commit ac6d5b27e31b9a6353c6424ac87961a2f816ab43
Author: Mateusz Guzik <mjg@freebsd.org>
Date:   Sun Aug 24 10:26:29 2014 +0200

    Properly reparent traced processes when the tracer dies.
    
    Previously they were uncoditionally reparented to init. In effect
    it was possible that tracee was never returned to original parent.

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 91357a6..e459919 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -156,7 +156,8 @@ sys_sys_exit(struct thread *td, struct sys_exit_args *uap)
 void
 exit1(struct thread *td, int rv)
 {
-	struct proc *p, *nq, *q;
+	struct proc *p, *nq, *q, *t;
+	struct thread *temp;
 	struct vnode *ttyvp = NULL;
 
 	mtx_assert(&Giant, MA_NOTOWNED);
@@ -437,7 +438,9 @@ exit1(struct thread *td, int rv)
 	WITNESS_WARN(WARN_PANIC, NULL, "process (pid %d) exiting", p->p_pid);
 
 	/*
-	 * Reparent all of our children to init.
+	 * Reparent all children processes:
+	 * - traced ones to the original parent (or init if we are that parent)
+	 * - the rest to init
 	 */
 	sx_xlock(&proctree_lock);
 	q = LIST_FIRST(&p->p_children);
@@ -446,15 +449,23 @@ exit1(struct thread *td, int rv)
 	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;
 
+		if (!(q->p_flag & P_TRACED)) {
+			proc_reparent(q, initproc);
+		} else {
+			/*
+			 * Traced processes are killed since their existence
+			 * means someone is screwing up.
+			 */
+			t = proc_realparent(q);
+			if (t == p) {
+				proc_reparent(q, initproc);
+			} else {
+				PROC_LOCK(t);
+				proc_reparent(q, t);
+				PROC_UNLOCK(t);
+			}
 			/*
 			 * Since q was found on our children list, the
 			 * proc_reparent() call moved q to the orphan