linux-kernel - Re: [PATCH 1/1] ptrace: do_wait(traced_leader_killed_by_mt

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Message-ID: <20110722084430.GF2622@htj.dyndns.org>
Date:	Fri, 22 Jul 2011 10:44:30 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>, mtk.manpages@...il.com,
	Jan Kratochvil <jan.kratochvil@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ptrace: do_wait(traced_leader_killed_by_mt_exec) can
 block forever

Hello,

On Thu, Jul 21, 2011 at 08:00:43PM +0200, Oleg Nesterov wrote:
> It is racy, exit_notify() does __wake_up_parent() too. But in the
> likely case it triggers the problem: de_thread() does release_task()
> and the old leader goes away without the notification, the tracer
> sleeps in do_wait() without children/tracees.
> 
> Change de_thread() to do __wake_up_parent(traced_leader->parent).
> Since it is already EXIT_DEAD we can do this without ptrace_unlink(),
> EXIT_DEAD threads do not exist from do_wait's pov.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Nice catch as always. :)

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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