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_adaptive_sx.h" 40 #include "opt_ddb.h" 41 42 #include <sys/cdefs.h> 43 __FBSDID("$FreeBSD: releng/6.3/sys/kern/kern_sx.c 173886 2007-11-24 19:45:58Z cvs2svn $"); 44 45 #include <sys/param.h> 46 #include <sys/ktr.h> 47 #include <sys/lock.h> 48 #include <sys/mutex.h> 49 #include <sys/proc.h> 50 #include <sys/sleepqueue.h> 51 #include <sys/sx.h> 52 #include <sys/systm.h> 53 54 #ifdef ADAPTIVE_SX 55 #include <machine/cpu.h> 56 #endif 57 58 #ifdef DDB 59 #include <ddb/ddb.h> 60 #endif 61 62 #if !defined(SMP) && defined(ADAPTIVE_SX) 63 #error "You must have SMP to enable the ADAPTIVE_SX option" 64 #endif 65 66 CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) == 67 (SX_ADAPTIVESPIN | SX_RECURSE)); 68 69 /* Handy macros for sleep queues. */ 70 #define SQ_EXCLUSIVE_QUEUE 0 71 #define SQ_SHARED_QUEUE 1 72 73 /* 74 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 75 * drop Giant anytime we have to sleep or if we adaptively spin. 76 */ 77 #define GIANT_DECLARE \ 78 int _giantcnt = 0; \ 79 WITNESS_SAVE_DECL(Giant) \ 80 81 #define GIANT_SAVE() do { \ 82 if (mtx_owned(&Giant)) { \ 83 WITNESS_SAVE(&Giant.mtx_object, Giant); \ 84 while (mtx_owned(&Giant)) { \ 85 _giantcnt++; \ 86 mtx_unlock(&Giant); \ 87 } \ 88 } \ 89 } while (0) 90 91 #define GIANT_RESTORE() do { \ 92 if (_giantcnt > 0) { \ 93 mtx_assert(&Giant, MA_NOTOWNED); \ 94 while (_giantcnt--) \ 95 mtx_lock(&Giant); \ 96 WITNESS_RESTORE(&Giant.mtx_object, Giant); \ 97 } \ 98 } while (0) 99 100 /* 101 * Returns true if an exclusive lock is recursed. It assumes 102 * curthread currently has an exclusive lock. 103 */ 104 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 105 106 #ifdef DDB 107 static void db_show_sx(struct lock_object *lock); 108 #endif 109 110 struct lock_class lock_class_sx = { 111 .lc_name = "sx", 112 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 113 #ifdef DDB 114 .lc_ddb_show = db_show_sx, 115 #endif 116 }; 117 118 #ifndef INVARIANTS 119 #define _sx_assert(sx, what, file, line) 120 #endif 121 122 void 123 sx_sysinit(void *arg) 124 { 125 struct sx_args *sargs = arg; 126 127 sx_init(sargs->sa_sx, sargs->sa_desc); 128 } 129 130 void 131 sx_init(struct sx *sx, const char *description) 132 { 133 134 sx_init_flags(sx, description, 0); 135 } 136 137 void 138 sx_init_flags(struct sx *sx, const char *description, int opts) 139 { 140 int flags; 141 142 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 143 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0); 144 145 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE; 146 if (opts & SX_DUPOK) 147 flags |= LO_DUPOK; 148 if (!(opts & SX_NOWITNESS)) 149 flags |= LO_WITNESS; 150 if (opts & SX_QUIET) 151 flags |= LO_QUIET; 152 153 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE); 154 sx->sx_lock = SX_LOCK_UNLOCKED; 155 sx->sx_recurse = 0; 156 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 157 } 158 159 void 160 sx_destroy(struct sx *sx) 161 { 162 163 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 164 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 165 sx->sx_lock = SX_LOCK_DESTROYED; 166 lock_destroy(&sx->lock_object); 167 } 168 169 int 170 _sx_slock(struct sx *sx, int opts, const char *file, int line) 171 { 172 int error = 0; 173 174 MPASS(curthread != NULL); 175 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 176 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 177 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line); 178 error = __sx_slock(sx, opts, file, line); 179 if (!error) { 180 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 181 WITNESS_LOCK(&sx->lock_object, 0, file, line); 182 curthread->td_locks++; 183 } 184 185 return (error); 186 } 187 188 int 189 _sx_try_slock(struct sx *sx, const char *file, int line) 190 { 191 uintptr_t x; 192 193 x = sx->sx_lock; 194 KASSERT(x != SX_LOCK_DESTROYED, 195 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 196 if ((x & SX_LOCK_SHARED) && atomic_cmpset_acq_ptr(&sx->sx_lock, x, 197 x + SX_ONE_SHARER)) { 198 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 199 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 200 curthread->td_locks++; 201 return (1); 202 } 203 204 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 205 return (0); 206 } 207 208 int 209 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 210 { 211 int error = 0; 212 213 MPASS(curthread != NULL); 214 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 215 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 216 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 217 line); 218 error = __sx_xlock(sx, curthread, opts, file, line); 219 if (!error) { 220 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 221 file, line); 222 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 223 curthread->td_locks++; 224 } 225 226 return (error); 227 } 228 229 int 230 _sx_try_xlock(struct sx *sx, const char *file, int line) 231 { 232 int rval; 233 234 MPASS(curthread != NULL); 235 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 236 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 237 238 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) { 239 sx->sx_recurse++; 240 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 241 rval = 1; 242 } else 243 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 244 (uintptr_t)curthread); 245 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 246 if (rval) { 247 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 248 file, line); 249 curthread->td_locks++; 250 } 251 252 return (rval); 253 } 254 255 void 256 _sx_sunlock(struct sx *sx, const char *file, int line) 257 { 258 259 MPASS(curthread != NULL); 260 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 261 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 262 _sx_assert(sx, SA_SLOCKED, file, line); 263 curthread->td_locks--; 264 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 265 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 266 #ifdef LOCK_PROFILING_SHARED 267 if (SX_SHARERS(sx->sx_lock) == 1) 268 lock_profile_release_lock(&sx->lock_object); 269 #endif 270 __sx_sunlock(sx, file, line); 271 } 272 273 void 274 _sx_xunlock(struct sx *sx, const char *file, int line) 275 { 276 277 MPASS(curthread != NULL); 278 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 279 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 280 _sx_assert(sx, SA_XLOCKED, file, line); 281 curthread->td_locks--; 282 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 283 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 284 line); 285 if (!sx_recursed(sx)) 286 lock_profile_release_lock(&sx->lock_object); 287 __sx_xunlock(sx, curthread, file, line); 288 } 289 290 /* 291 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 292 * This will only succeed if this thread holds a single shared lock. 293 * Return 1 if if the upgrade succeed, 0 otherwise. 294 */ 295 int 296 _sx_try_upgrade(struct sx *sx, const char *file, int line) 297 { 298 uintptr_t x; 299 int success; 300 301 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 302 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 303 _sx_assert(sx, SA_SLOCKED, file, line); 304 305 /* 306 * Try to switch from one shared lock to an exclusive lock. We need 307 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 308 * we will wake up the exclusive waiters when we drop the lock. 309 */ 310 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 311 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 312 (uintptr_t)curthread | x); 313 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 314 if (success) 315 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 316 file, line); 317 return (success); 318 } 319 320 /* 321 * Downgrade an unrecursed exclusive lock into a single shared lock. 322 */ 323 void 324 _sx_downgrade(struct sx *sx, const char *file, int line) 325 { 326 uintptr_t x; 327 328 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 329 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 330 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 331 #ifndef INVARIANTS 332 if (sx_recursed(sx)) 333 panic("downgrade of a recursed lock"); 334 #endif 335 336 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 337 338 /* 339 * Try to switch from an exclusive lock with no shared waiters 340 * to one sharer with no shared waiters. If there are 341 * exclusive waiters, we don't need to lock the sleep queue so 342 * long as we preserve the flag. We do one quick try and if 343 * that fails we grab the sleepq lock to keep the flags from 344 * changing and do it the slow way. 345 * 346 * We have to lock the sleep queue if there are shared waiters 347 * so we can wake them up. 348 */ 349 x = sx->sx_lock; 350 if (!(x & SX_LOCK_SHARED_WAITERS) && 351 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 352 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 353 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 354 return; 355 } 356 357 /* 358 * Lock the sleep queue so we can read the waiters bits 359 * without any races and wakeup any shared waiters. 360 */ 361 sleepq_lock(&sx->lock_object); 362 363 /* 364 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 365 * shared lock. If there are any shared waiters, wake them up. 366 */ 367 x = sx->sx_lock; 368 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 369 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 370 if (x & SX_LOCK_SHARED_WAITERS) 371 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 372 SQ_SHARED_QUEUE); 373 else 374 sleepq_release(&sx->lock_object); 375 376 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 377 } 378 379 /* 380 * This function represents the so-called 'hard case' for sx_xlock 381 * operation. All 'easy case' failures are redirected to this. Note 382 * that ideally this would be a static function, but it needs to be 383 * accessible from at least sx.h. 384 */ 385 int 386 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 387 int line) 388 { 389 GIANT_DECLARE; 390 #ifdef ADAPTIVE_SX 391 volatile struct thread *owner; 392 #endif 393 /* uint64_t waittime = 0; */ 394 uintptr_t x; 395 int /* contested = 0, */error = 0; 396 397 /* If we already hold an exclusive lock, then recurse. */ 398 if (sx_xlocked(sx)) { 399 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0, 400 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 401 sx->lock_object.lo_name, file, line)); 402 sx->sx_recurse++; 403 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 404 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 405 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 406 return (0); 407 } 408 409 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 410 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 411 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 412 413 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 414 #ifdef ADAPTIVE_SX 415 /* 416 * If the lock is write locked and the owner is 417 * running on another CPU, spin until the owner stops 418 * running or the state of the lock changes. 419 */ 420 x = sx->sx_lock; 421 if (!(x & SX_LOCK_SHARED) && 422 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 423 x = SX_OWNER(x); 424 owner = (struct thread *)x; 425 if (TD_IS_RUNNING(owner)) { 426 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 427 CTR3(KTR_LOCK, 428 "%s: spinning on %p held by %p", 429 __func__, sx, owner); 430 GIANT_SAVE(); 431 lock_profile_obtain_lock_failed( 432 &sx->lock_object, &contested, &waittime); 433 while (SX_OWNER(sx->sx_lock) == x && 434 TD_IS_RUNNING(owner)) 435 cpu_spinwait(); 436 continue; 437 } 438 } 439 #endif 440 441 sleepq_lock(&sx->lock_object); 442 x = sx->sx_lock; 443 444 /* 445 * If the lock was released while spinning on the 446 * sleep queue chain lock, try again. 447 */ 448 if (x == SX_LOCK_UNLOCKED) { 449 sleepq_release(&sx->lock_object); 450 continue; 451 } 452 453 #ifdef ADAPTIVE_SX 454 /* 455 * The current lock owner might have started executing 456 * on another CPU (or the lock could have changed 457 * owners) while we were waiting on the sleep queue 458 * chain lock. If so, drop the sleep queue lock and try 459 * again. 460 */ 461 if (!(x & SX_LOCK_SHARED) && 462 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 463 owner = (struct thread *)SX_OWNER(x); 464 if (TD_IS_RUNNING(owner)) { 465 sleepq_release(&sx->lock_object); 466 continue; 467 } 468 } 469 #endif 470 471 /* 472 * If an exclusive lock was released with both shared 473 * and exclusive waiters and a shared waiter hasn't 474 * woken up and acquired the lock yet, sx_lock will be 475 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 476 * If we see that value, try to acquire it once. Note 477 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 478 * as there are other exclusive waiters still. If we 479 * fail, restart the loop. 480 */ 481 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 482 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 483 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 484 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 485 sleepq_release(&sx->lock_object); 486 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 487 __func__, sx); 488 break; 489 } 490 sleepq_release(&sx->lock_object); 491 continue; 492 } 493 494 /* 495 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 496 * than loop back and retry. 497 */ 498 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 499 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 500 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 501 sleepq_release(&sx->lock_object); 502 continue; 503 } 504 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 505 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 506 __func__, sx); 507 } 508 509 /* 510 * Since we have been unable to acquire the exclusive 511 * lock and the exclusive waiters flag is set, we have 512 * to sleep. 513 */ 514 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 515 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 516 __func__, sx); 517 518 GIANT_SAVE(); 519 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 520 &waittime); 521 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 522 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 523 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 524 if (!(opts & SX_INTERRUPTIBLE)) 525 sleepq_wait(&sx->lock_object); 526 else 527 error = sleepq_wait_sig(&sx->lock_object); 528 529 if (error) { 530 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 531 CTR2(KTR_LOCK, 532 "%s: interruptible sleep by %p suspended by signal", 533 __func__, sx); 534 break; 535 } 536 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 537 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 538 __func__, sx); 539 } 540 541 GIANT_RESTORE(); 542 if (!error) 543 lock_profile_obtain_lock_success(&sx->lock_object, contested, 544 waittime, file, line); 545 return (error); 546 } 547 548 /* 549 * This function represents the so-called 'hard case' for sx_xunlock 550 * operation. All 'easy case' failures are redirected to this. Note 551 * that ideally this would be a static function, but it needs to be 552 * accessible from at least sx.h. 553 */ 554 void 555 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 556 { 557 uintptr_t x; 558 int queue; 559 560 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 561 562 /* If the lock is recursed, then unrecurse one level. */ 563 if (sx_xlocked(sx) && sx_recursed(sx)) { 564 if ((--sx->sx_recurse) == 0) 565 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 566 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 567 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 568 return; 569 } 570 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 571 SX_LOCK_EXCLUSIVE_WAITERS)); 572 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 573 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 574 575 sleepq_lock(&sx->lock_object); 576 x = SX_LOCK_UNLOCKED; 577 578 /* 579 * The wake up algorithm here is quite simple and probably not 580 * ideal. It gives precedence to shared waiters if they are 581 * present. For this condition, we have to preserve the 582 * state of the exclusive waiters flag. 583 */ 584 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) { 585 queue = SQ_SHARED_QUEUE; 586 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 587 } else 588 queue = SQ_EXCLUSIVE_QUEUE; 589 590 /* Wake up all the waiters for the specific queue. */ 591 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 592 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 593 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 594 "exclusive"); 595 atomic_store_rel_ptr(&sx->sx_lock, x); 596 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, queue); 597 } 598 599 /* 600 * This function represents the so-called 'hard case' for sx_slock 601 * operation. All 'easy case' failures are redirected to this. Note 602 * that ideally this would be a static function, but it needs to be 603 * accessible from at least sx.h. 604 */ 605 int 606 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line) 607 { 608 GIANT_DECLARE; 609 #ifdef ADAPTIVE_SX 610 volatile struct thread *owner; 611 #endif 612 #ifdef LOCK_PROFILING_SHARED 613 uint64_t waittime = 0; 614 int contested = 0; 615 #endif 616 uintptr_t x; 617 int error = 0; 618 619 /* 620 * As with rwlocks, we don't make any attempt to try to block 621 * shared locks once there is an exclusive waiter. 622 */ 623 for (;;) { 624 x = sx->sx_lock; 625 626 /* 627 * If no other thread has an exclusive lock then try to bump up 628 * the count of sharers. Since we have to preserve the state 629 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 630 * shared lock loop back and retry. 631 */ 632 if (x & SX_LOCK_SHARED) { 633 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 634 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 635 x + SX_ONE_SHARER)) { 636 #ifdef LOCK_PROFILING_SHARED 637 if (SX_SHARERS(x) == 0) 638 lock_profile_obtain_lock_success( 639 &sx->lock_object, contested, 640 waittime, file, line); 641 #endif 642 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 643 CTR4(KTR_LOCK, 644 "%s: %p succeed %p -> %p", __func__, 645 sx, (void *)x, 646 (void *)(x + SX_ONE_SHARER)); 647 break; 648 } 649 continue; 650 } 651 652 #ifdef ADAPTIVE_SX 653 /* 654 * If the owner is running on another CPU, spin until 655 * the owner stops running or the state of the lock 656 * changes. 657 */ 658 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) { 659 x = SX_OWNER(x); 660 owner = (struct thread *)x; 661 if (TD_IS_RUNNING(owner)) { 662 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 663 CTR3(KTR_LOCK, 664 "%s: spinning on %p held by %p", 665 __func__, sx, owner); 666 GIANT_SAVE(); 667 #ifdef LOCK_PROFILING_SHARED 668 lock_profile_obtain_lock_failed( 669 &sx->lock_object, &contested, &waittime); 670 #endif 671 while (SX_OWNER(sx->sx_lock) == x && 672 TD_IS_RUNNING(owner)) 673 cpu_spinwait(); 674 continue; 675 } 676 } 677 #endif 678 679 /* 680 * Some other thread already has an exclusive lock, so 681 * start the process of blocking. 682 */ 683 sleepq_lock(&sx->lock_object); 684 x = sx->sx_lock; 685 686 /* 687 * The lock could have been released while we spun. 688 * In this case loop back and retry. 689 */ 690 if (x & SX_LOCK_SHARED) { 691 sleepq_release(&sx->lock_object); 692 continue; 693 } 694 695 #ifdef ADAPTIVE_SX 696 /* 697 * If the owner is running on another CPU, spin until 698 * the owner stops running or the state of the lock 699 * changes. 700 */ 701 if (!(x & SX_LOCK_SHARED) && 702 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 703 owner = (struct thread *)SX_OWNER(x); 704 if (TD_IS_RUNNING(owner)) { 705 sleepq_release(&sx->lock_object); 706 continue; 707 } 708 } 709 #endif 710 711 /* 712 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 713 * fail to set it drop the sleep queue lock and loop 714 * back. 715 */ 716 if (!(x & SX_LOCK_SHARED_WAITERS)) { 717 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 718 x | SX_LOCK_SHARED_WAITERS)) { 719 sleepq_release(&sx->lock_object); 720 continue; 721 } 722 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 723 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 724 __func__, sx); 725 } 726 727 /* 728 * Since we have been unable to acquire the shared lock, 729 * we have to sleep. 730 */ 731 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 732 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 733 __func__, sx); 734 735 GIANT_SAVE(); 736 #ifdef LOCK_PROFILING_SHARED 737 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 738 &waittime); 739 #endif 740 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 741 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 742 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 743 if (!(opts & SX_INTERRUPTIBLE)) 744 sleepq_wait(&sx->lock_object); 745 else 746 error = sleepq_wait_sig(&sx->lock_object); 747 748 if (error) { 749 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 750 CTR2(KTR_LOCK, 751 "%s: interruptible sleep by %p suspended by signal", 752 __func__, sx); 753 break; 754 } 755 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 756 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 757 __func__, sx); 758 } 759 760 GIANT_RESTORE(); 761 return (error); 762 } 763 764 /* 765 * This function represents the so-called 'hard case' for sx_sunlock 766 * operation. All 'easy case' failures are redirected to this. Note 767 * that ideally this would be a static function, but it needs to be 768 * accessible from at least sx.h. 769 */ 770 void 771 _sx_sunlock_hard(struct sx *sx, const char *file, int line) 772 { 773 uintptr_t x; 774 775 for (;;) { 776 x = sx->sx_lock; 777 778 /* 779 * We should never have sharers while at least one thread 780 * holds a shared lock. 781 */ 782 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 783 ("%s: waiting sharers", __func__)); 784 785 /* 786 * See if there is more than one shared lock held. If 787 * so, just drop one and return. 788 */ 789 if (SX_SHARERS(x) > 1) { 790 if (atomic_cmpset_ptr(&sx->sx_lock, x, 791 x - SX_ONE_SHARER)) { 792 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 793 CTR4(KTR_LOCK, 794 "%s: %p succeeded %p -> %p", 795 __func__, sx, (void *)x, 796 (void *)(x - SX_ONE_SHARER)); 797 break; 798 } 799 continue; 800 } 801 802 /* 803 * If there aren't any waiters for an exclusive lock, 804 * then try to drop it quickly. 805 */ 806 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 807 MPASS(x == SX_SHARERS_LOCK(1)); 808 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1), 809 SX_LOCK_UNLOCKED)) { 810 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 811 CTR2(KTR_LOCK, "%s: %p last succeeded", 812 __func__, sx); 813 break; 814 } 815 continue; 816 } 817 818 /* 819 * At this point, there should just be one sharer with 820 * exclusive waiters. 821 */ 822 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 823 824 sleepq_lock(&sx->lock_object); 825 826 /* 827 * Wake up semantic here is quite simple: 828 * Just wake up all the exclusive waiters. 829 * Note that the state of the lock could have changed, 830 * so if it fails loop back and retry. 831 */ 832 if (!atomic_cmpset_ptr(&sx->sx_lock, 833 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 834 SX_LOCK_UNLOCKED)) { 835 sleepq_release(&sx->lock_object); 836 continue; 837 } 838 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 839 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 840 "exclusive queue", __func__, sx); 841 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 842 SQ_EXCLUSIVE_QUEUE); 843 break; 844 } 845 } 846 847 #ifdef INVARIANT_SUPPORT 848 #ifndef INVARIANTS 849 #undef _sx_assert 850 #endif 851 852 /* 853 * In the non-WITNESS case, sx_assert() can only detect that at least 854 * *some* thread owns an slock, but it cannot guarantee that *this* 855 * thread owns an slock. 856 */ 857 void 858 _sx_assert(struct sx *sx, int what, const char *file, int line) 859 { 860 #ifndef WITNESS 861 int slocked = 0; 862 #endif 863 864 if (panicstr != NULL) 865 return; 866 switch (what) { 867 case SA_SLOCKED: 868 case SA_SLOCKED | SA_NOTRECURSED: 869 case SA_SLOCKED | SA_RECURSED: 870 #ifndef WITNESS 871 slocked = 1; 872 /* FALLTHROUGH */ 873 #endif 874 case SA_LOCKED: 875 case SA_LOCKED | SA_NOTRECURSED: 876 case SA_LOCKED | SA_RECURSED: 877 #ifdef WITNESS 878 witness_assert(&sx->lock_object, what, file, line); 879 #else 880 /* 881 * If some other thread has an exclusive lock or we 882 * have one and are asserting a shared lock, fail. 883 * Also, if no one has a lock at all, fail. 884 */ 885 if (sx->sx_lock == SX_LOCK_UNLOCKED || 886 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 887 sx_xholder(sx) != curthread))) 888 panic("Lock %s not %slocked @ %s:%d\n", 889 sx->lock_object.lo_name, slocked ? "share " : "", 890 file, line); 891 892 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 893 if (sx_recursed(sx)) { 894 if (what & SA_NOTRECURSED) 895 panic("Lock %s recursed @ %s:%d\n", 896 sx->lock_object.lo_name, file, 897 line); 898 } else if (what & SA_RECURSED) 899 panic("Lock %s not recursed @ %s:%d\n", 900 sx->lock_object.lo_name, file, line); 901 } 902 #endif 903 break; 904 case SA_XLOCKED: 905 case SA_XLOCKED | SA_NOTRECURSED: 906 case SA_XLOCKED | SA_RECURSED: 907 if (sx_xholder(sx) != curthread) 908 panic("Lock %s not exclusively locked @ %s:%d\n", 909 sx->lock_object.lo_name, file, line); 910 if (sx_recursed(sx)) { 911 if (what & SA_NOTRECURSED) 912 panic("Lock %s recursed @ %s:%d\n", 913 sx->lock_object.lo_name, file, line); 914 } else if (what & SA_RECURSED) 915 panic("Lock %s not recursed @ %s:%d\n", 916 sx->lock_object.lo_name, file, line); 917 break; 918 case SA_UNLOCKED: 919 #ifdef WITNESS 920 witness_assert(&sx->lock_object, what, file, line); 921 #else 922 /* 923 * If we hold an exclusve lock fail. We can't 924 * reliably check to see if we hold a shared lock or 925 * not. 926 */ 927 if (sx_xholder(sx) == curthread) 928 panic("Lock %s exclusively locked @ %s:%d\n", 929 sx->lock_object.lo_name, file, line); 930 #endif 931 break; 932 default: 933 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 934 line); 935 } 936 } 937 #endif /* INVARIANT_SUPPORT */ 938 939 #ifdef DDB 940 static void 941 db_show_sx(struct lock_object *lock) 942 { 943 struct thread *td; 944 struct sx *sx; 945 946 sx = (struct sx *)lock; 947 948 db_printf(" state: "); 949 if (sx->sx_lock == SX_LOCK_UNLOCKED) 950 db_printf("UNLOCKED\n"); 951 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 952 db_printf("DESTROYED\n"); 953 return; 954 } else if (sx->sx_lock & SX_LOCK_SHARED) 955 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 956 else { 957 td = sx_xholder(sx); 958 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 959 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 960 if (sx_recursed(sx)) 961 db_printf(" recursed: %d\n", sx->sx_recurse); 962 } 963 964 db_printf(" waiters: "); 965 switch(sx->sx_lock & 966 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 967 case SX_LOCK_SHARED_WAITERS: 968 db_printf("shared\n"); 969 break; 970 case SX_LOCK_EXCLUSIVE_WAITERS: 971 db_printf("exclusive\n"); 972 break; 973 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 974 db_printf("exclusive and shared\n"); 975 break; 976 default: 977 db_printf("none\n"); 978 } 979 } 980 981 /* 982 * Check to see if a thread that is blocked on a sleep queue is actually 983 * blocked on an sx lock. If so, output some details and return true. 984 * If the lock has an exclusive owner, return that in *ownerp. 985 */ 986 int 987 sx_chain(struct thread *td, struct thread **ownerp) 988 { 989 struct sx *sx; 990 991 /* 992 * Check to see if this thread is blocked on an sx lock. 993 * First, we check the lock class. If that is ok, then we 994 * compare the lock name against the wait message. 995 */ 996 sx = td->td_wchan; 997 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 998 sx->lock_object.lo_name != td->td_wmesg) 999 return (0); 1000 1001 /* We think we have an sx lock, so output some details. */ 1002 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1003 *ownerp = sx_xholder(sx); 1004 if (sx->sx_lock & SX_LOCK_SHARED) 1005 db_printf("SLOCK (count %ju)\n", 1006 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1007 else 1008 db_printf("XLOCK\n"); 1009 return (1); 1010 } 1011 #endif
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