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_synch.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1990, 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  *      @(#)kern_synch.c        8.9 (Berkeley) 5/19/95
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: releng/6.3/sys/kern/kern_synch.c 173886 2007-11-24 19:45:58Z cvs2svn $");
   39 
   40 #include "opt_ktrace.h"
   41 
   42 #include <sys/param.h>
   43 #include <sys/systm.h>
   44 #include <sys/condvar.h>
   45 #include <sys/kdb.h>
   46 #include <sys/kernel.h>
   47 #include <sys/ktr.h>
   48 #include <sys/lock.h>
   49 #include <sys/mutex.h>
   50 #include <sys/proc.h>
   51 #include <sys/resourcevar.h>
   52 #include <sys/sched.h>
   53 #include <sys/signalvar.h>
   54 #include <sys/sleepqueue.h>
   55 #include <sys/smp.h>
   56 #include <sys/sx.h>
   57 #include <sys/sysctl.h>
   58 #include <sys/sysproto.h>
   59 #include <sys/vmmeter.h>
   60 #ifdef KTRACE
   61 #include <sys/uio.h>
   62 #include <sys/ktrace.h>
   63 #endif
   64 
   65 #include <machine/cpu.h>
   66 
   67 static void synch_setup(void *dummy);
   68 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, NULL)
   69 
   70 int     hogticks;
   71 int     lbolt;
   72 
   73 static struct callout loadav_callout;
   74 static struct callout lbolt_callout;
   75 
   76 struct loadavg averunnable =
   77         { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
   78 /*
   79  * Constants for averages over 1, 5, and 15 minutes
   80  * when sampling at 5 second intervals.
   81  */
   82 static fixpt_t cexp[3] = {
   83         0.9200444146293232 * FSCALE,    /* exp(-1/12) */
   84         0.9834714538216174 * FSCALE,    /* exp(-1/60) */
   85         0.9944598480048967 * FSCALE,    /* exp(-1/180) */
   86 };
   87 
   88 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
   89 static int      fscale __unused = FSCALE;
   90 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
   91 
   92 static void     loadav(void *arg);
   93 static void     lboltcb(void *arg);
   94 
   95 void
   96 sleepinit(void)
   97 {
   98 
   99         hogticks = (hz / 10) * 2;       /* Default only. */
  100         init_sleepqueues();
  101 }
  102 
  103 /*
  104  * General sleep call.  Suspends the current process until a wakeup is
  105  * performed on the specified identifier.  The process will then be made
  106  * runnable with the specified priority.  Sleeps at most timo/hz seconds
  107  * (0 means no timeout).  If pri includes PCATCH flag, signals are checked
  108  * before and after sleeping, else signals are not checked.  Returns 0 if
  109  * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
  110  * signal needs to be delivered, ERESTART is returned if the current system
  111  * call should be restarted if possible, and EINTR is returned if the system
  112  * call should be interrupted by the signal (return EINTR).
  113  *
  114  * The mutex argument is exited before the caller is suspended, and
  115  * entered before msleep returns.  If priority includes the PDROP
  116  * flag the mutex is not entered before returning.
  117  */
  118 int
  119 msleep(ident, mtx, priority, wmesg, timo)
  120         void *ident;
  121         struct mtx *mtx;
  122         int priority, timo;
  123         const char *wmesg;
  124 {
  125         struct thread *td;
  126         struct proc *p;
  127         int catch, rval, flags;
  128         WITNESS_SAVE_DECL(mtx);
  129 
  130         td = curthread;
  131         p = td->td_proc;
  132 #ifdef KTRACE
  133         if (KTRPOINT(td, KTR_CSW))
  134                 ktrcsw(1, 0);
  135 #endif
  136         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, mtx == NULL ? NULL :
  137             &mtx->mtx_object, "Sleeping on \"%s\"", wmesg);
  138         KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL,
  139             ("sleeping without a mutex"));
  140         KASSERT(p != NULL, ("msleep1"));
  141         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  142 
  143         if (cold) {
  144                 /*
  145                  * During autoconfiguration, just return;
  146                  * don't run any other threads or panic below,
  147                  * in case this is the idle thread and already asleep.
  148                  * XXX: this used to do "s = splhigh(); splx(safepri);
  149                  * splx(s);" to give interrupts a chance, but there is
  150                  * no way to give interrupts a chance now.
  151                  */
  152                 if (mtx != NULL && priority & PDROP)
  153                         mtx_unlock(mtx);
  154                 return (0);
  155         }
  156         catch = priority & PCATCH;
  157         rval = 0;
  158 
  159         /*
  160          * If we are already on a sleep queue, then remove us from that
  161          * sleep queue first.  We have to do this to handle recursive
  162          * sleeps.
  163          */
  164         if (TD_ON_SLEEPQ(td))
  165                 sleepq_remove(td, td->td_wchan);
  166 
  167         flags = SLEEPQ_MSLEEP;
  168         if (catch)
  169                 flags |= SLEEPQ_INTERRUPTIBLE;
  170 
  171         sleepq_lock(ident);
  172         CTR5(KTR_PROC, "msleep: thread %p (pid %ld, %s) on %s (%p)",
  173             (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident);
  174 
  175         DROP_GIANT();
  176         if (mtx != NULL) {
  177                 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  178                 WITNESS_SAVE(&mtx->mtx_object, mtx);
  179                 mtx_unlock(mtx);
  180         }
  181 
  182         /*
  183          * We put ourselves on the sleep queue and start our timeout
  184          * before calling thread_suspend_check, as we could stop there,
  185          * and a wakeup or a SIGCONT (or both) could occur while we were
  186          * stopped without resuming us.  Thus, we must be ready for sleep
  187          * when cursig() is called.  If the wakeup happens while we're
  188          * stopped, then td will no longer be on a sleep queue upon
  189          * return from cursig().
  190          */
  191         sleepq_add(ident, mtx, wmesg, flags, 0);
  192         if (timo)
  193                 sleepq_set_timeout(ident, timo);
  194 
  195         /*
  196          * Adjust this thread's priority.
  197          */
  198         if ((priority & PRIMASK) != 0) {
  199                 mtx_lock_spin(&sched_lock);
  200                 sched_prio(td, priority & PRIMASK);
  201                 mtx_unlock_spin(&sched_lock);
  202         }
  203 
  204         if (timo && catch)
  205                 rval = sleepq_timedwait_sig(ident);
  206         else if (timo)
  207                 rval = sleepq_timedwait(ident);
  208         else if (catch)
  209                 rval = sleepq_wait_sig(ident);
  210         else {
  211                 sleepq_wait(ident);
  212                 rval = 0;
  213         }
  214 #ifdef KTRACE
  215         if (KTRPOINT(td, KTR_CSW))
  216                 ktrcsw(0, 0);
  217 #endif
  218         PICKUP_GIANT();
  219         if (mtx != NULL && !(priority & PDROP)) {
  220                 mtx_lock(mtx);
  221                 WITNESS_RESTORE(&mtx->mtx_object, mtx);
  222         }
  223         return (rval);
  224 }
  225 
  226 int
  227 msleep_spin(ident, mtx, wmesg, timo)
  228         void *ident;
  229         struct mtx *mtx;
  230         const char *wmesg;
  231         int timo;
  232 {
  233         struct thread *td;
  234         struct proc *p;
  235         int rval;
  236         WITNESS_SAVE_DECL(mtx);
  237 
  238         td = curthread;
  239         p = td->td_proc;
  240         KASSERT(mtx != NULL, ("sleeping without a mutex"));
  241         KASSERT(p != NULL, ("msleep1"));
  242         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  243 
  244         if (cold) {
  245                 /*
  246                  * During autoconfiguration, just return;
  247                  * don't run any other threads or panic below,
  248                  * in case this is the idle thread and already asleep.
  249                  * XXX: this used to do "s = splhigh(); splx(safepri);
  250                  * splx(s);" to give interrupts a chance, but there is
  251                  * no way to give interrupts a chance now.
  252                  */
  253                 return (0);
  254         }
  255 
  256         sleepq_lock(ident);
  257         CTR5(KTR_PROC, "msleep_spin: thread %p (pid %ld, %s) on %s (%p)",
  258             (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident);
  259 
  260         DROP_GIANT();
  261         mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  262         WITNESS_SAVE(&mtx->mtx_object, mtx);
  263         mtx_unlock_spin(mtx);
  264 
  265         /*
  266          * We put ourselves on the sleep queue and start our timeout.
  267          */
  268         sleepq_add(ident, mtx, wmesg, SLEEPQ_MSLEEP, 0);
  269         if (timo)
  270                 sleepq_set_timeout(ident, timo);
  271 
  272         /*
  273          * Can't call ktrace with any spin locks held so it can lock the
  274          * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
  275          * any spin lock.  Thus, we have to drop the sleepq spin lock while
  276          * we handle those requests.  This is safe since we have placed our
  277          * thread on the sleep queue already.
  278          */
  279 #ifdef KTRACE
  280         if (KTRPOINT(td, KTR_CSW)) {
  281                 sleepq_release(ident);
  282                 ktrcsw(1, 0);
  283                 sleepq_lock(ident);
  284         }
  285 #endif
  286 #ifdef WITNESS
  287         sleepq_release(ident);
  288         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
  289             wmesg);
  290         sleepq_lock(ident);
  291 #endif
  292         if (timo)
  293                 rval = sleepq_timedwait(ident);
  294         else {
  295                 sleepq_wait(ident);
  296                 rval = 0;
  297         }
  298 #ifdef KTRACE
  299         if (KTRPOINT(td, KTR_CSW))
  300                 ktrcsw(0, 0);
  301 #endif
  302         PICKUP_GIANT();
  303         mtx_lock_spin(mtx);
  304         WITNESS_RESTORE(&mtx->mtx_object, mtx);
  305         return (rval);
  306 }
  307 
  308 /*
  309  * Make all threads sleeping on the specified identifier runnable.
  310  */
  311 void
  312 wakeup(ident)
  313         register void *ident;
  314 {
  315 
  316         sleepq_lock(ident);
  317         sleepq_broadcast(ident, SLEEPQ_MSLEEP, -1, 0);
  318 }
  319 
  320 /*
  321  * Make a thread sleeping on the specified identifier runnable.
  322  * May wake more than one thread if a target thread is currently
  323  * swapped out.
  324  */
  325 void
  326 wakeup_one(ident)
  327         register void *ident;
  328 {
  329 
  330         sleepq_lock(ident);
  331         sleepq_signal(ident, SLEEPQ_MSLEEP, -1, 0);
  332 }
  333 
  334 /*
  335  * The machine independent parts of context switching.
  336  */
  337 void
  338 mi_switch(int flags, struct thread *newtd)
  339 {
  340         struct bintime new_switchtime;
  341         struct thread *td;
  342         struct proc *p;
  343 
  344         mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED);
  345         td = curthread;                 /* XXX */
  346         p = td->td_proc;                /* XXX */
  347         KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
  348 #ifdef INVARIANTS
  349         if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
  350                 mtx_assert(&Giant, MA_NOTOWNED);
  351 #endif
  352         KASSERT(td->td_critnest == 1 || (td->td_critnest == 2 &&
  353             (td->td_owepreempt) && (flags & SW_INVOL) != 0 &&
  354             newtd == NULL) || panicstr,
  355             ("mi_switch: switch in a critical section"));
  356         KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
  357             ("mi_switch: switch must be voluntary or involuntary"));
  358         KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
  359 
  360         if (flags & SW_VOL)
  361                 p->p_stats->p_ru.ru_nvcsw++;
  362         else
  363                 p->p_stats->p_ru.ru_nivcsw++;
  364 
  365         /*
  366          * Compute the amount of time during which the current
  367          * process was running, and add that to its total so far.
  368          */
  369         binuptime(&new_switchtime);
  370         bintime_add(&p->p_rux.rux_runtime, &new_switchtime);
  371         bintime_sub(&p->p_rux.rux_runtime, PCPU_PTR(switchtime));
  372 
  373         td->td_generation++;    /* bump preempt-detect counter */
  374 
  375         /*
  376          * Don't perform context switches from the debugger.
  377          */
  378         if (kdb_active) {
  379                 mtx_unlock_spin(&sched_lock);
  380                 kdb_backtrace();
  381                 kdb_reenter();
  382                 panic("%s: did not reenter debugger", __func__);
  383         }
  384 
  385         /*
  386          * Check if the process exceeds its cpu resource allocation.  If
  387          * it reaches the max, arrange to kill the process in ast().
  388          */
  389         if (p->p_cpulimit != RLIM_INFINITY &&
  390             p->p_rux.rux_runtime.sec >= p->p_cpulimit) {
  391                 p->p_sflag |= PS_XCPU;
  392                 td->td_flags |= TDF_ASTPENDING;
  393         }
  394 
  395         /*
  396          * Finish up stats for outgoing thread.
  397          */
  398         cnt.v_swtch++;
  399         PCPU_SET(switchtime, new_switchtime);
  400         PCPU_SET(switchticks, ticks);
  401         CTR4(KTR_PROC, "mi_switch: old thread %p (kse %p, pid %ld, %s)",
  402             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  403         if ((flags & SW_VOL) && (td->td_proc->p_flag & P_SA))
  404                 newtd = thread_switchout(td, flags, newtd);
  405 #if (KTR_COMPILE & KTR_SCHED) != 0
  406         if (td == PCPU_GET(idlethread))
  407                 CTR3(KTR_SCHED, "mi_switch: %p(%s) prio %d idle",
  408                     td, td->td_proc->p_comm, td->td_priority);
  409         else if (newtd != NULL)
  410                 CTR5(KTR_SCHED,
  411                     "mi_switch: %p(%s) prio %d preempted by %p(%s)",
  412                     td, td->td_proc->p_comm, td->td_priority, newtd,
  413                     newtd->td_proc->p_comm);
  414         else
  415                 CTR6(KTR_SCHED,
  416                     "mi_switch: %p(%s) prio %d inhibit %d wmesg %s lock %s",
  417                     td, td->td_proc->p_comm, td->td_priority,
  418                     td->td_inhibitors, td->td_wmesg, td->td_lockname);
  419 #endif
  420         sched_switch(td, newtd, flags);
  421         CTR3(KTR_SCHED, "mi_switch: running %p(%s) prio %d",
  422             td, td->td_proc->p_comm, td->td_priority);
  423 
  424         CTR4(KTR_PROC, "mi_switch: new thread %p (kse %p, pid %ld, %s)",
  425             (void *)td, td->td_sched, (long)p->p_pid, p->p_comm);
  426 
  427         /* 
  428          * If the last thread was exiting, finish cleaning it up.
  429          */
  430         if ((td = PCPU_GET(deadthread))) {
  431                 PCPU_SET(deadthread, NULL);
  432                 thread_stash(td);
  433         }
  434 }
  435 
  436 /*
  437  * Change process state to be runnable,
  438  * placing it on the run queue if it is in memory,
  439  * and awakening the swapper if it isn't in memory.
  440  */
  441 void
  442 setrunnable(struct thread *td)
  443 {
  444         struct proc *p;
  445 
  446         p = td->td_proc;
  447         mtx_assert(&sched_lock, MA_OWNED);
  448         switch (p->p_state) {
  449         case PRS_ZOMBIE:
  450                 panic("setrunnable(1)");
  451         default:
  452                 break;
  453         }
  454         switch (td->td_state) {
  455         case TDS_RUNNING:
  456         case TDS_RUNQ:
  457                 return;
  458         case TDS_INHIBITED:
  459                 /*
  460                  * If we are only inhibited because we are swapped out
  461                  * then arange to swap in this process. Otherwise just return.
  462                  */
  463                 if (td->td_inhibitors != TDI_SWAPPED)
  464                         return;
  465                 /* XXX: intentional fall-through ? */
  466         case TDS_CAN_RUN:
  467                 break;
  468         default:
  469                 printf("state is 0x%x", td->td_state);
  470                 panic("setrunnable(2)");
  471         }
  472         if ((p->p_sflag & PS_INMEM) == 0) {
  473                 if ((p->p_sflag & PS_SWAPPINGIN) == 0) {
  474                         p->p_sflag |= PS_SWAPINREQ;
  475                         /*
  476                          * due to a LOR between sched_lock and
  477                          * the sleepqueue chain locks, use
  478                          * lower level scheduling functions.
  479                          */
  480                         kick_proc0();
  481                 }
  482         } else
  483                 sched_wakeup(td);
  484 }
  485 
  486 /*
  487  * Compute a tenex style load average of a quantity on
  488  * 1, 5 and 15 minute intervals.
  489  * XXXKSE   Needs complete rewrite when correct info is available.
  490  * Completely Bogus.. only works with 1:1 (but compiles ok now :-)
  491  */
  492 static void
  493 loadav(void *arg)
  494 {
  495         int i, nrun;
  496         struct loadavg *avg;
  497 
  498         nrun = sched_load();
  499         avg = &averunnable;
  500 
  501         for (i = 0; i < 3; i++)
  502                 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
  503                     nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
  504 
  505         /*
  506          * Schedule the next update to occur after 5 seconds, but add a
  507          * random variation to avoid synchronisation with processes that
  508          * run at regular intervals.
  509          */
  510         callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
  511             loadav, NULL);
  512 }
  513 
  514 static void
  515 lboltcb(void *arg)
  516 {
  517         wakeup(&lbolt);
  518         callout_reset(&lbolt_callout, hz, lboltcb, NULL);
  519 }
  520 
  521 /* ARGSUSED */
  522 static void
  523 synch_setup(dummy)
  524         void *dummy;
  525 {
  526         callout_init(&loadav_callout, CALLOUT_MPSAFE);
  527         callout_init(&lbolt_callout, CALLOUT_MPSAFE);
  528 
  529         /* Kick off timeout driven events by calling first time. */
  530         loadav(NULL);
  531         lboltcb(NULL);
  532 }
  533 
  534 /*
  535  * General purpose yield system call
  536  */
  537 int
  538 yield(struct thread *td, struct yield_args *uap)
  539 {
  540         struct ksegrp *kg;
  541 
  542         kg = td->td_ksegrp;
  543         mtx_assert(&Giant, MA_NOTOWNED);
  544         mtx_lock_spin(&sched_lock);
  545         sched_prio(td, PRI_MAX_TIMESHARE);
  546         mi_switch(SW_VOL, NULL);
  547         mtx_unlock_spin(&sched_lock);
  548         td->td_retval[0] = 0;
  549         return (0);
  550 }

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