 #define SQ_SHARED_QUEUE 1 82 83 /* 84 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 85 * drop Giant anytime we have to sleep or if we adaptively spin. 86 */ 87 #define GIANT_DECLARE \ 88 int _giantcnt = 0; \ 89 WITNESS_SAVE_DECL(Giant) \ 90 91 #define GIANT_SAVE() do { \ 92 if (mtx_owned(&Giant)) { \ 93 WITNESS_SAVE(&Giant.lock_object, Giant); \ 94 while (mtx_owned(&Giant)) { \ 95 _giantcnt++; \ 96 mtx_unlock(&Giant); \ 97 } \ 98 } \ 99 } while (0) 100 101 #define GIANT_RESTORE() do { \ 102 if (_giantcnt > 0) { \ 103 mtx_assert(&Giant, MA_NOTOWNED); \ 104 while (_giantcnt--) \ 105 mtx_lock(&Giant); \ 106 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 107 } \ 108 } while (0) 109 110 /* 111 * Returns true if an exclusive lock is recursed. It assumes 112 * curthread currently has an exclusive lock. 113 */ 114 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 115 116 static void assert_sx(const struct lock_object *lock, int what); 117 #ifdef DDB 118 static void db_show_sx(const struct lock_object *lock); 119 #endif 120 static void lock_sx(struct lock_object *lock, uintptr_t how); 121 #ifdef KDTRACE_HOOKS 122 static int owner_sx(const struct lock_object *lock, struct thread **owner); 123 #endif 124 static uintptr_t unlock_sx(struct lock_object *lock); 125 126 struct lock_class lock_class_sx = { 127 .lc_name = "sx", 128 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 129 .lc_assert = assert_sx, 130 #ifdef DDB 131 .lc_ddb_show = db_show_sx, 132 #endif 133 .lc_lock = lock_sx, 134 .lc_unlock = unlock_sx, 135 #ifdef KDTRACE_HOOKS 136 .lc_owner = owner_sx, 137 #endif 138 }; 139 140 #ifndef INVARIANTS 141 #define _sx_assert(sx, what, file, line) 142 #endif 143 144 #ifdef ADAPTIVE_SX 145 static u_int asx_retries = 10; 146 static u_int asx_loops = 10000; 147 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging"); 148 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, ""); 149 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, ""); 150 151 static struct lock_delay_config __read_mostly sx_delay; 152 153 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base, 154 0, ""); 155 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max, 156 0, ""); 157 158 LOCK_DELAY_SYSINIT_DEFAULT(sx_delay); 159 #endif 160 161 void 162 assert_sx(const struct lock_object *lock, int what) 163 { 164 165 sx_assert((const struct sx *)lock, what); 166 } 167 168 void 169 lock_sx(struct lock_object *lock, uintptr_t how) 170 { 171 struct sx *sx; 172 173 sx = (struct sx *)lock; 174 if (how) 175 sx_slock(sx); 176 else 177 sx_xlock(sx); 178 } 179 180 uintptr_t 181 unlock_sx(struct lock_object *lock) 182 { 183 struct sx *sx; 184 185 sx = (struct sx *)lock; 186 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 187 if (sx_xlocked(sx)) { 188 sx_xunlock(sx); 189 return (0); 190 } else { 191 sx_sunlock(sx); 192 return (1); 193 } 194 } 195 196 #ifdef KDTRACE_HOOKS 197 int 198 owner_sx(const struct lock_object *lock, struct thread **owner) 199 { 200 const struct sx *sx = (const struct sx *)lock; 201 uintptr_t x = sx->sx_lock; 202 203 *owner = (struct thread *)SX_OWNER(x); 204 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 205 (*owner != NULL)); 206 } 207 #endif 208 209 void 210 sx_sysinit(void *arg) 211 { 212 struct sx_args *sargs = arg; 213 214 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags); 215 } 216 217 void 218 sx_init_flags(struct sx *sx, const char *description, int opts) 219 { 220 int flags; 221 222 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 223 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0); 224 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 225 ("%s: sx_lock not aligned for %s: %p", __func__, description, 226 &sx->sx_lock)); 227 228 flags = LO_SLEEPABLE | LO_UPGRADABLE; 229 if (opts & SX_DUPOK) 230 flags |= LO_DUPOK; 231 if (opts & SX_NOPROFILE) 232 flags |= LO_NOPROFILE; 233 if (!(opts & SX_NOWITNESS)) 234 flags |= LO_WITNESS; 235 if (opts & SX_RECURSE) 236 flags |= LO_RECURSABLE; 237 if (opts & SX_QUIET) 238 flags |= LO_QUIET; 239 if (opts & SX_NEW) 240 flags |= LO_NEW; 241 242 flags |= opts & SX_NOADAPTIVE; 243 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 244 sx->sx_lock = SX_LOCK_UNLOCKED; 245 sx->sx_recurse = 0; 246 } 247 248 void 249 sx_destroy(struct sx *sx) 250 { 251 252 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 253 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 254 sx->sx_lock = SX_LOCK_DESTROYED; 255 lock_destroy(&sx->lock_object); 256 } 257 258 int 259 sx_try_slock_(struct sx *sx, const char *file, int line) 260 { 261 uintptr_t x; 262 263 if (SCHEDULER_STOPPED()) 264 return (1); 265 266 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 267 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d", 268 curthread, sx->lock_object.lo_name, file, line)); 269 270 x = sx->sx_lock; 271 for (;;) { 272 KASSERT(x != SX_LOCK_DESTROYED, 273 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 274 if (!(x & SX_LOCK_SHARED)) 275 break; 276 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) { 277 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 278 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 279 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 280 sx, 0, 0, file, line, LOCKSTAT_READER); 281 TD_LOCKS_INC(curthread); 282 return (1); 283 } 284 } 285 286 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 287 return (0); 288 } 289 290 int 291 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 292 { 293 uintptr_t tid, x; 294 int error = 0; 295 296 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 297 !TD_IS_IDLETHREAD(curthread), 298 ("sx_xlock() by idle thread %p on sx %s @ %s:%d", 299 curthread, sx->lock_object.lo_name, file, line)); 300 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 301 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 302 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 303 line, NULL); 304 tid = (uintptr_t)curthread; 305 x = SX_LOCK_UNLOCKED; 306 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 307 error = _sx_xlock_hard(sx, x, tid, opts, file, line); 308 else 309 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 310 0, 0, file, line, LOCKSTAT_WRITER); 311 if (!error) { 312 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 313 file, line); 314 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 315 TD_LOCKS_INC(curthread); 316 } 317 318 return (error); 319 } 320 321 int 322 sx_try_xlock_(struct sx *sx, const char *file, int line) 323 { 324 struct thread *td; 325 uintptr_t tid, x; 326 int rval; 327 bool recursed; 328 329 td = curthread; 330 tid = (uintptr_t)td; 331 if (SCHEDULER_STOPPED_TD(td)) 332 return (1); 333 334 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td), 335 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d", 336 curthread, sx->lock_object.lo_name, file, line)); 337 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 338 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 339 340 rval = 1; 341 recursed = false; 342 x = SX_LOCK_UNLOCKED; 343 for (;;) { 344 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 345 break; 346 if (x == SX_LOCK_UNLOCKED) 347 continue; 348 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) { 349 sx->sx_recurse++; 350 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 351 break; 352 } 353 rval = 0; 354 break; 355 } 356 357 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 358 if (rval) { 359 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 360 file, line); 361 if (!recursed) 362 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, 363 sx, 0, 0, file, line, LOCKSTAT_WRITER); 364 TD_LOCKS_INC(curthread); 365 } 366 367 return (rval); 368 } 369 370 void 371 _sx_xunlock(struct sx *sx, const char *file, int line) 372 { 373 374 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 375 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 376 _sx_assert(sx, SA_XLOCKED, file, line); 377 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 378 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 379 line); 380 #if LOCK_DEBUG > 0 381 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line); 382 #else 383 __sx_xunlock(sx, curthread, file, line); 384 #endif 385 TD_LOCKS_DEC(curthread); 386 } 387 388 /* 389 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 390 * This will only succeed if this thread holds a single shared lock. 391 * Return 1 if if the upgrade succeed, 0 otherwise. 392 */ 393 int 394 sx_try_upgrade_(struct sx *sx, const char *file, int line) 395 { 396 uintptr_t x; 397 int success; 398 399 if (SCHEDULER_STOPPED()) 400 return (1); 401 402 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 403 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 404 _sx_assert(sx, SA_SLOCKED, file, line); 405 406 /* 407 * Try to switch from one shared lock to an exclusive lock. We need 408 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 409 * we will wake up the exclusive waiters when we drop the lock. 410 */ 411 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 412 success = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 413 (uintptr_t)curthread | x); 414 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 415 if (success) { 416 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 417 file, line); 418 LOCKSTAT_RECORD0(sx__upgrade, sx); 419 } 420 return (success); 421 } 422 423 /* 424 * Downgrade an unrecursed exclusive lock into a single shared lock. 425 */ 426 void 427 sx_downgrade_(struct sx *sx, const char *file, int line) 428 { 429 uintptr_t x; 430 int wakeup_swapper; 431 432 if (SCHEDULER_STOPPED()) 433 return; 434 435 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 436 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 437 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 438 #ifndef INVARIANTS 439 if (sx_recursed(sx)) 440 panic("downgrade of a recursed lock"); 441 #endif 442 443 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 444 445 /* 446 * Try to switch from an exclusive lock with no shared waiters 447 * to one sharer with no shared waiters. If there are 448 * exclusive waiters, we don't need to lock the sleep queue so 449 * long as we preserve the flag. We do one quick try and if 450 * that fails we grab the sleepq lock to keep the flags from 451 * changing and do it the slow way. 452 * 453 * We have to lock the sleep queue if there are shared waiters 454 * so we can wake them up. 455 */ 456 x = sx->sx_lock; 457 if (!(x & SX_LOCK_SHARED_WAITERS) && 458 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 459 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 460 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 461 return; 462 } 463 464 /* 465 * Lock the sleep queue so we can read the waiters bits 466 * without any races and wakeup any shared waiters. 467 */ 468 sleepq_lock(&sx->lock_object); 469 470 /* 471 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 472 * shared lock. If there are any shared waiters, wake them up. 473 */ 474 wakeup_swapper = 0; 475 x = sx->sx_lock; 476 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 477 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 478 if (x & SX_LOCK_SHARED_WAITERS) 479 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 480 0, SQ_SHARED_QUEUE); 481 sleepq_release(&sx->lock_object); 482 483 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 484 LOCKSTAT_RECORD0(sx__downgrade, sx); 485 486 if (wakeup_swapper) 487 kick_proc0(); 488 } 489 490 /* 491 * This function represents the so-called 'hard case' for sx_xlock 492 * operation. All 'easy case' failures are redirected to this. Note 493 * that ideally this would be a static function, but it needs to be 494 * accessible from at least sx.h. 495 */ 496 int 497 _sx_xlock_hard(struct sx *sx, uintptr_t x, uintptr_t tid, int opts, 498 const char *file, int line) 499 { 500 GIANT_DECLARE; 501 #ifdef ADAPTIVE_SX 502 volatile struct thread *owner; 503 u_int i, spintries = 0; 504 #endif 505 #ifdef LOCK_PROFILING 506 uint64_t waittime = 0; 507 int contested = 0; 508 #endif 509 int error = 0; 510 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 511 struct lock_delay_arg lda; 512 #endif 513 #ifdef KDTRACE_HOOKS 514 uintptr_t state; 515 u_int sleep_cnt = 0; 516 int64_t sleep_time = 0; 517 int64_t all_time = 0; 518 #endif 519 520 if (SCHEDULER_STOPPED()) 521 return (0); 522 523 #if defined(ADAPTIVE_SX) 524 lock_delay_arg_init(&lda, &sx_delay); 525 #elif defined(KDTRACE_HOOKS) 526 lock_delay_arg_init(&lda, NULL); 527 #endif 528 529 if (__predict_false(x == SX_LOCK_UNLOCKED)) 530 x = SX_READ_VALUE(sx); 531 532 /* If we already hold an exclusive lock, then recurse. */ 533 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) { 534 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 535 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 536 sx->lock_object.lo_name, file, line)); 537 sx->sx_recurse++; 538 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 539 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 540 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 541 return (0); 542 } 543 544 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 545 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 546 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 547 548 #ifdef KDTRACE_HOOKS 549 all_time -= lockstat_nsecs(&sx->lock_object); 550 state = x; 551 #endif 552 for (;;) { 553 if (x == SX_LOCK_UNLOCKED) { 554 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid)) 555 break; 556 continue; 557 } 558 #ifdef KDTRACE_HOOKS 559 lda.spin_cnt++; 560 #endif 561 #ifdef HWPMC_HOOKS 562 PMC_SOFT_CALL( , , lock, failed); 563 #endif 564 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 565 &waittime); 566 #ifdef ADAPTIVE_SX 567 /* 568 * If the lock is write locked and the owner is 569 * running on another CPU, spin until the owner stops 570 * running or the state of the lock changes. 571 */ 572 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 573 if ((x & SX_LOCK_SHARED) == 0) { 574 owner = lv_sx_owner(x); 575 if (TD_IS_RUNNING(owner)) { 576 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 577 CTR3(KTR_LOCK, 578 "%s: spinning on %p held by %p", 579 __func__, sx, owner); 580 KTR_STATE1(KTR_SCHED, "thread", 581 sched_tdname(curthread), "spinning", 582 "lockname:\"%s\"", 583 sx->lock_object.lo_name); 584 GIANT_SAVE(); 585 do { 586 lock_delay(&lda); 587 x = SX_READ_VALUE(sx); 588 owner = lv_sx_owner(x); 589 } while (owner != NULL && 590 TD_IS_RUNNING(owner)); 591 KTR_STATE0(KTR_SCHED, "thread", 592 sched_tdname(curthread), "running"); 593 continue; 594 } 595 } else if (SX_SHARERS(x) && spintries < asx_retries) { 596 KTR_STATE1(KTR_SCHED, "thread", 597 sched_tdname(curthread), "spinning", 598 "lockname:\"%s\"", sx->lock_object.lo_name); 599 GIANT_SAVE(); 600 spintries++; 601 for (i = 0; i < asx_loops; i++) { 602 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 603 CTR4(KTR_LOCK, 604 "%s: shared spinning on %p with %u and %u", 605 __func__, sx, spintries, i); 606 x = sx->sx_lock; 607 if ((x & SX_LOCK_SHARED) == 0 || 608 SX_SHARERS(x) == 0) 609 break; 610 cpu_spinwait(); 611 #ifdef KDTRACE_HOOKS 612 lda.spin_cnt++; 613 #endif 614 } 615 KTR_STATE0(KTR_SCHED, "thread", 616 sched_tdname(curthread), "running"); 617 x = SX_READ_VALUE(sx); 618 if (i != asx_loops) 619 continue; 620 } 621 } 622 #endif 623 624 sleepq_lock(&sx->lock_object); 625 x = SX_READ_VALUE(sx); 626 627 /* 628 * If the lock was released while spinning on the 629 * sleep queue chain lock, try again. 630 */ 631 if (x == SX_LOCK_UNLOCKED) { 632 sleepq_release(&sx->lock_object); 633 continue; 634 } 635 636 #ifdef ADAPTIVE_SX 637 /* 638 * The current lock owner might have started executing 639 * on another CPU (or the lock could have changed 640 * owners) while we were waiting on the sleep queue 641 * chain lock. If so, drop the sleep queue lock and try 642 * again. 643 */ 644 if (!(x & SX_LOCK_SHARED) && 645 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 646 owner = (struct thread *)SX_OWNER(x); 647 if (TD_IS_RUNNING(owner)) { 648 sleepq_release(&sx->lock_object); 649 continue; 650 } 651 } 652 #endif 653 654 /* 655 * If an exclusive lock was released with both shared 656 * and exclusive waiters and a shared waiter hasn't 657 * woken up and acquired the lock yet, sx_lock will be 658 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 659 * If we see that value, try to acquire it once. Note 660 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 661 * as there are other exclusive waiters still. If we 662 * fail, restart the loop. 663 */ 664 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 665 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 666 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 667 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 668 sleepq_release(&sx->lock_object); 669 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 670 __func__, sx); 671 break; 672 } 673 sleepq_release(&sx->lock_object); 674 x = SX_READ_VALUE(sx); 675 continue; 676 } 677 678 /* 679 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 680 * than loop back and retry. 681 */ 682 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 683 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 684 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 685 sleepq_release(&sx->lock_object); 686 x = SX_READ_VALUE(sx); 687 continue; 688 } 689 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 690 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 691 __func__, sx); 692 } 693 694 /* 695 * Since we have been unable to acquire the exclusive 696 * lock and the exclusive waiters flag is set, we have 697 * to sleep. 698 */ 699 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 700 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 701 __func__, sx); 702 703 #ifdef KDTRACE_HOOKS 704 sleep_time -= lockstat_nsecs(&sx->lock_object); 705 #endif 706 GIANT_SAVE(); 707 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 708 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 709 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 710 if (!(opts & SX_INTERRUPTIBLE)) 711 sleepq_wait(&sx->lock_object, 0); 712 else 713 error = sleepq_wait_sig(&sx->lock_object, 0); 714 #ifdef KDTRACE_HOOKS 715 sleep_time += lockstat_nsecs(&sx->lock_object); 716 sleep_cnt++; 717 #endif 718 if (error) { 719 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 720 CTR2(KTR_LOCK, 721 "%s: interruptible sleep by %p suspended by signal", 722 __func__, sx); 723 break; 724 } 725 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 726 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 727 __func__, sx); 728 x = SX_READ_VALUE(sx); 729 } 730 #ifdef KDTRACE_HOOKS 731 all_time += lockstat_nsecs(&sx->lock_object); 732 if (sleep_time) 733 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 734 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 735 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 736 if (lda.spin_cnt > sleep_cnt) 737 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 738 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0, 739 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 740 #endif 741 if (!error) 742 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 743 contested, waittime, file, line, LOCKSTAT_WRITER); 744 GIANT_RESTORE(); 745 return (error); 746 } 747 748 /* 749 * This function represents the so-called 'hard case' for sx_xunlock 750 * operation. All 'easy case' failures are redirected to this. Note 751 * that ideally this would be a static function, but it needs to be 752 * accessible from at least sx.h. 753 */ 754 void 755 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 756 { 757 uintptr_t x; 758 int queue, wakeup_swapper; 759 760 if (SCHEDULER_STOPPED()) 761 return; 762 763 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 764 765 x = SX_READ_VALUE(sx); 766 if (x & SX_LOCK_RECURSED) { 767 /* The lock is recursed, unrecurse one level. */ 768 if ((--sx->sx_recurse) == 0) 769 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 770 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 771 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 772 return; 773 } 774 775 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER); 776 if (x == tid && 777 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 778 return; 779 780 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 781 SX_LOCK_EXCLUSIVE_WAITERS)); 782 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 783 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 784 785 sleepq_lock(&sx->lock_object); 786 x = SX_LOCK_UNLOCKED; 787 788 /* 789 * The wake up algorithm here is quite simple and probably not 790 * ideal. It gives precedence to shared waiters if they are 791 * present. For this condition, we have to preserve the 792 * state of the exclusive waiters flag. 793 * If interruptible sleeps left the shared queue empty avoid a 794 * starvation for the threads sleeping on the exclusive queue by giving 795 * them precedence and cleaning up the shared waiters bit anyway. 796 */ 797 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 && 798 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 799 queue = SQ_SHARED_QUEUE; 800 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 801 } else 802 queue = SQ_EXCLUSIVE_QUEUE; 803 804 /* Wake up all the waiters for the specific queue. */ 805 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 806 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 807 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 808 "exclusive"); 809 atomic_store_rel_ptr(&sx->sx_lock, x); 810 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 811 queue); 812 sleepq_release(&sx->lock_object); 813 if (wakeup_swapper) 814 kick_proc0(); 815 } 816 817 static bool __always_inline 818 __sx_slock_try(struct sx *sx, uintptr_t *xp, const char *file, int line) 819 { 820 821 /* 822 * If no other thread has an exclusive lock then try to bump up 823 * the count of sharers. Since we have to preserve the state 824 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 825 * shared lock loop back and retry. 826 */ 827 while (*xp & SX_LOCK_SHARED) { 828 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS)); 829 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp, 830 *xp + SX_ONE_SHARER)) { 831 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 832 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p", 833 __func__, sx, (void *)*xp, 834 (void *)(*xp + SX_ONE_SHARER)); 835 return (true); 836 } 837 } 838 return (false); 839 } 840 841 static int __noinline 842 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line, uintptr_t x) 843 { 844 GIANT_DECLARE; 845 #ifdef ADAPTIVE_SX 846 volatile struct thread *owner; 847 #endif 848 #ifdef LOCK_PROFILING 849 uint64_t waittime = 0; 850 int contested = 0; 851 #endif 852 int error = 0; 853 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS) 854 struct lock_delay_arg lda; 855 #endif 856 #ifdef KDTRACE_HOOKS 857 uintptr_t state; 858 u_int sleep_cnt = 0; 859 int64_t sleep_time = 0; 860 int64_t all_time = 0; 861 #endif 862 863 if (SCHEDULER_STOPPED()) 864 return (0); 865 866 #if defined(ADAPTIVE_SX) 867 lock_delay_arg_init(&lda, &sx_delay); 868 #elif defined(KDTRACE_HOOKS) 869 lock_delay_arg_init(&lda, NULL); 870 #endif 871 #ifdef KDTRACE_HOOKS 872 all_time -= lockstat_nsecs(&sx->lock_object); 873 state = x; 874 #endif 875 876 /* 877 * As with rwlocks, we don't make any attempt to try to block 878 * shared locks once there is an exclusive waiter. 879 */ 880 for (;;) { 881 if (__sx_slock_try(sx, &x, file, line)) 882 break; 883 #ifdef KDTRACE_HOOKS 884 lda.spin_cnt++; 885 #endif 886 887 #ifdef HWPMC_HOOKS 888 PMC_SOFT_CALL( , , lock, failed); 889 #endif 890 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 891 &waittime); 892 893 #ifdef ADAPTIVE_SX 894 /* 895 * If the owner is running on another CPU, spin until 896 * the owner stops running or the state of the lock 897 * changes. 898 */ 899 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 900 owner = lv_sx_owner(x); 901 if (TD_IS_RUNNING(owner)) { 902 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 903 CTR3(KTR_LOCK, 904 "%s: spinning on %p held by %p", 905 __func__, sx, owner); 906 KTR_STATE1(KTR_SCHED, "thread", 907 sched_tdname(curthread), "spinning", 908 "lockname:\"%s\"", sx->lock_object.lo_name); 909 GIANT_SAVE(); 910 do { 911 lock_delay(&lda); 912 x = SX_READ_VALUE(sx); 913 owner = lv_sx_owner(x); 914 } while (owner != NULL && TD_IS_RUNNING(owner)); 915 KTR_STATE0(KTR_SCHED, "thread", 916 sched_tdname(curthread), "running"); 917 continue; 918 } 919 } 920 #endif 921 922 /* 923 * Some other thread already has an exclusive lock, so 924 * start the process of blocking. 925 */ 926 sleepq_lock(&sx->lock_object); 927 x = SX_READ_VALUE(sx); 928 929 /* 930 * The lock could have been released while we spun. 931 * In this case loop back and retry. 932 */ 933 if (x & SX_LOCK_SHARED) { 934 sleepq_release(&sx->lock_object); 935 continue; 936 } 937 938 #ifdef ADAPTIVE_SX 939 /* 940 * If the owner is running on another CPU, spin until 941 * the owner stops running or the state of the lock 942 * changes. 943 */ 944 if (!(x & SX_LOCK_SHARED) && 945 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 946 owner = (struct thread *)SX_OWNER(x); 947 if (TD_IS_RUNNING(owner)) { 948 sleepq_release(&sx->lock_object); 949 x = SX_READ_VALUE(sx); 950 continue; 951 } 952 } 953 #endif 954 955 /* 956 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 957 * fail to set it drop the sleep queue lock and loop 958 * back. 959 */ 960 if (!(x & SX_LOCK_SHARED_WAITERS)) { 961 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 962 x | SX_LOCK_SHARED_WAITERS)) { 963 sleepq_release(&sx->lock_object); 964 x = SX_READ_VALUE(sx); 965 continue; 966 } 967 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 968 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 969 __func__, sx); 970 } 971 972 /* 973 * Since we have been unable to acquire the shared lock, 974 * we have to sleep. 975 */ 976 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 977 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 978 __func__, sx); 979 980 #ifdef KDTRACE_HOOKS 981 sleep_time -= lockstat_nsecs(&sx->lock_object); 982 #endif 983 GIANT_SAVE(); 984 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 985 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 986 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 987 if (!(opts & SX_INTERRUPTIBLE)) 988 sleepq_wait(&sx->lock_object, 0); 989 else 990 error = sleepq_wait_sig(&sx->lock_object, 0); 991 #ifdef KDTRACE_HOOKS 992 sleep_time += lockstat_nsecs(&sx->lock_object); 993 sleep_cnt++; 994 #endif 995 if (error) { 996 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 997 CTR2(KTR_LOCK, 998 "%s: interruptible sleep by %p suspended by signal", 999 __func__, sx); 1000 break; 1001 } 1002 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1003 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 1004 __func__, sx); 1005 x = SX_READ_VALUE(sx); 1006 } 1007 #ifdef KDTRACE_HOOKS 1008 all_time += lockstat_nsecs(&sx->lock_object); 1009 if (sleep_time) 1010 LOCKSTAT_RECORD4(sx__block, sx, sleep_time, 1011 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1012 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1013 if (lda.spin_cnt > sleep_cnt) 1014 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time, 1015 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0, 1016 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state)); 1017 #endif 1018 if (error == 0) { 1019 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx, 1020 contested, waittime, file, line, LOCKSTAT_READER); 1021 } 1022 GIANT_RESTORE(); 1023 return (error); 1024 } 1025 1026 int 1027 _sx_slock(struct sx *sx, int opts, const char *file, int line) 1028 { 1029 uintptr_t x; 1030 int error; 1031 1032 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() || 1033 !TD_IS_IDLETHREAD(curthread), 1034 ("sx_slock() by idle thread %p on sx %s @ %s:%d", 1035 curthread, sx->lock_object.lo_name, file, line)); 1036 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1037 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 1038 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 1039 1040 error = 0; 1041 x = SX_READ_VALUE(sx); 1042 if (__predict_false(LOCKSTAT_OOL_PROFILE_ENABLED(sx__acquire) || 1043 !__sx_slock_try(sx, &x, file, line))) 1044 error = _sx_slock_hard(sx, opts, file, line, x); 1045 if (error == 0) { 1046 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 1047 WITNESS_LOCK(&sx->lock_object, 0, file, line); 1048 TD_LOCKS_INC(curthread); 1049 } 1050 return (error); 1051 } 1052 1053 static bool __always_inline 1054 _sx_sunlock_try(struct sx *sx, uintptr_t *xp) 1055 { 1056 1057 for (;;) { 1058 /* 1059 * We should never have sharers while at least one thread 1060 * holds a shared lock. 1061 */ 1062 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS), 1063 ("%s: waiting sharers", __func__)); 1064 1065 /* 1066 * See if there is more than one shared lock held. If 1067 * so, just drop one and return. 1068 */ 1069 if (SX_SHARERS(*xp) > 1) { 1070 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp, 1071 *xp - SX_ONE_SHARER)) { 1072 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1073 CTR4(KTR_LOCK, 1074 "%s: %p succeeded %p -> %p", 1075 __func__, sx, (void *)*xp, 1076 (void *)(*xp - SX_ONE_SHARER)); 1077 return (true); 1078 } 1079 continue; 1080 } 1081 1082 /* 1083 * If there aren't any waiters for an exclusive lock, 1084 * then try to drop it quickly. 1085 */ 1086 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) { 1087 MPASS(*xp == SX_SHARERS_LOCK(1)); 1088 *xp = SX_SHARERS_LOCK(1); 1089 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, 1090 xp, SX_LOCK_UNLOCKED)) { 1091 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1092 CTR2(KTR_LOCK, "%s: %p last succeeded", 1093 __func__, sx); 1094 return (true); 1095 } 1096 continue; 1097 } 1098 break; 1099 } 1100 return (false); 1101 } 1102 1103 static void __noinline 1104 _sx_sunlock_hard(struct sx *sx, uintptr_t x, const char *file, int line) 1105 { 1106 int wakeup_swapper; 1107 1108 if (SCHEDULER_STOPPED()) 1109 return; 1110 1111 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER); 1112 1113 for (;;) { 1114 if (_sx_sunlock_try(sx, &x)) 1115 break; 1116 1117 /* 1118 * At this point, there should just be one sharer with 1119 * exclusive waiters. 1120 */ 1121 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 1122 1123 sleepq_lock(&sx->lock_object); 1124 1125 /* 1126 * Wake up semantic here is quite simple: 1127 * Just wake up all the exclusive waiters. 1128 * Note that the state of the lock could have changed, 1129 * so if it fails loop back and retry. 1130 */ 1131 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, 1132 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 1133 SX_LOCK_UNLOCKED)) { 1134 sleepq_release(&sx->lock_object); 1135 x = SX_READ_VALUE(sx); 1136 continue; 1137 } 1138 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1139 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1140 "exclusive queue", __func__, sx); 1141 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1142 0, SQ_EXCLUSIVE_QUEUE); 1143 sleepq_release(&sx->lock_object); 1144 if (wakeup_swapper) 1145 kick_proc0(); 1146 break; 1147 } 1148 } 1149 1150 void 1151 _sx_sunlock(struct sx *sx, const char *file, int line) 1152 { 1153 uintptr_t x; 1154 1155 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 1156 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 1157 _sx_assert(sx, SA_SLOCKED, file, line); 1158 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 1159 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 1160 1161 x = SX_READ_VALUE(sx); 1162 if (__predict_false(LOCKSTAT_OOL_PROFILE_ENABLED(sx__release) || 1163 !_sx_sunlock_try(sx, &x))) 1164 _sx_sunlock_hard(sx, x, file, line); 1165 1166 TD_LOCKS_DEC(curthread); 1167 } 1168 1169 #ifdef INVARIANT_SUPPORT 1170 #ifndef INVARIANTS 1171 #undef _sx_assert 1172 #endif 1173 1174 /* 1175 * In the non-WITNESS case, sx_assert() can only detect that at least 1176 * *some* thread owns an slock, but it cannot guarantee that *this* 1177 * thread owns an slock. 1178 */ 1179 void 1180 _sx_assert(const struct sx *sx, int what, const char *file, int line) 1181 { 1182 #ifndef WITNESS 1183 int slocked = 0; 1184 #endif 1185 1186 if (panicstr != NULL) 1187 return; 1188 switch (what) { 1189 case SA_SLOCKED: 1190 case SA_SLOCKED | SA_NOTRECURSED: 1191 case SA_SLOCKED | SA_RECURSED: 1192 #ifndef WITNESS 1193 slocked = 1; 1194 /* FALLTHROUGH */ 1195 #endif 1196 case SA_LOCKED: 1197 case SA_LOCKED | SA_NOTRECURSED: 1198 case SA_LOCKED | SA_RECURSED: 1199 #ifdef WITNESS 1200 witness_assert(&sx->lock_object, what, file, line); 1201 #else 1202 /* 1203 * If some other thread has an exclusive lock or we 1204 * have one and are asserting a shared lock, fail. 1205 * Also, if no one has a lock at all, fail. 1206 */ 1207 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1208 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1209 sx_xholder(sx) != curthread))) 1210 panic("Lock %s not %slocked @ %s:%d\n", 1211 sx->lock_object.lo_name, slocked ? "share " : "", 1212 file, line); 1213 1214 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1215 if (sx_recursed(sx)) { 1216 if (what & SA_NOTRECURSED) 1217 panic("Lock %s recursed @ %s:%d\n", 1218 sx->lock_object.lo_name, file, 1219 line); 1220 } else if (what & SA_RECURSED) 1221 panic("Lock %s not recursed @ %s:%d\n", 1222 sx->lock_object.lo_name, file, line); 1223 } 1224 #endif 1225 break; 1226 case SA_XLOCKED: 1227 case SA_XLOCKED | SA_NOTRECURSED: 1228 case SA_XLOCKED | SA_RECURSED: 1229 if (sx_xholder(sx) != curthread) 1230 panic("Lock %s not exclusively locked @ %s:%d\n", 1231 sx->lock_object.lo_name, file, line); 1232 if (sx_recursed(sx)) { 1233 if (what & SA_NOTRECURSED) 1234 panic("Lock %s recursed @ %s:%d\n", 1235 sx->lock_object.lo_name, file, line); 1236 } else if (what & SA_RECURSED) 1237 panic("Lock %s not recursed @ %s:%d\n", 1238 sx->lock_object.lo_name, file, line); 1239 break; 1240 case SA_UNLOCKED: 1241 #ifdef WITNESS 1242 witness_assert(&sx->lock_object, what, file, line); 1243 #else 1244 /* 1245 * If we hold an exclusve lock fail. We can't 1246 * reliably check to see if we hold a shared lock or 1247 * not. 1248 */ 1249 if (sx_xholder(sx) == curthread) 1250 panic("Lock %s exclusively locked @ %s:%d\n", 1251 sx->lock_object.lo_name, file, line); 1252 #endif 1253 break; 1254 default: 1255 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1256 line); 1257 } 1258 } 1259 #endif /* INVARIANT_SUPPORT */ 1260 1261 #ifdef DDB 1262 static void 1263 db_show_sx(const struct lock_object *lock) 1264 { 1265 struct thread *td; 1266 const struct sx *sx; 1267 1268 sx = (const struct sx *)lock; 1269 1270 db_printf(" state: "); 1271 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1272 db_printf("UNLOCKED\n"); 1273 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1274 db_printf("DESTROYED\n"); 1275 return; 1276 } else if (sx->sx_lock & SX_LOCK_SHARED) 1277 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1278 else { 1279 td = sx_xholder(sx); 1280 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1281 td->td_tid, td->td_proc->p_pid, td->td_name); 1282 if (sx_recursed(sx)) 1283 db_printf(" recursed: %d\n", sx->sx_recurse); 1284 } 1285 1286 db_printf(" waiters: "); 1287 switch(sx->sx_lock & 1288 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1289 case SX_LOCK_SHARED_WAITERS: 1290 db_printf("shared\n"); 1291 break; 1292 case SX_LOCK_EXCLUSIVE_WAITERS: 1293 db_printf("exclusive\n"); 1294 break; 1295 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1296 db_printf("exclusive and shared\n"); 1297 break; 1298 default: 1299 db_printf("none\n"); 1300 } 1301 } 1302 1303 /* 1304 * Check to see if a thread that is blocked on a sleep queue is actually 1305 * blocked on an sx lock. If so, output some details and return true. 1306 * If the lock has an exclusive owner, return that in *ownerp. 1307 */ 1308 int 1309 sx_chain(struct thread *td, struct thread **ownerp) 1310 { 1311 struct sx *sx; 1312 1313 /* 1314 * Check to see if this thread is blocked on an sx lock. 1315 * First, we check the lock class. If that is ok, then we 1316 * compare the lock name against the wait message. 1317 */ 1318 sx = td->td_wchan; 1319 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1320 sx->lock_object.lo_name != td->td_wmesg) 1321 return (0); 1322 1323 /* We think we have an sx lock, so output some details. */ 1324 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1325 *ownerp = sx_xholder(sx); 1326 if (sx->sx_lock & SX_LOCK_SHARED) 1327 db_printf("SLOCK (count %ju)\n", 1328 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1329 else 1330 db_printf("XLOCK\n"); 1331 return (1); 1332 } 1333 #endif
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