FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_thread.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: releng/5.0/sys/kern/kern_thread.c 107719 2002-12-10 02:33:45Z julian $
     */
    
    #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 thread_debug = 0;
    SYSCTL_INT(_kern_threads, OID_AUTO, debug, CTLFLAG_RW,
            &thread_debug, 0, "thread debug");
    
    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);
    
    static void kse_purge(struct proc *p, struct thread *td);
    
    /*
     * Prepare 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;
   
           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
   }
   
   /*
    * 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)) {
                   /* XXXSKE what if >1 KSE? check.... */
                   p->p_flag &= ~P_KSES;
                   mtx_unlock_spin(&sched_lock);
                   PROC_UNLOCK(p);
           } else {
                   td->td_kse->ke_flags |= KEF_EXIT;
                   thread_exit();
                   /* NOTREACHED */
           }
           return (0);
   }
   
   /*
    * Either returns as an upcall or exits
    */
   int
   kse_release(struct thread * td, struct kse_release_args * uap)
   {
           struct proc *p;
           struct ksegrp *kg;
   
           p = td->td_proc;
           kg = td->td_ksegrp;
           /*
            * Must be a bound thread. And kse must have a mailbox ready,
            * if not, the kse can not generate an upcall.
            */
           if (!(p->p_flag & P_KSES) ||
               (td->td_flags & TDF_UNBOUND) ||
               (td->td_kse->ke_mailbox == NULL))
                   return (EINVAL);
           PROC_LOCK(p);
           mtx_lock_spin(&sched_lock);
           if (kg->kg_completed == NULL) {
   #if 1       /* temp until signals make new threads */
                   if (p->p_numthreads == 1) {
                           /* change OURSELF to become an upcall */
                           td->td_flags = TDF_UPCALLING;
                           mtx_unlock_spin(&sched_lock);
                           PROC_UNLOCK(p);
                           /*
                            * msleep will not call thread_sched_upcall
                            * because thread is not UNBOUND.
                            */
                           msleep(p->p_sigacts, NULL,
                               PPAUSE | PCATCH, "ksepause", 0);
                           return (0);
                   }
   #endif      /* end temp */
                   thread_exit();
           }
           /* change OURSELF to become an upcall */
           td->td_flags = TDF_UPCALLING;
           mtx_unlock_spin(&sched_lock);
           PROC_UNLOCK(p);
           return (0);
   }
   
   /* 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;
           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 (thread_debug == 0) { /* if debugging, allow more */
   #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)
   {
   
           cpu_thread_clean(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 CPU's deadthread holder. This means
    * 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 (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"));
  
                  /* 
                   * decide what to do with the KSE attached to this thread.
                   */
                  if (ke->ke_flags & KEF_EXIT) {
                          kse_unlink(ke);
                  } else {
                          kse_reassign(ke);
                  }
                  PROC_UNLOCK(p);
                  td->td_state    = TDS_INACTIVE;
                  td->td_proc     = NULL;
                  td->td_ksegrp   = NULL;
                  td->td_last_kse = NULL;
                  PCPU_SET(deadthread, td);
          } else {
                  PROC_UNLOCK(p);
          }
          cpu_throw();
          /* NOTREACHED */
  }
  
  /* 
   * Do any thread specific cleanups that may be needed in wait()
   * called with Giant held, proc and schedlock not held.
   */
  void
  thread_wait(struct proc *p)
  {
          struct thread *td;
  
          KASSERT((p->p_numthreads == 1), ("Muliple threads in wait1()"));
          KASSERT((p->p_numksegrps == 1), ("Muliple ksegrps in wait1()"));
          FOREACH_THREAD_IN_PROC(p, td) {
                  if (td->td_standin != NULL) {
                          thread_free(td->td_standin);
                          td->td_standin = NULL;
                  }
                  cpu_thread_clean(td);
          }
          thread_reap();  /* check for zombie threads etc. */
  }
  
  /*
   * 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++;
          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--;
                          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;
                  p->p_stats->p_ru.ru_nvcsw++;
                  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) {
                  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.
           * Will use Giant in cpu_thread_clean() because it uses
           * kmem_free(kernel_map, ...)
           */
          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;
          mtx_assert(&Giant, MA_OWNED);
          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);
                  p->p_stats->p_ru.ru_nvcsw++;
                  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);
          }
  }
  
  

Cache object: ca2f53629beb9ce5f1088f07ae4486e9