Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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sys/kern/kern_lock.c
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1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2008 Attilio Rao <attilio@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice(s), this list of conditions and the following disclaimer as 12 * the first lines of this file unmodified other than the possible 13 * addition of one or more copyright notices. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice(s), this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 19 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 20 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 21 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 22 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 23 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 24 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 25 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 28 * DAMAGE. 29 */ 30 31 #include "opt_ddb.h" 32 #include "opt_hwpmc_hooks.h" 33 34 #include <sys/cdefs.h> 35 __FBSDID("$FreeBSD$"); 36 37 #include <sys/param.h> 38 #include <sys/kdb.h> 39 #include <sys/ktr.h> 40 #include <sys/lock.h> 41 #include <sys/lock_profile.h> 42 #include <sys/lockmgr.h> 43 #include <sys/lockstat.h> 44 #include <sys/mutex.h> 45 #include <sys/proc.h> 46 #include <sys/sleepqueue.h> 47 #ifdef DEBUG_LOCKS 48 #include <sys/stack.h> 49 #endif 50 #include <sys/sysctl.h> 51 #include <sys/systm.h> 52 53 #include <machine/cpu.h> 54 55 #ifdef DDB 56 #include <ddb/ddb.h> 57 #endif 58 59 #ifdef HWPMC_HOOKS 60 #include <sys/pmckern.h> 61 PMC_SOFT_DECLARE( , , lock, failed); 62 #endif 63 64 CTASSERT(((LK_ADAPTIVE | LK_NOSHARE) & LO_CLASSFLAGS) == 65 (LK_ADAPTIVE | LK_NOSHARE)); 66 CTASSERT(LK_UNLOCKED == (LK_UNLOCKED & 67 ~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS))); 68 69 #define SQ_EXCLUSIVE_QUEUE 0 70 #define SQ_SHARED_QUEUE 1 71 72 #ifndef INVARIANTS 73 #define _lockmgr_assert(lk, what, file, line) 74 #endif 75 76 #define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++) 77 #define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--) 78 79 #ifndef DEBUG_LOCKS 80 #define STACK_PRINT(lk) 81 #define STACK_SAVE(lk) 82 #define STACK_ZERO(lk) 83 #else 84 #define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack) 85 #define STACK_SAVE(lk) stack_save(&(lk)->lk_stack) 86 #define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack) 87 #endif 88 89 #define LOCK_LOG2(lk, string, arg1, arg2) \ 90 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ 91 CTR2(KTR_LOCK, (string), (arg1), (arg2)) 92 #define LOCK_LOG3(lk, string, arg1, arg2, arg3) \ 93 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ 94 CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3)) 95 96 #define GIANT_DECLARE \ 97 int _i = 0; \ 98 WITNESS_SAVE_DECL(Giant) 99 #define GIANT_RESTORE() do { \ 100 if (_i > 0) { \ 101 while (_i--) \ 102 mtx_lock(&Giant); \ 103 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 104 } \ 105 } while (0) 106 #define GIANT_SAVE() do { \ 107 if (mtx_owned(&Giant)) { \ 108 WITNESS_SAVE(&Giant.lock_object, Giant); \ 109 while (mtx_owned(&Giant)) { \ 110 _i++; \ 111 mtx_unlock(&Giant); \ 112 } \ 113 } \ 114 } while (0) 115 116 static bool __always_inline 117 LK_CAN_SHARE(uintptr_t x, int flags, bool fp) 118 { 119 120 if ((x & (LK_SHARE | LK_EXCLUSIVE_WAITERS | LK_EXCLUSIVE_SPINNERS)) == 121 LK_SHARE) 122 return (true); 123 if (fp || (!(x & LK_SHARE))) 124 return (false); 125 if ((curthread->td_lk_slocks != 0 && !(flags & LK_NODDLKTREAT)) || 126 (curthread->td_pflags & TDP_DEADLKTREAT)) 127 return (true); 128 return (false); 129 } 130 131 #define LK_TRYOP(x) \ 132 ((x) & LK_NOWAIT) 133 134 #define LK_CAN_WITNESS(x) \ 135 (((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x)) 136 #define LK_TRYWIT(x) \ 137 (LK_TRYOP(x) ? LOP_TRYLOCK : 0) 138 139 #define LK_CAN_ADAPT(lk, f) \ 140 (((lk)->lock_object.lo_flags & LK_ADAPTIVE) != 0 && \ 141 ((f) & LK_SLEEPFAIL) == 0) 142 143 #define lockmgr_disowned(lk) \ 144 (((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC) 145 146 #define lockmgr_xlocked_v(v) \ 147 (((v) & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread) 148 149 #define lockmgr_xlocked(lk) lockmgr_xlocked_v((lk)->lk_lock) 150 151 static void assert_lockmgr(const struct lock_object *lock, int how); 152 #ifdef DDB 153 static void db_show_lockmgr(const struct lock_object *lock); 154 #endif 155 static void lock_lockmgr(struct lock_object *lock, uintptr_t how); 156 #ifdef KDTRACE_HOOKS 157 static int owner_lockmgr(const struct lock_object *lock, 158 struct thread **owner); 159 #endif 160 static uintptr_t unlock_lockmgr(struct lock_object *lock); 161 162 struct lock_class lock_class_lockmgr = { 163 .lc_name = "lockmgr", 164 .lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE, 165 .lc_assert = assert_lockmgr, 166 #ifdef DDB 167 .lc_ddb_show = db_show_lockmgr, 168 #endif 169 .lc_lock = lock_lockmgr, 170 .lc_unlock = unlock_lockmgr, 171 #ifdef KDTRACE_HOOKS 172 .lc_owner = owner_lockmgr, 173 #endif 174 }; 175 176 struct lockmgr_wait { 177 const char *iwmesg; 178 int ipri; 179 int itimo; 180 }; 181 182 static bool __always_inline lockmgr_slock_try(struct lock *lk, uintptr_t *xp, 183 int flags, bool fp); 184 static bool __always_inline lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp); 185 186 static void 187 lockmgr_exit(u_int flags, struct lock_object *ilk, int wakeup_swapper) 188 { 189 struct lock_class *class; 190 191 if (flags & LK_INTERLOCK) { 192 class = LOCK_CLASS(ilk); 193 class->lc_unlock(ilk); 194 } 195 196 if (__predict_false(wakeup_swapper)) 197 kick_proc0(); 198 } 199 200 static void 201 lockmgr_note_shared_acquire(struct lock *lk, int contested, 202 uint64_t waittime, const char *file, int line, int flags) 203 { 204 205 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested, 206 waittime, file, line, LOCKSTAT_READER); 207 LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file, line); 208 WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file, line); 209 TD_LOCKS_INC(curthread); 210 TD_SLOCKS_INC(curthread); 211 STACK_SAVE(lk); 212 } 213 214 static void 215 lockmgr_note_shared_release(struct lock *lk, const char *file, int line) 216 { 217 218 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER); 219 WITNESS_UNLOCK(&lk->lock_object, 0, file, line); 220 LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line); 221 TD_LOCKS_DEC(curthread); 222 TD_SLOCKS_DEC(curthread); 223 } 224 225 static void 226 lockmgr_note_exclusive_acquire(struct lock *lk, int contested, 227 uint64_t waittime, const char *file, int line, int flags) 228 { 229 230 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested, 231 waittime, file, line, LOCKSTAT_WRITER); 232 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); 233 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, 234 line); 235 TD_LOCKS_INC(curthread); 236 STACK_SAVE(lk); 237 } 238 239 static void 240 lockmgr_note_exclusive_release(struct lock *lk, const char *file, int line) 241 { 242 243 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_WRITER); 244 LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file, 245 line); 246 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); 247 TD_LOCKS_DEC(curthread); 248 } 249 250 static __inline struct thread * 251 lockmgr_xholder(const struct lock *lk) 252 { 253 uintptr_t x; 254 255 x = lk->lk_lock; 256 return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x)); 257 } 258 259 /* 260 * It assumes sleepq_lock held and returns with this one unheld. 261 * It also assumes the generic interlock is sane and previously checked. 262 * If LK_INTERLOCK is specified the interlock is not reacquired after the 263 * sleep. 264 */ 265 static __inline int 266 sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk, 267 const char *wmesg, int pri, int timo, int queue) 268 { 269 GIANT_DECLARE; 270 struct lock_class *class; 271 int catch, error; 272 273 class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL; 274 catch = pri & PCATCH; 275 pri &= PRIMASK; 276 error = 0; 277 278 LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk, 279 (queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared"); 280 281 if (flags & LK_INTERLOCK) 282 class->lc_unlock(ilk); 283 if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0) 284 lk->lk_exslpfail++; 285 GIANT_SAVE(); 286 sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ? 287 SLEEPQ_INTERRUPTIBLE : 0), queue); 288 if ((flags & LK_TIMELOCK) && timo) 289 sleepq_set_timeout(&lk->lock_object, timo); 290 291 /* 292 * Decisional switch for real sleeping. 293 */ 294 if ((flags & LK_TIMELOCK) && timo && catch) 295 error = sleepq_timedwait_sig(&lk->lock_object, pri); 296 else if ((flags & LK_TIMELOCK) && timo) 297 error = sleepq_timedwait(&lk->lock_object, pri); 298 else if (catch) 299 error = sleepq_wait_sig(&lk->lock_object, pri); 300 else 301 sleepq_wait(&lk->lock_object, pri); 302 GIANT_RESTORE(); 303 if ((flags & LK_SLEEPFAIL) && error == 0) 304 error = ENOLCK; 305 306 return (error); 307 } 308 309 static __inline int 310 wakeupshlk(struct lock *lk, const char *file, int line) 311 { 312 uintptr_t v, x, orig_x; 313 u_int realexslp; 314 int queue, wakeup_swapper; 315 316 wakeup_swapper = 0; 317 for (;;) { 318 x = lk->lk_lock; 319 if (lockmgr_sunlock_try(lk, &x)) 320 break; 321 322 /* 323 * We should have a sharer with waiters, so enter the hard 324 * path in order to handle wakeups correctly. 325 */ 326 sleepq_lock(&lk->lock_object); 327 orig_x = lk->lk_lock; 328 retry_sleepq: 329 x = orig_x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); 330 v = LK_UNLOCKED; 331 332 /* 333 * If the lock has exclusive waiters, give them preference in 334 * order to avoid deadlock with shared runners up. 335 * If interruptible sleeps left the exclusive queue empty 336 * avoid a starvation for the threads sleeping on the shared 337 * queue by giving them precedence and cleaning up the 338 * exclusive waiters bit anyway. 339 * Please note that lk_exslpfail count may be lying about 340 * the real number of waiters with the LK_SLEEPFAIL flag on 341 * because they may be used in conjunction with interruptible 342 * sleeps so lk_exslpfail might be considered an 'upper limit' 343 * bound, including the edge cases. 344 */ 345 realexslp = sleepq_sleepcnt(&lk->lock_object, 346 SQ_EXCLUSIVE_QUEUE); 347 if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) { 348 if (lk->lk_exslpfail < realexslp) { 349 lk->lk_exslpfail = 0; 350 queue = SQ_EXCLUSIVE_QUEUE; 351 v |= (x & LK_SHARED_WAITERS); 352 } else { 353 lk->lk_exslpfail = 0; 354 LOCK_LOG2(lk, 355 "%s: %p has only LK_SLEEPFAIL sleepers", 356 __func__, lk); 357 LOCK_LOG2(lk, 358 "%s: %p waking up threads on the exclusive queue", 359 __func__, lk); 360 wakeup_swapper = 361 sleepq_broadcast(&lk->lock_object, 362 SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); 363 queue = SQ_SHARED_QUEUE; 364 } 365 366 } else { 367 368 /* 369 * Exclusive waiters sleeping with LK_SLEEPFAIL on 370 * and using interruptible sleeps/timeout may have 371 * left spourious lk_exslpfail counts on, so clean 372 * it up anyway. 373 */ 374 lk->lk_exslpfail = 0; 375 queue = SQ_SHARED_QUEUE; 376 } 377 378 if (lockmgr_sunlock_try(lk, &orig_x)) { 379 sleepq_release(&lk->lock_object); 380 break; 381 } 382 383 x |= LK_SHARERS_LOCK(1); 384 if (!atomic_fcmpset_rel_ptr(&lk->lk_lock, &x, v)) { 385 orig_x = x; 386 goto retry_sleepq; 387 } 388 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", 389 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : 390 "exclusive"); 391 wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 392 0, queue); 393 sleepq_release(&lk->lock_object); 394 break; 395 } 396 397 lockmgr_note_shared_release(lk, file, line); 398 return (wakeup_swapper); 399 } 400 401 static void 402 assert_lockmgr(const struct lock_object *lock, int what) 403 { 404 405 panic("lockmgr locks do not support assertions"); 406 } 407 408 static void 409 lock_lockmgr(struct lock_object *lock, uintptr_t how) 410 { 411 412 panic("lockmgr locks do not support sleep interlocking"); 413 } 414 415 static uintptr_t 416 unlock_lockmgr(struct lock_object *lock) 417 { 418 419 panic("lockmgr locks do not support sleep interlocking"); 420 } 421 422 #ifdef KDTRACE_HOOKS 423 static int 424 owner_lockmgr(const struct lock_object *lock, struct thread **owner) 425 { 426 427 panic("lockmgr locks do not support owner inquiring"); 428 } 429 #endif 430 431 void 432 lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags) 433 { 434 int iflags; 435 436 MPASS((flags & ~LK_INIT_MASK) == 0); 437 ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock, 438 ("%s: lockmgr not aligned for %s: %p", __func__, wmesg, 439 &lk->lk_lock)); 440 441 iflags = LO_SLEEPABLE | LO_UPGRADABLE; 442 if (flags & LK_CANRECURSE) 443 iflags |= LO_RECURSABLE; 444 if ((flags & LK_NODUP) == 0) 445 iflags |= LO_DUPOK; 446 if (flags & LK_NOPROFILE) 447 iflags |= LO_NOPROFILE; 448 if ((flags & LK_NOWITNESS) == 0) 449 iflags |= LO_WITNESS; 450 if (flags & LK_QUIET) 451 iflags |= LO_QUIET; 452 if (flags & LK_IS_VNODE) 453 iflags |= LO_IS_VNODE; 454 iflags |= flags & (LK_ADAPTIVE | LK_NOSHARE); 455 456 lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags); 457 lk->lk_lock = LK_UNLOCKED; 458 lk->lk_recurse = 0; 459 lk->lk_exslpfail = 0; 460 lk->lk_timo = timo; 461 lk->lk_pri = pri; 462 STACK_ZERO(lk); 463 } 464 465 /* 466 * XXX: Gross hacks to manipulate external lock flags after 467 * initialization. Used for certain vnode and buf locks. 468 */ 469 void 470 lockallowshare(struct lock *lk) 471 { 472 473 lockmgr_assert(lk, KA_XLOCKED); 474 lk->lock_object.lo_flags &= ~LK_NOSHARE; 475 } 476 477 void 478 lockdisableshare(struct lock *lk) 479 { 480 481 lockmgr_assert(lk, KA_XLOCKED); 482 lk->lock_object.lo_flags |= LK_NOSHARE; 483 } 484 485 void 486 lockallowrecurse(struct lock *lk) 487 { 488 489 lockmgr_assert(lk, KA_XLOCKED); 490 lk->lock_object.lo_flags |= LO_RECURSABLE; 491 } 492 493 void 494 lockdisablerecurse(struct lock *lk) 495 { 496 497 lockmgr_assert(lk, KA_XLOCKED); 498 lk->lock_object.lo_flags &= ~LO_RECURSABLE; 499 } 500 501 void 502 lockdestroy(struct lock *lk) 503 { 504 505 KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held")); 506 KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed")); 507 KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters")); 508 lock_destroy(&lk->lock_object); 509 } 510 511 static bool __always_inline 512 lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp) 513 { 514 515 /* 516 * If no other thread has an exclusive lock, or 517 * no exclusive waiter is present, bump the count of 518 * sharers. Since we have to preserve the state of 519 * waiters, if we fail to acquire the shared lock 520 * loop back and retry. 521 */ 522 *xp = lk->lk_lock; 523 while (LK_CAN_SHARE(*xp, flags, fp)) { 524 if (atomic_fcmpset_acq_ptr(&lk->lk_lock, xp, 525 *xp + LK_ONE_SHARER)) { 526 return (true); 527 } 528 } 529 return (false); 530 } 531 532 static bool __always_inline 533 lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp) 534 { 535 536 for (;;) { 537 if (LK_SHARERS(*xp) > 1 || !(*xp & LK_ALL_WAITERS)) { 538 if (atomic_fcmpset_rel_ptr(&lk->lk_lock, xp, 539 *xp - LK_ONE_SHARER)) 540 return (true); 541 continue; 542 } 543 break; 544 } 545 return (false); 546 } 547 548 static __noinline int 549 lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk, 550 const char *file, int line, struct lockmgr_wait *lwa) 551 { 552 uintptr_t tid, x; 553 int error = 0; 554 const char *iwmesg; 555 int ipri, itimo; 556 557 #ifdef KDTRACE_HOOKS 558 uint64_t sleep_time = 0; 559 #endif 560 #ifdef LOCK_PROFILING 561 uint64_t waittime = 0; 562 int contested = 0; 563 #endif 564 565 if (__predict_false(panicstr != NULL)) 566 goto out; 567 568 tid = (uintptr_t)curthread; 569 570 if (LK_CAN_WITNESS(flags)) 571 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, 572 file, line, flags & LK_INTERLOCK ? ilk : NULL); 573 for (;;) { 574 if (lockmgr_slock_try(lk, &x, flags, false)) 575 break; 576 #ifdef HWPMC_HOOKS 577 PMC_SOFT_CALL( , , lock, failed); 578 #endif 579 lock_profile_obtain_lock_failed(&lk->lock_object, 580 &contested, &waittime); 581 582 /* 583 * If the lock is already held by curthread in 584 * exclusive way avoid a deadlock. 585 */ 586 if (LK_HOLDER(x) == tid) { 587 LOCK_LOG2(lk, 588 "%s: %p already held in exclusive mode", 589 __func__, lk); 590 error = EDEADLK; 591 break; 592 } 593 594 /* 595 * If the lock is expected to not sleep just give up 596 * and return. 597 */ 598 if (LK_TRYOP(flags)) { 599 LOCK_LOG2(lk, "%s: %p fails the try operation", 600 __func__, lk); 601 error = EBUSY; 602 break; 603 } 604 605 /* 606 * Acquire the sleepqueue chain lock because we 607 * probabilly will need to manipulate waiters flags. 608 */ 609 sleepq_lock(&lk->lock_object); 610 x = lk->lk_lock; 611 retry_sleepq: 612 613 /* 614 * if the lock can be acquired in shared mode, try 615 * again. 616 */ 617 if (LK_CAN_SHARE(x, flags, false)) { 618 sleepq_release(&lk->lock_object); 619 continue; 620 } 621 622 /* 623 * Try to set the LK_SHARED_WAITERS flag. If we fail, 624 * loop back and retry. 625 */ 626 if ((x & LK_SHARED_WAITERS) == 0) { 627 if (!atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, 628 x | LK_SHARED_WAITERS)) { 629 goto retry_sleepq; 630 } 631 LOCK_LOG2(lk, "%s: %p set shared waiters flag", 632 __func__, lk); 633 } 634 635 if (lwa == NULL) { 636 iwmesg = lk->lock_object.lo_name; 637 ipri = lk->lk_pri; 638 itimo = lk->lk_timo; 639 } else { 640 iwmesg = lwa->iwmesg; 641 ipri = lwa->ipri; 642 itimo = lwa->itimo; 643 } 644 645 /* 646 * As far as we have been unable to acquire the 647 * shared lock and the shared waiters flag is set, 648 * we will sleep. 649 */ 650 #ifdef KDTRACE_HOOKS 651 sleep_time -= lockstat_nsecs(&lk->lock_object); 652 #endif 653 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, 654 SQ_SHARED_QUEUE); 655 #ifdef KDTRACE_HOOKS 656 sleep_time += lockstat_nsecs(&lk->lock_object); 657 #endif 658 flags &= ~LK_INTERLOCK; 659 if (error) { 660 LOCK_LOG3(lk, 661 "%s: interrupted sleep for %p with %d", 662 __func__, lk, error); 663 break; 664 } 665 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 666 __func__, lk); 667 } 668 if (error == 0) { 669 #ifdef KDTRACE_HOOKS 670 if (sleep_time != 0) 671 LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time, 672 LOCKSTAT_READER, (x & LK_SHARE) == 0, 673 (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x)); 674 #endif 675 #ifdef LOCK_PROFILING 676 lockmgr_note_shared_acquire(lk, contested, waittime, 677 file, line, flags); 678 #else 679 lockmgr_note_shared_acquire(lk, 0, 0, file, line, 680 flags); 681 #endif 682 } 683 684 out: 685 lockmgr_exit(flags, ilk, 0); 686 return (error); 687 } 688 689 static __noinline int 690 lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk, 691 const char *file, int line, struct lockmgr_wait *lwa) 692 { 693 struct lock_class *class; 694 uintptr_t tid, x, v; 695 int error = 0; 696 const char *iwmesg; 697 int ipri, itimo; 698 699 #ifdef KDTRACE_HOOKS 700 uint64_t sleep_time = 0; 701 #endif 702 #ifdef LOCK_PROFILING 703 uint64_t waittime = 0; 704 int contested = 0; 705 #endif 706 707 if (__predict_false(panicstr != NULL)) 708 goto out; 709 710 tid = (uintptr_t)curthread; 711 712 if (LK_CAN_WITNESS(flags)) 713 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 714 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 715 ilk : NULL); 716 717 /* 718 * If curthread already holds the lock and this one is 719 * allowed to recurse, simply recurse on it. 720 */ 721 if (lockmgr_xlocked(lk)) { 722 if ((flags & LK_CANRECURSE) == 0 && 723 (lk->lock_object.lo_flags & LO_RECURSABLE) == 0) { 724 /* 725 * If the lock is expected to not panic just 726 * give up and return. 727 */ 728 if (LK_TRYOP(flags)) { 729 LOCK_LOG2(lk, 730 "%s: %p fails the try operation", 731 __func__, lk); 732 error = EBUSY; 733 goto out; 734 } 735 if (flags & LK_INTERLOCK) { 736 class = LOCK_CLASS(ilk); 737 class->lc_unlock(ilk); 738 } 739 panic("%s: recursing on non recursive lockmgr %p " 740 "@ %s:%d\n", __func__, lk, file, line); 741 } 742 lk->lk_recurse++; 743 LOCK_LOG2(lk, "%s: %p recursing", __func__, lk); 744 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, 745 lk->lk_recurse, file, line); 746 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | 747 LK_TRYWIT(flags), file, line); 748 TD_LOCKS_INC(curthread); 749 goto out; 750 } 751 752 for (;;) { 753 if (lk->lk_lock == LK_UNLOCKED && 754 atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) 755 break; 756 #ifdef HWPMC_HOOKS 757 PMC_SOFT_CALL( , , lock, failed); 758 #endif 759 lock_profile_obtain_lock_failed(&lk->lock_object, 760 &contested, &waittime); 761 762 /* 763 * If the lock is expected to not sleep just give up 764 * and return. 765 */ 766 if (LK_TRYOP(flags)) { 767 LOCK_LOG2(lk, "%s: %p fails the try operation", 768 __func__, lk); 769 error = EBUSY; 770 break; 771 } 772 773 /* 774 * Acquire the sleepqueue chain lock because we 775 * probabilly will need to manipulate waiters flags. 776 */ 777 sleepq_lock(&lk->lock_object); 778 x = lk->lk_lock; 779 retry_sleepq: 780 781 /* 782 * if the lock has been released while we spun on 783 * the sleepqueue chain lock just try again. 784 */ 785 if (x == LK_UNLOCKED) { 786 sleepq_release(&lk->lock_object); 787 continue; 788 } 789 790 /* 791 * The lock can be in the state where there is a 792 * pending queue of waiters, but still no owner. 793 * This happens when the lock is contested and an 794 * owner is going to claim the lock. 795 * If curthread is the one successfully acquiring it 796 * claim lock ownership and return, preserving waiters 797 * flags. 798 */ 799 v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); 800 if ((x & ~v) == LK_UNLOCKED) { 801 v &= ~LK_EXCLUSIVE_SPINNERS; 802 if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, 803 tid | v)) { 804 sleepq_release(&lk->lock_object); 805 LOCK_LOG2(lk, 806 "%s: %p claimed by a new writer", 807 __func__, lk); 808 break; 809 } 810 goto retry_sleepq; 811 } 812 813 /* 814 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we 815 * fail, loop back and retry. 816 */ 817 if ((x & LK_EXCLUSIVE_WAITERS) == 0) { 818 if (!atomic_fcmpset_ptr(&lk->lk_lock, &x, 819 x | LK_EXCLUSIVE_WAITERS)) { 820 goto retry_sleepq; 821 } 822 LOCK_LOG2(lk, "%s: %p set excl waiters flag", 823 __func__, lk); 824 } 825 826 if (lwa == NULL) { 827 iwmesg = lk->lock_object.lo_name; 828 ipri = lk->lk_pri; 829 itimo = lk->lk_timo; 830 } else { 831 iwmesg = lwa->iwmesg; 832 ipri = lwa->ipri; 833 itimo = lwa->itimo; 834 } 835 836 /* 837 * As far as we have been unable to acquire the 838 * exclusive lock and the exclusive waiters flag 839 * is set, we will sleep. 840 */ 841 #ifdef KDTRACE_HOOKS 842 sleep_time -= lockstat_nsecs(&lk->lock_object); 843 #endif 844 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, 845 SQ_EXCLUSIVE_QUEUE); 846 #ifdef KDTRACE_HOOKS 847 sleep_time += lockstat_nsecs(&lk->lock_object); 848 #endif 849 flags &= ~LK_INTERLOCK; 850 if (error) { 851 LOCK_LOG3(lk, 852 "%s: interrupted sleep for %p with %d", 853 __func__, lk, error); 854 break; 855 } 856 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 857 __func__, lk); 858 } 859 if (error == 0) { 860 #ifdef KDTRACE_HOOKS 861 if (sleep_time != 0) 862 LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time, 863 LOCKSTAT_WRITER, (x & LK_SHARE) == 0, 864 (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x)); 865 #endif 866 #ifdef LOCK_PROFILING 867 lockmgr_note_exclusive_acquire(lk, contested, waittime, 868 file, line, flags); 869 #else 870 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line, 871 flags); 872 #endif 873 } 874 875 out: 876 lockmgr_exit(flags, ilk, 0); 877 return (error); 878 } 879 880 static __noinline int 881 lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk, 882 const char *file, int line, struct lockmgr_wait *lwa) 883 { 884 uintptr_t tid, x, v; 885 int error = 0; 886 int wakeup_swapper = 0; 887 int op; 888 889 if (__predict_false(panicstr != NULL)) 890 goto out; 891 892 tid = (uintptr_t)curthread; 893 894 _lockmgr_assert(lk, KA_SLOCKED, file, line); 895 v = lk->lk_lock; 896 x = v & LK_ALL_WAITERS; 897 v &= LK_EXCLUSIVE_SPINNERS; 898 899 /* 900 * Try to switch from one shared lock to an exclusive one. 901 * We need to preserve waiters flags during the operation. 902 */ 903 if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x | v, 904 tid | x)) { 905 LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file, 906 line); 907 WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE | 908 LK_TRYWIT(flags), file, line); 909 LOCKSTAT_RECORD0(lockmgr__upgrade, lk); 910 TD_SLOCKS_DEC(curthread); 911 goto out; 912 } 913 914 op = flags & LK_TYPE_MASK; 915 916 /* 917 * In LK_TRYUPGRADE mode, do not drop the lock, 918 * returning EBUSY instead. 919 */ 920 if (op == LK_TRYUPGRADE) { 921 LOCK_LOG2(lk, "%s: %p failed the nowait upgrade", 922 __func__, lk); 923 error = EBUSY; 924 goto out; 925 } 926 927 /* 928 * We have been unable to succeed in upgrading, so just 929 * give up the shared lock. 930 */ 931 wakeup_swapper |= wakeupshlk(lk, file, line); 932 error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa); 933 flags &= ~LK_INTERLOCK; 934 out: 935 lockmgr_exit(flags, ilk, wakeup_swapper); 936 return (error); 937 } 938 939 int 940 lockmgr_lock_fast_path(struct lock *lk, u_int flags, struct lock_object *ilk, 941 const char *file, int line) 942 { 943 struct lock_class *class; 944 uintptr_t x, tid; 945 u_int op; 946 bool locked; 947 948 if (__predict_false(panicstr != NULL)) 949 return (0); 950 951 op = flags & LK_TYPE_MASK; 952 locked = false; 953 switch (op) { 954 case LK_SHARED: 955 if (LK_CAN_WITNESS(flags)) 956 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, 957 file, line, flags & LK_INTERLOCK ? ilk : NULL); 958 if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE)) 959 break; 960 if (lockmgr_slock_try(lk, &x, flags, true)) { 961 lockmgr_note_shared_acquire(lk, 0, 0, 962 file, line, flags); 963 locked = true; 964 } else { 965 return (lockmgr_slock_hard(lk, flags, ilk, file, line, 966 NULL)); 967 } 968 break; 969 case LK_EXCLUSIVE: 970 if (LK_CAN_WITNESS(flags)) 971 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 972 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 973 ilk : NULL); 974 tid = (uintptr_t)curthread; 975 if (lk->lk_lock == LK_UNLOCKED && 976 atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) { 977 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line, 978 flags); 979 locked = true; 980 } else { 981 return (lockmgr_xlock_hard(lk, flags, ilk, file, line, 982 NULL)); 983 } 984 break; 985 case LK_UPGRADE: 986 case LK_TRYUPGRADE: 987 return (lockmgr_upgrade(lk, flags, ilk, file, line, NULL)); 988 default: 989 break; 990 } 991 if (__predict_true(locked)) { 992 if (__predict_false(flags & LK_INTERLOCK)) { 993 class = LOCK_CLASS(ilk); 994 class->lc_unlock(ilk); 995 } 996 return (0); 997 } else { 998 return (__lockmgr_args(lk, flags, ilk, LK_WMESG_DEFAULT, 999 LK_PRIO_DEFAULT, LK_TIMO_DEFAULT, file, line)); 1000 } 1001 } 1002 1003 static __noinline int 1004 lockmgr_sunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk, 1005 const char *file, int line) 1006 1007 { 1008 int wakeup_swapper = 0; 1009 1010 if (__predict_false(panicstr != NULL)) 1011 goto out; 1012 1013 wakeup_swapper = wakeupshlk(lk, file, line); 1014 1015 out: 1016 lockmgr_exit(flags, ilk, wakeup_swapper); 1017 return (0); 1018 } 1019 1020 static __noinline int 1021 lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk, 1022 const char *file, int line) 1023 { 1024 uintptr_t tid, v; 1025 int wakeup_swapper = 0; 1026 u_int realexslp; 1027 int queue; 1028 1029 if (__predict_false(panicstr != NULL)) 1030 goto out; 1031 1032 tid = (uintptr_t)curthread; 1033 1034 /* 1035 * As first option, treact the lock as if it has not 1036 * any waiter. 1037 * Fix-up the tid var if the lock has been disowned. 1038 */ 1039 if (LK_HOLDER(x) == LK_KERNPROC) 1040 tid = LK_KERNPROC; 1041 else { 1042 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); 1043 TD_LOCKS_DEC(curthread); 1044 } 1045 LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); 1046 1047 /* 1048 * The lock is held in exclusive mode. 1049 * If the lock is recursed also, then unrecurse it. 1050 */ 1051 if (lockmgr_xlocked_v(x) && lockmgr_recursed(lk)) { 1052 LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk); 1053 lk->lk_recurse--; 1054 goto out; 1055 } 1056 if (tid != LK_KERNPROC) 1057 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, 1058 LOCKSTAT_WRITER); 1059 1060 if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) 1061 goto out; 1062 1063 sleepq_lock(&lk->lock_object); 1064 x = lk->lk_lock; 1065 v = LK_UNLOCKED; 1066 1067 /* 1068 * If the lock has exclusive waiters, give them 1069 * preference in order to avoid deadlock with 1070 * shared runners up. 1071 * If interruptible sleeps left the exclusive queue 1072 * empty avoid a starvation for the threads sleeping 1073 * on the shared queue by giving them precedence 1074 * and cleaning up the exclusive waiters bit anyway. 1075 * Please note that lk_exslpfail count may be lying 1076 * about the real number of waiters with the 1077 * LK_SLEEPFAIL flag on because they may be used in 1078 * conjunction with interruptible sleeps so 1079 * lk_exslpfail might be considered an 'upper limit' 1080 * bound, including the edge cases. 1081 */ 1082 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1083 realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE); 1084 if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) { 1085 if (lk->lk_exslpfail < realexslp) { 1086 lk->lk_exslpfail = 0; 1087 queue = SQ_EXCLUSIVE_QUEUE; 1088 v |= (x & LK_SHARED_WAITERS); 1089 } else { 1090 lk->lk_exslpfail = 0; 1091 LOCK_LOG2(lk, 1092 "%s: %p has only LK_SLEEPFAIL sleepers", 1093 __func__, lk); 1094 LOCK_LOG2(lk, 1095 "%s: %p waking up threads on the exclusive queue", 1096 __func__, lk); 1097 wakeup_swapper = sleepq_broadcast(&lk->lock_object, 1098 SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); 1099 queue = SQ_SHARED_QUEUE; 1100 } 1101 } else { 1102 1103 /* 1104 * Exclusive waiters sleeping with LK_SLEEPFAIL 1105 * on and using interruptible sleeps/timeout 1106 * may have left spourious lk_exslpfail counts 1107 * on, so clean it up anyway. 1108 */ 1109 lk->lk_exslpfail = 0; 1110 queue = SQ_SHARED_QUEUE; 1111 } 1112 1113 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", 1114 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : 1115 "exclusive"); 1116 atomic_store_rel_ptr(&lk->lk_lock, v); 1117 wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue); 1118 sleepq_release(&lk->lock_object); 1119 1120 out: 1121 lockmgr_exit(flags, ilk, wakeup_swapper); 1122 return (0); 1123 } 1124 1125 int 1126 lockmgr_unlock_fast_path(struct lock *lk, u_int flags, struct lock_object *ilk) 1127 { 1128 struct lock_class *class; 1129 uintptr_t x, tid; 1130 const char *file; 1131 int line; 1132 1133 if (__predict_false(panicstr != NULL)) 1134 return (0); 1135 1136 file = __FILE__; 1137 line = __LINE__; 1138 1139 _lockmgr_assert(lk, KA_LOCKED, file, line); 1140 x = lk->lk_lock; 1141 if (__predict_true(x & LK_SHARE) != 0) { 1142 if (lockmgr_sunlock_try(lk, &x)) { 1143 lockmgr_note_shared_release(lk, file, line); 1144 } else { 1145 return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line)); 1146 } 1147 } else { 1148 tid = (uintptr_t)curthread; 1149 if (!lockmgr_recursed(lk) && 1150 atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) { 1151 lockmgr_note_exclusive_release(lk, file, line); 1152 } else { 1153 return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line)); 1154 } 1155 } 1156 if (__predict_false(flags & LK_INTERLOCK)) { 1157 class = LOCK_CLASS(ilk); 1158 class->lc_unlock(ilk); 1159 } 1160 return (0); 1161 } 1162 1163 int 1164 __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk, 1165 const char *wmesg, int pri, int timo, const char *file, int line) 1166 { 1167 GIANT_DECLARE; 1168 struct lockmgr_wait lwa; 1169 struct lock_class *class; 1170 const char *iwmesg; 1171 uintptr_t tid, v, x; 1172 u_int op, realexslp; 1173 int error, ipri, itimo, queue, wakeup_swapper; 1174 #ifdef LOCK_PROFILING 1175 uint64_t waittime = 0; 1176 int contested = 0; 1177 #endif 1178 1179 if (panicstr != NULL) 1180 return (0); 1181 1182 error = 0; 1183 tid = (uintptr_t)curthread; 1184 op = (flags & LK_TYPE_MASK); 1185 iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg; 1186 ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri; 1187 itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo; 1188 1189 lwa.iwmesg = iwmesg; 1190 lwa.ipri = ipri; 1191 lwa.itimo = itimo; 1192 1193 MPASS((flags & ~LK_TOTAL_MASK) == 0); 1194 KASSERT((op & (op - 1)) == 0, 1195 ("%s: Invalid requested operation @ %s:%d", __func__, file, line)); 1196 KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 || 1197 (op != LK_DOWNGRADE && op != LK_RELEASE), 1198 ("%s: Invalid flags in regard of the operation desired @ %s:%d", 1199 __func__, file, line)); 1200 KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL, 1201 ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d", 1202 __func__, file, line)); 1203 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 1204 ("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread, 1205 lk->lock_object.lo_name, file, line)); 1206 1207 class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL; 1208 1209 if (lk->lock_object.lo_flags & LK_NOSHARE) { 1210 switch (op) { 1211 case LK_SHARED: 1212 op = LK_EXCLUSIVE; 1213 break; 1214 case LK_UPGRADE: 1215 case LK_TRYUPGRADE: 1216 case LK_DOWNGRADE: 1217 _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, 1218 file, line); 1219 if (flags & LK_INTERLOCK) 1220 class->lc_unlock(ilk); 1221 return (0); 1222 } 1223 } 1224 1225 wakeup_swapper = 0; 1226 switch (op) { 1227 case LK_SHARED: 1228 return (lockmgr_slock_hard(lk, flags, ilk, file, line, &lwa)); 1229 break; 1230 case LK_UPGRADE: 1231 case LK_TRYUPGRADE: 1232 return (lockmgr_upgrade(lk, flags, ilk, file, line, &lwa)); 1233 break; 1234 case LK_EXCLUSIVE: 1235 return (lockmgr_xlock_hard(lk, flags, ilk, file, line, &lwa)); 1236 break; 1237 case LK_DOWNGRADE: 1238 _lockmgr_assert(lk, KA_XLOCKED, file, line); 1239 WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line); 1240 1241 /* 1242 * Panic if the lock is recursed. 1243 */ 1244 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) { 1245 if (flags & LK_INTERLOCK) 1246 class->lc_unlock(ilk); 1247 panic("%s: downgrade a recursed lockmgr %s @ %s:%d\n", 1248 __func__, iwmesg, file, line); 1249 } 1250 TD_SLOCKS_INC(curthread); 1251 1252 /* 1253 * In order to preserve waiters flags, just spin. 1254 */ 1255 for (;;) { 1256 x = lk->lk_lock; 1257 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1258 x &= LK_ALL_WAITERS; 1259 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, 1260 LK_SHARERS_LOCK(1) | x)) 1261 break; 1262 cpu_spinwait(); 1263 } 1264 LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line); 1265 LOCKSTAT_RECORD0(lockmgr__downgrade, lk); 1266 break; 1267 case LK_RELEASE: 1268 _lockmgr_assert(lk, KA_LOCKED, file, line); 1269 x = lk->lk_lock; 1270 1271 if (__predict_true(x & LK_SHARE) != 0) { 1272 return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line)); 1273 } else { 1274 return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line)); 1275 } 1276 break; 1277 case LK_DRAIN: 1278 if (LK_CAN_WITNESS(flags)) 1279 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 1280 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 1281 ilk : NULL); 1282 1283 /* 1284 * Trying to drain a lock we already own will result in a 1285 * deadlock. 1286 */ 1287 if (lockmgr_xlocked(lk)) { 1288 if (flags & LK_INTERLOCK) 1289 class->lc_unlock(ilk); 1290 panic("%s: draining %s with the lock held @ %s:%d\n", 1291 __func__, iwmesg, file, line); 1292 } 1293 1294 for (;;) { 1295 if (lk->lk_lock == LK_UNLOCKED && 1296 atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) 1297 break; 1298 1299 #ifdef HWPMC_HOOKS 1300 PMC_SOFT_CALL( , , lock, failed); 1301 #endif 1302 lock_profile_obtain_lock_failed(&lk->lock_object, 1303 &contested, &waittime); 1304 1305 /* 1306 * If the lock is expected to not sleep just give up 1307 * and return. 1308 */ 1309 if (LK_TRYOP(flags)) { 1310 LOCK_LOG2(lk, "%s: %p fails the try operation", 1311 __func__, lk); 1312 error = EBUSY; 1313 break; 1314 } 1315 1316 /* 1317 * Acquire the sleepqueue chain lock because we 1318 * probabilly will need to manipulate waiters flags. 1319 */ 1320 sleepq_lock(&lk->lock_object); 1321 x = lk->lk_lock; 1322 1323 /* 1324 * if the lock has been released while we spun on 1325 * the sleepqueue chain lock just try again. 1326 */ 1327 if (x == LK_UNLOCKED) { 1328 sleepq_release(&lk->lock_object); 1329 continue; 1330 } 1331 1332 v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); 1333 if ((x & ~v) == LK_UNLOCKED) { 1334 v = (x & ~LK_EXCLUSIVE_SPINNERS); 1335 1336 /* 1337 * If interruptible sleeps left the exclusive 1338 * queue empty avoid a starvation for the 1339 * threads sleeping on the shared queue by 1340 * giving them precedence and cleaning up the 1341 * exclusive waiters bit anyway. 1342 * Please note that lk_exslpfail count may be 1343 * lying about the real number of waiters with 1344 * the LK_SLEEPFAIL flag on because they may 1345 * be used in conjunction with interruptible 1346 * sleeps so lk_exslpfail might be considered 1347 * an 'upper limit' bound, including the edge 1348 * cases. 1349 */ 1350 if (v & LK_EXCLUSIVE_WAITERS) { 1351 queue = SQ_EXCLUSIVE_QUEUE; 1352 v &= ~LK_EXCLUSIVE_WAITERS; 1353 } else { 1354 1355 /* 1356 * Exclusive waiters sleeping with 1357 * LK_SLEEPFAIL on and using 1358 * interruptible sleeps/timeout may 1359 * have left spourious lk_exslpfail 1360 * counts on, so clean it up anyway. 1361 */ 1362 MPASS(v & LK_SHARED_WAITERS); 1363 lk->lk_exslpfail = 0; 1364 queue = SQ_SHARED_QUEUE; 1365 v &= ~LK_SHARED_WAITERS; 1366 } 1367 if (queue == SQ_EXCLUSIVE_QUEUE) { 1368 realexslp = 1369 sleepq_sleepcnt(&lk->lock_object, 1370 SQ_EXCLUSIVE_QUEUE); 1371 if (lk->lk_exslpfail >= realexslp) { 1372 lk->lk_exslpfail = 0; 1373 queue = SQ_SHARED_QUEUE; 1374 v &= ~LK_SHARED_WAITERS; 1375 if (realexslp != 0) { 1376 LOCK_LOG2(lk, 1377 "%s: %p has only LK_SLEEPFAIL sleepers", 1378 __func__, lk); 1379 LOCK_LOG2(lk, 1380 "%s: %p waking up threads on the exclusive queue", 1381 __func__, lk); 1382 wakeup_swapper = 1383 sleepq_broadcast( 1384 &lk->lock_object, 1385 SLEEPQ_LK, 0, 1386 SQ_EXCLUSIVE_QUEUE); 1387 } 1388 } else 1389 lk->lk_exslpfail = 0; 1390 } 1391 if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) { 1392 sleepq_release(&lk->lock_object); 1393 continue; 1394 } 1395 LOCK_LOG3(lk, 1396 "%s: %p waking up all threads on the %s queue", 1397 __func__, lk, queue == SQ_SHARED_QUEUE ? 1398 "shared" : "exclusive"); 1399 wakeup_swapper |= sleepq_broadcast( 1400 &lk->lock_object, SLEEPQ_LK, 0, queue); 1401 1402 /* 1403 * If shared waiters have been woken up we need 1404 * to wait for one of them to acquire the lock 1405 * before to set the exclusive waiters in 1406 * order to avoid a deadlock. 1407 */ 1408 if (queue == SQ_SHARED_QUEUE) { 1409 for (v = lk->lk_lock; 1410 (v & LK_SHARE) && !LK_SHARERS(v); 1411 v = lk->lk_lock) 1412 cpu_spinwait(); 1413 } 1414 } 1415 1416 /* 1417 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we 1418 * fail, loop back and retry. 1419 */ 1420 if ((x & LK_EXCLUSIVE_WAITERS) == 0) { 1421 if (!atomic_cmpset_ptr(&lk->lk_lock, x, 1422 x | LK_EXCLUSIVE_WAITERS)) { 1423 sleepq_release(&lk->lock_object); 1424 continue; 1425 } 1426 LOCK_LOG2(lk, "%s: %p set drain waiters flag", 1427 __func__, lk); 1428 } 1429 1430 /* 1431 * As far as we have been unable to acquire the 1432 * exclusive lock and the exclusive waiters flag 1433 * is set, we will sleep. 1434 */ 1435 if (flags & LK_INTERLOCK) { 1436 class->lc_unlock(ilk); 1437 flags &= ~LK_INTERLOCK; 1438 } 1439 GIANT_SAVE(); 1440 sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK, 1441 SQ_EXCLUSIVE_QUEUE); 1442 sleepq_wait(&lk->lock_object, ipri & PRIMASK); 1443 GIANT_RESTORE(); 1444 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 1445 __func__, lk); 1446 } 1447 1448 if (error == 0) { 1449 lock_profile_obtain_lock_success(&lk->lock_object, 1450 contested, waittime, file, line); 1451 LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0, 1452 lk->lk_recurse, file, line); 1453 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | 1454 LK_TRYWIT(flags), file, line); 1455 TD_LOCKS_INC(curthread); 1456 STACK_SAVE(lk); 1457 } 1458 break; 1459 default: 1460 if (flags & LK_INTERLOCK) 1461 class->lc_unlock(ilk); 1462 panic("%s: unknown lockmgr request 0x%x\n", __func__, op); 1463 } 1464 1465 if (flags & LK_INTERLOCK) 1466 class->lc_unlock(ilk); 1467 if (wakeup_swapper) 1468 kick_proc0(); 1469 1470 return (error); 1471 } 1472 1473 void 1474 _lockmgr_disown(struct lock *lk, const char *file, int line) 1475 { 1476 uintptr_t tid, x; 1477 1478 if (SCHEDULER_STOPPED()) 1479 return; 1480 1481 tid = (uintptr_t)curthread; 1482 _lockmgr_assert(lk, KA_XLOCKED, file, line); 1483 1484 /* 1485 * Panic if the lock is recursed. 1486 */ 1487 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) 1488 panic("%s: disown a recursed lockmgr @ %s:%d\n", 1489 __func__, file, line); 1490 1491 /* 1492 * If the owner is already LK_KERNPROC just skip the whole operation. 1493 */ 1494 if (LK_HOLDER(lk->lk_lock) != tid) 1495 return; 1496 lock_profile_release_lock(&lk->lock_object); 1497 LOCKSTAT_RECORD1(lockmgr__disown, lk, LOCKSTAT_WRITER); 1498 LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line); 1499 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); 1500 TD_LOCKS_DEC(curthread); 1501 STACK_SAVE(lk); 1502 1503 /* 1504 * In order to preserve waiters flags, just spin. 1505 */ 1506 for (;;) { 1507 x = lk->lk_lock; 1508 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1509 x &= LK_ALL_WAITERS; 1510 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, 1511 LK_KERNPROC | x)) 1512 return; 1513 cpu_spinwait(); 1514 } 1515 } 1516 1517 void 1518 lockmgr_printinfo(const struct lock *lk) 1519 { 1520 struct thread *td; 1521 uintptr_t x; 1522 1523 if (lk->lk_lock == LK_UNLOCKED) 1524 printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name); 1525 else if (lk->lk_lock & LK_SHARE) 1526 printf("lock type %s: SHARED (count %ju)\n", 1527 lk->lock_object.lo_name, 1528 (uintmax_t)LK_SHARERS(lk->lk_lock)); 1529 else { 1530 td = lockmgr_xholder(lk); 1531 if (td == (struct thread *)LK_KERNPROC) 1532 printf("lock type %s: EXCL by KERNPROC\n", 1533 lk->lock_object.lo_name); 1534 else 1535 printf("lock type %s: EXCL by thread %p " 1536 "(pid %d, %s, tid %d)\n", lk->lock_object.lo_name, 1537 td, td->td_proc->p_pid, td->td_proc->p_comm, 1538 td->td_tid); 1539 } 1540 1541 x = lk->lk_lock; 1542 if (x & LK_EXCLUSIVE_WAITERS) 1543 printf(" with exclusive waiters pending\n"); 1544 if (x & LK_SHARED_WAITERS) 1545 printf(" with shared waiters pending\n"); 1546 if (x & LK_EXCLUSIVE_SPINNERS) 1547 printf(" with exclusive spinners pending\n"); 1548 1549 STACK_PRINT(lk); 1550 } 1551 1552 int 1553 lockstatus(const struct lock *lk) 1554 { 1555 uintptr_t v, x; 1556 int ret; 1557 1558 ret = LK_SHARED; 1559 x = lk->lk_lock; 1560 v = LK_HOLDER(x); 1561 1562 if ((x & LK_SHARE) == 0) { 1563 if (v == (uintptr_t)curthread || v == LK_KERNPROC) 1564 ret = LK_EXCLUSIVE; 1565 else 1566 ret = LK_EXCLOTHER; 1567 } else if (x == LK_UNLOCKED) 1568 ret = 0; 1569 1570 return (ret); 1571 } 1572 1573 #ifdef INVARIANT_SUPPORT 1574 1575 FEATURE(invariant_support, 1576 "Support for modules compiled with INVARIANTS option"); 1577 1578 #ifndef INVARIANTS 1579 #undef _lockmgr_assert 1580 #endif 1581 1582 void 1583 _lockmgr_assert(const struct lock *lk, int what, const char *file, int line) 1584 { 1585 int slocked = 0; 1586 1587 if (panicstr != NULL) 1588 return; 1589 switch (what) { 1590 case KA_SLOCKED: 1591 case KA_SLOCKED | KA_NOTRECURSED: 1592 case KA_SLOCKED | KA_RECURSED: 1593 slocked = 1; 1594 case KA_LOCKED: 1595 case KA_LOCKED | KA_NOTRECURSED: 1596 case KA_LOCKED | KA_RECURSED: 1597 #ifdef WITNESS 1598 1599 /* 1600 * We cannot trust WITNESS if the lock is held in exclusive 1601 * mode and a call to lockmgr_disown() happened. 1602 * Workaround this skipping the check if the lock is held in 1603 * exclusive mode even for the KA_LOCKED case. 1604 */ 1605 if (slocked || (lk->lk_lock & LK_SHARE)) { 1606 witness_assert(&lk->lock_object, what, file, line); 1607 break; 1608 } 1609 #endif 1610 if (lk->lk_lock == LK_UNLOCKED || 1611 ((lk->lk_lock & LK_SHARE) == 0 && (slocked || 1612 (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))))) 1613 panic("Lock %s not %slocked @ %s:%d\n", 1614 lk->lock_object.lo_name, slocked ? "share" : "", 1615 file, line); 1616 1617 if ((lk->lk_lock & LK_SHARE) == 0) { 1618 if (lockmgr_recursed(lk)) { 1619 if (what & KA_NOTRECURSED) 1620 panic("Lock %s recursed @ %s:%d\n", 1621 lk->lock_object.lo_name, file, 1622 line); 1623 } else if (what & KA_RECURSED) 1624 panic("Lock %s not recursed @ %s:%d\n", 1625 lk->lock_object.lo_name, file, line); 1626 } 1627 break; 1628 case KA_XLOCKED: 1629 case KA_XLOCKED | KA_NOTRECURSED: 1630 case KA_XLOCKED | KA_RECURSED: 1631 if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)) 1632 panic("Lock %s not exclusively locked @ %s:%d\n", 1633 lk->lock_object.lo_name, file, line); 1634 if (lockmgr_recursed(lk)) { 1635 if (what & KA_NOTRECURSED) 1636 panic("Lock %s recursed @ %s:%d\n", 1637 lk->lock_object.lo_name, file, line); 1638 } else if (what & KA_RECURSED) 1639 panic("Lock %s not recursed @ %s:%d\n", 1640 lk->lock_object.lo_name, file, line); 1641 break; 1642 case KA_UNLOCKED: 1643 if (lockmgr_xlocked(lk) || lockmgr_disowned(lk)) 1644 panic("Lock %s exclusively locked @ %s:%d\n", 1645 lk->lock_object.lo_name, file, line); 1646 break; 1647 default: 1648 panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file, 1649 line); 1650 } 1651 } 1652 #endif 1653 1654 #ifdef DDB 1655 int 1656 lockmgr_chain(struct thread *td, struct thread **ownerp) 1657 { 1658 struct lock *lk; 1659 1660 lk = td->td_wchan; 1661 1662 if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr) 1663 return (0); 1664 db_printf("blocked on lockmgr %s", lk->lock_object.lo_name); 1665 if (lk->lk_lock & LK_SHARE) 1666 db_printf("SHARED (count %ju)\n", 1667 (uintmax_t)LK_SHARERS(lk->lk_lock)); 1668 else 1669 db_printf("EXCL\n"); 1670 *ownerp = lockmgr_xholder(lk); 1671 1672 return (1); 1673 } 1674 1675 static void 1676 db_show_lockmgr(const struct lock_object *lock) 1677 { 1678 struct thread *td; 1679 const struct lock *lk; 1680 1681 lk = (const struct lock *)lock; 1682 1683 db_printf(" state: "); 1684 if (lk->lk_lock == LK_UNLOCKED) 1685 db_printf("UNLOCKED\n"); 1686 else if (lk->lk_lock & LK_SHARE) 1687 db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock)); 1688 else { 1689 td = lockmgr_xholder(lk); 1690 if (td == (struct thread *)LK_KERNPROC) 1691 db_printf("XLOCK: LK_KERNPROC\n"); 1692 else 1693 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1694 td->td_tid, td->td_proc->p_pid, 1695 td->td_proc->p_comm); 1696 if (lockmgr_recursed(lk)) 1697 db_printf(" recursed: %d\n", lk->lk_recurse); 1698 } 1699 db_printf(" waiters: "); 1700 switch (lk->lk_lock & LK_ALL_WAITERS) { 1701 case LK_SHARED_WAITERS: 1702 db_printf("shared\n"); 1703 break; 1704 case LK_EXCLUSIVE_WAITERS: 1705 db_printf("exclusive\n"); 1706 break; 1707 case LK_ALL_WAITERS: 1708 db_printf("shared and exclusive\n"); 1709 break; 1710 default: 1711 db_printf("none\n"); 1712 } 1713 db_printf(" spinners: "); 1714 if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS) 1715 db_printf("exclusive\n"); 1716 else 1717 db_printf("none\n"); 1718 } 1719 #endif
Cache object: 53f7dcb08f7cd00875ad87b88556d5b7
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