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/8.3/sys/kern/kern_synch.c 227572 2011-11-16 17:48:05Z jhb $");
   39 
   40 #include "opt_ktrace.h"
   41 #include "opt_sched.h"
   42 
   43 #include <sys/param.h>
   44 #include <sys/systm.h>
   45 #include <sys/condvar.h>
   46 #include <sys/kdb.h>
   47 #include <sys/kernel.h>
   48 #include <sys/ktr.h>
   49 #include <sys/lock.h>
   50 #include <sys/mutex.h>
   51 #include <sys/proc.h>
   52 #include <sys/resourcevar.h>
   53 #include <sys/sched.h>
   54 #include <sys/signalvar.h>
   55 #include <sys/sleepqueue.h>
   56 #include <sys/smp.h>
   57 #include <sys/sx.h>
   58 #include <sys/sysctl.h>
   59 #include <sys/sysproto.h>
   60 #include <sys/vmmeter.h>
   61 #ifdef KTRACE
   62 #include <sys/uio.h>
   63 #include <sys/ktrace.h>
   64 #endif
   65 
   66 #include <machine/cpu.h>
   67 
   68 #ifdef XEN
   69 #include <vm/vm.h>
   70 #include <vm/vm_param.h>
   71 #include <vm/pmap.h>
   72 #endif
   73 
   74 #define KTDSTATE(td)                                                    \
   75         (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep"  :         \
   76         ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" :      \
   77         ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" :          \
   78         ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" :             \
   79         ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding")
   80 
   81 static void synch_setup(void *dummy);
   82 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
   83     NULL);
   84 
   85 int     hogticks;
   86 static int pause_wchan;
   87 
   88 static struct callout loadav_callout;
   89 
   90 struct loadavg averunnable =
   91         { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
   92 /*
   93  * Constants for averages over 1, 5, and 15 minutes
   94  * when sampling at 5 second intervals.
   95  */
   96 static fixpt_t cexp[3] = {
   97         0.9200444146293232 * FSCALE,    /* exp(-1/12) */
   98         0.9834714538216174 * FSCALE,    /* exp(-1/60) */
   99         0.9944598480048967 * FSCALE,    /* exp(-1/180) */
  100 };
  101 
  102 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
  103 static int      fscale __unused = FSCALE;
  104 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
  105 
  106 static void     loadav(void *arg);
  107 
  108 void
  109 sleepinit(void)
  110 {
  111 
  112         hogticks = (hz / 10) * 2;       /* Default only. */
  113         init_sleepqueues();
  114 }
  115 
  116 /*
  117  * General sleep call.  Suspends the current thread until a wakeup is
  118  * performed on the specified identifier.  The thread will then be made
  119  * runnable with the specified priority.  Sleeps at most timo/hz seconds
  120  * (0 means no timeout).  If pri includes PCATCH flag, signals are checked
  121  * before and after sleeping, else signals are not checked.  Returns 0 if
  122  * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
  123  * signal needs to be delivered, ERESTART is returned if the current system
  124  * call should be restarted if possible, and EINTR is returned if the system
  125  * call should be interrupted by the signal (return EINTR).
  126  *
  127  * The lock argument is unlocked before the caller is suspended, and
  128  * re-locked before _sleep() returns.  If priority includes the PDROP
  129  * flag the lock is not re-locked before returning.
  130  */
  131 int
  132 _sleep(void *ident, struct lock_object *lock, int priority,
  133     const char *wmesg, int timo)
  134 {
  135         struct thread *td;
  136         struct proc *p;
  137         struct lock_class *class;
  138         int catch, flags, lock_state, pri, rval;
  139         WITNESS_SAVE_DECL(lock_witness);
  140 
  141         td = curthread;
  142         p = td->td_proc;
  143 #ifdef KTRACE
  144         if (KTRPOINT(td, KTR_CSW))
  145                 ktrcsw(1, 0);
  146 #endif
  147         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  148             "Sleeping on \"%s\"", wmesg);
  149         KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL,
  150             ("sleeping without a lock"));
  151         KASSERT(p != NULL, ("msleep1"));
  152         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  153         if (priority & PDROP)
  154                 KASSERT(lock != NULL && lock != &Giant.lock_object,
  155                     ("PDROP requires a non-Giant lock"));
  156         if (lock != NULL)
  157                 class = LOCK_CLASS(lock);
  158         else
  159                 class = NULL;
  160 
  161         if (cold) {
  162                 /*
  163                  * During autoconfiguration, just return;
  164                  * don't run any other threads or panic below,
  165                  * in case this is the idle thread and already asleep.
  166                  * XXX: this used to do "s = splhigh(); splx(safepri);
  167                  * splx(s);" to give interrupts a chance, but there is
  168                  * no way to give interrupts a chance now.
  169                  */
  170                 if (lock != NULL && priority & PDROP)
  171                         class->lc_unlock(lock);
  172                 return (0);
  173         }
  174         catch = priority & PCATCH;
  175         pri = priority & PRIMASK;
  176 
  177         /*
  178          * If we are already on a sleep queue, then remove us from that
  179          * sleep queue first.  We have to do this to handle recursive
  180          * sleeps.
  181          */
  182         if (TD_ON_SLEEPQ(td))
  183                 sleepq_remove(td, td->td_wchan);
  184 
  185         if (ident == &pause_wchan)
  186                 flags = SLEEPQ_PAUSE;
  187         else
  188                 flags = SLEEPQ_SLEEP;
  189         if (catch)
  190                 flags |= SLEEPQ_INTERRUPTIBLE;
  191         if (priority & PBDRY)
  192                 flags |= SLEEPQ_STOP_ON_BDRY;
  193 
  194         sleepq_lock(ident);
  195         CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
  196             td->td_tid, p->p_pid, td->td_name, wmesg, ident);
  197 
  198         if (lock == &Giant.lock_object)
  199                 mtx_assert(&Giant, MA_OWNED);
  200         DROP_GIANT();
  201         if (lock != NULL && lock != &Giant.lock_object &&
  202             !(class->lc_flags & LC_SLEEPABLE)) {
  203                 WITNESS_SAVE(lock, lock_witness);
  204                 lock_state = class->lc_unlock(lock);
  205         } else
  206                 /* GCC needs to follow the Yellow Brick Road */
  207                 lock_state = -1;
  208 
  209         /*
  210          * We put ourselves on the sleep queue and start our timeout
  211          * before calling thread_suspend_check, as we could stop there,
  212          * and a wakeup or a SIGCONT (or both) could occur while we were
  213          * stopped without resuming us.  Thus, we must be ready for sleep
  214          * when cursig() is called.  If the wakeup happens while we're
  215          * stopped, then td will no longer be on a sleep queue upon
  216          * return from cursig().
  217          */
  218         sleepq_add(ident, lock, wmesg, flags, 0);
  219         if (timo)
  220                 sleepq_set_timeout(ident, timo);
  221         if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
  222                 sleepq_release(ident);
  223                 WITNESS_SAVE(lock, lock_witness);
  224                 lock_state = class->lc_unlock(lock);
  225                 sleepq_lock(ident);
  226         }
  227         if (timo && catch)
  228                 rval = sleepq_timedwait_sig(ident, pri);
  229         else if (timo)
  230                 rval = sleepq_timedwait(ident, pri);
  231         else if (catch)
  232                 rval = sleepq_wait_sig(ident, pri);
  233         else {
  234                 sleepq_wait(ident, pri);
  235                 rval = 0;
  236         }
  237 #ifdef KTRACE
  238         if (KTRPOINT(td, KTR_CSW))
  239                 ktrcsw(0, 0);
  240 #endif
  241         PICKUP_GIANT();
  242         if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
  243                 class->lc_lock(lock, lock_state);
  244                 WITNESS_RESTORE(lock, lock_witness);
  245         }
  246         return (rval);
  247 }
  248 
  249 int
  250 msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
  251 {
  252         struct thread *td;
  253         struct proc *p;
  254         int rval;
  255         WITNESS_SAVE_DECL(mtx);
  256 
  257         td = curthread;
  258         p = td->td_proc;
  259         KASSERT(mtx != NULL, ("sleeping without a mutex"));
  260         KASSERT(p != NULL, ("msleep1"));
  261         KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
  262 
  263         if (cold) {
  264                 /*
  265                  * During autoconfiguration, just return;
  266                  * don't run any other threads or panic below,
  267                  * in case this is the idle thread and already asleep.
  268                  * XXX: this used to do "s = splhigh(); splx(safepri);
  269                  * splx(s);" to give interrupts a chance, but there is
  270                  * no way to give interrupts a chance now.
  271                  */
  272                 return (0);
  273         }
  274 
  275         sleepq_lock(ident);
  276         CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
  277             td->td_tid, p->p_pid, td->td_name, wmesg, ident);
  278 
  279         DROP_GIANT();
  280         mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  281         WITNESS_SAVE(&mtx->lock_object, mtx);
  282         mtx_unlock_spin(mtx);
  283 
  284         /*
  285          * We put ourselves on the sleep queue and start our timeout.
  286          */
  287         sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
  288         if (timo)
  289                 sleepq_set_timeout(ident, timo);
  290 
  291         /*
  292          * Can't call ktrace with any spin locks held so it can lock the
  293          * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
  294          * any spin lock.  Thus, we have to drop the sleepq spin lock while
  295          * we handle those requests.  This is safe since we have placed our
  296          * thread on the sleep queue already.
  297          */
  298 #ifdef KTRACE
  299         if (KTRPOINT(td, KTR_CSW)) {
  300                 sleepq_release(ident);
  301                 ktrcsw(1, 0);
  302                 sleepq_lock(ident);
  303         }
  304 #endif
  305 #ifdef WITNESS
  306         sleepq_release(ident);
  307         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
  308             wmesg);
  309         sleepq_lock(ident);
  310 #endif
  311         if (timo)
  312                 rval = sleepq_timedwait(ident, 0);
  313         else {
  314                 sleepq_wait(ident, 0);
  315                 rval = 0;
  316         }
  317 #ifdef KTRACE
  318         if (KTRPOINT(td, KTR_CSW))
  319                 ktrcsw(0, 0);
  320 #endif
  321         PICKUP_GIANT();
  322         mtx_lock_spin(mtx);
  323         WITNESS_RESTORE(&mtx->lock_object, mtx);
  324         return (rval);
  325 }
  326 
  327 /*
  328  * pause() is like tsleep() except that the intention is to not be
  329  * explicitly woken up by another thread.  Instead, the current thread
  330  * simply wishes to sleep until the timeout expires.  It is
  331  * implemented using a dummy wait channel.
  332  */
  333 int
  334 pause(const char *wmesg, int timo)
  335 {
  336 
  337         KASSERT(timo != 0, ("pause: timeout required"));
  338         return (tsleep(&pause_wchan, 0, wmesg, timo));
  339 }
  340 
  341 /*
  342  * Make all threads sleeping on the specified identifier runnable.
  343  */
  344 void
  345 wakeup(void *ident)
  346 {
  347         int wakeup_swapper;
  348 
  349         sleepq_lock(ident);
  350         wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
  351         sleepq_release(ident);
  352         if (wakeup_swapper) {
  353                 KASSERT(ident != &proc0,
  354                     ("wakeup and wakeup_swapper and proc0"));
  355                 kick_proc0();
  356         }
  357 }
  358 
  359 /*
  360  * Make a thread sleeping on the specified identifier runnable.
  361  * May wake more than one thread if a target thread is currently
  362  * swapped out.
  363  */
  364 void
  365 wakeup_one(void *ident)
  366 {
  367         int wakeup_swapper;
  368 
  369         sleepq_lock(ident);
  370         wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
  371         sleepq_release(ident);
  372         if (wakeup_swapper)
  373                 kick_proc0();
  374 }
  375 
  376 static void
  377 kdb_switch(void)
  378 {
  379         thread_unlock(curthread);
  380         kdb_backtrace();
  381         kdb_reenter();
  382         panic("%s: did not reenter debugger", __func__);
  383 }
  384 
  385 /*
  386  * The machine independent parts of context switching.
  387  */
  388 void
  389 mi_switch(int flags, struct thread *newtd)
  390 {
  391         uint64_t runtime, new_switchtime;
  392         struct thread *td;
  393         struct proc *p;
  394 
  395         td = curthread;                 /* XXX */
  396         THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
  397         p = td->td_proc;                /* XXX */
  398         KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
  399 #ifdef INVARIANTS
  400         if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
  401                 mtx_assert(&Giant, MA_NOTOWNED);
  402 #endif
  403         KASSERT(td->td_critnest == 1 || panicstr,
  404             ("mi_switch: switch in a critical section"));
  405         KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
  406             ("mi_switch: switch must be voluntary or involuntary"));
  407         KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
  408 
  409         /*
  410          * Don't perform context switches from the debugger.
  411          */
  412         if (kdb_active)
  413                 kdb_switch();
  414         if (flags & SW_VOL)
  415                 td->td_ru.ru_nvcsw++;
  416         else
  417                 td->td_ru.ru_nivcsw++;
  418 #ifdef SCHED_STATS
  419         SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
  420 #endif
  421         /*
  422          * Compute the amount of time during which the current
  423          * thread was running, and add that to its total so far.
  424          */
  425         new_switchtime = cpu_ticks();
  426         runtime = new_switchtime - PCPU_GET(switchtime);
  427         td->td_runtime += runtime;
  428         td->td_incruntime += runtime;
  429         PCPU_SET(switchtime, new_switchtime);
  430         td->td_generation++;    /* bump preempt-detect counter */
  431         PCPU_INC(cnt.v_swtch);
  432         PCPU_SET(switchticks, ticks);
  433         CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
  434             td->td_tid, td->td_sched, p->p_pid, td->td_name);
  435 #if (KTR_COMPILE & KTR_SCHED) != 0
  436         if (TD_IS_IDLETHREAD(td))
  437                 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
  438                     "prio:%d", td->td_priority);
  439         else
  440                 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
  441                     "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
  442                     "lockname:\"%s\"", td->td_lockname);
  443 #endif
  444 #ifdef XEN
  445         PT_UPDATES_FLUSH();
  446 #endif
  447         sched_switch(td, newtd, flags);
  448         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
  449             "prio:%d", td->td_priority);
  450 
  451         CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
  452             td->td_tid, td->td_sched, p->p_pid, td->td_name);
  453 
  454         /* 
  455          * If the last thread was exiting, finish cleaning it up.
  456          */
  457         if ((td = PCPU_GET(deadthread))) {
  458                 PCPU_SET(deadthread, NULL);
  459                 thread_stash(td);
  460         }
  461 }
  462 
  463 /*
  464  * Change thread state to be runnable, placing it on the run queue if
  465  * it is in memory.  If it is swapped out, return true so our caller
  466  * will know to awaken the swapper.
  467  */
  468 int
  469 setrunnable(struct thread *td)
  470 {
  471 
  472         THREAD_LOCK_ASSERT(td, MA_OWNED);
  473         KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
  474             ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
  475         switch (td->td_state) {
  476         case TDS_RUNNING:
  477         case TDS_RUNQ:
  478                 return (0);
  479         case TDS_INHIBITED:
  480                 /*
  481                  * If we are only inhibited because we are swapped out
  482                  * then arange to swap in this process. Otherwise just return.
  483                  */
  484                 if (td->td_inhibitors != TDI_SWAPPED)
  485                         return (0);
  486                 /* FALLTHROUGH */
  487         case TDS_CAN_RUN:
  488                 break;
  489         default:
  490                 printf("state is 0x%x", td->td_state);
  491                 panic("setrunnable(2)");
  492         }
  493         if ((td->td_flags & TDF_INMEM) == 0) {
  494                 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
  495                         td->td_flags |= TDF_SWAPINREQ;
  496                         return (1);
  497                 }
  498         } else
  499                 sched_wakeup(td);
  500         return (0);
  501 }
  502 
  503 /*
  504  * Compute a tenex style load average of a quantity on
  505  * 1, 5 and 15 minute intervals.
  506  */
  507 static void
  508 loadav(void *arg)
  509 {
  510         int i, nrun;
  511         struct loadavg *avg;
  512 
  513         nrun = sched_load();
  514         avg = &averunnable;
  515 
  516         for (i = 0; i < 3; i++)
  517                 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
  518                     nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
  519 
  520         /*
  521          * Schedule the next update to occur after 5 seconds, but add a
  522          * random variation to avoid synchronisation with processes that
  523          * run at regular intervals.
  524          */
  525         callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
  526             loadav, NULL);
  527 }
  528 
  529 /* ARGSUSED */
  530 static void
  531 synch_setup(void *dummy)
  532 {
  533         callout_init(&loadav_callout, CALLOUT_MPSAFE);
  534 
  535         /* Kick off timeout driven events by calling first time. */
  536         loadav(NULL);
  537 }
  538 
  539 int
  540 should_yield(void)
  541 {
  542 
  543         return (ticks - PCPU_GET(switchticks) >= hogticks);
  544 }
  545 
  546 void
  547 maybe_yield(void)
  548 {
  549 
  550         if (should_yield())
  551                 kern_yield(PRI_USER);
  552 }
  553 
  554 void
  555 kern_yield(int prio)
  556 {
  557         struct thread *td;
  558 
  559         td = curthread;
  560         DROP_GIANT();
  561         thread_lock(td);
  562         if (prio == PRI_USER)
  563                 prio = td->td_user_pri;
  564         if (prio >= 0)
  565                 sched_prio(td, prio);
  566         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
  567         thread_unlock(td);
  568         PICKUP_GIANT();
  569 }
  570 
  571 /*
  572  * General purpose yield system call.
  573  */
  574 int
  575 yield(struct thread *td, struct yield_args *uap)
  576 {
  577 
  578         thread_lock(td);
  579         if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
  580                 sched_prio(td, PRI_MAX_TIMESHARE);
  581         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
  582         thread_unlock(td);
  583         td->td_retval[0] = 0;
  584         return (0);
  585 }

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