sys/kern/kern_sx.c

   1 /*-
   2  * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
   3  * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice(s), this list of conditions and the following disclaimer as
  11  *    the first lines of this file unmodified other than the possible
  12  *    addition of one or more copyright notices.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice(s), this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
  18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  20  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
  21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  23  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  24  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  27  * DAMAGE.
  28  */
  29
  30 /*
  31  * Shared/exclusive locks.  This implementation attempts to ensure
  32  * deterministic lock granting behavior, so that slocks and xlocks are
  33  * interleaved.
  34  *
  35  * Priority propagation will not generally raise the priority of lock holders,
  36  * so should not be relied upon in combination with sx locks.
  37  */
  38
  39 #include "opt_ddb.h"
  40 #include "opt_hwpmc_hooks.h"
  41 #include "opt_kdtrace.h"
  42 #include "opt_no_adaptive_sx.h"
  43
  44 #include <sys/cdefs.h>
  45 __FBSDID("$FreeBSD$");
  46
  47 #include <sys/param.h>
  48 #include <sys/systm.h>
  49 #include <sys/kdb.h>
  50 #include <sys/ktr.h>
  51 #include <sys/lock.h>
  52 #include <sys/mutex.h>
  53 #include <sys/proc.h>
  54 #include <sys/sleepqueue.h>
  55 #include <sys/sx.h>
  56 #include <sys/sysctl.h>
  57
  58 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  59 #include <machine/cpu.h>
  60 #endif
  61
  62 #ifdef DDB
  63 #include <ddb/ddb.h>
  64 #endif
  65
  66 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  67 #define ADAPTIVE_SX
  68 #endif
  69
  70 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
  71
  72 #ifdef HWPMC_HOOKS
  73 #include <sys/pmckern.h>
  74 PMC_SOFT_DECLARE( , , lock, failed);
  75 #endif
  76
  77 /* Handy macros for sleep queues. */
  78 #define SQ_EXCLUSIVE_QUEUE      0
  79 #define SQ_SHARED_QUEUE         1
  80
  81 #ifdef ADAPTIVE_SX
  82 #define ASX_RETRIES             10
  83 #define ASX_LOOPS               10000
  84 #endif
  85
  86 /*
  87  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  88  * drop Giant anytime we have to sleep or if we adaptively spin.
  89  */
  90 #define GIANT_DECLARE                                                   \
  91         int _giantcnt = 0;                                              \
  92         WITNESS_SAVE_DECL(Giant)                                        \
  93
  94 #define GIANT_SAVE() do {                                               \
  95         if (mtx_owned(&Giant)) {                                        \
  96                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  97                 while (mtx_owned(&Giant)) {                             \
  98                         _giantcnt++;                                    \
  99                         mtx_unlock(&Giant);                             \
 100                 }                                                       \
 101         }                                                               \
 102 } while (0)
 103
 104 #define GIANT_RESTORE() do {                                            \
 105         if (_giantcnt > 0) {                                            \
 106                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 107                 while (_giantcnt--)                                     \
 108                         mtx_lock(&Giant);                               \
 109                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 110         }                                                               \
 111 } while (0)
 112
 113 /*
 114  * Returns true if an exclusive lock is recursed.  It assumes
 115  * curthread currently has an exclusive lock.
 116  */
 117 #define sx_recurse              lock_object.lo_data
 118 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 119
 120 static void     assert_sx(struct lock_object *lock, int what);
 121 #ifdef DDB
 122 static void     db_show_sx(struct lock_object *lock);
 123 #endif
 124 static void     lock_sx(struct lock_object *lock, int how);
 125 #ifdef KDTRACE_HOOKS
 126 static int      owner_sx(struct lock_object *lock, struct thread **owner);
 127 #endif
 128 static int      unlock_sx(struct lock_object *lock);
 129
 130 struct lock_class lock_class_sx = {
 131         .lc_name = "sx",
 132         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 133         .lc_assert = assert_sx,
 134 #ifdef DDB
 135         .lc_ddb_show = db_show_sx,
 136 #endif
 137         .lc_lock = lock_sx,
 138         .lc_unlock = unlock_sx,
 139 #ifdef KDTRACE_HOOKS
 140         .lc_owner = owner_sx,
 141 #endif
 142 };
 143
 144 #ifndef INVARIANTS
 145 #define _sx_assert(sx, what, file, line)
 146 #endif
 147
 148 void
 149 assert_sx(struct lock_object *lock, int what)
 150 {
 151
 152         sx_assert((struct sx *)lock, what);
 153 }
 154
 155 void
 156 lock_sx(struct lock_object *lock, int how)
 157 {
 158         struct sx *sx;
 159
 160         sx = (struct sx *)lock;
 161         if (how)
 162                 sx_xlock(sx);
 163         else
 164                 sx_slock(sx);
 165 }
 166
 167 int
 168 unlock_sx(struct lock_object *lock)
 169 {
 170         struct sx *sx;
 171
 172         sx = (struct sx *)lock;
 173         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 174         if (sx_xlocked(sx)) {
 175                 sx_xunlock(sx);
 176                 return (1);
 177         } else {
 178                 sx_sunlock(sx);
 179                 return (0);
 180         }
 181 }
 182
 183 #ifdef KDTRACE_HOOKS
 184 int
 185 owner_sx(struct lock_object *lock, struct thread **owner)
 186 {
 187         struct sx *sx = (struct sx *)lock;
 188         uintptr_t x = sx->sx_lock;
 189
 190         *owner = (struct thread *)SX_OWNER(x);
 191         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 192             (*owner != NULL));
 193 }
 194 #endif
 195
 196 void
 197 sx_sysinit(void *arg)
 198 {
 199         struct sx_args *sargs = arg;
 200
 201         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 202 }
 203
 204 void
 205 sx_init_flags(struct sx *sx, const char *description, int opts)
 206 {
 207         int flags;
 208
 209         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 210             SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
 211         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 212             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 213             &sx->sx_lock));
 214
 215         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 216         if (opts & SX_DUPOK)
 217                 flags |= LO_DUPOK;
 218         if (opts & SX_NOPROFILE)
 219                 flags |= LO_NOPROFILE;
 220         if (!(opts & SX_NOWITNESS))
 221                 flags |= LO_WITNESS;
 222         if (opts & SX_RECURSE)
 223                 flags |= LO_RECURSABLE;
 224         if (opts & SX_QUIET)
 225                 flags |= LO_QUIET;
 226
 227         flags |= opts & SX_NOADAPTIVE;
 228         sx->sx_lock = SX_LOCK_UNLOCKED;
 229         sx->sx_recurse = 0;
 230         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 231 }
 232
 233 void
 234 sx_destroy(struct sx *sx)
 235 {
 236
 237         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 238         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 239         sx->sx_lock = SX_LOCK_DESTROYED;
 240         lock_destroy(&sx->lock_object);
 241 }
 242
 243 int
 244 _sx_slock(struct sx *sx, int opts, const char *file, int line)
 245 {
 246         int error = 0;
 247
 248         if (SCHEDULER_STOPPED())
 249                 return (0);
 250         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 251             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
 252             curthread, sx->lock_object.lo_name, file, line));
 253         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 254             ("sx_slock() of destroyed sx @ %s:%d", file, line));
 255         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
 256         error = __sx_slock(sx, opts, file, line);
 257         if (!error) {
 258                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
 259                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
 260                 curthread->td_locks++;
 261         }
 262
 263         return (error);
 264 }
 265
 266 int
 267 _sx_try_slock(struct sx *sx, const char *file, int line)
 268 {
 269         uintptr_t x;
 270
 271         if (SCHEDULER_STOPPED())
 272                 return (1);
 273
 274         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 275             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 276             curthread, sx->lock_object.lo_name, file, line));
 277
 278         for (;;) {
 279                 x = sx->sx_lock;
 280                 KASSERT(x != SX_LOCK_DESTROYED,
 281                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 282                 if (!(x & SX_LOCK_SHARED))
 283                         break;
 284                 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
 285                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 286                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 287                         curthread->td_locks++;
 288                         return (1);
 289                 }
 290         }
 291
 292         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 293         return (0);
 294 }
 295
 296 int
 297 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 298 {
 299         int error = 0;
 300
 301         if (SCHEDULER_STOPPED())
 302                 return (0);
 303         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 304             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 305             curthread, sx->lock_object.lo_name, file, line));
 306         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 307             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 308         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 309             line, NULL);
 310         error = __sx_xlock(sx, curthread, opts, file, line);
 311         if (!error) {
 312                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 313                     file, line);
 314                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 315                 curthread->td_locks++;
 316         }
 317
 318         return (error);
 319 }
 320
 321 int
 322 _sx_try_xlock(struct sx *sx, const char *file, int line)
 323 {
 324         int rval;
 325
 326         if (SCHEDULER_STOPPED())
 327                 return (1);
 328
 329         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 330             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 331             curthread, sx->lock_object.lo_name, file, line));
 332         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 333             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 334
 335         if (sx_xlocked(sx) &&
 336             (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 337                 sx->sx_recurse++;
 338                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 339                 rval = 1;
 340         } else
 341                 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
 342                     (uintptr_t)curthread);
 343         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 344         if (rval) {
 345                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 346                     file, line);
 347                 curthread->td_locks++;
 348         }
 349
 350         return (rval);
 351 }
 352
 353 void
 354 _sx_sunlock(struct sx *sx, const char *file, int line)
 355 {
 356
 357         if (SCHEDULER_STOPPED())
 358                 return;
 359         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 360             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
 361         _sx_assert(sx, SA_SLOCKED, file, line);
 362         curthread->td_locks--;
 363         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
 364         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
 365         __sx_sunlock(sx, file, line);
 366         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
 367 }
 368
 369 void
 370 _sx_xunlock(struct sx *sx, const char *file, int line)
 371 {
 372
 373         if (SCHEDULER_STOPPED())
 374                 return;
 375         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 376             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 377         _sx_assert(sx, SA_XLOCKED, file, line);
 378         curthread->td_locks--;
 379         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 380         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 381             line);
 382         if (!sx_recursed(sx))
 383                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
 384         __sx_xunlock(sx, curthread, file, line);
 385 }
 386
 387 /*
 388  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 389  * This will only succeed if this thread holds a single shared lock.
 390  * Return 1 if if the upgrade succeed, 0 otherwise.
 391  */
 392 int
 393 _sx_try_upgrade(struct sx *sx, const char *file, int line)
 394 {
 395         uintptr_t x;
 396         int success;
 397
 398         if (SCHEDULER_STOPPED())
 399                 return (1);
 400
 401         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 402             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 403         _sx_assert(sx, SA_SLOCKED, file, line);
 404
 405         /*
 406          * Try to switch from one shared lock to an exclusive lock.  We need
 407          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 408          * we will wake up the exclusive waiters when we drop the lock.
 409          */
 410         x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
 411         success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
 412             (uintptr_t)curthread | x);
 413         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 414         if (success) {
 415                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 416                     file, line);
 417                 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
 418         }
 419         return (success);
 420 }
 421
 422 /*
 423  * Downgrade an unrecursed exclusive lock into a single shared lock.
 424  */
 425 void
 426 _sx_downgrade(struct sx *sx, const char *file, int line)
 427 {
 428         uintptr_t x;
 429         int wakeup_swapper;
 430
 431         if (SCHEDULER_STOPPED())
 432                 return;
 433
 434         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 435             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 436         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 437 #ifndef INVARIANTS
 438         if (sx_recursed(sx))
 439                 panic("downgrade of a recursed lock");
 440 #endif
 441
 442         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 443
 444         /*
 445          * Try to switch from an exclusive lock with no shared waiters
 446          * to one sharer with no shared waiters.  If there are
 447          * exclusive waiters, we don't need to lock the sleep queue so
 448          * long as we preserve the flag.  We do one quick try and if
 449          * that fails we grab the sleepq lock to keep the flags from
 450          * changing and do it the slow way.
 451          *
 452          * We have to lock the sleep queue if there are shared waiters
 453          * so we can wake them up.
 454          */
 455         x = sx->sx_lock;
 456         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 457             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 458             (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 459                 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 460                 return;
 461         }
 462
 463         /*
 464          * Lock the sleep queue so we can read the waiters bits
 465          * without any races and wakeup any shared waiters.
 466          */
 467         sleepq_lock(&sx->lock_object);
 468
 469         /*
 470          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 471          * shared lock.  If there are any shared waiters, wake them up.
 472          */
 473         wakeup_swapper = 0;
 474         x = sx->sx_lock;
 475         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 476             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 477         if (x & SX_LOCK_SHARED_WAITERS)
 478                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 479                     0, SQ_SHARED_QUEUE);
 480         sleepq_release(&sx->lock_object);
 481
 482         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 483         LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
 484
 485         if (wakeup_swapper)
 486                 kick_proc0();
 487 }
 488
 489 /*
 490  * This function represents the so-called 'hard case' for sx_xlock
 491  * operation.  All 'easy case' failures are redirected to this.  Note
 492  * that ideally this would be a static function, but it needs to be
 493  * accessible from at least sx.h.
 494  */
 495 int
 496 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
 497     int line)
 498 {
 499         GIANT_DECLARE;
 500 #ifdef ADAPTIVE_SX
 501         volatile struct thread *owner;
 502         u_int i, spintries = 0;
 503 #endif
 504         uintptr_t x;
 505 #ifdef LOCK_PROFILING
 506         uint64_t waittime = 0;
 507         int contested = 0;
 508 #endif
 509         int error = 0;
 510 #ifdef  KDTRACE_HOOKS
 511         uint64_t spin_cnt = 0;
 512         uint64_t sleep_cnt = 0;
 513         int64_t sleep_time = 0;
 514 #endif
 515
 516         if (SCHEDULER_STOPPED())
 517                 return (0);
 518
 519         /* If we already hold an exclusive lock, then recurse. */
 520         if (sx_xlocked(sx)) {
 521                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 522             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 523                     sx->lock_object.lo_name, file, line));
 524                 sx->sx_recurse++;
 525                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 526                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 527                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 528                 return (0);
 529         }
 530
 531         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 532                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 533                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 534
 535         while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
 536 #ifdef KDTRACE_HOOKS
 537                 spin_cnt++;
 538 #endif
 539 #ifdef HWPMC_HOOKS
 540                 PMC_SOFT_CALL( , , lock, failed);
 541 #endif
 542                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 543                     &waittime);
 544 #ifdef ADAPTIVE_SX
 545                 /*
 546                  * If the lock is write locked and the owner is
 547                  * running on another CPU, spin until the owner stops
 548                  * running or the state of the lock changes.
 549                  */
 550                 x = sx->sx_lock;
 551                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 552                         if ((x & SX_LOCK_SHARED) == 0) {
 553                                 x = SX_OWNER(x);
 554                                 owner = (struct thread *)x;
 555                                 if (TD_IS_RUNNING(owner)) {
 556                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 557                                                 CTR3(KTR_LOCK,
 558                                             "%s: spinning on %p held by %p",
 559                                                     __func__, sx, owner);
 560                                         GIANT_SAVE();
 561                                         while (SX_OWNER(sx->sx_lock) == x &&
 562                                             TD_IS_RUNNING(owner)) {
 563                                                 cpu_spinwait();
 564 #ifdef KDTRACE_HOOKS
 565                                                 spin_cnt++;
 566 #endif
 567                                         }
 568                                         continue;
 569                                 }
 570                         } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) {
 571                                 GIANT_SAVE();
 572                                 spintries++;
 573                                 for (i = 0; i < ASX_LOOPS; i++) {
 574                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 575                                                 CTR4(KTR_LOCK,
 576                                     "%s: shared spinning on %p with %u and %u",
 577                                                     __func__, sx, spintries, i);
 578                                         x = sx->sx_lock;
 579                                         if ((x & SX_LOCK_SHARED) == 0 ||
 580                                             SX_SHARERS(x) == 0)
 581                                                 break;
 582                                         cpu_spinwait();
 583 #ifdef KDTRACE_HOOKS
 584                                         spin_cnt++;
 585 #endif
 586                                 }
 587                                 if (i != ASX_LOOPS)
 588                                         continue;
 589                         }
 590                 }
 591 #endif
 592
 593                 sleepq_lock(&sx->lock_object);
 594                 x = sx->sx_lock;
 595
 596                 /*
 597                  * If the lock was released while spinning on the
 598                  * sleep queue chain lock, try again.
 599                  */
 600                 if (x == SX_LOCK_UNLOCKED) {
 601                         sleepq_release(&sx->lock_object);
 602                         continue;
 603                 }
 604
 605 #ifdef ADAPTIVE_SX
 606                 /*
 607                  * The current lock owner might have started executing
 608                  * on another CPU (or the lock could have changed
 609                  * owners) while we were waiting on the sleep queue
 610                  * chain lock.  If so, drop the sleep queue lock and try
 611                  * again.
 612                  */
 613                 if (!(x & SX_LOCK_SHARED) &&
 614                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 615                         owner = (struct thread *)SX_OWNER(x);
 616                         if (TD_IS_RUNNING(owner)) {
 617                                 sleepq_release(&sx->lock_object);
 618                                 continue;
 619                         }
 620                 }
 621 #endif
 622
 623                 /*
 624                  * If an exclusive lock was released with both shared
 625                  * and exclusive waiters and a shared waiter hasn't
 626                  * woken up and acquired the lock yet, sx_lock will be
 627                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 628                  * If we see that value, try to acquire it once.  Note
 629                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 630                  * as there are other exclusive waiters still.  If we
 631                  * fail, restart the loop.
 632                  */
 633                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
 634                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
 635                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
 636                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
 637                                 sleepq_release(&sx->lock_object);
 638                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 639                                     __func__, sx);
 640                                 break;
 641                         }
 642                         sleepq_release(&sx->lock_object);
 643                         continue;
 644                 }
 645
 646                 /*
 647                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 648                  * than loop back and retry.
 649                  */
 650                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 651                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 652                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 653                                 sleepq_release(&sx->lock_object);
 654                                 continue;
 655                         }
 656                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 657                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 658                                     __func__, sx);
 659                 }
 660
 661                 /*
 662                  * Since we have been unable to acquire the exclusive
 663                  * lock and the exclusive waiters flag is set, we have
 664                  * to sleep.
 665                  */
 666                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 667                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 668                             __func__, sx);
 669
 670 #ifdef KDTRACE_HOOKS
 671                 sleep_time -= lockstat_nsecs();
 672 #endif
 673                 GIANT_SAVE();
 674                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 675                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 676                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 677                 if (!(opts & SX_INTERRUPTIBLE))
 678                         sleepq_wait(&sx->lock_object, 0);
 679                 else
 680                         error = sleepq_wait_sig(&sx->lock_object, 0);
 681 #ifdef KDTRACE_HOOKS
 682                 sleep_time += lockstat_nsecs();
 683                 sleep_cnt++;
 684 #endif
 685                 if (error) {
 686                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 687                                 CTR2(KTR_LOCK,
 688                         "%s: interruptible sleep by %p suspended by signal",
 689                                     __func__, sx);
 690                         break;
 691                 }
 692                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 693                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 694                             __func__, sx);
 695         }
 696
 697         GIANT_RESTORE();
 698         if (!error)
 699                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
 700                     contested, waittime, file, line);
 701 #ifdef KDTRACE_HOOKS
 702         if (sleep_time)
 703                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
 704         if (spin_cnt > sleep_cnt)
 705                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
 706 #endif
 707         return (error);
 708 }
 709
 710 /*
 711  * This function represents the so-called 'hard case' for sx_xunlock
 712  * operation.  All 'easy case' failures are redirected to this.  Note
 713  * that ideally this would be a static function, but it needs to be
 714  * accessible from at least sx.h.
 715  */
 716 void
 717 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
 718 {
 719         uintptr_t x;
 720         int queue, wakeup_swapper;
 721
 722         if (SCHEDULER_STOPPED())
 723                 return;
 724
 725         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
 726
 727         /* If the lock is recursed, then unrecurse one level. */
 728         if (sx_xlocked(sx) && sx_recursed(sx)) {
 729                 if ((--sx->sx_recurse) == 0)
 730                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 731                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 732                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 733                 return;
 734         }
 735         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
 736             SX_LOCK_EXCLUSIVE_WAITERS));
 737         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 738                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 739
 740         sleepq_lock(&sx->lock_object);
 741         x = SX_LOCK_UNLOCKED;
 742
 743         /*
 744          * The wake up algorithm here is quite simple and probably not
 745          * ideal.  It gives precedence to shared waiters if they are
 746          * present.  For this condition, we have to preserve the
 747          * state of the exclusive waiters flag.
 748          * If interruptible sleeps left the shared queue empty avoid a
 749          * starvation for the threads sleeping on the exclusive queue by giving
 750          * them precedence and cleaning up the shared waiters bit anyway.
 751          */
 752         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
 753             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
 754                 queue = SQ_SHARED_QUEUE;
 755                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
 756         } else
 757                 queue = SQ_EXCLUSIVE_QUEUE;
 758
 759         /* Wake up all the waiters for the specific queue. */
 760         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 761                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 762                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 763                     "exclusive");
 764         atomic_store_rel_ptr(&sx->sx_lock, x);
 765         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 766             queue);
 767         sleepq_release(&sx->lock_object);
 768         if (wakeup_swapper)
 769                 kick_proc0();
 770 }
 771
 772 /*
 773  * This function represents the so-called 'hard case' for sx_slock
 774  * operation.  All 'easy case' failures are redirected to this.  Note
 775  * that ideally this would be a static function, but it needs to be
 776  * accessible from at least sx.h.
 777  */
 778 int
 779 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
 780 {
 781         GIANT_DECLARE;
 782 #ifdef ADAPTIVE_SX
 783         volatile struct thread *owner;
 784 #endif
 785 #ifdef LOCK_PROFILING
 786         uint64_t waittime = 0;
 787         int contested = 0;
 788 #endif
 789         uintptr_t x;
 790         int error = 0;
 791 #ifdef KDTRACE_HOOKS
 792         uint64_t spin_cnt = 0;
 793         uint64_t sleep_cnt = 0;
 794         int64_t sleep_time = 0;
 795 #endif
 796
 797         if (SCHEDULER_STOPPED())
 798                 return (0);
 799
 800         /*
 801          * As with rwlocks, we don't make any attempt to try to block
 802          * shared locks once there is an exclusive waiter.
 803          */
 804         for (;;) {
 805 #ifdef KDTRACE_HOOKS
 806                 spin_cnt++;
 807 #endif
 808                 x = sx->sx_lock;
 809
 810                 /*
 811                  * If no other thread has an exclusive lock then try to bump up
 812                  * the count of sharers.  Since we have to preserve the state
 813                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 814                  * shared lock loop back and retry.
 815                  */
 816                 if (x & SX_LOCK_SHARED) {
 817                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
 818                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
 819                             x + SX_ONE_SHARER)) {
 820                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 821                                         CTR4(KTR_LOCK,
 822                                             "%s: %p succeed %p -> %p", __func__,
 823                                             sx, (void *)x,
 824                                             (void *)(x + SX_ONE_SHARER));
 825                                 break;
 826                         }
 827                         continue;
 828                 }
 829 #ifdef HWPMC_HOOKS
 830                 PMC_SOFT_CALL( , , lock, failed);
 831 #endif
 832                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 833                     &waittime);
 834
 835 #ifdef ADAPTIVE_SX
 836                 /*
 837                  * If the owner is running on another CPU, spin until
 838                  * the owner stops running or the state of the lock
 839                  * changes.
 840                  */
 841                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 842                         x = SX_OWNER(x);
 843                         owner = (struct thread *)x;
 844                         if (TD_IS_RUNNING(owner)) {
 845                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 846                                         CTR3(KTR_LOCK,
 847                                             "%s: spinning on %p held by %p",
 848                                             __func__, sx, owner);
 849                                 GIANT_SAVE();
 850                                 while (SX_OWNER(sx->sx_lock) == x &&
 851                                     TD_IS_RUNNING(owner)) {
 852 #ifdef KDTRACE_HOOKS
 853                                         spin_cnt++;
 854 #endif
 855                                         cpu_spinwait();
 856                                 }
 857                                 continue;
 858                         }
 859                 }
 860 #endif
 861
 862                 /*
 863                  * Some other thread already has an exclusive lock, so
 864                  * start the process of blocking.
 865                  */
 866                 sleepq_lock(&sx->lock_object);
 867                 x = sx->sx_lock;
 868
 869                 /*
 870                  * The lock could have been released while we spun.
 871                  * In this case loop back and retry.
 872                  */
 873                 if (x & SX_LOCK_SHARED) {
 874                         sleepq_release(&sx->lock_object);
 875                         continue;
 876                 }
 877
 878 #ifdef ADAPTIVE_SX
 879                 /*
 880                  * If the owner is running on another CPU, spin until
 881                  * the owner stops running or the state of the lock
 882                  * changes.
 883                  */
 884                 if (!(x & SX_LOCK_SHARED) &&
 885                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 886                         owner = (struct thread *)SX_OWNER(x);
 887                         if (TD_IS_RUNNING(owner)) {
 888                                 sleepq_release(&sx->lock_object);
 889                                 continue;
 890                         }
 891                 }
 892 #endif
 893
 894                 /*
 895                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
 896                  * fail to set it drop the sleep queue lock and loop
 897                  * back.
 898                  */
 899                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
 900                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 901                             x | SX_LOCK_SHARED_WAITERS)) {
 902                                 sleepq_release(&sx->lock_object);
 903                                 continue;
 904                         }
 905                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 906                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
 907                                     __func__, sx);
 908                 }
 909
 910                 /*
 911                  * Since we have been unable to acquire the shared lock,
 912                  * we have to sleep.
 913                  */
 914                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 915                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 916                             __func__, sx);
 917
 918 #ifdef KDTRACE_HOOKS
 919                 sleep_time -= lockstat_nsecs();
 920 #endif
 921                 GIANT_SAVE();
 922                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 923                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 924                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
 925                 if (!(opts & SX_INTERRUPTIBLE))
 926                         sleepq_wait(&sx->lock_object, 0);
 927                 else
 928                         error = sleepq_wait_sig(&sx->lock_object, 0);
 929 #ifdef KDTRACE_HOOKS
 930                 sleep_time += lockstat_nsecs();
 931                 sleep_cnt++;
 932 #endif
 933                 if (error) {
 934                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 935                                 CTR2(KTR_LOCK,
 936                         "%s: interruptible sleep by %p suspended by signal",
 937                                     __func__, sx);
 938                         break;
 939                 }
 940                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 941                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 942                             __func__, sx);
 943         }
 944         if (error == 0)
 945                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
 946                     contested, waittime, file, line);
 947 #ifdef KDTRACE_HOOKS
 948         if (sleep_time)
 949                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
 950         if (spin_cnt > sleep_cnt)
 951                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
 952 #endif
 953         GIANT_RESTORE();
 954         return (error);
 955 }
 956
 957 /*
 958  * This function represents the so-called 'hard case' for sx_sunlock
 959  * operation.  All 'easy case' failures are redirected to this.  Note
 960  * that ideally this would be a static function, but it needs to be
 961  * accessible from at least sx.h.
 962  */
 963 void
 964 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
 965 {
 966         uintptr_t x;
 967         int wakeup_swapper;
 968
 969         if (SCHEDULER_STOPPED())
 970                 return;
 971
 972         for (;;) {
 973                 x = sx->sx_lock;
 974
 975                 /*
 976                  * We should never have sharers while at least one thread
 977                  * holds a shared lock.
 978                  */
 979                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
 980                     ("%s: waiting sharers", __func__));
 981
 982                 /*
 983                  * See if there is more than one shared lock held.  If
 984                  * so, just drop one and return.
 985                  */
 986                 if (SX_SHARERS(x) > 1) {
 987                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
 988                             x - SX_ONE_SHARER)) {
 989                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 990                                         CTR4(KTR_LOCK,
 991                                             "%s: %p succeeded %p -> %p",
 992                                             __func__, sx, (void *)x,
 993                                             (void *)(x - SX_ONE_SHARER));
 994                                 break;
 995                         }
 996                         continue;
 997                 }
 998
 999                 /*
1000                  * If there aren't any waiters for an exclusive lock,
1001                  * then try to drop it quickly.
1002                  */
1003                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1004                         MPASS(x == SX_SHARERS_LOCK(1));
1005                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1006                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1007                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1008                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
1009                                             __func__, sx);
1010                                 break;
1011                         }
1012                         continue;
1013                 }
1014
1015                 /*
1016                  * At this point, there should just be one sharer with
1017                  * exclusive waiters.
1018                  */
1019                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1020
1021                 sleepq_lock(&sx->lock_object);
1022
1023                 /*
1024                  * Wake up semantic here is quite simple:
1025                  * Just wake up all the exclusive waiters.
1026                  * Note that the state of the lock could have changed,
1027                  * so if it fails loop back and retry.
1028                  */
1029                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1030                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1031                     SX_LOCK_UNLOCKED)) {
1032                         sleepq_release(&sx->lock_object);
1033                         continue;
1034                 }
1035                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1036                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1037                             "exclusive queue", __func__, sx);
1038                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1039                     0, SQ_EXCLUSIVE_QUEUE);
1040                 sleepq_release(&sx->lock_object);
1041                 if (wakeup_swapper)
1042                         kick_proc0();
1043                 break;
1044         }
1045 }
1046
1047 #ifdef INVARIANT_SUPPORT
1048 #ifndef INVARIANTS
1049 #undef  _sx_assert
1050 #endif
1051
1052 /*
1053  * In the non-WITNESS case, sx_assert() can only detect that at least
1054  * *some* thread owns an slock, but it cannot guarantee that *this*
1055  * thread owns an slock.
1056  */
1057 void
1058 _sx_assert(struct sx *sx, int what, const char *file, int line)
1059 {
1060 #ifndef WITNESS
1061         int slocked = 0;
1062 #endif
1063
1064         if (panicstr != NULL)
1065                 return;
1066         switch (what) {
1067         case SA_SLOCKED:
1068         case SA_SLOCKED | SA_NOTRECURSED:
1069         case SA_SLOCKED | SA_RECURSED:
1070 #ifndef WITNESS
1071                 slocked = 1;
1072                 /* FALLTHROUGH */
1073 #endif
1074         case SA_LOCKED:
1075         case SA_LOCKED | SA_NOTRECURSED:
1076         case SA_LOCKED | SA_RECURSED:
1077 #ifdef WITNESS
1078                 witness_assert(&sx->lock_object, what, file, line);
1079 #else
1080                 /*
1081                  * If some other thread has an exclusive lock or we
1082                  * have one and are asserting a shared lock, fail.
1083                  * Also, if no one has a lock at all, fail.
1084                  */
1085                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1086                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1087                     sx_xholder(sx) != curthread)))
1088                         panic("Lock %s not %slocked @ %s:%d\n",
1089                             sx->lock_object.lo_name, slocked ? "share " : "",
1090                             file, line);
1091
1092                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1093                         if (sx_recursed(sx)) {
1094                                 if (what & SA_NOTRECURSED)
1095                                         panic("Lock %s recursed @ %s:%d\n",
1096                                             sx->lock_object.lo_name, file,
1097                                             line);
1098                         } else if (what & SA_RECURSED)
1099                                 panic("Lock %s not recursed @ %s:%d\n",
1100                                     sx->lock_object.lo_name, file, line);
1101                 }
1102 #endif
1103                 break;
1104         case SA_XLOCKED:
1105         case SA_XLOCKED | SA_NOTRECURSED:
1106         case SA_XLOCKED | SA_RECURSED:
1107                 if (sx_xholder(sx) != curthread)
1108                         panic("Lock %s not exclusively locked @ %s:%d\n",
1109                             sx->lock_object.lo_name, file, line);
1110                 if (sx_recursed(sx)) {
1111                         if (what & SA_NOTRECURSED)
1112                                 panic("Lock %s recursed @ %s:%d\n",
1113                                     sx->lock_object.lo_name, file, line);
1114                 } else if (what & SA_RECURSED)
1115                         panic("Lock %s not recursed @ %s:%d\n",
1116                             sx->lock_object.lo_name, file, line);
1117                 break;
1118         case SA_UNLOCKED:
1119 #ifdef WITNESS
1120                 witness_assert(&sx->lock_object, what, file, line);
1121 #else
1122                 /*
1123                  * If we hold an exclusve lock fail.  We can't
1124                  * reliably check to see if we hold a shared lock or
1125                  * not.
1126                  */
1127                 if (sx_xholder(sx) == curthread)
1128                         panic("Lock %s exclusively locked @ %s:%d\n",
1129                             sx->lock_object.lo_name, file, line);
1130 #endif
1131                 break;
1132         default:
1133                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1134                     line);
1135         }
1136 }
1137 #endif  /* INVARIANT_SUPPORT */
1138
1139 #ifdef DDB
1140 static void
1141 db_show_sx(struct lock_object *lock)
1142 {
1143         struct thread *td;
1144         struct sx *sx;
1145
1146         sx = (struct sx *)lock;
1147
1148         db_printf(" state: ");
1149         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1150                 db_printf("UNLOCKED\n");
1151         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1152                 db_printf("DESTROYED\n");
1153                 return;
1154         } else if (sx->sx_lock & SX_LOCK_SHARED)
1155                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1156         else {
1157                 td = sx_xholder(sx);
1158                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1159                     td->td_tid, td->td_proc->p_pid, td->td_name);
1160                 if (sx_recursed(sx))
1161                         db_printf(" recursed: %d\n", sx->sx_recurse);
1162         }
1163
1164         db_printf(" waiters: ");
1165         switch(sx->sx_lock &
1166             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1167         case SX_LOCK_SHARED_WAITERS:
1168                 db_printf("shared\n");
1169                 break;
1170         case SX_LOCK_EXCLUSIVE_WAITERS:
1171                 db_printf("exclusive\n");
1172                 break;
1173         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1174                 db_printf("exclusive and shared\n");
1175                 break;
1176         default:
1177                 db_printf("none\n");
1178         }
1179 }
1180
1181 /*
1182  * Check to see if a thread that is blocked on a sleep queue is actually
1183  * blocked on an sx lock.  If so, output some details and return true.
1184  * If the lock has an exclusive owner, return that in *ownerp.
1185  */
1186 int
1187 sx_chain(struct thread *td, struct thread **ownerp)
1188 {
1189         struct sx *sx;
1190
1191         /*
1192          * Check to see if this thread is blocked on an sx lock.
1193          * First, we check the lock class.  If that is ok, then we
1194          * compare the lock name against the wait message.
1195          */
1196         sx = td->td_wchan;
1197         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1198             sx->lock_object.lo_name != td->td_wmesg)
1199                 return (0);
1200
1201         /* We think we have an sx lock, so output some details. */
1202         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1203         *ownerp = sx_xholder(sx);
1204         if (sx->sx_lock & SX_LOCK_SHARED)
1205                 db_printf("SLOCK (count %ju)\n",
1206                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1207         else
1208                 db_printf("XLOCK\n");
1209         return (1);
1210 }
1211 #endif