From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750720AbZESJAp (ORCPT ); Tue, 19 May 2009 05:00:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750778AbZESJAj (ORCPT ); Tue, 19 May 2009 05:00:39 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:39404 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751940AbZESJAi (ORCPT ); Tue, 19 May 2009 05:00:38 -0400 Subject: Re: [GIT PULL] cputime patch for 2.6.30-rc6 From: Peter Zijlstra To: Martin Schwidefsky Cc: Linus Torvalds , linux-kernel , Michael Abbott , Jan Engelhardt In-Reply-To: <20090519104900.12e1f80c@skybase> References: <20090518160904.7df88425@skybase> <1242660243.26820.439.camel@twins> <20090519104900.12e1f80c@skybase> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 19 May 2009 11:00:35 +0200 Message-Id: <1242723635.26820.471.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-05-19 at 10:49 +0200, Martin Schwidefsky wrote: > Well, don't do stupid things like that. That falls into the same > category as programs calling gettimeofday all the time. Is gtod a global DoS? The worry I have about these cputime for_each_cpu() loops in the proc code is that any odd unpriv user can take the whole machine down (provided the machine is large enough). Granted, this would only be a real problem for SGI and their insane boxes atm, but it might very well be a problem for us in the near future, given the rate Intel seems to increase cores. So, I'm really not objecting too much to the patch at hand, but I'd love to find a solution to this problem. My personal favourite is to lower the resolution/accuracy of the answer the bigger the box gets.