postgresql - FOR UPDATE lock postgresql 9.6

Question

CREATE OR REPLACE FUNCTION public.updatedata(userid_ integer)
RETURNS integer
AS $$
DECLARE
userdata_ integer;
BEGIN

LOOP
BEGIN
     PERFORM 1 FROM public.footable f WHERE f.userid=userid_ LIMIT 1 FOR UPDATE ;
    userdata_:=(SELECT f.userdata FROM public.footable f WHERE f.userid=userid_  );
    UPDATE public.footable f SET userdata = userdata_ + 1 WHERE f.userid=userid_ ;
EXIT ;
EXCEPTION WHEN others THEN
END;
END LOOP;

RETURN userdata_ + 1;
EXCEPTION WHEN others THEN
END $$ language plpgsql;

Can i prevent "lost update" issue for userdata column, when i use "FOR UPDATE" lock like this?

Actually i wanted to use serializable isolation in the first place, but it turns out that in serializable isolation some errors can only be detected after commıt(link)