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         while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
 551 #ifdef KDTRACE_HOOKS
 552                 spin_cnt++;
 553 #endif
 554 #ifdef HWPMC_HOOKS
 555                 PMC_SOFT_CALL( , , lock, failed);
 556 #endif
 557                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 558                     &waittime);
 559 #ifdef ADAPTIVE_SX
 560                 /*
 561                  * If the lock is write locked and the owner is
 562                  * running on another CPU, spin until the owner stops
 563                  * running or the state of the lock changes.
 564                  */
 565                 x = sx->sx_lock;
 566                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 567                         if ((x & SX_LOCK_SHARED) == 0) {
 568                                 x = SX_OWNER(x);
 569                                 owner = (struct thread *)x;
 570                                 if (TD_IS_RUNNING(owner)) {
 571                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 572                                                 CTR3(KTR_LOCK,
 573                                             "%s: spinning on %p held by %p",
 574                                                     __func__, sx, owner);
 575                                         KTR_STATE1(KTR_SCHED, "thread",
 576                                             sched_tdname(curthread), "spinning",
 577                                             "lockname:\"%s\"",
 578                                             sx->lock_object.lo_name);
 579                                         GIANT_SAVE();
 580                                         while (SX_OWNER(sx->sx_lock) == x &&
 581                                             TD_IS_RUNNING(owner)) {
 582                                                 cpu_spinwait();
 583 #ifdef KDTRACE_HOOKS
 584                                                 spin_cnt++;
 585 #endif
 586                                         }
 587                                         KTR_STATE0(KTR_SCHED, "thread",
 588                                             sched_tdname(curthread), "running");
 589                                         continue;
 590                                 }
 591                         } else if (SX_SHARERS(x) && spintries < asx_retries) {
 592                                 KTR_STATE1(KTR_SCHED, "thread",
 593                                     sched_tdname(curthread), "spinning",
 594                                     "lockname:\"%s\"", sx->lock_object.lo_name);
 595                                 GIANT_SAVE();
 596                                 spintries++;
 597                                 for (i = 0; i < asx_loops; i++) {
 598                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 599                                                 CTR4(KTR_LOCK,
 600                                     "%s: shared spinning on %p with %u and %u",
 601                                                     __func__, sx, spintries, i);
 602                                         x = sx->sx_lock;
 603                                         if ((x & SX_LOCK_SHARED) == 0 ||
 604                                             SX_SHARERS(x) == 0)
 605                                                 break;
 606                                         cpu_spinwait();
 607 #ifdef KDTRACE_HOOKS
 608                                         spin_cnt++;
 609 #endif
 610                                 }
 611                                 KTR_STATE0(KTR_SCHED, "thread",
 612                                     sched_tdname(curthread), "running");
 613                                 if (i != asx_loops)
 614                                         continue;
 615                         }
 616                 }
 617 #endif
 618
 619                 sleepq_lock(&sx->lock_object);
 620                 x = sx->sx_lock;
 621
 622                 /*
 623                  * If the lock was released while spinning on the
 624                  * sleep queue chain lock, try again.
 625                  */
 626                 if (x == SX_LOCK_UNLOCKED) {
 627                         sleepq_release(&sx->lock_object);
 628                         continue;
 629                 }
 630
 631 #ifdef ADAPTIVE_SX
 632                 /*
 633                  * The current lock owner might have started executing
 634                  * on another CPU (or the lock could have changed
 635                  * owners) while we were waiting on the sleep queue
 636                  * chain lock.  If so, drop the sleep queue lock and try
 637                  * again.
 638                  */
 639                 if (!(x & SX_LOCK_SHARED) &&
 640                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 641                         owner = (struct thread *)SX_OWNER(x);
 642                         if (TD_IS_RUNNING(owner)) {
 643                                 sleepq_release(&sx->lock_object);
 644                                 continue;
 645                         }
 646                 }
 647 #endif
 648
 649                 /*
 650                  * If an exclusive lock was released with both shared
 651                  * and exclusive waiters and a shared waiter hasn't
 652                  * woken up and acquired the lock yet, sx_lock will be
 653                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 654                  * If we see that value, try to acquire it once.  Note
 655                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 656                  * as there are other exclusive waiters still.  If we
 657                  * fail, restart the loop.
 658                  */
 659                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
 660                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
 661                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
 662                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
 663                                 sleepq_release(&sx->lock_object);
 664                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 665                                     __func__, sx);
 666                                 break;
 667                         }
 668                         sleepq_release(&sx->lock_object);
 669                         continue;
 670                 }
 671
 672                 /*
 673                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 674                  * than loop back and retry.
 675                  */
 676                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 677                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 678                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 679                                 sleepq_release(&sx->lock_object);
 680                                 continue;
 681                         }
 682                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 683                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 684                                     __func__, sx);
 685                 }
 686
 687                 /*
 688                  * Since we have been unable to acquire the exclusive
 689                  * lock and the exclusive waiters flag is set, we have
 690                  * to sleep.
 691                  */
 692                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 693                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 694                             __func__, sx);
 695
 696 #ifdef KDTRACE_HOOKS
 697                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 698 #endif
 699                 GIANT_SAVE();
 700                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 701                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 702                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 703                 if (!(opts & SX_INTERRUPTIBLE))
 704                         sleepq_wait(&sx->lock_object, 0);
 705                 else
 706                         error = sleepq_wait_sig(&sx->lock_object, 0);
 707 #ifdef KDTRACE_HOOKS
 708                 sleep_time += lockstat_nsecs(&sx->lock_object);
 709                 sleep_cnt++;
 710 #endif
 711                 if (error) {
 712                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 713                                 CTR2(KTR_LOCK,
 714                         "%s: interruptible sleep by %p suspended by signal",
 715                                     __func__, sx);
 716                         break;
 717                 }
 718                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 719                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 720                             __func__, sx);
 721         }
 722 #ifdef KDTRACE_HOOKS
 723         all_time += lockstat_nsecs(&sx->lock_object);
 724         if (sleep_time)
 725                 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time,
 726                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 727                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 728         if (spin_cnt > sleep_cnt)
 729                 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time,
 730                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 731                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 732 #endif
 733         if (!error)
 734                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
 735                     contested, waittime, file, line);
 736         GIANT_RESTORE();
 737         return (error);
 738 }
 739
 740 /*
 741  * This function represents the so-called 'hard case' for sx_xunlock
 742  * operation.  All 'easy case' failures are redirected to this.  Note
 743  * that ideally this would be a static function, but it needs to be
 744  * accessible from at least sx.h.
 745  */
 746 void
 747 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
 748 {
 749         uintptr_t x;
 750         int queue, wakeup_swapper;
 751
 752         if (SCHEDULER_STOPPED())
 753                 return;
 754
 755         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
 756
 757         /* If the lock is recursed, then unrecurse one level. */
 758         if (sx_xlocked(sx) && sx_recursed(sx)) {
 759                 if ((--sx->sx_recurse) == 0)
 760                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 761                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 762                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 763                 return;
 764         }
 765         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
 766             SX_LOCK_EXCLUSIVE_WAITERS));
 767         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 768                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 769
 770         sleepq_lock(&sx->lock_object);
 771         x = SX_LOCK_UNLOCKED;
 772
 773         /*
 774          * The wake up algorithm here is quite simple and probably not
 775          * ideal.  It gives precedence to shared waiters if they are
 776          * present.  For this condition, we have to preserve the
 777          * state of the exclusive waiters flag.
 778          * If interruptible sleeps left the shared queue empty avoid a
 779          * starvation for the threads sleeping on the exclusive queue by giving
 780          * them precedence and cleaning up the shared waiters bit anyway.
 781          */
 782         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
 783             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
 784                 queue = SQ_SHARED_QUEUE;
 785                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
 786         } else
 787                 queue = SQ_EXCLUSIVE_QUEUE;
 788
 789         /* Wake up all the waiters for the specific queue. */
 790         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 791                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 792                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 793                     "exclusive");
 794         atomic_store_rel_ptr(&sx->sx_lock, x);
 795         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 796             queue);
 797         sleepq_release(&sx->lock_object);
 798         if (wakeup_swapper)
 799                 kick_proc0();
 800 }
 801
 802 /*
 803  * This function represents the so-called 'hard case' for sx_slock
 804  * operation.  All 'easy case' failures are redirected to this.  Note
 805  * that ideally this would be a static function, but it needs to be
 806  * accessible from at least sx.h.
 807  */
 808 int
 809 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
 810 {
 811         GIANT_DECLARE;
 812 #ifdef ADAPTIVE_SX
 813         volatile struct thread *owner;
 814 #endif
 815 #ifdef LOCK_PROFILING
 816         uint64_t waittime = 0;
 817         int contested = 0;
 818 #endif
 819         uintptr_t x;
 820         int error = 0;
 821 #ifdef KDTRACE_HOOKS
 822         uintptr_t state;
 823         uint64_t spin_cnt = 0;
 824         uint64_t sleep_cnt = 0;
 825         int64_t sleep_time = 0;
 826         int64_t all_time = 0;
 827 #endif
 828
 829         if (SCHEDULER_STOPPED())
 830                 return (0);
 831
 832 #ifdef KDTRACE_HOOKS
 833         state = sx->sx_lock;
 834         all_time -= lockstat_nsecs(&sx->lock_object);
 835 #endif
 836
 837         /*
 838          * As with rwlocks, we don't make any attempt to try to block
 839          * shared locks once there is an exclusive waiter.
 840          */
 841         for (;;) {
 842 #ifdef KDTRACE_HOOKS
 843                 spin_cnt++;
 844 #endif
 845                 x = sx->sx_lock;
 846
 847                 /*
 848                  * If no other thread has an exclusive lock then try to bump up
 849                  * the count of sharers.  Since we have to preserve the state
 850                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 851                  * shared lock loop back and retry.
 852                  */
 853                 if (x & SX_LOCK_SHARED) {
 854                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
 855                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
 856                             x + SX_ONE_SHARER)) {
 857                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 858                                         CTR4(KTR_LOCK,
 859                                             "%s: %p succeed %p -> %p", __func__,
 860                                             sx, (void *)x,
 861                                             (void *)(x + SX_ONE_SHARER));
 862                                 break;
 863                         }
 864                         continue;
 865                 }
 866 #ifdef HWPMC_HOOKS
 867                 PMC_SOFT_CALL( , , lock, failed);
 868 #endif
 869                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 870                     &waittime);
 871
 872 #ifdef ADAPTIVE_SX
 873                 /*
 874                  * If the owner is running on another CPU, spin until
 875                  * the owner stops running or the state of the lock
 876                  * changes.
 877                  */
 878                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 879                         x = SX_OWNER(x);
 880                         owner = (struct thread *)x;
 881                         if (TD_IS_RUNNING(owner)) {
 882                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 883                                         CTR3(KTR_LOCK,
 884                                             "%s: spinning on %p held by %p",
 885                                             __func__, sx, owner);
 886                                 KTR_STATE1(KTR_SCHED, "thread",
 887                                     sched_tdname(curthread), "spinning",
 888                                     "lockname:\"%s\"", sx->lock_object.lo_name);
 889                                 GIANT_SAVE();
 890                                 while (SX_OWNER(sx->sx_lock) == x &&
 891                                     TD_IS_RUNNING(owner)) {
 892 #ifdef KDTRACE_HOOKS
 893                                         spin_cnt++;
 894 #endif
 895                                         cpu_spinwait();
 896                                 }
 897                                 KTR_STATE0(KTR_SCHED, "thread",
 898                                     sched_tdname(curthread), "running");
 899                                 continue;
 900                         }
 901                 }
 902 #endif
 903
 904                 /*
 905                  * Some other thread already has an exclusive lock, so
 906                  * start the process of blocking.
 907                  */
 908                 sleepq_lock(&sx->lock_object);
 909                 x = sx->sx_lock;
 910
 911                 /*
 912                  * The lock could have been released while we spun.
 913                  * In this case loop back and retry.
 914                  */
 915                 if (x & SX_LOCK_SHARED) {
 916                         sleepq_release(&sx->lock_object);
 917                         continue;
 918                 }
 919
 920 #ifdef ADAPTIVE_SX
 921                 /*
 922                  * If the owner is running on another CPU, spin until
 923                  * the owner stops running or the state of the lock
 924                  * changes.
 925                  */
 926                 if (!(x & SX_LOCK_SHARED) &&
 927                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
 928                         owner = (struct thread *)SX_OWNER(x);
 929                         if (TD_IS_RUNNING(owner)) {
 930                                 sleepq_release(&sx->lock_object);
 931                                 continue;
 932                         }
 933                 }
 934 #endif
 935
 936                 /*
 937                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
 938                  * fail to set it drop the sleep queue lock and loop
 939                  * back.
 940                  */
 941                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
 942                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
 943                             x | SX_LOCK_SHARED_WAITERS)) {
 944                                 sleepq_release(&sx->lock_object);
 945                                 continue;
 946                         }
 947                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 948                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
 949                                     __func__, sx);
 950                 }
 951
 952                 /*
 953                  * Since we have been unable to acquire the shared lock,
 954                  * we have to sleep.
 955                  */
 956                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 957                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 958                             __func__, sx);
 959
 960 #ifdef KDTRACE_HOOKS
 961                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 962 #endif
 963                 GIANT_SAVE();
 964                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 965                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 966                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
 967                 if (!(opts & SX_INTERRUPTIBLE))
 968                         sleepq_wait(&sx->lock_object, 0);
 969                 else
 970                         error = sleepq_wait_sig(&sx->lock_object, 0);
 971 #ifdef KDTRACE_HOOKS
 972                 sleep_time += lockstat_nsecs(&sx->lock_object);
 973                 sleep_cnt++;
 974 #endif
 975                 if (error) {
 976                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 977                                 CTR2(KTR_LOCK,
 978                         "%s: interruptible sleep by %p suspended by signal",
 979                                     __func__, sx);
 980                         break;
 981                 }
 982                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 983                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 984                             __func__, sx);
 985         }
 986 #ifdef KDTRACE_HOOKS
 987         all_time += lockstat_nsecs(&sx->lock_object);
 988         if (sleep_time)
 989                 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time,
 990                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 991                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 992         if (spin_cnt > sleep_cnt)
 993                 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time,
 994                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
 995                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 996 #endif
 997         if (error == 0)
 998                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
 999                     contested, waittime, file, line);
1000         GIANT_RESTORE();
1001         return (error);
1002 }
1003
1004 /*
1005  * This function represents the so-called 'hard case' for sx_sunlock
1006  * operation.  All 'easy case' failures are redirected to this.  Note
1007  * that ideally this would be a static function, but it needs to be
1008  * accessible from at least sx.h.
1009  */
1010 void
1011 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
1012 {
1013         uintptr_t x;
1014         int wakeup_swapper;
1015
1016         if (SCHEDULER_STOPPED())
1017                 return;
1018
1019         for (;;) {
1020                 x = sx->sx_lock;
1021
1022                 /*
1023                  * We should never have sharers while at least one thread
1024                  * holds a shared lock.
1025                  */
1026                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
1027                     ("%s: waiting sharers", __func__));
1028
1029                 /*
1030                  * See if there is more than one shared lock held.  If
1031                  * so, just drop one and return.
1032                  */
1033                 if (SX_SHARERS(x) > 1) {
1034                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
1035                             x - SX_ONE_SHARER)) {
1036                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1037                                         CTR4(KTR_LOCK,
1038                                             "%s: %p succeeded %p -> %p",
1039                                             __func__, sx, (void *)x,
1040                                             (void *)(x - SX_ONE_SHARER));
1041                                 break;
1042                         }
1043                         continue;
1044                 }
1045
1046                 /*
1047                  * If there aren't any waiters for an exclusive lock,
1048                  * then try to drop it quickly.
1049                  */
1050                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1051                         MPASS(x == SX_SHARERS_LOCK(1));
1052                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1053                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1054                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1055                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
1056                                             __func__, sx);
1057                                 break;
1058                         }
1059                         continue;
1060                 }
1061
1062                 /*
1063                  * At this point, there should just be one sharer with
1064                  * exclusive waiters.
1065                  */
1066                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1067
1068                 sleepq_lock(&sx->lock_object);
1069
1070                 /*
1071                  * Wake up semantic here is quite simple:
1072                  * Just wake up all the exclusive waiters.
1073                  * Note that the state of the lock could have changed,
1074                  * so if it fails loop back and retry.
1075                  */
1076                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1077                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1078                     SX_LOCK_UNLOCKED)) {
1079                         sleepq_release(&sx->lock_object);
1080                         continue;
1081                 }
1082                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1083                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1084                             "exclusive queue", __func__, sx);
1085                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1086                     0, SQ_EXCLUSIVE_QUEUE);
1087                 sleepq_release(&sx->lock_object);
1088                 if (wakeup_swapper)
1089                         kick_proc0();
1090                 break;
1091         }
1092 }
1093
1094 #ifdef INVARIANT_SUPPORT
1095 #ifndef INVARIANTS
1096 #undef  _sx_assert
1097 #endif
1098
1099 /*
1100  * In the non-WITNESS case, sx_assert() can only detect that at least
1101  * *some* thread owns an slock, but it cannot guarantee that *this*
1102  * thread owns an slock.
1103  */
1104 void
1105 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1106 {
1107 #ifndef WITNESS
1108         int slocked = 0;
1109 #endif
1110
1111         if (panicstr != NULL)
1112                 return;
1113         switch (what) {
1114         case SA_SLOCKED:
1115         case SA_SLOCKED | SA_NOTRECURSED:
1116         case SA_SLOCKED | SA_RECURSED:
1117 #ifndef WITNESS
1118                 slocked = 1;
1119                 /* FALLTHROUGH */
1120 #endif
1121         case SA_LOCKED:
1122         case SA_LOCKED | SA_NOTRECURSED:
1123         case SA_LOCKED | SA_RECURSED:
1124 #ifdef WITNESS
1125                 witness_assert(&sx->lock_object, what, file, line);
1126 #else
1127                 /*
1128                  * If some other thread has an exclusive lock or we
1129                  * have one and are asserting a shared lock, fail.
1130                  * Also, if no one has a lock at all, fail.
1131                  */
1132                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1133                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1134                     sx_xholder(sx) != curthread)))
1135                         panic("Lock %s not %slocked @ %s:%d\n",
1136                             sx->lock_object.lo_name, slocked ? "share " : "",
1137                             file, line);
1138
1139                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1140                         if (sx_recursed(sx)) {
1141                                 if (what & SA_NOTRECURSED)
1142                                         panic("Lock %s recursed @ %s:%d\n",
1143                                             sx->lock_object.lo_name, file,
1144                                             line);
1145                         } else if (what & SA_RECURSED)
1146                                 panic("Lock %s not recursed @ %s:%d\n",
1147                                     sx->lock_object.lo_name, file, line);
1148                 }
1149 #endif
1150                 break;
1151         case SA_XLOCKED:
1152         case SA_XLOCKED | SA_NOTRECURSED:
1153         case SA_XLOCKED | SA_RECURSED:
1154                 if (sx_xholder(sx) != curthread)
1155                         panic("Lock %s not exclusively locked @ %s:%d\n",
1156                             sx->lock_object.lo_name, file, line);
1157                 if (sx_recursed(sx)) {
1158                         if (what & SA_NOTRECURSED)
1159                                 panic("Lock %s recursed @ %s:%d\n",
1160                                     sx->lock_object.lo_name, file, line);
1161                 } else if (what & SA_RECURSED)
1162                         panic("Lock %s not recursed @ %s:%d\n",
1163                             sx->lock_object.lo_name, file, line);
1164                 break;
1165         case SA_UNLOCKED:
1166 #ifdef WITNESS
1167                 witness_assert(&sx->lock_object, what, file, line);
1168 #else
1169                 /*
1170                  * If we hold an exclusve lock fail.  We can't
1171                  * reliably check to see if we hold a shared lock or
1172                  * not.
1173                  */
1174                 if (sx_xholder(sx) == curthread)
1175                         panic("Lock %s exclusively locked @ %s:%d\n",
1176                             sx->lock_object.lo_name, file, line);
1177 #endif
1178                 break;
1179         default:
1180                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1181                     line);
1182         }
1183 }
1184 #endif  /* INVARIANT_SUPPORT */
1185
1186 #ifdef DDB
1187 static void
1188 db_show_sx(const struct lock_object *lock)
1189 {
1190         struct thread *td;
1191         const struct sx *sx;
1192
1193         sx = (const struct sx *)lock;
1194
1195         db_printf(" state: ");
1196         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1197                 db_printf("UNLOCKED\n");
1198         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1199                 db_printf("DESTROYED\n");
1200                 return;
1201         } else if (sx->sx_lock & SX_LOCK_SHARED)
1202                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1203         else {
1204                 td = sx_xholder(sx);
1205                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1206                     td->td_tid, td->td_proc->p_pid, td->td_name);
1207                 if (sx_recursed(sx))
1208                         db_printf(" recursed: %d\n", sx->sx_recurse);
1209         }
1210
1211         db_printf(" waiters: ");
1212         switch(sx->sx_lock &
1213             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1214         case SX_LOCK_SHARED_WAITERS:
1215                 db_printf("shared\n");
1216                 break;
1217         case SX_LOCK_EXCLUSIVE_WAITERS:
1218                 db_printf("exclusive\n");
1219                 break;
1220         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1221                 db_printf("exclusive and shared\n");
1222                 break;
1223         default:
1224                 db_printf("none\n");
1225         }
1226 }
1227
1228 /*
1229  * Check to see if a thread that is blocked on a sleep queue is actually
1230  * blocked on an sx lock.  If so, output some details and return true.
1231  * If the lock has an exclusive owner, return that in *ownerp.
1232  */
1233 int
1234 sx_chain(struct thread *td, struct thread **ownerp)
1235 {
1236         struct sx *sx;
1237
1238         /*
1239          * Check to see if this thread is blocked on an sx lock.
1240          * First, we check the lock class.  If that is ok, then we
1241          * compare the lock name against the wait message.
1242          */
1243         sx = td->td_wchan;
1244         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1245             sx->lock_object.lo_name != td->td_wmesg)
1246                 return (0);
1247
1248         /* We think we have an sx lock, so output some details. */
1249         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1250         *ownerp = sx_xholder(sx);
1251         if (sx->sx_lock & SX_LOCK_SHARED)
1252                 db_printf("SLOCK (count %ju)\n",
1253                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1254         else
1255                 db_printf("XLOCK\n");
1256         return (1);
1257 }
1258 #endif