linux-kernel - Re: [patch 4/4] taskstats: Export "cdata

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Message-ID: <20101129180854.GA21217@redhat.com>
Date:	Mon, 29 Nov 2010 19:08:54 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc:	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [patch 4/4] taskstats: Export "cdata_acct" with taskstats

On 11/29, Michael Holzheu wrote:
>
> Hello Oleg,
>
> On Mon, 2010-11-29 at 17:43 +0100, Oleg Nesterov wrote:
> > > I just did it like it is done in e.g. fs/proc/base.c (proc_pid_limits).
> > > Can we remove the locking there, too?
> >
> > We can certainly remove more siglock's which were previously
> > needed to access ->signal.
> >
> > This particular one is just wrong. We need task_lock(group_leader)
> > to read signal->rlim atomically. However, it is not trivial to do
> > this correctly. Probably we should ignore this minor problem.
> >
> > In any case, this ->siglock buys nothing today.
>
> But at least to get the two values cutime and cstime consistent we need
> the siglock? There could be a parallel update for
> tsk->signal->cutime/cstime, while the taskstats are created, no?

I guess you mean 4/4 you sent. Probably you are right, I'll try
to look tomorrow.

Oleg.

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