From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753813Ab0CZQPQ (ORCPT <rfc822;w@1wt.eu>);
	Fri, 26 Mar 2010 12:15:16 -0400
Received: from mx1.redhat.com ([209.132.183.28]:6625 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753149Ab0CZQPO (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 26 Mar 2010 12:15:14 -0400
Date: Fri, 26 Mar 2010 17:12:18 +0100
From: Stanislaw Gruszka <sgruszka@redhat.com>
To: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
       Americo Wang <xiyou.wangcong@gmail.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
       Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
       Roland McGrath <roland@redhat.com>,
       Spencer Candland <spencer@bluehost.com>, linux-kernel@vger.kernel.org
Subject: Re: [RFC,PATCH 1/2] cputimers/proc: do_task_stat()->task_times()
	can race with getrusage()
Message-ID: <20100326161218.GA3169@dhcp-lab-161.englab.brq.redhat.com>
References: <20100324204550.GA31777@redhat.com> <20100326035344.GQ3308@balbir.in.ibm.com> <20100326073723.GA2596@dhcp-lab-161.englab.brq.redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20100326073723.GA2596@dhcp-lab-161.englab.brq.redhat.com>
User-Agent: Mutt/1.5.19 (2009-01-05)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Mar 26, 2010 at 08:37:23AM +0100, Stanislaw Gruszka wrote:
> On Fri, Mar 26, 2010 at 09:23:44AM +0530, Balbir Singh wrote:
> > * Oleg Nesterov <oleg@redhat.com> [2010-03-24 21:45:50]:
> > 
> > > do_task_stat()->task_times() can race with getrusage(), they both can
> > > try to update task->prev_Xtime at the same time.
> > > 
> > > Remove this bit of d180c5bc "sched: Introduce task_times() to replace
> > > task_{u,s}time()".
> > 
> > One of the reasons for adding this accuracy was to avoid sampling
> > based noise and errors that occur with utime and stime.
> > 
> > As long as there is no preemption during the assignment, I think we
> > should be OK. 
> > 
> > I see two options
> > 
> > 1. Disable preemption around assignment
> That one sounds very good.
No. Preemption will not help here.

Stanislaw