linux-kernel - Re: [PATCH 2.6.27-rc5] Fix itimer/many thread hang.

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Message-ID: <20080910163205.GA478@tv-sign.ru>
Date:	Wed, 10 Sep 2008 20:32:05 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Frank Mayhar <fmayhar@...gle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2.6.27-rc5] Fix itimer/many thread hang.

On 09/09, Frank Mayhar wrote:
>
> On Tue, 2008-09-09 at 20:01 +0400, Oleg Nesterov wrote:
> > The patch has a lot of
> >
> > 	rcu_read_lock();
> > 	sig = rcu_dereference(tsk->signal);
> >
> > This is bogus, task_struct->signal is not protected by RCU.
>
> I just want to snapshot the field
> atomically.  I guess I can just do an atomic read...

Missed this part...

No, no, you don't need an atomic read. Just do

	sig = tsk->signal;
	if (sig)
		use(sig);

->signal must be stable, or the code is buggy anyway. (and the task
never changes its ->signal, it becomes NULL when the task dies).


BTW, thanks for doing this!

Oleg.

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