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/8.1/sys/kern/kern_timeout.c 204831 2010-03-07 14:29:12Z luigi $");
   39 
   40 #include "opt_kdtrace.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/bus.h>
   45 #include <sys/callout.h>
   46 #include <sys/condvar.h>
   47 #include <sys/interrupt.h>
   48 #include <sys/kernel.h>
   49 #include <sys/ktr.h>
   50 #include <sys/lock.h>
   51 #include <sys/malloc.h>
   52 #include <sys/mutex.h>
   53 #include <sys/proc.h>
   54 #include <sys/sdt.h>
   55 #include <sys/sleepqueue.h>
   56 #include <sys/sysctl.h>
   57 #include <sys/smp.h>
   58 
   59 SDT_PROVIDER_DEFINE(callout_execute);
   60 SDT_PROBE_DEFINE(callout_execute, kernel, , callout_start);
   61 SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_start, 0,
   62     "struct callout *");
   63 SDT_PROBE_DEFINE(callout_execute, kernel, , callout_end); 
   64 SDT_PROBE_ARGTYPE(callout_execute, kernel, , callout_end, 0,
   65     "struct callout *");
   66 
   67 static int avg_depth;
   68 SYSCTL_INT(_debug, OID_AUTO, to_avg_depth, CTLFLAG_RD, &avg_depth, 0,
   69     "Average number of items examined per softclock call. Units = 1/1000");
   70 static int avg_gcalls;
   71 SYSCTL_INT(_debug, OID_AUTO, to_avg_gcalls, CTLFLAG_RD, &avg_gcalls, 0,
   72     "Average number of Giant callouts made per softclock call. Units = 1/1000");
   73 static int avg_lockcalls;
   74 SYSCTL_INT(_debug, OID_AUTO, to_avg_lockcalls, CTLFLAG_RD, &avg_lockcalls, 0,
   75     "Average number of lock callouts made per softclock call. Units = 1/1000");
   76 static int avg_mpcalls;
   77 SYSCTL_INT(_debug, OID_AUTO, to_avg_mpcalls, CTLFLAG_RD, &avg_mpcalls, 0,
   78     "Average number of MP callouts made per softclock call. Units = 1/1000");
   79 /*
   80  * TODO:
   81  *      allocate more timeout table slots when table overflows.
   82  */
   83 int callwheelsize, callwheelbits, callwheelmask;
   84 
   85 /*
   86  * There is one struct callout_cpu per cpu, holding all relevant
   87  * state for the callout processing thread on the individual CPU.
   88  * In particular:
   89  *      cc_ticks is incremented once per tick in callout_cpu().
   90  *      It tracks the global 'ticks' but in a way that the individual
   91  *      threads should not worry about races in the order in which
   92  *      hardclock() and hardclock_cpu() run on the various CPUs.
   93  *      cc_softclock is advanced in callout_cpu() to point to the
   94  *      first entry in cc_callwheel that may need handling. In turn,
   95  *      a softclock() is scheduled so it can serve the various entries i
   96  *      such that cc_softclock <= i <= cc_ticks .
   97  *      XXX maybe cc_softclock and cc_ticks should be volatile ?
   98  *
   99  *      cc_ticks is also used in callout_reset_cpu() to determine
  100  *      when the callout should be served.
  101  */
  102 struct callout_cpu {
  103         struct mtx              cc_lock;
  104         struct callout          *cc_callout;
  105         struct callout_tailq    *cc_callwheel;
  106         struct callout_list     cc_callfree;
  107         struct callout          *cc_next;
  108         struct callout          *cc_curr;
  109         void                    *cc_cookie;
  110         int                     cc_ticks;
  111         int                     cc_softticks;
  112         int                     cc_cancel;
  113         int                     cc_waiting;
  114 };
  115 
  116 #ifdef SMP
  117 struct callout_cpu cc_cpu[MAXCPU];
  118 #define CC_CPU(cpu)     (&cc_cpu[(cpu)])
  119 #define CC_SELF()       CC_CPU(PCPU_GET(cpuid))
  120 #else
  121 struct callout_cpu cc_cpu;
  122 #define CC_CPU(cpu)     &cc_cpu
  123 #define CC_SELF()       &cc_cpu
  124 #endif
  125 #define CC_LOCK(cc)     mtx_lock_spin(&(cc)->cc_lock)
  126 #define CC_UNLOCK(cc)   mtx_unlock_spin(&(cc)->cc_lock)
  127 
  128 static int timeout_cpu;
  129 
  130 MALLOC_DEFINE(M_CALLOUT, "callout", "Callout datastructures");
  131 
  132 /**
  133  * Locked by cc_lock:
  134  *   cc_curr         - If a callout is in progress, it is curr_callout.
  135  *                     If curr_callout is non-NULL, threads waiting in
  136  *                     callout_drain() will be woken up as soon as the
  137  *                     relevant callout completes.
  138  *   cc_cancel       - Changing to 1 with both callout_lock and c_lock held
  139  *                     guarantees that the current callout will not run.
  140  *                     The softclock() function sets this to 0 before it
  141  *                     drops callout_lock to acquire c_lock, and it calls
  142  *                     the handler only if curr_cancelled is still 0 after
  143  *                     c_lock is successfully acquired.
  144  *   cc_waiting      - If a thread is waiting in callout_drain(), then
  145  *                     callout_wait is nonzero.  Set only when
  146  *                     curr_callout is non-NULL.
  147  */
  148 
  149 /*
  150  * kern_timeout_callwheel_alloc() - kernel low level callwheel initialization 
  151  *
  152  *      This code is called very early in the kernel initialization sequence,
  153  *      and may be called more then once.
  154  */
  155 caddr_t
  156 kern_timeout_callwheel_alloc(caddr_t v)
  157 {
  158         struct callout_cpu *cc;
  159 
  160         timeout_cpu = PCPU_GET(cpuid);
  161         cc = CC_CPU(timeout_cpu);
  162         /*
  163          * Calculate callout wheel size
  164          */
  165         for (callwheelsize = 1, callwheelbits = 0;
  166              callwheelsize < ncallout;
  167              callwheelsize <<= 1, ++callwheelbits)
  168                 ;
  169         callwheelmask = callwheelsize - 1;
  170 
  171         cc->cc_callout = (struct callout *)v;
  172         v = (caddr_t)(cc->cc_callout + ncallout);
  173         cc->cc_callwheel = (struct callout_tailq *)v;
  174         v = (caddr_t)(cc->cc_callwheel + callwheelsize);
  175         return(v);
  176 }
  177 
  178 static void
  179 callout_cpu_init(struct callout_cpu *cc)
  180 {
  181         struct callout *c;
  182         int i;
  183 
  184         mtx_init(&cc->cc_lock, "callout", NULL, MTX_SPIN | MTX_RECURSE);
  185         SLIST_INIT(&cc->cc_callfree);
  186         for (i = 0; i < callwheelsize; i++) {
  187                 TAILQ_INIT(&cc->cc_callwheel[i]);
  188         }
  189         if (cc->cc_callout == NULL)
  190                 return;
  191         for (i = 0; i < ncallout; i++) {
  192                 c = &cc->cc_callout[i];
  193                 callout_init(c, 0);
  194                 c->c_flags = CALLOUT_LOCAL_ALLOC;
  195                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  196         }
  197 }
  198 
  199 /*
  200  * kern_timeout_callwheel_init() - initialize previously reserved callwheel
  201  *                                 space.
  202  *
  203  *      This code is called just once, after the space reserved for the
  204  *      callout wheel has been finalized.
  205  */
  206 void
  207 kern_timeout_callwheel_init(void)
  208 {
  209         callout_cpu_init(CC_CPU(timeout_cpu));
  210 }
  211 
  212 /*
  213  * Start standard softclock thread.
  214  */
  215 void    *softclock_ih;
  216 
  217 static void
  218 start_softclock(void *dummy)
  219 {
  220         struct callout_cpu *cc;
  221 #ifdef SMP
  222         int cpu;
  223 #endif
  224 
  225         cc = CC_CPU(timeout_cpu);
  226         if (swi_add(&clk_intr_event, "clock", softclock, cc, SWI_CLOCK,
  227             INTR_MPSAFE, &softclock_ih))
  228                 panic("died while creating standard software ithreads");
  229         cc->cc_cookie = softclock_ih;
  230 #ifdef SMP
  231         for (cpu = 0; cpu <= mp_maxid; cpu++) {
  232                 if (cpu == timeout_cpu)
  233                         continue;
  234                 if (CPU_ABSENT(cpu))
  235                         continue;
  236                 cc = CC_CPU(cpu);
  237                 if (swi_add(NULL, "clock", softclock, cc, SWI_CLOCK,
  238                     INTR_MPSAFE, &cc->cc_cookie))
  239                         panic("died while creating standard software ithreads");
  240                 cc->cc_callout = NULL;  /* Only cpu0 handles timeout(). */
  241                 cc->cc_callwheel = malloc(
  242                     sizeof(struct callout_tailq) * callwheelsize, M_CALLOUT,
  243                     M_WAITOK);
  244                 callout_cpu_init(cc);
  245         }
  246 #endif
  247 }
  248 
  249 SYSINIT(start_softclock, SI_SUB_SOFTINTR, SI_ORDER_FIRST, start_softclock, NULL);
  250 
  251 void
  252 callout_tick(void)
  253 {
  254         struct callout_cpu *cc;
  255         int need_softclock;
  256         int bucket;
  257 
  258         /*
  259          * Process callouts at a very low cpu priority, so we don't keep the
  260          * relatively high clock interrupt priority any longer than necessary.
  261          */
  262         need_softclock = 0;
  263         cc = CC_SELF();
  264         mtx_lock_spin_flags(&cc->cc_lock, MTX_QUIET);
  265         cc->cc_ticks++;
  266         for (; (cc->cc_softticks - cc->cc_ticks) <= 0; cc->cc_softticks++) {
  267                 bucket = cc->cc_softticks & callwheelmask;
  268                 if (!TAILQ_EMPTY(&cc->cc_callwheel[bucket])) {
  269                         need_softclock = 1;
  270                         break;
  271                 }
  272         }
  273         mtx_unlock_spin_flags(&cc->cc_lock, MTX_QUIET);
  274         /*
  275          * swi_sched acquires the thread lock, so we don't want to call it
  276          * with cc_lock held; incorrect locking order.
  277          */
  278         if (need_softclock)
  279                 swi_sched(cc->cc_cookie, 0);
  280 }
  281 
  282 static struct callout_cpu *
  283 callout_lock(struct callout *c)
  284 {
  285         struct callout_cpu *cc;
  286         int cpu;
  287 
  288         for (;;) {
  289                 cpu = c->c_cpu;
  290                 cc = CC_CPU(cpu);
  291                 CC_LOCK(cc);
  292                 if (cpu == c->c_cpu)
  293                         break;
  294                 CC_UNLOCK(cc);
  295         }
  296         return (cc);
  297 }
  298 
  299 /*
  300  * The callout mechanism is based on the work of Adam M. Costello and 
  301  * George Varghese, published in a technical report entitled "Redesigning
  302  * the BSD Callout and Timer Facilities" and modified slightly for inclusion
  303  * in FreeBSD by Justin T. Gibbs.  The original work on the data structures
  304  * used in this implementation was published by G. Varghese and T. Lauck in
  305  * the paper "Hashed and Hierarchical Timing Wheels: Data Structures for
  306  * the Efficient Implementation of a Timer Facility" in the Proceedings of
  307  * the 11th ACM Annual Symposium on Operating Systems Principles,
  308  * Austin, Texas Nov 1987.
  309  */
  310 
  311 /*
  312  * Software (low priority) clock interrupt.
  313  * Run periodic events from timeout queue.
  314  */
  315 void
  316 softclock(void *arg)
  317 {
  318         struct callout_cpu *cc;
  319         struct callout *c;
  320         struct callout_tailq *bucket;
  321         int curticks;
  322         int steps;      /* #steps since we last allowed interrupts */
  323         int depth;
  324         int mpcalls;
  325         int lockcalls;
  326         int gcalls;
  327 #ifdef DIAGNOSTIC
  328         struct bintime bt1, bt2;
  329         struct timespec ts2;
  330         static uint64_t maxdt = 36893488147419102LL;    /* 2 msec */
  331         static timeout_t *lastfunc;
  332 #endif
  333 
  334 #ifndef MAX_SOFTCLOCK_STEPS
  335 #define MAX_SOFTCLOCK_STEPS 100 /* Maximum allowed value of steps. */
  336 #endif /* MAX_SOFTCLOCK_STEPS */
  337 
  338         mpcalls = 0;
  339         lockcalls = 0;
  340         gcalls = 0;
  341         depth = 0;
  342         steps = 0;
  343         cc = (struct callout_cpu *)arg;
  344         CC_LOCK(cc);
  345         while (cc->cc_softticks - 1 != cc->cc_ticks) {
  346                 /*
  347                  * cc_softticks may be modified by hard clock, so cache
  348                  * it while we work on a given bucket.
  349                  */
  350                 curticks = cc->cc_softticks;
  351                 cc->cc_softticks++;
  352                 bucket = &cc->cc_callwheel[curticks & callwheelmask];
  353                 c = TAILQ_FIRST(bucket);
  354                 while (c) {
  355                         depth++;
  356                         if (c->c_time != curticks) {
  357                                 c = TAILQ_NEXT(c, c_links.tqe);
  358                                 ++steps;
  359                                 if (steps >= MAX_SOFTCLOCK_STEPS) {
  360                                         cc->cc_next = c;
  361                                         /* Give interrupts a chance. */
  362                                         CC_UNLOCK(cc);
  363                                         ;       /* nothing */
  364                                         CC_LOCK(cc);
  365                                         c = cc->cc_next;
  366                                         steps = 0;
  367                                 }
  368                         } else {
  369                                 void (*c_func)(void *);
  370                                 void *c_arg;
  371                                 struct lock_class *class;
  372                                 struct lock_object *c_lock;
  373                                 int c_flags, sharedlock;
  374 
  375                                 cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  376                                 TAILQ_REMOVE(bucket, c, c_links.tqe);
  377                                 class = (c->c_lock != NULL) ?
  378                                     LOCK_CLASS(c->c_lock) : NULL;
  379                                 sharedlock = (c->c_flags & CALLOUT_SHAREDLOCK) ?
  380                                     0 : 1;
  381                                 c_lock = c->c_lock;
  382                                 c_func = c->c_func;
  383                                 c_arg = c->c_arg;
  384                                 c_flags = c->c_flags;
  385                                 if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  386                                         c->c_flags = CALLOUT_LOCAL_ALLOC;
  387                                 } else {
  388                                         c->c_flags =
  389                                             (c->c_flags & ~CALLOUT_PENDING);
  390                                 }
  391                                 cc->cc_curr = c;
  392                                 cc->cc_cancel = 0;
  393                                 CC_UNLOCK(cc);
  394                                 if (c_lock != NULL) {
  395                                         class->lc_lock(c_lock, sharedlock);
  396                                         /*
  397                                          * The callout may have been cancelled
  398                                          * while we switched locks.
  399                                          */
  400                                         if (cc->cc_cancel) {
  401                                                 class->lc_unlock(c_lock);
  402                                                 goto skip;
  403                                         }
  404                                         /* The callout cannot be stopped now. */
  405                                         cc->cc_cancel = 1;
  406 
  407                                         if (c_lock == &Giant.lock_object) {
  408                                                 gcalls++;
  409                                                 CTR3(KTR_CALLOUT,
  410                                                     "callout %p func %p arg %p",
  411                                                     c, c_func, c_arg);
  412                                         } else {
  413                                                 lockcalls++;
  414                                                 CTR3(KTR_CALLOUT, "callout lock"
  415                                                     " %p func %p arg %p",
  416                                                     c, c_func, c_arg);
  417                                         }
  418                                 } else {
  419                                         mpcalls++;
  420                                         CTR3(KTR_CALLOUT,
  421                                             "callout mpsafe %p func %p arg %p",
  422                                             c, c_func, c_arg);
  423                                 }
  424 #ifdef DIAGNOSTIC
  425                                 binuptime(&bt1);
  426 #endif
  427                                 THREAD_NO_SLEEPING();
  428                                 SDT_PROBE(callout_execute, kernel, ,
  429                                     callout_start, c, 0, 0, 0, 0);
  430                                 c_func(c_arg);
  431                                 SDT_PROBE(callout_execute, kernel, ,
  432                                     callout_end, c, 0, 0, 0, 0);
  433                                 THREAD_SLEEPING_OK();
  434 #ifdef DIAGNOSTIC
  435                                 binuptime(&bt2);
  436                                 bintime_sub(&bt2, &bt1);
  437                                 if (bt2.frac > maxdt) {
  438                                         if (lastfunc != c_func ||
  439                                             bt2.frac > maxdt * 2) {
  440                                                 bintime2timespec(&bt2, &ts2);
  441                                                 printf(
  442                         "Expensive timeout(9) function: %p(%p) %jd.%09ld s\n",
  443                                                     c_func, c_arg,
  444                                                     (intmax_t)ts2.tv_sec,
  445                                                     ts2.tv_nsec);
  446                                         }
  447                                         maxdt = bt2.frac;
  448                                         lastfunc = c_func;
  449                                 }
  450 #endif
  451                                 CTR1(KTR_CALLOUT, "callout %p finished", c);
  452                                 if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
  453                                         class->lc_unlock(c_lock);
  454                         skip:
  455                                 CC_LOCK(cc);
  456                                 /*
  457                                  * If the current callout is locally
  458                                  * allocated (from timeout(9))
  459                                  * then put it on the freelist.
  460                                  *
  461                                  * Note: we need to check the cached
  462                                  * copy of c_flags because if it was not
  463                                  * local, then it's not safe to deref the
  464                                  * callout pointer.
  465                                  */
  466                                 if (c_flags & CALLOUT_LOCAL_ALLOC) {
  467                                         KASSERT(c->c_flags ==
  468                                             CALLOUT_LOCAL_ALLOC,
  469                                             ("corrupted callout"));
  470                                         c->c_func = NULL;
  471                                         SLIST_INSERT_HEAD(&cc->cc_callfree, c,
  472                                             c_links.sle);
  473                                 }
  474                                 cc->cc_curr = NULL;
  475                                 if (cc->cc_waiting) {
  476                                         /*
  477                                          * There is someone waiting
  478                                          * for the callout to complete.
  479                                          */
  480                                         cc->cc_waiting = 0;
  481                                         CC_UNLOCK(cc);
  482                                         wakeup(&cc->cc_waiting);
  483                                         CC_LOCK(cc);
  484                                 }
  485                                 steps = 0;
  486                                 c = cc->cc_next;
  487                         }
  488                 }
  489         }
  490         avg_depth += (depth * 1000 - avg_depth) >> 8;
  491         avg_mpcalls += (mpcalls * 1000 - avg_mpcalls) >> 8;
  492         avg_lockcalls += (lockcalls * 1000 - avg_lockcalls) >> 8;
  493         avg_gcalls += (gcalls * 1000 - avg_gcalls) >> 8;
  494         cc->cc_next = NULL;
  495         CC_UNLOCK(cc);
  496 }
  497 
  498 /*
  499  * timeout --
  500  *      Execute a function after a specified length of time.
  501  *
  502  * untimeout --
  503  *      Cancel previous timeout function call.
  504  *
  505  * callout_handle_init --
  506  *      Initialize a handle so that using it with untimeout is benign.
  507  *
  508  *      See AT&T BCI Driver Reference Manual for specification.  This
  509  *      implementation differs from that one in that although an 
  510  *      identification value is returned from timeout, the original
  511  *      arguments to timeout as well as the identifier are used to
  512  *      identify entries for untimeout.
  513  */
  514 struct callout_handle
  515 timeout(ftn, arg, to_ticks)
  516         timeout_t *ftn;
  517         void *arg;
  518         int to_ticks;
  519 {
  520         struct callout_cpu *cc;
  521         struct callout *new;
  522         struct callout_handle handle;
  523 
  524         cc = CC_CPU(timeout_cpu);
  525         CC_LOCK(cc);
  526         /* Fill in the next free callout structure. */
  527         new = SLIST_FIRST(&cc->cc_callfree);
  528         if (new == NULL)
  529                 /* XXX Attempt to malloc first */
  530                 panic("timeout table full");
  531         SLIST_REMOVE_HEAD(&cc->cc_callfree, c_links.sle);
  532         callout_reset(new, to_ticks, ftn, arg);
  533         handle.callout = new;
  534         CC_UNLOCK(cc);
  535 
  536         return (handle);
  537 }
  538 
  539 void
  540 untimeout(ftn, arg, handle)
  541         timeout_t *ftn;
  542         void *arg;
  543         struct callout_handle handle;
  544 {
  545         struct callout_cpu *cc;
  546 
  547         /*
  548          * Check for a handle that was initialized
  549          * by callout_handle_init, but never used
  550          * for a real timeout.
  551          */
  552         if (handle.callout == NULL)
  553                 return;
  554 
  555         cc = callout_lock(handle.callout);
  556         if (handle.callout->c_func == ftn && handle.callout->c_arg == arg)
  557                 callout_stop(handle.callout);
  558         CC_UNLOCK(cc);
  559 }
  560 
  561 void
  562 callout_handle_init(struct callout_handle *handle)
  563 {
  564         handle->callout = NULL;
  565 }
  566 
  567 /*
  568  * New interface; clients allocate their own callout structures.
  569  *
  570  * callout_reset() - establish or change a timeout
  571  * callout_stop() - disestablish a timeout
  572  * callout_init() - initialize a callout structure so that it can
  573  *      safely be passed to callout_reset() and callout_stop()
  574  *
  575  * <sys/callout.h> defines three convenience macros:
  576  *
  577  * callout_active() - returns truth if callout has not been stopped,
  578  *      drained, or deactivated since the last time the callout was
  579  *      reset.
  580  * callout_pending() - returns truth if callout is still waiting for timeout
  581  * callout_deactivate() - marks the callout as having been serviced
  582  */
  583 int
  584 callout_reset_on(struct callout *c, int to_ticks, void (*ftn)(void *),
  585     void *arg, int cpu)
  586 {
  587         struct callout_cpu *cc;
  588         int cancelled = 0;
  589 
  590         /*
  591          * Don't allow migration of pre-allocated callouts lest they
  592          * become unbalanced.
  593          */
  594         if (c->c_flags & CALLOUT_LOCAL_ALLOC)
  595                 cpu = c->c_cpu;
  596 retry:
  597         cc = callout_lock(c);
  598         if (cc->cc_curr == c) {
  599                 /*
  600                  * We're being asked to reschedule a callout which is
  601                  * currently in progress.  If there is a lock then we
  602                  * can cancel the callout if it has not really started.
  603                  */
  604                 if (c->c_lock != NULL && !cc->cc_cancel)
  605                         cancelled = cc->cc_cancel = 1;
  606                 if (cc->cc_waiting) {
  607                         /*
  608                          * Someone has called callout_drain to kill this
  609                          * callout.  Don't reschedule.
  610                          */
  611                         CTR4(KTR_CALLOUT, "%s %p func %p arg %p",
  612                             cancelled ? "cancelled" : "failed to cancel",
  613                             c, c->c_func, c->c_arg);
  614                         CC_UNLOCK(cc);
  615                         return (cancelled);
  616                 }
  617         }
  618         if (c->c_flags & CALLOUT_PENDING) {
  619                 if (cc->cc_next == c) {
  620                         cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  621                 }
  622                 TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
  623                     c_links.tqe);
  624 
  625                 cancelled = 1;
  626                 c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  627         }
  628         /*
  629          * If the lock must migrate we have to check the state again as
  630          * we can't hold both the new and old locks simultaneously.
  631          */
  632         if (c->c_cpu != cpu) {
  633                 c->c_cpu = cpu;
  634                 CC_UNLOCK(cc);
  635                 goto retry;
  636         }
  637 
  638         if (to_ticks <= 0)
  639                 to_ticks = 1;
  640 
  641         c->c_arg = arg;
  642         c->c_flags |= (CALLOUT_ACTIVE | CALLOUT_PENDING);
  643         c->c_func = ftn;
  644         c->c_time = cc->cc_ticks + to_ticks;
  645         TAILQ_INSERT_TAIL(&cc->cc_callwheel[c->c_time & callwheelmask], 
  646                           c, c_links.tqe);
  647         CTR5(KTR_CALLOUT, "%sscheduled %p func %p arg %p in %d",
  648             cancelled ? "re" : "", c, c->c_func, c->c_arg, to_ticks);
  649         CC_UNLOCK(cc);
  650 
  651         return (cancelled);
  652 }
  653 
  654 /*
  655  * Common idioms that can be optimized in the future.
  656  */
  657 int
  658 callout_schedule_on(struct callout *c, int to_ticks, int cpu)
  659 {
  660         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, cpu);
  661 }
  662 
  663 int
  664 callout_schedule(struct callout *c, int to_ticks)
  665 {
  666         return callout_reset_on(c, to_ticks, c->c_func, c->c_arg, c->c_cpu);
  667 }
  668 
  669 int
  670 _callout_stop_safe(c, safe)
  671         struct  callout *c;
  672         int     safe;
  673 {
  674         struct callout_cpu *cc;
  675         struct lock_class *class;
  676         int use_lock, sq_locked;
  677 
  678         /*
  679          * Some old subsystems don't hold Giant while running a callout_stop(),
  680          * so just discard this check for the moment.
  681          */
  682         if (!safe && c->c_lock != NULL) {
  683                 if (c->c_lock == &Giant.lock_object)
  684                         use_lock = mtx_owned(&Giant);
  685                 else {
  686                         use_lock = 1;
  687                         class = LOCK_CLASS(c->c_lock);
  688                         class->lc_assert(c->c_lock, LA_XLOCKED);
  689                 }
  690         } else
  691                 use_lock = 0;
  692 
  693         sq_locked = 0;
  694 again:
  695         cc = callout_lock(c);
  696         /*
  697          * If the callout isn't pending, it's not on the queue, so
  698          * don't attempt to remove it from the queue.  We can try to
  699          * stop it by other means however.
  700          */
  701         if (!(c->c_flags & CALLOUT_PENDING)) {
  702                 c->c_flags &= ~CALLOUT_ACTIVE;
  703 
  704                 /*
  705                  * If it wasn't on the queue and it isn't the current
  706                  * callout, then we can't stop it, so just bail.
  707                  */
  708                 if (cc->cc_curr != c) {
  709                         CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  710                             c, c->c_func, c->c_arg);
  711                         CC_UNLOCK(cc);
  712                         if (sq_locked)
  713                                 sleepq_release(&cc->cc_waiting);
  714                         return (0);
  715                 }
  716 
  717                 if (safe) {
  718                         /*
  719                          * The current callout is running (or just
  720                          * about to run) and blocking is allowed, so
  721                          * just wait for the current invocation to
  722                          * finish.
  723                          */
  724                         while (cc->cc_curr == c) {
  725 
  726                                 /*
  727                                  * Use direct calls to sleepqueue interface
  728                                  * instead of cv/msleep in order to avoid
  729                                  * a LOR between cc_lock and sleepqueue
  730                                  * chain spinlocks.  This piece of code
  731                                  * emulates a msleep_spin() call actually.
  732                                  *
  733                                  * If we already have the sleepqueue chain
  734                                  * locked, then we can safely block.  If we
  735                                  * don't already have it locked, however,
  736                                  * we have to drop the cc_lock to lock
  737                                  * it.  This opens several races, so we
  738                                  * restart at the beginning once we have
  739                                  * both locks.  If nothing has changed, then
  740                                  * we will end up back here with sq_locked
  741                                  * set.
  742                                  */
  743                                 if (!sq_locked) {
  744                                         CC_UNLOCK(cc);
  745                                         sleepq_lock(&cc->cc_waiting);
  746                                         sq_locked = 1;
  747                                         goto again;
  748                                 }
  749                                 cc->cc_waiting = 1;
  750                                 DROP_GIANT();
  751                                 CC_UNLOCK(cc);
  752                                 sleepq_add(&cc->cc_waiting,
  753                                     &cc->cc_lock.lock_object, "codrain",
  754                                     SLEEPQ_SLEEP, 0);
  755                                 sleepq_wait(&cc->cc_waiting, 0);
  756                                 sq_locked = 0;
  757 
  758                                 /* Reacquire locks previously released. */
  759                                 PICKUP_GIANT();
  760                                 CC_LOCK(cc);
  761                         }
  762                 } else if (use_lock && !cc->cc_cancel) {
  763                         /*
  764                          * The current callout is waiting for its
  765                          * lock which we hold.  Cancel the callout
  766                          * and return.  After our caller drops the
  767                          * lock, the callout will be skipped in
  768                          * softclock().
  769                          */
  770                         cc->cc_cancel = 1;
  771                         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  772                             c, c->c_func, c->c_arg);
  773                         CC_UNLOCK(cc);
  774                         KASSERT(!sq_locked, ("sleepqueue chain locked"));
  775                         return (1);
  776                 }
  777                 CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
  778                     c, c->c_func, c->c_arg);
  779                 CC_UNLOCK(cc);
  780                 KASSERT(!sq_locked, ("sleepqueue chain still locked"));
  781                 return (0);
  782         }
  783         if (sq_locked)
  784                 sleepq_release(&cc->cc_waiting);
  785 
  786         c->c_flags &= ~(CALLOUT_ACTIVE | CALLOUT_PENDING);
  787 
  788         if (cc->cc_next == c) {
  789                 cc->cc_next = TAILQ_NEXT(c, c_links.tqe);
  790         }
  791         TAILQ_REMOVE(&cc->cc_callwheel[c->c_time & callwheelmask], c,
  792             c_links.tqe);
  793 
  794         CTR3(KTR_CALLOUT, "cancelled %p func %p arg %p",
  795             c, c->c_func, c->c_arg);
  796 
  797         if (c->c_flags & CALLOUT_LOCAL_ALLOC) {
  798                 c->c_func = NULL;
  799                 SLIST_INSERT_HEAD(&cc->cc_callfree, c, c_links.sle);
  800         }
  801         CC_UNLOCK(cc);
  802         return (1);
  803 }
  804 
  805 void
  806 callout_init(c, mpsafe)
  807         struct  callout *c;
  808         int mpsafe;
  809 {
  810         bzero(c, sizeof *c);
  811         if (mpsafe) {
  812                 c->c_lock = NULL;
  813                 c->c_flags = CALLOUT_RETURNUNLOCKED;
  814         } else {
  815                 c->c_lock = &Giant.lock_object;
  816                 c->c_flags = 0;
  817         }
  818         c->c_cpu = timeout_cpu;
  819 }
  820 
  821 void
  822 _callout_init_lock(c, lock, flags)
  823         struct  callout *c;
  824         struct  lock_object *lock;
  825         int flags;
  826 {
  827         bzero(c, sizeof *c);
  828         c->c_lock = lock;
  829         KASSERT((flags & ~(CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK)) == 0,
  830             ("callout_init_lock: bad flags %d", flags));
  831         KASSERT(lock != NULL || (flags & CALLOUT_RETURNUNLOCKED) == 0,
  832             ("callout_init_lock: CALLOUT_RETURNUNLOCKED with no lock"));
  833         KASSERT(lock == NULL || !(LOCK_CLASS(lock)->lc_flags &
  834             (LC_SPINLOCK | LC_SLEEPABLE)), ("%s: invalid lock class",
  835             __func__));
  836         c->c_flags = flags & (CALLOUT_RETURNUNLOCKED | CALLOUT_SHAREDLOCK);
  837         c->c_cpu = timeout_cpu;
  838 }
  839 
  840 #ifdef APM_FIXUP_CALLTODO
  841 /* 
  842  * Adjust the kernel calltodo timeout list.  This routine is used after 
  843  * an APM resume to recalculate the calltodo timer list values with the 
  844  * number of hz's we have been sleeping.  The next hardclock() will detect 
  845  * that there are fired timers and run softclock() to execute them.
  846  *
  847  * Please note, I have not done an exhaustive analysis of what code this
  848  * might break.  I am motivated to have my select()'s and alarm()'s that
  849  * have expired during suspend firing upon resume so that the applications
  850  * which set the timer can do the maintanence the timer was for as close
  851  * as possible to the originally intended time.  Testing this code for a 
  852  * week showed that resuming from a suspend resulted in 22 to 25 timers 
  853  * firing, which seemed independant on whether the suspend was 2 hours or
  854  * 2 days.  Your milage may vary.   - Ken Key <key@cs.utk.edu>
  855  */
  856 void
  857 adjust_timeout_calltodo(time_change)
  858     struct timeval *time_change;
  859 {
  860         register struct callout *p;
  861         unsigned long delta_ticks;
  862 
  863         /* 
  864          * How many ticks were we asleep?
  865          * (stolen from tvtohz()).
  866          */
  867 
  868         /* Don't do anything */
  869         if (time_change->tv_sec < 0)
  870                 return;
  871         else if (time_change->tv_sec <= LONG_MAX / 1000000)
  872                 delta_ticks = (time_change->tv_sec * 1000000 +
  873                                time_change->tv_usec + (tick - 1)) / tick + 1;
  874         else if (time_change->tv_sec <= LONG_MAX / hz)
  875                 delta_ticks = time_change->tv_sec * hz +
  876                               (time_change->tv_usec + (tick - 1)) / tick + 1;
  877         else
  878                 delta_ticks = LONG_MAX;
  879 
  880         if (delta_ticks > INT_MAX)
  881                 delta_ticks = INT_MAX;
  882 
  883         /* 
  884          * Now rip through the timer calltodo list looking for timers
  885          * to expire.
  886          */
  887 
  888         /* don't collide with softclock() */
  889         CC_LOCK(cc);
  890         for (p = calltodo.c_next; p != NULL; p = p->c_next) {
  891                 p->c_time -= delta_ticks;
  892 
  893                 /* Break if the timer had more time on it than delta_ticks */
  894                 if (p->c_time > 0)
  895                         break;
  896 
  897                 /* take back the ticks the timer didn't use (p->c_time <= 0) */
  898                 delta_ticks = -p->c_time;
  899         }
  900         CC_UNLOCK(cc);
  901 
  902         return;
  903 }
  904 #endif /* APM_FIXUP_CALLTODO */

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