freebsd-skq/sys/kern/kern_exit.c

/*-
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_exit.c	8.7 (Berkeley) 2/12/94
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_compat.h"
#include "opt_ktrace.h"
#include "opt_mac.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/pioctl.h>
#include <sys/tty.h>
#include <sys/wait.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/resourcevar.h>
#include <sys/signalvar.h>
#include <sys/sched.h>
#include <sys/sx.h>
#include <sys/syscallsubr.h>
#include <sys/ptrace.h>
#include <sys/acct.h>		/* for acct_process() function prototype */
#include <sys/filedesc.h>
#include <sys/mac.h>
#include <sys/shm.h>
#include <sys/sem.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <vm/vm.h>
#include <vm/vm_extern.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/uma.h>

/* Required to be non-static for SysVR4 emulator */
MALLOC_DEFINE(M_ZOMBIE, "zombie", "zombie proc status");

/*
 * exit --
 *	Death of process.
 *
 * MPSAFE
 */
void
sys_exit(struct thread *td, struct sys_exit_args *uap)
{

	exit1(td, W_EXITCODE(uap->rval, 0));
	/* NOTREACHED */
}

/*
 * Exit: deallocate address space and other resources, change proc state
 * to zombie, and unlink proc from allproc and parent's lists.  Save exit
 * status and rusage for wait().  Check for child processes and orphan them.
 */
void
exit1(struct thread *td, int rv)
{
	struct bintime new_switchtime;
	struct proc *p, *nq, *q;
	struct tty *tp;
	struct vnode *ttyvp;
	struct vmspace *vm;
	struct vnode *vtmp;
#ifdef KTRACE
	struct vnode *tracevp;
	struct ucred *tracecred;
#endif
	struct plimit *plim;
	int refcnt;

	/*
	 * Drop Giant if caller has it.  Eventually we should warn about
	 * being called with Giant held.
	 */ 
	while (mtx_owned(&Giant))
		mtx_unlock(&Giant);

	p = td->td_proc;
	if (p == initproc) {
		printf("init died (signal %d, exit %d)\n",
		    WTERMSIG(rv), WEXITSTATUS(rv));
		panic("Going nowhere without my init!");
	}

	/*
	 * MUST abort all other threads before proceeding past here.
	 */
	PROC_LOCK(p);
	if (p->p_flag & P_HADTHREADS) {
retry:
		/*
		 * First check if some other thread got here before us..
		 * if so, act apropriatly, (exit or suspend);
		 */
		thread_suspend_check(0);

		/*
		 * Kill off the other threads. This requires
		 * some co-operation from other parts of the kernel
		 * so it may not be instantaneous.  With this state set
		 * any thread entering the kernel from userspace will
		 * thread_exit() in trap().  Any thread attempting to
		 * sleep will return immediately with EINTR or EWOULDBLOCK
		 * which will hopefully force them to back out to userland
		 * freeing resources as they go.  Any thread attempting
		 * to return to userland will thread_exit() from userret().
		 * thread_exit() will unsuspend us when the last of the
		 * other threads exits.
		 * If there is already a thread singler after resumption,
		 * calling thread_single will fail; in that case, we just
		 * re-check all suspension request, the thread should
		 * either be suspended there or exit.
		 */
		if (thread_single(SINGLE_EXIT))
			goto retry;

		/*
		 * All other activity in this process is now stopped.
		 * Threading support has been turned off.
		 */
	}

	p->p_flag |= P_WEXIT;
	PROC_UNLOCK(p);

	/* Are we a task leader? */
	if (p == p->p_leader) {
		mtx_lock(&ppeers_lock);
		q = p->p_peers;
		while (q != NULL) {
			PROC_LOCK(q);
			psignal(q, SIGKILL);
			PROC_UNLOCK(q);
			q = q->p_peers;
		}
		while (p->p_peers != NULL)
			msleep(p, &ppeers_lock, PWAIT, "exit1", 0);
		mtx_unlock(&ppeers_lock);
	}

	PROC_LOCK(p);
	_STOPEVENT(p, S_EXIT, rv);
	wakeup(&p->p_stype);	/* Wakeup anyone in procfs' PIOCWAIT */
	PROC_UNLOCK(p);

	/*
	 * Check if any loadable modules need anything done at process exit.
	 * E.g. SYSV IPC stuff
	 * XXX what if one of these generates an error?
	 */
	EVENTHANDLER_INVOKE(process_exit, p);

	MALLOC(p->p_ru, struct rusage *, sizeof(struct rusage),
		M_ZOMBIE, M_WAITOK);
	/*
	 * If parent is waiting for us to exit or exec,
	 * P_PPWAIT is set; we will wakeup the parent below.
	 */
	PROC_LOCK(p);
	stopprofclock(p);
	p->p_flag &= ~(P_TRACED | P_PPWAIT);
	SIGEMPTYSET(p->p_siglist);
	SIGEMPTYSET(td->td_siglist);

	/*
	 * Stop the real interval timer.  If the handler is currently
	 * executing, prevent it from rearming itself and let it finish.
	 */
	if (timevalisset(&p->p_realtimer.it_value) &&
	    callout_stop(&p->p_itcallout) == 0) {
		timevalclear(&p->p_realtimer.it_interval);
		msleep(&p->p_itcallout, &p->p_mtx, PWAIT, "ritwait", 0);
		KASSERT(!timevalisset(&p->p_realtimer.it_value),
		    ("realtime timer is still armed"));
	}
	PROC_UNLOCK(p);

	/*
	 * Reset any sigio structures pointing to us as a result of
	 * F_SETOWN with our pid.
	 */
	mtx_lock(&Giant);	/* XXX: not sure if needed */
	funsetownlst(&p->p_sigiolst);

	/*
	 * Close open files and release open-file table.
	 * This may block!
	 */
	fdfree(td);
	mtx_unlock(&Giant);	

	/*
	 * If this thread tickled GEOM, we need to wait for the giggling to
	 * stop before we return to userland
	 */
	if (td->td_pflags & TDP_GEOM)
		g_waitidle();

	/*
	 * Remove ourself from our leader's peer list and wake our leader.
	 */
	mtx_lock(&ppeers_lock);
	if (p->p_leader->p_peers) {
		q = p->p_leader;
		while (q->p_peers != p)
			q = q->p_peers;
		q->p_peers = p->p_peers;
		wakeup(p->p_leader);
	}
	mtx_unlock(&ppeers_lock);

	/* The next two chunks should probably be moved to vmspace_exit. */
	vm = p->p_vmspace;
	/*
	 * Release user portion of address space.
	 * This releases references to vnodes,
	 * which could cause I/O if the file has been unlinked.
	 * Need to do this early enough that we can still sleep.
	 * Can't free the entire vmspace as the kernel stack
	 * may be mapped within that space also.
	 *
	 * Processes sharing the same vmspace may exit in one order, and
	 * get cleaned up by vmspace_exit() in a different order.  The
	 * last exiting process to reach this point releases as much of
	 * the environment as it can, and the last process cleaned up
	 * by vmspace_exit() (which decrements exitingcnt) cleans up the
	 * remainder.
	 */
	atomic_add_int(&vm->vm_exitingcnt, 1);
	do
		refcnt = vm->vm_refcnt;
	while (!atomic_cmpset_int(&vm->vm_refcnt, refcnt, refcnt - 1));
	if (refcnt == 1) {
		shmexit(vm);
		pmap_remove_pages(vmspace_pmap(vm), vm_map_min(&vm->vm_map),
		    vm_map_max(&vm->vm_map));
		(void) vm_map_remove(&vm->vm_map, vm_map_min(&vm->vm_map),
		    vm_map_max(&vm->vm_map));
	}

	mtx_lock(&Giant);	
	sx_xlock(&proctree_lock);
	if (SESS_LEADER(p)) {
		struct session *sp;

		sp = p->p_session;
		if (sp->s_ttyvp) {
			/*
			 * Controlling process.
			 * Signal foreground pgrp,
			 * drain controlling terminal
			 * and revoke access to controlling terminal.
			 */
			if (sp->s_ttyp && (sp->s_ttyp->t_session == sp)) {
				tp = sp->s_ttyp;
				if (sp->s_ttyp->t_pgrp) {
					PGRP_LOCK(sp->s_ttyp->t_pgrp);
					pgsignal(sp->s_ttyp->t_pgrp, SIGHUP, 1);
					PGRP_UNLOCK(sp->s_ttyp->t_pgrp);
				}
				/* XXX tp should be locked. */
				sx_xunlock(&proctree_lock);
				(void) ttywait(tp);
				sx_xlock(&proctree_lock);
				/*
				 * The tty could have been revoked
				 * if we blocked.
				 */
				if (sp->s_ttyvp) {
					ttyvp = sp->s_ttyvp;
					SESS_LOCK(p->p_session);
					sp->s_ttyvp = NULL;
					SESS_UNLOCK(p->p_session);
					sx_xunlock(&proctree_lock);
					VOP_REVOKE(ttyvp, REVOKEALL);
					vrele(ttyvp);
					sx_xlock(&proctree_lock);
				}
			}
			if (sp->s_ttyvp) {
				ttyvp = sp->s_ttyvp;
				SESS_LOCK(p->p_session);
				sp->s_ttyvp = NULL;
				SESS_UNLOCK(p->p_session);
				vrele(ttyvp);
			}
			/*
			 * s_ttyp is not zero'd; we use this to indicate
			 * that the session once had a controlling terminal.
			 * (for logging and informational purposes)
			 */
		}
		SESS_LOCK(p->p_session);
		sp->s_leader = NULL;
		SESS_UNLOCK(p->p_session);
	}
	fixjobc(p, p->p_pgrp, 0);
	sx_xunlock(&proctree_lock);
	(void)acct_process(td);
	mtx_unlock(&Giant);	
#ifdef KTRACE
	/*
	 * release trace file
	 */
	PROC_LOCK(p);
	mtx_lock(&ktrace_mtx);
	p->p_traceflag = 0;	/* don't trace the vrele() */
	tracevp = p->p_tracevp;
	p->p_tracevp = NULL;
	tracecred = p->p_tracecred;
	p->p_tracecred = NULL;
	mtx_unlock(&ktrace_mtx);
	PROC_UNLOCK(p);
	if (tracevp != NULL) {
		mtx_lock(&Giant);
		vrele(tracevp);
		mtx_unlock(&Giant);
	}
	if (tracecred != NULL)
		crfree(tracecred);
#endif
	/*
	 * Release reference to text vnode
	 */
	if ((vtmp = p->p_textvp) != NULL) {
		p->p_textvp = NULL;
		mtx_lock(&Giant);	
		vrele(vtmp);
		mtx_unlock(&Giant);	
	}

	/*
	 * Release our limits structure.
	 */
	PROC_LOCK(p);
	plim = p->p_limit;
	p->p_limit = NULL;
	PROC_UNLOCK(p);
	lim_free(plim);

	/*
	 * Remove proc from allproc queue and pidhash chain.
	 * Place onto zombproc.  Unlink from parent's child list.
	 */
	sx_xlock(&allproc_lock);
	LIST_REMOVE(p, p_list);
	LIST_INSERT_HEAD(&zombproc, p, p_list);
	LIST_REMOVE(p, p_hash);
	sx_xunlock(&allproc_lock);

	sx_xlock(&proctree_lock);
	q = LIST_FIRST(&p->p_children);
	if (q != NULL)		/* only need this if any child is S_ZOMB */
		wakeup(initproc);
	for (; q != NULL; q = nq) {
		nq = LIST_NEXT(q, p_sibling);
		PROC_LOCK(q);
		proc_reparent(q, initproc);
		q->p_sigparent = SIGCHLD;
		/*
		 * Traced processes are killed
		 * since their existence means someone is screwing up.
		 */
		if (q->p_flag & P_TRACED) {
			q->p_flag &= ~(P_TRACED | P_STOPPED_TRACE);
			psignal(q, SIGKILL);
		}
		PROC_UNLOCK(q);
	}

	/*
	 * Save exit status and finalize rusage info except for times,
	 * adding in child rusage info.
	 */
	PROC_LOCK(p);
	p->p_xstat = rv;
	p->p_xthread = td;
	p->p_stats->p_ru.ru_nvcsw++;
	*p->p_ru = p->p_stats->p_ru;
	ruadd(p->p_ru, &p->p_rux, &p->p_stats->p_cru, &p->p_crux);

	/*
	 * Notify interested parties of our demise.
	 */
	KNOTE_LOCKED(&p->p_klist, NOTE_EXIT);

	/*
	 * Just delete all entries in the p_klist. At this point we won't
	 * report any more events, and there are nasty race conditions that
	 * can beat us if we don't.
	 */
	knlist_clear(&p->p_klist, 1);

	/*
	 * Notify parent that we're gone.  If parent has the PS_NOCLDWAIT
	 * flag set, or if the handler is set to SIG_IGN, notify process
	 * 1 instead (and hope it will handle this situation).
	 */
	PROC_LOCK(p->p_pptr);
	mtx_lock(&p->p_pptr->p_sigacts->ps_mtx);
	if (p->p_pptr->p_sigacts->ps_flag & (PS_NOCLDWAIT | PS_CLDSIGIGN)) {
		struct proc *pp;

		mtx_unlock(&p->p_pptr->p_sigacts->ps_mtx);
		pp = p->p_pptr;
		PROC_UNLOCK(pp);
		proc_reparent(p, initproc);
		p->p_sigparent = SIGCHLD;
		PROC_LOCK(p->p_pptr);
		/*
		 * If this was the last child of our parent, notify
		 * parent, so in case he was wait(2)ing, he will
		 * continue.
		 */
		if (LIST_EMPTY(&pp->p_children))
			wakeup(pp);
	} else
		mtx_unlock(&p->p_pptr->p_sigacts->ps_mtx);

	if (p->p_pptr == initproc)
		psignal(p->p_pptr, SIGCHLD);
	else if (p->p_sigparent != 0)
		psignal(p->p_pptr, p->p_sigparent);
	PROC_UNLOCK(p->p_pptr);

	/*
	 * If this is a kthread, then wakeup anyone waiting for it to exit.
	 */
	if (p->p_flag & P_KTHREAD)
		wakeup(p);
	PROC_UNLOCK(p);

	/*
	 * Finally, call machine-dependent code to release the remaining
	 * resources including address space.
	 * The address space is released by "vmspace_exitfree(p)" in
	 * vm_waitproc().
	 */
	cpu_exit(td);

	PROC_LOCK(p);
	PROC_LOCK(p->p_pptr);
	sx_xunlock(&proctree_lock);

	/*
	 * We have to wait until after acquiring all locks before
	 * changing p_state.  We need to avoid all possible context
	 * switches (including ones from blocking on a mutex) while
	 * marked as a zombie.
	 */
	mtx_lock_spin(&sched_lock);
	p->p_state = PRS_ZOMBIE;

	critical_enter();
	mtx_unlock_spin(&sched_lock);
	wakeup(p->p_pptr);
	PROC_UNLOCK(p->p_pptr);
	mtx_lock_spin(&sched_lock);
	critical_exit();

	/* Do the same timestamp bookkeeping that mi_switch() would do. */
	binuptime(&new_switchtime);
	bintime_add(&p->p_rux.rux_runtime, &new_switchtime);
	bintime_sub(&p->p_rux.rux_runtime, PCPU_PTR(switchtime));
	PCPU_SET(switchtime, new_switchtime);
	PCPU_SET(switchticks, ticks);
	cnt.v_swtch++;

	sched_exit(p->p_pptr, td);

	/*
	 * Hopefully no one will try to deliver a signal to the process this
	 * late in the game.
	 */
	knlist_destroy(&p->p_klist);

	/*
	 * Make sure the scheduler takes this thread out of its tables etc.
	 * This will also release this thread's reference to the ucred.
	 * Other thread parts to release include pcb bits and such.
	 */
	thread_exit();
}

#ifdef COMPAT_43
/*
 * The dirty work is handled by kern_wait().
 *
 * MPSAFE.
 */
int
owait(struct thread *td, struct owait_args *uap __unused)
{
	int error, status;

	error = kern_wait(td, WAIT_ANY, &status, 0, NULL);
	if (error == 0)
		td->td_retval[1] = status;
	return (error);
}
#endif /* COMPAT_43 */

/*
 * The dirty work is handled by kern_wait().
 *
 * MPSAFE.
 */
int
wait4(struct thread *td, struct wait_args *uap)
{
	struct rusage ru, *rup;
	int error, status;

	if (uap->rusage != NULL)
		rup = &ru;
	else
		rup = NULL;
	error = kern_wait(td, uap->pid, &status, uap->options, rup);
	if (uap->status != NULL && error == 0)
		error = copyout(&status, uap->status, sizeof(status));
	if (uap->rusage != NULL && error == 0)
		error = copyout(&ru, uap->rusage, sizeof(struct rusage));
	return (error);
}

int
kern_wait(struct thread *td, pid_t pid, int *status, int options,
    struct rusage *rusage)
{
	struct proc *p, *q, *t;
	int error, nfound;

	q = td->td_proc;
	if (pid == 0) {
		PROC_LOCK(q);
		pid = -q->p_pgid;
		PROC_UNLOCK(q);
	}
	if (options &~ (WUNTRACED|WNOHANG|WCONTINUED|WLINUXCLONE))
		return (EINVAL);
loop:
	nfound = 0;
	sx_xlock(&proctree_lock);
	LIST_FOREACH(p, &q->p_children, p_sibling) {
		PROC_LOCK(p);
		if (pid != WAIT_ANY &&
		    p->p_pid != pid && p->p_pgid != -pid) {
			PROC_UNLOCK(p);
			continue;
		}

		/*
		 * This special case handles a kthread spawned by linux_clone
		 * (see linux_misc.c).  The linux_wait4 and linux_waitpid
		 * functions need to be able to distinguish between waiting
		 * on a process and waiting on a thread.  It is a thread if
		 * p_sigparent is not SIGCHLD, and the WLINUXCLONE option
		 * signifies we want to wait for threads and not processes.
		 */
		if ((p->p_sigparent != SIGCHLD) ^
		    ((options & WLINUXCLONE) != 0)) {
			PROC_UNLOCK(p);
			continue;
		}

		nfound++;
		if (p->p_state == PRS_ZOMBIE) {
			td->td_retval[0] = p->p_pid;
			if (status)
				*status = p->p_xstat;	/* convert to int */
			if (rusage) {
				*rusage = *p->p_ru;
				calcru(p, &rusage->ru_utime, &rusage->ru_stime);
			}

			/*
			 * If we got the child via a ptrace 'attach',
			 * we need to give it back to the old parent.
			 */
			PROC_UNLOCK(p);
			if (p->p_oppid && (t = pfind(p->p_oppid)) != NULL) {
				PROC_LOCK(p);
				p->p_oppid = 0;
				proc_reparent(p, t);
				PROC_UNLOCK(p);
				psignal(t, SIGCHLD);
				wakeup(t);
				PROC_UNLOCK(t);
				sx_xunlock(&proctree_lock);
				return (0);
			}

			/*
			 * Remove other references to this process to ensure
			 * we have an exclusive reference.
			 */
			sx_xlock(&allproc_lock);
			LIST_REMOVE(p, p_list);	/* off zombproc */
			sx_xunlock(&allproc_lock);
			LIST_REMOVE(p, p_sibling);
			leavepgrp(p);
			sx_xunlock(&proctree_lock);

			/*
			 * As a side effect of this lock, we know that
			 * all other writes to this proc are visible now, so
			 * no more locking is needed for p.
			 */
			PROC_LOCK(p);
			p->p_xstat = 0;		/* XXX: why? */
			PROC_UNLOCK(p);
			PROC_LOCK(q);
			ruadd(&q->p_stats->p_cru, &q->p_crux, p->p_ru,
			    &p->p_rux);
			PROC_UNLOCK(q);
			FREE(p->p_ru, M_ZOMBIE);
			p->p_ru = NULL;

			/*
			 * Decrement the count of procs running with this uid.
			 */
			(void)chgproccnt(p->p_ucred->cr_ruidinfo, -1, 0);

			/*
			 * Free credentials, arguments, and sigacts.
			 */
			crfree(p->p_ucred);
			p->p_ucred = NULL;
			pargs_drop(p->p_args);
			p->p_args = NULL;
			sigacts_free(p->p_sigacts);
			p->p_sigacts = NULL;

			/*
			 * Do any thread-system specific cleanups.
			 */
			thread_wait(p);

			/*
			 * Give vm and machine-dependent layer a chance
			 * to free anything that cpu_exit couldn't
			 * release while still running in process context.
			 */
			vm_waitproc(p);
#ifdef MAC
			mac_destroy_proc(p);
#endif
			KASSERT(FIRST_THREAD_IN_PROC(p),
			    ("kern_wait: no residual thread!"));
			uma_zfree(proc_zone, p);
			sx_xlock(&allproc_lock);
			nprocs--;
			sx_xunlock(&allproc_lock);
			return (0);
		}
		mtx_lock_spin(&sched_lock);
		if (P_SHOULDSTOP(p) && p->p_suspcount == p->p_numthreads &&
		    (p->p_flag & P_WAITED) == 0 &&
		    (p->p_flag & P_TRACED || options & WUNTRACED)) {
			mtx_unlock_spin(&sched_lock);
			p->p_flag |= P_WAITED;
			sx_xunlock(&proctree_lock);
			td->td_retval[0] = p->p_pid;
			if (status)
				*status = W_STOPCODE(p->p_xstat);
			PROC_UNLOCK(p);
			return (0);
		}
		mtx_unlock_spin(&sched_lock);
		if (options & WCONTINUED && (p->p_flag & P_CONTINUED)) {
			sx_xunlock(&proctree_lock);
			td->td_retval[0] = p->p_pid;
			p->p_flag &= ~P_CONTINUED;
			PROC_UNLOCK(p);

			if (status)
				*status = SIGCONT;
			return (0);
		}
		PROC_UNLOCK(p);
	}
	if (nfound == 0) {
		sx_xunlock(&proctree_lock);
		return (ECHILD);
	}
	if (options & WNOHANG) {
		sx_xunlock(&proctree_lock);
		td->td_retval[0] = 0;
		return (0);
	}
	PROC_LOCK(q);
	sx_xunlock(&proctree_lock);
	error = msleep(q, &q->p_mtx, PWAIT | PCATCH, "wait", 0);
	PROC_UNLOCK(q);
	if (error)
		return (error);	
	goto loop;
}

/*
 * Make process 'parent' the new parent of process 'child'.
 * Must be called with an exclusive hold of proctree lock.
 */
void
proc_reparent(struct proc *child, struct proc *parent)
{

	sx_assert(&proctree_lock, SX_XLOCKED);
	PROC_LOCK_ASSERT(child, MA_OWNED);
	if (child->p_pptr == parent)
		return;

	LIST_REMOVE(child, p_sibling);
	LIST_INSERT_HEAD(&parent->p_children, child, p_sibling);
	child->p_pptr = parent;
}