xref: /freebsd-11-stable/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.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/sys/kern/kern_thread.c 130199 2004-06-07 19:00:57Z julian $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sysctl.h>
#include <sys/sched.h>
#include <sys/sleepqueue.h>
#include <sys/turnstile.h>
#include <sys/ktr.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/uma.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");

int max_threads_per_proc = 1500;
SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
	&max_threads_per_proc, 0, "Limit on threads per proc");

int max_groups_per_proc = 500;
SYSCTL_INT(_kern_threads, OID_AUTO, max_groups_per_proc, CTLFLAG_RW,
	&max_groups_per_proc, 0, "Limit on thread groups per proc");

int max_threads_hits;
SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_hits, CTLFLAG_RD,
	&max_threads_hits, 0, "");


TAILQ_HEAD(, thread) 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 kse_zombie_lock;
MTX_SYSINIT(kse_zombie_lock, &kse_zombie_lock, "kse zombie lock", MTX_SPIN);

void kse_purge(struct proc *p, struct thread *td);
void kse_purge_group(struct thread *td);

/* move to proc.h */
extern void	kseinit(void);
extern void	kse_GC(void);



/*
 * Thread ID allocator. The allocator keeps track of assigned IDs by
 * using a bitmap. The bitmap is created in parts. The parts are linked
 * together.
 */
typedef u_long tid_bitmap_word;

#define	TID_IDS_PER_PART	1024
#define	TID_IDS_PER_IDX		(sizeof(tid_bitmap_word) << 3)
#define	TID_BITMAP_SIZE		(TID_IDS_PER_PART / TID_IDS_PER_IDX)
#define	TID_MIN			(PID_MAX + 1)

struct tid_bitmap_part {
	STAILQ_ENTRY(tid_bitmap_part) bmp_next;
	tid_bitmap_word	bmp_bitmap[TID_BITMAP_SIZE];
	int		bmp_base;
	int		bmp_free;
};

static STAILQ_HEAD(, tid_bitmap_part) tid_bitmap =
    STAILQ_HEAD_INITIALIZER(tid_bitmap);
static uma_zone_t tid_zone;

struct mtx tid_lock;
MTX_SYSINIT(tid_lock, &tid_lock, "TID lock", MTX_DEF);

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

	td = (struct thread *)mem;
	td->td_tid = 0;
	td->td_state = TDS_INACTIVE;
	td->td_oncpu	= NOCPU;
	td->td_critnest = 1;
}

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

	td = (struct thread *)mem;

	if (td->td_tid > PID_MAX) {
		STAILQ_FOREACH(bmp, &tid_bitmap, bmp_next) {
			if (td->td_tid >= bmp->bmp_base &&
			    td->td_tid < bmp->bmp_base + TID_IDS_PER_PART)
				break;
		}
		KASSERT(bmp != NULL, ("No TID bitmap?"));
		mtx_lock(&tid_lock);
		tid = td->td_tid - bmp->bmp_base;
		idx = tid / TID_IDS_PER_IDX;
		bit = 1UL << (tid % TID_IDS_PER_IDX);
		bmp->bmp_bitmap[idx] |= bit;
		bmp->bmp_free++;
		mtx_unlock(&tid_lock);
	}

#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;
	vm_thread_new(td, 0);
	cpu_thread_setup(td);
	td->td_sleepqueue = sleepq_alloc();
	td->td_turnstile = turnstile_alloc();
	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;
	turnstile_free(td->td_turnstile);
	sleepq_free(td->td_sleepqueue);
	vm_thread_dispose(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 into kse group.
 */
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;
	ke->ke_flags	= 0;
}

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

	mtx_assert(&sched_lock, MA_OWNED);
	kg = ke->ke_ksegrp;
	TAILQ_REMOVE(&kg->kg_kseq, ke, ke_kglist);
	if (ke->ke_state == KES_IDLE) {
		TAILQ_REMOVE(&kg->kg_iq, ke, ke_kgrlist);
		kg->kg_idle_kses--;
	}
	--kg->kg_kses;
	/*
	 * 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);		/* all idle kses in ksegrp */
	TAILQ_INIT(&kg->kg_upcalls);	/* all upcall structure 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_runq_kses  = 0; /* XXXKSE change name */
	kg->kg_idle_kses  = 0;
	kg->kg_numupcalls = 0;
	/* 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);
	KASSERT((kg->kg_numthreads == 0), ("ksegrp_unlink: residual threads"));
	KASSERT((kg->kg_kses == 0), ("ksegrp_unlink: residual kses"));
	KASSERT((kg->kg_numupcalls == 0), ("ksegrp_unlink: residual upcalls"));

	p = kg->kg_proc;
	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 all the structures 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);
}

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

	thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
	    thread_ctor, thread_dtor, thread_init, thread_fini,
	    UMA_ALIGN_CACHE, 0);
	tid_zone = uma_zcreate("TID", sizeof(struct tid_bitmap_part),
	    NULL, NULL, NULL, NULL, UMA_ALIGN_CACHE, 0);
	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);
	kseinit();
}

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

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

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

/*
 * Reap zombie kse resource.
 */
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(&kse_zombie_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(&kse_zombie_lock);
		while (td_first) {
			td_next = TAILQ_NEXT(td_first, td_runq);
			if (td_first->td_ucred)
				crfree(td_first->td_ucred);
			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;
		}
	}
	kse_GC();
}

/*
 * 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);
}

/*
 * Assign a thread ID.
 */
int
thread_new_tid(void)
{
	struct tid_bitmap_part *bmp, *new;
	int bit, idx, tid;

	mtx_lock(&tid_lock);
	STAILQ_FOREACH(bmp, &tid_bitmap, bmp_next) {
		if (bmp->bmp_free)
			break;
	}
	/* Create a new bitmap if we run out of free bits. */
	if (bmp == NULL) {
		mtx_unlock(&tid_lock);
		new = uma_zalloc(tid_zone, M_WAITOK);
		mtx_lock(&tid_lock);
		bmp = STAILQ_LAST(&tid_bitmap, tid_bitmap_part, bmp_next);
		if (bmp == NULL || bmp->bmp_free < TID_IDS_PER_PART/2) {
			/* 1=free, 0=assigned. This way we can use ffsl(). */
			memset(new->bmp_bitmap, ~0U, sizeof(new->bmp_bitmap));
			new->bmp_base = (bmp == NULL) ? TID_MIN :
			    bmp->bmp_base + TID_IDS_PER_PART;
			new->bmp_free = TID_IDS_PER_PART;
			STAILQ_INSERT_TAIL(&tid_bitmap, new, bmp_next);
			bmp = new;
			new = NULL;
		}
	} else
		new = NULL;
	/* We have a bitmap with available IDs. */
	idx = 0;
	while (idx < TID_BITMAP_SIZE && bmp->bmp_bitmap[idx] == 0UL)
		idx++;
	bit = ffsl(bmp->bmp_bitmap[idx]) - 1;
	tid = bmp->bmp_base + idx * TID_IDS_PER_IDX + bit;
	bmp->bmp_bitmap[idx] &= ~(1UL << bit);
	bmp->bmp_free--;
	mtx_unlock(&tid_lock);

	if (new != NULL)
		uma_zfree(tid_zone, new);
	return (tid);
}


/*
 * 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);
	mtx_assert(&Giant, MA_NOTOWNED);

	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) {
		thread_unlink(td);
		if (p->p_maxthrwaits)
			wakeup(&p->p_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);
			}
		}

		/*
		 * Because each upcall structure has an owner thread,
		 * owner thread exits only when process is in exiting
		 * state, so upcall to userland is no longer needed,
		 * deleting upcall structure is safe here.
		 * So when all threads in a group is exited, all upcalls
		 * in the group should be automatically freed.
		 */
		if (td->td_upcall)
			upcall_remove(td);

		sched_exit_thread(FIRST_THREAD_IN_PROC(p), td);
		sched_exit_kse(FIRST_KSE_IN_PROC(p), ke);
		ke->ke_state = KES_UNQUEUED;
		ke->ke_thread = NULL;
		/*
		 * Decide what to do with the KSE attached to this thread.
		 */
		if (ke->ke_flags & KEF_EXIT) {
			kse_unlink(ke);
			if (kg->kg_kses == 0) {
				sched_exit_ksegrp(FIRST_KSEGRP_IN_PROC(p), kg);
				ksegrp_unlink(kg);
			}
		}
		else
			kse_reassign(ke);
		PROC_UNLOCK(p);
		td->td_kse	= NULL;
		td->td_state	= TDS_INACTIVE;
#if 0
		td->td_proc	= NULL;
#endif
		td->td_ksegrp	= NULL;
		td->td_last_kse	= NULL;
		PCPU_SET(deadthread, td);
	} else {
		PROC_UNLOCK(p);
	}
	/* XXX Shouldn't cpu_throw() here. */
	mtx_assert(&sched_lock, MA_OWNED);
	cpu_throw(td, choosethread());
	panic("I'm a teapot!");
	/* NOTREACHED */
}

/*
 * Do any thread specific cleanups that may be needed in wait()
 * called with Giant, proc and schedlock not held.
 */
void
thread_wait(struct proc *p)
{
	struct thread *td;

	mtx_assert(&Giant, MA_NOTOWNED);
	KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
	KASSERT((p->p_numksegrps == 1), ("Multiple 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;
	td->td_flags    = 0;
	td->td_kflags	= 0;
	td->td_kse      = NULL;

	LIST_INIT(&td->td_contested);
	callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
	TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
	TAILQ_INSERT_HEAD(&kg->kg_threads, td, td_kglist);
	p->p_numthreads++;
	kg->kg_numthreads++;
}

void
thread_unlink(struct thread *td)
{
	struct proc *p = td->td_proc;
	struct ksegrp *kg = td->td_ksegrp;

	mtx_assert(&sched_lock, MA_OWNED);
	TAILQ_REMOVE(&p->p_threads, td, td_plist);
	p->p_numthreads--;
	TAILQ_REMOVE(&kg->kg_threads, td, td_kglist);
	kg->kg_numthreads--;
	/* could clear a few other things here */
}

/*
 * Purge a ksegrp resource. When a ksegrp is preparing to
 * exit, it calls this function.
 */
void
kse_purge_group(struct thread *td)
{
	struct ksegrp *kg;
	struct kse *ke;

	kg = td->td_ksegrp;
 	KASSERT(kg->kg_numthreads == 1, ("%s: bad thread number", __func__));
	while ((ke = TAILQ_FIRST(&kg->kg_iq)) != NULL) {
		KASSERT(ke->ke_state == KES_IDLE,
			("%s: wrong idle KSE state", __func__));
		kse_unlink(ke);
	}
	KASSERT((kg->kg_kses == 1),
		("%s: ksegrp still has %d KSEs", __func__, kg->kg_kses));
	KASSERT((kg->kg_numupcalls == 0),
	        ("%s: ksegrp still has %d upcall datas",
		__func__, kg->kg_numupcalls));
}

/*
 * Purge a process's KSE resource. When a process is preparing to
 * exit, it calls kse_purge to release any extra KSE resources in
 * the process.
 */
void
kse_purge(struct proc *p, struct thread *td)
{
	struct ksegrp *kg;
	struct kse *ke;

 	KASSERT(p->p_numthreads == 1, ("bad thread number"));
	while ((kg = TAILQ_FIRST(&p->p_ksegrps)) != NULL) {
		TAILQ_REMOVE(&p->p_ksegrps, kg, kg_ksegrp);
		p->p_numksegrps--;
		/*
		 * There is no ownership for KSE, after all threads
		 * in the group exited, it is possible that some KSEs
		 * were left in idle queue, gc them now.
		 */
		while ((ke = TAILQ_FIRST(&kg->kg_iq)) != NULL) {
			KASSERT(ke->ke_state == KES_IDLE,
			   ("%s: wrong idle KSE state", __func__));
			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);
		}
		KASSERT(((kg->kg_kses == 0) && (kg != td->td_ksegrp)) ||
		        ((kg->kg_kses == 1) && (kg == td->td_ksegrp)),
		        ("ksegrp has wrong kg_kses: %d", kg->kg_kses));
		KASSERT((kg->kg_numupcalls == 0),
		        ("%s: ksegrp still has %d upcall datas",
			__func__, kg->kg_numupcalls));

		if (kg != td->td_ksegrp)
			ksegrp_stash(kg);
	}
	TAILQ_INSERT_HEAD(&p->p_ksegrps, td->td_ksegrp, kg_ksegrp);
	p->p_numksegrps++;
}

/*
 * 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_NOTOWNED);
	PROC_LOCK_ASSERT(p, MA_OWNED);
	KASSERT((td != NULL), ("curthread is NULL"));

	if ((p->p_flag & P_SA) == 0 && p->p_numthreads == 1)
		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;
	mtx_lock_spin(&sched_lock);
	p->p_singlethread = td;
	while ((p->p_numthreads - p->p_suspcount) != 1) {
		FOREACH_THREAD_IN_PROC(p, td2) {
			if (td2 == td)
				continue;
			td2->td_flags |= TDF_ASTPENDING;
			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)) {
						sleepq_abort(td2);
					}
				} else {
					if (TD_IS_SUSPENDED(td2))
						continue;
					/*
					 * maybe other inhibitted states too?
					 * XXXKSE Is it totally safe to
					 * suspend a non-interruptable thread?
					 */
					if (td2->td_inhibitors &
					    (TDI_SLEEPING | TDI_SWAPPED))
						thread_suspend_one(td2);
				}
			}
		}
		/*
		 * Maybe we suspended some threads.. was it enough?
		 */
		if ((p->p_numthreads - p->p_suspcount) == 1)
			break;

		/*
		 * Wake us up when everyone else has suspended.
		 * In the mean time we suspend as well.
		 */
		thread_suspend_one(td);
		PROC_UNLOCK(p);
		mi_switch(SW_VOL);
		mtx_unlock_spin(&sched_lock);
		PROC_LOCK(p);
		mtx_lock_spin(&sched_lock);
	}
	if (force_exit == SINGLE_EXIT) {
		if (td->td_upcall)
			upcall_remove(td);
		kse_purge(p, td);
	}
	mtx_unlock_spin(&sched_lock);
	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;

	td = curthread;
	p = td->td_proc;
	mtx_assert(&Giant, MA_NOTOWNED);
	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);

		mtx_lock_spin(&sched_lock);
		thread_stopped(p);
		/*
		 * 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)) {
			if (p->p_flag & P_SA)
				thread_exit();
			else
				thr_exit1();
		}

		/*
		 * When a thread suspends, it just
		 * moves to the processes's suspend queue
		 * and stays there.
		 */
		thread_suspend_one(td);
		if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
			if (p->p_numthreads == p->p_suspcount) {
				thread_unsuspend_one(p->p_singlethread);
			}
		}
		PROC_UNLOCK(p);
		mi_switch(SW_INVOL);
		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);
	PROC_LOCK_ASSERT(p, MA_OWNED);
	KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
	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);
	PROC_LOCK_ASSERT(p, 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_SINGLE_EXIT);
	mtx_lock_spin(&sched_lock);
	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))) {
		while (( td = TAILQ_FIRST(&p->p_suspended))) {
			thread_unsuspend_one(td);
		}
	}
	mtx_unlock_spin(&sched_lock);
}