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Date: Wed, 10 Sep 2008 20:32:05 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Frank Mayhar <fmayhar@google.com>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Roland McGrath <roland@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       Alexey Dobriyan <adobriyan@gmail.com>,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2.6.27-rc5] Fix itimer/many thread hang.
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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.