Re: [rfc] "fair" rw spinlocks

[Oleg Nesterov <oleg@redhat.com>]

On 12/05, Eric W. Biederman wrote:
>
> Atomically sending signal to every member of a process group, is the
> big fly in the ointment I am aware of.  Last time I looked I could
> not see how to convert it rcu.

I am not sure, but iirc we can do this lockless (under rcu_lock).
We need to modify pid_link to use list_entry and attach_pid() should
add the new task to the end. Of course we need more changes, but
(again iirc) this is not too hard.

> This is a pain because we occasionally signal a process group from
> interrupt context.

Only send_sigio/etc does so, right?


I didn't read the previous discussion yet (will try tomorrow), sorry
if I am off-topic. But I think the nastiest problem with tasklist
is that it protects parent/child relationship. We need per-process
lock, but first we should change ptrace to avoid this lock somehow.
(this is one of the goals of ptrace-utrace, but not "immediate").

Oleg.