kernel - Fix excessive call stack depth on stuck interrupt

[dragonfly.git] / sys / kern / kern_synch.c

/*-
 * Copyright (c) 1982, 1986, 1990, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)kern_synch.c        8.9 (Berkeley) 5/19/95
 * $FreeBSD: src/sys/kern/kern_synch.c,v 1.87.2.6 2002/10/13 07:29:53 kbyanc Exp $
 */

#include "opt_ktrace.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/kernel.h>
#include <sys/signalvar.h>
#include <sys/resourcevar.h>
#include <sys/vmmeter.h>
#include <sys/sysctl.h>
#include <sys/lock.h>
#include <sys/uio.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif
#include <sys/ktr.h>
#include <sys/serialize.h>

#include <sys/signal2.h>
#include <sys/thread2.h>
#include <sys/spinlock2.h>
#include <sys/mutex2.h>

#include <machine/cpu.h>
#include <machine/smp.h>

TAILQ_HEAD(tslpque, thread);

static void sched_setup (void *dummy);
SYSINIT(sched_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, sched_setup, NULL);

int     lbolt;
void    *lbolt_syncer;
int     sched_quantum;          /* Roundrobin scheduling quantum in ticks. */
int     ncpus;
int     ncpus2, ncpus2_shift, ncpus2_mask;      /* note: mask not cpumask_t */
int     ncpus_fit, ncpus_fit_mask;              /* note: mask not cpumask_t */
int     safepri;
int     tsleep_now_works;
int     tsleep_crypto_dump = 0;

static struct callout loadav_callout;
static struct callout schedcpu_callout;
MALLOC_DEFINE(M_TSLEEP, "tslpque", "tsleep queues");

#define __DEALL(ident)  __DEQUALIFY(void *, ident)

#if !defined(KTR_TSLEEP)
#define KTR_TSLEEP      KTR_ALL
#endif
KTR_INFO_MASTER(tsleep);
KTR_INFO(KTR_TSLEEP, tsleep, tsleep_beg, 0, "tsleep enter %p", const volatile void *ident);
KTR_INFO(KTR_TSLEEP, tsleep, tsleep_end, 1, "tsleep exit");
KTR_INFO(KTR_TSLEEP, tsleep, wakeup_beg, 2, "wakeup enter %p", const volatile void *ident);
KTR_INFO(KTR_TSLEEP, tsleep, wakeup_end, 3, "wakeup exit");
KTR_INFO(KTR_TSLEEP, tsleep, ilockfail,  4, "interlock failed %p", const volatile void *ident);

#define logtsleep1(name)        KTR_LOG(tsleep_ ## name)
#define logtsleep2(name, val)   KTR_LOG(tsleep_ ## name, val)

struct loadavg averunnable =
        { {0, 0, 0}, FSCALE };  /* load average, of runnable procs */
/*
 * Constants for averages over 1, 5, and 15 minutes
 * when sampling at 5 second intervals.
 */
static fixpt_t cexp[3] = {
        0.9200444146293232 * FSCALE,    /* exp(-1/12) */
        0.9834714538216174 * FSCALE,    /* exp(-1/60) */
        0.9944598480048967 * FSCALE,    /* exp(-1/180) */
};

static void     endtsleep (void *);
static void     loadav (void *arg);
static void     schedcpu (void *arg);

/*
 * Adjust the scheduler quantum.  The quantum is specified in microseconds.
 * Note that 'tick' is in microseconds per tick.
 */
static int
sysctl_kern_quantum(SYSCTL_HANDLER_ARGS)
{
        int error, new_val;

        new_val = sched_quantum * ustick;
        error = sysctl_handle_int(oidp, &new_val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (new_val < ustick)
                return (EINVAL);
        sched_quantum = new_val / ustick;
        return (0);
}

SYSCTL_PROC(_kern, OID_AUTO, quantum, CTLTYPE_INT|CTLFLAG_RW,
        0, sizeof sched_quantum, sysctl_kern_quantum, "I", "");

static int pctcpu_decay = 10;
SYSCTL_INT(_kern, OID_AUTO, pctcpu_decay, CTLFLAG_RW, &pctcpu_decay, 0, "");

/*
 * kernel uses `FSCALE', userland (SHOULD) use kern.fscale 
 */
int     fscale __unused = FSCALE;       /* exported to systat */
SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");

/*
 * Recompute process priorities, once a second.
 *
 * Since the userland schedulers are typically event oriented, if the
 * estcpu calculation at wakeup() time is not sufficient to make a
 * process runnable relative to other processes in the system we have
 * a 1-second recalc to help out.
 *
 * This code also allows us to store sysclock_t data in the process structure
 * without fear of an overrun, since sysclock_t are guarenteed to hold 
 * several seconds worth of count.
 *
 * WARNING!  callouts can preempt normal threads.  However, they will not
 * preempt a thread holding a spinlock so we *can* safely use spinlocks.
 */
static int schedcpu_stats(struct proc *p, void *data __unused);
static int schedcpu_resource(struct proc *p, void *data __unused);

static void
schedcpu(void *arg)
{
        allproc_scan(schedcpu_stats, NULL);
        allproc_scan(schedcpu_resource, NULL);
        wakeup((caddr_t)&lbolt);
        wakeup(lbolt_syncer);
        callout_reset(&schedcpu_callout, hz, schedcpu, NULL);
}

/*
 * General process statistics once a second
 */
static int
schedcpu_stats(struct proc *p, void *data __unused)
{
        struct lwp *lp;

        /*
         * Threads may not be completely set up if process in SIDL state.
         */
        if (p->p_stat == SIDL)
                return(0);

        PHOLD(p);
        if (lwkt_trytoken(&p->p_token) == FALSE) {
                PRELE(p);
                return(0);
        }

        p->p_swtime++;
        FOREACH_LWP_IN_PROC(lp, p) {
                if (lp->lwp_stat == LSSLEEP) {
                        ++lp->lwp_slptime;
                        if (lp->lwp_slptime == 1)
                                p->p_usched->uload_update(lp);
                }

                /*
                 * Only recalculate processes that are active or have slept
                 * less then 2 seconds.  The schedulers understand this.
                 * Otherwise decay by 50% per second.
                 */
                if (lp->lwp_slptime <= 1) {
                        p->p_usched->recalculate(lp);
                } else {
                        int decay;

                        decay = pctcpu_decay;
                        cpu_ccfence();
                        if (decay <= 1)
                                decay = 1;
                        if (decay > 100)
                                decay = 100;
                        lp->lwp_pctcpu = (lp->lwp_pctcpu * (decay - 1)) / decay;
                }
        }
        lwkt_reltoken(&p->p_token);
        lwkt_yield();
        PRELE(p);
        return(0);
}

/*
 * Resource checks.  XXX break out since ksignal/killproc can block,
 * limiting us to one process killed per second.  There is probably
 * a better way.
 */
static int
schedcpu_resource(struct proc *p, void *data __unused)
{
        u_int64_t ttime;
        struct lwp *lp;

        if (p->p_stat == SIDL)
                return(0);

        PHOLD(p);
        if (lwkt_trytoken(&p->p_token) == FALSE) {
                PRELE(p);
                return(0);
        }

        if (p->p_stat == SZOMB || p->p_limit == NULL) {
                lwkt_reltoken(&p->p_token);
                PRELE(p);
                return(0);
        }

        ttime = 0;
        FOREACH_LWP_IN_PROC(lp, p) {
                /*
                 * We may have caught an lp in the middle of being
                 * created, lwp_thread can be NULL.
                 */
                if (lp->lwp_thread) {
                        ttime += lp->lwp_thread->td_sticks;
                        ttime += lp->lwp_thread->td_uticks;
                }
        }

        switch(plimit_testcpulimit(p->p_limit, ttime)) {
        case PLIMIT_TESTCPU_KILL:
                killproc(p, "exceeded maximum CPU limit");
                break;
        case PLIMIT_TESTCPU_XCPU:
                if ((p->p_flags & P_XCPU) == 0) {
                        p->p_flags |= P_XCPU;
                        ksignal(p, SIGXCPU);
                }
                break;
        default:
                break;
        }
        lwkt_reltoken(&p->p_token);
        lwkt_yield();
        PRELE(p);
        return(0);
}

/*
 * This is only used by ps.  Generate a cpu percentage use over
 * a period of one second.
 */
void
updatepcpu(struct lwp *lp, int cpticks, int ttlticks)
{
        fixpt_t acc;
        int remticks;

        acc = (cpticks << FSHIFT) / ttlticks;
        if (ttlticks >= ESTCPUFREQ) {
                lp->lwp_pctcpu = acc;
        } else {
                remticks = ESTCPUFREQ - ttlticks;
                lp->lwp_pctcpu = (acc * ttlticks + lp->lwp_pctcpu * remticks) /
                                ESTCPUFREQ;
        }
}

/*
 * tsleep/wakeup hash table parameters.  Try to find the sweet spot for
 * like addresses being slept on.
 */
#define TABLESIZE       4001
#define LOOKUP(x)       (((u_int)(uintptr_t)(x)) % TABLESIZE)

static cpumask_t slpque_cpumasks[TABLESIZE];

/*
 * General scheduler initialization.  We force a reschedule 25 times
 * a second by default.  Note that cpu0 is initialized in early boot and
 * cannot make any high level calls.
 *
 * Each cpu has its own sleep queue.
 */
void
sleep_gdinit(globaldata_t gd)
{
        static struct tslpque slpque_cpu0[TABLESIZE];
        int i;

        if (gd->gd_cpuid == 0) {
                sched_quantum = (hz + 24) / 25;
                gd->gd_tsleep_hash = slpque_cpu0;
        } else {
                gd->gd_tsleep_hash = kmalloc(sizeof(slpque_cpu0), 
                                            M_TSLEEP, M_WAITOK | M_ZERO);
        }
        for (i = 0; i < TABLESIZE; ++i)
                TAILQ_INIT(&gd->gd_tsleep_hash[i]);
}

/*
 * This is a dandy function that allows us to interlock tsleep/wakeup
 * operations with unspecified upper level locks, such as lockmgr locks,
 * simply by holding a critical section.  The sequence is:
 *
 *      (acquire upper level lock)
 *      tsleep_interlock(blah)
 *      (release upper level lock)
 *      tsleep(blah, ...)
 *
 * Basically this functions queues us on the tsleep queue without actually
 * descheduling us.  When tsleep() is later called with PINTERLOCK it
 * assumes the thread was already queued, otherwise it queues it there.
 *
 * Thus it is possible to receive the wakeup prior to going to sleep and
 * the race conditions are covered.
 */
static __inline void
_tsleep_interlock(globaldata_t gd, const volatile void *ident, int flags)
{
        thread_t td = gd->gd_curthread;
        int id;

        crit_enter_quick(td);
        if (td->td_flags & TDF_TSLEEPQ) {
                id = LOOKUP(td->td_wchan);
                TAILQ_REMOVE(&gd->gd_tsleep_hash[id], td, td_sleepq);
                if (TAILQ_FIRST(&gd->gd_tsleep_hash[id]) == NULL) {
                        ATOMIC_CPUMASK_NANDBIT(slpque_cpumasks[id],
                                               gd->gd_cpuid);
                }
        } else {
                td->td_flags |= TDF_TSLEEPQ;
        }
        id = LOOKUP(ident);
        TAILQ_INSERT_TAIL(&gd->gd_tsleep_hash[id], td, td_sleepq);
        ATOMIC_CPUMASK_ORBIT(slpque_cpumasks[id], gd->gd_cpuid);
        td->td_wchan = ident;
        td->td_wdomain = flags & PDOMAIN_MASK;
        crit_exit_quick(td);
}

void
tsleep_interlock(const volatile void *ident, int flags)
{
        _tsleep_interlock(mycpu, ident, flags);
}

/*
 * Remove thread from sleepq.  Must be called with a critical section held.
 * The thread must not be migrating.
 */
static __inline void
_tsleep_remove(thread_t td)
{
        globaldata_t gd = mycpu;
        int id;

        KKASSERT(td->td_gd == gd && IN_CRITICAL_SECT(td));
        KKASSERT((td->td_flags & TDF_MIGRATING) == 0);
        if (td->td_flags & TDF_TSLEEPQ) {
                td->td_flags &= ~TDF_TSLEEPQ;
                id = LOOKUP(td->td_wchan);
                TAILQ_REMOVE(&gd->gd_tsleep_hash[id], td, td_sleepq);
                if (TAILQ_FIRST(&gd->gd_tsleep_hash[id]) == NULL) {
                        ATOMIC_CPUMASK_NANDBIT(slpque_cpumasks[id],
                                               gd->gd_cpuid);
                }
                td->td_wchan = NULL;
                td->td_wdomain = 0;
        }
}

void
tsleep_remove(thread_t td)
{
        _tsleep_remove(td);
}

/*
 * General sleep call.  Suspends the current process until a wakeup is
 * performed on the specified identifier.  The process will then be made
 * runnable with the specified priority.  Sleeps at most timo/hz seconds
 * (0 means no timeout).  If flags includes PCATCH flag, signals are checked
 * before and after sleeping, else signals are not checked.  Returns 0 if
 * awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is set and a
 * signal needs to be delivered, ERESTART is returned if the current system
 * call should be restarted if possible, and EINTR is returned if the system
 * call should be interrupted by the signal (return EINTR).
 *
 * Note that if we are a process, we release_curproc() before messing with
 * the LWKT scheduler.
 *
 * During autoconfiguration or after a panic, a sleep will simply
 * lower the priority briefly to allow interrupts, then return.
 *
 * WARNING!  This code can't block (short of switching away), or bad things
 *           will happen.  No getting tokens, no blocking locks, etc.
 */
int
tsleep(const volatile void *ident, int flags, const char *wmesg, int timo)
{
        struct thread *td = curthread;
        struct lwp *lp = td->td_lwp;
        struct proc *p = td->td_proc;           /* may be NULL */
        globaldata_t gd;
        int sig;
        int catch;
        int error;
        int oldpri;
        struct callout thandle;

        /*
         * Currently a severe hack.  Make sure any delayed wakeups
         * are flushed before we sleep or we might deadlock on whatever
         * event we are sleeping on.
         */
        if (td->td_flags & TDF_DELAYED_WAKEUP)
                wakeup_end_delayed();

        /*
         * NOTE: removed KTRPOINT, it could cause races due to blocking
         * even in stable.  Just scrap it for now.
         */
        if (!tsleep_crypto_dump && (tsleep_now_works == 0 || panicstr)) {
                /*
                 * After a panic, or before we actually have an operational
                 * softclock, just give interrupts a chance, then just return;
                 *
                 * don't run any other procs or panic below,
                 * in case this is the idle process and already asleep.
                 */
                splz();
                oldpri = td->td_pri;
                lwkt_setpri_self(safepri);
                lwkt_switch();
                lwkt_setpri_self(oldpri);
                return (0);
        }
        logtsleep2(tsleep_beg, ident);
        gd = td->td_gd;
        KKASSERT(td != &gd->gd_idlethread);     /* you must be kidding! */
        td->td_wakefromcpu = -1;                /* overwritten by _wakeup */

        /*
         * NOTE: all of this occurs on the current cpu, including any
         * callout-based wakeups, so a critical section is a sufficient
         * interlock.
         *
         * The entire sequence through to where we actually sleep must
         * run without breaking the critical section.
         */
        catch = flags & PCATCH;
        error = 0;
        sig = 0;

        crit_enter_quick(td);

        KASSERT(ident != NULL, ("tsleep: no ident"));
        KASSERT(lp == NULL ||
                lp->lwp_stat == LSRUN ||        /* Obvious */
                lp->lwp_stat == LSSTOP,         /* Set in tstop */
                ("tsleep %p %s %d",
                        ident, wmesg, lp->lwp_stat));

        /*
         * We interlock the sleep queue if the caller has not already done
         * it for us.  This must be done before we potentially acquire any
         * tokens or we can loose the wakeup.
         */
        if ((flags & PINTERLOCKED) == 0) {
                _tsleep_interlock(gd, ident, flags);
        }

        /*
         * Setup for the current process (if this is a process).  We must
         * interlock with lwp_token to avoid remote wakeup races via
         * setrunnable()
         */
        if (lp) {
                lwkt_gettoken(&lp->lwp_token);

                /*
                 * If the umbrella process is in the SCORE state then
                 * make sure that the thread is flagged going into a
                 * normal sleep to allow the core dump to proceed, otherwise
                 * the coredump can end up waiting forever.  If the normal
                 * sleep is woken up, the thread will enter a stopped state
                 * upon return to userland.
                 *
                 * We do not want to interrupt or cause a thread exist at
                 * this juncture because that will mess-up the state the
                 * coredump is trying to save.
                 */
                if (p->p_stat == SCORE &&
                    (lp->lwp_mpflags & LWP_MP_WSTOP) == 0) {
                        atomic_set_int(&lp->lwp_mpflags, LWP_MP_WSTOP);
                        ++p->p_nstopped;
                }

                /*
                 * PCATCH requested.
                 */
                if (catch) {
                        /*
                         * Early termination if PCATCH was set and a
                         * signal is pending, interlocked with the
                         * critical section.
                         *
                         * Early termination only occurs when tsleep() is
                         * entered while in a normal LSRUN state.
                         */
                        if ((sig = CURSIG(lp)) != 0)
                                goto resume;

                        /*
                         * Causes ksignal to wake us up if a signal is
                         * received (interlocked with lp->lwp_token).
                         */
                        lp->lwp_flags |= LWP_SINTR;
                }
        } else {
                KKASSERT(p == NULL);
        }

        /*
         * Make sure the current process has been untangled from
         * the userland scheduler and initialize slptime to start
         * counting.
         *
         * NOTE: td->td_wakefromcpu is pre-set by the release function
         *       for the dfly scheduler, and then adjusted by _wakeup()
         */
        if (lp) {
                p->p_usched->release_curproc(lp);
                lp->lwp_slptime = 0;
        }

        /*
         * If the interlocked flag is set but our cpu bit in the slpqueue
         * is no longer set, then a wakeup was processed inbetween the
         * tsleep_interlock() (ours or the callers), and here.  This can
         * occur under numerous circumstances including when we release the
         * current process.
         *
         * Extreme loads can cause the sending of an IPI (e.g. wakeup()'s)
         * to process incoming IPIs, thus draining incoming wakeups.
         */
        if ((td->td_flags & TDF_TSLEEPQ) == 0) {
                logtsleep2(ilockfail, ident);
                goto resume;
        }

        /*
         * scheduling is blocked while in a critical section.  Coincide
         * the descheduled-by-tsleep flag with the descheduling of the
         * lwkt.
         *
         * The timer callout is localized on our cpu and interlocked by
         * our critical section.
         */
        lwkt_deschedule_self(td);
        td->td_flags |= TDF_TSLEEP_DESCHEDULED;
        td->td_wmesg = wmesg;

        /*
         * Setup the timeout, if any.  The timeout is only operable while
         * the thread is flagged descheduled.
         */
        KKASSERT((td->td_flags & TDF_TIMEOUT) == 0);
        if (timo) {
                callout_init_mp(&thandle);
                callout_reset(&thandle, timo, endtsleep, td);
        }

        /*
         * Beddy bye bye.
         */
        if (lp) {
                /*
                 * Ok, we are sleeping.  Place us in the SSLEEP state.
                 */
                KKASSERT((lp->lwp_mpflags & LWP_MP_ONRUNQ) == 0);

                /*
                 * tstop() sets LSSTOP, so don't fiddle with that.
                 */
                if (lp->lwp_stat != LSSTOP)
                        lp->lwp_stat = LSSLEEP;
                lp->lwp_ru.ru_nvcsw++;
                p->p_usched->uload_update(lp);
                lwkt_switch();

                /*
                 * And when we are woken up, put us back in LSRUN.  If we
                 * slept for over a second, recalculate our estcpu.
                 */
                lp->lwp_stat = LSRUN;
                if (lp->lwp_slptime) {
                        p->p_usched->uload_update(lp);
                        p->p_usched->recalculate(lp);
                }
                lp->lwp_slptime = 0;
        } else {
                lwkt_switch();
        }

        /* 
         * Make sure we haven't switched cpus while we were asleep.  It's
         * not supposed to happen.  Cleanup our temporary flags.
         */
        KKASSERT(gd == td->td_gd);

        /*
         * Cleanup the timeout.  If the timeout has already occured thandle
         * has already been stopped, otherwise stop thandle.  If the timeout
         * is running (the callout thread must be blocked trying to get
         * lwp_token) then wait for us to get scheduled.
         */
        if (timo) {
                while (td->td_flags & TDF_TIMEOUT_RUNNING) {
                        /* else we won't get rescheduled! */
                        if (lp->lwp_stat != LSSTOP)
                                lp->lwp_stat = LSSLEEP;
                        lwkt_deschedule_self(td);
                        td->td_wmesg = "tsrace";
                        lwkt_switch();
                        kprintf("td %p %s: timeout race\n", td, td->td_comm);
                }
                if (td->td_flags & TDF_TIMEOUT) {
                        td->td_flags &= ~TDF_TIMEOUT;
                        error = EWOULDBLOCK;
                } else {
                        /* does not block when on same cpu */
                        callout_stop(&thandle);
                }
        }
        td->td_flags &= ~TDF_TSLEEP_DESCHEDULED;

        /*
         * Make sure we have been removed from the sleepq.  In most
         * cases this will have been done for us already but it is
         * possible for a scheduling IPI to be in-flight from a
         * previous tsleep/tsleep_interlock() or due to a straight-out
         * call to lwkt_schedule() (in the case of an interrupt thread),
         * causing a spurious wakeup.
         */
        _tsleep_remove(td);
        td->td_wmesg = NULL;

        /*
         * Figure out the correct error return.  If interrupted by a
         * signal we want to return EINTR or ERESTART.  
         */
resume:
        if (lp) {
                if (catch && error == 0) {
                        if (sig != 0 || (sig = CURSIG(lp))) {
                                if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig))
                                        error = EINTR;
                                else
                                        error = ERESTART;
                        }
                }

                lp->lwp_flags &= ~LWP_SINTR;

                /*
                 * Unconditionally set us to LSRUN on resume.  lwp_stat could
                 * be in a weird state due to the goto resume, particularly
                 * when tsleep() is called from tstop().
                 */
                lp->lwp_stat = LSRUN;
                lwkt_reltoken(&lp->lwp_token);
        }
        logtsleep1(tsleep_end);
        crit_exit_quick(td);
        return (error);
}

/*
 * Interlocked spinlock sleep.  An exclusively held spinlock must
 * be passed to ssleep().  The function will atomically release the
 * spinlock and tsleep on the ident, then reacquire the spinlock and
 * return.
 *
 * This routine is fairly important along the critical path, so optimize it
 * heavily.
 */
int
ssleep(const volatile void *ident, struct spinlock *spin, int flags,
       const char *wmesg, int timo)
{
        globaldata_t gd = mycpu;
        int error;

        _tsleep_interlock(gd, ident, flags);
        spin_unlock_quick(gd, spin);
        error = tsleep(ident, flags | PINTERLOCKED, wmesg, timo);
        _spin_lock_quick(gd, spin, wmesg);

        return (error);
}

int
lksleep(const volatile void *ident, struct lock *lock, int flags,
        const char *wmesg, int timo)
{
        globaldata_t gd = mycpu;
        int error;

        _tsleep_interlock(gd, ident, flags);
        lockmgr(lock, LK_RELEASE);
        error = tsleep(ident, flags | PINTERLOCKED, wmesg, timo);
        lockmgr(lock, LK_EXCLUSIVE);

        return (error);
}

/*
 * Interlocked mutex sleep.  An exclusively held mutex must be passed
 * to mtxsleep().  The function will atomically release the mutex
 * and tsleep on the ident, then reacquire the mutex and return.
 */
int
mtxsleep(const volatile void *ident, struct mtx *mtx, int flags,
         const char *wmesg, int timo)
{
        globaldata_t gd = mycpu;
        int error;

        _tsleep_interlock(gd, ident, flags);
        mtx_unlock(mtx);
        error = tsleep(ident, flags | PINTERLOCKED, wmesg, timo);
        mtx_lock_ex_quick(mtx);

        return (error);
}

/*
 * Interlocked serializer sleep.  An exclusively held serializer must
 * be passed to zsleep().  The function will atomically release
 * the serializer and tsleep on the ident, then reacquire the serializer
 * and return.
 */
int
zsleep(const volatile void *ident, struct lwkt_serialize *slz, int flags,
       const char *wmesg, int timo)
{
        globaldata_t gd = mycpu;
        int ret;

        ASSERT_SERIALIZED(slz);

        _tsleep_interlock(gd, ident, flags);
        lwkt_serialize_exit(slz);
        ret = tsleep(ident, flags | PINTERLOCKED, wmesg, timo);
        lwkt_serialize_enter(slz);

        return ret;
}

/*
 * Directly block on the LWKT thread by descheduling it.  This
 * is much faster then tsleep(), but the only legal way to wake
 * us up is to directly schedule the thread.
 *
 * Setting TDF_SINTR will cause new signals to directly schedule us.
 *
 * This routine must be called while in a critical section.
 */
int
lwkt_sleep(const char *wmesg, int flags)
{
        thread_t td = curthread;
        int sig;

        if ((flags & PCATCH) == 0 || td->td_lwp == NULL) {
                td->td_flags |= TDF_BLOCKED;
                td->td_wmesg = wmesg;
                lwkt_deschedule_self(td);
                lwkt_switch();
                td->td_wmesg = NULL;
                td->td_flags &= ~TDF_BLOCKED;
                return(0);
        }
        if ((sig = CURSIG(td->td_lwp)) != 0) {
                if (SIGISMEMBER(td->td_proc->p_sigacts->ps_sigintr, sig))
                        return(EINTR);
                else
                        return(ERESTART);
                        
        }
        td->td_flags |= TDF_BLOCKED | TDF_SINTR;
        td->td_wmesg = wmesg;
        lwkt_deschedule_self(td);
        lwkt_switch();
        td->td_flags &= ~(TDF_BLOCKED | TDF_SINTR);
        td->td_wmesg = NULL;
        return(0);
}

/*
 * Implement the timeout for tsleep.
 *
 * This type of callout timeout is scheduled on the same cpu the process
 * is sleeping on.  Also, at the moment, the MP lock is held.
 */
static void
endtsleep(void *arg)
{
        thread_t td = arg;
        struct lwp *lp;

        /*
         * We are going to have to get the lwp_token, which means we might
         * block.  This can race a tsleep getting woken up by other means
         * so set TDF_TIMEOUT_RUNNING to force the tsleep to wait for our
         * processing to complete (sorry tsleep!).
         *
         * We can safely set td_flags because td MUST be on the same cpu
         * as we are.
         */
        KKASSERT(td->td_gd == mycpu);
        crit_enter();
        td->td_flags |= TDF_TIMEOUT_RUNNING | TDF_TIMEOUT;

        /*
         * This can block but TDF_TIMEOUT_RUNNING will prevent the thread
         * from exiting the tsleep on us.  The flag is interlocked by virtue
         * of lp being on the same cpu as we are.
         */
        if ((lp = td->td_lwp) != NULL)
                lwkt_gettoken(&lp->lwp_token);

        KKASSERT(td->td_flags & TDF_TSLEEP_DESCHEDULED);

        if (lp) {
                /*
                 * callout timer should normally never be set in tstop()
                 * because it passes a timeout of 0.  However, there is a
                 * case during thread exit (which SSTOP's all the threads)
                 * for which tstop() must break out and can (properly) leave
                 * the thread in LSSTOP.
                 */
                KKASSERT(lp->lwp_stat != LSSTOP ||
                         (lp->lwp_mpflags & LWP_MP_WEXIT));
                setrunnable(lp);
                lwkt_reltoken(&lp->lwp_token);
        } else {
                _tsleep_remove(td);
                lwkt_schedule(td);
        }
        KKASSERT(td->td_gd == mycpu);
        td->td_flags &= ~TDF_TIMEOUT_RUNNING;
        crit_exit();
}

/*
 * Make all processes sleeping on the specified identifier runnable.
 * count may be zero or one only.
 *
 * The domain encodes the sleep/wakeup domain, flags, plus the originating
 * cpu.
 *
 * This call may run without the MP lock held.  We can only manipulate thread
 * state on the cpu owning the thread.  We CANNOT manipulate process state
 * at all.
 *
 * _wakeup() can be passed to an IPI so we can't use (const volatile
 * void *ident).
 */
static void
_wakeup(void *ident, int domain)
{
        struct tslpque *qp;
        struct thread *td;
        struct thread *ntd;
        globaldata_t gd;
        cpumask_t mask;
        int id;

        crit_enter();
        logtsleep2(wakeup_beg, ident);
        gd = mycpu;
        id = LOOKUP(ident);
        qp = &gd->gd_tsleep_hash[id];
restart:
        for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) {
                ntd = TAILQ_NEXT(td, td_sleepq);
                if (td->td_wchan == ident && 
                    td->td_wdomain == (domain & PDOMAIN_MASK)
                ) {
                        KKASSERT(td->td_gd == gd);
                        _tsleep_remove(td);
                        td->td_wakefromcpu = PWAKEUP_DECODE(domain);
                        if (td->td_flags & TDF_TSLEEP_DESCHEDULED) {
                                lwkt_schedule(td);
                                if (domain & PWAKEUP_ONE)
                                        goto done;
                        }
                        goto restart;
                }
        }

        /*
         * We finished checking the current cpu but there still may be
         * more work to do.  Either wakeup_one was requested and no matching
         * thread was found, or a normal wakeup was requested and we have
         * to continue checking cpus.
         *
         * It should be noted that this scheme is actually less expensive then
         * the old scheme when waking up multiple threads, since we send 
         * only one IPI message per target candidate which may then schedule
         * multiple threads.  Before we could have wound up sending an IPI
         * message for each thread on the target cpu (!= current cpu) that
         * needed to be woken up.
         *
         * NOTE: Wakeups occuring on remote cpus are asynchronous.  This
         * should be ok since we are passing idents in the IPI rather then
         * thread pointers.
         */
        if ((domain & PWAKEUP_MYCPU) == 0) {
                mask = slpque_cpumasks[id];
                CPUMASK_ANDMASK(mask, gd->gd_other_cpus);
                if (CPUMASK_TESTNZERO(mask)) {
                        lwkt_send_ipiq2_mask(mask, _wakeup, ident,
                                             domain | PWAKEUP_MYCPU);
                }
        }
done:
        logtsleep1(wakeup_end);
        crit_exit();
}

/*
 * Wakeup all threads tsleep()ing on the specified ident, on all cpus
 */
void
wakeup(const volatile void *ident)
{
    globaldata_t gd = mycpu;
    thread_t td = gd->gd_curthread;

    if (td && (td->td_flags & TDF_DELAYED_WAKEUP)) {
        /*
         * If we are in a delayed wakeup section, record up to two wakeups in
         * a per-CPU queue and issue them when we block or exit the delayed
         * wakeup section.
         */
        if (atomic_cmpset_ptr(&gd->gd_delayed_wakeup[0], NULL, ident))
                return;
        if (atomic_cmpset_ptr(&gd->gd_delayed_wakeup[1], NULL, ident))
                return;

        ident = atomic_swap_ptr(__DEQUALIFY(volatile void **, &gd->gd_delayed_wakeup[1]),
                                __DEALL(ident));
        ident = atomic_swap_ptr(__DEQUALIFY(volatile void **, &gd->gd_delayed_wakeup[0]),
                                __DEALL(ident));
    }

    _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, gd->gd_cpuid));
}

/*
 * Wakeup one thread tsleep()ing on the specified ident, on any cpu.
 */
void
wakeup_one(const volatile void *ident)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, mycpu->gd_cpuid) |
                            PWAKEUP_ONE);
}

/*
 * Wakeup threads tsleep()ing on the specified ident on the current cpu
 * only.
 */
void
wakeup_mycpu(const volatile void *ident)
{
    _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, mycpu->gd_cpuid) |
                            PWAKEUP_MYCPU);
}

/*
 * Wakeup one thread tsleep()ing on the specified ident on the current cpu
 * only.
 */
void
wakeup_mycpu_one(const volatile void *ident)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, mycpu->gd_cpuid) |
                            PWAKEUP_MYCPU | PWAKEUP_ONE);
}

/*
 * Wakeup all thread tsleep()ing on the specified ident on the specified cpu
 * only.
 */
void
wakeup_oncpu(globaldata_t gd, const volatile void *ident)
{
    globaldata_t mygd = mycpu;
    if (gd == mycpu) {
        _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, mygd->gd_cpuid) |
                                PWAKEUP_MYCPU);
    } else {
        lwkt_send_ipiq2(gd, _wakeup, __DEALL(ident),
                        PWAKEUP_ENCODE(0, mygd->gd_cpuid) |
                        PWAKEUP_MYCPU);
    }
}

/*
 * Wakeup one thread tsleep()ing on the specified ident on the specified cpu
 * only.
 */
void
wakeup_oncpu_one(globaldata_t gd, const volatile void *ident)
{
    globaldata_t mygd = mycpu;
    if (gd == mygd) {
        _wakeup(__DEALL(ident), PWAKEUP_ENCODE(0, mygd->gd_cpuid) |
                                PWAKEUP_MYCPU | PWAKEUP_ONE);
    } else {
        lwkt_send_ipiq2(gd, _wakeup, __DEALL(ident),
                        PWAKEUP_ENCODE(0, mygd->gd_cpuid) |
                        PWAKEUP_MYCPU | PWAKEUP_ONE);
    }
}

/*
 * Wakeup all threads waiting on the specified ident that slept using
 * the specified domain, on all cpus.
 */
void
wakeup_domain(const volatile void *ident, int domain)
{
    _wakeup(__DEALL(ident), PWAKEUP_ENCODE(domain, mycpu->gd_cpuid));
}

/*
 * Wakeup one thread waiting on the specified ident that slept using
 * the specified  domain, on any cpu.
 */
void
wakeup_domain_one(const volatile void *ident, int domain)
{
    /* XXX potentially round-robin the first responding cpu */
    _wakeup(__DEALL(ident),
            PWAKEUP_ENCODE(domain, mycpu->gd_cpuid) | PWAKEUP_ONE);
}

void
wakeup_start_delayed(void)
{
    globaldata_t gd = mycpu;

    crit_enter();
    gd->gd_curthread->td_flags |= TDF_DELAYED_WAKEUP;
    crit_exit();
}

void
wakeup_end_delayed(void)
{
    globaldata_t gd = mycpu;

    if (gd->gd_curthread->td_flags & TDF_DELAYED_WAKEUP) {
        crit_enter();
        gd->gd_curthread->td_flags &= ~TDF_DELAYED_WAKEUP;
        if (gd->gd_delayed_wakeup[0] || gd->gd_delayed_wakeup[1]) {
            if (gd->gd_delayed_wakeup[0]) {
                    wakeup(gd->gd_delayed_wakeup[0]);
                    gd->gd_delayed_wakeup[0] = NULL;
            }
            if (gd->gd_delayed_wakeup[1]) {
                    wakeup(gd->gd_delayed_wakeup[1]);
                    gd->gd_delayed_wakeup[1] = NULL;
            }
        }
        crit_exit();
    }
}

/*
 * setrunnable()
 *
 * Make a process runnable.  lp->lwp_token must be held on call and this
 * function must be called from the cpu owning lp.
 *
 * This only has an effect if we are in LSSTOP or LSSLEEP.
 */
void
setrunnable(struct lwp *lp)
{
        thread_t td = lp->lwp_thread;

        ASSERT_LWKT_TOKEN_HELD(&lp->lwp_token);
        KKASSERT(td->td_gd == mycpu);
        crit_enter();
        if (lp->lwp_stat == LSSTOP)
                lp->lwp_stat = LSSLEEP;
        if (lp->lwp_stat == LSSLEEP) {
                _tsleep_remove(td);
                lwkt_schedule(td);
        } else if (td->td_flags & TDF_SINTR) {
                lwkt_schedule(td);
        }
        crit_exit();
}

/*
 * The process is stopped due to some condition, usually because p_stat is
 * set to SSTOP, but also possibly due to being traced.  
 *
 * Caller must hold p->p_token
 *
 * NOTE!  If the caller sets SSTOP, the caller must also clear P_WAITED
 * because the parent may check the child's status before the child actually
 * gets to this routine.
 *
 * This routine is called with the current lwp only, typically just
 * before returning to userland if the process state is detected as
 * possibly being in a stopped state.
 */
void
tstop(void)
{
        struct lwp *lp = curthread->td_lwp;
        struct proc *p = lp->lwp_proc;
        struct proc *q;

        lwkt_gettoken(&lp->lwp_token);
        crit_enter();

        /*
         * If LWP_MP_WSTOP is set, we were sleeping
         * while our process was stopped.  At this point
         * we were already counted as stopped.
         */
        if ((lp->lwp_mpflags & LWP_MP_WSTOP) == 0) {
                /*
                 * If we're the last thread to stop, signal
                 * our parent.
                 */
                p->p_nstopped++;
                atomic_set_int(&lp->lwp_mpflags, LWP_MP_WSTOP);
                wakeup(&p->p_nstopped);
                if (p->p_nstopped == p->p_nthreads) {
                        /*
                         * Token required to interlock kern_wait()
                         */
                        q = p->p_pptr;
                        PHOLD(q);
                        lwkt_gettoken(&q->p_token);
                        p->p_flags &= ~P_WAITED;
                        wakeup(p->p_pptr);
                        if ((q->p_sigacts->ps_flag & PS_NOCLDSTOP) == 0)
                                ksignal(q, SIGCHLD);
                        lwkt_reltoken(&q->p_token);
                        PRELE(q);
                }
        }

        /*
         * Wait here while in a stopped state, interlocked with lwp_token.
         * We must break-out if the whole process is trying to exit.
         */
        while (STOPLWP(p, lp)) {
                lp->lwp_stat = LSSTOP;
                tsleep(p, 0, "stop", 0);
        }
        p->p_nstopped--;
        atomic_clear_int(&lp->lwp_mpflags, LWP_MP_WSTOP);
        crit_exit();
        lwkt_reltoken(&lp->lwp_token);
}

/*
 * Compute a tenex style load average of a quantity on
 * 1, 5 and 15 minute intervals.
 */
static int loadav_count_runnable(struct lwp *p, void *data);

static void
loadav(void *arg)
{
        struct loadavg *avg;
        int i, nrun;

        nrun = 0;
        alllwp_scan(loadav_count_runnable, &nrun);
        avg = &averunnable;
        for (i = 0; i < 3; i++) {
                avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
                    nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
        }

        /*
         * Schedule the next update to occur after 5 seconds, but add a
         * random variation to avoid synchronisation with processes that
         * run at regular intervals.
         */
        callout_reset(&loadav_callout, hz * 4 + (int)(krandom() % (hz * 2 + 1)),
                      loadav, NULL);
}

static int
loadav_count_runnable(struct lwp *lp, void *data)
{
        int *nrunp = data;
        thread_t td;

        switch (lp->lwp_stat) {
        case LSRUN:
                if ((td = lp->lwp_thread) == NULL)
                        break;
                if (td->td_flags & TDF_BLOCKED)
                        break;
                ++*nrunp;
                break;
        default:
                break;
        }
        lwkt_yield();
        return(0);
}

/* ARGSUSED */
static void
sched_setup(void *dummy)
{
        callout_init_mp(&loadav_callout);
        callout_init_mp(&schedcpu_callout);

        /* Kick off timeout driven events by calling first time. */
        schedcpu(NULL);
        loadav(NULL);
}