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/sched.h>
  55 #include <sys/sleepqueue.h>
  56 #include <sys/sx.h>
  57 #include <sys/sysctl.h>
  58
  59 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  60 #include <machine/cpu.h>
  61 #endif
  62
  63 #ifdef DDB
  64 #include <ddb/ddb.h>
  65 #endif
  66
  67 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  68 #define ADAPTIVE_SX
  69 #endif
  70
  71 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
  72
  73 #ifdef HWPMC_HOOKS
  74 #include <sys/pmckern.h>
  75 PMC_SOFT_DECLARE( , , lock, failed);
  76 #endif
  77
  78 /* Handy macros for sleep queues. */
  79 #define SQ_EXCLUSIVE_QUEUE      0
  80 #define SQ_SHARED_QUEUE         1
  81
  82 /*
  83  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  84  * drop Giant anytime we have to sleep or if we adaptively spin.
  85  */
  86 #define GIANT_DECLARE                                                   \
  87         int _giantcnt = 0;                                              \
  88         WITNESS_SAVE_DECL(Giant)                                        \
  89
  90 #define GIANT_SAVE() do {                                               \
  91         if (mtx_owned(&Giant)) {                                        \
  92                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  93                 while (mtx_owned(&Giant)) {                             \
  94                         _giantcnt++;                                    \
  95                         mtx_unlock(&Giant);                             \
  96                 }                                                       \
  97         }                                                               \
  98 } while (0)
  99
 100 #define GIANT_RESTORE() do {                                            \
 101         if (_giantcnt > 0) {                                            \
 102                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 103                 while (_giantcnt--)                                     \
 104                         mtx_lock(&Giant);                               \
 105                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 106         }                                                               \
 107 } while (0)
 108
 109 /*
 110  * Returns true if an exclusive lock is recursed.  It assumes
 111  * curthread currently has an exclusive lock.
 112  */
 113 #define sx_recurse              lock_object.lo_data
 114 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 115
 116 static void     assert_sx(const struct lock_object *lock, int what);
 117 #ifdef DDB
 118 static void     db_show_sx(const struct lock_object *lock);
 119 #endif
 120 static void     lock_sx(struct lock_object *lock, uintptr_t how);
 121 #ifdef KDTRACE_HOOKS
 122 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 123 #endif
 124 static uintptr_t unlock_sx(struct lock_object *lock);
 125
 126 struct lock_class lock_class_sx = {
 127         .lc_name = "sx",
 128         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 129         .lc_assert = assert_sx,
 130 #ifdef DDB
 131         .lc_ddb_show = db_show_sx,
 132 #endif
 133         .lc_lock = lock_sx,
 134         .lc_unlock = unlock_sx,
 135 #ifdef KDTRACE_HOOKS
 136         .lc_owner = owner_sx,
 137 #endif
 138 };
 139
 140 #ifndef INVARIANTS
 141 #define _sx_assert(sx, what, file, line)
 142 #endif
 143
 144 #ifdef ADAPTIVE_SX
 145 static u_int asx_retries = 10;
 146 static u_int asx_loops = 10000;
 147 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
 148 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 149 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 150 #endif
 151
 152 void
 153 assert_sx(const struct lock_object *lock, int what)
 154 {
 155
 156         sx_assert((const struct sx *)lock, what);
 157 }
 158
 159 void
 160 lock_sx(struct lock_object *lock, uintptr_t how)
 161 {
 162         struct sx *sx;
 163
 164         sx = (struct sx *)lock;
 165         if (how)
 166                 sx_slock(sx);
 167         else
 168                 sx_xlock(sx);
 169 }
 170
 171 uintptr_t
 172 unlock_sx(struct lock_object *lock)
 173 {
 174         struct sx *sx;
 175
 176         sx = (struct sx *)lock;
 177         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 178         if (sx_xlocked(sx)) {
 179                 sx_xunlock(sx);
 180                 return (0);
 181         } else {
 182                 sx_sunlock(sx);
 183                 return (1);
 184         }
 185 }
 186
 187 #ifdef KDTRACE_HOOKS
 188 int
 189 owner_sx(const struct lock_object *lock, struct thread **owner)
 190 {
 191         const struct sx *sx = (const struct sx *)lock;
 192         uintptr_t x = sx->sx_lock;
 193
 194         *owner = (struct thread *)SX_OWNER(x);
 195         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 196             (*owner != NULL));
 197 }
 198 #endif
 199
 200 void
 201 sx_sysinit(void *arg)
 202 {
 203         struct sx_args *sargs = arg;
 204
 205         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 206 }
 207
 208 void
 209 sx_init_flags(struct sx *sx, const char *description, int opts)
 210 {
 211         int flags;
 212
 213         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 214             SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
 215         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 216             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 217             &sx->sx_lock));
 218
 219         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 220         if (opts & SX_DUPOK)
 221                 flags |= LO_DUPOK;
 222         if (opts & SX_NOPROFILE)
 223                 flags |= LO_NOPROFILE;
 224         if (!(opts & SX_NOWITNESS))
 225                 flags |= LO_WITNESS;
 226         if (opts & SX_RECURSE)
 227                 flags |= LO_RECURSABLE;
 228         if (opts & SX_QUIET)
 229                 flags |= LO_QUIET;
 230
 231         flags |= opts & SX_NOADAPTIVE;
 232         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 233         sx->sx_lock = SX_LOCK_UNLOCKED;
 234         sx->sx_recurse = 0;
 235 }
 236
 237 void
 238 sx_destroy(struct sx *sx)
 239 {
 240
 241         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 242         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 243         sx->sx_lock = SX_LOCK_DESTROYED;
 244         lock_destroy(&sx->lock_object);
 245 }
 246
 247 int
 248 _sx_slock(struct sx *sx, int opts, const char *file, int line)
 249 {
 250         int error = 0;
 251
 252         if (SCHEDULER_STOPPED())
 253                 return (0);
 254         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 255             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
 256             curthread, sx->lock_object.lo_name, file, line));
 257         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 258             ("sx_slock() of destroyed sx @ %s:%d", file, line));
 259         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
 260         error = __sx_slock(sx, opts, file, line);
 261         if (!error) {
 262                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
 263                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
 264                 curthread->td_locks++;
 265         }
 266
 267         return (error);
 268 }
 269
 270 int
 271 sx_try_slock_(struct sx *sx, const char *file, int line)
 272 {
 273         uintptr_t x;
 274
 275         if (SCHEDULER_STOPPED())
 276                 return (1);
 277
 278         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 279             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 280             curthread, sx->lock_object.lo_name, file, line));
 281
 282         for (;;) {
 283                 x = sx->sx_lock;
 284                 KASSERT(x != SX_LOCK_DESTROYED,
 285                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 286                 if (!(x & SX_LOCK_SHARED))
 287                         break;
 288                 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
 289                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 290                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 291                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE,
 292                             sx, 0, 0, file, line);
 293                         curthread->td_locks++;
 294                         return (1);
 295                 }
 296         }
 297
 298         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 299         return (0);
 300 }
 301
 302 int
 303 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 304 {
 305         int error = 0;
 306
 307         if (SCHEDULER_STOPPED())
 308                 return (0);
 309         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 310             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 311             curthread, sx->lock_object.lo_name, file, line));
 312         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 313             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 314         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 315             line, NULL);
 316         error = __sx_xlock(sx, curthread, opts, file, line);
 317         if (!error) {
 318                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 319                     file, line);
 320                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 321                 curthread->td_locks++;
 322         }
 323
 324         return (error);
 325 }
 326
 327 int
 328 sx_try_xlock_(struct sx *sx, const char *file, int line)
 329 {
 330         int rval;
 331
 332         if (SCHEDULER_STOPPED())
 333                 return (1);
 334
 335         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 336             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 337             curthread, sx->lock_object.lo_name, file, line));
 338         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 339             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 340
 341         if (sx_xlocked(sx) &&
 342             (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 343                 sx->sx_recurse++;
 344                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 345                 rval = 1;
 346         } else
 347                 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
 348                     (uintptr_t)curthread);
 349         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 350         if (rval) {
 351                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 352                     file, line);
 353                 if (!sx_recursed(sx))
 354                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
 355                             sx, 0, 0, file, line);
 356                 curthread->td_locks++;
 357         }
 358
 359         return (rval);
 360 }
 361
 362 void
 363 _sx_sunlock(struct sx *sx, const char *file, int line)
 364 {
 365
 366         if (SCHEDULER_STOPPED())
 367                 return;
 368         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 369             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
 370         _sx_assert(sx, SA_SLOCKED, file, line);
 371         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
 372         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
 373         __sx_sunlock(sx, file, line);
 374         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
 375         curthread->td_locks--;
 376 }
 377
 378 void
 379 _sx_xunlock(struct sx *sx, const char *file, int line)
 380 {
 381
 382         if (SCHEDULER_STOPPED())
 383                 return;
 384         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 385             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 386         _sx_assert(sx, SA_XLOCKED, file, line);
 387         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 388         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 389             line);
 390         if (!sx_recursed(sx))
 391                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
 392         __sx_xunlock(sx, curthread, file, line);
 393         curthread->td_locks--;
 394 }
 395
 396 /*
 397  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 398  * This will only succeed if this thread holds a single shared lock.
 399  * Return 1 if if the upgrade succeed, 0 otherwise.
 400  */
 401 int
 402 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 403 {
 404         uintptr_t x;
 405         int success;
 406
 407         if (SCHEDULER_STOPPED())
 408                 return (1);
 409
 410         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 411             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 412         _sx_assert(sx, SA_SLOCKED, file, line);
 413
 414         /*
 415          * Try to switch from one shared lock to an exclusive lock.  We need
 416          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 417          * we will wake up the exclusive waiters when we drop the lock.
 418          */
 419         x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
 420         success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
 421             (uintptr_t)curthread | x);
 422         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 423         if (success) {
 424                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 425                     file, line);
 426                 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
 427         }
 428         return (success);
 429 }
 430
 431 /*
 432  * Downgrade an unrecursed exclusive lock into a single shared lock.
 433  */
 434 void
 435 sx_downgrade_(struct sx *sx, const char *file, int line)
 436 {
 437         uintptr_t x;
 438         int wakeup_swapper;
 439
 440         if (SCHEDULER_STOPPED())
 441                 return;
 442
 443         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 444             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 445         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 446 #ifndef INVARIANTS
 447         if (sx_recursed(sx))
 448                 panic("downgrade of a recursed lock");
 449 #endif
 450
 451         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 452
 453         /*
 454          * Try to switch from an exclusive lock with no shared waiters
 455          * to one sharer with no shared waiters.  If there are
 456          * exclusive waiters, we don't need to lock the sleep queue so
 457          * long as we preserve the flag.  We do one quick try and if
 458          * that fails we grab the sleepq lock to keep the flags from
 459          * changing and do it the slow way.
 460          *
 461          * We have to lock the sleep queue if there are shared waiters
 462          * so we can wake them up.
 463          */
 464         x = sx->sx_lock;
 465         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 466             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 467             (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 468                 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 469                 return;
 470         }
 471
 472         /*
 473          * Lock the sleep queue so we can read the waiters bits
 474          * without any races and wakeup any shared waiters.
 475          */
 476         sleepq_lock(&sx->lock_object);
 477
 478         /*
 479          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 480          * shared lock.  If there are any shared waiters, wake them up.
 481          */
 482         wakeup_swapper = 0;
 483         x = sx->sx_lock;
 484         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 485             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 486         if (x & SX_LOCK_SHARED_WAITERS)
 487                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 488                     0, SQ_SHARED_QUEUE);
 489         sleepq_release(&sx->lock_object);
 490
 491         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 492         LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
 493
 494         if (wakeup_swapper)
 495                 kick_proc0();
 496 }
 497
 498 /*
 499  * This function represents the so-called 'hard case' for sx_xlock
 500  * operation.  All 'easy case' failures are redirected to this.  Note
 501  * that ideally this would be a static function, but it needs to be
 502  * accessible from at least sx.h.
 503  */
 504 int
 505 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
 506     int line)
 507 {
 508         GIANT_DECLARE;
 509 #ifdef ADAPTIVE_SX
 510         volatile struct thread *owner;
 511         u_int i, spintries = 0;
 512 #endif
 513         uintptr_t x;
 514 #ifdef LOCK_PROFILING
 515         uint64_t waittime = 0;
 516         int contested = 0;
 517 #endif
 518         int error = 0;
 519 #ifdef  KDTRACE_HOOKS
 520         uintptr_t state;
 521         uint64_t spin_cnt = 0;
 522         uint64_t sleep_cnt = 0;
 523         int64_t sleep_time = 0;
 524         int64_t all_time = 0;
 525 #endif
 526
 527         if (SCHEDULER_STOPPED())
 528                 return (0);
 529
 530         /* If we already hold an exclusive lock, then recurse. */
 531         if (sx_xlocked(sx)) {
 532                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 533             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 534                     sx->lock_object.lo_name, file, line));
 535                 sx->sx_recurse++;
 536                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 537                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 538                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 539                 return (0);
 540         }
 541
 542         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 543                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 544                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 545
 546 #ifdef KDTRACE_HOOKS
 547         all_time -= lockstat_nsecs(&sx->lock_object);
 548         state = sx->sx_lock;
 549 #endif
 550         for (;;) {
 551                 if (sx->sx_lock == SX_LOCK_UNLOCKED &&
 552                     atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
 553                         break;
 554 #ifdef KDTRACE_HOOKS
 555                 spin_cnt++;
 556 #endif
 557 #ifdef HWPMC_HOOKS
 558                 PMC_SOFT_CALL( , , lock, failed);
 559 #endif
 560                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 561                     &waittime);
 562 #ifdef ADAPTIVE_SX
 563                 /*
 564                  * If the lock is write locked and the owner is
 565                  * running on another CPU, spin until the owner stops
 566                  * running or the state of the lock changes.
 567                  */
 568                 x = sx->sx_lock;
 569                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 570                         if ((x & SX_LOCK_SHARED) == 0) {
 571                                 x = SX_OWNER(x);
 572                                 owner = (struct thread *)x;
 573                                 if (TD_IS_RUNNING(owner)) {
 574                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 575                                                 CTR3(KTR_LOCK,
 576                                             "%s: spinning on %p held by %p",
 577                                                     __func__, sx, owner);
 578                                         KTR_STATE1(KTR_SCHED, "thread",
 579                                             sched_tdname(curthread), "spinning",
 580                                             "lockname:\"%s\"",
 581                                             sx->lock_object.lo_name);
 582                                         GIANT_SAVE();
 583                                         while (SX_OWNER(sx->sx_lock) == x &&
 584                                             TD_IS_RUNNING(owner)) {
 585                                                 cpu_spinwait();
 586 #ifdef KDTRACE_HOOKS
 587                                                 spin_cnt++;
 588 #endif
 589                                         }
 590                                         KTR_STATE0(KTR_SCHED, "thread",
 591                                             sched_tdname(curthread), "running");
 592                                         continue;
 593                                 }
 594                         } else if (SX_SHARERS(x) && spintries < asx_retries) {
 595                                 KTR_STATE1(KTR_SCHED, "thread",
 596                                     sched_tdname(curthread), "spinning",
 597                                     "lockname:\"%s\"", sx->lock_object.lo_name);
 598                                 GIANT_SAVE();
 599                                 spintries++;
 600                                 for (i = 0; i < asx_loops; i++) {
 601                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 602                                                 CTR4(KTR_LOCK,
 603                                     "%s: shared spinning on %p with %u and %u",
 604                                                     __func__, sx, spintries, i);
 605                                         x = sx->sx_lock;
 606                                         if ((x & SX_LOCK_SHARED) == 0 ||
 607                                             SX_SHARERS(x) == 0)
 608                                                 break;
 609                                         cpu_spinwait();
 610 #ifdef KDTRACE_HOOKS
 611                                         spin_cnt++;
 612 #endif
 613                                 }
 614                                 KTR_STATE0(KTR_SCHED, "thread",
 615                                     sched_tdname(curthread), "running");
 616                                 if (i != asx_loops)
 617                                         continue;
 618                         }
 619                 }
 620 #endif
 621
 622                 sleepq_lock(&sx->lock_object);
 623                 x = sx->sx_lock;
 624
 625                 /*
 626                  * If the lock was released while spinning on the
 627                  * sleep queue chain lock, try again.
 628                  */
 629                 if (x == SX_LOCK_UNLOCKED) {
 630                         sleepq_release(&sx->lock_object);
 631                         continue;
 632                 }
 633
 634 #ifdef ADAPTIVE_SX
 635                 /*
 636                  * The current lock owner might have started executing
 637                  * on another CPU (or the lock could have changed
 638                  * owners) while we were waiting on the sleep queue
 639                  * chain lock.  If so, drop the sleep queue lock and try
 640                  * again.
 641                  */
 642                 if (!(x & SX_LOCK_SHARED) &&
 643                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 644                         owner = (struct thread *)SX_OWNER(x);
 645                         if (TD_IS_RUNNING(owner)) {
 646                                 sleepq_release(&sx->lock_object);
 647                                 continue;
 648                         }
 649                 }
 650 #endif
 651
 652                 /*
 653                  * If an exclusive lock was released with both shared
 654                  * and exclusive waiters and a shared waiter hasn't
 655                  * woken up and acquired the lock yet, sx_lock will be
 656                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 657                  * If we see that value, try to acquire it once.  Note
 658                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 659                  * as there are other exclusive waiters still.  If we
 660                  * fail, restart the loop.
 661                  */
 662                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
 663                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
 664                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
 665                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
 666                                 sleepq_release(&sx->lock_object);
 667                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 668                                     __func__, sx);
 669                                 break;
 670                         }
 671                         sleepq_release(&sx->lock_object);
 672                         continue;
 673                 }
 674
 675                 /*
 676                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 677                  * than loop back and retry.
 678                  */
 679                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 680                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 681                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 682                                 sleepq_release(&sx->lock_object);
 683                                 continue;
 684                         }
 685                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 686                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 687                                     __func__, sx);
 688                 }
 689
 690                 /*
 691                  * Since we have been unable to acquire the exclusive
 692                  * lock and the exclusive waiters flag is set, we have
 693                  * to sleep.
 694                  */
 695                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 696                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 697                             __func__, sx);
 698
 699 #ifdef KDTRACE_HOOKS
 700                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 701 #endif
 702                 GIANT_SAVE();
 703                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 704                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 705                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 706                 if (!(opts & SX_INTERRUPTIBLE))
 707                         sleepq_wait(&sx->lock_object, 0);
 708                 else
 709                         error = sleepq_wait_sig(&sx->lock_object, 0);
 710 #ifdef KDTRACE_HOOKS
 711                 sleep_time += lockstat_nsecs(&sx->lock_object);
 712                 sleep_cnt++;
 713 #endif
 714                 if (error) {
 715                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 716                                 CTR2(KTR_LOCK,
 717                         "%s: interruptible sleep by %p suspended by signal",
 718                                     __func__, sx);
 719                         break;
 720                 }
 721                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 722                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 723                             __func__, sx);
 724         }
 725 #ifdef KDTRACE_HOOKS
 726         all_time += lockstat_nsecs(&sx->lock_object);
 727         if (sleep_time)
 728                 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time,
 729                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 730                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 731         if (spin_cnt > sleep_cnt)
 732                 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time,
 733                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 734                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 735 #endif
 736         if (!error)
 737                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
 738                     contested, waittime, file, line);
 739         GIANT_RESTORE();
 740         return (error);
 741 }
 742
 743 /*
 744  * This function represents the so-called 'hard case' for sx_xunlock
 745  * operation.  All 'easy case' failures are redirected to this.  Note
 746  * that ideally this would be a static function, but it needs to be
 747  * accessible from at least sx.h.
 748  */
 749 void
 750 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
 751 {
 752         uintptr_t x;
 753         int queue, wakeup_swapper;
 754
 755         if (SCHEDULER_STOPPED())
 756                 return;
 757
 758         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
 759
 760         /* If the lock is recursed, then unrecurse one level. */
 761         if (sx_xlocked(sx) && sx_recursed(sx)) {
 762                 if ((--sx->sx_recurse) == 0)
 763                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 764                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 765                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 766                 return;
 767         }
 768         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
 769             SX_LOCK_EXCLUSIVE_WAITERS));
 770         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 771                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 772
 773         sleepq_lock(&sx->lock_object);
 774         x = SX_LOCK_UNLOCKED;
 775
 776         /*
 777          * The wake up algorithm here is quite simple and probably not
 778          * ideal.  It gives precedence to shared waiters if they are
 779          * present.  For this condition, we have to preserve the
 780          * state of the exclusive waiters flag.
 781          * If interruptible sleeps left the shared queue empty avoid a
 782          * starvation for the threads sleeping on the exclusive queue by giving
 783          * them precedence and cleaning up the shared waiters bit anyway.
 784          */
 785         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
 786             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
 787                 queue = SQ_SHARED_QUEUE;
 788                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
 789         } else
 790                 queue = SQ_EXCLUSIVE_QUEUE;
 791
 792         /* Wake up all the waiters for the specific queue. */
 793         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 794                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 795                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 796                     "exclusive");
 797         atomic_store_rel_ptr(&sx->sx_lock, x);
 798         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 799             queue);
 800         sleepq_release(&sx->lock_object);
 801         if (wakeup_swapper)
 802                 kick_proc0();
 803 }
 804
 805 /*
 806  * This function represents the so-called 'hard case' for sx_slock
 807  * operation.  All 'easy case' failures are redirected to this.  Note
 808  * that ideally this would be a static function, but it needs to be
 809  * accessible from at least sx.h.
 810  */
 811 int
 812 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
 813 {
 814         GIANT_DECLARE;
 815 #ifdef ADAPTIVE_SX
 816         volatile struct thread *owner;
 817 #endif
 818 #ifdef LOCK_PROFILING
 819         uint64_t waittime = 0;
 820         int contested = 0;
 821 #endif
 822         uintptr_t x;
 823         int error = 0;
 824 #ifdef KDTRACE_HOOKS
 825         uintptr_t state;
 826         uint64_t spin_cnt = 0;
 827         uint64_t sleep_cnt = 0;
 828         int64_t sleep_time = 0;
 829         int64_t all_time = 0;
 830 #endif
 831
 832         if (SCHEDULER_STOPPED())
 833                 return (0);
 834
 835 #ifdef KDTRACE_HOOKS
 836         state = sx->sx_lock;
 837         all_time -= lockstat_nsecs(&sx->lock_object);
 838 #endif
 839
 840         /*
 841          * As with rwlocks, we don't make any attempt to try to block
 842          * shared locks once there is an exclusive waiter.
 843          */
 844         for (;;) {
 845 #ifdef KDTRACE_HOOKS
 846                 spin_cnt++;
 847 #endif
 848                 x = sx->sx_lock;
 849
 850                 /*
 851                  * If no other thread has an exclusive lock then try to bump up
 852                  * the count of sharers.  Since we have to preserve the state
 853                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 854                  * shared lock loop back and retry.
 855                  */
 856                 if (x & SX_LOCK_SHARED) {
 857                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
 858                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
 859                             x + SX_ONE_SHARER)) {
 860                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 861                                         CTR4(KTR_LOCK,
 862                                             "%s: %p succeed %p -> %p", __func__,
 863                                             sx, (void *)x,
 864                                             (void *)(x + SX_ONE_SHARER));
 865                                 break;
 866                         }
 867                         continue;
 868                 }
 869 #ifdef HWPMC_HOOKS
 870                 PMC_SOFT_CALL( , , lock, failed);
 871 #endif
 872                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 873                     &waittime);
 874
 875 #ifdef ADAPTIVE_SX
 876                 /*
 877                  * If the owner is running on another CPU, spin until
 878                  * the owner stops running or the state of the lock
 879                  * changes.
 880                  */
 881                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 882                         x = SX_OWNER(x);
 883                         owner = (struct thread *)x;
 884                         if (TD_IS_RUNNING(owner)) {
 885                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 886                                         CTR3(KTR_LOCK,
 887                                             "%s: spinning on %p held by %p",
 888                                             __func__, sx, owner);
 889                                 KTR_STATE1(KTR_SCHED, "thread",
 890                                     sched_tdname(curthread), "spinning",
 891                                     "lockname:\"%s\"", sx->lock_object.lo_name);
 892                                 GIANT_SAVE();
 893                                 while (SX_OWNER(sx->sx_lock) == x &&
 894                                     TD_IS_RUNNING(owner)) {
 895 #ifdef KDTRACE_HOOKS
 896                                         spin_cnt++;
 897 #endif
 898                                         cpu_spinwait();
 899                                 }
 900                                 KTR_STATE0(KTR_SCHED, "thread",
 901                                     sched_tdname(curthread), "running");
 902                                 continue;
 903                         }
 904                 }
 905 #endif
 906
 907                 /*
 908                  * Some other thread already has an exclusive lock, so
 909                  * start the process of blocking.
 910                  */
 911                 sleepq_lock(&sx->lock_object);
 912                 x = sx->sx_lock;
 913
 914                 /*
 915                  * The lock could have been released while we spun.
 916                  * In this case loop back and retry.
 917                  */
 918                 if (x & SX_LOCK_SHARED) {
 919                         sleepq_release(&sx->lock_object);
 920                         continue;
 921                 }
 922
 923 #ifdef ADAPTIVE_SX
 924                 /*
 925                  * If the owner is running on another CPU, spin until
 926                  * the owner stops running or the state of the lock
 927                  * changes.
 928                  */
 929                 if (!(x & SX_LOCK_SHARED) &&
 930                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 931                         owner = (struct thread *)SX_OWNER(x);
 932                         if (TD_IS_RUNNING(owner)) {
 933                                 sleepq_release(&sx->lock_object);
 934                                 continue;
 935                         }
 936                 }
 937 #endif
 938
 939                 /*
 940                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
 941                  * fail to set it drop the sleep queue lock and loop
 942                  * back.
 943                  */
 944                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
 945                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 946                             x | SX_LOCK_SHARED_WAITERS)) {
 947                                 sleepq_release(&sx->lock_object);
 948                                 continue;
 949                         }
 950                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 951                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
 952                                     __func__, sx);
 953                 }
 954
 955                 /*
 956                  * Since we have been unable to acquire the shared lock,
 957                  * we have to sleep.
 958                  */
 959                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 960                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 961                             __func__, sx);
 962
 963 #ifdef KDTRACE_HOOKS
 964                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 965 #endif
 966                 GIANT_SAVE();
 967                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 968                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 969                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
 970                 if (!(opts & SX_INTERRUPTIBLE))
 971                         sleepq_wait(&sx->lock_object, 0);
 972                 else
 973                         error = sleepq_wait_sig(&sx->lock_object, 0);
 974 #ifdef KDTRACE_HOOKS
 975                 sleep_time += lockstat_nsecs(&sx->lock_object);
 976                 sleep_cnt++;
 977 #endif
 978                 if (error) {
 979                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 980                                 CTR2(KTR_LOCK,
 981                         "%s: interruptible sleep by %p suspended by signal",
 982                                     __func__, sx);
 983                         break;
 984                 }
 985                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 986                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 987                             __func__, sx);
 988         }
 989 #ifdef KDTRACE_HOOKS
 990         all_time += lockstat_nsecs(&sx->lock_object);
 991         if (sleep_time)
 992                 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time,
 993                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 994                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 995         if (spin_cnt > sleep_cnt)
 996                 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time,
 997                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 998                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 999 #endif
1000         if (error == 0)
1001                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
1002                     contested, waittime, file, line);
1003         GIANT_RESTORE();
1004         return (error);
1005 }
1006
1007 /*
1008  * This function represents the so-called 'hard case' for sx_sunlock
1009  * operation.  All 'easy case' failures are redirected to this.  Note
1010  * that ideally this would be a static function, but it needs to be
1011  * accessible from at least sx.h.
1012  */
1013 void
1014 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
1015 {
1016         uintptr_t x;
1017         int wakeup_swapper;
1018
1019         if (SCHEDULER_STOPPED())
1020                 return;
1021
1022         for (;;) {
1023                 x = sx->sx_lock;
1024
1025                 /*
1026                  * We should never have sharers while at least one thread
1027                  * holds a shared lock.
1028                  */
1029                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
1030                     ("%s: waiting sharers", __func__));
1031
1032                 /*
1033                  * See if there is more than one shared lock held.  If
1034                  * so, just drop one and return.
1035                  */
1036                 if (SX_SHARERS(x) > 1) {
1037                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
1038                             x - SX_ONE_SHARER)) {
1039                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1040                                         CTR4(KTR_LOCK,
1041                                             "%s: %p succeeded %p -> %p",
1042                                             __func__, sx, (void *)x,
1043                                             (void *)(x - SX_ONE_SHARER));
1044                                 break;
1045                         }
1046                         continue;
1047                 }
1048
1049                 /*
1050                  * If there aren't any waiters for an exclusive lock,
1051                  * then try to drop it quickly.
1052                  */
1053                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1054                         MPASS(x == SX_SHARERS_LOCK(1));
1055                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1056                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1057                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1058                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
1059                                             __func__, sx);
1060                                 break;
1061                         }
1062                         continue;
1063                 }
1064
1065                 /*
1066                  * At this point, there should just be one sharer with
1067                  * exclusive waiters.
1068                  */
1069                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1070
1071                 sleepq_lock(&sx->lock_object);
1072
1073                 /*
1074                  * Wake up semantic here is quite simple:
1075                  * Just wake up all the exclusive waiters.
1076                  * Note that the state of the lock could have changed,
1077                  * so if it fails loop back and retry.
1078                  */
1079                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1080                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1081                     SX_LOCK_UNLOCKED)) {
1082                         sleepq_release(&sx->lock_object);
1083                         continue;
1084                 }
1085                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1086                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1087                             "exclusive queue", __func__, sx);
1088                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1089                     0, SQ_EXCLUSIVE_QUEUE);
1090                 sleepq_release(&sx->lock_object);
1091                 if (wakeup_swapper)
1092                         kick_proc0();
1093                 break;
1094         }
1095 }
1096
1097 #ifdef INVARIANT_SUPPORT
1098 #ifndef INVARIANTS
1099 #undef  _sx_assert
1100 #endif
1101
1102 /*
1103  * In the non-WITNESS case, sx_assert() can only detect that at least
1104  * *some* thread owns an slock, but it cannot guarantee that *this*
1105  * thread owns an slock.
1106  */
1107 void
1108 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1109 {
1110 #ifndef WITNESS
1111         int slocked = 0;
1112 #endif
1113
1114         if (panicstr != NULL)
1115                 return;
1116         switch (what) {
1117         case SA_SLOCKED:
1118         case SA_SLOCKED | SA_NOTRECURSED:
1119         case SA_SLOCKED | SA_RECURSED:
1120 #ifndef WITNESS
1121                 slocked = 1;
1122                 /* FALLTHROUGH */
1123 #endif
1124         case SA_LOCKED:
1125         case SA_LOCKED | SA_NOTRECURSED:
1126         case SA_LOCKED | SA_RECURSED:
1127 #ifdef WITNESS
1128                 witness_assert(&sx->lock_object, what, file, line);
1129 #else
1130                 /*
1131                  * If some other thread has an exclusive lock or we
1132                  * have one and are asserting a shared lock, fail.
1133                  * Also, if no one has a lock at all, fail.
1134                  */
1135                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1136                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1137                     sx_xholder(sx) != curthread)))
1138                         panic("Lock %s not %slocked @ %s:%d\n",
1139                             sx->lock_object.lo_name, slocked ? "share " : "",
1140                             file, line);
1141
1142                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1143                         if (sx_recursed(sx)) {
1144                                 if (what & SA_NOTRECURSED)
1145                                         panic("Lock %s recursed @ %s:%d\n",
1146                                             sx->lock_object.lo_name, file,
1147                                             line);
1148                         } else if (what & SA_RECURSED)
1149                                 panic("Lock %s not recursed @ %s:%d\n",
1150                                     sx->lock_object.lo_name, file, line);
1151                 }
1152 #endif
1153                 break;
1154         case SA_XLOCKED:
1155         case SA_XLOCKED | SA_NOTRECURSED:
1156         case SA_XLOCKED | SA_RECURSED:
1157                 if (sx_xholder(sx) != curthread)
1158                         panic("Lock %s not exclusively locked @ %s:%d\n",
1159                             sx->lock_object.lo_name, file, line);
1160                 if (sx_recursed(sx)) {
1161                         if (what & SA_NOTRECURSED)
1162                                 panic("Lock %s recursed @ %s:%d\n",
1163                                     sx->lock_object.lo_name, file, line);
1164                 } else if (what & SA_RECURSED)
1165                         panic("Lock %s not recursed @ %s:%d\n",
1166                             sx->lock_object.lo_name, file, line);
1167                 break;
1168         case SA_UNLOCKED:
1169 #ifdef WITNESS
1170                 witness_assert(&sx->lock_object, what, file, line);
1171 #else
1172                 /*
1173                  * If we hold an exclusve lock fail.  We can't
1174                  * reliably check to see if we hold a shared lock or
1175                  * not.
1176                  */
1177                 if (sx_xholder(sx) == curthread)
1178                         panic("Lock %s exclusively locked @ %s:%d\n",
1179                             sx->lock_object.lo_name, file, line);
1180 #endif
1181                 break;
1182         default:
1183                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1184                     line);
1185         }
1186 }
1187 #endif  /* INVARIANT_SUPPORT */
1188
1189 #ifdef DDB
1190 static void
1191 db_show_sx(const struct lock_object *lock)
1192 {
1193         struct thread *td;
1194         const struct sx *sx;
1195
1196         sx = (const struct sx *)lock;
1197
1198         db_printf(" state: ");
1199         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1200                 db_printf("UNLOCKED\n");
1201         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1202                 db_printf("DESTROYED\n");
1203                 return;
1204         } else if (sx->sx_lock & SX_LOCK_SHARED)
1205                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1206         else {
1207                 td = sx_xholder(sx);
1208                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1209                     td->td_tid, td->td_proc->p_pid, td->td_name);
1210                 if (sx_recursed(sx))
1211                         db_printf(" recursed: %d\n", sx->sx_recurse);
1212         }
1213
1214         db_printf(" waiters: ");
1215         switch(sx->sx_lock &
1216             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1217         case SX_LOCK_SHARED_WAITERS:
1218                 db_printf("shared\n");
1219                 break;
1220         case SX_LOCK_EXCLUSIVE_WAITERS:
1221                 db_printf("exclusive\n");
1222                 break;
1223         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1224                 db_printf("exclusive and shared\n");
1225                 break;
1226         default:
1227                 db_printf("none\n");
1228         }
1229 }
1230
1231 /*
1232  * Check to see if a thread that is blocked on a sleep queue is actually
1233  * blocked on an sx lock.  If so, output some details and return true.
1234  * If the lock has an exclusive owner, return that in *ownerp.
1235  */
1236 int
1237 sx_chain(struct thread *td, struct thread **ownerp)
1238 {
1239         struct sx *sx;
1240
1241         /*
1242          * Check to see if this thread is blocked on an sx lock.
1243          * First, we check the lock class.  If that is ok, then we
1244          * compare the lock name against the wait message.
1245          */
1246         sx = td->td_wchan;
1247         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1248             sx->lock_object.lo_name != td->td_wmesg)
1249                 return (0);
1250
1251         /* We think we have an sx lock, so output some details. */
1252         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1253         *ownerp = sx_xholder(sx);
1254         if (sx->sx_lock & SX_LOCK_SHARED)
1255                 db_printf("SLOCK (count %ju)\n",
1256                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1257         else
1258                 db_printf("XLOCK\n");
1259         return (1);
1260 }
1261 #endif