get rid of propagate_umount() mistakenly treating slaves as busy.

commit 88b368f27a094277143d8ecd5a056116f6a41520 upstream.

The check in __propagate_umount() ("has somebody explicitly mounted
something on that slave?") is done *before* taking the already doomed
victims out of the child lists.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/pnode.c b/fs/pnode.c
index a364a70..b7f8310 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -381,6 +381,7 @@
 		 * other children
 		 */
 		if (child && list_empty(&child->mnt_mounts)) {
+			list_del_init(&child->mnt_child);
 			hlist_del_init_rcu(&child->mnt_hash);
 			hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
 		}