Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
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_kdtrace.h" 41 #include "opt_no_adaptive_sx.h" 42 43 #include <sys/cdefs.h> 44 __FBSDID("$FreeBSD: releng/8.4/sys/kern/kern_sx.c 235502 2012-05-16 09:03:29Z avg $"); 45 46 #include <sys/param.h> 47 #include <sys/systm.h> 48 #include <sys/ktr.h> 49 #include <sys/lock.h> 50 #include <sys/mutex.h> 51 #include <sys/proc.h> 52 #include <sys/sleepqueue.h> 53 #include <sys/sx.h> 54 #include <sys/sysctl.h> 55 56 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 57 #include <machine/cpu.h> 58 #endif 59 60 #ifdef DDB 61 #include <ddb/ddb.h> 62 #endif 63 64 #if defined(SMP) && !defined(NO_ADAPTIVE_SX) 65 #define ADAPTIVE_SX 66 #endif 67 68 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE); 69 70 /* Handy macros for sleep queues. */ 71 #define SQ_EXCLUSIVE_QUEUE 0 72 #define SQ_SHARED_QUEUE 1 73 74 #ifdef ADAPTIVE_SX 75 #define ASX_RETRIES 10 76 #define ASX_LOOPS 10000 77 #endif 78 79 /* 80 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 81 * drop Giant anytime we have to sleep or if we adaptively spin. 82 */ 83 #define GIANT_DECLARE \ 84 int _giantcnt = 0; \ 85 WITNESS_SAVE_DECL(Giant) \ 86 87 #define GIANT_SAVE() do { \ 88 if (mtx_owned(&Giant)) { \ 89 WITNESS_SAVE(&Giant.lock_object, Giant); \ 90 while (mtx_owned(&Giant)) { \ 91 _giantcnt++; \ 92 mtx_unlock(&Giant); \ 93 } \ 94 } \ 95 } while (0) 96 97 #define GIANT_RESTORE() do { \ 98 if (_giantcnt > 0) { \ 99 mtx_assert(&Giant, MA_NOTOWNED); \ 100 while (_giantcnt--) \ 101 mtx_lock(&Giant); \ 102 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 103 } \ 104 } while (0) 105 106 /* 107 * Returns true if an exclusive lock is recursed. It assumes 108 * curthread currently has an exclusive lock. 109 */ 110 #define sx_recurse lock_object.lo_data 111 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 112 113 static void assert_sx(struct lock_object *lock, int what); 114 #ifdef DDB 115 static void db_show_sx(struct lock_object *lock); 116 #endif 117 static void lock_sx(struct lock_object *lock, int how); 118 #ifdef KDTRACE_HOOKS 119 static int owner_sx(struct lock_object *lock, struct thread **owner); 120 #endif 121 static int unlock_sx(struct lock_object *lock); 122 123 struct lock_class lock_class_sx = { 124 .lc_name = "sx", 125 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 126 .lc_assert = assert_sx, 127 #ifdef DDB 128 .lc_ddb_show = db_show_sx, 129 #endif 130 .lc_lock = lock_sx, 131 .lc_unlock = unlock_sx, 132 #ifdef KDTRACE_HOOKS 133 .lc_owner = owner_sx, 134 #endif 135 }; 136 137 #ifndef INVARIANTS 138 #define _sx_assert(sx, what, file, line) 139 #endif 140 141 void 142 assert_sx(struct lock_object *lock, int what) 143 { 144 145 sx_assert((struct sx *)lock, what); 146 } 147 148 void 149 lock_sx(struct lock_object *lock, int how) 150 { 151 struct sx *sx; 152 153 sx = (struct sx *)lock; 154 if (how) 155 sx_xlock(sx); 156 else 157 sx_slock(sx); 158 } 159 160 int 161 unlock_sx(struct lock_object *lock) 162 { 163 struct sx *sx; 164 165 sx = (struct sx *)lock; 166 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED); 167 if (sx_xlocked(sx)) { 168 sx_xunlock(sx); 169 return (1); 170 } else { 171 sx_sunlock(sx); 172 return (0); 173 } 174 } 175 176 #ifdef KDTRACE_HOOKS 177 int 178 owner_sx(struct lock_object *lock, struct thread **owner) 179 { 180 struct sx *sx = (struct sx *)lock; 181 uintptr_t x = sx->sx_lock; 182 183 *owner = (struct thread *)SX_OWNER(x); 184 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) : 185 (*owner != NULL)); 186 } 187 #endif 188 189 void 190 sx_sysinit(void *arg) 191 { 192 struct sx_args *sargs = arg; 193 194 sx_init(sargs->sa_sx, sargs->sa_desc); 195 } 196 197 void 198 sx_init_flags(struct sx *sx, const char *description, int opts) 199 { 200 int flags; 201 202 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 203 SX_NOPROFILE | SX_NOADAPTIVE)) == 0); 204 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock, 205 ("%s: sx_lock not aligned for %s: %p", __func__, description, 206 &sx->sx_lock)); 207 208 flags = LO_SLEEPABLE | LO_UPGRADABLE; 209 if (opts & SX_DUPOK) 210 flags |= LO_DUPOK; 211 if (opts & SX_NOPROFILE) 212 flags |= LO_NOPROFILE; 213 if (!(opts & SX_NOWITNESS)) 214 flags |= LO_WITNESS; 215 if (opts & SX_RECURSE) 216 flags |= LO_RECURSABLE; 217 if (opts & SX_QUIET) 218 flags |= LO_QUIET; 219 220 flags |= opts & SX_NOADAPTIVE; 221 sx->sx_lock = SX_LOCK_UNLOCKED; 222 sx->sx_recurse = 0; 223 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 224 } 225 226 void 227 sx_destroy(struct sx *sx) 228 { 229 230 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 231 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 232 sx->sx_lock = SX_LOCK_DESTROYED; 233 lock_destroy(&sx->lock_object); 234 } 235 236 int 237 _sx_slock(struct sx *sx, int opts, const char *file, int line) 238 { 239 int error = 0; 240 241 if (SCHEDULER_STOPPED()) 242 return (0); 243 MPASS(curthread != NULL); 244 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 245 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 246 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL); 247 error = __sx_slock(sx, opts, file, line); 248 if (!error) { 249 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 250 WITNESS_LOCK(&sx->lock_object, 0, file, line); 251 curthread->td_locks++; 252 } 253 254 return (error); 255 } 256 257 int 258 _sx_try_slock(struct sx *sx, const char *file, int line) 259 { 260 uintptr_t x; 261 262 if (SCHEDULER_STOPPED()) 263 return (1); 264 265 for (;;) { 266 x = sx->sx_lock; 267 KASSERT(x != SX_LOCK_DESTROYED, 268 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 269 if (!(x & SX_LOCK_SHARED)) 270 break; 271 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) { 272 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 273 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 274 curthread->td_locks++; 275 return (1); 276 } 277 } 278 279 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 280 return (0); 281 } 282 283 int 284 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 285 { 286 int error = 0; 287 288 if (SCHEDULER_STOPPED()) 289 return (0); 290 MPASS(curthread != NULL); 291 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 292 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 293 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 294 line, NULL); 295 error = __sx_xlock(sx, curthread, opts, file, line); 296 if (!error) { 297 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 298 file, line); 299 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 300 curthread->td_locks++; 301 } 302 303 return (error); 304 } 305 306 int 307 _sx_try_xlock(struct sx *sx, const char *file, int line) 308 { 309 int rval; 310 311 if (SCHEDULER_STOPPED()) 312 return (1); 313 314 MPASS(curthread != NULL); 315 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 316 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 317 318 if (sx_xlocked(sx) && 319 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) { 320 sx->sx_recurse++; 321 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 322 rval = 1; 323 } else 324 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 325 (uintptr_t)curthread); 326 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 327 if (rval) { 328 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 329 file, line); 330 curthread->td_locks++; 331 } 332 333 return (rval); 334 } 335 336 void 337 _sx_sunlock(struct sx *sx, const char *file, int line) 338 { 339 340 if (SCHEDULER_STOPPED()) 341 return; 342 MPASS(curthread != NULL); 343 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 344 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 345 _sx_assert(sx, SA_SLOCKED, file, line); 346 curthread->td_locks--; 347 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 348 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 349 __sx_sunlock(sx, file, line); 350 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx); 351 } 352 353 void 354 _sx_xunlock(struct sx *sx, const char *file, int line) 355 { 356 357 if (SCHEDULER_STOPPED()) 358 return; 359 MPASS(curthread != NULL); 360 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 361 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 362 _sx_assert(sx, SA_XLOCKED, file, line); 363 curthread->td_locks--; 364 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 365 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 366 line); 367 if (!sx_recursed(sx)) 368 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx); 369 __sx_xunlock(sx, curthread, file, line); 370 } 371 372 /* 373 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 374 * This will only succeed if this thread holds a single shared lock. 375 * Return 1 if if the upgrade succeed, 0 otherwise. 376 */ 377 int 378 _sx_try_upgrade(struct sx *sx, const char *file, int line) 379 { 380 uintptr_t x; 381 int success; 382 383 if (SCHEDULER_STOPPED()) 384 return (1); 385 386 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 387 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 388 _sx_assert(sx, SA_SLOCKED, file, line); 389 390 /* 391 * Try to switch from one shared lock to an exclusive lock. We need 392 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 393 * we will wake up the exclusive waiters when we drop the lock. 394 */ 395 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 396 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 397 (uintptr_t)curthread | x); 398 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 399 if (success) { 400 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 401 file, line); 402 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx); 403 } 404 return (success); 405 } 406 407 /* 408 * Downgrade an unrecursed exclusive lock into a single shared lock. 409 */ 410 void 411 _sx_downgrade(struct sx *sx, const char *file, int line) 412 { 413 uintptr_t x; 414 int wakeup_swapper; 415 416 if (SCHEDULER_STOPPED()) 417 return; 418 419 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 420 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 421 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 422 #ifndef INVARIANTS 423 if (sx_recursed(sx)) 424 panic("downgrade of a recursed lock"); 425 #endif 426 427 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 428 429 /* 430 * Try to switch from an exclusive lock with no shared waiters 431 * to one sharer with no shared waiters. If there are 432 * exclusive waiters, we don't need to lock the sleep queue so 433 * long as we preserve the flag. We do one quick try and if 434 * that fails we grab the sleepq lock to keep the flags from 435 * changing and do it the slow way. 436 * 437 * We have to lock the sleep queue if there are shared waiters 438 * so we can wake them up. 439 */ 440 x = sx->sx_lock; 441 if (!(x & SX_LOCK_SHARED_WAITERS) && 442 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 443 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 444 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 445 return; 446 } 447 448 /* 449 * Lock the sleep queue so we can read the waiters bits 450 * without any races and wakeup any shared waiters. 451 */ 452 sleepq_lock(&sx->lock_object); 453 454 /* 455 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 456 * shared lock. If there are any shared waiters, wake them up. 457 */ 458 wakeup_swapper = 0; 459 x = sx->sx_lock; 460 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 461 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 462 if (x & SX_LOCK_SHARED_WAITERS) 463 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 464 0, SQ_SHARED_QUEUE); 465 sleepq_release(&sx->lock_object); 466 467 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 468 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx); 469 470 if (wakeup_swapper) 471 kick_proc0(); 472 } 473 474 /* 475 * This function represents the so-called 'hard case' for sx_xlock 476 * operation. All 'easy case' failures are redirected to this. Note 477 * that ideally this would be a static function, but it needs to be 478 * accessible from at least sx.h. 479 */ 480 int 481 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 482 int line) 483 { 484 GIANT_DECLARE; 485 #ifdef ADAPTIVE_SX 486 volatile struct thread *owner; 487 u_int i, spintries = 0; 488 #endif 489 uintptr_t x; 490 #ifdef LOCK_PROFILING 491 uint64_t waittime = 0; 492 int contested = 0; 493 #endif 494 int error = 0; 495 #ifdef KDTRACE_HOOKS 496 uint64_t spin_cnt = 0; 497 uint64_t sleep_cnt = 0; 498 int64_t sleep_time = 0; 499 #endif 500 501 if (SCHEDULER_STOPPED()) 502 return (0); 503 504 /* If we already hold an exclusive lock, then recurse. */ 505 if (sx_xlocked(sx)) { 506 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0, 507 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 508 sx->lock_object.lo_name, file, line)); 509 sx->sx_recurse++; 510 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 511 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 512 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 513 return (0); 514 } 515 516 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 517 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 518 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 519 520 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 521 #ifdef KDTRACE_HOOKS 522 spin_cnt++; 523 #endif 524 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 525 &waittime); 526 #ifdef ADAPTIVE_SX 527 /* 528 * If the lock is write locked and the owner is 529 * running on another CPU, spin until the owner stops 530 * running or the state of the lock changes. 531 */ 532 x = sx->sx_lock; 533 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 534 if ((x & SX_LOCK_SHARED) == 0) { 535 x = SX_OWNER(x); 536 owner = (struct thread *)x; 537 if (TD_IS_RUNNING(owner)) { 538 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 539 CTR3(KTR_LOCK, 540 "%s: spinning on %p held by %p", 541 __func__, sx, owner); 542 GIANT_SAVE(); 543 while (SX_OWNER(sx->sx_lock) == x && 544 TD_IS_RUNNING(owner)) { 545 cpu_spinwait(); 546 #ifdef KDTRACE_HOOKS 547 spin_cnt++; 548 #endif 549 } 550 continue; 551 } 552 } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) { 553 GIANT_SAVE(); 554 spintries++; 555 for (i = 0; i < ASX_LOOPS; i++) { 556 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 557 CTR4(KTR_LOCK, 558 "%s: shared spinning on %p with %u and %u", 559 __func__, sx, spintries, i); 560 x = sx->sx_lock; 561 if ((x & SX_LOCK_SHARED) == 0 || 562 SX_SHARERS(x) == 0) 563 break; 564 cpu_spinwait(); 565 #ifdef KDTRACE_HOOKS 566 spin_cnt++; 567 #endif 568 } 569 if (i != ASX_LOOPS) 570 continue; 571 } 572 } 573 #endif 574 575 sleepq_lock(&sx->lock_object); 576 x = sx->sx_lock; 577 578 /* 579 * If the lock was released while spinning on the 580 * sleep queue chain lock, try again. 581 */ 582 if (x == SX_LOCK_UNLOCKED) { 583 sleepq_release(&sx->lock_object); 584 continue; 585 } 586 587 #ifdef ADAPTIVE_SX 588 /* 589 * The current lock owner might have started executing 590 * on another CPU (or the lock could have changed 591 * owners) while we were waiting on the sleep queue 592 * chain lock. If so, drop the sleep queue lock and try 593 * again. 594 */ 595 if (!(x & SX_LOCK_SHARED) && 596 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 597 owner = (struct thread *)SX_OWNER(x); 598 if (TD_IS_RUNNING(owner)) { 599 sleepq_release(&sx->lock_object); 600 continue; 601 } 602 } 603 #endif 604 605 /* 606 * If an exclusive lock was released with both shared 607 * and exclusive waiters and a shared waiter hasn't 608 * woken up and acquired the lock yet, sx_lock will be 609 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 610 * If we see that value, try to acquire it once. Note 611 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 612 * as there are other exclusive waiters still. If we 613 * fail, restart the loop. 614 */ 615 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 616 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 617 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 618 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 619 sleepq_release(&sx->lock_object); 620 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 621 __func__, sx); 622 break; 623 } 624 sleepq_release(&sx->lock_object); 625 continue; 626 } 627 628 /* 629 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 630 * than loop back and retry. 631 */ 632 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 633 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 634 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 635 sleepq_release(&sx->lock_object); 636 continue; 637 } 638 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 639 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 640 __func__, sx); 641 } 642 643 /* 644 * Since we have been unable to acquire the exclusive 645 * lock and the exclusive waiters flag is set, we have 646 * to sleep. 647 */ 648 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 649 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 650 __func__, sx); 651 652 #ifdef KDTRACE_HOOKS 653 sleep_time -= lockstat_nsecs(); 654 #endif 655 GIANT_SAVE(); 656 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 657 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 658 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 659 if (!(opts & SX_INTERRUPTIBLE)) 660 sleepq_wait(&sx->lock_object, 0); 661 else 662 error = sleepq_wait_sig(&sx->lock_object, 0); 663 #ifdef KDTRACE_HOOKS 664 sleep_time += lockstat_nsecs(); 665 sleep_cnt++; 666 #endif 667 if (error) { 668 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 669 CTR2(KTR_LOCK, 670 "%s: interruptible sleep by %p suspended by signal", 671 __func__, sx); 672 break; 673 } 674 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 675 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 676 __func__, sx); 677 } 678 679 GIANT_RESTORE(); 680 if (!error) 681 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx, 682 contested, waittime, file, line); 683 #ifdef KDTRACE_HOOKS 684 if (sleep_time) 685 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time); 686 if (spin_cnt > sleep_cnt) 687 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt)); 688 #endif 689 return (error); 690 } 691 692 /* 693 * This function represents the so-called 'hard case' for sx_xunlock 694 * operation. All 'easy case' failures are redirected to this. Note 695 * that ideally this would be a static function, but it needs to be 696 * accessible from at least sx.h. 697 */ 698 void 699 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 700 { 701 uintptr_t x; 702 int queue, wakeup_swapper; 703 704 if (SCHEDULER_STOPPED()) 705 return; 706 707 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 708 709 /* If the lock is recursed, then unrecurse one level. */ 710 if (sx_xlocked(sx) && sx_recursed(sx)) { 711 if ((--sx->sx_recurse) == 0) 712 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 713 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 714 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 715 return; 716 } 717 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 718 SX_LOCK_EXCLUSIVE_WAITERS)); 719 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 720 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 721 722 sleepq_lock(&sx->lock_object); 723 x = SX_LOCK_UNLOCKED; 724 725 /* 726 * The wake up algorithm here is quite simple and probably not 727 * ideal. It gives precedence to shared waiters if they are 728 * present. For this condition, we have to preserve the 729 * state of the exclusive waiters flag. 730 * If interruptible sleeps left the shared queue empty avoid a 731 * starvation for the threads sleeping on the exclusive queue by giving 732 * them precedence and cleaning up the shared waiters bit anyway. 733 */ 734 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 && 735 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) { 736 queue = SQ_SHARED_QUEUE; 737 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 738 } else 739 queue = SQ_EXCLUSIVE_QUEUE; 740 741 /* Wake up all the waiters for the specific queue. */ 742 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 743 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 744 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 745 "exclusive"); 746 atomic_store_rel_ptr(&sx->sx_lock, x); 747 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, 748 queue); 749 sleepq_release(&sx->lock_object); 750 if (wakeup_swapper) 751 kick_proc0(); 752 } 753 754 /* 755 * This function represents the so-called 'hard case' for sx_slock 756 * operation. All 'easy case' failures are redirected to this. Note 757 * that ideally this would be a static function, but it needs to be 758 * accessible from at least sx.h. 759 */ 760 int 761 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line) 762 { 763 GIANT_DECLARE; 764 #ifdef ADAPTIVE_SX 765 volatile struct thread *owner; 766 #endif 767 #ifdef LOCK_PROFILING 768 uint64_t waittime = 0; 769 int contested = 0; 770 #endif 771 uintptr_t x; 772 int error = 0; 773 #ifdef KDTRACE_HOOKS 774 uint64_t spin_cnt = 0; 775 uint64_t sleep_cnt = 0; 776 int64_t sleep_time = 0; 777 #endif 778 779 if (SCHEDULER_STOPPED()) 780 return (0); 781 782 /* 783 * As with rwlocks, we don't make any attempt to try to block 784 * shared locks once there is an exclusive waiter. 785 */ 786 for (;;) { 787 #ifdef KDTRACE_HOOKS 788 spin_cnt++; 789 #endif 790 x = sx->sx_lock; 791 792 /* 793 * If no other thread has an exclusive lock then try to bump up 794 * the count of sharers. Since we have to preserve the state 795 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 796 * shared lock loop back and retry. 797 */ 798 if (x & SX_LOCK_SHARED) { 799 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 800 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 801 x + SX_ONE_SHARER)) { 802 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 803 CTR4(KTR_LOCK, 804 "%s: %p succeed %p -> %p", __func__, 805 sx, (void *)x, 806 (void *)(x + SX_ONE_SHARER)); 807 break; 808 } 809 continue; 810 } 811 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 812 &waittime); 813 814 #ifdef ADAPTIVE_SX 815 /* 816 * If the owner is running on another CPU, spin until 817 * the owner stops running or the state of the lock 818 * changes. 819 */ 820 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 821 x = SX_OWNER(x); 822 owner = (struct thread *)x; 823 if (TD_IS_RUNNING(owner)) { 824 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 825 CTR3(KTR_LOCK, 826 "%s: spinning on %p held by %p", 827 __func__, sx, owner); 828 GIANT_SAVE(); 829 while (SX_OWNER(sx->sx_lock) == x && 830 TD_IS_RUNNING(owner)) { 831 #ifdef KDTRACE_HOOKS 832 spin_cnt++; 833 #endif 834 cpu_spinwait(); 835 } 836 continue; 837 } 838 } 839 #endif 840 841 /* 842 * Some other thread already has an exclusive lock, so 843 * start the process of blocking. 844 */ 845 sleepq_lock(&sx->lock_object); 846 x = sx->sx_lock; 847 848 /* 849 * The lock could have been released while we spun. 850 * In this case loop back and retry. 851 */ 852 if (x & SX_LOCK_SHARED) { 853 sleepq_release(&sx->lock_object); 854 continue; 855 } 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 (!(x & SX_LOCK_SHARED) && 864 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) { 865 owner = (struct thread *)SX_OWNER(x); 866 if (TD_IS_RUNNING(owner)) { 867 sleepq_release(&sx->lock_object); 868 continue; 869 } 870 } 871 #endif 872 873 /* 874 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 875 * fail to set it drop the sleep queue lock and loop 876 * back. 877 */ 878 if (!(x & SX_LOCK_SHARED_WAITERS)) { 879 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 880 x | SX_LOCK_SHARED_WAITERS)) { 881 sleepq_release(&sx->lock_object); 882 continue; 883 } 884 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 885 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 886 __func__, sx); 887 } 888 889 /* 890 * Since we have been unable to acquire the shared lock, 891 * we have to sleep. 892 */ 893 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 894 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 895 __func__, sx); 896 897 #ifdef KDTRACE_HOOKS 898 sleep_time -= lockstat_nsecs(); 899 #endif 900 GIANT_SAVE(); 901 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 902 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 903 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 904 if (!(opts & SX_INTERRUPTIBLE)) 905 sleepq_wait(&sx->lock_object, 0); 906 else 907 error = sleepq_wait_sig(&sx->lock_object, 0); 908 #ifdef KDTRACE_HOOKS 909 sleep_time += lockstat_nsecs(); 910 sleep_cnt++; 911 #endif 912 if (error) { 913 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 914 CTR2(KTR_LOCK, 915 "%s: interruptible sleep by %p suspended by signal", 916 __func__, sx); 917 break; 918 } 919 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 920 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 921 __func__, sx); 922 } 923 if (error == 0) 924 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 925 contested, waittime, file, line); 926 #ifdef KDTRACE_HOOKS 927 if (sleep_time) 928 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time); 929 if (spin_cnt > sleep_cnt) 930 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt)); 931 #endif 932 GIANT_RESTORE(); 933 return (error); 934 } 935 936 /* 937 * This function represents the so-called 'hard case' for sx_sunlock 938 * operation. All 'easy case' failures are redirected to this. Note 939 * that ideally this would be a static function, but it needs to be 940 * accessible from at least sx.h. 941 */ 942 void 943 _sx_sunlock_hard(struct sx *sx, const char *file, int line) 944 { 945 uintptr_t x; 946 int wakeup_swapper; 947 948 if (SCHEDULER_STOPPED()) 949 return; 950 951 for (;;) { 952 x = sx->sx_lock; 953 954 /* 955 * We should never have sharers while at least one thread 956 * holds a shared lock. 957 */ 958 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 959 ("%s: waiting sharers", __func__)); 960 961 /* 962 * See if there is more than one shared lock held. If 963 * so, just drop one and return. 964 */ 965 if (SX_SHARERS(x) > 1) { 966 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x, 967 x - SX_ONE_SHARER)) { 968 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 969 CTR4(KTR_LOCK, 970 "%s: %p succeeded %p -> %p", 971 __func__, sx, (void *)x, 972 (void *)(x - SX_ONE_SHARER)); 973 break; 974 } 975 continue; 976 } 977 978 /* 979 * If there aren't any waiters for an exclusive lock, 980 * then try to drop it quickly. 981 */ 982 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 983 MPASS(x == SX_SHARERS_LOCK(1)); 984 if (atomic_cmpset_rel_ptr(&sx->sx_lock, 985 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) { 986 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 987 CTR2(KTR_LOCK, "%s: %p last succeeded", 988 __func__, sx); 989 break; 990 } 991 continue; 992 } 993 994 /* 995 * At this point, there should just be one sharer with 996 * exclusive waiters. 997 */ 998 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 999 1000 sleepq_lock(&sx->lock_object); 1001 1002 /* 1003 * Wake up semantic here is quite simple: 1004 * Just wake up all the exclusive waiters. 1005 * Note that the state of the lock could have changed, 1006 * so if it fails loop back and retry. 1007 */ 1008 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, 1009 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 1010 SX_LOCK_UNLOCKED)) { 1011 sleepq_release(&sx->lock_object); 1012 continue; 1013 } 1014 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 1015 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 1016 "exclusive queue", __func__, sx); 1017 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 1018 0, SQ_EXCLUSIVE_QUEUE); 1019 sleepq_release(&sx->lock_object); 1020 if (wakeup_swapper) 1021 kick_proc0(); 1022 break; 1023 } 1024 } 1025 1026 #ifdef INVARIANT_SUPPORT 1027 #ifndef INVARIANTS 1028 #undef _sx_assert 1029 #endif 1030 1031 /* 1032 * In the non-WITNESS case, sx_assert() can only detect that at least 1033 * *some* thread owns an slock, but it cannot guarantee that *this* 1034 * thread owns an slock. 1035 */ 1036 void 1037 _sx_assert(struct sx *sx, int what, const char *file, int line) 1038 { 1039 #ifndef WITNESS 1040 int slocked = 0; 1041 #endif 1042 1043 if (panicstr != NULL) 1044 return; 1045 switch (what) { 1046 case SA_SLOCKED: 1047 case SA_SLOCKED | SA_NOTRECURSED: 1048 case SA_SLOCKED | SA_RECURSED: 1049 #ifndef WITNESS 1050 slocked = 1; 1051 /* FALLTHROUGH */ 1052 #endif 1053 case SA_LOCKED: 1054 case SA_LOCKED | SA_NOTRECURSED: 1055 case SA_LOCKED | SA_RECURSED: 1056 #ifdef WITNESS 1057 witness_assert(&sx->lock_object, what, file, line); 1058 #else 1059 /* 1060 * If some other thread has an exclusive lock or we 1061 * have one and are asserting a shared lock, fail. 1062 * Also, if no one has a lock at all, fail. 1063 */ 1064 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1065 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1066 sx_xholder(sx) != curthread))) 1067 panic("Lock %s not %slocked @ %s:%d\n", 1068 sx->lock_object.lo_name, slocked ? "share " : "", 1069 file, line); 1070 1071 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1072 if (sx_recursed(sx)) { 1073 if (what & SA_NOTRECURSED) 1074 panic("Lock %s recursed @ %s:%d\n", 1075 sx->lock_object.lo_name, file, 1076 line); 1077 } else if (what & SA_RECURSED) 1078 panic("Lock %s not recursed @ %s:%d\n", 1079 sx->lock_object.lo_name, file, line); 1080 } 1081 #endif 1082 break; 1083 case SA_XLOCKED: 1084 case SA_XLOCKED | SA_NOTRECURSED: 1085 case SA_XLOCKED | SA_RECURSED: 1086 if (sx_xholder(sx) != curthread) 1087 panic("Lock %s not exclusively locked @ %s:%d\n", 1088 sx->lock_object.lo_name, file, line); 1089 if (sx_recursed(sx)) { 1090 if (what & SA_NOTRECURSED) 1091 panic("Lock %s recursed @ %s:%d\n", 1092 sx->lock_object.lo_name, file, line); 1093 } else if (what & SA_RECURSED) 1094 panic("Lock %s not recursed @ %s:%d\n", 1095 sx->lock_object.lo_name, file, line); 1096 break; 1097 case SA_UNLOCKED: 1098 #ifdef WITNESS 1099 witness_assert(&sx->lock_object, what, file, line); 1100 #else 1101 /* 1102 * If we hold an exclusve lock fail. We can't 1103 * reliably check to see if we hold a shared lock or 1104 * not. 1105 */ 1106 if (sx_xholder(sx) == curthread) 1107 panic("Lock %s exclusively locked @ %s:%d\n", 1108 sx->lock_object.lo_name, file, line); 1109 #endif 1110 break; 1111 default: 1112 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1113 line); 1114 } 1115 } 1116 #endif /* INVARIANT_SUPPORT */ 1117 1118 #ifdef DDB 1119 static void 1120 db_show_sx(struct lock_object *lock) 1121 { 1122 struct thread *td; 1123 struct sx *sx; 1124 1125 sx = (struct sx *)lock; 1126 1127 db_printf(" state: "); 1128 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1129 db_printf("UNLOCKED\n"); 1130 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1131 db_printf("DESTROYED\n"); 1132 return; 1133 } else if (sx->sx_lock & SX_LOCK_SHARED) 1134 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1135 else { 1136 td = sx_xholder(sx); 1137 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1138 td->td_tid, td->td_proc->p_pid, td->td_name); 1139 if (sx_recursed(sx)) 1140 db_printf(" recursed: %d\n", sx->sx_recurse); 1141 } 1142 1143 db_printf(" waiters: "); 1144 switch(sx->sx_lock & 1145 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1146 case SX_LOCK_SHARED_WAITERS: 1147 db_printf("shared\n"); 1148 break; 1149 case SX_LOCK_EXCLUSIVE_WAITERS: 1150 db_printf("exclusive\n"); 1151 break; 1152 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1153 db_printf("exclusive and shared\n"); 1154 break; 1155 default: 1156 db_printf("none\n"); 1157 } 1158 } 1159 1160 /* 1161 * Check to see if a thread that is blocked on a sleep queue is actually 1162 * blocked on an sx lock. If so, output some details and return true. 1163 * If the lock has an exclusive owner, return that in *ownerp. 1164 */ 1165 int 1166 sx_chain(struct thread *td, struct thread **ownerp) 1167 { 1168 struct sx *sx; 1169 1170 /* 1171 * Check to see if this thread is blocked on an sx lock. 1172 * First, we check the lock class. If that is ok, then we 1173 * compare the lock name against the wait message. 1174 */ 1175 sx = td->td_wchan; 1176 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1177 sx->lock_object.lo_name != td->td_wmesg) 1178 return (0); 1179 1180 /* We think we have an sx lock, so output some details. */ 1181 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1182 *ownerp = sx_xholder(sx); 1183 if (sx->sx_lock & SX_LOCK_SHARED) 1184 db_printf("SLOCK (count %ju)\n", 1185 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1186 else 1187 db_printf("XLOCK\n"); 1188 return (1); 1189 } 1190 #endif
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