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("$FreeBSD$"); 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/sched.h> 51 #include <sys/sleepqueue.h> 52 #include <sys/sx.h> 53 #include <sys/systm.h> 54 55 #ifdef ADAPTIVE_SX 56 #include <machine/cpu.h> 57 #endif 58 59 #ifdef DDB 60 #include <ddb/ddb.h> 61 #endif 62 63 #if !defined(SMP) && defined(ADAPTIVE_SX) 64 #error "You must have SMP to enable the ADAPTIVE_SX option" 65 #endif 66 67 CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) == 68 (SX_ADAPTIVESPIN | SX_RECURSE)); 69 70 /* Handy macros for sleep queues. */ 71 #define SQ_EXCLUSIVE_QUEUE 0 72 #define SQ_SHARED_QUEUE 1 73 74 /* 75 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We 76 * drop Giant anytime we have to sleep or if we adaptively spin. 77 */ 78 #define GIANT_DECLARE \ 79 int _giantcnt = 0; \ 80 WITNESS_SAVE_DECL(Giant) \ 81 82 #define GIANT_SAVE() do { \ 83 if (mtx_owned(&Giant)) { \ 84 WITNESS_SAVE(&Giant.mtx_object, Giant); \ 85 while (mtx_owned(&Giant)) { \ 86 _giantcnt++; \ 87 mtx_unlock(&Giant); \ 88 } \ 89 } \ 90 } while (0) 91 92 #define GIANT_RESTORE() do { \ 93 if (_giantcnt > 0) { \ 94 mtx_assert(&Giant, MA_NOTOWNED); \ 95 while (_giantcnt--) \ 96 mtx_lock(&Giant); \ 97 WITNESS_RESTORE(&Giant.mtx_object, Giant); \ 98 } \ 99 } while (0) 100 101 /* 102 * Returns true if an exclusive lock is recursed. It assumes 103 * curthread currently has an exclusive lock. 104 */ 105 #define sx_recursed(sx) ((sx)->sx_recurse != 0) 106 107 #ifdef DDB 108 static void db_show_sx(struct lock_object *lock); 109 #endif 110 111 struct lock_class lock_class_sx = { 112 .lc_name = "sx", 113 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE, 114 #ifdef DDB 115 .lc_ddb_show = db_show_sx, 116 #endif 117 }; 118 119 #ifndef INVARIANTS 120 #define _sx_assert(sx, what, file, line) 121 #endif 122 123 void 124 sx_sysinit(void *arg) 125 { 126 struct sx_args *sargs = arg; 127 128 sx_init(sargs->sa_sx, sargs->sa_desc); 129 } 130 131 void 132 sx_init(struct sx *sx, const char *description) 133 { 134 135 sx_init_flags(sx, description, 0); 136 } 137 138 void 139 sx_init_flags(struct sx *sx, const char *description, int opts) 140 { 141 int flags; 142 143 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK | 144 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0); 145 146 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE; 147 if (opts & SX_DUPOK) 148 flags |= LO_DUPOK; 149 if (!(opts & SX_NOWITNESS)) 150 flags |= LO_WITNESS; 151 if (opts & SX_QUIET) 152 flags |= LO_QUIET; 153 154 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE); 155 sx->sx_lock = SX_LOCK_UNLOCKED; 156 sx->sx_recurse = 0; 157 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags); 158 } 159 160 void 161 sx_destroy(struct sx *sx) 162 { 163 164 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held")); 165 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed")); 166 sx->sx_lock = SX_LOCK_DESTROYED; 167 lock_destroy(&sx->lock_object); 168 } 169 170 int 171 _sx_slock(struct sx *sx, int opts, const char *file, int line) 172 { 173 int error = 0; 174 175 MPASS(curthread != NULL); 176 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 177 ("sx_slock() of destroyed sx @ %s:%d", file, line)); 178 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line); 179 error = __sx_slock(sx, opts, file, line); 180 if (!error) { 181 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line); 182 WITNESS_LOCK(&sx->lock_object, 0, file, line); 183 curthread->td_locks++; 184 } 185 186 return (error); 187 } 188 189 int 190 _sx_try_slock(struct sx *sx, const char *file, int line) 191 { 192 uintptr_t x; 193 194 x = sx->sx_lock; 195 KASSERT(x != SX_LOCK_DESTROYED, 196 ("sx_try_slock() of destroyed sx @ %s:%d", file, line)); 197 if ((x & SX_LOCK_SHARED) && atomic_cmpset_acq_ptr(&sx->sx_lock, x, 198 x + SX_ONE_SHARER)) { 199 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line); 200 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line); 201 curthread->td_locks++; 202 return (1); 203 } 204 205 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line); 206 return (0); 207 } 208 209 int 210 _sx_xlock(struct sx *sx, int opts, const char *file, int line) 211 { 212 int error = 0; 213 214 MPASS(curthread != NULL); 215 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 216 ("sx_xlock() of destroyed sx @ %s:%d", file, line)); 217 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 218 line); 219 error = __sx_xlock(sx, curthread, opts, file, line); 220 if (!error) { 221 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse, 222 file, line); 223 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 224 curthread->td_locks++; 225 } 226 227 return (error); 228 } 229 230 int 231 _sx_try_xlock(struct sx *sx, const char *file, int line) 232 { 233 int rval; 234 235 MPASS(curthread != NULL); 236 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 237 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line)); 238 239 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) { 240 sx->sx_recurse++; 241 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 242 rval = 1; 243 } else 244 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, 245 (uintptr_t)curthread); 246 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line); 247 if (rval) { 248 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 249 file, line); 250 curthread->td_locks++; 251 } 252 253 return (rval); 254 } 255 256 void 257 _sx_sunlock(struct sx *sx, const char *file, int line) 258 { 259 260 MPASS(curthread != NULL); 261 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 262 ("sx_sunlock() of destroyed sx @ %s:%d", file, line)); 263 _sx_assert(sx, SA_SLOCKED, file, line); 264 curthread->td_locks--; 265 WITNESS_UNLOCK(&sx->lock_object, 0, file, line); 266 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line); 267 #ifdef LOCK_PROFILING_SHARED 268 if (SX_SHARERS(sx->sx_lock) == 1) 269 lock_profile_release_lock(&sx->lock_object); 270 #endif 271 __sx_sunlock(sx, file, line); 272 } 273 274 void 275 _sx_xunlock(struct sx *sx, const char *file, int line) 276 { 277 278 MPASS(curthread != NULL); 279 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 280 ("sx_xunlock() of destroyed sx @ %s:%d", file, line)); 281 _sx_assert(sx, SA_XLOCKED, file, line); 282 curthread->td_locks--; 283 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line); 284 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file, 285 line); 286 if (!sx_recursed(sx)) 287 lock_profile_release_lock(&sx->lock_object); 288 __sx_xunlock(sx, curthread, file, line); 289 } 290 291 /* 292 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock. 293 * This will only succeed if this thread holds a single shared lock. 294 * Return 1 if if the upgrade succeed, 0 otherwise. 295 */ 296 int 297 _sx_try_upgrade(struct sx *sx, const char *file, int line) 298 { 299 uintptr_t x; 300 int success; 301 302 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 303 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line)); 304 _sx_assert(sx, SA_SLOCKED, file, line); 305 306 /* 307 * Try to switch from one shared lock to an exclusive lock. We need 308 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that 309 * we will wake up the exclusive waiters when we drop the lock. 310 */ 311 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS; 312 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x, 313 (uintptr_t)curthread | x); 314 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line); 315 if (success) 316 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 317 file, line); 318 return (success); 319 } 320 321 /* 322 * Downgrade an unrecursed exclusive lock into a single shared lock. 323 */ 324 void 325 _sx_downgrade(struct sx *sx, const char *file, int line) 326 { 327 uintptr_t x; 328 329 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED, 330 ("sx_downgrade() of destroyed sx @ %s:%d", file, line)); 331 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line); 332 #ifndef INVARIANTS 333 if (sx_recursed(sx)) 334 panic("downgrade of a recursed lock"); 335 #endif 336 337 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line); 338 339 /* 340 * Try to switch from an exclusive lock with no shared waiters 341 * to one sharer with no shared waiters. If there are 342 * exclusive waiters, we don't need to lock the sleep queue so 343 * long as we preserve the flag. We do one quick try and if 344 * that fails we grab the sleepq lock to keep the flags from 345 * changing and do it the slow way. 346 * 347 * We have to lock the sleep queue if there are shared waiters 348 * so we can wake them up. 349 */ 350 x = sx->sx_lock; 351 if (!(x & SX_LOCK_SHARED_WAITERS) && 352 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) | 353 (x & SX_LOCK_EXCLUSIVE_WAITERS))) { 354 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 355 return; 356 } 357 358 /* 359 * Lock the sleep queue so we can read the waiters bits 360 * without any races and wakeup any shared waiters. 361 */ 362 sleepq_lock(&sx->lock_object); 363 364 /* 365 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single 366 * shared lock. If there are any shared waiters, wake them up. 367 */ 368 x = sx->sx_lock; 369 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | 370 (x & SX_LOCK_EXCLUSIVE_WAITERS)); 371 if (x & SX_LOCK_SHARED_WAITERS) 372 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 373 SQ_SHARED_QUEUE); 374 else 375 sleepq_release(&sx->lock_object); 376 377 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line); 378 } 379 380 /* 381 * This function represents the so-called 'hard case' for sx_xlock 382 * operation. All 'easy case' failures are redirected to this. Note 383 * that ideally this would be a static function, but it needs to be 384 * accessible from at least sx.h. 385 */ 386 int 387 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, 388 int line) 389 { 390 GIANT_DECLARE; 391 #ifdef ADAPTIVE_SX 392 volatile struct thread *owner; 393 #endif 394 /* uint64_t waittime = 0; */ 395 uintptr_t x; 396 int /* contested = 0, */error = 0; 397 398 /* If we already hold an exclusive lock, then recurse. */ 399 if (sx_xlocked(sx)) { 400 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0, 401 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n", 402 sx->lock_object.lo_name, file, line)); 403 sx->sx_recurse++; 404 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 405 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 406 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx); 407 return (0); 408 } 409 410 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 411 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 412 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line); 413 414 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { 415 #ifdef ADAPTIVE_SX 416 /* 417 * If the lock is write locked and the owner is 418 * running on another CPU, spin until the owner stops 419 * running or the state of the lock changes. 420 */ 421 x = sx->sx_lock; 422 if (!(x & SX_LOCK_SHARED) && 423 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 424 x = SX_OWNER(x); 425 owner = (struct thread *)x; 426 if (TD_IS_RUNNING(owner)) { 427 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 428 CTR3(KTR_LOCK, 429 "%s: spinning on %p held by %p", 430 __func__, sx, owner); 431 GIANT_SAVE(); 432 lock_profile_obtain_lock_failed( 433 &sx->lock_object, &contested, &waittime); 434 while (SX_OWNER(sx->sx_lock) == x && 435 TD_IS_RUNNING(owner)) 436 cpu_spinwait(); 437 continue; 438 } 439 } 440 #endif 441 442 sleepq_lock(&sx->lock_object); 443 x = sx->sx_lock; 444 445 /* 446 * If the lock was released while spinning on the 447 * sleep queue chain lock, try again. 448 */ 449 if (x == SX_LOCK_UNLOCKED) { 450 sleepq_release(&sx->lock_object); 451 continue; 452 } 453 454 #ifdef ADAPTIVE_SX 455 /* 456 * The current lock owner might have started executing 457 * on another CPU (or the lock could have changed 458 * owners) while we were waiting on the sleep queue 459 * chain lock. If so, drop the sleep queue lock and try 460 * again. 461 */ 462 if (!(x & SX_LOCK_SHARED) && 463 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 464 owner = (struct thread *)SX_OWNER(x); 465 if (TD_IS_RUNNING(owner)) { 466 sleepq_release(&sx->lock_object); 467 continue; 468 } 469 } 470 #endif 471 472 /* 473 * If an exclusive lock was released with both shared 474 * and exclusive waiters and a shared waiter hasn't 475 * woken up and acquired the lock yet, sx_lock will be 476 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS. 477 * If we see that value, try to acquire it once. Note 478 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS 479 * as there are other exclusive waiters still. If we 480 * fail, restart the loop. 481 */ 482 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) { 483 if (atomic_cmpset_acq_ptr(&sx->sx_lock, 484 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS, 485 tid | SX_LOCK_EXCLUSIVE_WAITERS)) { 486 sleepq_release(&sx->lock_object); 487 CTR2(KTR_LOCK, "%s: %p claimed by new writer", 488 __func__, sx); 489 break; 490 } 491 sleepq_release(&sx->lock_object); 492 continue; 493 } 494 495 /* 496 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail, 497 * than loop back and retry. 498 */ 499 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 500 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 501 x | SX_LOCK_EXCLUSIVE_WAITERS)) { 502 sleepq_release(&sx->lock_object); 503 continue; 504 } 505 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 506 CTR2(KTR_LOCK, "%s: %p set excl waiters flag", 507 __func__, sx); 508 } 509 510 /* 511 * Since we have been unable to acquire the exclusive 512 * lock and the exclusive waiters flag is set, we have 513 * to sleep. 514 */ 515 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 516 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 517 __func__, sx); 518 519 GIANT_SAVE(); 520 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 521 &waittime); 522 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 523 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 524 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE); 525 if (!(opts & SX_INTERRUPTIBLE)) 526 sleepq_wait(&sx->lock_object); 527 else 528 error = sleepq_wait_sig(&sx->lock_object); 529 530 if (error) { 531 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 532 CTR2(KTR_LOCK, 533 "%s: interruptible sleep by %p suspended by signal", 534 __func__, sx); 535 break; 536 } 537 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 538 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 539 __func__, sx); 540 } 541 542 GIANT_RESTORE(); 543 if (!error) 544 lock_profile_obtain_lock_success(&sx->lock_object, contested, 545 waittime, file, line); 546 return (error); 547 } 548 549 /* 550 * This function represents the so-called 'hard case' for sx_xunlock 551 * operation. All 'easy case' failures are redirected to this. Note 552 * that ideally this would be a static function, but it needs to be 553 * accessible from at least sx.h. 554 */ 555 void 556 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line) 557 { 558 uintptr_t x; 559 int queue; 560 561 MPASS(!(sx->sx_lock & SX_LOCK_SHARED)); 562 563 /* If the lock is recursed, then unrecurse one level. */ 564 if (sx_xlocked(sx) && sx_recursed(sx)) { 565 if ((--sx->sx_recurse) == 0) 566 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED); 567 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 568 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx); 569 return; 570 } 571 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS | 572 SX_LOCK_EXCLUSIVE_WAITERS)); 573 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 574 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx); 575 576 sleepq_lock(&sx->lock_object); 577 x = SX_LOCK_UNLOCKED; 578 579 /* 580 * The wake up algorithm here is quite simple and probably not 581 * ideal. It gives precedence to shared waiters if they are 582 * present. For this condition, we have to preserve the 583 * state of the exclusive waiters flag. 584 */ 585 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) { 586 queue = SQ_SHARED_QUEUE; 587 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS); 588 } else 589 queue = SQ_EXCLUSIVE_QUEUE; 590 591 /* Wake up all the waiters for the specific queue. */ 592 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 593 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue", 594 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" : 595 "exclusive"); 596 atomic_store_rel_ptr(&sx->sx_lock, x); 597 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, queue); 598 } 599 600 /* 601 * This function represents the so-called 'hard case' for sx_slock 602 * operation. All 'easy case' failures are redirected to this. Note 603 * that ideally this would be a static function, but it needs to be 604 * accessible from at least sx.h. 605 */ 606 int 607 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line) 608 { 609 GIANT_DECLARE; 610 #ifdef ADAPTIVE_SX 611 volatile struct thread *owner; 612 #endif 613 #ifdef LOCK_PROFILING_SHARED 614 uint64_t waittime = 0; 615 int contested = 0; 616 #endif 617 uintptr_t x; 618 int error = 0; 619 620 /* 621 * As with rwlocks, we don't make any attempt to try to block 622 * shared locks once there is an exclusive waiter. 623 */ 624 for (;;) { 625 x = sx->sx_lock; 626 627 /* 628 * If no other thread has an exclusive lock then try to bump up 629 * the count of sharers. Since we have to preserve the state 630 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the 631 * shared lock loop back and retry. 632 */ 633 if (x & SX_LOCK_SHARED) { 634 MPASS(!(x & SX_LOCK_SHARED_WAITERS)); 635 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, 636 x + SX_ONE_SHARER)) { 637 #ifdef LOCK_PROFILING_SHARED 638 if (SX_SHARERS(x) == 0) 639 lock_profile_obtain_lock_success( 640 &sx->lock_object, contested, 641 waittime, file, line); 642 #endif 643 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 644 CTR4(KTR_LOCK, 645 "%s: %p succeed %p -> %p", __func__, 646 sx, (void *)x, 647 (void *)(x + SX_ONE_SHARER)); 648 break; 649 } 650 continue; 651 } 652 653 #ifdef ADAPTIVE_SX 654 /* 655 * If the owner is running on another CPU, spin until 656 * the owner stops running or the state of the lock 657 * changes. 658 */ 659 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) { 660 x = SX_OWNER(x); 661 owner = (struct thread *)x; 662 if (TD_IS_RUNNING(owner)) { 663 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 664 CTR3(KTR_LOCK, 665 "%s: spinning on %p held by %p", 666 __func__, sx, owner); 667 GIANT_SAVE(); 668 #ifdef LOCK_PROFILING_SHARED 669 lock_profile_obtain_lock_failed( 670 &sx->lock_object, &contested, &waittime); 671 #endif 672 while (SX_OWNER(sx->sx_lock) == x && 673 TD_IS_RUNNING(owner)) 674 cpu_spinwait(); 675 continue; 676 } 677 } 678 #endif 679 680 /* 681 * Some other thread already has an exclusive lock, so 682 * start the process of blocking. 683 */ 684 sleepq_lock(&sx->lock_object); 685 x = sx->sx_lock; 686 687 /* 688 * The lock could have been released while we spun. 689 * In this case loop back and retry. 690 */ 691 if (x & SX_LOCK_SHARED) { 692 sleepq_release(&sx->lock_object); 693 continue; 694 } 695 696 #ifdef ADAPTIVE_SX 697 /* 698 * If the owner is running on another CPU, spin until 699 * the owner stops running or the state of the lock 700 * changes. 701 */ 702 if (!(x & SX_LOCK_SHARED) && 703 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) { 704 owner = (struct thread *)SX_OWNER(x); 705 if (TD_IS_RUNNING(owner)) { 706 sleepq_release(&sx->lock_object); 707 continue; 708 } 709 } 710 #endif 711 712 /* 713 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we 714 * fail to set it drop the sleep queue lock and loop 715 * back. 716 */ 717 if (!(x & SX_LOCK_SHARED_WAITERS)) { 718 if (!atomic_cmpset_ptr(&sx->sx_lock, x, 719 x | SX_LOCK_SHARED_WAITERS)) { 720 sleepq_release(&sx->lock_object); 721 continue; 722 } 723 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 724 CTR2(KTR_LOCK, "%s: %p set shared waiters flag", 725 __func__, sx); 726 } 727 728 /* 729 * Since we have been unable to acquire the shared lock, 730 * we have to sleep. 731 */ 732 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 733 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue", 734 __func__, sx); 735 736 GIANT_SAVE(); 737 #ifdef LOCK_PROFILING_SHARED 738 lock_profile_obtain_lock_failed(&sx->lock_object, &contested, 739 &waittime); 740 #endif 741 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name, 742 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ? 743 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE); 744 if (!(opts & SX_INTERRUPTIBLE)) 745 sleepq_wait(&sx->lock_object); 746 else 747 error = sleepq_wait_sig(&sx->lock_object); 748 749 if (error) { 750 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 751 CTR2(KTR_LOCK, 752 "%s: interruptible sleep by %p suspended by signal", 753 __func__, sx); 754 break; 755 } 756 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 757 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue", 758 __func__, sx); 759 } 760 761 GIANT_RESTORE(); 762 return (error); 763 } 764 765 /* 766 * This function represents the so-called 'hard case' for sx_sunlock 767 * operation. All 'easy case' failures are redirected to this. Note 768 * that ideally this would be a static function, but it needs to be 769 * accessible from at least sx.h. 770 */ 771 void 772 _sx_sunlock_hard(struct sx *sx, const char *file, int line) 773 { 774 uintptr_t x; 775 776 for (;;) { 777 x = sx->sx_lock; 778 779 /* 780 * We should never have sharers while at least one thread 781 * holds a shared lock. 782 */ 783 KASSERT(!(x & SX_LOCK_SHARED_WAITERS), 784 ("%s: waiting sharers", __func__)); 785 786 /* 787 * See if there is more than one shared lock held. If 788 * so, just drop one and return. 789 */ 790 if (SX_SHARERS(x) > 1) { 791 if (atomic_cmpset_ptr(&sx->sx_lock, x, 792 x - SX_ONE_SHARER)) { 793 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 794 CTR4(KTR_LOCK, 795 "%s: %p succeeded %p -> %p", 796 __func__, sx, (void *)x, 797 (void *)(x - SX_ONE_SHARER)); 798 break; 799 } 800 continue; 801 } 802 803 /* 804 * If there aren't any waiters for an exclusive lock, 805 * then try to drop it quickly. 806 */ 807 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) { 808 MPASS(x == SX_SHARERS_LOCK(1)); 809 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1), 810 SX_LOCK_UNLOCKED)) { 811 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 812 CTR2(KTR_LOCK, "%s: %p last succeeded", 813 __func__, sx); 814 break; 815 } 816 continue; 817 } 818 819 /* 820 * At this point, there should just be one sharer with 821 * exclusive waiters. 822 */ 823 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS)); 824 825 sleepq_lock(&sx->lock_object); 826 827 /* 828 * Wake up semantic here is quite simple: 829 * Just wake up all the exclusive waiters. 830 * Note that the state of the lock could have changed, 831 * so if it fails loop back and retry. 832 */ 833 if (!atomic_cmpset_ptr(&sx->sx_lock, 834 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS, 835 SX_LOCK_UNLOCKED)) { 836 sleepq_release(&sx->lock_object); 837 continue; 838 } 839 if (LOCK_LOG_TEST(&sx->lock_object, 0)) 840 CTR2(KTR_LOCK, "%s: %p waking up all thread on" 841 "exclusive queue", __func__, sx); 842 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, 843 SQ_EXCLUSIVE_QUEUE); 844 break; 845 } 846 } 847 848 /* 849 * Atomically drop an sx lock while going to sleep. This is just a hack 850 * for 6.x. In 7.0 and later this is done more cleanly. 851 */ 852 int 853 sx_sleep(void *ident, struct sx *sx, int priority, const char *wmesg, int timo) 854 { 855 struct thread *td; 856 struct proc *p; 857 int catch, rval, flags, xlocked; 858 WITNESS_SAVE_DECL(sx_witness); 859 860 td = curthread; 861 p = td->td_proc; 862 #ifdef KTRACE 863 if (KTRPOINT(td, KTR_CSW)) 864 ktrcsw(1, 0); 865 #endif 866 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, 867 "Sleeping on \"%s\"", wmesg); 868 KASSERT(sx != NULL, ("sx_sleep w/o an sx lock")); 869 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("sx_sleep")); 870 871 if (cold) { 872 /* 873 * During autoconfiguration, just return; 874 * don't run any other threads or panic below, 875 * in case this is the idle thread and already asleep. 876 * XXX: this used to do "s = splhigh(); splx(safepri); 877 * splx(s);" to give interrupts a chance, but there is 878 * no way to give interrupts a chance now. 879 */ 880 if (priority & PDROP) 881 sx_unlock(sx); 882 return (0); 883 } 884 catch = priority & PCATCH; 885 rval = 0; 886 887 /* 888 * If we are already on a sleep queue, then remove us from that 889 * sleep queue first. We have to do this to handle recursive 890 * sleeps. 891 */ 892 if (TD_ON_SLEEPQ(td)) 893 sleepq_remove(td, td->td_wchan); 894 895 flags = SLEEPQ_MSLEEP; 896 if (catch) 897 flags |= SLEEPQ_INTERRUPTIBLE; 898 899 sleepq_lock(ident); 900 CTR5(KTR_PROC, "sx_sleep: thread %p (pid %ld, %s) on %s (%p)", 901 (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident); 902 903 DROP_GIANT(); 904 905 /* 906 * We put ourselves on the sleep queue and start our timeout 907 * before calling thread_suspend_check, as we could stop there, 908 * and a wakeup or a SIGCONT (or both) could occur while we were 909 * stopped without resuming us. Thus, we must be ready for sleep 910 * when cursig() is called. If the wakeup happens while we're 911 * stopped, then td will no longer be on a sleep queue upon 912 * return from cursig(). 913 */ 914 sleepq_add(ident, &sx->lock_object, wmesg, flags, 0); 915 if (timo) 916 sleepq_set_timeout(ident, timo); 917 918 /* 919 * Now that we are on the queue, drop the sleepq lock so we 920 * can safely unlock the sx lock. 921 */ 922 sleepq_release(ident); 923 WITNESS_SAVE(&sx->lock_object, sx_witness); 924 xlocked = sx_xlocked(sx); 925 if (xlocked) 926 sx_xunlock(sx); 927 else 928 sx_sunlock(sx); 929 sleepq_lock(ident); 930 931 /* 932 * Adjust this thread's priority. 933 */ 934 if ((priority & PRIMASK) != 0) { 935 mtx_lock_spin(&sched_lock); 936 sched_prio(td, priority & PRIMASK); 937 mtx_unlock_spin(&sched_lock); 938 } 939 940 if (timo && catch) 941 rval = sleepq_timedwait_sig(ident); 942 else if (timo) 943 rval = sleepq_timedwait(ident); 944 else if (catch) 945 rval = sleepq_wait_sig(ident); 946 else { 947 sleepq_wait(ident); 948 rval = 0; 949 } 950 #ifdef KTRACE 951 if (KTRPOINT(td, KTR_CSW)) 952 ktrcsw(0, 0); 953 #endif 954 PICKUP_GIANT(); 955 if (!(priority & PDROP)) { 956 if (xlocked) 957 sx_xlock(sx); 958 else 959 sx_slock(sx); 960 WITNESS_RESTORE(&sx->lock_object, sx_witness); 961 } 962 return (rval); 963 } 964 965 #ifdef INVARIANT_SUPPORT 966 #ifndef INVARIANTS 967 #undef _sx_assert 968 #endif 969 970 /* 971 * In the non-WITNESS case, sx_assert() can only detect that at least 972 * *some* thread owns an slock, but it cannot guarantee that *this* 973 * thread owns an slock. 974 */ 975 void 976 _sx_assert(struct sx *sx, int what, const char *file, int line) 977 { 978 #ifndef WITNESS 979 int slocked = 0; 980 #endif 981 982 if (panicstr != NULL) 983 return; 984 switch (what) { 985 case SA_SLOCKED: 986 case SA_SLOCKED | SA_NOTRECURSED: 987 case SA_SLOCKED | SA_RECURSED: 988 #ifndef WITNESS 989 slocked = 1; 990 /* FALLTHROUGH */ 991 #endif 992 case SA_LOCKED: 993 case SA_LOCKED | SA_NOTRECURSED: 994 case SA_LOCKED | SA_RECURSED: 995 #ifdef WITNESS 996 witness_assert(&sx->lock_object, what, file, line); 997 #else 998 /* 999 * If some other thread has an exclusive lock or we 1000 * have one and are asserting a shared lock, fail. 1001 * Also, if no one has a lock at all, fail. 1002 */ 1003 if (sx->sx_lock == SX_LOCK_UNLOCKED || 1004 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked || 1005 sx_xholder(sx) != curthread))) 1006 panic("Lock %s not %slocked @ %s:%d\n", 1007 sx->lock_object.lo_name, slocked ? "share " : "", 1008 file, line); 1009 1010 if (!(sx->sx_lock & SX_LOCK_SHARED)) { 1011 if (sx_recursed(sx)) { 1012 if (what & SA_NOTRECURSED) 1013 panic("Lock %s recursed @ %s:%d\n", 1014 sx->lock_object.lo_name, file, 1015 line); 1016 } else if (what & SA_RECURSED) 1017 panic("Lock %s not recursed @ %s:%d\n", 1018 sx->lock_object.lo_name, file, line); 1019 } 1020 #endif 1021 break; 1022 case SA_XLOCKED: 1023 case SA_XLOCKED | SA_NOTRECURSED: 1024 case SA_XLOCKED | SA_RECURSED: 1025 if (sx_xholder(sx) != curthread) 1026 panic("Lock %s not exclusively locked @ %s:%d\n", 1027 sx->lock_object.lo_name, file, line); 1028 if (sx_recursed(sx)) { 1029 if (what & SA_NOTRECURSED) 1030 panic("Lock %s recursed @ %s:%d\n", 1031 sx->lock_object.lo_name, file, line); 1032 } else if (what & SA_RECURSED) 1033 panic("Lock %s not recursed @ %s:%d\n", 1034 sx->lock_object.lo_name, file, line); 1035 break; 1036 case SA_UNLOCKED: 1037 #ifdef WITNESS 1038 witness_assert(&sx->lock_object, what, file, line); 1039 #else 1040 /* 1041 * If we hold an exclusve lock fail. We can't 1042 * reliably check to see if we hold a shared lock or 1043 * not. 1044 */ 1045 if (sx_xholder(sx) == curthread) 1046 panic("Lock %s exclusively locked @ %s:%d\n", 1047 sx->lock_object.lo_name, file, line); 1048 #endif 1049 break; 1050 default: 1051 panic("Unknown sx lock assertion: %d @ %s:%d", what, file, 1052 line); 1053 } 1054 } 1055 #endif /* INVARIANT_SUPPORT */ 1056 1057 #ifdef DDB 1058 static void 1059 db_show_sx(struct lock_object *lock) 1060 { 1061 struct thread *td; 1062 struct sx *sx; 1063 1064 sx = (struct sx *)lock; 1065 1066 db_printf(" state: "); 1067 if (sx->sx_lock == SX_LOCK_UNLOCKED) 1068 db_printf("UNLOCKED\n"); 1069 else if (sx->sx_lock == SX_LOCK_DESTROYED) { 1070 db_printf("DESTROYED\n"); 1071 return; 1072 } else if (sx->sx_lock & SX_LOCK_SHARED) 1073 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock)); 1074 else { 1075 td = sx_xholder(sx); 1076 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1077 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm); 1078 if (sx_recursed(sx)) 1079 db_printf(" recursed: %d\n", sx->sx_recurse); 1080 } 1081 1082 db_printf(" waiters: "); 1083 switch(sx->sx_lock & 1084 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) { 1085 case SX_LOCK_SHARED_WAITERS: 1086 db_printf("shared\n"); 1087 break; 1088 case SX_LOCK_EXCLUSIVE_WAITERS: 1089 db_printf("exclusive\n"); 1090 break; 1091 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS: 1092 db_printf("exclusive and shared\n"); 1093 break; 1094 default: 1095 db_printf("none\n"); 1096 } 1097 } 1098 1099 /* 1100 * Check to see if a thread that is blocked on a sleep queue is actually 1101 * blocked on an sx lock. If so, output some details and return true. 1102 * If the lock has an exclusive owner, return that in *ownerp. 1103 */ 1104 int 1105 sx_chain(struct thread *td, struct thread **ownerp) 1106 { 1107 struct sx *sx; 1108 1109 /* 1110 * Check to see if this thread is blocked on an sx lock. 1111 * First, we check the lock class. If that is ok, then we 1112 * compare the lock name against the wait message. 1113 */ 1114 sx = td->td_wchan; 1115 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx || 1116 sx->lock_object.lo_name != td->td_wmesg) 1117 return (0); 1118 1119 /* We think we have an sx lock, so output some details. */ 1120 db_printf("blocked on sx \"%s\" ", td->td_wmesg); 1121 *ownerp = sx_xholder(sx); 1122 if (sx->sx_lock & SX_LOCK_SHARED) 1123 db_printf("SLOCK (count %ju)\n", 1124 (uintmax_t)SX_SHARERS(sx->sx_lock)); 1125 else 1126 db_printf("XLOCK\n"); 1127 return (1); 1128 } 1129 #endif
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