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("$FreeBSD$");
   45 
   46 #include "opt_ddb.h"
   47 #include "opt_global.h"
   48 
   49 #include <sys/param.h>
   50 #include <sys/kdb.h>
   51 #include <sys/kernel.h>
   52 #include <sys/ktr.h>
   53 #include <sys/lock.h>
   54 #include <sys/lockmgr.h>
   55 #include <sys/mutex.h>
   56 #include <sys/proc.h>
   57 #include <sys/systm.h>
   58 #include <sys/lock_profile.h>
   59 #ifdef DEBUG_LOCKS
   60 #include <sys/stack.h>
   61 #endif
   62 
   63 #ifdef DDB
   64 #include <ddb/ddb.h>
   65 static void     db_show_lockmgr(struct lock_object *lock);
   66 #endif
   67 static void     lock_lockmgr(struct lock_object *lock, int how);
   68 static int      unlock_lockmgr(struct lock_object *lock);
   69 
   70 struct lock_class lock_class_lockmgr = {
   71         .lc_name = "lockmgr",
   72         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
   73 #ifdef DDB
   74         .lc_ddb_show = db_show_lockmgr,
   75 #endif
   76         .lc_lock = lock_lockmgr,
   77         .lc_unlock = unlock_lockmgr,
   78 };
   79 
   80 /*
   81  * Locking primitives implementation.
   82  * Locks provide shared/exclusive sychronization.
   83  */
   84 
   85 void
   86 lock_lockmgr(struct lock_object *lock, int how)
   87 {
   88 
   89         panic("lockmgr locks do not support sleep interlocking");
   90 }
   91 
   92 int
   93 unlock_lockmgr(struct lock_object *lock)
   94 {
   95 
   96         panic("lockmgr locks do not support sleep interlocking");
   97 }
   98 
   99 #define COUNT(td, x)    if ((td)) (td)->td_locks += (x)
  100 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
  101         LK_SHARE_NONZERO | LK_WAIT_NONZERO)
  102 
  103 static int acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime);
  104 static int acquiredrain(struct lock *lkp, int extflags) ;
  105 
  106 static __inline void
  107 sharelock(struct thread *td, struct lock *lkp, int incr) {
  108         lkp->lk_flags |= LK_SHARE_NONZERO;
  109         lkp->lk_sharecount += incr;
  110         COUNT(td, incr);
  111 }
  112 
  113 static __inline void
  114 shareunlock(struct thread *td, struct lock *lkp, int decr) {
  115 
  116         KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
  117 
  118         COUNT(td, -decr);
  119         if (lkp->lk_sharecount == decr) {
  120                 lkp->lk_flags &= ~LK_SHARE_NONZERO;
  121                 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
  122                         wakeup(lkp);
  123                 }
  124                 lkp->lk_sharecount = 0;
  125         } else {
  126                 lkp->lk_sharecount -= decr;
  127         }
  128 }
  129 
  130 static int
  131 acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime)
  132 {
  133         struct lock *lkp = *lkpp;
  134         int error;
  135         CTR3(KTR_LOCK,
  136             "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
  137             lkp, extflags, wanted);
  138 
  139         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted))
  140                 return EBUSY;
  141         error = 0;
  142         if ((lkp->lk_flags & wanted) != 0)
  143                 lock_profile_obtain_lock_failed(&lkp->lk_object, contested, waittime);
  144         
  145         while ((lkp->lk_flags & wanted) != 0) {
  146                 CTR2(KTR_LOCK,
  147                     "acquire(): lkp == %p, lk_flags == 0x%x sleeping",
  148                     lkp, lkp->lk_flags);
  149                 lkp->lk_flags |= LK_WAIT_NONZERO;
  150                 lkp->lk_waitcount++;
  151                 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
  152                     lkp->lk_wmesg, 
  153                     ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
  154                 lkp->lk_waitcount--;
  155                 if (lkp->lk_waitcount == 0)
  156                         lkp->lk_flags &= ~LK_WAIT_NONZERO;
  157                 if (error)
  158                         break;
  159                 if (extflags & LK_SLEEPFAIL) {
  160                         error = ENOLCK;
  161                         break;
  162                 }
  163                 if (lkp->lk_newlock != NULL) {
  164                         mtx_lock(lkp->lk_newlock->lk_interlock);
  165                         mtx_unlock(lkp->lk_interlock);
  166                         if (lkp->lk_waitcount == 0)
  167                                 wakeup((void *)(&lkp->lk_newlock));
  168                         *lkpp = lkp = lkp->lk_newlock;
  169                 }
  170         }
  171         mtx_assert(lkp->lk_interlock, MA_OWNED);
  172         return (error);
  173 }
  174 
  175 /*
  176  * Set, change, or release a lock.
  177  *
  178  * Shared requests increment the shared count. Exclusive requests set the
  179  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
  180  * accepted shared locks and shared-to-exclusive upgrades to go away.
  181  */
  182 int
  183 _lockmgr(struct lock *lkp, u_int flags, struct mtx *interlkp, 
  184          struct thread *td, char *file, int line)
  185 
  186 {
  187         int error;
  188         struct thread *thr;
  189         int extflags, lockflags;
  190         int contested = 0;
  191         uint64_t waitstart = 0;
  192         
  193         error = 0;
  194         if (td == NULL)
  195                 thr = LK_KERNPROC;
  196         else
  197                 thr = td;
  198 
  199         if ((flags & LK_INTERNAL) == 0)
  200                 mtx_lock(lkp->lk_interlock);
  201         CTR6(KTR_LOCK,
  202             "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, "
  203             "td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder,
  204             lkp->lk_exclusivecount, flags, td);
  205 #ifdef DEBUG_LOCKS
  206         {
  207                 struct stack stack; /* XXX */
  208                 stack_save(&stack);
  209                 CTRSTACK(KTR_LOCK, &stack, 0, 1);
  210         }
  211 #endif
  212 
  213         if (flags & LK_INTERLOCK) {
  214                 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
  215                 mtx_unlock(interlkp);
  216         }
  217 
  218         if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
  219                 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
  220                     &lkp->lk_interlock->lock_object,
  221                     "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
  222 
  223         if (panicstr != NULL) {
  224                 mtx_unlock(lkp->lk_interlock);
  225                 return (0);
  226         }
  227         if ((lkp->lk_flags & LK_NOSHARE) &&
  228             (flags & LK_TYPE_MASK) == LK_SHARED) {
  229                 flags &= ~LK_TYPE_MASK;
  230                 flags |= LK_EXCLUSIVE;
  231         }
  232         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
  233 
  234         switch (flags & LK_TYPE_MASK) {
  235 
  236         case LK_SHARED:
  237                 /*
  238                  * If we are not the exclusive lock holder, we have to block
  239                  * while there is an exclusive lock holder or while an
  240                  * exclusive lock request or upgrade request is in progress.
  241                  *
  242                  * However, if TDP_DEADLKTREAT is set, we override exclusive
  243                  * lock requests or upgrade requests ( but not the exclusive
  244                  * lock itself ).
  245                  */
  246                 if (lkp->lk_lockholder != thr) {
  247                         lockflags = LK_HAVE_EXCL;
  248                         if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
  249                                 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
  250                         error = acquire(&lkp, extflags, lockflags, &contested, &waitstart);
  251                         if (error)
  252                                 break;
  253                         sharelock(td, lkp, 1);
  254                         if (lkp->lk_sharecount == 1)
  255                                 lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
  256 
  257 #if defined(DEBUG_LOCKS)
  258                         stack_save(&lkp->lk_stack);
  259 #endif
  260                         break;
  261                 }
  262                 /*
  263                  * We hold an exclusive lock, so downgrade it to shared.
  264                  * An alternative would be to fail with EDEADLK.
  265                  */
  266                 sharelock(td, lkp, 1);
  267                 if (lkp->lk_sharecount == 1)
  268                         lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
  269                 /* FALLTHROUGH downgrade */
  270 
  271         case LK_DOWNGRADE:
  272                 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0,
  273                         ("lockmgr: not holding exclusive lock "
  274                         "(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
  275                         lkp->lk_lockholder, thr, lkp->lk_exclusivecount));
  276                 sharelock(td, lkp, lkp->lk_exclusivecount);
  277                 COUNT(td, -lkp->lk_exclusivecount);
  278                 lkp->lk_exclusivecount = 0;
  279                 lkp->lk_flags &= ~LK_HAVE_EXCL;
  280                 lkp->lk_lockholder = LK_NOPROC;
  281                 if (lkp->lk_waitcount)
  282                         wakeup((void *)lkp);
  283                 break;
  284 
  285         case LK_EXCLUPGRADE:
  286                 /*
  287                  * If another process is ahead of us to get an upgrade,
  288                  * then we want to fail rather than have an intervening
  289                  * exclusive access.
  290                  */
  291                 if (lkp->lk_flags & LK_WANT_UPGRADE) {
  292                         shareunlock(td, lkp, 1);
  293                         error = EBUSY;
  294                         break;
  295                 }
  296                 /* FALLTHROUGH normal upgrade */
  297 
  298         case LK_UPGRADE:
  299                 /*
  300                  * Upgrade a shared lock to an exclusive one. If another
  301                  * shared lock has already requested an upgrade to an
  302                  * exclusive lock, our shared lock is released and an
  303                  * exclusive lock is requested (which will be granted
  304                  * after the upgrade). If we return an error, the file
  305                  * will always be unlocked.
  306                  */
  307                 if (lkp->lk_lockholder == thr)
  308                         panic("lockmgr: upgrade exclusive lock");
  309                 if (lkp->lk_sharecount <= 0)
  310                         panic("lockmgr: upgrade without shared");
  311                 shareunlock(td, lkp, 1);
  312                 if (lkp->lk_sharecount == 0)
  313                         lock_profile_release_lock(&lkp->lk_object);
  314                 /*
  315                  * If we are just polling, check to see if we will block.
  316                  */
  317                 if ((extflags & LK_NOWAIT) &&
  318                     ((lkp->lk_flags & LK_WANT_UPGRADE) ||
  319                      lkp->lk_sharecount > 1)) {
  320                         error = EBUSY;
  321                         break;
  322                 }
  323                 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
  324                         /*
  325                          * We are first shared lock to request an upgrade, so
  326                          * request upgrade and wait for the shared count to
  327                          * drop to zero, then take exclusive lock.
  328                          */
  329                         lkp->lk_flags |= LK_WANT_UPGRADE;
  330                         error = acquire(&lkp, extflags, LK_SHARE_NONZERO, &contested, &waitstart);
  331                         lkp->lk_flags &= ~LK_WANT_UPGRADE;
  332 
  333                         if (error) {
  334                                  if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
  335                                            wakeup((void *)lkp);
  336                                  break;
  337                         }
  338                         if (lkp->lk_exclusivecount != 0)
  339                                 panic("lockmgr: non-zero exclusive count");
  340                         lkp->lk_flags |= LK_HAVE_EXCL;
  341                         lkp->lk_lockholder = thr;
  342                         lkp->lk_exclusivecount = 1;
  343                         COUNT(td, 1);
  344                         lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
  345 #if defined(DEBUG_LOCKS)
  346                         stack_save(&lkp->lk_stack);
  347 #endif
  348                         break;
  349                 }
  350                 /*
  351                  * Someone else has requested upgrade. Release our shared
  352                  * lock, awaken upgrade requestor if we are the last shared
  353                  * lock, then request an exclusive lock.
  354                  */
  355                 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
  356                         LK_WAIT_NONZERO)
  357                         wakeup((void *)lkp);
  358                 /* FALLTHROUGH exclusive request */
  359 
  360         case LK_EXCLUSIVE:
  361                 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) {
  362                         /*
  363                          *      Recursive lock.
  364                          */
  365                         if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
  366                                 panic("lockmgr: locking against myself");
  367                         if ((extflags & LK_CANRECURSE) != 0) {
  368                                 lkp->lk_exclusivecount++;
  369                                 COUNT(td, 1);
  370                                 break;
  371                         }
  372                 }
  373                 /*
  374                  * If we are just polling, check to see if we will sleep.
  375                  */
  376                 if ((extflags & LK_NOWAIT) &&
  377                     (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
  378                         error = EBUSY;
  379                         break;
  380                 }
  381                 /*
  382                  * Try to acquire the want_exclusive flag.
  383                  */
  384                 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL), &contested, &waitstart);
  385                 if (error)
  386                         break;
  387                 lkp->lk_flags |= LK_WANT_EXCL;
  388                 /*
  389                  * Wait for shared locks and upgrades to finish.
  390                  */
  391                 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO, &contested, &waitstart);
  392                 lkp->lk_flags &= ~LK_WANT_EXCL;
  393                 if (error) {
  394                         if (lkp->lk_flags & LK_WAIT_NONZERO)            
  395                                  wakeup((void *)lkp);
  396                         break;
  397                 }       
  398                 lkp->lk_flags |= LK_HAVE_EXCL;
  399                 lkp->lk_lockholder = thr;
  400                 if (lkp->lk_exclusivecount != 0)
  401                         panic("lockmgr: non-zero exclusive count");
  402                 lkp->lk_exclusivecount = 1;
  403                 COUNT(td, 1);
  404                 lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
  405 #if defined(DEBUG_LOCKS)
  406                 stack_save(&lkp->lk_stack);
  407 #endif
  408                 break;
  409 
  410         case LK_RELEASE:
  411                 if (lkp->lk_exclusivecount != 0) {
  412                         if (lkp->lk_lockholder != thr &&
  413                             lkp->lk_lockholder != LK_KERNPROC) {
  414                                 panic("lockmgr: thread %p, not %s %p unlocking",
  415                                     thr, "exclusive lock holder",
  416                                     lkp->lk_lockholder);
  417                         }
  418                         if (lkp->lk_lockholder != LK_KERNPROC)
  419                                 COUNT(td, -1);
  420                         if (lkp->lk_exclusivecount == 1) {
  421                                 lkp->lk_flags &= ~LK_HAVE_EXCL;
  422                                 lkp->lk_lockholder = LK_NOPROC;
  423                                 lkp->lk_exclusivecount = 0;
  424                                 lock_profile_release_lock(&lkp->lk_object);
  425                         } else {
  426                                 lkp->lk_exclusivecount--;
  427                         }
  428                 } else if (lkp->lk_flags & LK_SHARE_NONZERO)
  429                         shareunlock(td, lkp, 1);
  430                 else  {
  431                         printf("lockmgr: thread %p unlocking unheld lock\n",
  432                             thr);
  433                         kdb_backtrace();
  434                 }
  435 
  436                 if (lkp->lk_flags & LK_WAIT_NONZERO)
  437                         wakeup((void *)lkp);
  438                 break;
  439 
  440         case LK_DRAIN:
  441                 /*
  442                  * Check that we do not already hold the lock, as it can 
  443                  * never drain if we do. Unfortunately, we have no way to
  444                  * check for holding a shared lock, but at least we can
  445                  * check for an exclusive one.
  446                  */
  447                 if (lkp->lk_lockholder == thr)
  448                         panic("lockmgr: draining against myself");
  449 
  450                 error = acquiredrain(lkp, extflags);
  451                 if (error)
  452                         break;
  453                 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
  454                 lkp->lk_lockholder = thr;
  455                 lkp->lk_exclusivecount = 1;
  456                 COUNT(td, 1);
  457 #if defined(DEBUG_LOCKS)
  458                 stack_save(&lkp->lk_stack);
  459 #endif
  460                 break;
  461 
  462         default:
  463                 mtx_unlock(lkp->lk_interlock);
  464                 panic("lockmgr: unknown locktype request %d",
  465                     flags & LK_TYPE_MASK);
  466                 /* NOTREACHED */
  467         }
  468         if ((lkp->lk_flags & LK_WAITDRAIN) &&
  469             (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
  470                 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
  471                 lkp->lk_flags &= ~LK_WAITDRAIN;
  472                 wakeup((void *)&lkp->lk_flags);
  473         }
  474         mtx_unlock(lkp->lk_interlock);
  475         return (error);
  476 }
  477 
  478 static int
  479 acquiredrain(struct lock *lkp, int extflags) {
  480         int error;
  481 
  482         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
  483                 return EBUSY;
  484         }
  485         while (lkp->lk_flags & LK_ALL) {
  486                 lkp->lk_flags |= LK_WAITDRAIN;
  487                 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
  488                         lkp->lk_wmesg, 
  489                         ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
  490                 if (error)
  491                         return error;
  492                 if (extflags & LK_SLEEPFAIL) {
  493                         return ENOLCK;
  494                 }
  495         }
  496         return 0;
  497 }
  498 
  499 /*
  500  * Transfer any waiting processes from one lock to another.
  501  */
  502 void
  503 transferlockers(from, to)
  504         struct lock *from;
  505         struct lock *to;
  506 {
  507 
  508         KASSERT(from != to, ("lock transfer to self"));
  509         KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock"));
  510 
  511         mtx_lock(from->lk_interlock);
  512         if (from->lk_waitcount == 0) {
  513                 mtx_unlock(from->lk_interlock);
  514                 return;
  515         }
  516         from->lk_newlock = to;
  517         wakeup((void *)from);
  518         msleep(&from->lk_newlock, from->lk_interlock, from->lk_prio,
  519             "lkxfer", 0);
  520         from->lk_newlock = NULL;
  521         from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE);
  522         KASSERT(from->lk_waitcount == 0, ("active lock"));
  523         mtx_unlock(from->lk_interlock);
  524 }
  525 
  526 
  527 /*
  528  * Initialize a lock; required before use.
  529  */
  530 void
  531 lockinit(lkp, prio, wmesg, timo, flags)
  532         struct lock *lkp;
  533         int prio;
  534         const char *wmesg;
  535         int timo;
  536         int flags;
  537 {
  538         CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
  539             "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
  540 
  541         lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
  542         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
  543         lkp->lk_sharecount = 0;
  544         lkp->lk_waitcount = 0;
  545         lkp->lk_exclusivecount = 0;
  546         lkp->lk_prio = prio;
  547         lkp->lk_timo = timo;
  548         lkp->lk_lockholder = LK_NOPROC;
  549         lkp->lk_newlock = NULL;
  550 #ifdef DEBUG_LOCKS
  551         stack_zero(&lkp->lk_stack);
  552 #endif
  553         lock_init(&lkp->lk_object, &lock_class_lockmgr, wmesg, NULL,
  554             LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE);
  555 }
  556 
  557 /*
  558  * Destroy a lock.
  559  */
  560 void
  561 lockdestroy(lkp)
  562         struct lock *lkp;
  563 {
  564 
  565         CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
  566             lkp, lkp->lk_wmesg);
  567         lock_destroy(&lkp->lk_object);
  568 }
  569 
  570 /*
  571  * Determine the status of a lock.
  572  */
  573 int
  574 lockstatus(lkp, td)
  575         struct lock *lkp;
  576         struct thread *td;
  577 {
  578         int lock_type = 0;
  579         int interlocked;
  580 
  581         if (!kdb_active) {
  582                 interlocked = 1;
  583                 mtx_lock(lkp->lk_interlock);
  584         } else
  585                 interlocked = 0;
  586         if (lkp->lk_exclusivecount != 0) {
  587                 if (td == NULL || lkp->lk_lockholder == td)
  588                         lock_type = LK_EXCLUSIVE;
  589                 else
  590                         lock_type = LK_EXCLOTHER;
  591         } else if (lkp->lk_sharecount != 0)
  592                 lock_type = LK_SHARED;
  593         if (interlocked)
  594                 mtx_unlock(lkp->lk_interlock);
  595         return (lock_type);
  596 }
  597 
  598 /*
  599  * Determine the number of holders of a lock.
  600  */
  601 int
  602 lockcount(lkp)
  603         struct lock *lkp;
  604 {
  605         int count;
  606 
  607         mtx_lock(lkp->lk_interlock);
  608         count = lkp->lk_exclusivecount + lkp->lk_sharecount;
  609         mtx_unlock(lkp->lk_interlock);
  610         return (count);
  611 }
  612 
  613 /*
  614  * Determine the number of waiters on a lock.
  615  */
  616 int
  617 lockwaiters(lkp)
  618         struct lock *lkp;
  619 {
  620         int count;
  621 
  622         mtx_lock(lkp->lk_interlock);
  623         count = lkp->lk_waitcount;
  624         mtx_unlock(lkp->lk_interlock);
  625         return (count);
  626 }
  627 
  628 /*
  629  * Print out information about state of a lock. Used by VOP_PRINT
  630  * routines to display status about contained locks.
  631  */
  632 void
  633 lockmgr_printinfo(lkp)
  634         struct lock *lkp;
  635 {
  636 
  637         if (lkp->lk_sharecount)
  638                 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
  639                     lkp->lk_sharecount);
  640         else if (lkp->lk_flags & LK_HAVE_EXCL)
  641                 printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)",
  642                     lkp->lk_wmesg, lkp->lk_exclusivecount,
  643                     lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
  644         if (lkp->lk_waitcount > 0)
  645                 printf(" with %d pending", lkp->lk_waitcount);
  646 #ifdef DEBUG_LOCKS
  647         stack_print_ddb(&lkp->lk_stack);
  648 #endif
  649 }
  650 
  651 #ifdef DDB
  652 /*
  653  * Check to see if a thread that is blocked on a sleep queue is actually
  654  * blocked on a 'struct lock'.  If so, output some details and return true.
  655  * If the lock has an exclusive owner, return that in *ownerp.
  656  */
  657 int
  658 lockmgr_chain(struct thread *td, struct thread **ownerp)
  659 {
  660         struct lock *lkp;
  661 
  662         lkp = td->td_wchan;
  663 
  664         /* Simple test to see if wchan points to a lockmgr lock. */
  665         if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
  666             lkp->lk_wmesg == td->td_wmesg)
  667                 goto ok;
  668 
  669         /*
  670          * If this thread is doing a DRAIN, then it would be asleep on
  671          * &lkp->lk_flags rather than lkp.
  672          */
  673         lkp = (struct lock *)((char *)td->td_wchan -
  674             offsetof(struct lock, lk_flags));
  675         if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
  676             lkp->lk_wmesg == td->td_wmesg && (lkp->lk_flags & LK_WAITDRAIN))
  677                 goto ok;
  678 
  679         /* Doen't seem to be a lockmgr lock. */
  680         return (0);
  681 
  682 ok:
  683         /* Ok, we think we have a lockmgr lock, so output some details. */
  684         db_printf("blocked on lk \"%s\" ", lkp->lk_wmesg);
  685         if (lkp->lk_sharecount) {
  686                 db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
  687                 *ownerp = NULL;
  688         } else {
  689                 db_printf("EXCL (count %d)\n", lkp->lk_exclusivecount);
  690                 *ownerp = lkp->lk_lockholder;
  691         }
  692         return (1);
  693 }
  694 
  695 void
  696 db_show_lockmgr(struct lock_object *lock)
  697 {
  698         struct thread *td;
  699         struct lock *lkp;
  700 
  701         lkp = (struct lock *)lock;
  702 
  703         db_printf(" lock type: %s\n", lkp->lk_wmesg);
  704         db_printf(" state: ");
  705         if (lkp->lk_sharecount)
  706                 db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
  707         else if (lkp->lk_flags & LK_HAVE_EXCL) {
  708                 td = lkp->lk_lockholder;
  709                 db_printf("EXCL (count %d) %p ", lkp->lk_exclusivecount, td);
  710                 db_printf("(tid %d, pid %d, \"%s\")\n", td->td_tid,
  711                     td->td_proc->p_pid, td->td_proc->p_comm);
  712         } else
  713                 db_printf("UNLOCKED\n");
  714         if (lkp->lk_waitcount > 0)
  715                 db_printf(" waiters: %d\n", lkp->lk_waitcount);
  716 }
  717 #endif

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