Re: while_each_thread() under rcu_read_lock() is broken?

[Oleg Nesterov <oleg@redhat.com>]

On 06/24, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
>
> If what we are looking for is a stable list_head that won't disappear
> on us we should be able to put one in sighand_struct or signal_struct
> (I forget which is which at the moment) and have a list_head that
> lives for the life of the longest living thread, and that won't get
> messed up by things like de_thread, and then next_thread could simply
> return NULL when we hit the end of the list.

This was already discussed.

Yes, we can add list_head into signal_struct. But this breaks, say,
thread_group_empty() and the similar code. This is fixeable.

But. We need to convert the code which does while_each_thread(g, t) to
use list_for_each(t, head). And, if g != group_leader this can't work.

Not to mention the increase of sizeof(signal_struct).

Oleg.