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

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Message-ID: <20080910121251.GB220@tv-sign.ru>
Date:	Wed, 10 Sep 2008 16:12:51 +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:
>
> > As for this particular function, it seems to me that ->signal == NULL
> > is not possible, no?
>
> That's not completely clear to me.  I'm allowing for the possibility
> that it might be called during, say, process teardown.  It's used in so
> many places that I'm uncomfortable leaving the == NULL check out.

Please see my reply to Roland.

> > Btw, this function has a lot of callers, perhaps it is better to
> > uninline it.
>
> If that's the consensus I'll do so.  I assumed that speed was more
> important than space in this case.  Am I mistaken?

Are you sure inline will be faster? It has a lot of calllers, think
about i-cache. And the function call is not that expensive.

But I am not expert.

> > So, the first CLONE_THREAD creates ->cputime.totals. After that
> > thread_group_cputime_account_xxx() start to use it even if the task
> > doesn't have the attached cpu timers.
> >
> > Stupid question: can't we allocate .totals in posix_cpu_timer_create() /
> > set_process_cpu_timer() ?
>
> That was the original plan but we (that is, Roland and I) decided to
> eliminate the separate storage for the dead-threads totals.  It's now
> all kept in the totals field, for the whole thread group.

I see, thanks.

Oleg.

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