Re: [PATCH] fix group stop with exit race

[Davide Libenzi <davidel@xmailserver.org>]

On Wed, 5 Dec 2007, Oleg Nesterov wrote:

> do_signal_stop() counts all sub-thread and sets ->group_stop_count accordingly.
> Every thread should decrement ->group_stop_count and stop, the last one should
> notify the parent.
> 
> However a sub-thread can exit before it notices the signal_pending(), or it may
> be somewhere in do_exit() already. In that case the group stop never finishes
> properly.
> 
> Note: this is a minimal fix, we can add some optimizations later. Say we can
> return quickly if thread_group_empty(). Also, we can move some signal related
> code from exit_notify() to exit_signals().
> 
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

Looks OK for me, even though we're doing more work on the exit path. OTOH 
I don't see a non-racy way of doing it w/out grabbing the lock. Did you 
try to bench how much this change costs?
Anyway, looks sane to me...

Acked-by: Davide Libenzi <davidel@xmailserver.org>



- Davide