On Sun, Sep 11, 2011 at 08:14:42PM +0200, Oleg Nesterov wrote:
> We need to rework the locking, yes. But we need the lock which protects
> the parent's list_head (currently we rely on tasklist). Yes, a single
> lock can't help. We already use ->cred_guard_mutex though.
> 
> This needs more thinking, but imho child->siglock is pointless here.

But we can at least guarantee that if ->ptrace is set (or clear) while
tracee's siglock is held, its ->parent points to the tracer (or not).
At any rate, AFAICS, this currently doesn't really matter.  I
suggested it mainly because it would make the locking change easier.

Thanks.

-- 
tejun