sys/kern/kern_lock.c

   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((lk)->lk_lock)
 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 struct lockmgr_wait {
 171         const char *iwmesg;
 172         int ipri;
 173         int itimo;
 174 };
 175
 176 static bool __always_inline lockmgr_slock_try(struct lock *lk, uintptr_t *xp,
 177     int flags, bool fp);
 178 static bool __always_inline lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp);
 179
 180 static void
 181 lockmgr_exit(u_int flags, struct lock_object *ilk, int wakeup_swapper)
 182 {
 183         struct lock_class *class;
 184
 185         if (flags & LK_INTERLOCK) {
 186                 class = LOCK_CLASS(ilk);
 187                 class->lc_unlock(ilk);
 188         }
 189
 190         if (__predict_false(wakeup_swapper))
 191                 kick_proc0();
 192 }
 193
 194 static void
 195 lockmgr_note_shared_acquire(struct lock *lk, int contested,
 196     uint64_t waittime, const char *file, int line, int flags)
 197 {
 198
 199         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
 200             waittime, file, line, LOCKSTAT_READER);
 201         LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file, line);
 202         WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file, line);
 203         TD_LOCKS_INC(curthread);
 204         TD_SLOCKS_INC(curthread);
 205         STACK_SAVE(lk);
 206 }
 207
 208 static void
 209 lockmgr_note_shared_release(struct lock *lk, const char *file, int line)
 210 {
 211
 212         WITNESS_UNLOCK(&lk->lock_object, 0, file, line);
 213         LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line);
 214         TD_LOCKS_DEC(curthread);
 215         TD_SLOCKS_DEC(curthread);
 216 }
 217
 218 static void
 219 lockmgr_note_exclusive_acquire(struct lock *lk, int contested,
 220     uint64_t waittime, const char *file, int line, int flags)
 221 {
 222
 223         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(lockmgr__acquire, lk, contested,
 224             waittime, file, line, LOCKSTAT_WRITER);
 225         LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0, lk->lk_recurse, file, line);
 226         WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE | LK_TRYWIT(flags), file,
 227             line);
 228         TD_LOCKS_INC(curthread);
 229         STACK_SAVE(lk);
 230 }
 231
 232 static void
 233 lockmgr_note_exclusive_release(struct lock *lk, const char *file, int line)
 234 {
 235
 236         if (LK_HOLDER(lk->lk_lock) != LK_KERNPROC) {
 237                 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
 238                 TD_LOCKS_DEC(curthread);
 239         }
 240         LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0, lk->lk_recurse, file,
 241             line);
 242 }
 243
 244 static __inline struct thread *
 245 lockmgr_xholder(const struct lock *lk)
 246 {
 247         uintptr_t x;
 248
 249         x = lk->lk_lock;
 250         return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x));
 251 }
 252
 253 /*
 254  * It assumes sleepq_lock held and returns with this one unheld.
 255  * It also assumes the generic interlock is sane and previously checked.
 256  * If LK_INTERLOCK is specified the interlock is not reacquired after the
 257  * sleep.
 258  */
 259 static __inline int
 260 sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk,
 261     const char *wmesg, int pri, int timo, int queue)
 262 {
 263         GIANT_DECLARE;
 264         struct lock_class *class;
 265         int catch, error;
 266
 267         class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
 268         catch = pri & PCATCH;
 269         pri &= PRIMASK;
 270         error = 0;
 271
 272         LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk,
 273             (queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared");
 274
 275         if (flags & LK_INTERLOCK)
 276                 class->lc_unlock(ilk);
 277         if (queue == SQ_EXCLUSIVE_QUEUE && (flags & LK_SLEEPFAIL) != 0)
 278                 lk->lk_exslpfail++;
 279         GIANT_SAVE();
 280         sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ?
 281             SLEEPQ_INTERRUPTIBLE : 0), queue);
 282         if ((flags & LK_TIMELOCK) && timo)
 283                 sleepq_set_timeout(&lk->lock_object, timo);
 284
 285         /*
 286          * Decisional switch for real sleeping.
 287          */
 288         if ((flags & LK_TIMELOCK) && timo && catch)
 289                 error = sleepq_timedwait_sig(&lk->lock_object, pri);
 290         else if ((flags & LK_TIMELOCK) && timo)
 291                 error = sleepq_timedwait(&lk->lock_object, pri);
 292         else if (catch)
 293                 error = sleepq_wait_sig(&lk->lock_object, pri);
 294         else
 295                 sleepq_wait(&lk->lock_object, pri);
 296         GIANT_RESTORE();
 297         if ((flags & LK_SLEEPFAIL) && error == 0)
 298                 error = ENOLCK;
 299
 300         return (error);
 301 }
 302
 303 static __inline int
 304 wakeupshlk(struct lock *lk, const char *file, int line)
 305 {
 306         uintptr_t v, x, orig_x;
 307         u_int realexslp;
 308         int queue, wakeup_swapper;
 309
 310         wakeup_swapper = 0;
 311         for (;;) {
 312                 x = lk->lk_lock;
 313                 if (lockmgr_sunlock_try(lk, &x))
 314                         break;
 315
 316                 /*
 317                  * We should have a sharer with waiters, so enter the hard
 318                  * path in order to handle wakeups correctly.
 319                  */
 320                 sleepq_lock(&lk->lock_object);
 321                 orig_x = lk->lk_lock;
 322 retry_sleepq:
 323                 x = orig_x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
 324                 v = LK_UNLOCKED;
 325
 326                 /*
 327                  * If the lock has exclusive waiters, give them preference in
 328                  * order to avoid deadlock with shared runners up.
 329                  * If interruptible sleeps left the exclusive queue empty
 330                  * avoid a starvation for the threads sleeping on the shared
 331                  * queue by giving them precedence and cleaning up the
 332                  * exclusive waiters bit anyway.
 333                  * Please note that lk_exslpfail count may be lying about
 334                  * the real number of waiters with the LK_SLEEPFAIL flag on
 335                  * because they may be used in conjunction with interruptible
 336                  * sleeps so lk_exslpfail might be considered an 'upper limit'
 337                  * bound, including the edge cases.
 338                  */
 339                 realexslp = sleepq_sleepcnt(&lk->lock_object,
 340                     SQ_EXCLUSIVE_QUEUE);
 341                 if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
 342                         if (lk->lk_exslpfail < realexslp) {
 343                                 lk->lk_exslpfail = 0;
 344                                 queue = SQ_EXCLUSIVE_QUEUE;
 345                                 v |= (x & LK_SHARED_WAITERS);
 346                         } else {
 347                                 lk->lk_exslpfail = 0;
 348                                 LOCK_LOG2(lk,
 349                                     "%s: %p has only LK_SLEEPFAIL sleepers",
 350                                     __func__, lk);
 351                                 LOCK_LOG2(lk,
 352                             "%s: %p waking up threads on the exclusive queue",
 353                                     __func__, lk);
 354                                 wakeup_swapper =
 355                                     sleepq_broadcast(&lk->lock_object,
 356                                     SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
 357                                 queue = SQ_SHARED_QUEUE;
 358                         }
 359
 360                 } else {
 361
 362                         /*
 363                          * Exclusive waiters sleeping with LK_SLEEPFAIL on
 364                          * and using interruptible sleeps/timeout may have
 365                          * left spourious lk_exslpfail counts on, so clean
 366                          * it up anyway.
 367                          */
 368                         lk->lk_exslpfail = 0;
 369                         queue = SQ_SHARED_QUEUE;
 370                 }
 371
 372                 if (lockmgr_sunlock_try(lk, &orig_x)) {
 373                         sleepq_release(&lk->lock_object);
 374                         break;
 375                 }
 376
 377                 x |= LK_SHARERS_LOCK(1);
 378                 if (!atomic_fcmpset_rel_ptr(&lk->lk_lock, &x, v)) {
 379                         orig_x = x;
 380                         goto retry_sleepq;
 381                 }
 382                 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
 383                     __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
 384                     "exclusive");
 385                 wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK,
 386                     0, queue);
 387                 sleepq_release(&lk->lock_object);
 388                 break;
 389         }
 390
 391         LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
 392         return (wakeup_swapper);
 393 }
 394
 395 static void
 396 assert_lockmgr(const struct lock_object *lock, int what)
 397 {
 398
 399         panic("lockmgr locks do not support assertions");
 400 }
 401
 402 static void
 403 lock_lockmgr(struct lock_object *lock, uintptr_t how)
 404 {
 405
 406         panic("lockmgr locks do not support sleep interlocking");
 407 }
 408
 409 static uintptr_t
 410 unlock_lockmgr(struct lock_object *lock)
 411 {
 412
 413         panic("lockmgr locks do not support sleep interlocking");
 414 }
 415
 416 #ifdef KDTRACE_HOOKS
 417 static int
 418 owner_lockmgr(const struct lock_object *lock, struct thread **owner)
 419 {
 420
 421         panic("lockmgr locks do not support owner inquiring");
 422 }
 423 #endif
 424
 425 void
 426 lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags)
 427 {
 428         int iflags;
 429
 430         MPASS((flags & ~LK_INIT_MASK) == 0);
 431         ASSERT_ATOMIC_LOAD_PTR(lk->lk_lock,
 432             ("%s: lockmgr not aligned for %s: %p", __func__, wmesg,
 433             &lk->lk_lock));
 434
 435         iflags = LO_SLEEPABLE | LO_UPGRADABLE;
 436         if (flags & LK_CANRECURSE)
 437                 iflags |= LO_RECURSABLE;
 438         if ((flags & LK_NODUP) == 0)
 439                 iflags |= LO_DUPOK;
 440         if (flags & LK_NOPROFILE)
 441                 iflags |= LO_NOPROFILE;
 442         if ((flags & LK_NOWITNESS) == 0)
 443                 iflags |= LO_WITNESS;
 444         if (flags & LK_QUIET)
 445                 iflags |= LO_QUIET;
 446         if (flags & LK_IS_VNODE)
 447                 iflags |= LO_IS_VNODE;
 448         if (flags & LK_NEW)
 449                 iflags |= LO_NEW;
 450         iflags |= flags & LK_NOSHARE;
 451
 452         lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags);
 453         lk->lk_lock = LK_UNLOCKED;
 454         lk->lk_recurse = 0;
 455         lk->lk_exslpfail = 0;
 456         lk->lk_timo = timo;
 457         lk->lk_pri = pri;
 458         STACK_ZERO(lk);
 459 }
 460
 461 /*
 462  * XXX: Gross hacks to manipulate external lock flags after
 463  * initialization.  Used for certain vnode and buf locks.
 464  */
 465 void
 466 lockallowshare(struct lock *lk)
 467 {
 468
 469         lockmgr_assert(lk, KA_XLOCKED);
 470         lk->lock_object.lo_flags &= ~LK_NOSHARE;
 471 }
 472
 473 void
 474 lockdisableshare(struct lock *lk)
 475 {
 476
 477         lockmgr_assert(lk, KA_XLOCKED);
 478         lk->lock_object.lo_flags |= LK_NOSHARE;
 479 }
 480
 481 void
 482 lockallowrecurse(struct lock *lk)
 483 {
 484
 485         lockmgr_assert(lk, KA_XLOCKED);
 486         lk->lock_object.lo_flags |= LO_RECURSABLE;
 487 }
 488
 489 void
 490 lockdisablerecurse(struct lock *lk)
 491 {
 492
 493         lockmgr_assert(lk, KA_XLOCKED);
 494         lk->lock_object.lo_flags &= ~LO_RECURSABLE;
 495 }
 496
 497 void
 498 lockdestroy(struct lock *lk)
 499 {
 500
 501         KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held"));
 502         KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed"));
 503         KASSERT(lk->lk_exslpfail == 0, ("lockmgr still exclusive waiters"));
 504         lock_destroy(&lk->lock_object);
 505 }
 506
 507 static bool __always_inline
 508 lockmgr_slock_try(struct lock *lk, uintptr_t *xp, int flags, bool fp)
 509 {
 510
 511         /*
 512          * If no other thread has an exclusive lock, or
 513          * no exclusive waiter is present, bump the count of
 514          * sharers.  Since we have to preserve the state of
 515          * waiters, if we fail to acquire the shared lock
 516          * loop back and retry.
 517          */
 518         *xp = lk->lk_lock;
 519         while (LK_CAN_SHARE(*xp, flags, fp)) {
 520                 if (atomic_fcmpset_acq_ptr(&lk->lk_lock, xp,
 521                     *xp + LK_ONE_SHARER)) {
 522                         return (true);
 523                 }
 524         }
 525         return (false);
 526 }
 527
 528 static bool __always_inline
 529 lockmgr_sunlock_try(struct lock *lk, uintptr_t *xp)
 530 {
 531
 532         for (;;) {
 533                 if (LK_SHARERS(*xp) > 1 || !(*xp & LK_ALL_WAITERS)) {
 534                         if (atomic_fcmpset_rel_ptr(&lk->lk_lock, xp,
 535                             *xp - LK_ONE_SHARER))
 536                                 return (true);
 537                         continue;
 538                 }
 539                 break;
 540         }
 541         return (false);
 542 }
 543
 544 static __noinline int
 545 lockmgr_slock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
 546     const char *file, int line, struct lockmgr_wait *lwa)
 547 {
 548         uintptr_t tid, x;
 549         int error = 0;
 550         const char *iwmesg;
 551         int ipri, itimo;
 552
 553 #ifdef KDTRACE_HOOKS
 554         uint64_t sleep_time = 0;
 555 #endif
 556 #ifdef LOCK_PROFILING
 557         uint64_t waittime = 0;
 558         int contested = 0;
 559 #endif
 560
 561         if (KERNEL_PANICKED())
 562                 goto out;
 563
 564         tid = (uintptr_t)curthread;
 565
 566         if (LK_CAN_WITNESS(flags))
 567                 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
 568                     file, line, flags & LK_INTERLOCK ? ilk : NULL);
 569         for (;;) {
 570                 if (lockmgr_slock_try(lk, &x, flags, false))
 571                         break;
 572 #ifdef HWPMC_HOOKS
 573                 PMC_SOFT_CALL( , , lock, failed);
 574 #endif
 575                 lock_profile_obtain_lock_failed(&lk->lock_object,
 576                     &contested, &waittime);
 577
 578                 /*
 579                  * If the lock is already held by curthread in
 580                  * exclusive way avoid a deadlock.
 581                  */
 582                 if (LK_HOLDER(x) == tid) {
 583                         LOCK_LOG2(lk,
 584                             "%s: %p already held in exclusive mode",
 585                             __func__, lk);
 586                         error = EDEADLK;
 587                         break;
 588                 }
 589
 590                 /*
 591                  * If the lock is expected to not sleep just give up
 592                  * and return.
 593                  */
 594                 if (LK_TRYOP(flags)) {
 595                         LOCK_LOG2(lk, "%s: %p fails the try operation",
 596                             __func__, lk);
 597                         error = EBUSY;
 598                         break;
 599                 }
 600
 601                 /*
 602                  * Acquire the sleepqueue chain lock because we
 603                  * probabilly will need to manipulate waiters flags.
 604                  */
 605                 sleepq_lock(&lk->lock_object);
 606                 x = lk->lk_lock;
 607 retry_sleepq:
 608
 609                 /*
 610                  * if the lock can be acquired in shared mode, try
 611                  * again.
 612                  */
 613                 if (LK_CAN_SHARE(x, flags, false)) {
 614                         sleepq_release(&lk->lock_object);
 615                         continue;
 616                 }
 617
 618                 /*
 619                  * Try to set the LK_SHARED_WAITERS flag.  If we fail,
 620                  * loop back and retry.
 621                  */
 622                 if ((x & LK_SHARED_WAITERS) == 0) {
 623                         if (!atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
 624                             x | LK_SHARED_WAITERS)) {
 625                                 goto retry_sleepq;
 626                         }
 627                         LOCK_LOG2(lk, "%s: %p set shared waiters flag",
 628                             __func__, lk);
 629                 }
 630
 631                 if (lwa == NULL) {
 632                         iwmesg = lk->lock_object.lo_name;
 633                         ipri = lk->lk_pri;
 634                         itimo = lk->lk_timo;
 635                 } else {
 636                         iwmesg = lwa->iwmesg;
 637                         ipri = lwa->ipri;
 638                         itimo = lwa->itimo;
 639                 }
 640
 641                 /*
 642                  * As far as we have been unable to acquire the
 643                  * shared lock and the shared waiters flag is set,
 644                  * we will sleep.
 645                  */
 646 #ifdef KDTRACE_HOOKS
 647                 sleep_time -= lockstat_nsecs(&lk->lock_object);
 648 #endif
 649                 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
 650                     SQ_SHARED_QUEUE);
 651 #ifdef KDTRACE_HOOKS
 652                 sleep_time += lockstat_nsecs(&lk->lock_object);
 653 #endif
 654                 flags &= ~LK_INTERLOCK;
 655                 if (error) {
 656                         LOCK_LOG3(lk,
 657                             "%s: interrupted sleep for %p with %d",
 658                             __func__, lk, error);
 659                         break;
 660                 }
 661                 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
 662                     __func__, lk);
 663         }
 664         if (error == 0) {
 665 #ifdef KDTRACE_HOOKS
 666                 if (sleep_time != 0)
 667                         LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
 668                             LOCKSTAT_READER, (x & LK_SHARE) == 0,
 669                             (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
 670 #endif
 671 #ifdef LOCK_PROFILING
 672                 lockmgr_note_shared_acquire(lk, contested, waittime,
 673                     file, line, flags);
 674 #else
 675                 lockmgr_note_shared_acquire(lk, 0, 0, file, line,
 676                     flags);
 677 #endif
 678         }
 679
 680 out:
 681         lockmgr_exit(flags, ilk, 0);
 682         return (error);
 683 }
 684
 685 static __noinline int
 686 lockmgr_xlock_hard(struct lock *lk, u_int flags, struct lock_object *ilk,
 687     const char *file, int line, struct lockmgr_wait *lwa)
 688 {
 689         struct lock_class *class;
 690         uintptr_t tid, x, v;
 691         int error = 0;
 692         const char *iwmesg;
 693         int ipri, itimo;
 694
 695 #ifdef KDTRACE_HOOKS
 696         uint64_t sleep_time = 0;
 697 #endif
 698 #ifdef LOCK_PROFILING
 699         uint64_t waittime = 0;
 700         int contested = 0;
 701 #endif
 702
 703         if (KERNEL_PANICKED())
 704                 goto out;
 705
 706         tid = (uintptr_t)curthread;
 707
 708         if (LK_CAN_WITNESS(flags))
 709                 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
 710                     LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
 711                     ilk : NULL);
 712
 713         /*
 714          * If curthread already holds the lock and this one is
 715          * allowed to recurse, simply recurse on it.
 716          */
 717         if (lockmgr_xlocked(lk)) {
 718                 if ((flags & LK_CANRECURSE) == 0 &&
 719                     (lk->lock_object.lo_flags & LO_RECURSABLE) == 0) {
 720                         /*
 721                          * If the lock is expected to not panic just
 722                          * give up and return.
 723                          */
 724                         if (LK_TRYOP(flags)) {
 725                                 LOCK_LOG2(lk,
 726                                     "%s: %p fails the try operation",
 727                                     __func__, lk);
 728                                 error = EBUSY;
 729                                 goto out;
 730                         }
 731                         if (flags & LK_INTERLOCK) {
 732                                 class = LOCK_CLASS(ilk);
 733                                 class->lc_unlock(ilk);
 734                         }
 735                         panic("%s: recursing on non recursive lockmgr %p "
 736                             "@ %s:%d\n", __func__, lk, file, line);
 737                 }
 738                 lk->lk_recurse++;
 739                 LOCK_LOG2(lk, "%s: %p recursing", __func__, lk);
 740                 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
 741                     lk->lk_recurse, file, line);
 742                 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
 743                     LK_TRYWIT(flags), file, line);
 744                 TD_LOCKS_INC(curthread);
 745                 goto out;
 746         }
 747
 748         for (;;) {
 749                 if (lk->lk_lock == LK_UNLOCKED &&
 750                     atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid))
 751                         break;
 752 #ifdef HWPMC_HOOKS
 753                 PMC_SOFT_CALL( , , lock, failed);
 754 #endif
 755                 lock_profile_obtain_lock_failed(&lk->lock_object,
 756                     &contested, &waittime);
 757
 758                 /*
 759                  * If the lock is expected to not sleep just give up
 760                  * and return.
 761                  */
 762                 if (LK_TRYOP(flags)) {
 763                         LOCK_LOG2(lk, "%s: %p fails the try operation",
 764                             __func__, lk);
 765                         error = EBUSY;
 766                         break;
 767                 }
 768
 769                 /*
 770                  * Acquire the sleepqueue chain lock because we
 771                  * probabilly will need to manipulate waiters flags.
 772                  */
 773                 sleepq_lock(&lk->lock_object);
 774                 x = lk->lk_lock;
 775 retry_sleepq:
 776
 777                 /*
 778                  * if the lock has been released while we spun on
 779                  * the sleepqueue chain lock just try again.
 780                  */
 781                 if (x == LK_UNLOCKED) {
 782                         sleepq_release(&lk->lock_object);
 783                         continue;
 784                 }
 785
 786                 /*
 787                  * The lock can be in the state where there is a
 788                  * pending queue of waiters, but still no owner.
 789                  * This happens when the lock is contested and an
 790                  * owner is going to claim the lock.
 791                  * If curthread is the one successfully acquiring it
 792                  * claim lock ownership and return, preserving waiters
 793                  * flags.
 794                  */
 795                 v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
 796                 if ((x & ~v) == LK_UNLOCKED) {
 797                         v &= ~LK_EXCLUSIVE_SPINNERS;
 798                         if (atomic_fcmpset_acq_ptr(&lk->lk_lock, &x,
 799                             tid | v)) {
 800                                 sleepq_release(&lk->lock_object);
 801                                 LOCK_LOG2(lk,
 802                                     "%s: %p claimed by a new writer",
 803                                     __func__, lk);
 804                                 break;
 805                         }
 806                         goto retry_sleepq;
 807                 }
 808
 809                 /*
 810                  * Try to set the LK_EXCLUSIVE_WAITERS flag.  If we
 811                  * fail, loop back and retry.
 812                  */
 813                 if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
 814                         if (!atomic_fcmpset_ptr(&lk->lk_lock, &x,
 815                             x | LK_EXCLUSIVE_WAITERS)) {
 816                                 goto retry_sleepq;
 817                         }
 818                         LOCK_LOG2(lk, "%s: %p set excl waiters flag",
 819                             __func__, lk);
 820                 }
 821
 822                 if (lwa == NULL) {
 823                         iwmesg = lk->lock_object.lo_name;
 824                         ipri = lk->lk_pri;
 825                         itimo = lk->lk_timo;
 826                 } else {
 827                         iwmesg = lwa->iwmesg;
 828                         ipri = lwa->ipri;
 829                         itimo = lwa->itimo;
 830                 }
 831
 832                 /*
 833                  * As far as we have been unable to acquire the
 834                  * exclusive lock and the exclusive waiters flag
 835                  * is set, we will sleep.
 836                  */
 837 #ifdef KDTRACE_HOOKS
 838                 sleep_time -= lockstat_nsecs(&lk->lock_object);
 839 #endif
 840                 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
 841                     SQ_EXCLUSIVE_QUEUE);
 842 #ifdef KDTRACE_HOOKS
 843                 sleep_time += lockstat_nsecs(&lk->lock_object);
 844 #endif
 845                 flags &= ~LK_INTERLOCK;
 846                 if (error) {
 847                         LOCK_LOG3(lk,
 848                             "%s: interrupted sleep for %p with %d",
 849                             __func__, lk, error);
 850                         break;
 851                 }
 852                 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
 853                     __func__, lk);
 854         }
 855         if (error == 0) {
 856 #ifdef KDTRACE_HOOKS
 857                 if (sleep_time != 0)
 858                         LOCKSTAT_RECORD4(lockmgr__block, lk, sleep_time,
 859                             LOCKSTAT_WRITER, (x & LK_SHARE) == 0,
 860                             (x & LK_SHARE) == 0 ? 0 : LK_SHARERS(x));
 861 #endif
 862 #ifdef LOCK_PROFILING
 863                 lockmgr_note_exclusive_acquire(lk, contested, waittime,
 864                     file, line, flags);
 865 #else
 866                 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
 867                     flags);
 868 #endif
 869         }
 870
 871 out:
 872         lockmgr_exit(flags, ilk, 0);
 873         return (error);
 874 }
 875
 876 static __noinline int
 877 lockmgr_upgrade(struct lock *lk, u_int flags, struct lock_object *ilk,
 878     const char *file, int line, struct lockmgr_wait *lwa)
 879 {
 880         uintptr_t tid, x, v;
 881         int error = 0;
 882         int wakeup_swapper = 0;
 883         int op;
 884
 885         if (KERNEL_PANICKED())
 886                 goto out;
 887
 888         tid = (uintptr_t)curthread;
 889
 890         _lockmgr_assert(lk, KA_SLOCKED, file, line);
 891         v = lk->lk_lock;
 892         x = v & LK_ALL_WAITERS;
 893         v &= LK_EXCLUSIVE_SPINNERS;
 894
 895         /*
 896          * Try to switch from one shared lock to an exclusive one.
 897          * We need to preserve waiters flags during the operation.
 898          */
 899         if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x | v,
 900             tid | x)) {
 901                 LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
 902                     line);
 903                 WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
 904                     LK_TRYWIT(flags), file, line);
 905                 LOCKSTAT_RECORD0(lockmgr__upgrade, lk);
 906                 TD_SLOCKS_DEC(curthread);
 907                 goto out;
 908         }
 909
 910         op = flags & LK_TYPE_MASK;
 911
 912         /*
 913          * In LK_TRYUPGRADE mode, do not drop the lock,
 914          * returning EBUSY instead.
 915          */
 916         if (op == LK_TRYUPGRADE) {
 917                 LOCK_LOG2(lk, "%s: %p failed the nowait upgrade",
 918                     __func__, lk);
 919                 error = EBUSY;
 920                 goto out;
 921         }
 922
 923         /*
 924          * We have been unable to succeed in upgrading, so just
 925          * give up the shared lock.
 926          */
 927         lockmgr_note_shared_release(lk, file, line);
 928         wakeup_swapper |= wakeupshlk(lk, file, line);
 929         error = lockmgr_xlock_hard(lk, flags, ilk, file, line, lwa);
 930         flags &= ~LK_INTERLOCK;
 931 out:
 932         lockmgr_exit(flags, ilk, wakeup_swapper);
 933         return (error);
 934 }
 935
 936 int
 937 lockmgr_lock_fast_path(struct lock *lk, u_int flags, struct lock_object *ilk,
 938     const char *file, int line)
 939 {
 940         struct lock_class *class;
 941         uintptr_t x, tid;
 942         u_int op;
 943         bool locked;
 944
 945         if (KERNEL_PANICKED())
 946                 return (0);
 947
 948         op = flags & LK_TYPE_MASK;
 949         locked = false;
 950         switch (op) {
 951         case LK_SHARED:
 952                 if (LK_CAN_WITNESS(flags))
 953                         WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
 954                             file, line, flags & LK_INTERLOCK ? ilk : NULL);
 955                 if (__predict_false(lk->lock_object.lo_flags & LK_NOSHARE))
 956                         break;
 957                 if (lockmgr_slock_try(lk, &x, flags, true)) {
 958                         lockmgr_note_shared_acquire(lk, 0, 0,
 959                             file, line, flags);
 960                         locked = true;
 961                 } else {
 962                         return (lockmgr_slock_hard(lk, flags, ilk, file, line,
 963                             NULL));
 964                 }
 965                 break;
 966         case LK_EXCLUSIVE:
 967                 if (LK_CAN_WITNESS(flags))
 968                         WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
 969                             LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
 970                             ilk : NULL);
 971                 tid = (uintptr_t)curthread;
 972                 if (lk->lk_lock == LK_UNLOCKED &&
 973                     atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
 974                         lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
 975                             flags);
 976                         locked = true;
 977                 } else {
 978                         return (lockmgr_xlock_hard(lk, flags, ilk, file, line,
 979                             NULL));
 980                 }
 981                 break;
 982         case LK_UPGRADE:
 983         case LK_TRYUPGRADE:
 984                 return (lockmgr_upgrade(lk, flags, ilk, file, line, NULL));
 985         default:
 986                 break;
 987         }
 988         if (__predict_true(locked)) {
 989                 if (__predict_false(flags & LK_INTERLOCK)) {
 990                         class = LOCK_CLASS(ilk);
 991                         class->lc_unlock(ilk);
 992                 }
 993                 return (0);
 994         } else {
 995                 return (__lockmgr_args(lk, flags, ilk, LK_WMESG_DEFAULT,
 996                     LK_PRIO_DEFAULT, LK_TIMO_DEFAULT, file, line));
 997         }
 998 }
 999
1000 static __noinline int
1001 lockmgr_sunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
1002     const char *file, int line)
1003
1004 {
1005         int wakeup_swapper = 0;
1006
1007         if (KERNEL_PANICKED())
1008                 goto out;
1009
1010         wakeup_swapper = wakeupshlk(lk, file, line);
1011
1012 out:
1013         lockmgr_exit(flags, ilk, wakeup_swapper);
1014         return (0);
1015 }
1016
1017 static __noinline int
1018 lockmgr_xunlock_hard(struct lock *lk, uintptr_t x, u_int flags, struct lock_object *ilk,
1019     const char *file, int line)
1020 {
1021         uintptr_t tid, v;
1022         int wakeup_swapper = 0;
1023         u_int realexslp;
1024         int queue;
1025
1026         if (KERNEL_PANICKED())
1027                 goto out;
1028
1029         tid = (uintptr_t)curthread;
1030
1031         /*
1032          * As first option, treact the lock as if it has not
1033          * any waiter.
1034          * Fix-up the tid var if the lock has been disowned.
1035          */
1036         if (LK_HOLDER(x) == LK_KERNPROC)
1037                 tid = LK_KERNPROC;
1038
1039         /*
1040          * The lock is held in exclusive mode.
1041          * If the lock is recursed also, then unrecurse it.
1042          */
1043         if (lockmgr_xlocked_v(x) && lockmgr_recursed(lk)) {
1044                 LOCK_LOG2(lk, "%s: %p unrecursing", __func__, lk);
1045                 lk->lk_recurse--;
1046                 goto out;
1047         }
1048         if (tid != LK_KERNPROC)
1049                 LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk,
1050                     LOCKSTAT_WRITER);
1051
1052         if (x == tid && atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED))
1053                 goto out;
1054
1055         sleepq_lock(&lk->lock_object);
1056         x = lk->lk_lock;
1057         v = LK_UNLOCKED;
1058
1059         /*
1060          * If the lock has exclusive waiters, give them
1061          * preference in order to avoid deadlock with
1062          * shared runners up.
1063          * If interruptible sleeps left the exclusive queue
1064          * empty avoid a starvation for the threads sleeping
1065          * on the shared queue by giving them precedence
1066          * and cleaning up the exclusive waiters bit anyway.
1067          * Please note that lk_exslpfail count may be lying
1068          * about the real number of waiters with the
1069          * LK_SLEEPFAIL flag on because they may be used in
1070          * conjunction with interruptible sleeps so
1071          * lk_exslpfail might be considered an 'upper limit'
1072          * bound, including the edge cases.
1073          */
1074         MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1075         realexslp = sleepq_sleepcnt(&lk->lock_object, SQ_EXCLUSIVE_QUEUE);
1076         if ((x & LK_EXCLUSIVE_WAITERS) != 0 && realexslp != 0) {
1077                 if (lk->lk_exslpfail < realexslp) {
1078                         lk->lk_exslpfail = 0;
1079                         queue = SQ_EXCLUSIVE_QUEUE;
1080                         v |= (x & LK_SHARED_WAITERS);
1081                 } else {
1082                         lk->lk_exslpfail = 0;
1083                         LOCK_LOG2(lk,
1084                             "%s: %p has only LK_SLEEPFAIL sleepers",
1085                             __func__, lk);
1086                         LOCK_LOG2(lk,
1087                             "%s: %p waking up threads on the exclusive queue",
1088                             __func__, lk);
1089                         wakeup_swapper = sleepq_broadcast(&lk->lock_object,
1090                             SLEEPQ_LK, 0, SQ_EXCLUSIVE_QUEUE);
1091                         queue = SQ_SHARED_QUEUE;
1092                 }
1093         } else {
1094
1095                 /*
1096                  * Exclusive waiters sleeping with LK_SLEEPFAIL
1097                  * on and using interruptible sleeps/timeout
1098                  * may have left spourious lk_exslpfail counts
1099                  * on, so clean it up anyway.
1100                  */
1101                 lk->lk_exslpfail = 0;
1102                 queue = SQ_SHARED_QUEUE;
1103         }
1104
1105         LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
1106             __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
1107             "exclusive");
1108         atomic_store_rel_ptr(&lk->lk_lock, v);
1109         wakeup_swapper |= sleepq_broadcast(&lk->lock_object, SLEEPQ_LK, 0, queue);
1110         sleepq_release(&lk->lock_object);
1111
1112 out:
1113         lockmgr_exit(flags, ilk, wakeup_swapper);
1114         return (0);
1115 }
1116
1117 int
1118 lockmgr_unlock_fast_path(struct lock *lk, u_int flags, struct lock_object *ilk)
1119 {
1120         struct lock_class *class;
1121         uintptr_t x, tid;
1122         const char *file;
1123         int line;
1124
1125         if (KERNEL_PANICKED())
1126                 return (0);
1127
1128         file = __FILE__;
1129         line = __LINE__;
1130
1131         _lockmgr_assert(lk, KA_LOCKED, file, line);
1132         x = lk->lk_lock;
1133         if (__predict_true(x & LK_SHARE) != 0) {
1134                 lockmgr_note_shared_release(lk, file, line);
1135                 if (lockmgr_sunlock_try(lk, &x)) {
1136                         LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
1137                 } else {
1138                         return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line));
1139                 }
1140         } else {
1141                 tid = (uintptr_t)curthread;
1142                 lockmgr_note_exclusive_release(lk, file, line);
1143                 if (!lockmgr_recursed(lk) &&
1144                     atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) {
1145                         LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_WRITER);
1146                 } else {
1147                         return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line));
1148                 }
1149         }
1150         if (__predict_false(flags & LK_INTERLOCK)) {
1151                 class = LOCK_CLASS(ilk);
1152                 class->lc_unlock(ilk);
1153         }
1154         return (0);
1155 }
1156
1157 /*
1158  * Lightweight entry points for common operations.
1159  *
1160  * Functionality is similar to sx locks, in that none of the additional lockmgr
1161  * features are supported. To be clear, these are NOT supported:
1162  * 1. shared locking disablement
1163  * 2. returning with an error after sleep
1164  * 3. unlocking the interlock
1165  *
1166  * If in doubt, use lockmgr_*_fast_path.
1167  */
1168 int
1169 lockmgr_slock(struct lock *lk, u_int flags, const char *file, int line)
1170 {
1171         uintptr_t x;
1172
1173         MPASS((flags & LK_TYPE_MASK) == LK_SHARED);
1174         MPASS((flags & LK_INTERLOCK) == 0);
1175         MPASS((lk->lock_object.lo_flags & LK_NOSHARE) == 0);
1176
1177         if (LK_CAN_WITNESS(flags))
1178                 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
1179                     file, line, NULL);
1180         if (__predict_true(lockmgr_slock_try(lk, &x, flags, true))) {
1181                 lockmgr_note_shared_acquire(lk, 0, 0, file, line, flags);
1182                 return (0);
1183         }
1184
1185         return (lockmgr_slock_hard(lk, flags, NULL, file, line, NULL));
1186 }
1187
1188 int
1189 lockmgr_xlock(struct lock *lk, u_int flags, const char *file, int line)
1190 {
1191         uintptr_t tid;
1192
1193         MPASS((flags & LK_TYPE_MASK) == LK_EXCLUSIVE);
1194         MPASS((flags & LK_INTERLOCK) == 0);
1195
1196         if (LK_CAN_WITNESS(flags))
1197                 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
1198                     LOP_EXCLUSIVE, file, line, NULL);
1199         tid = (uintptr_t)curthread;
1200         if (atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
1201                 lockmgr_note_exclusive_acquire(lk, 0, 0, file, line,
1202                     flags);
1203                 return (0);
1204         }
1205
1206         return (lockmgr_xlock_hard(lk, flags, NULL, file, line, NULL));
1207 }
1208
1209 int
1210 lockmgr_unlock(struct lock *lk)
1211 {
1212         uintptr_t x, tid;
1213         const char *file;
1214         int line;
1215
1216         file = __FILE__;
1217         line = __LINE__;
1218
1219         _lockmgr_assert(lk, KA_LOCKED, file, line);
1220         x = lk->lk_lock;
1221         if (__predict_true(x & LK_SHARE) != 0) {
1222                 lockmgr_note_shared_release(lk, file, line);
1223                 if (lockmgr_sunlock_try(lk, &x)) {
1224                         LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_READER);
1225                 } else {
1226                         return (lockmgr_sunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
1227                 }
1228         } else {
1229                 tid = (uintptr_t)curthread;
1230                 lockmgr_note_exclusive_release(lk, file, line);
1231                 if (!lockmgr_recursed(lk) &&
1232                     atomic_cmpset_rel_ptr(&lk->lk_lock, tid, LK_UNLOCKED)) {
1233                         LOCKSTAT_PROFILE_RELEASE_RWLOCK(lockmgr__release, lk, LOCKSTAT_WRITER);
1234                 } else {
1235                         return (lockmgr_xunlock_hard(lk, x, LK_RELEASE, NULL, file, line));
1236                 }
1237         }
1238         return (0);
1239 }
1240
1241 int
1242 __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
1243     const char *wmesg, int pri, int timo, const char *file, int line)
1244 {
1245         GIANT_DECLARE;
1246         struct lockmgr_wait lwa;
1247         struct lock_class *class;
1248         const char *iwmesg;
1249         uintptr_t tid, v, x;
1250         u_int op, realexslp;
1251         int error, ipri, itimo, queue, wakeup_swapper;
1252 #ifdef LOCK_PROFILING
1253         uint64_t waittime = 0;
1254         int contested = 0;
1255 #endif
1256
1257         if (KERNEL_PANICKED())
1258                 return (0);
1259
1260         error = 0;
1261         tid = (uintptr_t)curthread;
1262         op = (flags & LK_TYPE_MASK);
1263         iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg;
1264         ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri;
1265         itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo;
1266
1267         lwa.iwmesg = iwmesg;
1268         lwa.ipri = ipri;
1269         lwa.itimo = itimo;
1270
1271         MPASS((flags & ~LK_TOTAL_MASK) == 0);
1272         KASSERT((op & (op - 1)) == 0,
1273             ("%s: Invalid requested operation @ %s:%d", __func__, file, line));
1274         KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 ||
1275             (op != LK_DOWNGRADE && op != LK_RELEASE),
1276             ("%s: Invalid flags in regard of the operation desired @ %s:%d",
1277             __func__, file, line));
1278         KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
1279             ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
1280             __func__, file, line));
1281         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
1282             ("%s: idle thread %p on lockmgr %s @ %s:%d", __func__, curthread,
1283             lk->lock_object.lo_name, file, line));
1284
1285         class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
1286
1287         if (lk->lock_object.lo_flags & LK_NOSHARE) {
1288                 switch (op) {
1289                 case LK_SHARED:
1290                         op = LK_EXCLUSIVE;
1291                         break;
1292                 case LK_UPGRADE:
1293                 case LK_TRYUPGRADE:
1294                 case LK_DOWNGRADE:
1295                         _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED,
1296                             file, line);
1297                         if (flags & LK_INTERLOCK)
1298                                 class->lc_unlock(ilk);
1299                         return (0);
1300                 }
1301         }
1302
1303         wakeup_swapper = 0;
1304         switch (op) {
1305         case LK_SHARED:
1306                 return (lockmgr_slock_hard(lk, flags, ilk, file, line, &lwa));
1307                 break;
1308         case LK_UPGRADE:
1309         case LK_TRYUPGRADE:
1310                 return (lockmgr_upgrade(lk, flags, ilk, file, line, &lwa));
1311                 break;
1312         case LK_EXCLUSIVE:
1313                 return (lockmgr_xlock_hard(lk, flags, ilk, file, line, &lwa));
1314                 break;
1315         case LK_DOWNGRADE:
1316                 _lockmgr_assert(lk, KA_XLOCKED, file, line);
1317                 WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line);
1318
1319                 /*
1320                  * Panic if the lock is recursed.
1321                  */
1322                 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
1323                         if (flags & LK_INTERLOCK)
1324                                 class->lc_unlock(ilk);
1325                         panic("%s: downgrade a recursed lockmgr %s @ %s:%d\n",
1326                             __func__, iwmesg, file, line);
1327                 }
1328                 TD_SLOCKS_INC(curthread);
1329
1330                 /*
1331                  * In order to preserve waiters flags, just spin.
1332                  */
1333                 for (;;) {
1334                         x = lk->lk_lock;
1335                         MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1336                         x &= LK_ALL_WAITERS;
1337                         if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
1338                             LK_SHARERS_LOCK(1) | x))
1339                                 break;
1340                         cpu_spinwait();
1341                 }
1342                 LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line);
1343                 LOCKSTAT_RECORD0(lockmgr__downgrade, lk);
1344                 break;
1345         case LK_RELEASE:
1346                 _lockmgr_assert(lk, KA_LOCKED, file, line);
1347                 x = lk->lk_lock;
1348
1349                 if (__predict_true(x & LK_SHARE) != 0) {
1350                         lockmgr_note_shared_release(lk, file, line);
1351                         return (lockmgr_sunlock_hard(lk, x, flags, ilk, file, line));
1352                 } else {
1353                         lockmgr_note_exclusive_release(lk, file, line);
1354                         return (lockmgr_xunlock_hard(lk, x, flags, ilk, file, line));
1355                 }
1356                 break;
1357         case LK_DRAIN:
1358                 if (LK_CAN_WITNESS(flags))
1359                         WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
1360                             LOP_EXCLUSIVE, file, line, flags & LK_INTERLOCK ?
1361                             ilk : NULL);
1362
1363                 /*
1364                  * Trying to drain a lock we already own will result in a
1365                  * deadlock.
1366                  */
1367                 if (lockmgr_xlocked(lk)) {
1368                         if (flags & LK_INTERLOCK)
1369                                 class->lc_unlock(ilk);
1370                         panic("%s: draining %s with the lock held @ %s:%d\n",
1371                             __func__, iwmesg, file, line);
1372                 }
1373
1374                 for (;;) {
1375                         if (lk->lk_lock == LK_UNLOCKED &&
1376                             atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid))
1377                                 break;
1378
1379 #ifdef HWPMC_HOOKS
1380                         PMC_SOFT_CALL( , , lock, failed);
1381 #endif
1382                         lock_profile_obtain_lock_failed(&lk->lock_object,
1383                             &contested, &waittime);
1384
1385                         /*
1386                          * If the lock is expected to not sleep just give up
1387                          * and return.
1388                          */
1389                         if (LK_TRYOP(flags)) {
1390                                 LOCK_LOG2(lk, "%s: %p fails the try operation",
1391                                     __func__, lk);
1392                                 error = EBUSY;
1393                                 break;
1394                         }
1395
1396                         /*
1397                          * Acquire the sleepqueue chain lock because we
1398                          * probabilly will need to manipulate waiters flags.
1399                          */
1400                         sleepq_lock(&lk->lock_object);
1401                         x = lk->lk_lock;
1402
1403                         /*
1404                          * if the lock has been released while we spun on
1405                          * the sleepqueue chain lock just try again.
1406                          */
1407                         if (x == LK_UNLOCKED) {
1408                                 sleepq_release(&lk->lock_object);
1409                                 continue;
1410                         }
1411
1412                         v = x & (LK_ALL_WAITERS | LK_EXCLUSIVE_SPINNERS);
1413                         if ((x & ~v) == LK_UNLOCKED) {
1414                                 v = (x & ~LK_EXCLUSIVE_SPINNERS);
1415
1416                                 /*
1417                                  * If interruptible sleeps left the exclusive
1418                                  * queue empty avoid a starvation for the
1419                                  * threads sleeping on the shared queue by
1420                                  * giving them precedence and cleaning up the
1421                                  * exclusive waiters bit anyway.
1422                                  * Please note that lk_exslpfail count may be
1423                                  * lying about the real number of waiters with
1424                                  * the LK_SLEEPFAIL flag on because they may
1425                                  * be used in conjunction with interruptible
1426                                  * sleeps so lk_exslpfail might be considered
1427                                  * an 'upper limit' bound, including the edge
1428                                  * cases.
1429                                  */
1430                                 if (v & LK_EXCLUSIVE_WAITERS) {
1431                                         queue = SQ_EXCLUSIVE_QUEUE;
1432                                         v &= ~LK_EXCLUSIVE_WAITERS;
1433                                 } else {
1434
1435                                         /*
1436                                          * Exclusive waiters sleeping with
1437                                          * LK_SLEEPFAIL on and using
1438                                          * interruptible sleeps/timeout may
1439                                          * have left spourious lk_exslpfail
1440                                          * counts on, so clean it up anyway.
1441                                          */
1442                                         MPASS(v & LK_SHARED_WAITERS);
1443                                         lk->lk_exslpfail = 0;
1444                                         queue = SQ_SHARED_QUEUE;
1445                                         v &= ~LK_SHARED_WAITERS;
1446                                 }
1447                                 if (queue == SQ_EXCLUSIVE_QUEUE) {
1448                                         realexslp =
1449                                             sleepq_sleepcnt(&lk->lock_object,
1450                                             SQ_EXCLUSIVE_QUEUE);
1451                                         if (lk->lk_exslpfail >= realexslp) {
1452                                                 lk->lk_exslpfail = 0;
1453                                                 queue = SQ_SHARED_QUEUE;
1454                                                 v &= ~LK_SHARED_WAITERS;
1455                                                 if (realexslp != 0) {
1456                                                         LOCK_LOG2(lk,
1457                                         "%s: %p has only LK_SLEEPFAIL sleepers",
1458                                                             __func__, lk);
1459                                                         LOCK_LOG2(lk,
1460                         "%s: %p waking up threads on the exclusive queue",
1461                                                             __func__, lk);
1462                                                         wakeup_swapper =
1463                                                             sleepq_broadcast(
1464                                                             &lk->lock_object,
1465                                                             SLEEPQ_LK, 0,
1466                                                             SQ_EXCLUSIVE_QUEUE);
1467                                                 }
1468                                         } else
1469                                                 lk->lk_exslpfail = 0;
1470                                 }
1471                                 if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) {
1472                                         sleepq_release(&lk->lock_object);
1473                                         continue;
1474                                 }
1475                                 LOCK_LOG3(lk,
1476                                 "%s: %p waking up all threads on the %s queue",
1477                                     __func__, lk, queue == SQ_SHARED_QUEUE ?
1478                                     "shared" : "exclusive");
1479                                 wakeup_swapper |= sleepq_broadcast(
1480                                     &lk->lock_object, SLEEPQ_LK, 0, queue);
1481
1482                                 /*
1483                                  * If shared waiters have been woken up we need
1484                                  * to wait for one of them to acquire the lock
1485                                  * before to set the exclusive waiters in
1486                                  * order to avoid a deadlock.
1487                                  */
1488                                 if (queue == SQ_SHARED_QUEUE) {
1489                                         for (v = lk->lk_lock;
1490                                             (v & LK_SHARE) && !LK_SHARERS(v);
1491                                             v = lk->lk_lock)
1492                                                 cpu_spinwait();
1493                                 }
1494                         }
1495
1496                         /*
1497                          * Try to set the LK_EXCLUSIVE_WAITERS flag.  If we
1498                          * fail, loop back and retry.
1499                          */
1500                         if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
1501                                 if (!atomic_cmpset_ptr(&lk->lk_lock, x,
1502                                     x | LK_EXCLUSIVE_WAITERS)) {
1503                                         sleepq_release(&lk->lock_object);
1504                                         continue;
1505                                 }
1506                                 LOCK_LOG2(lk, "%s: %p set drain waiters flag",
1507                                     __func__, lk);
1508                         }
1509
1510                         /*
1511                          * As far as we have been unable to acquire the
1512                          * exclusive lock and the exclusive waiters flag
1513                          * is set, we will sleep.
1514                          */
1515                         if (flags & LK_INTERLOCK) {
1516                                 class->lc_unlock(ilk);
1517                                 flags &= ~LK_INTERLOCK;
1518                         }
1519                         GIANT_SAVE();
1520                         sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK,
1521                             SQ_EXCLUSIVE_QUEUE);
1522                         sleepq_wait(&lk->lock_object, ipri & PRIMASK);
1523                         GIANT_RESTORE();
1524                         LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
1525                             __func__, lk);
1526                 }
1527
1528                 if (error == 0) {
1529                         lock_profile_obtain_lock_success(&lk->lock_object,
1530                             contested, waittime, file, line);
1531                         LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0,
1532                             lk->lk_recurse, file, line);
1533                         WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
1534                             LK_TRYWIT(flags), file, line);
1535                         TD_LOCKS_INC(curthread);
1536                         STACK_SAVE(lk);
1537                 }
1538                 break;
1539         default:
1540                 if (flags & LK_INTERLOCK)
1541                         class->lc_unlock(ilk);
1542                 panic("%s: unknown lockmgr request 0x%x\n", __func__, op);
1543         }
1544
1545         if (flags & LK_INTERLOCK)
1546                 class->lc_unlock(ilk);
1547         if (wakeup_swapper)
1548                 kick_proc0();
1549
1550         return (error);
1551 }
1552
1553 void
1554 _lockmgr_disown(struct lock *lk, const char *file, int line)
1555 {
1556         uintptr_t tid, x;
1557
1558         if (SCHEDULER_STOPPED())
1559                 return;
1560
1561         tid = (uintptr_t)curthread;
1562         _lockmgr_assert(lk, KA_XLOCKED, file, line);
1563
1564         /*
1565          * Panic if the lock is recursed.
1566          */
1567         if (lockmgr_xlocked(lk) && lockmgr_recursed(lk))
1568                 panic("%s: disown a recursed lockmgr @ %s:%d\n",
1569                     __func__,  file, line);
1570
1571         /*
1572          * If the owner is already LK_KERNPROC just skip the whole operation.
1573          */
1574         if (LK_HOLDER(lk->lk_lock) != tid)
1575                 return;
1576         lock_profile_release_lock(&lk->lock_object);
1577         LOCKSTAT_RECORD1(lockmgr__disown, lk, LOCKSTAT_WRITER);
1578         LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line);
1579         WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
1580         TD_LOCKS_DEC(curthread);
1581         STACK_SAVE(lk);
1582
1583         /*
1584          * In order to preserve waiters flags, just spin.
1585          */
1586         for (;;) {
1587                 x = lk->lk_lock;
1588                 MPASS((x & LK_EXCLUSIVE_SPINNERS) == 0);
1589                 x &= LK_ALL_WAITERS;
1590                 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
1591                     LK_KERNPROC | x))
1592                         return;
1593                 cpu_spinwait();
1594         }
1595 }
1596
1597 void
1598 lockmgr_printinfo(const struct lock *lk)
1599 {
1600         struct thread *td;
1601         uintptr_t x;
1602
1603         if (lk->lk_lock == LK_UNLOCKED)
1604                 printf("lock type %s: UNLOCKED\n", lk->lock_object.lo_name);
1605         else if (lk->lk_lock & LK_SHARE)
1606                 printf("lock type %s: SHARED (count %ju)\n",
1607                     lk->lock_object.lo_name,
1608                     (uintmax_t)LK_SHARERS(lk->lk_lock));
1609         else {
1610                 td = lockmgr_xholder(lk);
1611                 if (td == (struct thread *)LK_KERNPROC)
1612                         printf("lock type %s: EXCL by KERNPROC\n",
1613                             lk->lock_object.lo_name);
1614                 else
1615                         printf("lock type %s: EXCL by thread %p "
1616                             "(pid %d, %s, tid %d)\n", lk->lock_object.lo_name,
1617                             td, td->td_proc->p_pid, td->td_proc->p_comm,
1618                             td->td_tid);
1619         }
1620
1621         x = lk->lk_lock;
1622         if (x & LK_EXCLUSIVE_WAITERS)
1623                 printf(" with exclusive waiters pending\n");
1624         if (x & LK_SHARED_WAITERS)
1625                 printf(" with shared waiters pending\n");
1626         if (x & LK_EXCLUSIVE_SPINNERS)
1627                 printf(" with exclusive spinners pending\n");
1628
1629         STACK_PRINT(lk);
1630 }
1631
1632 int
1633 lockstatus(const struct lock *lk)
1634 {
1635         uintptr_t v, x;
1636         int ret;
1637
1638         ret = LK_SHARED;
1639         x = lk->lk_lock;
1640         v = LK_HOLDER(x);
1641
1642         if ((x & LK_SHARE) == 0) {
1643                 if (v == (uintptr_t)curthread || v == LK_KERNPROC)
1644                         ret = LK_EXCLUSIVE;
1645                 else
1646                         ret = LK_EXCLOTHER;
1647         } else if (x == LK_UNLOCKED)
1648                 ret = 0;
1649
1650         return (ret);
1651 }
1652
1653 #ifdef INVARIANT_SUPPORT
1654
1655 FEATURE(invariant_support,
1656     "Support for modules compiled with INVARIANTS option");
1657
1658 #ifndef INVARIANTS
1659 #undef  _lockmgr_assert
1660 #endif
1661
1662 void
1663 _lockmgr_assert(const struct lock *lk, int what, const char *file, int line)
1664 {
1665         int slocked = 0;
1666
1667         if (KERNEL_PANICKED())
1668                 return;
1669         switch (what) {
1670         case KA_SLOCKED:
1671         case KA_SLOCKED | KA_NOTRECURSED:
1672         case KA_SLOCKED | KA_RECURSED:
1673                 slocked = 1;
1674         case KA_LOCKED:
1675         case KA_LOCKED | KA_NOTRECURSED:
1676         case KA_LOCKED | KA_RECURSED:
1677 #ifdef WITNESS
1678
1679                 /*
1680                  * We cannot trust WITNESS if the lock is held in exclusive
1681                  * mode and a call to lockmgr_disown() happened.
1682                  * Workaround this skipping the check if the lock is held in
1683                  * exclusive mode even for the KA_LOCKED case.
1684                  */
1685                 if (slocked || (lk->lk_lock & LK_SHARE)) {
1686                         witness_assert(&lk->lock_object, what, file, line);
1687                         break;
1688                 }
1689 #endif
1690                 if (lk->lk_lock == LK_UNLOCKED ||
1691                     ((lk->lk_lock & LK_SHARE) == 0 && (slocked ||
1692                     (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk)))))
1693                         panic("Lock %s not %slocked @ %s:%d\n",
1694                             lk->lock_object.lo_name, slocked ? "share" : "",
1695                             file, line);
1696
1697                 if ((lk->lk_lock & LK_SHARE) == 0) {
1698                         if (lockmgr_recursed(lk)) {
1699                                 if (what & KA_NOTRECURSED)
1700                                         panic("Lock %s recursed @ %s:%d\n",
1701                                             lk->lock_object.lo_name, file,
1702                                             line);
1703                         } else if (what & KA_RECURSED)
1704                                 panic("Lock %s not recursed @ %s:%d\n",
1705                                     lk->lock_object.lo_name, file, line);
1706                 }
1707                 break;
1708         case KA_XLOCKED:
1709         case KA_XLOCKED | KA_NOTRECURSED:
1710         case KA_XLOCKED | KA_RECURSED:
1711                 if (!lockmgr_xlocked(lk) && !lockmgr_disowned(lk))
1712                         panic("Lock %s not exclusively locked @ %s:%d\n",
1713                             lk->lock_object.lo_name, file, line);
1714                 if (lockmgr_recursed(lk)) {
1715                         if (what & KA_NOTRECURSED)
1716                                 panic("Lock %s recursed @ %s:%d\n",
1717                                     lk->lock_object.lo_name, file, line);
1718                 } else if (what & KA_RECURSED)
1719                         panic("Lock %s not recursed @ %s:%d\n",
1720                             lk->lock_object.lo_name, file, line);
1721                 break;
1722         case KA_UNLOCKED:
1723                 if (lockmgr_xlocked(lk) || lockmgr_disowned(lk))
1724                         panic("Lock %s exclusively locked @ %s:%d\n",
1725                             lk->lock_object.lo_name, file, line);
1726                 break;
1727         default:
1728                 panic("Unknown lockmgr assertion: %d @ %s:%d\n", what, file,
1729                     line);
1730         }
1731 }
1732 #endif
1733
1734 #ifdef DDB
1735 int
1736 lockmgr_chain(struct thread *td, struct thread **ownerp)
1737 {
1738         const struct lock *lk;
1739
1740         lk = td->td_wchan;
1741
1742         if (LOCK_CLASS(&lk->lock_object) != &lock_class_lockmgr)
1743                 return (0);
1744         db_printf("blocked on lockmgr %s", lk->lock_object.lo_name);
1745         if (lk->lk_lock & LK_SHARE)
1746                 db_printf("SHARED (count %ju)\n",
1747                     (uintmax_t)LK_SHARERS(lk->lk_lock));
1748         else
1749                 db_printf("EXCL\n");
1750         *ownerp = lockmgr_xholder(lk);
1751
1752         return (1);
1753 }
1754
1755 static void
1756 db_show_lockmgr(const struct lock_object *lock)
1757 {
1758         struct thread *td;
1759         const struct lock *lk;
1760
1761         lk = (const struct lock *)lock;
1762
1763         db_printf(" state: ");
1764         if (lk->lk_lock == LK_UNLOCKED)
1765                 db_printf("UNLOCKED\n");
1766         else if (lk->lk_lock & LK_SHARE)
1767                 db_printf("SLOCK: %ju\n", (uintmax_t)LK_SHARERS(lk->lk_lock));
1768         else {
1769                 td = lockmgr_xholder(lk);
1770                 if (td == (struct thread *)LK_KERNPROC)
1771                         db_printf("XLOCK: LK_KERNPROC\n");
1772                 else
1773                         db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1774                             td->td_tid, td->td_proc->p_pid,
1775                             td->td_proc->p_comm);
1776                 if (lockmgr_recursed(lk))
1777                         db_printf(" recursed: %d\n", lk->lk_recurse);
1778         }
1779         db_printf(" waiters: ");
1780         switch (lk->lk_lock & LK_ALL_WAITERS) {
1781         case LK_SHARED_WAITERS:
1782                 db_printf("shared\n");
1783                 break;
1784         case LK_EXCLUSIVE_WAITERS:
1785                 db_printf("exclusive\n");
1786                 break;
1787         case LK_ALL_WAITERS:
1788                 db_printf("shared and exclusive\n");
1789                 break;
1790         default:
1791                 db_printf("none\n");
1792         }
1793         db_printf(" spinners: ");
1794         if (lk->lk_lock & LK_EXCLUSIVE_SPINNERS)
1795                 db_printf("exclusive\n");
1796         else
1797                 db_printf("none\n");
1798 }
1799 #endif