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  * SPDX-License-Identifier: BSD-3-Clause
    3  *
    4  * Copyright (c) 1982, 1986, 1990, 1991, 1993
    5  *      The Regents of the University of California.  All rights reserved.
    6  * (c) UNIX System Laboratories, Inc.
    7  * All or some portions of this file are derived from material licensed
    8  * to the University of California by American Telephone and Telegraph
    9  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   10  * the permission of UNIX System Laboratories, Inc.
   11  *
   12  * Redistribution and use in source and binary forms, with or without
   13  * modification, are permitted provided that the following conditions
   14  * are met:
   15  * 1. Redistributions of source code must retain the above copyright
   16  *    notice, this list of conditions and the following disclaimer.
   17  * 2. Redistributions in binary form must reproduce the above copyright
   18  *    notice, this list of conditions and the following disclaimer in the
   19  *    documentation and/or other materials provided with the distribution.
   20  * 3. Neither the name of the University nor the names of its contributors
   21  *    may be used to endorse or promote products derived from this software
   22  *    without specific prior written permission.
   23  *
   24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   34  * SUCH DAMAGE.
   35  *
   36  *      @(#)kern_synch.c        8.9 (Berkeley) 5/19/95
   37  */
   38 
   39 #include <sys/cdefs.h>
   40 __FBSDID("$FreeBSD: head/sys/kern/kern_synch.c 341720 2018-12-08 06:30:41Z mjg $");
   41 
   42 #include "opt_ktrace.h"
   43 #include "opt_sched.h"
   44 
   45 #include <sys/param.h>
   46 #include <sys/systm.h>
   47 #include <sys/condvar.h>
   48 #include <sys/kdb.h>
   49 #include <sys/kernel.h>
   50 #include <sys/ktr.h>
   51 #include <sys/lock.h>
   52 #include <sys/mutex.h>
   53 #include <sys/proc.h>
   54 #include <sys/resourcevar.h>
   55 #include <sys/sched.h>
   56 #include <sys/sdt.h>
   57 #include <sys/signalvar.h>
   58 #include <sys/sleepqueue.h>
   59 #include <sys/smp.h>
   60 #include <sys/sx.h>
   61 #include <sys/sysctl.h>
   62 #include <sys/sysproto.h>
   63 #include <sys/vmmeter.h>
   64 #ifdef KTRACE
   65 #include <sys/uio.h>
   66 #include <sys/ktrace.h>
   67 #endif
   68 
   69 #include <machine/cpu.h>
   70 
   71 static void synch_setup(void *dummy);
   72 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
   73     NULL);
   74 
   75 int     hogticks;
   76 static uint8_t pause_wchan[MAXCPU];
   77 
   78 static struct callout loadav_callout;
   79 
   80 struct loadavg averunnable =
   81         { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
   82 /*
   83  * Constants for averages over 1, 5, and 15 minutes
   84  * when sampling at 5 second intervals.
   85  */
   86 static fixpt_t cexp[3] = {
   87         0.9200444146293232 * FSCALE,    /* exp(-1/12) */
   88         0.9834714538216174 * FSCALE,    /* exp(-1/60) */
   89         0.9944598480048967 * FSCALE,    /* exp(-1/180) */
   90 };
   91 
   92 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
   93 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, SYSCTL_NULL_INT_PTR, FSCALE, "");
   94 
   95 static void     loadav(void *arg);
   96 
   97 SDT_PROVIDER_DECLARE(sched);
   98 SDT_PROBE_DEFINE(sched, , , preempt);
   99 
  100 static void
  101 sleepinit(void *unused)
  102 {
  103 
  104         hogticks = (hz / 10) * 2;       /* Default only. */
  105         init_sleepqueues();
  106 }
  107 
  108 /*
  109  * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure
  110  * it is available.
  111  */
  112 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, NULL);
  113 
  114 /*
  115  * General sleep call.  Suspends the current thread until a wakeup is
  116  * performed on the specified identifier.  The thread will then be made
  117  * runnable with the specified priority.  Sleeps at most sbt units of time
  118  * (0 means no timeout).  If pri includes the PCATCH flag, let signals
  119  * interrupt the sleep, otherwise ignore them while sleeping.  Returns 0 if
  120  * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
  121  * signal becomes pending, ERESTART is returned if the current system
  122  * call should be restarted if possible, and EINTR is returned if the system
  123  * call should be interrupted by the signal (return EINTR).
  124  *
  125  * The lock argument is unlocked before the caller is suspended, and
  126  * re-locked before _sleep() returns.  If priority includes the PDROP
  127  * flag the lock is not re-locked before returning.
  128  */
  129 int
  130 _sleep(void *ident, struct lock_object *lock, int priority,
  131     const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
  132 {
  133         struct thread *td;
  134         struct lock_class *class;
  135         uintptr_t lock_state;
  136         int catch, pri, rval, sleepq_flags;
  137         WITNESS_SAVE_DECL(lock_witness);
  138 
  139         td = curthread;
  140 #ifdef KTRACE
  141         if (KTRPOINT(td, KTR_CSW))
  142                 ktrcsw(1, 0, wmesg);
  143 #endif
  144         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
  145             "Sleeping on \"%s\"", wmesg);
  146         KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL,
  147             ("sleeping without a lock"));
  148         KASSERT(ident != NULL, ("_sleep: NULL ident"));
  149         KASSERT(TD_IS_RUNNING(td), ("_sleep: curthread not running"));
  150         KASSERT(td->td_epochnest == 0, ("sleeping in an epoch section"));
  151         if (priority & PDROP)
  152                 KASSERT(lock != NULL && lock != &Giant.lock_object,
  153                     ("PDROP requires a non-Giant lock"));
  154         if (lock != NULL)
  155                 class = LOCK_CLASS(lock);
  156         else
  157                 class = NULL;
  158 
  159         if (SCHEDULER_STOPPED_TD(td)) {
  160                 if (lock != NULL && priority & PDROP)
  161                         class->lc_unlock(lock);
  162                 return (0);
  163         }
  164         catch = priority & PCATCH;
  165         pri = priority & PRIMASK;
  166 
  167         KASSERT(!TD_ON_SLEEPQ(td), ("recursive sleep"));
  168 
  169         if ((uint8_t *)ident >= &pause_wchan[0] &&
  170             (uint8_t *)ident <= &pause_wchan[MAXCPU - 1])
  171                 sleepq_flags = SLEEPQ_PAUSE;
  172         else
  173                 sleepq_flags = SLEEPQ_SLEEP;
  174         if (catch)
  175                 sleepq_flags |= SLEEPQ_INTERRUPTIBLE;
  176 
  177         sleepq_lock(ident);
  178         CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
  179             td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
  180 
  181         if (lock == &Giant.lock_object)
  182                 mtx_assert(&Giant, MA_OWNED);
  183         DROP_GIANT();
  184         if (lock != NULL && lock != &Giant.lock_object &&
  185             !(class->lc_flags & LC_SLEEPABLE)) {
  186                 WITNESS_SAVE(lock, lock_witness);
  187                 lock_state = class->lc_unlock(lock);
  188         } else
  189                 /* GCC needs to follow the Yellow Brick Road */
  190                 lock_state = -1;
  191 
  192         /*
  193          * We put ourselves on the sleep queue and start our timeout
  194          * before calling thread_suspend_check, as we could stop there,
  195          * and a wakeup or a SIGCONT (or both) could occur while we were
  196          * stopped without resuming us.  Thus, we must be ready for sleep
  197          * when cursig() is called.  If the wakeup happens while we're
  198          * stopped, then td will no longer be on a sleep queue upon
  199          * return from cursig().
  200          */
  201         sleepq_add(ident, lock, wmesg, sleepq_flags, 0);
  202         if (sbt != 0)
  203                 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
  204         if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
  205                 sleepq_release(ident);
  206                 WITNESS_SAVE(lock, lock_witness);
  207                 lock_state = class->lc_unlock(lock);
  208                 sleepq_lock(ident);
  209         }
  210         if (sbt != 0 && catch)
  211                 rval = sleepq_timedwait_sig(ident, pri);
  212         else if (sbt != 0)
  213                 rval = sleepq_timedwait(ident, pri);
  214         else if (catch)
  215                 rval = sleepq_wait_sig(ident, pri);
  216         else {
  217                 sleepq_wait(ident, pri);
  218                 rval = 0;
  219         }
  220 #ifdef KTRACE
  221         if (KTRPOINT(td, KTR_CSW))
  222                 ktrcsw(0, 0, wmesg);
  223 #endif
  224         PICKUP_GIANT();
  225         if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
  226                 class->lc_lock(lock, lock_state);
  227                 WITNESS_RESTORE(lock, lock_witness);
  228         }
  229         return (rval);
  230 }
  231 
  232 int
  233 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg,
  234     sbintime_t sbt, sbintime_t pr, int flags)
  235 {
  236         struct thread *td;
  237         int rval;
  238         WITNESS_SAVE_DECL(mtx);
  239 
  240         td = curthread;
  241         KASSERT(mtx != NULL, ("sleeping without a mutex"));
  242         KASSERT(ident != NULL, ("msleep_spin_sbt: NULL ident"));
  243         KASSERT(TD_IS_RUNNING(td), ("msleep_spin_sbt: curthread not running"));
  244 
  245         if (SCHEDULER_STOPPED_TD(td))
  246                 return (0);
  247 
  248         sleepq_lock(ident);
  249         CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
  250             td->td_tid, td->td_proc->p_pid, td->td_name, wmesg, ident);
  251 
  252         DROP_GIANT();
  253         mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
  254         WITNESS_SAVE(&mtx->lock_object, mtx);
  255         mtx_unlock_spin(mtx);
  256 
  257         /*
  258          * We put ourselves on the sleep queue and start our timeout.
  259          */
  260         sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
  261         if (sbt != 0)
  262                 sleepq_set_timeout_sbt(ident, sbt, pr, flags);
  263 
  264         /*
  265          * Can't call ktrace with any spin locks held so it can lock the
  266          * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
  267          * any spin lock.  Thus, we have to drop the sleepq spin lock while
  268          * we handle those requests.  This is safe since we have placed our
  269          * thread on the sleep queue already.
  270          */
  271 #ifdef KTRACE
  272         if (KTRPOINT(td, KTR_CSW)) {
  273                 sleepq_release(ident);
  274                 ktrcsw(1, 0, wmesg);
  275                 sleepq_lock(ident);
  276         }
  277 #endif
  278 #ifdef WITNESS
  279         sleepq_release(ident);
  280         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
  281             wmesg);
  282         sleepq_lock(ident);
  283 #endif
  284         if (sbt != 0)
  285                 rval = sleepq_timedwait(ident, 0);
  286         else {
  287                 sleepq_wait(ident, 0);
  288                 rval = 0;
  289         }
  290 #ifdef KTRACE
  291         if (KTRPOINT(td, KTR_CSW))
  292                 ktrcsw(0, 0, wmesg);
  293 #endif
  294         PICKUP_GIANT();
  295         mtx_lock_spin(mtx);
  296         WITNESS_RESTORE(&mtx->lock_object, mtx);
  297         return (rval);
  298 }
  299 
  300 /*
  301  * pause_sbt() delays the calling thread by the given signed binary
  302  * time. During cold bootup, pause_sbt() uses the DELAY() function
  303  * instead of the _sleep() function to do the waiting. The "sbt"
  304  * argument must be greater than or equal to zero. A "sbt" value of
  305  * zero is equivalent to a "sbt" value of one tick.
  306  */
  307 int
  308 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags)
  309 {
  310         KASSERT(sbt >= 0, ("pause_sbt: timeout must be >= 0"));
  311 
  312         /* silently convert invalid timeouts */
  313         if (sbt == 0)
  314                 sbt = tick_sbt;
  315 
  316         if ((cold && curthread == &thread0) || kdb_active ||
  317             SCHEDULER_STOPPED()) {
  318                 /*
  319                  * We delay one second at a time to avoid overflowing the
  320                  * system specific DELAY() function(s):
  321                  */
  322                 while (sbt >= SBT_1S) {
  323                         DELAY(1000000);
  324                         sbt -= SBT_1S;
  325                 }
  326                 /* Do the delay remainder, if any */
  327                 sbt = howmany(sbt, SBT_1US);
  328                 if (sbt > 0)
  329                         DELAY(sbt);
  330                 return (EWOULDBLOCK);
  331         }
  332         return (_sleep(&pause_wchan[curcpu], NULL,
  333             (flags & C_CATCH) ? PCATCH : 0, wmesg, sbt, pr, flags));
  334 }
  335 
  336 /*
  337  * Make all threads sleeping on the specified identifier runnable.
  338  */
  339 void
  340 wakeup(void *ident)
  341 {
  342         int wakeup_swapper;
  343 
  344         sleepq_lock(ident);
  345         wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
  346         sleepq_release(ident);
  347         if (wakeup_swapper) {
  348                 KASSERT(ident != &proc0,
  349                     ("wakeup and wakeup_swapper and proc0"));
  350                 kick_proc0();
  351         }
  352 }
  353 
  354 /*
  355  * Make a thread sleeping on the specified identifier runnable.
  356  * May wake more than one thread if a target thread is currently
  357  * swapped out.
  358  */
  359 void
  360 wakeup_one(void *ident)
  361 {
  362         int wakeup_swapper;
  363 
  364         sleepq_lock(ident);
  365         wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
  366         sleepq_release(ident);
  367         if (wakeup_swapper)
  368                 kick_proc0();
  369 }
  370 
  371 static void
  372 kdb_switch(void)
  373 {
  374         thread_unlock(curthread);
  375         kdb_backtrace();
  376         kdb_reenter();
  377         panic("%s: did not reenter debugger", __func__);
  378 }
  379 
  380 /*
  381  * The machine independent parts of context switching.
  382  */
  383 void
  384 mi_switch(int flags, struct thread *newtd)
  385 {
  386         uint64_t runtime, new_switchtime;
  387         struct thread *td;
  388 
  389         td = curthread;                 /* XXX */
  390         THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
  391         KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
  392 #ifdef INVARIANTS
  393         if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
  394                 mtx_assert(&Giant, MA_NOTOWNED);
  395 #endif
  396         KASSERT(td->td_critnest == 1 || panicstr,
  397             ("mi_switch: switch in a critical section"));
  398         KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
  399             ("mi_switch: switch must be voluntary or involuntary"));
  400         KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
  401 
  402         /*
  403          * Don't perform context switches from the debugger.
  404          */
  405         if (kdb_active)
  406                 kdb_switch();
  407         if (SCHEDULER_STOPPED_TD(td))
  408                 return;
  409         if (flags & SW_VOL) {
  410                 td->td_ru.ru_nvcsw++;
  411                 td->td_swvoltick = ticks;
  412         } else {
  413                 td->td_ru.ru_nivcsw++;
  414                 td->td_swinvoltick = ticks;
  415         }
  416 #ifdef SCHED_STATS
  417         SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
  418 #endif
  419         /*
  420          * Compute the amount of time during which the current
  421          * thread was running, and add that to its total so far.
  422          */
  423         new_switchtime = cpu_ticks();
  424         runtime = new_switchtime - PCPU_GET(switchtime);
  425         td->td_runtime += runtime;
  426         td->td_incruntime += runtime;
  427         PCPU_SET(switchtime, new_switchtime);
  428         td->td_generation++;    /* bump preempt-detect counter */
  429         VM_CNT_INC(v_swtch);
  430         PCPU_SET(switchticks, ticks);
  431         CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
  432             td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
  433 #ifdef KDTRACE_HOOKS
  434         if (SDT_PROBES_ENABLED() &&
  435             ((flags & SW_PREEMPT) != 0 || ((flags & SW_INVOL) != 0 &&
  436             (flags & SW_TYPE_MASK) == SWT_NEEDRESCHED)))
  437                 SDT_PROBE0(sched, , , preempt);
  438 #endif
  439         sched_switch(td, newtd, flags);
  440         CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
  441             td->td_tid, td_get_sched(td), td->td_proc->p_pid, td->td_name);
  442 
  443         /* 
  444          * If the last thread was exiting, finish cleaning it up.
  445          */
  446         if ((td = PCPU_GET(deadthread))) {
  447                 PCPU_SET(deadthread, NULL);
  448                 thread_stash(td);
  449         }
  450 }
  451 
  452 /*
  453  * Change thread state to be runnable, placing it on the run queue if
  454  * it is in memory.  If it is swapped out, return true so our caller
  455  * will know to awaken the swapper.
  456  */
  457 int
  458 setrunnable(struct thread *td)
  459 {
  460 
  461         THREAD_LOCK_ASSERT(td, MA_OWNED);
  462         KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
  463             ("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
  464         switch (td->td_state) {
  465         case TDS_RUNNING:
  466         case TDS_RUNQ:
  467                 return (0);
  468         case TDS_INHIBITED:
  469                 /*
  470                  * If we are only inhibited because we are swapped out
  471                  * then arange to swap in this process. Otherwise just return.
  472                  */
  473                 if (td->td_inhibitors != TDI_SWAPPED)
  474                         return (0);
  475                 /* FALLTHROUGH */
  476         case TDS_CAN_RUN:
  477                 break;
  478         default:
  479                 printf("state is 0x%x", td->td_state);
  480                 panic("setrunnable(2)");
  481         }
  482         if ((td->td_flags & TDF_INMEM) == 0) {
  483                 if ((td->td_flags & TDF_SWAPINREQ) == 0) {
  484                         td->td_flags |= TDF_SWAPINREQ;
  485                         return (1);
  486                 }
  487         } else
  488                 sched_wakeup(td);
  489         return (0);
  490 }
  491 
  492 /*
  493  * Compute a tenex style load average of a quantity on
  494  * 1, 5 and 15 minute intervals.
  495  */
  496 static void
  497 loadav(void *arg)
  498 {
  499         int i, nrun;
  500         struct loadavg *avg;
  501 
  502         nrun = sched_load();
  503         avg = &averunnable;
  504 
  505         for (i = 0; i < 3; i++)
  506                 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
  507                     nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
  508 
  509         /*
  510          * Schedule the next update to occur after 5 seconds, but add a
  511          * random variation to avoid synchronisation with processes that
  512          * run at regular intervals.
  513          */
  514         callout_reset_sbt(&loadav_callout,
  515             SBT_1US * (4000000 + (int)(random() % 2000001)), SBT_1US,
  516             loadav, NULL, C_DIRECT_EXEC | C_PREL(32));
  517 }
  518 
  519 /* ARGSUSED */
  520 static void
  521 synch_setup(void *dummy)
  522 {
  523         callout_init(&loadav_callout, 1);
  524 
  525         /* Kick off timeout driven events by calling first time. */
  526         loadav(NULL);
  527 }
  528 
  529 int
  530 should_yield(void)
  531 {
  532 
  533         return ((u_int)ticks - (u_int)curthread->td_swvoltick >= hogticks);
  534 }
  535 
  536 void
  537 maybe_yield(void)
  538 {
  539 
  540         if (should_yield())
  541                 kern_yield(PRI_USER);
  542 }
  543 
  544 void
  545 kern_yield(int prio)
  546 {
  547         struct thread *td;
  548 
  549         td = curthread;
  550         DROP_GIANT();
  551         thread_lock(td);
  552         if (prio == PRI_USER)
  553                 prio = td->td_user_pri;
  554         if (prio >= 0)
  555                 sched_prio(td, prio);
  556         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
  557         thread_unlock(td);
  558         PICKUP_GIANT();
  559 }
  560 
  561 /*
  562  * General purpose yield system call.
  563  */
  564 int
  565 sys_yield(struct thread *td, struct yield_args *uap)
  566 {
  567 
  568         thread_lock(td);
  569         if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
  570                 sched_prio(td, PRI_MAX_TIMESHARE);
  571         mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
  572         thread_unlock(td);
  573         td->td_retval[0] = 0;
  574         return (0);
  575 }

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