Fix a panic unloading the bktr driver when devfs is in use.

[FreeBSD/FreeBSD.git] / sys / kern / kern_kse.c

/* 
 * Copyright (C) 2001 Julian Elischer <julian@freebsd.org>.
 *  All rights reserved.
 *
 * 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(s), this list of conditions and the following disclaimer as
 *    the first lines of this file unmodified other than the possible 
 *    addition of one or more copyright notices.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice(s), this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``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 COPYRIGHT HOLDER(S) 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.
 *
 * $FreeBSD$
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/smp.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/filedesc.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/sx.h>
#include <sys/tty.h>
#include <sys/user.h>
#include <sys/jail.h>
#include <sys/kse.h>
#include <sys/ktr.h>
#include <sys/ucontext.h>

#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/pmap.h>
#include <vm/uma.h>
#include <vm/vm_map.h>

#include <machine/frame.h>

/*
 * KSEGRP related storage.
 */
static uma_zone_t ksegrp_zone;
static uma_zone_t kse_zone;
static uma_zone_t thread_zone;

/* DEBUG ONLY */
SYSCTL_NODE(_kern, OID_AUTO, threads, CTLFLAG_RW, 0, "thread allocation");
static int oiks_debug = 0;      /* 0 disable, 1 printf, 2 enter debugger */
SYSCTL_INT(_kern_threads, OID_AUTO, oiks, CTLFLAG_RW,
        &oiks_debug, 0, "OIKS thread debug");

static int oiks_max_threads_per_proc = 10;
SYSCTL_INT(_kern_threads, OID_AUTO, oiks_max_per_proc, CTLFLAG_RW,
        &oiks_max_threads_per_proc, 0, "Debug limit on threads per proc");

static int max_threads_per_proc = 30;
SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
        &max_threads_per_proc, 0, "Limit on threads per proc");

static int max_groups_per_proc = 5;
SYSCTL_INT(_kern_threads, OID_AUTO, max_groups_per_proc, CTLFLAG_RW,
        &max_groups_per_proc, 0, "Limit on thread groups per proc");

#define RANGEOF(type, start, end) (offsetof(type, end) - offsetof(type, start))

struct threadqueue zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
TAILQ_HEAD(, kse) zombie_kses = TAILQ_HEAD_INITIALIZER(zombie_kses);
TAILQ_HEAD(, ksegrp) zombie_ksegrps = TAILQ_HEAD_INITIALIZER(zombie_ksegrps);
struct mtx zombie_thread_lock;
MTX_SYSINIT(zombie_thread_lock, &zombie_thread_lock,
    "zombie_thread_lock", MTX_SPIN);



void kse_purge(struct proc *p, struct thread *td);
/*
 * Pepare a thread for use.
 */
static void
thread_ctor(void *mem, int size, void *arg)
{
        struct thread   *td;

        td = (struct thread *)mem;
        td->td_state = TDS_INACTIVE;
        td->td_flags |= TDF_UNBOUND;
}

/*
 * Reclaim a thread after use.
 */
static void
thread_dtor(void *mem, int size, void *arg)
{
        struct thread   *td;

        mtx_assert(&Giant, MA_OWNED);
        td = (struct thread *)mem;

#ifdef INVARIANTS
        /* Verify that this thread is in a safe state to free. */
        switch (td->td_state) {
        case TDS_INHIBITED:
        case TDS_RUNNING:
        case TDS_CAN_RUN:
        case TDS_RUNQ:
                /*
                 * We must never unlink a thread that is in one of
                 * these states, because it is currently active.
                 */
                panic("bad state for thread unlinking");
                /* NOTREACHED */
        case TDS_INACTIVE:
                break;
        default:
                panic("bad thread state");
                /* NOTREACHED */
        }
#endif

        cpu_thread_dtor(td);
}

/*
 * Initialize type-stable parts of a thread (when newly created).
 */
static void
thread_init(void *mem, int size)
{
        struct thread   *td;

        td = (struct thread *)mem;
        mtx_lock(&Giant);
        pmap_new_thread(td, 0);
        mtx_unlock(&Giant);
        cpu_thread_setup(td);
        td->td_sched = (struct td_sched *)&td[1];
}

/*
 * Tear down type-stable parts of a thread (just before being discarded).
 */
static void
thread_fini(void *mem, int size)
{
        struct thread   *td;

        td = (struct thread *)mem;
        pmap_dispose_thread(td);
}
/*
 * Initialize type-stable parts of a kse (when newly created).
 */
static void
kse_init(void *mem, int size)
{
        struct kse      *ke;

        ke = (struct kse *)mem;
        ke->ke_sched = (struct ke_sched *)&ke[1];
}
/*
 * Initialize type-stable parts of a ksegrp (when newly created).
 */
static void
ksegrp_init(void *mem, int size)
{
        struct ksegrp   *kg;

        kg = (struct ksegrp *)mem;
        kg->kg_sched = (struct kg_sched *)&kg[1];
}

/* 
 * KSE is linked onto the idle queue.
 */
void
kse_link(struct kse *ke, struct ksegrp *kg)
{
        struct proc *p = kg->kg_proc;

        TAILQ_INSERT_HEAD(&kg->kg_kseq, ke, ke_kglist);
        kg->kg_kses++;
        ke->ke_state = KES_UNQUEUED;
        ke->ke_proc     = p;
        ke->ke_ksegrp   = kg;
        ke->ke_thread   = NULL;
        ke->ke_oncpu = NOCPU;
}

void
kse_unlink(struct kse *ke)
{
        struct ksegrp *kg;

        mtx_assert(&sched_lock, MA_OWNED);
        kg = ke->ke_ksegrp;
        if (ke->ke_state == KES_IDLE) {
                kg->kg_idle_kses--;
                TAILQ_REMOVE(&kg->kg_iq, ke, ke_kgrlist);
        }

        TAILQ_REMOVE(&kg->kg_kseq, ke, ke_kglist);
        if (--kg->kg_kses == 0) {
                        ksegrp_unlink(kg);
        }
        /*
         * Aggregate stats from the KSE
         */
        kse_stash(ke);
}

void
ksegrp_link(struct ksegrp *kg, struct proc *p)
{

        TAILQ_INIT(&kg->kg_threads);
        TAILQ_INIT(&kg->kg_runq);       /* links with td_runq */
        TAILQ_INIT(&kg->kg_slpq);       /* links with td_runq */
        TAILQ_INIT(&kg->kg_kseq);       /* all kses in ksegrp */
        TAILQ_INIT(&kg->kg_iq);         /* idle kses in ksegrp */
        TAILQ_INIT(&kg->kg_lq);         /* loan kses in ksegrp */
        kg->kg_proc     = p;
/* the following counters are in the -zero- section and may not need clearing */
        kg->kg_numthreads = 0;
        kg->kg_runnable = 0;
        kg->kg_kses = 0;
        kg->kg_idle_kses = 0;
        kg->kg_loan_kses = 0;
        kg->kg_runq_kses = 0; /* XXXKSE change name */
/* link it in now that it's consistent */
        p->p_numksegrps++;
        TAILQ_INSERT_HEAD(&p->p_ksegrps, kg, kg_ksegrp);
}

void
ksegrp_unlink(struct ksegrp *kg)
{
        struct proc *p;

        mtx_assert(&sched_lock, MA_OWNED);
        p = kg->kg_proc;
        KASSERT(((kg->kg_numthreads == 0) && (kg->kg_kses == 0)),
            ("kseg_unlink: residual threads or KSEs"));
        TAILQ_REMOVE(&p->p_ksegrps, kg, kg_ksegrp);
        p->p_numksegrps--;
        /*
         * Aggregate stats from the KSE
         */
        ksegrp_stash(kg);
}

/*
 * for a newly created process,
 * link up a the structure and its initial threads etc.
 */
void
proc_linkup(struct proc *p, struct ksegrp *kg,
                        struct kse *ke, struct thread *td)
{

        TAILQ_INIT(&p->p_ksegrps);           /* all ksegrps in proc */
        TAILQ_INIT(&p->p_threads);           /* all threads in proc */
        TAILQ_INIT(&p->p_suspended);         /* Threads suspended */
        p->p_numksegrps = 0;
        p->p_numthreads = 0;

        ksegrp_link(kg, p);
        kse_link(ke, kg);
        thread_link(td, kg);
}

int
kse_thr_interrupt(struct thread *td, struct kse_thr_interrupt_args *uap)
{
        struct proc *p;
        struct thread *td2;

        p = td->td_proc;
        /* KSE-enabled processes only, please. */
        if (!(p->p_flag & P_KSES))
                return (EINVAL);
        if (uap->tmbx == NULL)
                return (EINVAL);
        mtx_lock_spin(&sched_lock);
        FOREACH_THREAD_IN_PROC(p, td2) {
                if (td2->td_mailbox == uap->tmbx) {
                        td2->td_flags |= TDF_INTERRUPT;
                        if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR)) {
                                if (td2->td_flags & TDF_CVWAITQ)
                                        cv_abort(td2);
                                else
                                        abortsleep(td2);
                        }       
                        mtx_unlock_spin(&sched_lock);
                        td->td_retval[0] = 0;
                        td->td_retval[1] = 0;
                        return (0);
                }
        }
        mtx_unlock_spin(&sched_lock);
        return (ESRCH);
}

int
kse_exit(struct thread *td, struct kse_exit_args *uap)
{
        struct proc *p;
        struct ksegrp *kg;

        p = td->td_proc;
        /* KSE-enabled processes only, please. */
        if (!(p->p_flag & P_KSES))
                return (EINVAL);
        /* must be a bound thread */ 
        if (td->td_flags & TDF_UNBOUND)
                return (EINVAL);
        kg = td->td_ksegrp;
        /* serialize killing kse */
        PROC_LOCK(p);
        mtx_lock_spin(&sched_lock);
        if ((kg->kg_kses == 1) && (kg->kg_numthreads > 1)) {
                mtx_unlock_spin(&sched_lock);
                PROC_UNLOCK(p);
                return (EDEADLK);
        }
        if ((p->p_numthreads == 1) && (p->p_numksegrps == 1)) {
                p->p_flag &= ~P_KSES;
                mtx_unlock_spin(&sched_lock);
                PROC_UNLOCK(p);
        } else {
                while (mtx_owned(&Giant))
                        mtx_unlock(&Giant);
                td->td_kse->ke_flags |= KEF_EXIT;
                thread_exit();
                /* NOTREACHED */
        }
        return (0);
}

int
kse_release(struct thread *td, struct kse_release_args *uap)
{
        struct proc *p;

        p = td->td_proc;
        /* KSE-enabled processes only */ 
        if (!(p->p_flag & P_KSES))
                return (EINVAL);
        /*
         * Must be a bound thread. And kse must have a mailbox ready,
         * if not, the kse would can not generate an upcall.
         */
        if (!(td->td_flags & TDF_UNBOUND) && (td->td_kse->ke_mailbox != NULL)) {
                PROC_LOCK(p);
                mtx_lock_spin(&sched_lock);
                /* prevent last thread from exiting */
                if (p->p_numthreads == 1) {
                        mtx_unlock_spin(&sched_lock);
                        if (td->td_standin == NULL) {
                                PROC_UNLOCK(p);
                                td->td_standin = thread_alloc();
                                PROC_LOCK(p);
                        }
                        msleep(p->p_sigacts, &p->p_mtx, PPAUSE|PCATCH,
                               "pause", 0); 
                        mtx_lock_spin(&sched_lock);
                        td->td_flags |= TDF_UNBOUND;
                        thread_schedule_upcall(td, td->td_kse);
                }
                thread_exit();
                /* NOTREACHED */
        }
        return (EINVAL);
}

/* struct kse_wakeup_args {
        struct kse_mailbox *mbx;
}; */
int
kse_wakeup(struct thread *td, struct kse_wakeup_args *uap)
{
        struct proc *p;
        struct kse *ke, *ke2;
        struct ksegrp *kg;

        p = td->td_proc;
        /* KSE-enabled processes only, please. */
        if (!(p->p_flag & P_KSES))
                return EINVAL;
        if (td->td_standin == NULL)
                td->td_standin = thread_alloc();
        ke = NULL;
        mtx_lock_spin(&sched_lock);
        if (uap->mbx) {
                FOREACH_KSEGRP_IN_PROC(p, kg) {
                        FOREACH_KSE_IN_GROUP(kg, ke2) {
                                if (ke2->ke_mailbox != uap->mbx) 
                                        continue;
                                if (ke2->ke_state == KES_IDLE) {
                                        ke = ke2;
                                        goto found;
                                } else {
                                        mtx_unlock_spin(&sched_lock);
                                        td->td_retval[0] = 0;
                                        td->td_retval[1] = 0;
                                        return (0);
                                }
                        }       
                }
        } else {
                kg = td->td_ksegrp;
                ke = TAILQ_FIRST(&kg->kg_iq);
        }
        if (ke == NULL) {
                mtx_unlock_spin(&sched_lock);
                return (ESRCH);
        }
found:
        thread_schedule_upcall(td, ke);
        mtx_unlock_spin(&sched_lock);
        td->td_retval[0] = 0;
        td->td_retval[1] = 0;
        return (0);
}

/* 
 * No new KSEG: first call: use current KSE, don't schedule an upcall
 * All other situations, do allocate a new KSE and schedule an upcall on it.
 */
/* struct kse_create_args {
        struct kse_mailbox *mbx;
        int newgroup;
}; */
int
kse_create(struct thread *td, struct kse_create_args *uap)
{
        struct kse *newke;
        struct kse *ke;
        struct ksegrp *newkg;
        struct ksegrp *kg;
        struct proc *p;
        struct kse_mailbox mbx;
        int err;

        p = td->td_proc;
        if ((err = copyin(uap->mbx, &mbx, sizeof(mbx))))
                return (err);

        p->p_flag |= P_KSES; /* easier to just set it than to test and set */
        kg = td->td_ksegrp;
        if (uap->newgroup) {
                if (p->p_numksegrps >= max_groups_per_proc) 
                        return (EPROCLIM);
                /* 
                 * If we want a new KSEGRP it doesn't matter whether
                 * we have already fired up KSE mode before or not.
                 * We put the process in KSE mode and create a new KSEGRP
                 * and KSE. If our KSE has not got a mailbox yet then
                 * that doesn't matter, just leave it that way. It will 
                 * ensure that this thread stay BOUND. It's possible
                 * that the call came form a threaded library and the main 
                 * program knows nothing of threads.
                 */
                newkg = ksegrp_alloc();
                bzero(&newkg->kg_startzero, RANGEOF(struct ksegrp,
                      kg_startzero, kg_endzero)); 
                bcopy(&kg->kg_startcopy, &newkg->kg_startcopy,
                      RANGEOF(struct ksegrp, kg_startcopy, kg_endcopy));
                newke = kse_alloc();
        } else {
                /* 
                 * Otherwise, if we have already set this KSE
                 * to have a mailbox, we want to make another KSE here,
                 * but only if there are not already the limit, which 
                 * is 1 per CPU max.
                 * 
                 * If the current KSE doesn't have a mailbox we just use it
                 * and give it one.
                 *
                 * Because we don't like to access
                 * the KSE outside of schedlock if we are UNBOUND,
                 * (because it can change if we are preempted by an interrupt) 
                 * we can deduce it as having a mailbox if we are UNBOUND,
                 * and only need to actually look at it if we are BOUND,
                 * which is safe.
                 */
                if ((td->td_flags & TDF_UNBOUND) || td->td_kse->ke_mailbox) {
                        if (oiks_debug == 0) {
#ifdef SMP
                        if (kg->kg_kses > mp_ncpus)
#endif
                                return (EPROCLIM);
                        }
                        newke = kse_alloc();
                } else {
                        newke = NULL;
                }
                newkg = NULL;
        }
        if (newke) {
                bzero(&newke->ke_startzero, RANGEOF(struct kse,
                      ke_startzero, ke_endzero));
#if 0
                bcopy(&ke->ke_startcopy, &newke->ke_startcopy,
                      RANGEOF(struct kse, ke_startcopy, ke_endcopy));
#endif
                /* For the first call this may not have been set */
                if (td->td_standin == NULL) {
                        td->td_standin = thread_alloc();
                }
                mtx_lock_spin(&sched_lock);
                if (newkg) {
                        if (p->p_numksegrps >= max_groups_per_proc) {
                                mtx_unlock_spin(&sched_lock);
                                ksegrp_free(newkg); 
                                kse_free(newke);
                                return (EPROCLIM);
                        }
                        ksegrp_link(newkg, p);
                }
                else
                        newkg = kg;
                kse_link(newke, newkg);
                if (p->p_sflag & PS_NEEDSIGCHK)
                        newke->ke_flags |= KEF_ASTPENDING;
                newke->ke_mailbox = uap->mbx;
                newke->ke_upcall = mbx.km_func;
                bcopy(&mbx.km_stack, &newke->ke_stack, sizeof(stack_t));
                thread_schedule_upcall(td, newke);
                mtx_unlock_spin(&sched_lock);
        } else {
                /*
                 * If we didn't allocate a new KSE then the we are using
                 * the exisiting (BOUND) kse.
                 */
                ke = td->td_kse;
                ke->ke_mailbox = uap->mbx;
                ke->ke_upcall = mbx.km_func;
                bcopy(&mbx.km_stack, &ke->ke_stack, sizeof(stack_t));
        }
        /*
         * Fill out the KSE-mode specific fields of the new kse.
         */

        td->td_retval[0] = 0;
        td->td_retval[1] = 0;
        return (0);
}

/*
 * Fill a ucontext_t with a thread's context information.
 *
 * This is an analogue to getcontext(3).
 */
void
thread_getcontext(struct thread *td, ucontext_t *uc)
{

/*
 * XXX this is declared in a MD include file, i386/include/ucontext.h but
 * is used in MI code.
 */
#ifdef __i386__
        get_mcontext(td, &uc->uc_mcontext);
#endif
        uc->uc_sigmask = td->td_proc->p_sigmask;
}

/*
 * Set a thread's context from a ucontext_t.
 *
 * This is an analogue to setcontext(3).
 */
int
thread_setcontext(struct thread *td, ucontext_t *uc)
{
        int ret;

/*
 * XXX this is declared in a MD include file, i386/include/ucontext.h but
 * is used in MI code.
 */
#ifdef __i386__
        ret = set_mcontext(td, &uc->uc_mcontext);
#else
        ret = ENOSYS;
#endif
        if (ret == 0) {
                SIG_CANTMASK(uc->uc_sigmask);
                PROC_LOCK(td->td_proc);
                td->td_proc->p_sigmask = uc->uc_sigmask;
                PROC_UNLOCK(td->td_proc);
        }
        return (ret);
}

/*
 * Initialize global thread allocation resources.
 */
void
threadinit(void)
{

#ifndef __ia64__
        thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
            thread_ctor, thread_dtor, thread_init, thread_fini,
            UMA_ALIGN_CACHE, 0);
#else
        /*
         * XXX the ia64 kstack allocator is really lame and is at the mercy
         * of contigmallloc().  This hackery is to pre-construct a whole
         * pile of thread structures with associated kernel stacks early
         * in the system startup while contigmalloc() still works. Once we
         * have them, keep them.  Sigh.
         */
        thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
            thread_ctor, thread_dtor, thread_init, thread_fini,
            UMA_ALIGN_CACHE, UMA_ZONE_NOFREE);
        uma_prealloc(thread_zone, 512);         /* XXX arbitary */
#endif
        ksegrp_zone = uma_zcreate("KSEGRP", sched_sizeof_ksegrp(),
            NULL, NULL, ksegrp_init, NULL,
            UMA_ALIGN_CACHE, 0);
        kse_zone = uma_zcreate("KSE", sched_sizeof_kse(),
            NULL, NULL, kse_init, NULL,
            UMA_ALIGN_CACHE, 0);
}

/*
 * Stash an embarasingly extra thread into the zombie thread queue.
 */
void
thread_stash(struct thread *td)
{
        mtx_lock_spin(&zombie_thread_lock);
        TAILQ_INSERT_HEAD(&zombie_threads, td, td_runq);
        mtx_unlock_spin(&zombie_thread_lock);
}

/*
 * Stash an embarasingly extra kse into the zombie kse queue.
 */
void
kse_stash(struct kse *ke)
{
        mtx_lock_spin(&zombie_thread_lock);
        TAILQ_INSERT_HEAD(&zombie_kses, ke, ke_procq);
        mtx_unlock_spin(&zombie_thread_lock);
}

/*
 * Stash an embarasingly extra ksegrp into the zombie ksegrp queue.
 */
void
ksegrp_stash(struct ksegrp *kg)
{
        mtx_lock_spin(&zombie_thread_lock);
        TAILQ_INSERT_HEAD(&zombie_ksegrps, kg, kg_ksegrp);
        mtx_unlock_spin(&zombie_thread_lock);
}

/*
 * Reap zombie threads.
 */
void
thread_reap(void)
{
        struct thread *td_first, *td_next;
        struct kse *ke_first, *ke_next;
        struct ksegrp *kg_first, * kg_next;

        /*
         * don't even bother to lock if none at this instant
         * We really don't care about the next instant..
         */
        if ((!TAILQ_EMPTY(&zombie_threads))
            || (!TAILQ_EMPTY(&zombie_kses))
            || (!TAILQ_EMPTY(&zombie_ksegrps))) {
                mtx_lock_spin(&zombie_thread_lock);
                td_first = TAILQ_FIRST(&zombie_threads);
                ke_first = TAILQ_FIRST(&zombie_kses);
                kg_first = TAILQ_FIRST(&zombie_ksegrps);
                if (td_first)
                        TAILQ_INIT(&zombie_threads);
                if (ke_first)
                        TAILQ_INIT(&zombie_kses);
                if (kg_first)
                        TAILQ_INIT(&zombie_ksegrps);
                mtx_unlock_spin(&zombie_thread_lock);
                while (td_first) {
                        td_next = TAILQ_NEXT(td_first, td_runq);
                        thread_free(td_first);
                        td_first = td_next;
                }
                while (ke_first) {
                        ke_next = TAILQ_NEXT(ke_first, ke_procq);
                        kse_free(ke_first);
                        ke_first = ke_next;
                }
                while (kg_first) {
                        kg_next = TAILQ_NEXT(kg_first, kg_ksegrp);
                        ksegrp_free(kg_first);
                        kg_first = kg_next;
                }
        }
}

/*
 * Allocate a ksegrp.
 */
struct ksegrp *
ksegrp_alloc(void)
{
        return (uma_zalloc(ksegrp_zone, M_WAITOK));
}

/*
 * Allocate a kse.
 */
struct kse *
kse_alloc(void)
{
        return (uma_zalloc(kse_zone, M_WAITOK));
}

/*
 * Allocate a thread.
 */
struct thread *
thread_alloc(void)
{
        thread_reap(); /* check if any zombies to get */
        return (uma_zalloc(thread_zone, M_WAITOK));
}

/*
 * Deallocate a ksegrp.
 */
void
ksegrp_free(struct ksegrp *td)
{
        uma_zfree(ksegrp_zone, td);
}

/*
 * Deallocate a kse.
 */
void
kse_free(struct kse *td)
{
        uma_zfree(kse_zone, td);
}

/*
 * Deallocate a thread.
 */
void
thread_free(struct thread *td)
{
        uma_zfree(thread_zone, td);
}

/*
 * Store the thread context in the UTS's mailbox.
 * then add the mailbox at the head of a list we are building in user space.
 * The list is anchored in the ksegrp structure.
 */
int
thread_export_context(struct thread *td)
{
        struct proc *p;
        struct ksegrp *kg;
        uintptr_t mbx;
        void *addr;
        int error;
        ucontext_t uc;
        uint temp;

        p = td->td_proc;
        kg = td->td_ksegrp;

        /* Export the user/machine context. */
#if 0
        addr = (caddr_t)td->td_mailbox +
            offsetof(struct kse_thr_mailbox, tm_context);
#else /* if user pointer arithmetic is valid in the kernel */
                addr = (void *)(&td->td_mailbox->tm_context);
#endif
        error = copyin(addr, &uc, sizeof(ucontext_t));
        if (error == 0) {
                thread_getcontext(td, &uc);
                error = copyout(&uc, addr, sizeof(ucontext_t));

        }
        if (error) {
                PROC_LOCK(p);
                psignal(p, SIGSEGV);
                PROC_UNLOCK(p);
                return (error);
        }
        /* get address in latest mbox of list pointer */
#if 0
        addr = (caddr_t)td->td_mailbox
            + offsetof(struct kse_thr_mailbox , tm_next);
#else /* if user pointer arithmetic is valid in the kernel */
        addr = (void *)(&td->td_mailbox->tm_next);
#endif
        /*
         * Put the saved address of the previous first
         * entry into this one
         */
        for (;;) {
                mbx = (uintptr_t)kg->kg_completed;
                if (suword(addr, mbx)) {
                        goto bad;
                }
                PROC_LOCK(p);
                if (mbx == (uintptr_t)kg->kg_completed) {
                        kg->kg_completed = td->td_mailbox;
                        PROC_UNLOCK(p);
                        break;
                }
                PROC_UNLOCK(p);
        }
        addr = (caddr_t)td->td_mailbox
                 + offsetof(struct kse_thr_mailbox, tm_sticks);
        temp = fuword(addr) + td->td_usticks;
        if (suword(addr, temp))
                goto bad;
        return (0);

bad:
        PROC_LOCK(p);
        psignal(p, SIGSEGV);
        PROC_UNLOCK(p);
        return (EFAULT);
}

/*
 * Take the list of completed mailboxes for this KSEGRP and put them on this
 * KSE's mailbox as it's the next one going up.
 */
static int
thread_link_mboxes(struct ksegrp *kg, struct kse *ke)
{
        struct proc *p = kg->kg_proc;
        void *addr;
        uintptr_t mbx;

#if 0
        addr = (caddr_t)ke->ke_mailbox
            + offsetof(struct kse_mailbox, km_completed);
#else /* if user pointer arithmetic is valid in the kernel */
                addr = (void *)(&ke->ke_mailbox->km_completed);
#endif
        for (;;) {
                mbx = (uintptr_t)kg->kg_completed;
                if (suword(addr, mbx)) {
                        PROC_LOCK(p);
                        psignal(p, SIGSEGV);
                        PROC_UNLOCK(p);
                        return (EFAULT);
                }
                /* XXXKSE could use atomic CMPXCH here */
                PROC_LOCK(p);
                if (mbx == (uintptr_t)kg->kg_completed) {
                        kg->kg_completed = NULL;
                        PROC_UNLOCK(p);
                        break;
                }
                PROC_UNLOCK(p);
        }
        return (0);
}

/*
 * This function should be called at statclock interrupt time
 */
int
thread_add_ticks_intr(int user, uint ticks)
{
        struct thread *td = curthread;
        struct kse *ke = td->td_kse;
        
        if (ke->ke_mailbox == NULL)
                return -1;
        if (user) {
                /* Current always do via ast() */
                ke->ke_flags |= KEF_ASTPENDING;
                ke->ke_uuticks += ticks;
        } else {
                if (td->td_mailbox != NULL)
                        td->td_usticks += ticks;
                else 
                        ke->ke_usticks += ticks;
        }
        return 0;
}

static int
thread_update_uticks(void)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct kse *ke = td->td_kse;
        struct kse_thr_mailbox *tmbx;
        caddr_t addr;
        uint uticks, sticks;

        KASSERT(!(td->td_flags & TDF_UNBOUND), ("thread not bound."));

        if (ke->ke_mailbox == NULL)
                return 0;

        uticks = ke->ke_uuticks;
        ke->ke_uuticks = 0;
        sticks = ke->ke_usticks;
        ke->ke_usticks = 0;
        tmbx = (void *)fuword((caddr_t)ke->ke_mailbox
                        + offsetof(struct kse_mailbox, km_curthread));
        if ((tmbx == NULL) || (tmbx == (void *)-1))
                return 0;
        if (uticks) {
                addr = (caddr_t)tmbx + offsetof(struct kse_thr_mailbox, tm_uticks);
                uticks += fuword(addr);
                if (suword(addr, uticks))
                        goto bad;
        }
        if (sticks) {
                addr = (caddr_t)tmbx + offsetof(struct kse_thr_mailbox, tm_sticks);
                sticks += fuword(addr);
                if (suword(addr, sticks))
                        goto bad;
        }
        return 0;
bad:
        PROC_LOCK(p);
        psignal(p, SIGSEGV);
        PROC_UNLOCK(p);
        return -1;
}

/*
 * Discard the current thread and exit from its context.
 *
 * Because we can't free a thread while we're operating under its context,
 * push the current thread into our KSE's ke_tdspare slot, freeing the
 * thread that might be there currently. Because we know that only this
 * processor will run our KSE, we needn't worry about someone else grabbing
 * our context before we do a cpu_throw.
 */
void
thread_exit(void)
{
        struct thread *td;
        struct kse *ke;
        struct proc *p;
        struct ksegrp   *kg;

        td = curthread;
        kg = td->td_ksegrp;
        p = td->td_proc;
        ke = td->td_kse;

        mtx_assert(&sched_lock, MA_OWNED);
        KASSERT(p != NULL, ("thread exiting without a process"));
        KASSERT(ke != NULL, ("thread exiting without a kse"));
        KASSERT(kg != NULL, ("thread exiting without a kse group"));
        PROC_LOCK_ASSERT(p, MA_OWNED);
        CTR1(KTR_PROC, "thread_exit: thread %p", td);
        KASSERT(!mtx_owned(&Giant), ("dying thread owns giant"));

        if (ke->ke_tdspare != NULL) {
                thread_stash(ke->ke_tdspare);
                ke->ke_tdspare = NULL;
        }
        if (td->td_standin != NULL) {
                thread_stash(td->td_standin);
                td->td_standin = NULL;
        }

        cpu_thread_exit(td);    /* XXXSMP */

        /*
         * The last thread is left attached to the process
         * So that the whole bundle gets recycled. Skip
         * all this stuff.
         */
        if (p->p_numthreads > 1) {
                /*
                 * Unlink this thread from its proc and the kseg.
                 * In keeping with the other structs we probably should
                 * have a thread_unlink() that does some of this but it
                 * would only be called from here (I think) so it would
                 * be a waste. (might be useful for proc_fini() as well.)
                 */
                TAILQ_REMOVE(&p->p_threads, td, td_plist);
                p->p_numthreads--;
                TAILQ_REMOVE(&kg->kg_threads, td, td_kglist);
                kg->kg_numthreads--;
                /*
                 * The test below is NOT true if we are the
                 * sole exiting thread. P_STOPPED_SNGL is unset
                 * in exit1() after it is the only survivor.
                 */
                if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                        if (p->p_numthreads == p->p_suspcount) {
                                thread_unsuspend_one(p->p_singlethread);
                        }
                }

                /* Reassign this thread's KSE. */
                ke->ke_thread = NULL;
                td->td_kse = NULL;
                ke->ke_state = KES_UNQUEUED;
                KASSERT((ke->ke_bound != td),
                    ("thread_exit: entered with ke_bound set"));

                /* 
                 * The reason for all this hoopla is 
                 * an attempt to stop our thread stack from being freed 
                 * until AFTER we have stopped running on it.
                 * Since we are under schedlock, almost any method where
                 * it is eventually freed by someone else is probably ok.
                 * (Especially if they do it under schedlock). We could 
                 * almost free it here if we could be certain that 
                 * the uma code wouldn't pull it apart immediatly, 
                 * but unfortunatly we can not guarantee that.
                 *
                 * For threads that are exiting and NOT killing their
                 * KSEs we can just stash it in the KSE, however
                 * in the case where the KSE is also being deallocated,
                 * we need to store it somewhere else. It turns out that
                 * we will never free the last KSE, so there is always one
                 * other KSE available. We might as well just choose one
                 * and stash it there. Being under schedlock should make that
                 * safe.
                 *
                 * In borrower threads, we can stash it in the lender
                 * Where it won't be needed until this thread is long gone.
                 * Borrower threads can't kill their KSE anyhow, so even
                 * the KSE would be a safe place for them. It is not
                 * necessary to have a KSE (or KSEGRP) at all beyond this
                 * point, while we are under the protection of schedlock.
                 *
                 * Either give the KSE to another thread to use (or make
                 * it idle), or free it entirely, possibly along with its
                 * ksegrp if it's the last one.
                 */
                if (ke->ke_flags & KEF_EXIT) {
                        kse_unlink(ke);
                        /*
                         * Designate another KSE to hold our thread.
                         * Safe as long as we abide by whatever lock 
                         * we control it with.. The other KSE will not
                         * be able to run it until we release the schelock,
                         * but we need to be careful about it deciding to 
                         * write to the stack before then. Luckily
                         * I believe that while another thread's
                         * standin thread can be used in this way, the
                         * spare thread for the KSE cannot be used without
                         * holding schedlock at least once.
                         */
                        ke =  FIRST_KSE_IN_PROC(p);
                } else {
                        kse_reassign(ke);
                }
#if 0
                if (ke->ke_bound) {
                        /*
                         * WE are a borrower..
                         * stash our thread with the owner.
                         */
                        if (ke->ke_bound->td_standin) {
                                thread_stash(ke->ke_bound->td_standin);
                        }
                        ke->ke_bound->td_standin = td;
                } else {
#endif
                        if (ke->ke_tdspare != NULL) {
                                thread_stash(ke->ke_tdspare);
                                ke->ke_tdspare = NULL;
                        }
                        ke->ke_tdspare = td;
#if 0
                }
#endif
                PROC_UNLOCK(p);
                td->td_state    = TDS_INACTIVE;
                td->td_proc     = NULL;
                td->td_ksegrp   = NULL;
                td->td_last_kse = NULL;
        } else {
                PROC_UNLOCK(p);
        }

        cpu_throw();
        /* NOTREACHED */
}

/*
 * Link a thread to a process.
 * set up anything that needs to be initialized for it to
 * be used by the process.
 *
 * Note that we do not link to the proc's ucred here.
 * The thread is linked as if running but no KSE assigned.
 */
void
thread_link(struct thread *td, struct ksegrp *kg)
{
        struct proc *p;

        p = kg->kg_proc;
        td->td_state = TDS_INACTIVE;
        td->td_proc     = p;
        td->td_ksegrp   = kg;
        td->td_last_kse = NULL;

        LIST_INIT(&td->td_contested);
        callout_init(&td->td_slpcallout, 1);
        TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
        TAILQ_INSERT_HEAD(&kg->kg_threads, td, td_kglist);
        p->p_numthreads++;
        kg->kg_numthreads++;
        if (oiks_debug && (p->p_numthreads > oiks_max_threads_per_proc)) {
                printf("OIKS %d\n", p->p_numthreads);
                if (oiks_debug > 1)
                        Debugger("OIKS");
        }
        td->td_kse      = NULL;
}

void
kse_purge(struct proc *p, struct thread *td)
{
        struct kse *ke;
        struct ksegrp *kg;

        KASSERT(p->p_numthreads == 1, ("bad thread number"));
        mtx_lock_spin(&sched_lock);
        while ((kg = TAILQ_FIRST(&p->p_ksegrps)) != NULL) {
                while ((ke = TAILQ_FIRST(&kg->kg_iq)) != NULL) {
                        TAILQ_REMOVE(&kg->kg_iq, ke, ke_kgrlist);
                        kg->kg_idle_kses--;
                        TAILQ_REMOVE(&kg->kg_kseq, ke, ke_kglist);
                        kg->kg_kses--;
                        if (ke->ke_tdspare)
                                thread_stash(ke->ke_tdspare);
                        kse_stash(ke);
                }
                TAILQ_REMOVE(&p->p_ksegrps, kg, kg_ksegrp);
                p->p_numksegrps--;
                KASSERT(((kg->kg_kses == 0) && (kg != td->td_ksegrp)) ||
                    ((kg->kg_kses == 1) && (kg == td->td_ksegrp)),
                        ("wrong kg_kses"));
                if (kg != td->td_ksegrp) {
                        ksegrp_stash(kg);
                }
        }
        TAILQ_INSERT_HEAD(&p->p_ksegrps, td->td_ksegrp, kg_ksegrp);
        p->p_numksegrps++;
        mtx_unlock_spin(&sched_lock);
}


/*
 * Create a thread and schedule it for upcall on the KSE given.
 */
struct thread *
thread_schedule_upcall(struct thread *td, struct kse *ke)
{
        struct thread *td2;
        struct ksegrp *kg;
        int newkse;

        mtx_assert(&sched_lock, MA_OWNED);
        newkse = (ke != td->td_kse);

        /* 
         * If the kse is already owned by another thread then we can't
         * schedule an upcall because the other thread must be BOUND
         * which means it is not in a position to take an upcall.
         * We must be borrowing the KSE to allow us to complete some in-kernel
         * work. When we complete, the Bound thread will have teh chance to 
         * complete. This thread will sleep as planned. Hopefully there will
         * eventually be un unbound thread that can be converted to an
         * upcall to report the completion of this thread.
         */
        if (ke->ke_bound && ((ke->ke_bound->td_flags & TDF_UNBOUND) == 0)) {
                return (NULL);
        }
        KASSERT((ke->ke_bound == NULL), ("kse already bound"));

        if (ke->ke_state == KES_IDLE) {
                kg = ke->ke_ksegrp;
                TAILQ_REMOVE(&kg->kg_iq, ke, ke_kgrlist);
                kg->kg_idle_kses--;
                ke->ke_state = KES_UNQUEUED;
        }
        if ((td2 = td->td_standin) != NULL) {
                td->td_standin = NULL;
        } else {
                if (newkse)
                        panic("no reserve thread when called with a new kse");
                /*
                 * If called from (e.g.) sleep and we do not have
                 * a reserve thread, then we've used it, so do not
                 * create an upcall.
                 */
                return (NULL);
        }
        CTR3(KTR_PROC, "thread_schedule_upcall: thread %p (pid %d, %s)",
             td2, td->td_proc->p_pid, td->td_proc->p_comm);
        bzero(&td2->td_startzero,
            (unsigned)RANGEOF(struct thread, td_startzero, td_endzero));
        bcopy(&td->td_startcopy, &td2->td_startcopy,
            (unsigned) RANGEOF(struct thread, td_startcopy, td_endcopy));
        thread_link(td2, ke->ke_ksegrp);
        cpu_set_upcall(td2, td->td_pcb);

        /*
         * XXXKSE do we really need this? (default values for the
         * frame).
         */
        bcopy(td->td_frame, td2->td_frame, sizeof(struct trapframe));

        /*
         * Bind the new thread to the KSE,
         * and if it's our KSE, lend it back to ourself
         * so we can continue running.
         */
        td2->td_ucred = crhold(td->td_ucred);
        td2->td_flags = TDF_UPCALLING; /* note: BOUND */
        td2->td_kse = ke;
        td2->td_state = TDS_CAN_RUN;
        td2->td_inhibitors = 0;
        /*
         * If called from msleep(), we are working on the current
         * KSE so fake that we borrowed it. If called from
         * kse_create(), don't, as we have a new kse too.
         */
        if (!newkse) {
                /*
                 * This thread will be scheduled when the current thread
                 * blocks, exits or tries to enter userspace, (which ever
                 * happens first). When that happens the KSe will "revert"
                 * to this thread in a BOUND manner. Since we are called
                 * from msleep() this is going to be "very soon" in nearly
                 * all cases.
                 */
                ke->ke_bound = td2;
                TD_SET_LOAN(td2);
        } else {
                ke->ke_bound = NULL;
                ke->ke_thread = td2;
                ke->ke_state = KES_THREAD;
                setrunqueue(td2);
        }
        return (td2);   /* bogus.. should be a void function */
}

/*
 * Schedule an upcall to notify a KSE process recieved signals.
 *
 * XXX - Modifying a sigset_t like this is totally bogus.
 */
struct thread *
signal_upcall(struct proc *p, int sig)
{
        struct thread *td, *td2;
        struct kse *ke;
        sigset_t ss;
        int error;

        PROC_LOCK_ASSERT(p, MA_OWNED);
return (NULL);

        td = FIRST_THREAD_IN_PROC(p);
        ke = td->td_kse;
        PROC_UNLOCK(p);
        error = copyin(&ke->ke_mailbox->km_sigscaught, &ss, sizeof(sigset_t));
        PROC_LOCK(p);
        if (error)
                return (NULL);
        SIGADDSET(ss, sig);
        PROC_UNLOCK(p);
        error = copyout(&ss, &ke->ke_mailbox->km_sigscaught, sizeof(sigset_t));
        PROC_LOCK(p);
        if (error)
                return (NULL);
        if (td->td_standin == NULL)
                td->td_standin = thread_alloc();
        mtx_lock_spin(&sched_lock);
        td2 = thread_schedule_upcall(td, ke); /* Bogus JRE */
        mtx_unlock_spin(&sched_lock);
        return (td2);
}

/*
 * setup done on the thread when it enters the kernel.
 * XXXKSE Presently only for syscalls but eventually all kernel entries.
 */
void
thread_user_enter(struct proc *p, struct thread *td)
{
        struct kse *ke;

        /*
         * First check that we shouldn't just abort.
         * But check if we are the single thread first!
         * XXX p_singlethread not locked, but should be safe.
         */
        if ((p->p_flag & P_WEXIT) && (p->p_singlethread != td)) {
                PROC_LOCK(p);
                mtx_lock_spin(&sched_lock);
                thread_exit();
                /* NOTREACHED */
        }

        /*
         * If we are doing a syscall in a KSE environment,
         * note where our mailbox is. There is always the
         * possibility that we could do this lazily (in sleep()),
         * but for now do it every time.
         */
        ke = td->td_kse;
        if (ke->ke_mailbox != NULL) {
#if 0
                td->td_mailbox = (void *)fuword((caddr_t)ke->ke_mailbox
                    + offsetof(struct kse_mailbox, km_curthread));
#else /* if user pointer arithmetic is ok in the kernel */
                td->td_mailbox =
                    (void *)fuword( (void *)&ke->ke_mailbox->km_curthread);
#endif
                if ((td->td_mailbox == NULL) ||
                    (td->td_mailbox == (void *)-1)) {
                        td->td_mailbox = NULL;  /* single thread it.. */
                        mtx_lock_spin(&sched_lock);
                        td->td_flags &= ~TDF_UNBOUND;
                        mtx_unlock_spin(&sched_lock);
                } else {
                        /* 
                         * when thread limit reached, act like that the thread
                         * has already done an upcall.
                         */
                        if (p->p_numthreads > max_threads_per_proc) {
                                if (td->td_standin != NULL)
                                        thread_stash(td->td_standin);
                                td->td_standin = NULL;
                        } else {
                                if (td->td_standin == NULL)
                                        td->td_standin = thread_alloc();
                        }
                        mtx_lock_spin(&sched_lock);
                        td->td_flags |= TDF_UNBOUND;
                        mtx_unlock_spin(&sched_lock);
                        td->td_usticks = 0;
                }
        }
}

/*
 * The extra work we go through if we are a threaded process when we
 * return to userland.
 *
 * If we are a KSE process and returning to user mode, check for
 * extra work to do before we return (e.g. for more syscalls
 * to complete first).  If we were in a critical section, we should
 * just return to let it finish. Same if we were in the UTS (in
 * which case the mailbox's context's busy indicator will be set).
 * The only traps we suport will have set the mailbox.
 * We will clear it here.
 */
int
thread_userret(struct thread *td, struct trapframe *frame)
{
        int error;
        int unbound;
        struct kse *ke;
        struct ksegrp *kg;
        struct thread *td2;
        struct proc *p;
        struct timespec ts;

        error = 0;

        unbound = td->td_flags & TDF_UNBOUND;

        kg = td->td_ksegrp;
        p = td->td_proc;

        /*
         * Originally bound threads never upcall but they may 
         * loan out their KSE at this point.
         * Upcalls imply bound.. They also may want to do some Philantropy.
         * Unbound threads on the other hand either yield to other work
         * or transform into an upcall.
         * (having saved their context to user space in both cases)
         */
        if (unbound) {
                /*
                 * We are an unbound thread, looking to return to 
                 * user space.
                 * THere are several possibilities:
                 * 1) we are using a borrowed KSE. save state and exit.
                 *    kse_reassign() will recycle the kse as needed,
                 * 2) we are not.. save state, and then convert ourself
                 *    to be an upcall, bound to the KSE.
                 *    if there are others that need the kse,
                 *    give them a chance by doing an mi_switch().
                 *    Because we are bound, control will eventually return
                 *    to us here.
                 * ***
                 * Save the thread's context, and link it
                 * into the KSEGRP's list of completed threads.
                 */
                error = thread_export_context(td);
                td->td_mailbox = NULL;
                td->td_usticks = 0;
                if (error) {
                        /*
                         * If we are not running on a borrowed KSE, then
                         * failing to do the KSE operation just defaults
                         * back to synchonous operation, so just return from
                         * the syscall. If it IS borrowed, there is nothing
                         * we can do. We just lose that context. We
                         * probably should note this somewhere and send
                         * the process a signal.
                         */
                        PROC_LOCK(td->td_proc);
                        psignal(td->td_proc, SIGSEGV);
                        mtx_lock_spin(&sched_lock);
                        if (td->td_kse->ke_bound == NULL) {
                                td->td_flags &= ~TDF_UNBOUND;
                                PROC_UNLOCK(td->td_proc);
                                mtx_unlock_spin(&sched_lock);
                                thread_update_uticks();
                                return (error); /* go sync */
                        }
                        thread_exit();
                }

                /*
                 * if the KSE is owned and we are borrowing it,
                 * don't make an upcall, just exit so that the owner
                 * can get its KSE if it wants it.
                 * Our context is already safely stored for later
                 * use by the UTS.
                 */
                PROC_LOCK(p);
                mtx_lock_spin(&sched_lock);
                if (td->td_kse->ke_bound) {
                        thread_exit();
                }
                PROC_UNLOCK(p);
                                
                /*
                 * Turn ourself into a bound upcall.
                 * We will rely on kse_reassign()
                 * to make us run at a later time.
                 * We should look just like a sheduled upcall
                 * from msleep() or cv_wait().
                 */
                td->td_flags &= ~TDF_UNBOUND;
                td->td_flags |= TDF_UPCALLING;
                /* Only get here if we have become an upcall */

        } else {
                mtx_lock_spin(&sched_lock);
        }
        /* 
         * We ARE going back to userland with this KSE.
         * Check for threads that need to borrow it.
         * Optimisation: don't call mi_switch if no-one wants the KSE.
         * Any other thread that comes ready after this missed the boat.
         */
        ke = td->td_kse;
        if ((td2 = kg->kg_last_assigned)) 
                td2 = TAILQ_NEXT(td2, td_runq);
        else
                td2 = TAILQ_FIRST(&kg->kg_runq);
        if (td2)  {
                /* 
                 * force a switch to more urgent 'in kernel'
                 * work. Control will return to this thread
                 * when there is no more work to do.
                 * kse_reassign() will do tha for us.
                 */
                TD_SET_LOAN(td);
                ke->ke_bound = td;
                ke->ke_thread = NULL;
                mi_switch(); /* kse_reassign() will (re)find td2 */
        }
        mtx_unlock_spin(&sched_lock);

        /*
         * Optimisation:
         * Ensure that we have a spare thread available,
         * for when we re-enter the kernel.
         */
        if (td->td_standin == NULL) {
                if (ke->ke_tdspare) {
                        td->td_standin = ke->ke_tdspare;
                        ke->ke_tdspare = NULL;
                } else {
                        td->td_standin = thread_alloc();
                }
        }

        thread_update_uticks();
        /* 
         * To get here, we know there is no other need for our
         * KSE so we can proceed. If not upcalling, go back to 
         * userspace. If we are, get the upcall set up.
         */
        if ((td->td_flags & TDF_UPCALLING) == 0)
                return (0);

        /* 
         * We must be an upcall to get this far.
         * There is no more work to do and we are going to ride
         * this thead/KSE up to userland as an upcall.
         * Do the last parts of the setup needed for the upcall.
         */
        CTR3(KTR_PROC, "userret: upcall thread %p (pid %d, %s)",
            td, td->td_proc->p_pid, td->td_proc->p_comm);

        /*
         * Set user context to the UTS.
         */
        cpu_set_upcall_kse(td, ke);

        /*
         * Put any completed mailboxes on this KSE's list.
         */
        error = thread_link_mboxes(kg, ke);
        if (error)
                goto bad;

        /*
         * Set state and mailbox.
         * From now on we are just a bound outgoing process.
         * **Problem** userret is often called several times.
         * it would be nice if this all happenned only on the first time 
         * through. (the scan for extra work etc.)
         */
        mtx_lock_spin(&sched_lock);
        td->td_flags &= ~TDF_UPCALLING;
        mtx_unlock_spin(&sched_lock);
#if 0
        error = suword((caddr_t)ke->ke_mailbox +
            offsetof(struct kse_mailbox, km_curthread), 0);
#else   /* if user pointer arithmetic is ok in the kernel */
        error = suword((caddr_t)&ke->ke_mailbox->km_curthread, 0);
#endif
        ke->ke_uuticks = ke->ke_usticks = 0;
        if (!error) {
                nanotime(&ts);
                if (copyout(&ts, (caddr_t)&ke->ke_mailbox->km_timeofday,
                    sizeof(ts))) {
                        goto bad;
                }
        }
        return (0);

bad:
        /*
         * Things are going to be so screwed we should just kill the process.
         * how do we do that?
         */
        PROC_LOCK(td->td_proc);
        psignal(td->td_proc, SIGSEGV);
        PROC_UNLOCK(td->td_proc);
        return (error); /* go sync */
}

/*
 * Enforce single-threading.
 *
 * Returns 1 if the caller must abort (another thread is waiting to
 * exit the process or similar). Process is locked!
 * Returns 0 when you are successfully the only thread running.
 * A process has successfully single threaded in the suspend mode when
 * There are no threads in user mode. Threads in the kernel must be
 * allowed to continue until they get to the user boundary. They may even
 * copy out their return values and data before suspending. They may however be
 * accellerated in reaching the user boundary as we will wake up
 * any sleeping threads that are interruptable. (PCATCH).
 */
int
thread_single(int force_exit)
{
        struct thread *td;
        struct thread *td2;
        struct proc *p;

        td = curthread;
        p = td->td_proc;
        PROC_LOCK_ASSERT(p, MA_OWNED);
        KASSERT((td != NULL), ("curthread is NULL"));

        if ((p->p_flag & P_KSES) == 0)
                return (0);

        /* Is someone already single threading? */
        if (p->p_singlethread) 
                return (1);

        if (force_exit == SINGLE_EXIT)
                p->p_flag |= P_SINGLE_EXIT;
        else
                p->p_flag &= ~P_SINGLE_EXIT;
        p->p_flag |= P_STOPPED_SINGLE;
        p->p_singlethread = td;
        /* XXXKSE Which lock protects the below values? */
        while ((p->p_numthreads - p->p_suspcount) != 1) {
                mtx_lock_spin(&sched_lock);
                FOREACH_THREAD_IN_PROC(p, td2) {
                        if (td2 == td)
                                continue;
                        if (TD_IS_INHIBITED(td2)) {
                                if (force_exit == SINGLE_EXIT) {
                                        if (TD_IS_SUSPENDED(td2)) {
                                                thread_unsuspend_one(td2);
                                        }
                                        if (TD_ON_SLEEPQ(td2) &&
                                            (td2->td_flags & TDF_SINTR)) {
                                                if (td2->td_flags & TDF_CVWAITQ)
                                                        cv_abort(td2);
                                                else
                                                        abortsleep(td2);
                                        }
                                } else {
                                        if (TD_IS_SUSPENDED(td2))
                                                continue;
                                        /* maybe other inhibitted states too? */
                                        if (TD_IS_SLEEPING(td2)) 
                                                thread_suspend_one(td2);
                                }
                        }
                }
                /* 
                 * Maybe we suspended some threads.. was it enough? 
                 */
                if ((p->p_numthreads - p->p_suspcount) == 1) {
                        mtx_unlock_spin(&sched_lock);
                        break;
                }

                /*
                 * Wake us up when everyone else has suspended.
                 * In the mean time we suspend as well.
                 */
                thread_suspend_one(td);
                mtx_unlock(&Giant);
                PROC_UNLOCK(p);
                mi_switch();
                mtx_unlock_spin(&sched_lock);
                mtx_lock(&Giant);
                PROC_LOCK(p);
        }
        if (force_exit == SINGLE_EXIT)
                kse_purge(p, td);
        return (0);
}

/*
 * Called in from locations that can safely check to see
 * whether we have to suspend or at least throttle for a
 * single-thread event (e.g. fork).
 *
 * Such locations include userret().
 * If the "return_instead" argument is non zero, the thread must be able to
 * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 *
 * The 'return_instead' argument tells the function if it may do a
 * thread_exit() or suspend, or whether the caller must abort and back
 * out instead.
 *
 * If the thread that set the single_threading request has set the
 * P_SINGLE_EXIT bit in the process flags then this call will never return
 * if 'return_instead' is false, but will exit.
 *
 * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 *---------------+--------------------+---------------------
 *       0       | returns 0          |   returns 0 or 1
 *               | when ST ends       |   immediatly
 *---------------+--------------------+---------------------
 *       1       | thread exits       |   returns 1
 *               |                    |  immediatly
 * 0 = thread_exit() or suspension ok,
 * other = return error instead of stopping the thread.
 *
 * While a full suspension is under effect, even a single threading
 * thread would be suspended if it made this call (but it shouldn't).
 * This call should only be made from places where
 * thread_exit() would be safe as that may be the outcome unless 
 * return_instead is set.
 */
int
thread_suspend_check(int return_instead)
{
        struct thread *td;
        struct proc *p;
        struct kse *ke;
        struct ksegrp *kg;

        td = curthread;
        p = td->td_proc;
        kg = td->td_ksegrp;
        PROC_LOCK_ASSERT(p, MA_OWNED);
        while (P_SHOULDSTOP(p)) {
                if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                        KASSERT(p->p_singlethread != NULL,
                            ("singlethread not set"));
                        /*
                         * The only suspension in action is a
                         * single-threading. Single threader need not stop.
                         * XXX Should be safe to access unlocked 
                         * as it can only be set to be true by us.
                         */
                        if (p->p_singlethread == td)
                                return (0);     /* Exempt from stopping. */
                } 
                if (return_instead)
                        return (1);

                /*
                 * If the process is waiting for us to exit,
                 * this thread should just suicide.
                 * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
                 */
                if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
                        mtx_lock_spin(&sched_lock);
                        while (mtx_owned(&Giant))
                                mtx_unlock(&Giant);
                        /* 
                         * free extra kses and ksegrps, we needn't worry 
                         * about if current thread is in same ksegrp as 
                         * p_singlethread and last kse in the group
                         * could be killed, this is protected by kg_numthreads,
                         * in this case, we deduce that kg_numthreads must > 1.
                         */
                        ke = td->td_kse;
                        if (ke->ke_bound == NULL && 
                            ((kg->kg_kses != 1) || (kg->kg_numthreads == 1)))
                                ke->ke_flags |= KEF_EXIT;
                        thread_exit();
                }

                /*
                 * When a thread suspends, it just
                 * moves to the processes's suspend queue
                 * and stays there.
                 *
                 * XXXKSE if TDF_BOUND is true
                 * it will not release it's KSE which might
                 * lead to deadlock if there are not enough KSEs
                 * to complete all waiting threads.
                 * Maybe be able to 'lend' it out again.
                 * (lent kse's can not go back to userland?)
                 * and can only be lent in STOPPED state.
                 */
                mtx_lock_spin(&sched_lock);
                if ((p->p_flag & P_STOPPED_SIG) &&
                    (p->p_suspcount+1 == p->p_numthreads)) {
                        mtx_unlock_spin(&sched_lock);
                        PROC_LOCK(p->p_pptr);
                        if ((p->p_pptr->p_procsig->ps_flag &
                                PS_NOCLDSTOP) == 0) {
                                psignal(p->p_pptr, SIGCHLD);
                        }
                        PROC_UNLOCK(p->p_pptr);
                        mtx_lock_spin(&sched_lock);
                }
                mtx_assert(&Giant, MA_NOTOWNED);
                thread_suspend_one(td);
                PROC_UNLOCK(p);
                if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                        if (p->p_numthreads == p->p_suspcount) {
                                thread_unsuspend_one(p->p_singlethread);
                        }
                }
                p->p_stats->p_ru.ru_nivcsw++;
                mi_switch();
                mtx_unlock_spin(&sched_lock);
                PROC_LOCK(p);
        }
        return (0);
}

void
thread_suspend_one(struct thread *td)
{
        struct proc *p = td->td_proc;

        mtx_assert(&sched_lock, MA_OWNED);
        p->p_suspcount++;
        TD_SET_SUSPENDED(td);
        TAILQ_INSERT_TAIL(&p->p_suspended, td, td_runq);
        /*
         * Hack: If we are suspending but are on the sleep queue
         * then we are in msleep or the cv equivalent. We
         * want to look like we have two Inhibitors.
         * May already be set.. doesn't matter.
         */
        if (TD_ON_SLEEPQ(td))
                TD_SET_SLEEPING(td);
}

void
thread_unsuspend_one(struct thread *td)
{
        struct proc *p = td->td_proc;

        mtx_assert(&sched_lock, MA_OWNED);
        TAILQ_REMOVE(&p->p_suspended, td, td_runq);
        TD_CLR_SUSPENDED(td);
        p->p_suspcount--;
        setrunnable(td);
}

/*
 * Allow all threads blocked by single threading to continue running.
 */
void
thread_unsuspend(struct proc *p)
{
        struct thread *td;

        mtx_assert(&sched_lock, MA_OWNED);
        PROC_LOCK_ASSERT(p, MA_OWNED);
        if (!P_SHOULDSTOP(p)) {
                while (( td = TAILQ_FIRST(&p->p_suspended))) {
                        thread_unsuspend_one(td);
                }
        } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
            (p->p_numthreads == p->p_suspcount)) {
                /*
                 * Stopping everything also did the job for the single
                 * threading request. Now we've downgraded to single-threaded,
                 * let it continue.
                 */
                thread_unsuspend_one(p->p_singlethread);
        }
}

void
thread_single_end(void)
{
        struct thread *td;
        struct proc *p;

        td = curthread;
        p = td->td_proc;
        PROC_LOCK_ASSERT(p, MA_OWNED);
        p->p_flag &= ~P_STOPPED_SINGLE;
        p->p_singlethread = NULL;
        /*
         * If there are other threads they mey now run,
         * unless of course there is a blanket 'stop order'
         * on the process. The single threader must be allowed
         * to continue however as this is a bad place to stop.
         */
        if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
                mtx_lock_spin(&sched_lock);
                while (( td = TAILQ_FIRST(&p->p_suspended))) {
                        thread_unsuspend_one(td);
                }
                mtx_unlock_spin(&sched_lock);
        }
}