daemonizing tasks detach controlling tty?

Hija,

I'm trying to spawn new threads from a function called from alloc_uid using daemonize as soon as a new user appears on the system. Somehow this detaches the original shell from the tty causing an exit not only of the child but also it's parent.

A diagram of the situation would lock like this:

getty -> (login of root) bash -> (su to another user) bash -> [new thread is spawned] (whatever) -> exit -> getty

Alternativly, when directly logging in a non-root user:
getty -> (login of foo) motd -> [hang]

How can I daemonize something without disturbing other processes? I already tried playing with reparent_to_init and some signal stuff as done by other parts of the kernel but to no avail.

Servus,
       Daniel