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_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_UNLOCKED == (LK_UNLOCKED & 65 ~(LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS))); 66 67 #define SQ_EXCLUSIVE_QUEUE 0 68 #define SQ_SHARED_QUEUE 1 69 70 #ifndef INVARIANTS 71 #define _lockmgr_assert(lk, what, file, line) 72 #endif 73 74 #define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++) 75 #define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--) 76 77 #ifndef DEBUG_LOCKS 78 #define STACK_PRINT(lk) 79 #define STACK_SAVE(lk) 80 #define STACK_ZERO(lk) 81 #else 82 #define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack) 83 #define STACK_SAVE(lk) stack_save(&(lk)->lk_stack) 84 #define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack) 85 #endif 86 87 #define LOCK_LOG2(lk, string, arg1, arg2) \ 88 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ 89 CTR2(KTR_LOCK, (string), (arg1), (arg2)) 90 #define LOCK_LOG3(lk, string, arg1, arg2, arg3) \ 91 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \ 92 CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3)) 93 94 #define GIANT_DECLARE \ 95 int _i = 0; \ 96 WITNESS_SAVE_DECL(Giant) 97 #define GIANT_RESTORE() do { \ 98 if (__predict_false(_i > 0)) { \ 99 while (_i--) \ 100 mtx_lock(&Giant); \ 101 WITNESS_RESTORE(&Giant.lock_object, Giant); \ 102 } \ 103 } while (0) 104 #define GIANT_SAVE() do { \ 105 if (__predict_false(mtx_owned(&Giant))) { \ 106 WITNESS_SAVE(&Giant.lock_object, Giant); \ 107 while (mtx_owned(&Giant)) { \ 108 _i++; \ 109 mtx_unlock(&Giant); \ 110 } \ 111 } \ 112 } while (0) 113 114 static bool __always_inline 115 LK_CAN_SHARE(uintptr_t x, int flags, bool fp) 116 { 117 118 if ((x & (LK_SHARE | LK_EXCLUSIVE_WAITERS | LK_EXCLUSIVE_SPINNERS)) == 119 LK_SHARE) 120 return (true); 121 if (fp || (!(x & LK_SHARE))) 122 return (false); 123 if ((curthread->td_lk_slocks != 0 && !(flags & LK_NODDLKTREAT)) || 124 (curthread->td_pflags & TDP_DEADLKTREAT)) 125 return (true); 126 return (false); 127 } 128 129 #define LK_TRYOP(x) \ 130 ((x) & LK_NOWAIT) 131 132 #define LK_CAN_WITNESS(x) \ 133 (((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x)) 134 #define LK_TRYWIT(x) \ 135 (LK_TRYOP(x) ? LOP_TRYLOCK : 0) 136 137 #define lockmgr_disowned(lk) \ 138 (((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC) 139 140 #define lockmgr_xlocked_v(v) \ 141 (((v) & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread) 142 143 #define lockmgr_xlocked(lk) lockmgr_xlocked_v(lockmgr_read_value(lk)) 144 145 static void assert_lockmgr(const struct lock_object *lock, int how); 146 #ifdef DDB 147 static void db_show_lockmgr(const struct lock_object *lock); 148 #endif 149 static void lock_lockmgr(struct lock_object *lock, uintptr_t how); 150 #ifdef KDTRACE_HOOKS 151 static int owner_lockmgr(const struct lock_object *lock, 152 struct thread **owner); 153 #endif 154 static uintptr_t unlock_lockmgr(struct lock_object *lock); 155 156 struct lock_class lock_class_lockmgr = { 157 .lc_name = "lockmgr", 158 .lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE, 159 .lc_assert = assert_lockmgr, 160 #ifdef DDB 161 .lc_ddb_show = db_show_lockmgr, 162 #endif 163 .lc_lock = lock_lockmgr, 164 .lc_unlock = unlock_lockmgr, 165 #ifdef KDTRACE_HOOKS 166 .lc_owner = owner_lockmgr, 167 #endif 168 }; 169 170 static __read_mostly bool lk_adaptive = true; 171 static SYSCTL_NODE(_debug, OID_AUTO, lockmgr, CTLFLAG_RD, NULL, "lockmgr debugging"); 172 SYSCTL_BOOL(_debug_lockmgr, OID_AUTO, adaptive_spinning, CTLFLAG_RW, &lk_adaptive, 173 0, ""); 174 #define lockmgr_delay locks_delay 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 WITNESS_UNLOCK(&lk->lock_object, 0, file, line); 219 LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line); 220 TD_LOCKS_DEC(curthread); 221 TD_SLOCKS_DEC(curthread); 222 } 223 224 static void 225 lockmgr_note_exclusive_acquire(struct lock *lk, int contested, 226 uint64_t waittime, const char *file, int line, int flags) 227 { 228 229 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested, 230 waittime, file, line, LOCKSTAT_WRITER); 231 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line); 232 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file, 233 line); 234 TD_LOCKS_INC(curthread); 235 STACK_SAVE(lk); 236 } 237 238 static void 239 lockmgr_note_exclusive_release(struct lock *lk, const char *file, int line) 240 { 241 242 if (LK_HOLDER(lockmgr_read_value(lk)) != LK_KERNPROC) { 243 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); 244 TD_LOCKS_DEC(curthread); 245 } 246 LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file, 247 line); 248 } 249 250 static __inline struct thread * 251 lockmgr_xholder(const struct lock *lk) 252 { 253 uintptr_t x; 254 255 x = lockmgr_read_value(lk); 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 = lockmgr_read_value(lk); 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 = lockmgr_read_value(lk); 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 * Exclusive waiters sleeping with LK_SLEEPFAIL on 369 * and using interruptible sleeps/timeout may have 370 * left spourious lk_exslpfail counts on, so clean 371 * it up anyway. 372 */ 373 lk->lk_exslpfail = 0; 374 queue = SQ_SHARED_QUEUE; 375 } 376 377 if (lockmgr_sunlock_try(lk, &orig_x)) { 378 sleepq_release(&lk->lock_object); 379 break; 380 } 381 382 x |= LK_SHARERS_LOCK(1); 383 if (!atomic_fcmpset_rel_ptr(&lk->lk_lock, &x, v)) { 384 orig_x = x; 385 goto retry_sleepq; 386 } 387 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", 388 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : 389 "exclusive"); 390 wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 391 0, queue); 392 sleepq_release(&lk->lock_object); 393 break; 394 } 395 396 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER); 397 return (wakeup_swapper); 398 } 399 400 static void 401 assert_lockmgr(const struct lock_object *lock, int what) 402 { 403 404 panic("lockmgr locks do not support assertions"); 405 } 406 407 static void 408 lock_lockmgr(struct lock_object *lock, uintptr_t how) 409 { 410 411 panic("lockmgr locks do not support sleep interlocking"); 412 } 413 414 static uintptr_t 415 unlock_lockmgr(struct lock_object *lock) 416 { 417 418 panic("lockmgr locks do not support sleep interlocking"); 419 } 420 421 #ifdef KDTRACE_HOOKS 422 static int 423 owner_lockmgr(const struct lock_object *lock, struct thread **owner) 424 { 425 426 panic("lockmgr locks do not support owner inquiring"); 427 } 428 #endif 429 430 void 431 lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags) 432 { 433 int iflags; 434 435 MPASS((flags & ~LK_INIT_MASK) == 0); 436 ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock, 437 ("%s: lockmgr not aligned for %s: %p", __func__, wmesg, 438 &lk->lk_lock)); 439 440 iflags = LO_SLEEPABLE | LO_UPGRADABLE; 441 if (flags & LK_CANRECURSE) 442 iflags |= LO_RECURSABLE; 443 if ((flags & LK_NODUP) == 0) 444 iflags |= LO_DUPOK; 445 if (flags & LK_NOPROFILE) 446 iflags |= LO_NOPROFILE; 447 if ((flags & LK_NOWITNESS) == 0) 448 iflags |= LO_WITNESS; 449 if (flags & LK_QUIET) 450 iflags |= LO_QUIET; 451 if (flags & LK_IS_VNODE) 452 iflags |= LO_IS_VNODE; 453 if (flags & LK_NEW) 454 iflags |= LO_NEW; 455 iflags |= flags & LK_NOSHARE; 456 457 lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags); 458 lk->lk_lock = LK_UNLOCKED; 459 lk->lk_recurse = 0; 460 lk->lk_exslpfail = 0; 461 lk->lk_timo = timo; 462 lk->lk_pri = pri; 463 STACK_ZERO(lk); 464 } 465 466 /* 467 * XXX: Gross hacks to manipulate external lock flags after 468 * initialization. Used for certain vnode and buf locks. 469 */ 470 void 471 lockallowshare(struct lock *lk) 472 { 473 474 lockmgr_assert(lk, KA_XLOCKED); 475 lk->lock_object.lo_flags &= ~LK_NOSHARE; 476 } 477 478 void 479 lockdisableshare(struct lock *lk) 480 { 481 482 lockmgr_assert(lk, KA_XLOCKED); 483 lk->lock_object.lo_flags |= LK_NOSHARE; 484 } 485 486 void 487 lockallowrecurse(struct lock *lk) 488 { 489 490 lockmgr_assert(lk, KA_XLOCKED); 491 lk->lock_object.lo_flags |= LO_RECURSABLE; 492 } 493 494 void 495 lockdisablerecurse(struct lock *lk) 496 { 497 498 lockmgr_assert(lk, KA_XLOCKED); 499 lk->lock_object.lo_flags &= ~LO_RECURSABLE; 500 } 501 502 void 503 lockdestroy(struct lock *lk) 504 { 505 506 KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held")); 507 KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed")); 508 KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters")); 509 lock_destroy(&lk->lock_object); 510 } 511 512 static bool __always_inline 513 lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp) 514 { 515 516 /* 517 * If no other thread has an exclusive lock, or 518 * no exclusive waiter is present, bump the count of 519 * sharers. Since we have to preserve the state of 520 * waiters, if we fail to acquire the shared lock 521 * loop back and retry. 522 */ 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 bool 549 lockmgr_slock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp, 550 int flags) 551 { 552 struct thread *owner; 553 uintptr_t x; 554 555 x = *xp; 556 MPASS(x != LK_UNLOCKED); 557 owner = (struct thread *)LK_HOLDER(x); 558 for (;;) { 559 MPASS(owner != curthread); 560 if (owner == (struct thread *)LK_KERNPROC) 561 return (false); 562 if ((x & LK_SHARE) && LK_SHARERS(x) > 0) 563 return (false); 564 if (owner == NULL) 565 return (false); 566 if (!TD_IS_RUNNING(owner)) 567 return (false); 568 if ((x & LK_ALL_WAITERS) != 0) 569 return (false); 570 lock_delay(lda); 571 x = lockmgr_read_value(lk); 572 if (LK_CAN_SHARE(x, flags, false)) { 573 *xp = x; 574 return (true); 575 } 576 owner = (struct thread *)LK_HOLDER(x); 577 } 578 } 579 580 static __noinline int 581 lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk, 582 const char *file, int line, struct lockmgr_wait *lwa) 583 { 584 uintptr_t tid, x; 585 int error = 0; 586 const char *iwmesg; 587 int ipri, itimo; 588 589 #ifdef KDTRACE_HOOKS 590 uint64_t sleep_time = 0; 591 #endif 592 #ifdef LOCK_PROFILING 593 uint64_t waittime = 0; 594 int contested = 0; 595 #endif 596 struct lock_delay_arg lda; 597 598 if (KERNEL_PANICKED()) 599 goto out; 600 601 tid = (uintptr_t)curthread; 602 603 if (LK_CAN_WITNESS(flags)) 604 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, 605 file, line, flags & LK_INTERLOCK ? ilk : NULL); 606 x = lockmgr_read_value(lk); 607 lock_delay_arg_init(&lda, &lockmgr_delay); 608 if (!lk_adaptive) 609 flags &= ~LK_ADAPTIVE; 610 /* 611 * The lock may already be locked exclusive by curthread, 612 * avoid deadlock. 613 */ 614 if (LK_HOLDER(x) == tid) { 615 LOCK_LOG2(lk, 616 "%s: %p already held in exclusive mode", 617 __func__, lk); 618 error = EDEADLK; 619 goto out; 620 } 621 622 for (;;) { 623 if (lockmgr_slock_try(lk, &x, flags, false)) 624 break; 625 626 lock_profile_obtain_lock_failed(&lk->lock_object, false, 627 &contested, &waittime); 628 629 if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) { 630 if (lockmgr_slock_adaptive(&lda, lk, &x, flags)) 631 continue; 632 } 633 634 #ifdef HWPMC_HOOKS 635 PMC_SOFT_CALL( , , lock, failed); 636 #endif 637 638 /* 639 * If the lock is expected to not sleep just give up 640 * and return. 641 */ 642 if (LK_TRYOP(flags)) { 643 LOCK_LOG2(lk, "%s: %p fails the try operation", 644 __func__, lk); 645 error = EBUSY; 646 break; 647 } 648 649 /* 650 * Acquire the sleepqueue chain lock because we 651 * probabilly will need to manipulate waiters flags. 652 */ 653 sleepq_lock(&lk->lock_object); 654 x = lockmgr_read_value(lk); 655 retry_sleepq: 656 657 /* 658 * if the lock can be acquired in shared mode, try 659 * again. 660 */ 661 if (LK_CAN_SHARE(x, flags, false)) { 662 sleepq_release(&lk->lock_object); 663 continue; 664 } 665 666 /* 667 * Try to set the LK_SHARED_WAITERS flag. If we fail, 668 * loop back and retry. 669 */ 670 if ((x & LK_SHARED_WAITERS) == 0) { 671 if (!atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, 672 x | LK_SHARED_WAITERS)) { 673 goto retry_sleepq; 674 } 675 LOCK_LOG2(lk, "%s: %p set shared waiters flag", 676 __func__, lk); 677 } 678 679 if (lwa == NULL) { 680 iwmesg = lk->lock_object.lo_name; 681 ipri = lk->lk_pri; 682 itimo = lk->lk_timo; 683 } else { 684 iwmesg = lwa->iwmesg; 685 ipri = lwa->ipri; 686 itimo = lwa->itimo; 687 } 688 689 /* 690 * As far as we have been unable to acquire the 691 * shared lock and the shared waiters flag is set, 692 * we will sleep. 693 */ 694 #ifdef KDTRACE_HOOKS 695 sleep_time -= lockstat_nsecs(&lk->lock_object); 696 #endif 697 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, 698 SQ_SHARED_QUEUE); 699 #ifdef KDTRACE_HOOKS 700 sleep_time += lockstat_nsecs(&lk->lock_object); 701 #endif 702 flags &= ~LK_INTERLOCK; 703 if (error) { 704 LOCK_LOG3(lk, 705 "%s: interrupted sleep for %p with %d", 706 __func__, lk, error); 707 break; 708 } 709 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 710 __func__, lk); 711 x = lockmgr_read_value(lk); 712 } 713 if (error == 0) { 714 #ifdef KDTRACE_HOOKS 715 if (sleep_time != 0) 716 LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time, 717 LOCKSTAT_READER, (x & LK_SHARE) == 0, 718 (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x)); 719 #endif 720 #ifdef LOCK_PROFILING 721 lockmgr_note_shared_acquire(lk, contested, waittime, 722 file, line, flags); 723 #else 724 lockmgr_note_shared_acquire(lk, 0, 0, file, line, 725 flags); 726 #endif 727 } 728 729 out: 730 lockmgr_exit(flags, ilk, 0); 731 return (error); 732 } 733 734 static bool 735 lockmgr_xlock_adaptive(struct lock_delay_arg *lda, struct lock *lk, uintptr_t *xp) 736 { 737 struct thread *owner; 738 uintptr_t x; 739 740 x = *xp; 741 MPASS(x != LK_UNLOCKED); 742 owner = (struct thread *)LK_HOLDER(x); 743 for (;;) { 744 MPASS(owner != curthread); 745 if (owner == NULL) 746 return (false); 747 if ((x & LK_SHARE) && LK_SHARERS(x) > 0) 748 return (false); 749 if (owner == (struct thread *)LK_KERNPROC) 750 return (false); 751 if (!TD_IS_RUNNING(owner)) 752 return (false); 753 if ((x & LK_ALL_WAITERS) != 0) 754 return (false); 755 lock_delay(lda); 756 x = lockmgr_read_value(lk); 757 if (x == LK_UNLOCKED) { 758 *xp = x; 759 return (true); 760 } 761 owner = (struct thread *)LK_HOLDER(x); 762 } 763 } 764 765 static __noinline int 766 lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk, 767 const char *file, int line, struct lockmgr_wait *lwa) 768 { 769 struct lock_class *class; 770 uintptr_t tid, x, v; 771 int error = 0; 772 const char *iwmesg; 773 int ipri, itimo; 774 775 #ifdef KDTRACE_HOOKS 776 uint64_t sleep_time = 0; 777 #endif 778 #ifdef LOCK_PROFILING 779 uint64_t waittime = 0; 780 int contested = 0; 781 #endif 782 struct lock_delay_arg lda; 783 784 if (KERNEL_PANICKED()) 785 goto out; 786 787 tid = (uintptr_t)curthread; 788 789 if (LK_CAN_WITNESS(flags)) 790 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 791 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 792 ilk : NULL); 793 794 /* 795 * If curthread already holds the lock and this one is 796 * allowed to recurse, simply recurse on it. 797 */ 798 if (lockmgr_xlocked(lk)) { 799 if ((flags & LK_CANRECURSE) == 0 && 800 (lk->lock_object.lo_flags & LO_RECURSABLE) == 0) { 801 /* 802 * If the lock is expected to not panic just 803 * give up and return. 804 */ 805 if (LK_TRYOP(flags)) { 806 LOCK_LOG2(lk, 807 "%s: %p fails the try operation", 808 __func__, lk); 809 error = EBUSY; 810 goto out; 811 } 812 if (flags & LK_INTERLOCK) { 813 class = LOCK_CLASS(ilk); 814 class->lc_unlock(ilk); 815 } 816 STACK_PRINT(lk); 817 panic("%s: recursing on non recursive lockmgr %p " 818 "@ %s:%d\n", __func__, lk, file, line); 819 } 820 atomic_set_ptr(&lk->lk_lock, LK_WRITER_RECURSED); 821 lk->lk_recurse++; 822 LOCK_LOG2(lk, "%s: %p recursing", __func__, lk); 823 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, 824 lk->lk_recurse, file, line); 825 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | 826 LK_TRYWIT(flags), file, line); 827 TD_LOCKS_INC(curthread); 828 goto out; 829 } 830 831 x = LK_UNLOCKED; 832 lock_delay_arg_init(&lda, &lockmgr_delay); 833 if (!lk_adaptive) 834 flags &= ~LK_ADAPTIVE; 835 for (;;) { 836 if (x == LK_UNLOCKED) { 837 if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, tid)) 838 break; 839 continue; 840 } 841 842 lock_profile_obtain_lock_failed(&lk->lock_object, false, 843 &contested, &waittime); 844 845 if ((flags & (LK_ADAPTIVE | LK_INTERLOCK)) == LK_ADAPTIVE) { 846 if (lockmgr_xlock_adaptive(&lda, lk, &x)) 847 continue; 848 } 849 #ifdef HWPMC_HOOKS 850 PMC_SOFT_CALL( , , lock, failed); 851 #endif 852 853 /* 854 * If the lock is expected to not sleep just give up 855 * and return. 856 */ 857 if (LK_TRYOP(flags)) { 858 LOCK_LOG2(lk, "%s: %p fails the try operation", 859 __func__, lk); 860 error = EBUSY; 861 break; 862 } 863 864 /* 865 * Acquire the sleepqueue chain lock because we 866 * probabilly will need to manipulate waiters flags. 867 */ 868 sleepq_lock(&lk->lock_object); 869 x = lockmgr_read_value(lk); 870 retry_sleepq: 871 872 /* 873 * if the lock has been released while we spun on 874 * the sleepqueue chain lock just try again. 875 */ 876 if (x == LK_UNLOCKED) { 877 sleepq_release(&lk->lock_object); 878 continue; 879 } 880 881 /* 882 * The lock can be in the state where there is a 883 * pending queue of waiters, but still no owner. 884 * This happens when the lock is contested and an 885 * owner is going to claim the lock. 886 * If curthread is the one successfully acquiring it 887 * claim lock ownership and return, preserving waiters 888 * flags. 889 */ 890 v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); 891 if ((x & ~v) == LK_UNLOCKED) { 892 v &= ~LK_EXCLUSIVE_SPINNERS; 893 if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x, 894 tid | v)) { 895 sleepq_release(&lk->lock_object); 896 LOCK_LOG2(lk, 897 "%s: %p claimed by a new writer", 898 __func__, lk); 899 break; 900 } 901 goto retry_sleepq; 902 } 903 904 /* 905 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we 906 * fail, loop back and retry. 907 */ 908 if ((x & LK_EXCLUSIVE_WAITERS) == 0) { 909 if (!atomic_fcmpset_ptr(&lk->lk_lock, &x, 910 x | LK_EXCLUSIVE_WAITERS)) { 911 goto retry_sleepq; 912 } 913 LOCK_LOG2(lk, "%s: %p set excl waiters flag", 914 __func__, lk); 915 } 916 917 if (lwa == NULL) { 918 iwmesg = lk->lock_object.lo_name; 919 ipri = lk->lk_pri; 920 itimo = lk->lk_timo; 921 } else { 922 iwmesg = lwa->iwmesg; 923 ipri = lwa->ipri; 924 itimo = lwa->itimo; 925 } 926 927 /* 928 * As far as we have been unable to acquire the 929 * exclusive lock and the exclusive waiters flag 930 * is set, we will sleep. 931 */ 932 #ifdef KDTRACE_HOOKS 933 sleep_time -= lockstat_nsecs(&lk->lock_object); 934 #endif 935 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo, 936 SQ_EXCLUSIVE_QUEUE); 937 #ifdef KDTRACE_HOOKS 938 sleep_time += lockstat_nsecs(&lk->lock_object); 939 #endif 940 flags &= ~LK_INTERLOCK; 941 if (error) { 942 LOCK_LOG3(lk, 943 "%s: interrupted sleep for %p with %d", 944 __func__, lk, error); 945 break; 946 } 947 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 948 __func__, lk); 949 x = lockmgr_read_value(lk); 950 } 951 if (error == 0) { 952 #ifdef KDTRACE_HOOKS 953 if (sleep_time != 0) 954 LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time, 955 LOCKSTAT_WRITER, (x & LK_SHARE) == 0, 956 (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x)); 957 #endif 958 #ifdef LOCK_PROFILING 959 lockmgr_note_exclusive_acquire(lk, contested, waittime, 960 file, line, flags); 961 #else 962 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line, 963 flags); 964 #endif 965 } 966 967 out: 968 lockmgr_exit(flags, ilk, 0); 969 return (error); 970 } 971 972 static __noinline int 973 lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk, 974 const char *file, int line, struct lockmgr_wait *lwa) 975 { 976 uintptr_t tid, v, setv; 977 int error = 0; 978 int op; 979 980 if (KERNEL_PANICKED()) 981 goto out; 982 983 tid = (uintptr_t)curthread; 984 985 _lockmgr_assert(lk, KA_SLOCKED, file, line); 986 987 op = flags & LK_TYPE_MASK; 988 v = lockmgr_read_value(lk); 989 for (;;) { 990 if (LK_SHARERS(v) > 1) { 991 if (op == LK_TRYUPGRADE) { 992 LOCK_LOG2(lk, "%s: %p failed the nowait upgrade", 993 __func__, lk); 994 error = EBUSY; 995 goto out; 996 } 997 if (atomic_fcmpset_rel_ptr(&lk->lk_lock, &v, 998 v - LK_ONE_SHARER)) { 999 lockmgr_note_shared_release(lk, file, line); 1000 goto out_xlock; 1001 } 1002 continue; 1003 } 1004 MPASS((v & ~LK_ALL_WAITERS) == LK_SHARERS_LOCK(1)); 1005 1006 setv = tid; 1007 setv |= (v & LK_ALL_WAITERS); 1008 1009 /* 1010 * Try to switch from one shared lock to an exclusive one. 1011 * We need to preserve waiters flags during the operation. 1012 */ 1013 if (atomic_fcmpset_ptr(&lk->lk_lock, &v, setv)) { 1014 LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file, 1015 line); 1016 WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE | 1017 LK_TRYWIT(flags), file, line); 1018 LOCKSTAT_RECORD0(lockmgr__upgrade, lk); 1019 TD_SLOCKS_DEC(curthread); 1020 goto out; 1021 } 1022 } 1023 1024 out_xlock: 1025 error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa); 1026 flags &= ~LK_INTERLOCK; 1027 out: 1028 lockmgr_exit(flags, ilk, 0); 1029 return (error); 1030 } 1031 1032 int 1033 lockmgr_lock_flags(struct lock *lk, u_int flags, struct lock_object *ilk, 1034 const char *file, int line) 1035 { 1036 struct lock_class *class; 1037 uintptr_t x, tid; 1038 u_int op; 1039 bool locked; 1040 1041 if (KERNEL_PANICKED()) 1042 return (0); 1043 1044 op = flags & LK_TYPE_MASK; 1045 locked = false; 1046 switch (op) { 1047 case LK_SHARED: 1048 if (LK_CAN_WITNESS(flags)) 1049 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, 1050 file, line, flags & LK_INTERLOCK ? ilk : NULL); 1051 if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE)) 1052 break; 1053 x = lockmgr_read_value(lk); 1054 if (lockmgr_slock_try(lk, &x, flags, true)) { 1055 lockmgr_note_shared_acquire(lk, 0, 0, 1056 file, line, flags); 1057 locked = true; 1058 } else { 1059 return (lockmgr_slock_hard(lk, flags, ilk, file, line, 1060 NULL)); 1061 } 1062 break; 1063 case LK_EXCLUSIVE: 1064 if (LK_CAN_WITNESS(flags)) 1065 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 1066 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 1067 ilk : NULL); 1068 tid = (uintptr_t)curthread; 1069 if (lockmgr_read_value(lk) == LK_UNLOCKED && 1070 atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) { 1071 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line, 1072 flags); 1073 locked = true; 1074 } else { 1075 return (lockmgr_xlock_hard(lk, flags, ilk, file, line, 1076 NULL)); 1077 } 1078 break; 1079 case LK_UPGRADE: 1080 case LK_TRYUPGRADE: 1081 return (lockmgr_upgrade(lk, flags, ilk, file, line, NULL)); 1082 default: 1083 break; 1084 } 1085 if (__predict_true(locked)) { 1086 if (__predict_false(flags & LK_INTERLOCK)) { 1087 class = LOCK_CLASS(ilk); 1088 class->lc_unlock(ilk); 1089 } 1090 return (0); 1091 } else { 1092 return (__lockmgr_args(lk, flags, ilk, LK_WMESG_DEFAULT, 1093 LK_PRIO_DEFAULT, LK_TIMO_DEFAULT, file, line)); 1094 } 1095 } 1096 1097 static __noinline int 1098 lockmgr_sunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk, 1099 const char *file, int line) 1100 1101 { 1102 int wakeup_swapper = 0; 1103 1104 if (KERNEL_PANICKED()) 1105 goto out; 1106 1107 wakeup_swapper = wakeupshlk(lk, file, line); 1108 1109 out: 1110 lockmgr_exit(flags, ilk, wakeup_swapper); 1111 return (0); 1112 } 1113 1114 static __noinline int 1115 lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk, 1116 const char *file, int line) 1117 { 1118 uintptr_t tid, v; 1119 int wakeup_swapper = 0; 1120 u_int realexslp; 1121 int queue; 1122 1123 if (KERNEL_PANICKED()) 1124 goto out; 1125 1126 tid = (uintptr_t)curthread; 1127 1128 /* 1129 * As first option, treact the lock as if it has not 1130 * any waiter. 1131 * Fix-up the tid var if the lock has been disowned. 1132 */ 1133 if (LK_HOLDER(x) == LK_KERNPROC) 1134 tid = LK_KERNPROC; 1135 1136 /* 1137 * The lock is held in exclusive mode. 1138 * If the lock is recursed also, then unrecurse it. 1139 */ 1140 if (lockmgr_recursed_v(x)) { 1141 LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk); 1142 lk->lk_recurse--; 1143 if (lk->lk_recurse == 0) 1144 atomic_clear_ptr(&lk->lk_lock, LK_WRITER_RECURSED); 1145 goto out; 1146 } 1147 if (tid != LK_KERNPROC) 1148 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, 1149 LOCKSTAT_WRITER); 1150 1151 if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) 1152 goto out; 1153 1154 sleepq_lock(&lk->lock_object); 1155 x = lockmgr_read_value(lk); 1156 v = LK_UNLOCKED; 1157 1158 /* 1159 * If the lock has exclusive waiters, give them 1160 * preference in order to avoid deadlock with 1161 * shared runners up. 1162 * If interruptible sleeps left the exclusive queue 1163 * empty avoid a starvation for the threads sleeping 1164 * on the shared queue by giving them precedence 1165 * and cleaning up the exclusive waiters bit anyway. 1166 * Please note that lk_exslpfail count may be lying 1167 * about the real number of waiters with the 1168 * LK_SLEEPFAIL flag on because they may be used in 1169 * conjunction with interruptible sleeps so 1170 * lk_exslpfail might be considered an 'upper limit' 1171 * bound, including the edge cases. 1172 */ 1173 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1174 realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE); 1175 if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) { 1176 if (lk->lk_exslpfail < realexslp) { 1177 lk->lk_exslpfail = 0; 1178 queue = SQ_EXCLUSIVE_QUEUE; 1179 v |= (x & LK_SHARED_WAITERS); 1180 } else { 1181 lk->lk_exslpfail = 0; 1182 LOCK_LOG2(lk, 1183 "%s: %p has only LK_SLEEPFAIL sleepers", 1184 __func__, lk); 1185 LOCK_LOG2(lk, 1186 "%s: %p waking up threads on the exclusive queue", 1187 __func__, lk); 1188 wakeup_swapper = sleepq_broadcast(&lk->lock_object, 1189 SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE); 1190 queue = SQ_SHARED_QUEUE; 1191 } 1192 } else { 1193 /* 1194 * Exclusive waiters sleeping with LK_SLEEPFAIL 1195 * on and using interruptible sleeps/timeout 1196 * may have left spourious lk_exslpfail counts 1197 * on, so clean it up anyway. 1198 */ 1199 lk->lk_exslpfail = 0; 1200 queue = SQ_SHARED_QUEUE; 1201 } 1202 1203 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue", 1204 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" : 1205 "exclusive"); 1206 atomic_store_rel_ptr(&lk->lk_lock, v); 1207 wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue); 1208 sleepq_release(&lk->lock_object); 1209 1210 out: 1211 lockmgr_exit(flags, ilk, wakeup_swapper); 1212 return (0); 1213 } 1214 1215 /* 1216 * Lightweight entry points for common operations. 1217 * 1218 * Functionality is similar to sx locks, in that none of the additional lockmgr 1219 * features are supported. To be clear, these are NOT supported: 1220 * 1. shared locking disablement 1221 * 2. returning with an error after sleep 1222 * 3. unlocking the interlock 1223 * 1224 * If in doubt, use lockmgr_lock_flags. 1225 */ 1226 int 1227 lockmgr_slock(struct lock *lk, u_int flags, const char *file, int line) 1228 { 1229 uintptr_t x; 1230 1231 MPASS((flags & LK_TYPE_MASK) == LK_SHARED); 1232 MPASS((flags & LK_INTERLOCK) == 0); 1233 MPASS((lk->lock_object.lo_flags & LK_NOSHARE) == 0); 1234 1235 if (LK_CAN_WITNESS(flags)) 1236 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER, 1237 file, line, NULL); 1238 x = lockmgr_read_value(lk); 1239 if (__predict_true(lockmgr_slock_try(lk, &x, flags, true))) { 1240 lockmgr_note_shared_acquire(lk, 0, 0, file, line, flags); 1241 return (0); 1242 } 1243 1244 return (lockmgr_slock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL)); 1245 } 1246 1247 int 1248 lockmgr_xlock(struct lock *lk, u_int flags, const char *file, int line) 1249 { 1250 uintptr_t tid; 1251 1252 MPASS((flags & LK_TYPE_MASK) == LK_EXCLUSIVE); 1253 MPASS((flags & LK_INTERLOCK) == 0); 1254 1255 if (LK_CAN_WITNESS(flags)) 1256 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 1257 LOP_EXCLUSIVE, file, line, NULL); 1258 tid = (uintptr_t)curthread; 1259 if (atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) { 1260 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line, 1261 flags); 1262 return (0); 1263 } 1264 1265 return (lockmgr_xlock_hard(lk, flags | LK_ADAPTIVE, NULL, file, line, NULL)); 1266 } 1267 1268 int 1269 lockmgr_unlock(struct lock *lk) 1270 { 1271 uintptr_t x, tid; 1272 const char *file; 1273 int line; 1274 1275 file = __FILE__; 1276 line = __LINE__; 1277 1278 _lockmgr_assert(lk, KA_LOCKED, file, line); 1279 x = lockmgr_read_value(lk); 1280 if (__predict_true(x & LK_SHARE) != 0) { 1281 lockmgr_note_shared_release(lk, file, line); 1282 if (lockmgr_sunlock_try(lk, &x)) { 1283 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER); 1284 } else { 1285 return (lockmgr_sunlock_hard(lk, x, LK_RELEASE, NULL, file, line)); 1286 } 1287 } else { 1288 tid = (uintptr_t)curthread; 1289 lockmgr_note_exclusive_release(lk, file, line); 1290 if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) { 1291 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,LOCKSTAT_WRITER); 1292 } else { 1293 return (lockmgr_xunlock_hard(lk, x, LK_RELEASE, NULL, file, line)); 1294 } 1295 } 1296 return (0); 1297 } 1298 1299 int 1300 __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk, 1301 const char *wmesg, int pri, int timo, const char *file, int line) 1302 { 1303 GIANT_DECLARE; 1304 struct lockmgr_wait lwa; 1305 struct lock_class *class; 1306 const char *iwmesg; 1307 uintptr_t tid, v, x; 1308 u_int op, realexslp; 1309 int error, ipri, itimo, queue, wakeup_swapper; 1310 #ifdef LOCK_PROFILING 1311 uint64_t waittime = 0; 1312 int contested = 0; 1313 #endif 1314 1315 if (KERNEL_PANICKED()) 1316 return (0); 1317 1318 error = 0; 1319 tid = (uintptr_t)curthread; 1320 op = (flags & LK_TYPE_MASK); 1321 iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg; 1322 ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri; 1323 itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo; 1324 1325 lwa.iwmesg = iwmesg; 1326 lwa.ipri = ipri; 1327 lwa.itimo = itimo; 1328 1329 MPASS((flags & ~LK_TOTAL_MASK) == 0); 1330 KASSERT((op & (op - 1)) == 0, 1331 ("%s: Invalid requested operation @ %s:%d", __func__, file, line)); 1332 KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 || 1333 (op != LK_DOWNGRADE && op != LK_RELEASE), 1334 ("%s: Invalid flags in regard of the operation desired @ %s:%d", 1335 __func__, file, line)); 1336 KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL, 1337 ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d", 1338 __func__, file, line)); 1339 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread), 1340 ("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread, 1341 lk->lock_object.lo_name, file, line)); 1342 1343 class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL; 1344 1345 if (lk->lock_object.lo_flags & LK_NOSHARE) { 1346 switch (op) { 1347 case LK_SHARED: 1348 op = LK_EXCLUSIVE; 1349 break; 1350 case LK_UPGRADE: 1351 case LK_TRYUPGRADE: 1352 case LK_DOWNGRADE: 1353 _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, 1354 file, line); 1355 if (flags & LK_INTERLOCK) 1356 class->lc_unlock(ilk); 1357 return (0); 1358 } 1359 } 1360 1361 wakeup_swapper = 0; 1362 switch (op) { 1363 case LK_SHARED: 1364 return (lockmgr_slock_hard(lk, flags, ilk, file, line, &lwa)); 1365 break; 1366 case LK_UPGRADE: 1367 case LK_TRYUPGRADE: 1368 return (lockmgr_upgrade(lk, flags, ilk, file, line, &lwa)); 1369 break; 1370 case LK_EXCLUSIVE: 1371 return (lockmgr_xlock_hard(lk, flags, ilk, file, line, &lwa)); 1372 break; 1373 case LK_DOWNGRADE: 1374 _lockmgr_assert(lk, KA_XLOCKED, file, line); 1375 WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line); 1376 1377 /* 1378 * Panic if the lock is recursed. 1379 */ 1380 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) { 1381 if (flags & LK_INTERLOCK) 1382 class->lc_unlock(ilk); 1383 panic("%s: downgrade a recursed lockmgr %s @ %s:%d\n", 1384 __func__, iwmesg, file, line); 1385 } 1386 TD_SLOCKS_INC(curthread); 1387 1388 /* 1389 * In order to preserve waiters flags, just spin. 1390 */ 1391 for (;;) { 1392 x = lockmgr_read_value(lk); 1393 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1394 x &= LK_ALL_WAITERS; 1395 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, 1396 LK_SHARERS_LOCK(1) | x)) 1397 break; 1398 cpu_spinwait(); 1399 } 1400 LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line); 1401 LOCKSTAT_RECORD0(lockmgr__downgrade, lk); 1402 break; 1403 case LK_RELEASE: 1404 _lockmgr_assert(lk, KA_LOCKED, file, line); 1405 x = lockmgr_read_value(lk); 1406 1407 if (__predict_true(x & LK_SHARE) != 0) { 1408 lockmgr_note_shared_release(lk, file, line); 1409 return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line)); 1410 } else { 1411 lockmgr_note_exclusive_release(lk, file, line); 1412 return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line)); 1413 } 1414 break; 1415 case LK_DRAIN: 1416 if (LK_CAN_WITNESS(flags)) 1417 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER | 1418 LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ? 1419 ilk : NULL); 1420 1421 /* 1422 * Trying to drain a lock we already own will result in a 1423 * deadlock. 1424 */ 1425 if (lockmgr_xlocked(lk)) { 1426 if (flags & LK_INTERLOCK) 1427 class->lc_unlock(ilk); 1428 panic("%s: draining %s with the lock held @ %s:%d\n", 1429 __func__, iwmesg, file, line); 1430 } 1431 1432 for (;;) { 1433 if (lk->lk_lock == LK_UNLOCKED && 1434 atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) 1435 break; 1436 1437 #ifdef HWPMC_HOOKS 1438 PMC_SOFT_CALL( , , lock, failed); 1439 #endif 1440 lock_profile_obtain_lock_failed(&lk->lock_object, false, 1441 &contested, &waittime); 1442 1443 /* 1444 * If the lock is expected to not sleep just give up 1445 * and return. 1446 */ 1447 if (LK_TRYOP(flags)) { 1448 LOCK_LOG2(lk, "%s: %p fails the try operation", 1449 __func__, lk); 1450 error = EBUSY; 1451 break; 1452 } 1453 1454 /* 1455 * Acquire the sleepqueue chain lock because we 1456 * probabilly will need to manipulate waiters flags. 1457 */ 1458 sleepq_lock(&lk->lock_object); 1459 x = lockmgr_read_value(lk); 1460 1461 /* 1462 * if the lock has been released while we spun on 1463 * the sleepqueue chain lock just try again. 1464 */ 1465 if (x == LK_UNLOCKED) { 1466 sleepq_release(&lk->lock_object); 1467 continue; 1468 } 1469 1470 v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS); 1471 if ((x & ~v) == LK_UNLOCKED) { 1472 v = (x & ~LK_EXCLUSIVE_SPINNERS); 1473 1474 /* 1475 * If interruptible sleeps left the exclusive 1476 * queue empty avoid a starvation for the 1477 * threads sleeping on the shared queue by 1478 * giving them precedence and cleaning up the 1479 * exclusive waiters bit anyway. 1480 * Please note that lk_exslpfail count may be 1481 * lying about the real number of waiters with 1482 * the LK_SLEEPFAIL flag on because they may 1483 * be used in conjunction with interruptible 1484 * sleeps so lk_exslpfail might be considered 1485 * an 'upper limit' bound, including the edge 1486 * cases. 1487 */ 1488 if (v & LK_EXCLUSIVE_WAITERS) { 1489 queue = SQ_EXCLUSIVE_QUEUE; 1490 v &= ~LK_EXCLUSIVE_WAITERS; 1491 } else { 1492 /* 1493 * Exclusive waiters sleeping with 1494 * LK_SLEEPFAIL on and using 1495 * interruptible sleeps/timeout may 1496 * have left spourious lk_exslpfail 1497 * counts on, so clean it up anyway. 1498 */ 1499 MPASS(v & LK_SHARED_WAITERS); 1500 lk->lk_exslpfail = 0; 1501 queue = SQ_SHARED_QUEUE; 1502 v &= ~LK_SHARED_WAITERS; 1503 } 1504 if (queue == SQ_EXCLUSIVE_QUEUE) { 1505 realexslp = 1506 sleepq_sleepcnt(&lk->lock_object, 1507 SQ_EXCLUSIVE_QUEUE); 1508 if (lk->lk_exslpfail >= realexslp) { 1509 lk->lk_exslpfail = 0; 1510 queue = SQ_SHARED_QUEUE; 1511 v &= ~LK_SHARED_WAITERS; 1512 if (realexslp != 0) { 1513 LOCK_LOG2(lk, 1514 "%s: %p has only LK_SLEEPFAIL sleepers", 1515 __func__, lk); 1516 LOCK_LOG2(lk, 1517 "%s: %p waking up threads on the exclusive queue", 1518 __func__, lk); 1519 wakeup_swapper = 1520 sleepq_broadcast( 1521 &lk->lock_object, 1522 SLEEPQ_LK, 0, 1523 SQ_EXCLUSIVE_QUEUE); 1524 } 1525 } else 1526 lk->lk_exslpfail = 0; 1527 } 1528 if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) { 1529 sleepq_release(&lk->lock_object); 1530 continue; 1531 } 1532 LOCK_LOG3(lk, 1533 "%s: %p waking up all threads on the %s queue", 1534 __func__, lk, queue == SQ_SHARED_QUEUE ? 1535 "shared" : "exclusive"); 1536 wakeup_swapper |= sleepq_broadcast( 1537 &lk->lock_object, SLEEPQ_LK, 0, queue); 1538 1539 /* 1540 * If shared waiters have been woken up we need 1541 * to wait for one of them to acquire the lock 1542 * before to set the exclusive waiters in 1543 * order to avoid a deadlock. 1544 */ 1545 if (queue == SQ_SHARED_QUEUE) { 1546 for (v = lk->lk_lock; 1547 (v & LK_SHARE) && !LK_SHARERS(v); 1548 v = lk->lk_lock) 1549 cpu_spinwait(); 1550 } 1551 } 1552 1553 /* 1554 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we 1555 * fail, loop back and retry. 1556 */ 1557 if ((x & LK_EXCLUSIVE_WAITERS) == 0) { 1558 if (!atomic_cmpset_ptr(&lk->lk_lock, x, 1559 x | LK_EXCLUSIVE_WAITERS)) { 1560 sleepq_release(&lk->lock_object); 1561 continue; 1562 } 1563 LOCK_LOG2(lk, "%s: %p set drain waiters flag", 1564 __func__, lk); 1565 } 1566 1567 /* 1568 * As far as we have been unable to acquire the 1569 * exclusive lock and the exclusive waiters flag 1570 * is set, we will sleep. 1571 */ 1572 if (flags & LK_INTERLOCK) { 1573 class->lc_unlock(ilk); 1574 flags &= ~LK_INTERLOCK; 1575 } 1576 GIANT_SAVE(); 1577 sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK, 1578 SQ_EXCLUSIVE_QUEUE); 1579 sleepq_wait(&lk->lock_object, ipri & PRIMASK); 1580 GIANT_RESTORE(); 1581 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue", 1582 __func__, lk); 1583 } 1584 1585 if (error == 0) { 1586 lock_profile_obtain_lock_success(&lk->lock_object, 1587 false, contested, waittime, file, line); 1588 LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0, 1589 lk->lk_recurse, file, line); 1590 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | 1591 LK_TRYWIT(flags), file, line); 1592 TD_LOCKS_INC(curthread); 1593 STACK_SAVE(lk); 1594 } 1595 break; 1596 default: 1597 if (flags & LK_INTERLOCK) 1598 class->lc_unlock(ilk); 1599 panic("%s: unknown lockmgr request 0x%x\n", __func__, op); 1600 } 1601 1602 if (flags & LK_INTERLOCK) 1603 class->lc_unlock(ilk); 1604 if (wakeup_swapper) 1605 kick_proc0(); 1606 1607 return (error); 1608 } 1609 1610 void 1611 _lockmgr_disown(struct lock *lk, const char *file, int line) 1612 { 1613 uintptr_t tid, x; 1614 1615 if (SCHEDULER_STOPPED()) 1616 return; 1617 1618 tid = (uintptr_t)curthread; 1619 _lockmgr_assert(lk, KA_XLOCKED, file, line); 1620 1621 /* 1622 * Panic if the lock is recursed. 1623 */ 1624 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) 1625 panic("%s: disown a recursed lockmgr @ %s:%d\n", 1626 __func__, file, line); 1627 1628 /* 1629 * If the owner is already LK_KERNPROC just skip the whole operation. 1630 */ 1631 if (LK_HOLDER(lk->lk_lock) != tid) 1632 return; 1633 lock_profile_release_lock(&lk->lock_object, false); 1634 LOCKSTAT_RECORD1(lockmgr__disown, lk, LOCKSTAT_WRITER); 1635 LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line); 1636 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line); 1637 TD_LOCKS_DEC(curthread); 1638 STACK_SAVE(lk); 1639 1640 /* 1641 * In order to preserve waiters flags, just spin. 1642 */ 1643 for (;;) { 1644 x = lockmgr_read_value(lk); 1645 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0); 1646 x &= LK_ALL_WAITERS; 1647 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x, 1648 LK_KERNPROC | x)) 1649 return; 1650 cpu_spinwait(); 1651 } 1652 } 1653 1654 void 1655 lockmgr_printinfo(const struct lock *lk) 1656 { 1657 struct thread *td; 1658 uintptr_t x; 1659 1660 if (lk->lk_lock == LK_UNLOCKED) 1661 printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name); 1662 else if (lk->lk_lock & LK_SHARE) 1663 printf("lock type %s: SHARED (count %ju)\n", 1664 lk->lock_object.lo_name, 1665 (uintmax_t)LK_SHARERS(lk->lk_lock)); 1666 else { 1667 td = lockmgr_xholder(lk); 1668 if (td == (struct thread *)LK_KERNPROC) 1669 printf("lock type %s: EXCL by KERNPROC\n", 1670 lk->lock_object.lo_name); 1671 else 1672 printf("lock type %s: EXCL by thread %p " 1673 "(pid %d, %s, tid %d)\n", lk->lock_object.lo_name, 1674 td, td->td_proc->p_pid, td->td_proc->p_comm, 1675 td->td_tid); 1676 } 1677 1678 x = lk->lk_lock; 1679 if (x & LK_EXCLUSIVE_WAITERS) 1680 printf(" with exclusive waiters pending\n"); 1681 if (x & LK_SHARED_WAITERS) 1682 printf(" with shared waiters pending\n"); 1683 if (x & LK_EXCLUSIVE_SPINNERS) 1684 printf(" with exclusive spinners pending\n"); 1685 1686 STACK_PRINT(lk); 1687 } 1688 1689 int 1690 lockstatus(const struct lock *lk) 1691 { 1692 uintptr_t v, x; 1693 int ret; 1694 1695 ret = LK_SHARED; 1696 x = lockmgr_read_value(lk); 1697 v = LK_HOLDER(x); 1698 1699 if ((x & LK_SHARE) == 0) { 1700 if (v == (uintptr_t)curthread || v == LK_KERNPROC) 1701 ret = LK_EXCLUSIVE; 1702 else 1703 ret = LK_EXCLOTHER; 1704 } else if (x == LK_UNLOCKED) 1705 ret = 0; 1706 1707 return (ret); 1708 } 1709 1710 #ifdef INVARIANT_SUPPORT 1711 1712 FEATURE(invariant_support, 1713 "Support for modules compiled with INVARIANTS option"); 1714 1715 #ifndef INVARIANTS 1716 #undef _lockmgr_assert 1717 #endif 1718 1719 void 1720 _lockmgr_assert(const struct lock *lk, int what, const char *file, int line) 1721 { 1722 int slocked = 0; 1723 1724 if (KERNEL_PANICKED()) 1725 return; 1726 switch (what) { 1727 case KA_SLOCKED: 1728 case KA_SLOCKED | KA_NOTRECURSED: 1729 case KA_SLOCKED | KA_RECURSED: 1730 slocked = 1; 1731 case KA_LOCKED: 1732 case KA_LOCKED | KA_NOTRECURSED: 1733 case KA_LOCKED | KA_RECURSED: 1734 #ifdef WITNESS 1735 1736 /* 1737 * We cannot trust WITNESS if the lock is held in exclusive 1738 * mode and a call to lockmgr_disown() happened. 1739 * Workaround this skipping the check if the lock is held in 1740 * exclusive mode even for the KA_LOCKED case. 1741 */ 1742 if (slocked || (lk->lk_lock & LK_SHARE)) { 1743 witness_assert(&lk->lock_object, what, file, line); 1744 break; 1745 } 1746 #endif 1747 if (lk->lk_lock == LK_UNLOCKED || 1748 ((lk->lk_lock & LK_SHARE) == 0 && (slocked || 1749 (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))))) 1750 panic("Lock %s not %slocked @ %s:%d\n", 1751 lk->lock_object.lo_name, slocked ? "share" : "", 1752 file, line); 1753 1754 if ((lk->lk_lock & LK_SHARE) == 0) { 1755 if (lockmgr_recursed(lk)) { 1756 if (what & KA_NOTRECURSED) 1757 panic("Lock %s recursed @ %s:%d\n", 1758 lk->lock_object.lo_name, file, 1759 line); 1760 } else if (what & KA_RECURSED) 1761 panic("Lock %s not recursed @ %s:%d\n", 1762 lk->lock_object.lo_name, file, line); 1763 } 1764 break; 1765 case KA_XLOCKED: 1766 case KA_XLOCKED | KA_NOTRECURSED: 1767 case KA_XLOCKED | KA_RECURSED: 1768 if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)) 1769 panic("Lock %s not exclusively locked @ %s:%d\n", 1770 lk->lock_object.lo_name, file, line); 1771 if (lockmgr_recursed(lk)) { 1772 if (what & KA_NOTRECURSED) 1773 panic("Lock %s recursed @ %s:%d\n", 1774 lk->lock_object.lo_name, file, line); 1775 } else if (what & KA_RECURSED) 1776 panic("Lock %s not recursed @ %s:%d\n", 1777 lk->lock_object.lo_name, file, line); 1778 break; 1779 case KA_UNLOCKED: 1780 if (lockmgr_xlocked(lk) || lockmgr_disowned(lk)) 1781 panic("Lock %s exclusively locked @ %s:%d\n", 1782 lk->lock_object.lo_name, file, line); 1783 break; 1784 default: 1785 panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file, 1786 line); 1787 } 1788 } 1789 #endif 1790 1791 #ifdef DDB 1792 int 1793 lockmgr_chain(struct thread *td, struct thread **ownerp) 1794 { 1795 const struct lock *lk; 1796 1797 lk = td->td_wchan; 1798 1799 if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr) 1800 return (0); 1801 db_printf("blocked on lockmgr %s", lk->lock_object.lo_name); 1802 if (lk->lk_lock & LK_SHARE) 1803 db_printf("SHARED (count %ju)\n", 1804 (uintmax_t)LK_SHARERS(lk->lk_lock)); 1805 else 1806 db_printf("EXCL\n"); 1807 *ownerp = lockmgr_xholder(lk); 1808 1809 return (1); 1810 } 1811 1812 static void 1813 db_show_lockmgr(const struct lock_object *lock) 1814 { 1815 struct thread *td; 1816 const struct lock *lk; 1817 1818 lk = (const struct lock *)lock; 1819 1820 db_printf(" state: "); 1821 if (lk->lk_lock == LK_UNLOCKED) 1822 db_printf("UNLOCKED\n"); 1823 else if (lk->lk_lock & LK_SHARE) 1824 db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock)); 1825 else { 1826 td = lockmgr_xholder(lk); 1827 if (td == (struct thread *)LK_KERNPROC) 1828 db_printf("XLOCK: LK_KERNPROC\n"); 1829 else 1830 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 1831 td->td_tid, td->td_proc->p_pid, 1832 td->td_proc->p_comm); 1833 if (lockmgr_recursed(lk)) 1834 db_printf(" recursed: %d\n", lk->lk_recurse); 1835 } 1836 db_printf(" waiters: "); 1837 switch (lk->lk_lock & LK_ALL_WAITERS) { 1838 case LK_SHARED_WAITERS: 1839 db_printf("shared\n"); 1840 break; 1841 case LK_EXCLUSIVE_WAITERS: 1842 db_printf("exclusive\n"); 1843 break; 1844 case LK_ALL_WAITERS: 1845 db_printf("shared and exclusive\n"); 1846 break; 1847 default: 1848 db_printf("none\n"); 1849 } 1850 db_printf(" spinners: "); 1851 if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS) 1852 db_printf("exclusive\n"); 1853 else 1854 db_printf("none\n"); 1855 } 1856 #endif
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