Ignore stop and continue signals sent to an exiting process. Stop signals

[FreeBSD/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_procdesc.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysproto.h>
#include <sys/capability.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/procdesc.h>
#include <sys/pioctl.h>
#include <sys/jail.h>
#include <sys/tty.h>
#include <sys/wait.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/racct.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, exit);
SDT_PROBE_ARGTYPE(proc, kernel, , exit, 0, "int");

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

static void
clear_orphan(struct proc *p)
{

        PROC_LOCK_ASSERT(p, MA_OWNED);

        if (p->p_flag & P_ORPHAN) {
                LIST_REMOVE(p, p_orphan);
                p->p_flag &= ~P_ORPHAN;
        }
}

/*
 * exit -- death of process.
 */
void
sys_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;
        struct plimit *plim;
        int locked;

        mtx_assert(&Giant, MA_NOTOWNED);

        p = td->td_proc;
        /*
         * XXX in case we're rebooting we just let init die in order to
         * work around an unsolved stack overflow seen very late during
         * shutdown on sparc64 when the gmirror worker process exists.
         */ 
        if (p == initproc && rebooting == 0) {
                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 appropriately: 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));
        racct_sub(p, RACCT_NTHR, 1);
        /*
         * 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);

        /*
         * Ignore any pending request to stop due to a stop signal.
         * Once P_WEXIT is set, future requests will be ignored as
         * well.
         */
        p->p_flag &= ~P_STOPPED_SIG;
        KASSERT(!P_SHOULDSTOP(p), ("exiting process is stopped"));

        /*
         * 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);

        p->p_xstat = rv;        /* Let event handler change exit status */
        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);
                        kern_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);
        rv = p->p_xstat;        /* Event handler could change exit status */
        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 = p->p_session;
                struct tty *tp;

                /*
                 * 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(sp);
                ttyvp = sp->s_ttyvp;
                tp = sp->s_ttyp;
                sp->s_ttyvp = NULL;
                sp->s_ttydp = NULL;
                sp->s_leader = NULL;
                SESS_UNLOCK(sp);

                /*
                 * Signal foreground pgrp and revoke access to
                 * controlling terminal if it has not been revoked
                 * already.
                 *
                 * Because the TTY may have been revoked in the mean
                 * time and could already have a new session associated
                 * with it, make sure we don't send a SIGHUP to a
                 * foreground process group that does not belong to this
                 * session.
                 */

                if (tp != NULL) {
                        tty_lock(tp);
                        if (tp->t_session == sp)
                                tty_signal_pgrp(tp, SIGHUP);
                        tty_unlock(tp);
                }

                if (ttyvp != NULL) {
                        sx_xunlock(&proctree_lock);
                        if (vn_lock(ttyvp, LK_EXCLUSIVE) == 0) {
                                VOP_REVOKE(ttyvp, REVOKEALL);
                                VOP_UNLOCK(ttyvp, 0);
                        }
                        sx_xlock(&proctree_lock);
                }
        }
        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
        ktrprocexit(td);
#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);

        tidhash_remove(td);

        /*
         * 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) {
                        struct thread *temp;

                        /*
                         * Since q was found on our children list, the
                         * proc_reparent() call moved q to the orphan
                         * list due to present P_TRACED flag. Clear
                         * orphan link for q now while q is locked.
                         */
                        clear_orphan(q);
                        q->p_flag &= ~(P_TRACED | P_STOPPED_TRACE);
                        FOREACH_THREAD_IN_PROC(q, temp)
                                temp->td_dbgflags &= ~TDB_SUSPEND;
                        kern_psignal(q, SIGKILL);
                }
                PROC_UNLOCK(q);
        }

        /*
         * Also get rid of our orphans.
         */
        while ((q = LIST_FIRST(&p->p_orphans)) != NULL) {
                PROC_LOCK(q);
                clear_orphan(q);
                PROC_UNLOCK(q);
        }

        /* Save exit status. */
        PROC_LOCK(p);
        p->p_xthread = td;

        /* Tell the prison that we are gone. */
        prison_proc_free(p->p_ucred->cr_prison);

#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);

        /*
         * If this is a process with a descriptor, we may not need to deliver
         * a signal to the parent.  proctree_lock is held over
         * procdesc_exit() to serialize concurrent calls to close() and
         * exit().
         */
#ifdef PROCDESC
        if (p->p_procdesc == NULL || procdesc_exit(p)) {
#endif
                /*
                 * 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);

                        /*
                         * Notify parent, so in case he was wait(2)ing or
                         * executing waitpid(2) with our pid, he will
                         * continue.
                         */
                        wakeup(pp);
                } else
                        mtx_unlock(&p->p_pptr->p_sigacts->ps_mtx);

                if (p->p_pptr == initproc)
                        kern_psignal(p->p_pptr, SIGCHLD);
                else if (p->p_sigparent != 0) {
                        if (p->p_sigparent == SIGCHLD)
                                childproc_exited(p);
                        else    /* LINUX thread */
                                kern_psignal(p->p_pptr, p->p_sigparent);
                }
#ifdef PROCDESC
        } else
                PROC_LOCK(p->p_pptr);
#endif
        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);
        cv_broadcast(&p->p_pwait);
        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
sys_abort2(struct thread *td, struct abort2_args *uap)
{
        struct proc *p = td->td_proc;
        struct sbuf *sb;
        void *uargs[16];
        int error, i, sig;

        /*
         * 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
sys_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);
}

/*
 * Reap the remains of a zombie process and optionally return status and
 * rusage.  Asserts and will release both the proctree_lock and the process
 * lock as part of its work.
 */
void
proc_reap(struct thread *td, struct proc *p, int *status, int options,
    struct rusage *rusage)
{
        struct proc *q, *t;

        sx_assert(&proctree_lock, SA_XLOCKED);
        PROC_LOCK_ASSERT(p, MA_OWNED);
        PROC_SLOCK_ASSERT(p, MA_OWNED);
        KASSERT(p->p_state == PRS_ZOMBIE, ("proc_reap: !PRS_ZOMBIE"));

        q = td->td_proc;
        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;
        }

        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);
                proc_reparent(p, t);
                p->p_oppid = 0;
                PROC_UNLOCK(p);
                pksignal(t, SIGCHLD, p->p_ksi);
                wakeup(t);
                cv_broadcast(&p->p_pwait);
                PROC_UNLOCK(t);
                sx_xunlock(&proctree_lock);
                return;
        }

        /*
         * 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);
        PROC_LOCK(p);
        clear_orphan(p);
        PROC_UNLOCK(p);
        leavepgrp(p);
#ifdef PROCDESC
        if (p->p_procdesc != NULL)
                procdesc_reap(p);
#endif
        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);

        /*
         * Destroy resource accounting information associated with the process.
         */
#ifdef RACCT
        PROC_LOCK(p);
        racct_sub(p, RACCT_NPROC, 1);
        PROC_UNLOCK(p);
#endif
        racct_proc_exit(p);

        /*
         * 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),
            ("proc_reap: no residual thread!"));
        uma_zfree(proc_zone, p);
        sx_xlock(&allproc_lock);
        nprocs--;
        sx_xunlock(&allproc_lock);
}

static int
proc_to_reap(struct thread *td, struct proc *p, pid_t pid, int *status,
    int options, struct rusage *rusage)
{
        struct proc *q;

        sx_assert(&proctree_lock, SA_XLOCKED);

        q = td->td_proc;
        PROC_LOCK(p);
        if (pid != WAIT_ANY && p->p_pid != pid && p->p_pgid != -pid) {
                PROC_UNLOCK(p);
                return (0);
        }
        if (p_canwait(td, p)) {
                PROC_UNLOCK(p);
                return (0);
        }

        /*
         * 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);
                return (0);
        }

        PROC_SLOCK(p);
        if (p->p_state == PRS_ZOMBIE) {
                proc_reap(td, p, status, options, rusage);
                return (-1);
        }
        PROC_SUNLOCK(p);
        PROC_UNLOCK(p);
        return (1);
}

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

        AUDIT_ARG_PID(pid);
        AUDIT_ARG_VALUE(options);

        q = td->td_proc;
        if (pid == 0) {
                PROC_LOCK(q);
                pid = -q->p_pgid;
                PROC_UNLOCK(q);
        }
        /* If we don't know the option, just return. */
        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) {
                ret = proc_to_reap(td, p, pid, status, options, rusage);
                if (ret == 0)
                        continue;
                else if (ret == 1)
                        nfound++;
                else
                        return (0);

                PROC_LOCK(p);
                PROC_SLOCK(p);
                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);
        }

        /*
         * Look in the orphans list too, to allow the parent to
         * collect it's child exit status even if child is being
         * debugged.
         *
         * Debugger detaches from the parent upon successful
         * switch-over from parent to child.  At this point due to
         * re-parenting the parent loses the child to debugger and a
         * wait4(2) call would report that it has no children to wait
         * for.  By maintaining a list of orphans we allow the parent
         * to successfully wait until the child becomes a zombie.
         */
        LIST_FOREACH(p, &q->p_orphans, p_orphan) {
                ret = proc_to_reap(td, p, pid, status, options, rusage);
                if (ret == 0)
                        continue;
                else if (ret == 1)
                        nfound++;
                else
                        return (0);
        }
        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);

        clear_orphan(child);
        if (child->p_flag & P_TRACED) {
                LIST_INSERT_HEAD(&child->p_pptr->p_orphans, child, p_orphan);
                child->p_flag |= P_ORPHAN;
        }

        child->p_pptr = parent;
}