Ignore machine-check MSRs

[freebsd-src/fkvm-freebsd.git] / 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_kdtrace.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/sbuf.h>
#include <sys/signalvar.h>
#include <sys/sched.h>
#include <sys/sx.h>
#include <sys/syscallsubr.h>
#include <sys/syslog.h>
#include <sys/ptrace.h>
#include <sys/acct.h>           /* for acct_process() function prototype */
#include <sys/filedesc.h>
#include <sys/sdt.h>
#include <sys/shm.h>
#include <sys/sem.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#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>

#ifdef KDTRACE_HOOKS
#include <sys/dtrace_bsd.h>
dtrace_execexit_func_t  dtrace_fasttrap_exit;
#endif

SDT_PROVIDER_DECLARE(proc);
SDT_PROBE_DEFINE(proc, kernel, , exit);
SDT_PROBE_ARGTYPE(proc, kernel, , exit, 0, "int");

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

/* Hook for NFS teardown procedure. */
void (*nlminfo_release_p)(struct proc *p);

/*
 * exit -- death of process.
 */
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 proc *p, *nq, *q;
        struct vnode *vtmp;
        struct vnode *ttyvp = NULL;
#ifdef KTRACE
        struct vnode *tracevp;
        struct ucred *tracecred;
#endif
        struct plimit *plim;
        int locked;

        mtx_assert(&Giant, MA_NOTOWNED);

        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);
        while (p->p_flag & P_HADTHREADS) {
                /*
                 * 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))
                        break;

                /*
                 * All other activity in this process is now stopped.
                 * Threading support has been turned off.
                 */
        }
        KASSERT(p->p_numthreads == 1,
            ("exit1: proc %p exiting with %d threads", p, p->p_numthreads));
        /*
         * Wakeup anyone in procfs' PIOCWAIT.  They should have a hold
         * on our vmspace, so we should block below until they have
         * released their reference to us.  Note that if they have
         * requested S_EXIT stops we will block here until they ack
         * via PIOCCONT.
         */
        _STOPEVENT(p, S_EXIT, rv);

        /*
         * Note that we are exiting and do another wakeup of anyone in
         * PIOCWAIT in case they aren't listening for S_EXIT stops or
         * decided to wait again after we told them we are exiting.
         */
        p->p_flag |= P_WEXIT;
        wakeup(&p->p_stype);

        /*
         * Wait for any processes that have a hold on our vmspace to
         * release their reference.
         */
        while (p->p_lock > 0)
                msleep(&p->p_lock, &p->p_mtx, PWAIT, "exithold", 0);

        PROC_UNLOCK(p);
        /* Drain the limit callout while we don't have the proc locked */
        callout_drain(&p->p_limco);

#ifdef AUDIT
        /*
         * The Sun BSM exit token contains two components: an exit status as
         * passed to exit(), and a return value to indicate what sort of exit
         * it was.  The exit status is WEXITSTATUS(rv), but it's not clear
         * what the return value is.
         */
        AUDIT_ARG(exit, WEXITSTATUS(rv), 0);
        AUDIT_SYSCALL_EXIT(0, td);
#endif

        /* 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);
        }

        /*
         * 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);

        /*
         * 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);

        /*
         * 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.
         */
        funsetownlst(&p->p_sigiolst);

        /*
         * If this process has an nlminfo data area (for lockd), release it
         */
        if (nlminfo_release_p != NULL && p->p_nlminfo != NULL)
                (*nlminfo_release_p)(p);

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

        /*
         * 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);

        vmspace_exit(td);

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

                sp = p->p_session;

                SESS_LOCK(sp);
                ttyvp = sp->s_ttyvp;
                sp->s_ttyvp = NULL;
                SESS_UNLOCK(sp);

                if (ttyvp != NULL) {
                        /*
                         * Controlling process.
                         * Signal foreground pgrp and revoke access to
                         * controlling terminal.
                         *
                         * There is no need to drain the terminal here,
                         * because this will be done on revocation.
                         */
                        if (sp->s_ttyp != NULL) {
                                struct tty *tp = sp->s_ttyp;

                                tty_lock(tp);
                                tty_signal_pgrp(tp, SIGHUP);
                                tty_unlock(tp);

                                /*
                                 * The tty could have been revoked
                                 * if we blocked.
                                 */
                                if (ttyvp->v_type != VBAD) {
                                        sx_xunlock(&proctree_lock);
                                        VOP_LOCK(ttyvp, LK_EXCLUSIVE);
                                        VOP_REVOKE(ttyvp, REVOKEALL);
                                        VOP_UNLOCK(ttyvp, 0);
                                        sx_xlock(&proctree_lock);
                                }
                        }
                        /*
                         * 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);

        /* Release the TTY now we've unlocked everything. */
        if (ttyvp != NULL)
                vrele(ttyvp);
#ifdef KTRACE
        /*
         * Disable tracing, then drain any pending records and release
         * the trace file.
         */
        if (p->p_traceflag != 0) {
                PROC_LOCK(p);
                mtx_lock(&ktrace_mtx);
                p->p_traceflag = 0;
                mtx_unlock(&ktrace_mtx);
                PROC_UNLOCK(p);
                ktrprocexit(td);
                PROC_LOCK(p);
                mtx_lock(&ktrace_mtx);
                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) {
                        locked = VFS_LOCK_GIANT(tracevp->v_mount);
                        vrele(tracevp);
                        VFS_UNLOCK_GIANT(locked);
                }
                if (tracecred != NULL)
                        crfree(tracecred);
        }
#endif
        /*
         * Release reference to text vnode
         */
        if ((vtmp = p->p_textvp) != NULL) {
                p->p_textvp = NULL;
                locked = VFS_LOCK_GIANT(vtmp->v_mount);
                vrele(vtmp);
                VFS_UNLOCK_GIANT(locked);
        }

        /*
         * 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);

        /*
         * Call machine-dependent code to release any
         * machine-dependent resources other than the address space.
         * The address space is released by "vmspace_exitfree(p)" in
         * vm_waitproc().
         */
        cpu_exit(td);

        WITNESS_WARN(WARN_PANIC, NULL, "process (pid %d) exiting", p->p_pid);

        /*
         * Reparent all of our children to init.
         */
        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. */
        PROC_LOCK(p);
        p->p_xstat = rv;
        p->p_xthread = td;

#ifdef KDTRACE_HOOKS
        /*
         * Tell the DTrace fasttrap provider about the exit if it
         * has declared an interest.
         */
        if (dtrace_fasttrap_exit)
                dtrace_fasttrap_exit(p);
#endif

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

#ifdef KDTRACE_HOOKS
        int reason = CLD_EXITED;
        if (WCOREDUMP(rv))
                reason = CLD_DUMPED;
        else if (WIFSIGNALED(rv))
                reason = CLD_KILLED;
        SDT_PROBE(proc, kernel, , exit, reason, 0, 0, 0, 0);
#endif

        /*
         * 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) {
                if (p->p_sigparent == SIGCHLD)
                        childproc_exited(p);
                else    /* LINUX thread */
                        psignal(p->p_pptr, p->p_sigparent);
        }
        sx_xunlock(&proctree_lock);

        /*
         * The state PRS_ZOMBIE prevents other proesses from sending
         * signal to the process, to avoid memory leak, we free memory
         * for signal queue at the time when the state is set.
         */
        sigqueue_flush(&p->p_sigqueue);
        sigqueue_flush(&td->td_sigqueue);

        /*
         * 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.  We also have to set the zombie state
         * before we release the parent process' proc lock to avoid
         * a lost wakeup.  So, we first call wakeup, then we grab the
         * sched lock, update the state, and release the parent process'
         * proc lock.
         */
        wakeup(p->p_pptr);
        sched_exit(p->p_pptr, td);
        PROC_SLOCK(p);
        p->p_state = PRS_ZOMBIE;
        PROC_UNLOCK(p->p_pptr);

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

        /*
         * Save our children's rusage information in our exit rusage.
         */
        ruadd(&p->p_ru, &p->p_rux, &p->p_stats->p_cru, &p->p_crux);

        /*
         * 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();
}


#ifndef _SYS_SYSPROTO_H_
struct abort2_args {
        char *why;
        int nargs;
        void **args;
};
#endif

int
abort2(struct thread *td, struct abort2_args *uap)
{
        struct proc *p = td->td_proc;
        struct sbuf *sb;
        void *uargs[16];
        int error, i, sig;

        error = 0;      /* satisfy compiler */

        /*
         * Do it right now so we can log either proper call of abort2(), or
         * note, that invalid argument was passed. 512 is big enough to
         * handle 16 arguments' descriptions with additional comments.
         */
        sb = sbuf_new(NULL, NULL, 512, SBUF_FIXEDLEN);
        sbuf_clear(sb);
        sbuf_printf(sb, "%s(pid %d uid %d) aborted: ",
            p->p_comm, p->p_pid, td->td_ucred->cr_uid);
        /* 
         * Since we can't return from abort2(), send SIGKILL in cases, where
         * abort2() was called improperly
         */
        sig = SIGKILL;
        /* Prevent from DoSes from user-space. */
        if (uap->nargs < 0 || uap->nargs > 16)
                goto out;
        if (uap->nargs > 0) {
                if (uap->args == NULL)
                        goto out;
                error = copyin(uap->args, uargs, uap->nargs * sizeof(void *));
                if (error != 0)
                        goto out;
        }
        /*
         * Limit size of 'reason' string to 128. Will fit even when
         * maximal number of arguments was chosen to be logged.
         */
        if (uap->why != NULL) {
                error = sbuf_copyin(sb, uap->why, 128);
                if (error < 0)
                        goto out;
        } else {
                sbuf_printf(sb, "(null)");
        }
        if (uap->nargs > 0) {
                sbuf_printf(sb, "(");
                for (i = 0;i < uap->nargs; i++)
                        sbuf_printf(sb, "%s%p", i == 0 ? "" : ", ", uargs[i]);
                sbuf_printf(sb, ")");
        }
        /*
         * Final stage: arguments were proper, string has been
         * successfully copied from userspace, and copying pointers
         * from user-space succeed.
         */
        sig = SIGABRT;
out:
        if (sig == SIGKILL) {
                sbuf_trim(sb);
                sbuf_printf(sb, " (Reason text inaccessible)");
        }
        sbuf_cat(sb, "\n");
        sbuf_finish(sb);
        log(LOG_INFO, "%s", sbuf_data(sb));
        sbuf_delete(sb);
        exit1(td, W_EXITCODE(0, sig));
        return (0);
}


#ifdef COMPAT_43
/*
 * The dirty work is handled by kern_wait().
 */
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().
 */
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;

        AUDIT_ARG(pid, pid);

        q = td->td_proc;
        if (pid == 0) {
                PROC_LOCK(q);
                pid = -q->p_pgid;
                PROC_UNLOCK(q);
        }
        if (options &~ (WUNTRACED|WNOHANG|WCONTINUED|WNOWAIT|WLINUXCLONE))
                return (EINVAL);
loop:
        if (q->p_flag & P_STATCHILD) {
                PROC_LOCK(q);
                q->p_flag &= ~P_STATCHILD;
                PROC_UNLOCK(q);
        }
        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;
                }
                if (p_canwait(td, p)) {
                        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++;
                PROC_SLOCK(p);
                if (p->p_state == PRS_ZOMBIE) {
                        if (rusage) {
                                *rusage = p->p_ru;
                                calcru(p, &rusage->ru_utime, &rusage->ru_stime);
                        }
                        PROC_SUNLOCK(p);
                        td->td_retval[0] = p->p_pid;
                        if (status)
                                *status = p->p_xstat;   /* convert to int */
                        if (options & WNOWAIT) {

                                /*
                                 *  Only poll, returning the status.
                                 *  Caller does not wish to release the proc
                                 *  struct just yet.
                                 */
                                PROC_UNLOCK(p);
                                sx_xunlock(&proctree_lock);
                                return (0);
                        }

                        PROC_LOCK(q);
                        sigqueue_take(p->p_ksi);
                        PROC_UNLOCK(q);
                        PROC_UNLOCK(p);

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

                        /*
                         * 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_proc_destroy(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);
                }
                if ((p->p_flag & P_STOPPED_SIG) &&
                    (p->p_suspcount == p->p_numthreads) &&
                    (p->p_flag & P_WAITED) == 0 &&
                    (p->p_flag & P_TRACED || options & WUNTRACED)) {
                        PROC_SUNLOCK(p);
                        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_LOCK(q);
                        sigqueue_take(p->p_ksi);
                        PROC_UNLOCK(q);
                        PROC_UNLOCK(p);

                        return (0);
                }
                PROC_SUNLOCK(p);
                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_LOCK(q);
                        sigqueue_take(p->p_ksi);
                        PROC_UNLOCK(q);
                        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);
        if (q->p_flag & P_STATCHILD) {
                q->p_flag &= ~P_STATCHILD;
                error = 0;
        } else
                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;

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