linux-kernel - Re: [PATCH] fix group stop with exit race

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Date:	Wed, 5 Dec 2007 17:08:47 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fix group stop with exit race

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@...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@...ilserver.org>



- Davide


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