The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_timeout.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      From: @(#)kern_clock.c  8.5 (Berkeley) 1/21/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: releng/6.4/sys/kern/kern_timeout.c 181936 2008-08-20 19:07:21Z jhb $");
   39 
   40 #include <sys/param.h>
   41 #include <sys/systm.h>
   42 #include <sys/callout.h>
   43 #include <sys/condvar.h>
   44 #include <sys/kernel.h>
   45 #include <sys/ktr.h>
   46 #include <sys/lock.h>
   47 #include <sys/mutex.h>
   48 #include <sys/proc.h>
   49 #include <sys/sleepqueue.h>
   50 #include <sys/sysctl.h>
   51 
   52 static int avg_depth;
   53 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   54     "Average number of items examined per softclock call. Units = 1/1000");
   55 static int avg_gcalls;
   56 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   57     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   58 static int avg_mtxcalls;
   59 SYSCTL_INT(_debug, OID_AUTO, to_avg_mtxcalls, CTLFLAG_RD, &avg_mtxcalls, 0,
   60     "Average number of mtx callouts made per softclock call. Units = 1/1000");
   61 static int avg_mpcalls;
   62 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   63     "Average number of MP callouts made per softclock call. Units = 1/1000");
   64 /*
   65  * TODO:
   66  *      allocate more timeout table slots when table overflows.
   67  */
   68 
   69 /* Exported to machdep.c and/or kern_clock.c.  */
   70 struct callout *callout;
   71 struct callout_list callfree;
   72 int callwheelsize, callwheelbits, callwheelmask;
   73 struct callout_tailq *callwheel;
   74 int softticks;                  /* Like ticks, but for softclock(). */
   75 struct mtx callout_lock;
   76 
   77 static struct callout *nextsoftcheck;   /* Next callout to be checked. */
   78 
   79 /**
   80  * Locked by callout_lock:
   81  *   curr_callout    - If a callout is in progress, it is curr_callout.
   82  *                     If curr_callout is non-NULL, threads waiting in
   83  *                     callout_drain() will be woken up as soon as the 
   84  *                     relevant callout completes.
   85  *   curr_cancelled  - Changing to 1 with both callout_lock and c_mtx held
   86  *                     guarantees that the current callout will not run.
   87  *                     The softclock() function sets this to 0 before it
   88  *                     drops callout_lock to acquire c_mtx, and it calls
   89  *                     the handler only if curr_cancelled is still 0 after
   90  *                     c_mtx is successfully acquired.
   91  *   callout_wait    - If a thread is waiting in callout_drain(), then
   92  *                     callout_wait is nonzero.  Set only when
   93  *                     curr_callout is non-NULL.
   94  */
   95 static struct callout *curr_callout;
   96 static int curr_cancelled;
   97 static int callout_wait;
   98 
   99 /*
  100  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  101  *
  102  *      This code is called very early in the kernel initialization sequence,
  103  *      and may be called more then once.
  104  */
  105 caddr_t
  106 kern_timeout_callwheel_alloc(caddr_t v)
  107 {
  108         /*
  109          * Calculate callout wheel size
  110          */
  111         for (callwheelsize = 1, callwheelbits = 0;
  112              callwheelsize < ncallout;
  113              callwheelsize <<= 1, ++callwheelbits)
  114                 ;
  115         callwheelmask = callwheelsize - 1;
  116 
  117         callout = (struct callout *)v;
  118         v = (caddr_t)(callout + ncallout);
  119         callwheel = (struct callout_tailq *)v;
  120         v = (caddr_t)(callwheel + callwheelsize);
  121         return(v);
  122 }
  123 
  124 /*
  125  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  126  *                                 space.
  127  *
  128  *      This code is called just once, after the space reserved for the
  129  *      callout wheel has been finalized.
  130  */
  131 void
  132 kern_timeout_callwheel_init(void)
  133 {
  134         int i;
  135 
  136         SLIST_INIT(&callfree);
  137         for (i = 0; i < ncallout; i++) {
  138                 callout_init(&callout[i], 0);
  139                 callout[i].c_flags = CALLOUT_LOCAL_ALLOC;
  140                 SLIST_INSERT_HEAD(&callfree, &callout[i], c_links.sle);
  141         }
  142         for (i = 0; i < callwheelsize; i++) {
  143                 TAILQ_INIT(&callwheel[i]);
  144         }
  145         mtx_init(&callout_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  146 }
  147 
  148 /*
  149  * The callout mechanism is based on the work of Adam M. Costello and 
  150  * George Varghese, published in a technical report entitled "Redesigning
  151  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  152  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  153  * used in this implementation was published by G. Varghese and T. Lauck in
  154  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  155  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  156  * the 11th ACM Annual Symposium on Operating Systems Principles,
  157  * Austin, Texas Nov 1987.
  158  */
  159 
  160 /*
  161  * Software (low priority) clock interrupt.
  162  * Run periodic events from timeout queue.
  163  */
  164 void
  165 softclock(void *dummy)
  166 {
  167         struct callout *c;
  168         struct callout_tailq *bucket;
  169         int curticks;
  170         int steps;      /* #steps since we last allowed interrupts */
  171         int depth;
  172         int mpcalls;
  173         int mtxcalls;
  174         int gcalls;
  175 #ifdef DIAGNOSTIC
  176         struct bintime bt1, bt2;
  177         struct timespec ts2;
  178         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  179         static timeout_t *lastfunc;
  180 #endif
  181 
  182 #ifndef MAX_SOFTCLOCK_STEPS
  183 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  184 #endif /* MAX_SOFTCLOCK_STEPS */
  185 
  186         mpcalls = 0;
  187         mtxcalls = 0;
  188         gcalls = 0;
  189         depth = 0;
  190         steps = 0;
  191         mtx_lock_spin(&callout_lock);
  192         while (softticks != ticks) {
  193                 softticks++;
  194                 /*
  195                  * softticks may be modified by hard clock, so cache
  196                  * it while we work on a given bucket.
  197                  */
  198                 curticks = softticks;
  199                 bucket = &callwheel[curticks & callwheelmask];
  200                 c = TAILQ_FIRST(bucket);
  201                 while (c) {
  202                         depth++;
  203                         if (c->c_time != curticks) {
  204                                 c = TAILQ_NEXT(c, c_links.tqe);
  205                                 ++steps;
  206                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  207                                         nextsoftcheck = c;
  208                                         /* Give interrupts a chance. */
  209                                         mtx_unlock_spin(&callout_lock);
  210                                         ;       /* nothing */
  211                                         mtx_lock_spin(&callout_lock);
  212                                         c = nextsoftcheck;
  213                                         steps = 0;
  214                                 }
  215                         } else {
  216                                 void (*c_func)(void *);
  217                                 void *c_arg;
  218                                 struct mtx *c_mtx;
  219                                 int c_flags;
  220 
  221                                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  222                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  223                                 c_func = c->c_func;
  224                                 c_arg = c->c_arg;
  225                                 c_mtx = c->c_mtx;
  226                                 c_flags = c->c_flags;
  227                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  228                                         c->c_func = NULL;
  229                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  230                                         SLIST_INSERT_HEAD(&callfree, c,
  231                                                           c_links.sle);
  232                                         curr_callout = NULL;
  233                                 } else {
  234                                         c->c_flags =
  235                                             (c->c_flags & ~CALLOUT_PENDING);
  236                                         curr_callout = c;
  237                                 }
  238                                 curr_cancelled = 0;
  239                                 mtx_unlock_spin(&callout_lock);
  240                                 if (c_mtx != NULL) {
  241                                         mtx_lock(c_mtx);
  242                                         /*
  243                                          * The callout may have been cancelled
  244                                          * while we switched locks.
  245                                          */
  246                                         if (curr_cancelled) {
  247                                                 mtx_unlock(c_mtx);
  248                                                 goto skip;
  249                                         }
  250                                         /* The callout cannot be stopped now. */
  251                                         curr_cancelled = 1;
  252 
  253                                         if (c_mtx == &Giant) {
  254                                                 gcalls++;
  255                                                 CTR3(KTR_CALLOUT,
  256                                                     "callout %p func %p arg %p",
  257                                                     c, c_func, c_arg);
  258                                         } else {
  259                                                 mtxcalls++;
  260                                                 CTR3(KTR_CALLOUT, "callout mtx"
  261                                                     " %p func %p arg %p",
  262                                                     c, c_func, c_arg);
  263                                         }
  264                                 } else {
  265                                         mpcalls++;
  266                                         CTR3(KTR_CALLOUT,
  267                                             "callout mpsafe %p func %p arg %p",
  268                                             c, c_func, c_arg);
  269                                 }
  270 #ifdef DIAGNOSTIC
  271                                 binuptime(&bt1);
  272 #endif
  273                                 THREAD_NO_SLEEPING();
  274                                 c_func(c_arg);
  275                                 THREAD_SLEEPING_OK();
  276 #ifdef DIAGNOSTIC
  277                                 binuptime(&bt2);
  278                                 bintime_sub(&bt2, &bt1);
  279                                 if (bt2.frac > maxdt) {
  280                                         if (lastfunc != c_func ||
  281                                             bt2.frac > maxdt * 2) {
  282                                                 bintime2timespec(&bt2, &ts2);
  283                                                 printf(
  284                         "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  285                                                     c_func, c_arg,
  286                                                     (intmax_t)ts2.tv_sec,
  287                                                     ts2.tv_nsec);
  288                                         }
  289                                         maxdt = bt2.frac;
  290                                         lastfunc = c_func;
  291                                 }
  292 #endif
  293                                 if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  294                                         mtx_unlock(c_mtx);
  295                         skip:
  296                                 mtx_lock_spin(&callout_lock);
  297                                 curr_callout = NULL;
  298                                 if (callout_wait) {
  299                                         /*
  300                                          * There is someone waiting
  301                                          * for the callout to complete.
  302                                          */
  303                                         callout_wait = 0;
  304                                         mtx_unlock_spin(&callout_lock);
  305                                         wakeup(&callout_wait);
  306                                         mtx_lock_spin(&callout_lock);
  307                                 }
  308                                 steps = 0;
  309                                 c = nextsoftcheck;
  310                         }
  311                 }
  312         }
  313         avg_depth += (depth * 1000 - avg_depth) >> 8;
  314         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  315         avg_mtxcalls += (mtxcalls * 1000 - avg_mtxcalls) >> 8;
  316         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  317         nextsoftcheck = NULL;
  318         mtx_unlock_spin(&callout_lock);
  319 }
  320 
  321 /*
  322  * timeout --
  323  *      Execute a function after a specified length of time.
  324  *
  325  * untimeout --
  326  *      Cancel previous timeout function call.
  327  *
  328  * callout_handle_init --
  329  *      Initialize a handle so that using it with untimeout is benign.
  330  *
  331  *      See AT&T BCI Driver Reference Manual for specification.  This
  332  *      implementation differs from that one in that although an 
  333  *      identification value is returned from timeout, the original
  334  *      arguments to timeout as well as the identifier are used to
  335  *      identify entries for untimeout.
  336  */
  337 struct callout_handle
  338 timeout(ftn, arg, to_ticks)
  339         timeout_t *ftn;
  340         void *arg;
  341         int to_ticks;
  342 {
  343         struct callout *new;
  344         struct callout_handle handle;
  345 
  346         mtx_lock_spin(&callout_lock);
  347 
  348         /* Fill in the next free callout structure. */
  349         new = SLIST_FIRST(&callfree);
  350         if (new == NULL)
  351                 /* XXX Attempt to malloc first */
  352                 panic("timeout table full");
  353         SLIST_REMOVE_HEAD(&callfree, c_links.sle);
  354         
  355         callout_reset(new, to_ticks, ftn, arg);
  356 
  357         handle.callout = new;
  358         mtx_unlock_spin(&callout_lock);
  359         return (handle);
  360 }
  361 
  362 void
  363 untimeout(ftn, arg, handle)
  364         timeout_t *ftn;
  365         void *arg;
  366         struct callout_handle handle;
  367 {
  368 
  369         /*
  370          * Check for a handle that was initialized
  371          * by callout_handle_init, but never used
  372          * for a real timeout.
  373          */
  374         if (handle.callout == NULL)
  375                 return;
  376 
  377         mtx_lock_spin(&callout_lock);
  378         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  379                 callout_stop(handle.callout);
  380         mtx_unlock_spin(&callout_lock);
  381 }
  382 
  383 void
  384 callout_handle_init(struct callout_handle *handle)
  385 {
  386         handle->callout = NULL;
  387 }
  388 
  389 /*
  390  * New interface; clients allocate their own callout structures.
  391  *
  392  * callout_reset() - establish or change a timeout
  393  * callout_stop() - disestablish a timeout
  394  * callout_init() - initialize a callout structure so that it can
  395  *      safely be passed to callout_reset() and callout_stop()
  396  *
  397  * <sys/callout.h> defines three convenience macros:
  398  *
  399  * callout_active() - returns truth if callout has not been stopped,
  400  *      drained, or deactivated since the last time the callout was
  401  *      reset.
  402  * callout_pending() - returns truth if callout is still waiting for timeout
  403  * callout_deactivate() - marks the callout as having been serviced
  404  */
  405 int
  406 callout_reset(c, to_ticks, ftn, arg)
  407         struct  callout *c;
  408         int     to_ticks;
  409         void    (*ftn)(void *);
  410         void    *arg;
  411 {
  412         int cancelled = 0;
  413 
  414 #ifdef notyet /* Some callers of timeout() do not hold Giant. */
  415         if (c->c_mtx != NULL)
  416                 mtx_assert(c->c_mtx, MA_OWNED);
  417 #endif
  418 
  419         mtx_lock_spin(&callout_lock);
  420         if (c == curr_callout) {
  421                 /*
  422                  * We're being asked to reschedule a callout which is
  423                  * currently in progress.  If there is a mutex then we
  424                  * can cancel the callout if it has not really started.
  425                  */
  426                 if (c->c_mtx != NULL && !curr_cancelled)
  427                         cancelled = curr_cancelled = 1;
  428                 if (callout_wait) {
  429                         /*
  430                          * Someone has called callout_drain to kill this
  431                          * callout.  Don't reschedule.
  432                          */
  433                         CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
  434                             cancelled ? "cancelled" : "failed to cancel",
  435                             c, c->c_func, c->c_arg);
  436                         mtx_unlock_spin(&callout_lock);
  437                         return (cancelled);
  438                 }
  439         }
  440         if (c->c_flags & CALLOUT_PENDING) {
  441                 if (nextsoftcheck == c) {
  442                         nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  443                 }
  444                 TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c,
  445                     c_links.tqe);
  446 
  447                 cancelled = 1;
  448 
  449                 /*
  450                  * Part of the normal "stop a pending callout" process
  451                  * is to clear the CALLOUT_ACTIVE and CALLOUT_PENDING
  452                  * flags.  We're not going to bother doing that here,
  453                  * because we're going to be setting those flags ten lines
  454                  * after this point, and we're holding callout_lock
  455                  * between now and then.
  456                  */
  457         }
  458 
  459         /*
  460          * We could unlock callout_lock here and lock it again before the
  461          * TAILQ_INSERT_TAIL, but there's no point since doing this setup
  462          * doesn't take much time.
  463          */
  464         if (to_ticks <= 0)
  465                 to_ticks = 1;
  466 
  467         c->c_arg = arg;
  468         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  469         c->c_func = ftn;
  470         c->c_time = ticks + to_ticks;
  471         TAILQ_INSERT_TAIL(&callwheel[c->c_time & callwheelmask], 
  472                           c, c_links.tqe);
  473         CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
  474             cancelled ? "re" : "", c, c->c_func, c->c_arg, to_ticks);
  475         mtx_unlock_spin(&callout_lock);
  476 
  477         return (cancelled);
  478 }
  479 
  480 int
  481 _callout_stop_safe(c, safe)
  482         struct  callout *c;
  483         int     safe;
  484 {
  485         int use_mtx, sq_locked;
  486 
  487         if (!safe && c->c_mtx != NULL) {
  488 #ifdef notyet /* Some callers do not hold Giant for Giant-locked callouts. */
  489                 mtx_assert(c->c_mtx, MA_OWNED);
  490                 use_mtx = 1;
  491 #else
  492                 use_mtx = mtx_owned(c->c_mtx);
  493 #endif
  494         } else {
  495                 use_mtx = 0;
  496         }
  497 
  498         sq_locked = 0;
  499 again:
  500         mtx_lock_spin(&callout_lock);
  501         /*
  502          * If the callout isn't pending, it's not on the queue, so
  503          * don't attempt to remove it from the queue.  We can try to
  504          * stop it by other means however.
  505          */
  506         if (!(c->c_flags & CALLOUT_PENDING)) {
  507                 c->c_flags &= ~CALLOUT_ACTIVE;
  508 
  509                 /*
  510                  * If it wasn't on the queue and it isn't the current
  511                  * callout, then we can't stop it, so just bail.
  512                  */
  513                 if (c != curr_callout) {
  514                         CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  515                             c, c->c_func, c->c_arg);
  516                         mtx_unlock_spin(&callout_lock);
  517                         if (sq_locked)
  518                                 sleepq_release(&callout_wait);
  519                         return (0);
  520                 }
  521 
  522                 if (safe) {
  523                         /*
  524                          * The current callout is running (or just
  525                          * about to run) and blocking is allowed, so
  526                          * just wait for the current invocation to
  527                          * finish.
  528                          */
  529                         while (c == curr_callout) {
  530 
  531                                 /*
  532                                  * Use direct calls to sleepqueue interface
  533                                  * instead of cv/msleep in order to avoid
  534                                  * a LOR between callout_lock and sleepqueue
  535                                  * chain spinlocks.  This piece of code
  536                                  * emulates a msleep_spin() call actually.
  537                                  *
  538                                  * If we already have the sleepqueue chain
  539                                  * locked, then we can safely block.  If we
  540                                  * don't already have it locked, however,
  541                                  * we have to drop the callout_lock to lock
  542                                  * it.  This opens several races, so we
  543                                  * restart at the beginning once we have
  544                                  * both locks.  If nothing has changed, then
  545                                  * we will end up back here with sq_locked
  546                                  * set.
  547                                  */
  548                                 if (!sq_locked) {
  549                                         mtx_unlock_spin(&callout_lock);
  550                                         sleepq_lock(&callout_wait);
  551                                         sq_locked = 1;
  552                                         goto again;
  553                                 }
  554 
  555                                 callout_wait = 1;
  556                                 DROP_GIANT();
  557                                 mtx_unlock_spin(&callout_lock);
  558                                 sleepq_add(&callout_wait,
  559                                     &callout_lock.mtx_object, "codrain",
  560                                     SLEEPQ_MSLEEP, 0);
  561                                 sleepq_wait(&callout_wait);
  562                                 sq_locked = 0;
  563 
  564                                 /* Reacquire locks previously released. */
  565                                 PICKUP_GIANT();
  566                                 mtx_lock_spin(&callout_lock);
  567                         }
  568                 } else if (use_mtx && !curr_cancelled) {
  569                         /*
  570                          * The current callout is waiting for it's
  571                          * mutex which we hold.  Cancel the callout
  572                          * and return.  After our caller drops the
  573                          * mutex, the callout will be skipped in
  574                          * softclock().
  575                          */
  576                         curr_cancelled = 1;
  577                         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  578                             c, c->c_func, c->c_arg);
  579                         mtx_unlock_spin(&callout_lock);
  580                         KASSERT(!sq_locked, ("sleepqueue chain locked"));
  581                         return (1);
  582                 }
  583                 CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  584                     c, c->c_func, c->c_arg);
  585                 mtx_unlock_spin(&callout_lock);
  586                 KASSERT(!sq_locked, ("sleepqueue chain still locked"));
  587                 return (0);
  588         }
  589         if (sq_locked)
  590                 sleepq_release(&callout_wait);
  591 
  592         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  593 
  594         if (nextsoftcheck == c) {
  595                 nextsoftcheck = TAILQ_NEXT(c, c_links.tqe);
  596         }
  597         TAILQ_REMOVE(&callwheel[c->c_time & callwheelmask], c, c_links.tqe);
  598 
  599         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  600             c, c->c_func, c->c_arg);
  601 
  602         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  603                 c->c_func = NULL;
  604                 SLIST_INSERT_HEAD(&callfree, c, c_links.sle);
  605         }
  606         mtx_unlock_spin(&callout_lock);
  607         return (1);
  608 }
  609 
  610 void
  611 callout_init(c, mpsafe)
  612         struct  callout *c;
  613         int mpsafe;
  614 {
  615         bzero(c, sizeof *c);
  616         if (mpsafe) {
  617                 c->c_mtx = NULL;
  618                 c->c_flags = CALLOUT_RETURNUNLOCKED;
  619         } else {
  620                 c->c_mtx = &Giant;
  621                 c->c_flags = 0;
  622         }
  623 }
  624 
  625 void
  626 callout_init_mtx(c, mtx, flags)
  627         struct  callout *c;
  628         struct  mtx *mtx;
  629         int flags;
  630 {
  631         bzero(c, sizeof *c);
  632         c->c_mtx = mtx;
  633         KASSERT((flags & ~CALLOUT_RETURNUNLOCKED) == 0,
  634             ("callout_init_mtx: bad flags %d", flags));
  635         /* CALLOUT_RETURNUNLOCKED makes no sense without a mutex. */
  636         KASSERT(mtx != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
  637             ("callout_init_mtx: CALLOUT_RETURNUNLOCKED with no mutex"));
  638         c->c_flags = flags & CALLOUT_RETURNUNLOCKED;
  639 }
  640 
  641 #ifdef APM_FIXUP_CALLTODO
  642 /* 
  643  * Adjust the kernel calltodo timeout list.  This routine is used after 
  644  * an APM resume to recalculate the calltodo timer list values with the 
  645  * number of hz's we have been sleeping.  The next hardclock() will detect 
  646  * that there are fired timers and run softclock() to execute them.
  647  *
  648  * Please note, I have not done an exhaustive analysis of what code this
  649  * might break.  I am motivated to have my select()'s and alarm()'s that
  650  * have expired during suspend firing upon resume so that the applications
  651  * which set the timer can do the maintanence the timer was for as close
  652  * as possible to the originally intended time.  Testing this code for a 
  653  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  654  * firing, which seemed independant on whether the suspend was 2 hours or
  655  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  656  */
  657 void
  658 adjust_timeout_calltodo(time_change)
  659     struct timeval *time_change;
  660 {
  661         register struct callout *p;
  662         unsigned long delta_ticks;
  663 
  664         /* 
  665          * How many ticks were we asleep?
  666          * (stolen from tvtohz()).
  667          */
  668 
  669         /* Don't do anything */
  670         if (time_change->tv_sec < 0)
  671                 return;
  672         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  673                 delta_ticks = (time_change->tv_sec * 1000000 +
  674                                time_change->tv_usec + (tick - 1)) / tick + 1;
  675         else if (time_change->tv_sec <= LONG_MAX / hz)
  676                 delta_ticks = time_change->tv_sec * hz +
  677                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  678         else
  679                 delta_ticks = LONG_MAX;
  680 
  681         if (delta_ticks > INT_MAX)
  682                 delta_ticks = INT_MAX;
  683 
  684         /* 
  685          * Now rip through the timer calltodo list looking for timers
  686          * to expire.
  687          */
  688 
  689         /* don't collide with softclock() */
  690         mtx_lock_spin(&callout_lock);
  691         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  692                 p->c_time -= delta_ticks;
  693 
  694                 /* Break if the timer had more time on it than delta_ticks */
  695                 if (p->c_time > 0)
  696                         break;
  697 
  698                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  699                 delta_ticks = -p->c_time;
  700         }
  701         mtx_unlock_spin(&callout_lock);
  702 
  703         return;
  704 }
  705 #endif /* APM_FIXUP_CALLTODO */

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