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/ktr.h>
  50 #include <sys/lock.h>
  51 #include <sys/mutex.h>
  52 #include <sys/proc.h>
  53 #include <sys/sleepqueue.h>
  54 #include <sys/sx.h>
  55 #include <sys/sysctl.h>
  56
  57 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  58 #include <machine/cpu.h>
  59 #endif
  60
  61 #ifdef DDB
  62 #include <ddb/ddb.h>
  63 #endif
  64
  65 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  66 #define ADAPTIVE_SX
  67 #endif
  68
  69 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
  70
  71 #ifdef HWPMC_HOOKS
  72 #include <sys/pmckern.h>
  73 PMC_SOFT_DECLARE( , , lock, failed);
  74 #endif
  75
  76 /* Handy macros for sleep queues. */
  77 #define SQ_EXCLUSIVE_QUEUE      0
  78 #define SQ_SHARED_QUEUE         1
  79
  80 /*
  81  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  82  * drop Giant anytime we have to sleep or if we adaptively spin.
  83  */
  84 #define GIANT_DECLARE                                                   \
  85         int _giantcnt = 0;                                              \
  86         WITNESS_SAVE_DECL(Giant)                                        \
  87
  88 #define GIANT_SAVE() do {                                               \
  89         if (mtx_owned(&Giant)) {                                        \
  90                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  91                 while (mtx_owned(&Giant)) {                             \
  92                         _giantcnt++;                                    \
  93                         mtx_unlock(&Giant);                             \
  94                 }                                                       \
  95         }                                                               \
  96 } while (0)
  97
  98 #define GIANT_RESTORE() do {                                            \
  99         if (_giantcnt > 0) {                                            \
 100                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 101                 while (_giantcnt--)                                     \
 102                         mtx_lock(&Giant);                               \
 103                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 104         }                                                               \
 105 } while (0)
 106
 107 /*
 108  * Returns true if an exclusive lock is recursed.  It assumes
 109  * curthread currently has an exclusive lock.
 110  */
 111 #define sx_recurse              lock_object.lo_data
 112 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 113
 114 static void     assert_sx(const struct lock_object *lock, int what);
 115 #ifdef DDB
 116 static void     db_show_sx(const struct lock_object *lock);
 117 #endif
 118 static void     lock_sx(struct lock_object *lock, int how);
 119 #ifdef KDTRACE_HOOKS
 120 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 121 #endif
 122 static int      unlock_sx(struct lock_object *lock);
 123
 124 struct lock_class lock_class_sx = {
 125         .lc_name = "sx",
 126         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 127         .lc_assert = assert_sx,
 128 #ifdef DDB
 129         .lc_ddb_show = db_show_sx,
 130 #endif
 131         .lc_lock = lock_sx,
 132         .lc_unlock = unlock_sx,
 133 #ifdef KDTRACE_HOOKS
 134         .lc_owner = owner_sx,
 135 #endif
 136 };
 137
 138 #ifndef INVARIANTS
 139 #define _sx_assert(sx, what, file, line)
 140 #endif
 141
 142 #ifdef ADAPTIVE_SX
 143 static u_int asx_retries = 10;
 144 static u_int asx_loops = 10000;
 145 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
 146 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 147 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 148 #endif
 149
 150 void
 151 assert_sx(const struct lock_object *lock, int what)
 152 {
 153
 154         sx_assert((const struct sx *)lock, what);
 155 }
 156
 157 void
 158 lock_sx(struct lock_object *lock, int how)
 159 {
 160         struct sx *sx;
 161
 162         sx = (struct sx *)lock;
 163         if (how)
 164                 sx_xlock(sx);
 165         else
 166                 sx_slock(sx);
 167 }
 168
 169 int
 170 unlock_sx(struct lock_object *lock)
 171 {
 172         struct sx *sx;
 173
 174         sx = (struct sx *)lock;
 175         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 176         if (sx_xlocked(sx)) {
 177                 sx_xunlock(sx);
 178                 return (1);
 179         } else {
 180                 sx_sunlock(sx);
 181                 return (0);
 182         }
 183 }
 184
 185 #ifdef KDTRACE_HOOKS
 186 int
 187 owner_sx(const struct lock_object *lock, struct thread **owner)
 188 {
 189         const struct sx *sx = (const struct sx *)lock;
 190         uintptr_t x = sx->sx_lock;
 191
 192         *owner = (struct thread *)SX_OWNER(x);
 193         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 194             (*owner != NULL));
 195 }
 196 #endif
 197
 198 void
 199 sx_sysinit(void *arg)
 200 {
 201         struct sx_args *sargs = arg;
 202
 203         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 204 }
 205
 206 void
 207 sx_init_flags(struct sx *sx, const char *description, int opts)
 208 {
 209         int flags;
 210
 211         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 212             SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
 213         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 214             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 215             &sx->sx_lock));
 216
 217         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 218         if (opts & SX_DUPOK)
 219                 flags |= LO_DUPOK;
 220         if (opts & SX_NOPROFILE)
 221                 flags |= LO_NOPROFILE;
 222         if (!(opts & SX_NOWITNESS))
 223                 flags |= LO_WITNESS;
 224         if (opts & SX_RECURSE)
 225                 flags |= LO_RECURSABLE;
 226         if (opts & SX_QUIET)
 227                 flags |= LO_QUIET;
 228
 229         flags |= opts & SX_NOADAPTIVE;
 230         sx->sx_lock = SX_LOCK_UNLOCKED;
 231         sx->sx_recurse = 0;
 232         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 233 }
 234
 235 void
 236 sx_destroy(struct sx *sx)
 237 {
 238
 239         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 240         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 241         sx->sx_lock = SX_LOCK_DESTROYED;
 242         lock_destroy(&sx->lock_object);
 243 }
 244
 245 int
 246 _sx_slock(struct sx *sx, int opts, const char *file, int line)
 247 {
 248         int error = 0;
 249
 250         if (SCHEDULER_STOPPED())
 251                 return (0);
 252         KASSERT(!TD_IS_IDLETHREAD(curthread),
 253             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
 254             curthread, sx->lock_object.lo_name, file, line));
 255         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 256             ("sx_slock() of destroyed sx @ %s:%d", file, line));
 257         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
 258         error = __sx_slock(sx, opts, file, line);
 259         if (!error) {
 260                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
 261                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
 262                 curthread->td_locks++;
 263         }
 264
 265         return (error);
 266 }
 267
 268 int
 269 sx_try_slock_(struct sx *sx, const char *file, int line)
 270 {
 271         uintptr_t x;
 272
 273         if (SCHEDULER_STOPPED())
 274                 return (1);
 275
 276         KASSERT(!TD_IS_IDLETHREAD(curthread),
 277             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 278             curthread, sx->lock_object.lo_name, file, line));
 279
 280         for (;;) {
 281                 x = sx->sx_lock;
 282                 KASSERT(x != SX_LOCK_DESTROYED,
 283                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 284                 if (!(x & SX_LOCK_SHARED))
 285                         break;
 286                 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
 287                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 288                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 289                         curthread->td_locks++;
 290                         return (1);
 291                 }
 292         }
 293
 294         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 295         return (0);
 296 }
 297
 298 int
 299 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 300 {
 301         int error = 0;
 302
 303         if (SCHEDULER_STOPPED())
 304                 return (0);
 305         KASSERT(!TD_IS_IDLETHREAD(curthread),
 306             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 307             curthread, sx->lock_object.lo_name, file, line));
 308         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 309             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 310         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 311             line, NULL);
 312         error = __sx_xlock(sx, curthread, opts, file, line);
 313         if (!error) {
 314                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 315                     file, line);
 316                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 317                 curthread->td_locks++;
 318         }
 319
 320         return (error);
 321 }
 322
 323 int
 324 sx_try_xlock_(struct sx *sx, const char *file, int line)
 325 {
 326         int rval;
 327
 328         if (SCHEDULER_STOPPED())
 329                 return (1);
 330
 331         KASSERT(!TD_IS_IDLETHREAD(curthread),
 332             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 333             curthread, sx->lock_object.lo_name, file, line));
 334         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 335             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 336
 337         if (sx_xlocked(sx) &&
 338             (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 339                 sx->sx_recurse++;
 340                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 341                 rval = 1;
 342         } else
 343                 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
 344                     (uintptr_t)curthread);
 345         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 346         if (rval) {
 347                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 348                     file, line);
 349                 curthread->td_locks++;
 350         }
 351
 352         return (rval);
 353 }
 354
 355 void
 356 _sx_sunlock(struct sx *sx, const char *file, int line)
 357 {
 358
 359         if (SCHEDULER_STOPPED())
 360                 return;
 361         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 362             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
 363         _sx_assert(sx, SA_SLOCKED, file, line);
 364         curthread->td_locks--;
 365         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
 366         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
 367         __sx_sunlock(sx, file, line);
 368         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
 369 }
 370
 371 void
 372 _sx_xunlock(struct sx *sx, const char *file, int line)
 373 {
 374
 375         if (SCHEDULER_STOPPED())
 376                 return;
 377         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 378             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 379         _sx_assert(sx, SA_XLOCKED, file, line);
 380         curthread->td_locks--;
 381         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 382         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 383             line);
 384         if (!sx_recursed(sx))
 385                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
 386         __sx_xunlock(sx, curthread, file, line);
 387 }
 388
 389 /*
 390  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 391  * This will only succeed if this thread holds a single shared lock.
 392  * Return 1 if if the upgrade succeed, 0 otherwise.
 393  */
 394 int
 395 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 396 {
 397         uintptr_t x;
 398         int success;
 399
 400         if (SCHEDULER_STOPPED())
 401                 return (1);
 402
 403         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 404             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 405         _sx_assert(sx, SA_SLOCKED, file, line);
 406
 407         /*
 408          * Try to switch from one shared lock to an exclusive lock.  We need
 409          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 410          * we will wake up the exclusive waiters when we drop the lock.
 411          */
 412         x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
 413         success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
 414             (uintptr_t)curthread | x);
 415         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 416         if (success) {
 417                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 418                     file, line);
 419                 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
 420         }
 421         return (success);
 422 }
 423
 424 /*
 425  * Downgrade an unrecursed exclusive lock into a single shared lock.
 426  */
 427 void
 428 sx_downgrade_(struct sx *sx, const char *file, int line)
 429 {
 430         uintptr_t x;
 431         int wakeup_swapper;
 432
 433         if (SCHEDULER_STOPPED())
 434                 return;
 435
 436         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 437             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 438         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 439 #ifndef INVARIANTS
 440         if (sx_recursed(sx))
 441                 panic("downgrade of a recursed lock");
 442 #endif
 443
 444         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 445
 446         /*
 447          * Try to switch from an exclusive lock with no shared waiters
 448          * to one sharer with no shared waiters.  If there are
 449          * exclusive waiters, we don't need to lock the sleep queue so
 450          * long as we preserve the flag.  We do one quick try and if
 451          * that fails we grab the sleepq lock to keep the flags from
 452          * changing and do it the slow way.
 453          *
 454          * We have to lock the sleep queue if there are shared waiters
 455          * so we can wake them up.
 456          */
 457         x = sx->sx_lock;
 458         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 459             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 460             (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 461                 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 462                 return;
 463         }
 464
 465         /*
 466          * Lock the sleep queue so we can read the waiters bits
 467          * without any races and wakeup any shared waiters.
 468          */
 469         sleepq_lock(&sx->lock_object);
 470
 471         /*
 472          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 473          * shared lock.  If there are any shared waiters, wake them up.
 474          */
 475         wakeup_swapper = 0;
 476         x = sx->sx_lock;
 477         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 478             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 479         if (x & SX_LOCK_SHARED_WAITERS)
 480                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 481                     0, SQ_SHARED_QUEUE);
 482         sleepq_release(&sx->lock_object);
 483
 484         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 485         LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
 486
 487         if (wakeup_swapper)
 488                 kick_proc0();
 489 }
 490
 491 /*
 492  * This function represents the so-called 'hard case' for sx_xlock
 493  * operation.  All 'easy case' failures are redirected to this.  Note
 494  * that ideally this would be a static function, but it needs to be
 495  * accessible from at least sx.h.
 496  */
 497 int
 498 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
 499     int line)
 500 {
 501         GIANT_DECLARE;
 502 #ifdef ADAPTIVE_SX
 503         volatile struct thread *owner;
 504         u_int i, spintries = 0;
 505 #endif
 506         uintptr_t x;
 507 #ifdef LOCK_PROFILING
 508         uint64_t waittime = 0;
 509         int contested = 0;
 510 #endif
 511         int error = 0;
 512 #ifdef  KDTRACE_HOOKS
 513         uint64_t spin_cnt = 0;
 514         uint64_t sleep_cnt = 0;
 515         int64_t sleep_time = 0;
 516 #endif
 517
 518         if (SCHEDULER_STOPPED())
 519                 return (0);
 520
 521         /* If we already hold an exclusive lock, then recurse. */
 522         if (sx_xlocked(sx)) {
 523                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 524             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 525                     sx->lock_object.lo_name, file, line));
 526                 sx->sx_recurse++;
 527                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 528                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 529                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 530                 return (0);
 531         }
 532
 533         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 534                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 535                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 536
 537         while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
 538 #ifdef KDTRACE_HOOKS
 539                 spin_cnt++;
 540 #endif
 541 #ifdef HWPMC_HOOKS
 542                 PMC_SOFT_CALL( , , lock, failed);
 543 #endif
 544                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 545                     &waittime);
 546 #ifdef ADAPTIVE_SX
 547                 /*
 548                  * If the lock is write locked and the owner is
 549                  * running on another CPU, spin until the owner stops
 550                  * running or the state of the lock changes.
 551                  */
 552                 x = sx->sx_lock;
 553                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 554                         if ((x & SX_LOCK_SHARED) == 0) {
 555                                 x = SX_OWNER(x);
 556                                 owner = (struct thread *)x;
 557                                 if (TD_IS_RUNNING(owner)) {
 558                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 559                                                 CTR3(KTR_LOCK,
 560                                             "%s: spinning on %p held by %p",
 561                                                     __func__, sx, owner);
 562                                         GIANT_SAVE();
 563                                         while (SX_OWNER(sx->sx_lock) == x &&
 564                                             TD_IS_RUNNING(owner)) {
 565                                                 cpu_spinwait();
 566 #ifdef KDTRACE_HOOKS
 567                                                 spin_cnt++;
 568 #endif
 569                                         }
 570                                         continue;
 571                                 }
 572                         } else if (SX_SHARERS(x) && spintries < asx_retries) {
 573                                 GIANT_SAVE();
 574                                 spintries++;
 575                                 for (i = 0; i < asx_loops; i++) {
 576                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 577                                                 CTR4(KTR_LOCK,
 578                                     "%s: shared spinning on %p with %u and %u",
 579                                                     __func__, sx, spintries, i);
 580                                         x = sx->sx_lock;
 581                                         if ((x & SX_LOCK_SHARED) == 0 ||
 582                                             SX_SHARERS(x) == 0)
 583                                                 break;
 584                                         cpu_spinwait();
 585 #ifdef KDTRACE_HOOKS
 586                                         spin_cnt++;
 587 #endif
 588                                 }
 589                                 if (i != asx_loops)
 590                                         continue;
 591                         }
 592                 }
 593 #endif
 594
 595                 sleepq_lock(&sx->lock_object);
 596                 x = sx->sx_lock;
 597
 598                 /*
 599                  * If the lock was released while spinning on the
 600                  * sleep queue chain lock, try again.
 601                  */
 602                 if (x == SX_LOCK_UNLOCKED) {
 603                         sleepq_release(&sx->lock_object);
 604                         continue;
 605                 }
 606
 607 #ifdef ADAPTIVE_SX
 608                 /*
 609                  * The current lock owner might have started executing
 610                  * on another CPU (or the lock could have changed
 611                  * owners) while we were waiting on the sleep queue
 612                  * chain lock.  If so, drop the sleep queue lock and try
 613                  * again.
 614                  */
 615                 if (!(x & SX_LOCK_SHARED) &&
 616                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 617                         owner = (struct thread *)SX_OWNER(x);
 618                         if (TD_IS_RUNNING(owner)) {
 619                                 sleepq_release(&sx->lock_object);
 620                                 continue;
 621                         }
 622                 }
 623 #endif
 624
 625                 /*
 626                  * If an exclusive lock was released with both shared
 627                  * and exclusive waiters and a shared waiter hasn't
 628                  * woken up and acquired the lock yet, sx_lock will be
 629                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 630                  * If we see that value, try to acquire it once.  Note
 631                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 632                  * as there are other exclusive waiters still.  If we
 633                  * fail, restart the loop.
 634                  */
 635                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
 636                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
 637                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
 638                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
 639                                 sleepq_release(&sx->lock_object);
 640                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 641                                     __func__, sx);
 642                                 break;
 643                         }
 644                         sleepq_release(&sx->lock_object);
 645                         continue;
 646                 }
 647
 648                 /*
 649                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 650                  * than loop back and retry.
 651                  */
 652                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 653                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 654                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 655                                 sleepq_release(&sx->lock_object);
 656                                 continue;
 657                         }
 658                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 659                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 660                                     __func__, sx);
 661                 }
 662
 663                 /*
 664                  * Since we have been unable to acquire the exclusive
 665                  * lock and the exclusive waiters flag is set, we have
 666                  * to sleep.
 667                  */
 668                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 669                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 670                             __func__, sx);
 671
 672 #ifdef KDTRACE_HOOKS
 673                 sleep_time -= lockstat_nsecs();
 674 #endif
 675                 GIANT_SAVE();
 676                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 677                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 678                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 679                 if (!(opts & SX_INTERRUPTIBLE))
 680                         sleepq_wait(&sx->lock_object, 0);
 681                 else
 682                         error = sleepq_wait_sig(&sx->lock_object, 0);
 683 #ifdef KDTRACE_HOOKS
 684                 sleep_time += lockstat_nsecs();
 685                 sleep_cnt++;
 686 #endif
 687                 if (error) {
 688                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 689                                 CTR2(KTR_LOCK,
 690                         "%s: interruptible sleep by %p suspended by signal",
 691                                     __func__, sx);
 692                         break;
 693                 }
 694                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 695                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 696                             __func__, sx);
 697         }
 698
 699         GIANT_RESTORE();
 700         if (!error)
 701                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
 702                     contested, waittime, file, line);
 703 #ifdef KDTRACE_HOOKS
 704         if (sleep_time)
 705                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
 706         if (spin_cnt > sleep_cnt)
 707                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
 708 #endif
 709         return (error);
 710 }
 711
 712 /*
 713  * This function represents the so-called 'hard case' for sx_xunlock
 714  * operation.  All 'easy case' failures are redirected to this.  Note
 715  * that ideally this would be a static function, but it needs to be
 716  * accessible from at least sx.h.
 717  */
 718 void
 719 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
 720 {
 721         uintptr_t x;
 722         int queue, wakeup_swapper;
 723
 724         if (SCHEDULER_STOPPED())
 725                 return;
 726
 727         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
 728
 729         /* If the lock is recursed, then unrecurse one level. */
 730         if (sx_xlocked(sx) && sx_recursed(sx)) {
 731                 if ((--sx->sx_recurse) == 0)
 732                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 733                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 734                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 735                 return;
 736         }
 737         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
 738             SX_LOCK_EXCLUSIVE_WAITERS));
 739         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 740                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 741
 742         sleepq_lock(&sx->lock_object);
 743         x = SX_LOCK_UNLOCKED;
 744
 745         /*
 746          * The wake up algorithm here is quite simple and probably not
 747          * ideal.  It gives precedence to shared waiters if they are
 748          * present.  For this condition, we have to preserve the
 749          * state of the exclusive waiters flag.
 750          * If interruptible sleeps left the shared queue empty avoid a
 751          * starvation for the threads sleeping on the exclusive queue by giving
 752          * them precedence and cleaning up the shared waiters bit anyway.
 753          */
 754         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
 755             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
 756                 queue = SQ_SHARED_QUEUE;
 757                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
 758         } else
 759                 queue = SQ_EXCLUSIVE_QUEUE;
 760
 761         /* Wake up all the waiters for the specific queue. */
 762         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 763                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 764                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 765                     "exclusive");
 766         atomic_store_rel_ptr(&sx->sx_lock, x);
 767         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 768             queue);
 769         sleepq_release(&sx->lock_object);
 770         if (wakeup_swapper)
 771                 kick_proc0();
 772 }
 773
 774 /*
 775  * This function represents the so-called 'hard case' for sx_slock
 776  * operation.  All 'easy case' failures are redirected to this.  Note
 777  * that ideally this would be a static function, but it needs to be
 778  * accessible from at least sx.h.
 779  */
 780 int
 781 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
 782 {
 783         GIANT_DECLARE;
 784 #ifdef ADAPTIVE_SX
 785         volatile struct thread *owner;
 786 #endif
 787 #ifdef LOCK_PROFILING
 788         uint64_t waittime = 0;
 789         int contested = 0;
 790 #endif
 791         uintptr_t x;
 792         int error = 0;
 793 #ifdef KDTRACE_HOOKS
 794         uint64_t spin_cnt = 0;
 795         uint64_t sleep_cnt = 0;
 796         int64_t sleep_time = 0;
 797 #endif
 798
 799         if (SCHEDULER_STOPPED())
 800                 return (0);
 801
 802         /*
 803          * As with rwlocks, we don't make any attempt to try to block
 804          * shared locks once there is an exclusive waiter.
 805          */
 806         for (;;) {
 807 #ifdef KDTRACE_HOOKS
 808                 spin_cnt++;
 809 #endif
 810                 x = sx->sx_lock;
 811
 812                 /*
 813                  * If no other thread has an exclusive lock then try to bump up
 814                  * the count of sharers.  Since we have to preserve the state
 815                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 816                  * shared lock loop back and retry.
 817                  */
 818                 if (x & SX_LOCK_SHARED) {
 819                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
 820                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
 821                             x + SX_ONE_SHARER)) {
 822                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 823                                         CTR4(KTR_LOCK,
 824                                             "%s: %p succeed %p -> %p", __func__,
 825                                             sx, (void *)x,
 826                                             (void *)(x + SX_ONE_SHARER));
 827                                 break;
 828                         }
 829                         continue;
 830                 }
 831 #ifdef HWPMC_HOOKS
 832                 PMC_SOFT_CALL( , , lock, failed);
 833 #endif
 834                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 835                     &waittime);
 836
 837 #ifdef ADAPTIVE_SX
 838                 /*
 839                  * If the owner is running on another CPU, spin until
 840                  * the owner stops running or the state of the lock
 841                  * changes.
 842                  */
 843                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 844                         x = SX_OWNER(x);
 845                         owner = (struct thread *)x;
 846                         if (TD_IS_RUNNING(owner)) {
 847                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 848                                         CTR3(KTR_LOCK,
 849                                             "%s: spinning on %p held by %p",
 850                                             __func__, sx, owner);
 851                                 GIANT_SAVE();
 852                                 while (SX_OWNER(sx->sx_lock) == x &&
 853                                     TD_IS_RUNNING(owner)) {
 854 #ifdef KDTRACE_HOOKS
 855                                         spin_cnt++;
 856 #endif
 857                                         cpu_spinwait();
 858                                 }
 859                                 continue;
 860                         }
 861                 }
 862 #endif
 863
 864                 /*
 865                  * Some other thread already has an exclusive lock, so
 866                  * start the process of blocking.
 867                  */
 868                 sleepq_lock(&sx->lock_object);
 869                 x = sx->sx_lock;
 870
 871                 /*
 872                  * The lock could have been released while we spun.
 873                  * In this case loop back and retry.
 874                  */
 875                 if (x & SX_LOCK_SHARED) {
 876                         sleepq_release(&sx->lock_object);
 877                         continue;
 878                 }
 879
 880 #ifdef ADAPTIVE_SX
 881                 /*
 882                  * If the owner is running on another CPU, spin until
 883                  * the owner stops running or the state of the lock
 884                  * changes.
 885                  */
 886                 if (!(x & SX_LOCK_SHARED) &&
 887                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 888                         owner = (struct thread *)SX_OWNER(x);
 889                         if (TD_IS_RUNNING(owner)) {
 890                                 sleepq_release(&sx->lock_object);
 891                                 continue;
 892                         }
 893                 }
 894 #endif
 895
 896                 /*
 897                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
 898                  * fail to set it drop the sleep queue lock and loop
 899                  * back.
 900                  */
 901                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
 902                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 903                             x | SX_LOCK_SHARED_WAITERS)) {
 904                                 sleepq_release(&sx->lock_object);
 905                                 continue;
 906                         }
 907                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 908                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
 909                                     __func__, sx);
 910                 }
 911
 912                 /*
 913                  * Since we have been unable to acquire the shared lock,
 914                  * we have to sleep.
 915                  */
 916                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 917                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 918                             __func__, sx);
 919
 920 #ifdef KDTRACE_HOOKS
 921                 sleep_time -= lockstat_nsecs();
 922 #endif
 923                 GIANT_SAVE();
 924                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 925                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 926                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
 927                 if (!(opts & SX_INTERRUPTIBLE))
 928                         sleepq_wait(&sx->lock_object, 0);
 929                 else
 930                         error = sleepq_wait_sig(&sx->lock_object, 0);
 931 #ifdef KDTRACE_HOOKS
 932                 sleep_time += lockstat_nsecs();
 933                 sleep_cnt++;
 934 #endif
 935                 if (error) {
 936                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 937                                 CTR2(KTR_LOCK,
 938                         "%s: interruptible sleep by %p suspended by signal",
 939                                     __func__, sx);
 940                         break;
 941                 }
 942                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 943                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 944                             __func__, sx);
 945         }
 946         if (error == 0)
 947                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
 948                     contested, waittime, file, line);
 949 #ifdef KDTRACE_HOOKS
 950         if (sleep_time)
 951                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
 952         if (spin_cnt > sleep_cnt)
 953                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
 954 #endif
 955         GIANT_RESTORE();
 956         return (error);
 957 }
 958
 959 /*
 960  * This function represents the so-called 'hard case' for sx_sunlock
 961  * operation.  All 'easy case' failures are redirected to this.  Note
 962  * that ideally this would be a static function, but it needs to be
 963  * accessible from at least sx.h.
 964  */
 965 void
 966 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
 967 {
 968         uintptr_t x;
 969         int wakeup_swapper;
 970
 971         if (SCHEDULER_STOPPED())
 972                 return;
 973
 974         for (;;) {
 975                 x = sx->sx_lock;
 976
 977                 /*
 978                  * We should never have sharers while at least one thread
 979                  * holds a shared lock.
 980                  */
 981                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
 982                     ("%s: waiting sharers", __func__));
 983
 984                 /*
 985                  * See if there is more than one shared lock held.  If
 986                  * so, just drop one and return.
 987                  */
 988                 if (SX_SHARERS(x) > 1) {
 989                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
 990                             x - SX_ONE_SHARER)) {
 991                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 992                                         CTR4(KTR_LOCK,
 993                                             "%s: %p succeeded %p -> %p",
 994                                             __func__, sx, (void *)x,
 995                                             (void *)(x - SX_ONE_SHARER));
 996                                 break;
 997                         }
 998                         continue;
 999                 }
1000
1001                 /*
1002                  * If there aren't any waiters for an exclusive lock,
1003                  * then try to drop it quickly.
1004                  */
1005                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1006                         MPASS(x == SX_SHARERS_LOCK(1));
1007                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1008                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1009                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1010                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
1011                                             __func__, sx);
1012                                 break;
1013                         }
1014                         continue;
1015                 }
1016
1017                 /*
1018                  * At this point, there should just be one sharer with
1019                  * exclusive waiters.
1020                  */
1021                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1022
1023                 sleepq_lock(&sx->lock_object);
1024
1025                 /*
1026                  * Wake up semantic here is quite simple:
1027                  * Just wake up all the exclusive waiters.
1028                  * Note that the state of the lock could have changed,
1029                  * so if it fails loop back and retry.
1030                  */
1031                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1032                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1033                     SX_LOCK_UNLOCKED)) {
1034                         sleepq_release(&sx->lock_object);
1035                         continue;
1036                 }
1037                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1038                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1039                             "exclusive queue", __func__, sx);
1040                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1041                     0, SQ_EXCLUSIVE_QUEUE);
1042                 sleepq_release(&sx->lock_object);
1043                 if (wakeup_swapper)
1044                         kick_proc0();
1045                 break;
1046         }
1047 }
1048
1049 #ifdef INVARIANT_SUPPORT
1050 #ifndef INVARIANTS
1051 #undef  _sx_assert
1052 #endif
1053
1054 /*
1055  * In the non-WITNESS case, sx_assert() can only detect that at least
1056  * *some* thread owns an slock, but it cannot guarantee that *this*
1057  * thread owns an slock.
1058  */
1059 void
1060 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1061 {
1062 #ifndef WITNESS
1063         int slocked = 0;
1064 #endif
1065
1066         if (panicstr != NULL)
1067                 return;
1068         switch (what) {
1069         case SA_SLOCKED:
1070         case SA_SLOCKED | SA_NOTRECURSED:
1071         case SA_SLOCKED | SA_RECURSED:
1072 #ifndef WITNESS
1073                 slocked = 1;
1074                 /* FALLTHROUGH */
1075 #endif
1076         case SA_LOCKED:
1077         case SA_LOCKED | SA_NOTRECURSED:
1078         case SA_LOCKED | SA_RECURSED:
1079 #ifdef WITNESS
1080                 witness_assert(&sx->lock_object, what, file, line);
1081 #else
1082                 /*
1083                  * If some other thread has an exclusive lock or we
1084                  * have one and are asserting a shared lock, fail.
1085                  * Also, if no one has a lock at all, fail.
1086                  */
1087                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1088                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1089                     sx_xholder(sx) != curthread)))
1090                         panic("Lock %s not %slocked @ %s:%d\n",
1091                             sx->lock_object.lo_name, slocked ? "share " : "",
1092                             file, line);
1093
1094                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1095                         if (sx_recursed(sx)) {
1096                                 if (what & SA_NOTRECURSED)
1097                                         panic("Lock %s recursed @ %s:%d\n",
1098                                             sx->lock_object.lo_name, file,
1099                                             line);
1100                         } else if (what & SA_RECURSED)
1101                                 panic("Lock %s not recursed @ %s:%d\n",
1102                                     sx->lock_object.lo_name, file, line);
1103                 }
1104 #endif
1105                 break;
1106         case SA_XLOCKED:
1107         case SA_XLOCKED | SA_NOTRECURSED:
1108         case SA_XLOCKED | SA_RECURSED:
1109                 if (sx_xholder(sx) != curthread)
1110                         panic("Lock %s not exclusively locked @ %s:%d\n",
1111                             sx->lock_object.lo_name, file, line);
1112                 if (sx_recursed(sx)) {
1113                         if (what & SA_NOTRECURSED)
1114                                 panic("Lock %s recursed @ %s:%d\n",
1115                                     sx->lock_object.lo_name, file, line);
1116                 } else if (what & SA_RECURSED)
1117                         panic("Lock %s not recursed @ %s:%d\n",
1118                             sx->lock_object.lo_name, file, line);
1119                 break;
1120         case SA_UNLOCKED:
1121 #ifdef WITNESS
1122                 witness_assert(&sx->lock_object, what, file, line);
1123 #else
1124                 /*
1125                  * If we hold an exclusve lock fail.  We can't
1126                  * reliably check to see if we hold a shared lock or
1127                  * not.
1128                  */
1129                 if (sx_xholder(sx) == curthread)
1130                         panic("Lock %s exclusively locked @ %s:%d\n",
1131                             sx->lock_object.lo_name, file, line);
1132 #endif
1133                 break;
1134         default:
1135                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1136                     line);
1137         }
1138 }
1139 #endif  /* INVARIANT_SUPPORT */
1140
1141 #ifdef DDB
1142 static void
1143 db_show_sx(const struct lock_object *lock)
1144 {
1145         struct thread *td;
1146         const struct sx *sx;
1147
1148         sx = (const struct sx *)lock;
1149
1150         db_printf(" state: ");
1151         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1152                 db_printf("UNLOCKED\n");
1153         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1154                 db_printf("DESTROYED\n");
1155                 return;
1156         } else if (sx->sx_lock & SX_LOCK_SHARED)
1157                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1158         else {
1159                 td = sx_xholder(sx);
1160                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1161                     td->td_tid, td->td_proc->p_pid, td->td_name);
1162                 if (sx_recursed(sx))
1163                         db_printf(" recursed: %d\n", sx->sx_recurse);
1164         }
1165
1166         db_printf(" waiters: ");
1167         switch(sx->sx_lock &
1168             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1169         case SX_LOCK_SHARED_WAITERS:
1170                 db_printf("shared\n");
1171                 break;
1172         case SX_LOCK_EXCLUSIVE_WAITERS:
1173                 db_printf("exclusive\n");
1174                 break;
1175         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1176                 db_printf("exclusive and shared\n");
1177                 break;
1178         default:
1179                 db_printf("none\n");
1180         }
1181 }
1182
1183 /*
1184  * Check to see if a thread that is blocked on a sleep queue is actually
1185  * blocked on an sx lock.  If so, output some details and return true.
1186  * If the lock has an exclusive owner, return that in *ownerp.
1187  */
1188 int
1189 sx_chain(struct thread *td, struct thread **ownerp)
1190 {
1191         struct sx *sx;
1192
1193         /*
1194          * Check to see if this thread is blocked on an sx lock.
1195          * First, we check the lock class.  If that is ok, then we
1196          * compare the lock name against the wait message.
1197          */
1198         sx = td->td_wchan;
1199         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1200             sx->lock_object.lo_name != td->td_wmesg)
1201                 return (0);
1202
1203         /* We think we have an sx lock, so output some details. */
1204         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1205         *ownerp = sx_xholder(sx);
1206         if (sx->sx_lock & SX_LOCK_SHARED)
1207                 db_printf("SLOCK (count %ju)\n",
1208                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1209         else
1210                 db_printf("XLOCK\n");
1211         return (1);
1212 }
1213 #endif