The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_sx.c

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    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: releng/9.2/sys/kern/kern_sx.c 250581 2013-05-12 22:01:22Z hiren $");
   46 
   47 #include <sys/param.h>
   48 #include <sys/systm.h>
   49 #include <sys/ktr.h>
   50 #include <sys/lock.h>
   51 #include <sys/mutex.h>
   52 #include <sys/proc.h>
   53 #include <sys/sleepqueue.h>
   54 #include <sys/sx.h>
   55 #include <sys/sysctl.h>
   56 
   57 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
   58 #include <machine/cpu.h>
   59 #endif
   60 
   61 #ifdef DDB
   62 #include <ddb/ddb.h>
   63 #endif
   64 
   65 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
   66 #define ADAPTIVE_SX
   67 #endif
   68 
   69 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
   70 
   71 #ifdef HWPMC_HOOKS
   72 #include <sys/pmckern.h>
   73 PMC_SOFT_DECLARE( , , lock, failed);
   74 #endif
   75 
   76 /* Handy macros for sleep queues. */
   77 #define SQ_EXCLUSIVE_QUEUE      0
   78 #define SQ_SHARED_QUEUE         1
   79 
   80 #ifdef ADAPTIVE_SX
   81 #define ASX_RETRIES             10
   82 #define ASX_LOOPS               10000
   83 #endif
   84 
   85 /*
   86  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
   87  * drop Giant anytime we have to sleep or if we adaptively spin.
   88  */
   89 #define GIANT_DECLARE                                                   \
   90         int _giantcnt = 0;                                              \
   91         WITNESS_SAVE_DECL(Giant)                                        \
   92 
   93 #define GIANT_SAVE() do {                                               \
   94         if (mtx_owned(&Giant)) {                                        \
   95                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
   96                 while (mtx_owned(&Giant)) {                             \
   97                         _giantcnt++;                                    \
   98                         mtx_unlock(&Giant);                             \
   99                 }                                                       \
  100         }                                                               \
  101 } while (0)
  102 
  103 #define GIANT_RESTORE() do {                                            \
  104         if (_giantcnt > 0) {                                            \
  105                 mtx_assert(&Giant, MA_NOTOWNED);                        \
  106                 while (_giantcnt--)                                     \
  107                         mtx_lock(&Giant);                               \
  108                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
  109         }                                                               \
  110 } while (0)
  111 
  112 /*
  113  * Returns true if an exclusive lock is recursed.  It assumes
  114  * curthread currently has an exclusive lock.
  115  */
  116 #define sx_recurse              lock_object.lo_data
  117 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
  118 
  119 static void     assert_sx(struct lock_object *lock, int what);
  120 #ifdef DDB
  121 static void     db_show_sx(struct lock_object *lock);
  122 #endif
  123 static void     lock_sx(struct lock_object *lock, int how);
  124 #ifdef KDTRACE_HOOKS
  125 static int      owner_sx(struct lock_object *lock, struct thread **owner);
  126 #endif
  127 static int      unlock_sx(struct lock_object *lock);
  128 
  129 struct lock_class lock_class_sx = {
  130         .lc_name = "sx",
  131         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
  132         .lc_assert = assert_sx,
  133 #ifdef DDB
  134         .lc_ddb_show = db_show_sx,
  135 #endif
  136         .lc_lock = lock_sx,
  137         .lc_unlock = unlock_sx,
  138 #ifdef KDTRACE_HOOKS
  139         .lc_owner = owner_sx,
  140 #endif
  141 };
  142 
  143 #ifndef INVARIANTS
  144 #define _sx_assert(sx, what, file, line)
  145 #endif
  146 
  147 void
  148 assert_sx(struct lock_object *lock, int what)
  149 {
  150 
  151         sx_assert((struct sx *)lock, what);
  152 }
  153 
  154 void
  155 lock_sx(struct lock_object *lock, int how)
  156 {
  157         struct sx *sx;
  158 
  159         sx = (struct sx *)lock;
  160         if (how)
  161                 sx_xlock(sx);
  162         else
  163                 sx_slock(sx);
  164 }
  165 
  166 int
  167 unlock_sx(struct lock_object *lock)
  168 {
  169         struct sx *sx;
  170 
  171         sx = (struct sx *)lock;
  172         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
  173         if (sx_xlocked(sx)) {
  174                 sx_xunlock(sx);
  175                 return (1);
  176         } else {
  177                 sx_sunlock(sx);
  178                 return (0);
  179         }
  180 }
  181 
  182 #ifdef KDTRACE_HOOKS
  183 int
  184 owner_sx(struct lock_object *lock, struct thread **owner)
  185 {
  186         struct sx *sx = (struct sx *)lock;
  187         uintptr_t x = sx->sx_lock;
  188 
  189         *owner = (struct thread *)SX_OWNER(x);
  190         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
  191             (*owner != NULL));
  192 }
  193 #endif
  194 
  195 void
  196 sx_sysinit(void *arg)
  197 {
  198         struct sx_args *sargs = arg;
  199 
  200         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
  201 }
  202 
  203 void
  204 sx_init_flags(struct sx *sx, const char *description, int opts)
  205 {
  206         int flags;
  207 
  208         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
  209             SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
  210         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
  211             ("%s: sx_lock not aligned for %s: %p", __func__, description,
  212             &sx->sx_lock));
  213 
  214         flags = LO_SLEEPABLE | LO_UPGRADABLE;
  215         if (opts & SX_DUPOK)
  216                 flags |= LO_DUPOK;
  217         if (opts & SX_NOPROFILE)
  218                 flags |= LO_NOPROFILE;
  219         if (!(opts & SX_NOWITNESS))
  220                 flags |= LO_WITNESS;
  221         if (opts & SX_RECURSE)
  222                 flags |= LO_RECURSABLE;
  223         if (opts & SX_QUIET)
  224                 flags |= LO_QUIET;
  225 
  226         flags |= opts & SX_NOADAPTIVE;
  227         sx->sx_lock = SX_LOCK_UNLOCKED;
  228         sx->sx_recurse = 0;
  229         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
  230 }
  231 
  232 void
  233 sx_destroy(struct sx *sx)
  234 {
  235 
  236         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
  237         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
  238         sx->sx_lock = SX_LOCK_DESTROYED;
  239         lock_destroy(&sx->lock_object);
  240 }
  241 
  242 int
  243 _sx_slock(struct sx *sx, int opts, const char *file, int line)
  244 {
  245         int error = 0;
  246 
  247         if (SCHEDULER_STOPPED())
  248                 return (0);
  249         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  250             ("sx_slock() of destroyed sx @ %s:%d", file, line));
  251         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
  252         error = __sx_slock(sx, opts, file, line);
  253         if (!error) {
  254                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
  255                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
  256                 curthread->td_locks++;
  257         }
  258 
  259         return (error);
  260 }
  261 
  262 int
  263 _sx_try_slock(struct sx *sx, const char *file, int line)
  264 {
  265         uintptr_t x;
  266 
  267         if (SCHEDULER_STOPPED())
  268                 return (1);
  269 
  270         for (;;) {
  271                 x = sx->sx_lock;
  272                 KASSERT(x != SX_LOCK_DESTROYED,
  273                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
  274                 if (!(x & SX_LOCK_SHARED))
  275                         break;
  276                 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
  277                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
  278                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
  279                         curthread->td_locks++;
  280                         return (1);
  281                 }
  282         }
  283 
  284         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
  285         return (0);
  286 }
  287 
  288 int
  289 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
  290 {
  291         int error = 0;
  292 
  293         if (SCHEDULER_STOPPED())
  294                 return (0);
  295         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  296             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
  297         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
  298             line, NULL);
  299         error = __sx_xlock(sx, curthread, opts, file, line);
  300         if (!error) {
  301                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
  302                     file, line);
  303                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
  304                 curthread->td_locks++;
  305         }
  306 
  307         return (error);
  308 }
  309 
  310 int
  311 _sx_try_xlock(struct sx *sx, const char *file, int line)
  312 {
  313         int rval;
  314 
  315         if (SCHEDULER_STOPPED())
  316                 return (1);
  317 
  318         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  319             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
  320 
  321         if (sx_xlocked(sx) &&
  322             (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
  323                 sx->sx_recurse++;
  324                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  325                 rval = 1;
  326         } else
  327                 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
  328                     (uintptr_t)curthread);
  329         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
  330         if (rval) {
  331                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
  332                     file, line);
  333                 curthread->td_locks++;
  334         }
  335 
  336         return (rval);
  337 }
  338 
  339 void
  340 _sx_sunlock(struct sx *sx, const char *file, int line)
  341 {
  342 
  343         if (SCHEDULER_STOPPED())
  344                 return;
  345         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  346             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
  347         _sx_assert(sx, SA_SLOCKED, file, line);
  348         curthread->td_locks--;
  349         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
  350         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
  351         __sx_sunlock(sx, file, line);
  352         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
  353 }
  354 
  355 void
  356 _sx_xunlock(struct sx *sx, const char *file, int line)
  357 {
  358 
  359         if (SCHEDULER_STOPPED())
  360                 return;
  361         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  362             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
  363         _sx_assert(sx, SA_XLOCKED, file, line);
  364         curthread->td_locks--;
  365         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
  366         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
  367             line);
  368         if (!sx_recursed(sx))
  369                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
  370         __sx_xunlock(sx, curthread, file, line);
  371 }
  372 
  373 /*
  374  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
  375  * This will only succeed if this thread holds a single shared lock.
  376  * Return 1 if if the upgrade succeed, 0 otherwise.
  377  */
  378 int
  379 _sx_try_upgrade(struct sx *sx, const char *file, int line)
  380 {
  381         uintptr_t x;
  382         int success;
  383 
  384         if (SCHEDULER_STOPPED())
  385                 return (1);
  386 
  387         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  388             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
  389         _sx_assert(sx, SA_SLOCKED, file, line);
  390 
  391         /*
  392          * Try to switch from one shared lock to an exclusive lock.  We need
  393          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
  394          * we will wake up the exclusive waiters when we drop the lock.
  395          */
  396         x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
  397         success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
  398             (uintptr_t)curthread | x);
  399         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
  400         if (success) {
  401                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
  402                     file, line);
  403                 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
  404         }
  405         return (success);
  406 }
  407 
  408 /*
  409  * Downgrade an unrecursed exclusive lock into a single shared lock.
  410  */
  411 void
  412 _sx_downgrade(struct sx *sx, const char *file, int line)
  413 {
  414         uintptr_t x;
  415         int wakeup_swapper;
  416 
  417         if (SCHEDULER_STOPPED())
  418                 return;
  419 
  420         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
  421             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
  422         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
  423 #ifndef INVARIANTS
  424         if (sx_recursed(sx))
  425                 panic("downgrade of a recursed lock");
  426 #endif
  427 
  428         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
  429 
  430         /*
  431          * Try to switch from an exclusive lock with no shared waiters
  432          * to one sharer with no shared waiters.  If there are
  433          * exclusive waiters, we don't need to lock the sleep queue so
  434          * long as we preserve the flag.  We do one quick try and if
  435          * that fails we grab the sleepq lock to keep the flags from
  436          * changing and do it the slow way.
  437          *
  438          * We have to lock the sleep queue if there are shared waiters
  439          * so we can wake them up.
  440          */
  441         x = sx->sx_lock;
  442         if (!(x & SX_LOCK_SHARED_WAITERS) &&
  443             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
  444             (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
  445                 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
  446                 return;
  447         }
  448 
  449         /*
  450          * Lock the sleep queue so we can read the waiters bits
  451          * without any races and wakeup any shared waiters.
  452          */
  453         sleepq_lock(&sx->lock_object);
  454 
  455         /*
  456          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
  457          * shared lock.  If there are any shared waiters, wake them up.
  458          */
  459         wakeup_swapper = 0;
  460         x = sx->sx_lock;
  461         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
  462             (x & SX_LOCK_EXCLUSIVE_WAITERS));
  463         if (x & SX_LOCK_SHARED_WAITERS)
  464                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
  465                     0, SQ_SHARED_QUEUE);
  466         sleepq_release(&sx->lock_object);
  467 
  468         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
  469         LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
  470 
  471         if (wakeup_swapper)
  472                 kick_proc0();
  473 }
  474 
  475 /*
  476  * This function represents the so-called 'hard case' for sx_xlock
  477  * operation.  All 'easy case' failures are redirected to this.  Note
  478  * that ideally this would be a static function, but it needs to be
  479  * accessible from at least sx.h.
  480  */
  481 int
  482 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
  483     int line)
  484 {
  485         GIANT_DECLARE;
  486 #ifdef ADAPTIVE_SX
  487         volatile struct thread *owner;
  488         u_int i, spintries = 0;
  489 #endif
  490         uintptr_t x;
  491 #ifdef LOCK_PROFILING
  492         uint64_t waittime = 0;
  493         int contested = 0;
  494 #endif
  495         int error = 0;
  496 #ifdef  KDTRACE_HOOKS
  497         uint64_t spin_cnt = 0;
  498         uint64_t sleep_cnt = 0;
  499         int64_t sleep_time = 0;
  500 #endif
  501 
  502         if (SCHEDULER_STOPPED())
  503                 return (0);
  504 
  505         /* If we already hold an exclusive lock, then recurse. */
  506         if (sx_xlocked(sx)) {
  507                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
  508             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
  509                     sx->lock_object.lo_name, file, line));
  510                 sx->sx_recurse++;
  511                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  512                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  513                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
  514                 return (0);
  515         }
  516 
  517         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  518                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
  519                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
  520 
  521         while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
  522 #ifdef KDTRACE_HOOKS
  523                 spin_cnt++;
  524 #endif
  525 #ifdef HWPMC_HOOKS
  526                 PMC_SOFT_CALL( , , lock, failed);
  527 #endif
  528                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
  529                     &waittime);
  530 #ifdef ADAPTIVE_SX
  531                 /*
  532                  * If the lock is write locked and the owner is
  533                  * running on another CPU, spin until the owner stops
  534                  * running or the state of the lock changes.
  535                  */
  536                 x = sx->sx_lock;
  537                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  538                         if ((x & SX_LOCK_SHARED) == 0) {
  539                                 x = SX_OWNER(x);
  540                                 owner = (struct thread *)x;
  541                                 if (TD_IS_RUNNING(owner)) {
  542                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  543                                                 CTR3(KTR_LOCK,
  544                                             "%s: spinning on %p held by %p",
  545                                                     __func__, sx, owner);
  546                                         GIANT_SAVE();
  547                                         while (SX_OWNER(sx->sx_lock) == x &&
  548                                             TD_IS_RUNNING(owner)) {
  549                                                 cpu_spinwait();
  550 #ifdef KDTRACE_HOOKS
  551                                                 spin_cnt++;
  552 #endif
  553                                         }
  554                                         continue;
  555                                 }
  556                         } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) {
  557                                 GIANT_SAVE();
  558                                 spintries++;
  559                                 for (i = 0; i < ASX_LOOPS; i++) {
  560                                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  561                                                 CTR4(KTR_LOCK,
  562                                     "%s: shared spinning on %p with %u and %u",
  563                                                     __func__, sx, spintries, i);
  564                                         x = sx->sx_lock;
  565                                         if ((x & SX_LOCK_SHARED) == 0 ||
  566                                             SX_SHARERS(x) == 0)
  567                                                 break;
  568                                         cpu_spinwait();
  569 #ifdef KDTRACE_HOOKS
  570                                         spin_cnt++;
  571 #endif
  572                                 }
  573                                 if (i != ASX_LOOPS)
  574                                         continue;
  575                         }
  576                 }
  577 #endif
  578 
  579                 sleepq_lock(&sx->lock_object);
  580                 x = sx->sx_lock;
  581 
  582                 /*
  583                  * If the lock was released while spinning on the
  584                  * sleep queue chain lock, try again.
  585                  */
  586                 if (x == SX_LOCK_UNLOCKED) {
  587                         sleepq_release(&sx->lock_object);
  588                         continue;
  589                 }
  590 
  591 #ifdef ADAPTIVE_SX
  592                 /*
  593                  * The current lock owner might have started executing
  594                  * on another CPU (or the lock could have changed
  595                  * owners) while we were waiting on the sleep queue
  596                  * chain lock.  If so, drop the sleep queue lock and try
  597                  * again.
  598                  */
  599                 if (!(x & SX_LOCK_SHARED) &&
  600                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  601                         owner = (struct thread *)SX_OWNER(x);
  602                         if (TD_IS_RUNNING(owner)) {
  603                                 sleepq_release(&sx->lock_object);
  604                                 continue;
  605                         }
  606                 }
  607 #endif
  608 
  609                 /*
  610                  * If an exclusive lock was released with both shared
  611                  * and exclusive waiters and a shared waiter hasn't
  612                  * woken up and acquired the lock yet, sx_lock will be
  613                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
  614                  * If we see that value, try to acquire it once.  Note
  615                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
  616                  * as there are other exclusive waiters still.  If we
  617                  * fail, restart the loop.
  618                  */
  619                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
  620                         if (atomic_cmpset_acq_ptr(&sx->sx_lock,
  621                             SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
  622                             tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
  623                                 sleepq_release(&sx->lock_object);
  624                                 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
  625                                     __func__, sx);
  626                                 break;
  627                         }
  628                         sleepq_release(&sx->lock_object);
  629                         continue;
  630                 }
  631 
  632                 /*
  633                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
  634                  * than loop back and retry.
  635                  */
  636                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
  637                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
  638                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
  639                                 sleepq_release(&sx->lock_object);
  640                                 continue;
  641                         }
  642                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  643                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
  644                                     __func__, sx);
  645                 }
  646 
  647                 /*
  648                  * Since we have been unable to acquire the exclusive
  649                  * lock and the exclusive waiters flag is set, we have
  650                  * to sleep.
  651                  */
  652                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  653                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
  654                             __func__, sx);
  655 
  656 #ifdef KDTRACE_HOOKS
  657                 sleep_time -= lockstat_nsecs();
  658 #endif
  659                 GIANT_SAVE();
  660                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
  661                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
  662                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
  663                 if (!(opts & SX_INTERRUPTIBLE))
  664                         sleepq_wait(&sx->lock_object, 0);
  665                 else
  666                         error = sleepq_wait_sig(&sx->lock_object, 0);
  667 #ifdef KDTRACE_HOOKS
  668                 sleep_time += lockstat_nsecs();
  669                 sleep_cnt++;
  670 #endif
  671                 if (error) {
  672                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  673                                 CTR2(KTR_LOCK,
  674                         "%s: interruptible sleep by %p suspended by signal",
  675                                     __func__, sx);
  676                         break;
  677                 }
  678                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  679                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
  680                             __func__, sx);
  681         }
  682 
  683         GIANT_RESTORE();
  684         if (!error)
  685                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
  686                     contested, waittime, file, line);
  687 #ifdef KDTRACE_HOOKS
  688         if (sleep_time)
  689                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
  690         if (spin_cnt > sleep_cnt)
  691                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
  692 #endif
  693         return (error);
  694 }
  695 
  696 /*
  697  * This function represents the so-called 'hard case' for sx_xunlock
  698  * operation.  All 'easy case' failures are redirected to this.  Note
  699  * that ideally this would be a static function, but it needs to be
  700  * accessible from at least sx.h.
  701  */
  702 void
  703 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
  704 {
  705         uintptr_t x;
  706         int queue, wakeup_swapper;
  707 
  708         if (SCHEDULER_STOPPED())
  709                 return;
  710 
  711         MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
  712 
  713         /* If the lock is recursed, then unrecurse one level. */
  714         if (sx_xlocked(sx) && sx_recursed(sx)) {
  715                 if ((--sx->sx_recurse) == 0)
  716                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
  717                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  718                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
  719                 return;
  720         }
  721         MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
  722             SX_LOCK_EXCLUSIVE_WAITERS));
  723         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  724                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
  725 
  726         sleepq_lock(&sx->lock_object);
  727         x = SX_LOCK_UNLOCKED;
  728 
  729         /*
  730          * The wake up algorithm here is quite simple and probably not
  731          * ideal.  It gives precedence to shared waiters if they are
  732          * present.  For this condition, we have to preserve the
  733          * state of the exclusive waiters flag.
  734          * If interruptible sleeps left the shared queue empty avoid a
  735          * starvation for the threads sleeping on the exclusive queue by giving
  736          * them precedence and cleaning up the shared waiters bit anyway.
  737          */
  738         if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
  739             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
  740                 queue = SQ_SHARED_QUEUE;
  741                 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
  742         } else
  743                 queue = SQ_EXCLUSIVE_QUEUE;
  744 
  745         /* Wake up all the waiters for the specific queue. */
  746         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  747                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
  748                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
  749                     "exclusive");
  750         atomic_store_rel_ptr(&sx->sx_lock, x);
  751         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
  752             queue);
  753         sleepq_release(&sx->lock_object);
  754         if (wakeup_swapper)
  755                 kick_proc0();
  756 }
  757 
  758 /*
  759  * This function represents the so-called 'hard case' for sx_slock
  760  * operation.  All 'easy case' failures are redirected to this.  Note
  761  * that ideally this would be a static function, but it needs to be
  762  * accessible from at least sx.h.
  763  */
  764 int
  765 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
  766 {
  767         GIANT_DECLARE;
  768 #ifdef ADAPTIVE_SX
  769         volatile struct thread *owner;
  770 #endif
  771 #ifdef LOCK_PROFILING
  772         uint64_t waittime = 0;
  773         int contested = 0;
  774 #endif
  775         uintptr_t x;
  776         int error = 0;
  777 #ifdef KDTRACE_HOOKS
  778         uint64_t spin_cnt = 0;
  779         uint64_t sleep_cnt = 0;
  780         int64_t sleep_time = 0;
  781 #endif
  782 
  783         if (SCHEDULER_STOPPED())
  784                 return (0);
  785 
  786         /*
  787          * As with rwlocks, we don't make any attempt to try to block
  788          * shared locks once there is an exclusive waiter.
  789          */
  790         for (;;) {
  791 #ifdef KDTRACE_HOOKS
  792                 spin_cnt++;
  793 #endif
  794                 x = sx->sx_lock;
  795 
  796                 /*
  797                  * If no other thread has an exclusive lock then try to bump up
  798                  * the count of sharers.  Since we have to preserve the state
  799                  * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
  800                  * shared lock loop back and retry.
  801                  */
  802                 if (x & SX_LOCK_SHARED) {
  803                         MPASS(!(x & SX_LOCK_SHARED_WAITERS));
  804                         if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
  805                             x + SX_ONE_SHARER)) {
  806                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  807                                         CTR4(KTR_LOCK,
  808                                             "%s: %p succeed %p -> %p", __func__,
  809                                             sx, (void *)x,
  810                                             (void *)(x + SX_ONE_SHARER));
  811                                 break;
  812                         }
  813                         continue;
  814                 }
  815 #ifdef HWPMC_HOOKS
  816                 PMC_SOFT_CALL( , , lock, failed);
  817 #endif
  818                 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
  819                     &waittime);
  820 
  821 #ifdef ADAPTIVE_SX
  822                 /*
  823                  * If the owner is running on another CPU, spin until
  824                  * the owner stops running or the state of the lock
  825                  * changes.
  826                  */
  827                 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  828                         x = SX_OWNER(x);
  829                         owner = (struct thread *)x;
  830                         if (TD_IS_RUNNING(owner)) {
  831                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  832                                         CTR3(KTR_LOCK,
  833                                             "%s: spinning on %p held by %p",
  834                                             __func__, sx, owner);
  835                                 GIANT_SAVE();
  836                                 while (SX_OWNER(sx->sx_lock) == x &&
  837                                     TD_IS_RUNNING(owner)) {
  838 #ifdef KDTRACE_HOOKS
  839                                         spin_cnt++;
  840 #endif
  841                                         cpu_spinwait();
  842                                 }
  843                                 continue;
  844                         }
  845                 }
  846 #endif
  847 
  848                 /*
  849                  * Some other thread already has an exclusive lock, so
  850                  * start the process of blocking.
  851                  */
  852                 sleepq_lock(&sx->lock_object);
  853                 x = sx->sx_lock;
  854 
  855                 /*
  856                  * The lock could have been released while we spun.
  857                  * In this case loop back and retry.
  858                  */
  859                 if (x & SX_LOCK_SHARED) {
  860                         sleepq_release(&sx->lock_object);
  861                         continue;
  862                 }
  863 
  864 #ifdef ADAPTIVE_SX
  865                 /*
  866                  * If the owner is running on another CPU, spin until
  867                  * the owner stops running or the state of the lock
  868                  * changes.
  869                  */
  870                 if (!(x & SX_LOCK_SHARED) &&
  871                     (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
  872                         owner = (struct thread *)SX_OWNER(x);
  873                         if (TD_IS_RUNNING(owner)) {
  874                                 sleepq_release(&sx->lock_object);
  875                                 continue;
  876                         }
  877                 }
  878 #endif
  879 
  880                 /*
  881                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
  882                  * fail to set it drop the sleep queue lock and loop
  883                  * back.
  884                  */
  885                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
  886                         if (!atomic_cmpset_ptr(&sx->sx_lock, x,
  887                             x | SX_LOCK_SHARED_WAITERS)) {
  888                                 sleepq_release(&sx->lock_object);
  889                                 continue;
  890                         }
  891                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  892                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
  893                                     __func__, sx);
  894                 }
  895 
  896                 /*
  897                  * Since we have been unable to acquire the shared lock,
  898                  * we have to sleep.
  899                  */
  900                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  901                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
  902                             __func__, sx);
  903 
  904 #ifdef KDTRACE_HOOKS
  905                 sleep_time -= lockstat_nsecs();
  906 #endif
  907                 GIANT_SAVE();
  908                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
  909                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
  910                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
  911                 if (!(opts & SX_INTERRUPTIBLE))
  912                         sleepq_wait(&sx->lock_object, 0);
  913                 else
  914                         error = sleepq_wait_sig(&sx->lock_object, 0);
  915 #ifdef KDTRACE_HOOKS
  916                 sleep_time += lockstat_nsecs();
  917                 sleep_cnt++;
  918 #endif
  919                 if (error) {
  920                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
  921                                 CTR2(KTR_LOCK,
  922                         "%s: interruptible sleep by %p suspended by signal",
  923                                     __func__, sx);
  924                         break;
  925                 }
  926                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  927                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
  928                             __func__, sx);
  929         }
  930         if (error == 0)
  931                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
  932                     contested, waittime, file, line);
  933 #ifdef KDTRACE_HOOKS
  934         if (sleep_time)
  935                 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
  936         if (spin_cnt > sleep_cnt)
  937                 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
  938 #endif
  939         GIANT_RESTORE();
  940         return (error);
  941 }
  942 
  943 /*
  944  * This function represents the so-called 'hard case' for sx_sunlock
  945  * operation.  All 'easy case' failures are redirected to this.  Note
  946  * that ideally this would be a static function, but it needs to be
  947  * accessible from at least sx.h.
  948  */
  949 void
  950 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
  951 {
  952         uintptr_t x;
  953         int wakeup_swapper;
  954 
  955         if (SCHEDULER_STOPPED())
  956                 return;
  957 
  958         for (;;) {
  959                 x = sx->sx_lock;
  960 
  961                 /*
  962                  * We should never have sharers while at least one thread
  963                  * holds a shared lock.
  964                  */
  965                 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
  966                     ("%s: waiting sharers", __func__));
  967 
  968                 /*
  969                  * See if there is more than one shared lock held.  If
  970                  * so, just drop one and return.
  971                  */
  972                 if (SX_SHARERS(x) > 1) {
  973                         if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
  974                             x - SX_ONE_SHARER)) {
  975                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  976                                         CTR4(KTR_LOCK,
  977                                             "%s: %p succeeded %p -> %p",
  978                                             __func__, sx, (void *)x,
  979                                             (void *)(x - SX_ONE_SHARER));
  980                                 break;
  981                         }
  982                         continue;
  983                 }
  984 
  985                 /*
  986                  * If there aren't any waiters for an exclusive lock,
  987                  * then try to drop it quickly.
  988                  */
  989                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
  990                         MPASS(x == SX_SHARERS_LOCK(1));
  991                         if (atomic_cmpset_rel_ptr(&sx->sx_lock,
  992                             SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
  993                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
  994                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
  995                                             __func__, sx);
  996                                 break;
  997                         }
  998                         continue;
  999                 }
 1000 
 1001                 /*
 1002                  * At this point, there should just be one sharer with
 1003                  * exclusive waiters.
 1004                  */
 1005                 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
 1006 
 1007                 sleepq_lock(&sx->lock_object);
 1008 
 1009                 /*
 1010                  * Wake up semantic here is quite simple:
 1011                  * Just wake up all the exclusive waiters.
 1012                  * Note that the state of the lock could have changed,
 1013                  * so if it fails loop back and retry.
 1014                  */
 1015                 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
 1016                     SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
 1017                     SX_LOCK_UNLOCKED)) {
 1018                         sleepq_release(&sx->lock_object);
 1019                         continue;
 1020                 }
 1021                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 1022                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
 1023                             "exclusive queue", __func__, sx);
 1024                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 1025                     0, SQ_EXCLUSIVE_QUEUE);
 1026                 sleepq_release(&sx->lock_object);
 1027                 if (wakeup_swapper)
 1028                         kick_proc0();
 1029                 break;
 1030         }
 1031 }
 1032 
 1033 #ifdef INVARIANT_SUPPORT
 1034 #ifndef INVARIANTS
 1035 #undef  _sx_assert
 1036 #endif
 1037 
 1038 /*
 1039  * In the non-WITNESS case, sx_assert() can only detect that at least
 1040  * *some* thread owns an slock, but it cannot guarantee that *this*
 1041  * thread owns an slock.
 1042  */
 1043 void
 1044 _sx_assert(struct sx *sx, int what, const char *file, int line)
 1045 {
 1046 #ifndef WITNESS
 1047         int slocked = 0;
 1048 #endif
 1049 
 1050         if (panicstr != NULL)
 1051                 return;
 1052         switch (what) {
 1053         case SA_SLOCKED:
 1054         case SA_SLOCKED | SA_NOTRECURSED:
 1055         case SA_SLOCKED | SA_RECURSED:
 1056 #ifndef WITNESS
 1057                 slocked = 1;
 1058                 /* FALLTHROUGH */
 1059 #endif
 1060         case SA_LOCKED:
 1061         case SA_LOCKED | SA_NOTRECURSED:
 1062         case SA_LOCKED | SA_RECURSED:
 1063 #ifdef WITNESS
 1064                 witness_assert(&sx->lock_object, what, file, line);
 1065 #else
 1066                 /*
 1067                  * If some other thread has an exclusive lock or we
 1068                  * have one and are asserting a shared lock, fail.
 1069                  * Also, if no one has a lock at all, fail.
 1070                  */
 1071                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
 1072                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
 1073                     sx_xholder(sx) != curthread)))
 1074                         panic("Lock %s not %slocked @ %s:%d\n",
 1075                             sx->lock_object.lo_name, slocked ? "share " : "",
 1076                             file, line);
 1077 
 1078                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
 1079                         if (sx_recursed(sx)) {
 1080                                 if (what & SA_NOTRECURSED)
 1081                                         panic("Lock %s recursed @ %s:%d\n",
 1082                                             sx->lock_object.lo_name, file,
 1083                                             line);
 1084                         } else if (what & SA_RECURSED)
 1085                                 panic("Lock %s not recursed @ %s:%d\n",
 1086                                     sx->lock_object.lo_name, file, line);
 1087                 }
 1088 #endif
 1089                 break;
 1090         case SA_XLOCKED:
 1091         case SA_XLOCKED | SA_NOTRECURSED:
 1092         case SA_XLOCKED | SA_RECURSED:
 1093                 if (sx_xholder(sx) != curthread)
 1094                         panic("Lock %s not exclusively locked @ %s:%d\n",
 1095                             sx->lock_object.lo_name, file, line);
 1096                 if (sx_recursed(sx)) {
 1097                         if (what & SA_NOTRECURSED)
 1098                                 panic("Lock %s recursed @ %s:%d\n",
 1099                                     sx->lock_object.lo_name, file, line);
 1100                 } else if (what & SA_RECURSED)
 1101                         panic("Lock %s not recursed @ %s:%d\n",
 1102                             sx->lock_object.lo_name, file, line);
 1103                 break;
 1104         case SA_UNLOCKED:
 1105 #ifdef WITNESS
 1106                 witness_assert(&sx->lock_object, what, file, line);
 1107 #else
 1108                 /*
 1109                  * If we hold an exclusve lock fail.  We can't
 1110                  * reliably check to see if we hold a shared lock or
 1111                  * not.
 1112                  */
 1113                 if (sx_xholder(sx) == curthread)
 1114                         panic("Lock %s exclusively locked @ %s:%d\n",
 1115                             sx->lock_object.lo_name, file, line);
 1116 #endif
 1117                 break;
 1118         default:
 1119                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
 1120                     line);
 1121         }
 1122 }
 1123 #endif  /* INVARIANT_SUPPORT */
 1124 
 1125 #ifdef DDB
 1126 static void
 1127 db_show_sx(struct lock_object *lock)
 1128 {
 1129         struct thread *td;
 1130         struct sx *sx;
 1131 
 1132         sx = (struct sx *)lock;
 1133 
 1134         db_printf(" state: ");
 1135         if (sx->sx_lock == SX_LOCK_UNLOCKED)
 1136                 db_printf("UNLOCKED\n");
 1137         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
 1138                 db_printf("DESTROYED\n");
 1139                 return;
 1140         } else if (sx->sx_lock & SX_LOCK_SHARED)
 1141                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
 1142         else {
 1143                 td = sx_xholder(sx);
 1144                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
 1145                     td->td_tid, td->td_proc->p_pid, td->td_name);
 1146                 if (sx_recursed(sx))
 1147                         db_printf(" recursed: %d\n", sx->sx_recurse);
 1148         }
 1149 
 1150         db_printf(" waiters: ");
 1151         switch(sx->sx_lock &
 1152             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
 1153         case SX_LOCK_SHARED_WAITERS:
 1154                 db_printf("shared\n");
 1155                 break;
 1156         case SX_LOCK_EXCLUSIVE_WAITERS:
 1157                 db_printf("exclusive\n");
 1158                 break;
 1159         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
 1160                 db_printf("exclusive and shared\n");
 1161                 break;
 1162         default:
 1163                 db_printf("none\n");
 1164         }
 1165 }
 1166 
 1167 /*
 1168  * Check to see if a thread that is blocked on a sleep queue is actually
 1169  * blocked on an sx lock.  If so, output some details and return true.
 1170  * If the lock has an exclusive owner, return that in *ownerp.
 1171  */
 1172 int
 1173 sx_chain(struct thread *td, struct thread **ownerp)
 1174 {
 1175         struct sx *sx;
 1176 
 1177         /*
 1178          * Check to see if this thread is blocked on an sx lock.
 1179          * First, we check the lock class.  If that is ok, then we
 1180          * compare the lock name against the wait message.
 1181          */
 1182         sx = td->td_wchan;
 1183         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
 1184             sx->lock_object.lo_name != td->td_wmesg)
 1185                 return (0);
 1186 
 1187         /* We think we have an sx lock, so output some details. */
 1188         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
 1189         *ownerp = sx_xholder(sx);
 1190         if (sx->sx_lock & SX_LOCK_SHARED)
 1191                 db_printf("SLOCK (count %ju)\n",
 1192                     (uintmax_t)SX_SHARERS(sx->sx_lock));
 1193         else
 1194                 db_printf("XLOCK\n");
 1195         return (1);
 1196 }
 1197 #endif

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