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

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    1 /*-
    2  * Copyright (c) 1995
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Copyright (C) 1997
    6  *      John S. Dyson.  All rights reserved.
    7  *
    8  * This code contains ideas from software contributed to Berkeley by
    9  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
   10  * System project at Carnegie-Mellon University.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. All advertising materials mentioning features or use of this software
   21  *    must display the following acknowledgement:
   22  *      This product includes software developed by the University of
   23  *      California, Berkeley and its contributors.
   24  * 4. Neither the name of the University nor the names of its contributors
   25  *    may be used to endorse or promote products derived from this software
   26  *    without specific prior written permission.
   27  *
   28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   38  * SUCH DAMAGE.
   39  *
   40  *      @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
   41  */
   42 
   43 #include <sys/cdefs.h>
   44 __FBSDID("$FreeBSD: releng/6.1/sys/kern/kern_lock.c 158179 2006-04-30 16:44:43Z cvs2svn $");
   45 
   46 #include <sys/param.h>
   47 #include <sys/kdb.h>
   48 #include <sys/kernel.h>
   49 #include <sys/ktr.h>
   50 #include <sys/lock.h>
   51 #include <sys/lockmgr.h>
   52 #include <sys/mutex.h>
   53 #include <sys/proc.h>
   54 #include <sys/systm.h>
   55 #ifdef DEBUG_LOCKS
   56 #include <sys/stack.h>
   57 #endif
   58 
   59 /*
   60  * Locking primitives implementation.
   61  * Locks provide shared/exclusive sychronization.
   62  */
   63 
   64 #define COUNT(td, x)    if ((td)) (td)->td_locks += (x)
   65 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
   66         LK_SHARE_NONZERO | LK_WAIT_NONZERO)
   67 
   68 static int acquire(struct lock **lkpp, int extflags, int wanted);
   69 static int acquiredrain(struct lock *lkp, int extflags) ;
   70 
   71 static __inline void
   72 sharelock(struct thread *td, struct lock *lkp, int incr) {
   73         lkp->lk_flags |= LK_SHARE_NONZERO;
   74         lkp->lk_sharecount += incr;
   75         COUNT(td, incr);
   76 }
   77 
   78 static __inline void
   79 shareunlock(struct thread *td, struct lock *lkp, int decr) {
   80 
   81         KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
   82 
   83         COUNT(td, -decr);
   84         if (lkp->lk_sharecount == decr) {
   85                 lkp->lk_flags &= ~LK_SHARE_NONZERO;
   86                 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
   87                         wakeup(lkp);
   88                 }
   89                 lkp->lk_sharecount = 0;
   90         } else {
   91                 lkp->lk_sharecount -= decr;
   92         }
   93 }
   94 
   95 static int
   96 acquire(struct lock **lkpp, int extflags, int wanted)
   97 {
   98         struct lock *lkp = *lkpp;
   99         int error;
  100         CTR3(KTR_LOCK,
  101             "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
  102             lkp, extflags, wanted);
  103 
  104         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted))
  105                 return EBUSY;
  106         error = 0;
  107         while ((lkp->lk_flags & wanted) != 0) {
  108                 CTR2(KTR_LOCK,
  109                     "acquire(): lkp == %p, lk_flags == 0x%x sleeping",
  110                     lkp, lkp->lk_flags);
  111                 lkp->lk_flags |= LK_WAIT_NONZERO;
  112                 lkp->lk_waitcount++;
  113                 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
  114                     lkp->lk_wmesg, 
  115                     ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
  116                 lkp->lk_waitcount--;
  117                 if (lkp->lk_waitcount == 0)
  118                         lkp->lk_flags &= ~LK_WAIT_NONZERO;
  119                 if (error)
  120                         break;
  121                 if (extflags & LK_SLEEPFAIL) {
  122                         error = ENOLCK;
  123                         break;
  124                 }
  125                 if (lkp->lk_newlock != NULL) {
  126                         mtx_lock(lkp->lk_newlock->lk_interlock);
  127                         mtx_unlock(lkp->lk_interlock);
  128                         if (lkp->lk_waitcount == 0)
  129                                 wakeup((void *)(&lkp->lk_newlock));
  130                         *lkpp = lkp = lkp->lk_newlock;
  131                 }
  132         }
  133         mtx_assert(lkp->lk_interlock, MA_OWNED);
  134         return (error);
  135 }
  136 
  137 /*
  138  * Set, change, or release a lock.
  139  *
  140  * Shared requests increment the shared count. Exclusive requests set the
  141  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
  142  * accepted shared locks and shared-to-exclusive upgrades to go away.
  143  */
  144 int
  145 lockmgr(lkp, flags, interlkp, td)
  146         struct lock *lkp;
  147         u_int flags;
  148         struct mtx *interlkp;
  149         struct thread *td;
  150 {
  151         int error;
  152         struct thread *thr;
  153         int extflags, lockflags;
  154 
  155         error = 0;
  156         if (td == NULL)
  157                 thr = LK_KERNPROC;
  158         else
  159                 thr = td;
  160 
  161         if ((flags & LK_INTERNAL) == 0)
  162                 mtx_lock(lkp->lk_interlock);
  163         CTR6(KTR_LOCK,
  164             "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, "
  165             "td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder,
  166             lkp->lk_exclusivecount, flags, td);
  167 #ifdef DEBUG_LOCKS
  168         {
  169                 struct stack stack; /* XXX */
  170                 stack_save(&stack);
  171                 CTRSTACK(KTR_LOCK, &stack, 0, 1);
  172         }
  173 #endif
  174 
  175         if (flags & LK_INTERLOCK) {
  176                 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
  177                 mtx_unlock(interlkp);
  178         }
  179 
  180         if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
  181                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
  182                     &lkp->lk_interlock->mtx_object,
  183                     "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
  184 
  185         if (panicstr != NULL) {
  186                 mtx_unlock(lkp->lk_interlock);
  187                 return (0);
  188         }
  189         if ((lkp->lk_flags & LK_NOSHARE) &&
  190             (flags & LK_TYPE_MASK) == LK_SHARED) {
  191                 flags &= ~LK_TYPE_MASK;
  192                 flags |= LK_EXCLUSIVE;
  193         }
  194         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
  195 
  196         switch (flags & LK_TYPE_MASK) {
  197 
  198         case LK_SHARED:
  199                 /*
  200                  * If we are not the exclusive lock holder, we have to block
  201                  * while there is an exclusive lock holder or while an
  202                  * exclusive lock request or upgrade request is in progress.
  203                  *
  204                  * However, if TDP_DEADLKTREAT is set, we override exclusive
  205                  * lock requests or upgrade requests ( but not the exclusive
  206                  * lock itself ).
  207                  */
  208                 if (lkp->lk_lockholder != thr) {
  209                         lockflags = LK_HAVE_EXCL;
  210                         if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
  211                                 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
  212                         error = acquire(&lkp, extflags, lockflags);
  213                         if (error)
  214                                 break;
  215                         sharelock(td, lkp, 1);
  216 #if defined(DEBUG_LOCKS)
  217                         stack_save(&lkp->lk_stack);
  218 #endif
  219                         break;
  220                 }
  221                 /*
  222                  * We hold an exclusive lock, so downgrade it to shared.
  223                  * An alternative would be to fail with EDEADLK.
  224                  */
  225                 sharelock(td, lkp, 1);
  226                 /* FALLTHROUGH downgrade */
  227 
  228         case LK_DOWNGRADE:
  229                 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0,
  230                         ("lockmgr: not holding exclusive lock "
  231                         "(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
  232                         lkp->lk_lockholder, thr, lkp->lk_exclusivecount));
  233                 sharelock(td, lkp, lkp->lk_exclusivecount);
  234                 COUNT(td, -lkp->lk_exclusivecount);
  235                 lkp->lk_exclusivecount = 0;
  236                 lkp->lk_flags &= ~LK_HAVE_EXCL;
  237                 lkp->lk_lockholder = LK_NOPROC;
  238                 if (lkp->lk_waitcount)
  239                         wakeup((void *)lkp);
  240                 break;
  241 
  242         case LK_EXCLUPGRADE:
  243                 /*
  244                  * If another process is ahead of us to get an upgrade,
  245                  * then we want to fail rather than have an intervening
  246                  * exclusive access.
  247                  */
  248                 if (lkp->lk_flags & LK_WANT_UPGRADE) {
  249                         shareunlock(td, lkp, 1);
  250                         error = EBUSY;
  251                         break;
  252                 }
  253                 /* FALLTHROUGH normal upgrade */
  254 
  255         case LK_UPGRADE:
  256                 /*
  257                  * Upgrade a shared lock to an exclusive one. If another
  258                  * shared lock has already requested an upgrade to an
  259                  * exclusive lock, our shared lock is released and an
  260                  * exclusive lock is requested (which will be granted
  261                  * after the upgrade). If we return an error, the file
  262                  * will always be unlocked.
  263                  */
  264                 if (lkp->lk_lockholder == thr)
  265                         panic("lockmgr: upgrade exclusive lock");
  266                 if (lkp->lk_sharecount <= 0)
  267                         panic("lockmgr: upgrade without shared");
  268                 shareunlock(td, lkp, 1);
  269                 /*
  270                  * If we are just polling, check to see if we will block.
  271                  */
  272                 if ((extflags & LK_NOWAIT) &&
  273                     ((lkp->lk_flags & LK_WANT_UPGRADE) ||
  274                      lkp->lk_sharecount > 1)) {
  275                         error = EBUSY;
  276                         break;
  277                 }
  278                 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
  279                         /*
  280                          * We are first shared lock to request an upgrade, so
  281                          * request upgrade and wait for the shared count to
  282                          * drop to zero, then take exclusive lock.
  283                          */
  284                         lkp->lk_flags |= LK_WANT_UPGRADE;
  285                         error = acquire(&lkp, extflags, LK_SHARE_NONZERO);
  286                         lkp->lk_flags &= ~LK_WANT_UPGRADE;
  287 
  288                         if (error) {
  289                                  if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
  290                                            wakeup((void *)lkp);
  291                                  break;
  292                         }
  293                         if (lkp->lk_exclusivecount != 0)
  294                                 panic("lockmgr: non-zero exclusive count");
  295                         lkp->lk_flags |= LK_HAVE_EXCL;
  296                         lkp->lk_lockholder = thr;
  297                         lkp->lk_exclusivecount = 1;
  298                         COUNT(td, 1);
  299 #if defined(DEBUG_LOCKS)
  300                         stack_save(&lkp->lk_stack);
  301 #endif
  302                         break;
  303                 }
  304                 /*
  305                  * Someone else has requested upgrade. Release our shared
  306                  * lock, awaken upgrade requestor if we are the last shared
  307                  * lock, then request an exclusive lock.
  308                  */
  309                 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
  310                         LK_WAIT_NONZERO)
  311                         wakeup((void *)lkp);
  312                 /* FALLTHROUGH exclusive request */
  313 
  314         case LK_EXCLUSIVE:
  315                 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) {
  316                         /*
  317                          *      Recursive lock.
  318                          */
  319                         if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
  320                                 panic("lockmgr: locking against myself");
  321                         if ((extflags & LK_CANRECURSE) != 0) {
  322                                 lkp->lk_exclusivecount++;
  323                                 COUNT(td, 1);
  324                                 break;
  325                         }
  326                 }
  327                 /*
  328                  * If we are just polling, check to see if we will sleep.
  329                  */
  330                 if ((extflags & LK_NOWAIT) &&
  331                     (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
  332                         error = EBUSY;
  333                         break;
  334                 }
  335                 /*
  336                  * Try to acquire the want_exclusive flag.
  337                  */
  338                 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
  339                 if (error)
  340                         break;
  341                 lkp->lk_flags |= LK_WANT_EXCL;
  342                 /*
  343                  * Wait for shared locks and upgrades to finish.
  344                  */
  345                 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO);
  346                 lkp->lk_flags &= ~LK_WANT_EXCL;
  347                 if (error) {
  348                         if (lkp->lk_flags & LK_WAIT_NONZERO)            
  349                                  wakeup((void *)lkp);
  350                         break;
  351                 }       
  352                 lkp->lk_flags |= LK_HAVE_EXCL;
  353                 lkp->lk_lockholder = thr;
  354                 if (lkp->lk_exclusivecount != 0)
  355                         panic("lockmgr: non-zero exclusive count");
  356                 lkp->lk_exclusivecount = 1;
  357                 COUNT(td, 1);
  358 #if defined(DEBUG_LOCKS)
  359                 stack_save(&lkp->lk_stack);
  360 #endif
  361                 break;
  362 
  363         case LK_RELEASE:
  364                 if (lkp->lk_exclusivecount != 0) {
  365                         if (lkp->lk_lockholder != thr &&
  366                             lkp->lk_lockholder != LK_KERNPROC) {
  367                                 panic("lockmgr: thread %p, not %s %p unlocking",
  368                                     thr, "exclusive lock holder",
  369                                     lkp->lk_lockholder);
  370                         }
  371                         if (lkp->lk_lockholder != LK_KERNPROC)
  372                                 COUNT(td, -1);
  373                         if (lkp->lk_exclusivecount == 1) {
  374                                 lkp->lk_flags &= ~LK_HAVE_EXCL;
  375                                 lkp->lk_lockholder = LK_NOPROC;
  376                                 lkp->lk_exclusivecount = 0;
  377                         } else {
  378                                 lkp->lk_exclusivecount--;
  379                         }
  380                 } else if (lkp->lk_flags & LK_SHARE_NONZERO)
  381                         shareunlock(td, lkp, 1);
  382                 if (lkp->lk_flags & LK_WAIT_NONZERO)
  383                         wakeup((void *)lkp);
  384                 break;
  385 
  386         case LK_DRAIN:
  387                 /*
  388                  * Check that we do not already hold the lock, as it can 
  389                  * never drain if we do. Unfortunately, we have no way to
  390                  * check for holding a shared lock, but at least we can
  391                  * check for an exclusive one.
  392                  */
  393                 if (lkp->lk_lockholder == thr)
  394                         panic("lockmgr: draining against myself");
  395 
  396                 error = acquiredrain(lkp, extflags);
  397                 if (error)
  398                         break;
  399                 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
  400                 lkp->lk_lockholder = thr;
  401                 lkp->lk_exclusivecount = 1;
  402                 COUNT(td, 1);
  403 #if defined(DEBUG_LOCKS)
  404                 stack_save(&lkp->lk_stack);
  405 #endif
  406                 break;
  407 
  408         default:
  409                 mtx_unlock(lkp->lk_interlock);
  410                 panic("lockmgr: unknown locktype request %d",
  411                     flags & LK_TYPE_MASK);
  412                 /* NOTREACHED */
  413         }
  414         if ((lkp->lk_flags & LK_WAITDRAIN) &&
  415             (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
  416                 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
  417                 lkp->lk_flags &= ~LK_WAITDRAIN;
  418                 wakeup((void *)&lkp->lk_flags);
  419         }
  420         mtx_unlock(lkp->lk_interlock);
  421         return (error);
  422 }
  423 
  424 static int
  425 acquiredrain(struct lock *lkp, int extflags) {
  426         int error;
  427 
  428         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
  429                 return EBUSY;
  430         }
  431         while (lkp->lk_flags & LK_ALL) {
  432                 lkp->lk_flags |= LK_WAITDRAIN;
  433                 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
  434                         lkp->lk_wmesg, 
  435                         ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
  436                 if (error)
  437                         return error;
  438                 if (extflags & LK_SLEEPFAIL) {
  439                         return ENOLCK;
  440                 }
  441         }
  442         return 0;
  443 }
  444 
  445 /*
  446  * Transfer any waiting processes from one lock to another.
  447  */
  448 void
  449 transferlockers(from, to)
  450         struct lock *from;
  451         struct lock *to;
  452 {
  453 
  454         KASSERT(from != to, ("lock transfer to self"));
  455         KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock"));
  456 
  457         mtx_lock(from->lk_interlock);
  458         if (from->lk_waitcount == 0) {
  459                 mtx_unlock(from->lk_interlock);
  460                 return;
  461         }
  462         from->lk_newlock = to;
  463         wakeup((void *)from);
  464         msleep(&from->lk_newlock, from->lk_interlock, from->lk_prio,
  465             "lkxfer", 0);
  466         from->lk_newlock = NULL;
  467         from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE);
  468         KASSERT(from->lk_waitcount == 0, ("active lock"));
  469         mtx_unlock(from->lk_interlock);
  470 }
  471 
  472 
  473 /*
  474  * Initialize a lock; required before use.
  475  */
  476 void
  477 lockinit(lkp, prio, wmesg, timo, flags)
  478         struct lock *lkp;
  479         int prio;
  480         const char *wmesg;
  481         int timo;
  482         int flags;
  483 {
  484         CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
  485             "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
  486 
  487         lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
  488         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
  489         lkp->lk_sharecount = 0;
  490         lkp->lk_waitcount = 0;
  491         lkp->lk_exclusivecount = 0;
  492         lkp->lk_prio = prio;
  493         lkp->lk_wmesg = wmesg;
  494         lkp->lk_timo = timo;
  495         lkp->lk_lockholder = LK_NOPROC;
  496         lkp->lk_newlock = NULL;
  497 #ifdef DEBUG_LOCKS
  498         stack_zero(&lkp->lk_stack);
  499 #endif
  500 }
  501 
  502 /*
  503  * Destroy a lock.
  504  */
  505 void
  506 lockdestroy(lkp)
  507         struct lock *lkp;
  508 {
  509         CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
  510             lkp, lkp->lk_wmesg);
  511 }
  512 
  513 /*
  514  * Determine the status of a lock.
  515  */
  516 int
  517 lockstatus(lkp, td)
  518         struct lock *lkp;
  519         struct thread *td;
  520 {
  521         int lock_type = 0;
  522         int interlocked;
  523 
  524         if (!kdb_active) {
  525                 interlocked = 1;
  526                 mtx_lock(lkp->lk_interlock);
  527         } else
  528                 interlocked = 0;
  529         if (lkp->lk_exclusivecount != 0) {
  530                 if (td == NULL || lkp->lk_lockholder == td)
  531                         lock_type = LK_EXCLUSIVE;
  532                 else
  533                         lock_type = LK_EXCLOTHER;
  534         } else if (lkp->lk_sharecount != 0)
  535                 lock_type = LK_SHARED;
  536         if (interlocked)
  537                 mtx_unlock(lkp->lk_interlock);
  538         return (lock_type);
  539 }
  540 
  541 /*
  542  * Determine the number of holders of a lock.
  543  */
  544 int
  545 lockcount(lkp)
  546         struct lock *lkp;
  547 {
  548         int count;
  549 
  550         mtx_lock(lkp->lk_interlock);
  551         count = lkp->lk_exclusivecount + lkp->lk_sharecount;
  552         mtx_unlock(lkp->lk_interlock);
  553         return (count);
  554 }
  555 
  556 /*
  557  * Print out information about state of a lock. Used by VOP_PRINT
  558  * routines to display status about contained locks.
  559  */
  560 void
  561 lockmgr_printinfo(lkp)
  562         struct lock *lkp;
  563 {
  564 
  565         if (lkp->lk_sharecount)
  566                 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
  567                     lkp->lk_sharecount);
  568         else if (lkp->lk_flags & LK_HAVE_EXCL)
  569                 printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)",
  570                     lkp->lk_wmesg, lkp->lk_exclusivecount,
  571                     lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
  572         if (lkp->lk_waitcount > 0)
  573                 printf(" with %d pending", lkp->lk_waitcount);
  574 #ifdef DEBUG_LOCKS
  575         stack_print(&lkp->lk_stack);
  576 #endif
  577 }

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