diff -NurpP --minimal linux-2.6.10-rc1/fs/namespace.c linux-2.6.10-rc1-umount_tree/fs/namespace.c
--- linux-2.6.10-rc1/fs/namespace.c	2004-10-31 00:41:02.000000000 +0200
+++ linux-2.6.10-rc1-umount_tree/fs/namespace.c	2004-11-06 04:38:37.299013810 +0100
@@ -358,6 +358,7 @@ void umount_tree(struct vfsmount *mnt)
 		} else {
 			struct nameidata old_nd;
 			detach_mnt(mnt, &old_nd);
+			mnt->mnt_namespace = NULL;
 			spin_unlock(&vfsmount_lock);
 			path_release(&old_nd);
 		}