From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753634AbYHLBX2 (ORCPT ); Mon, 11 Aug 2008 21:23:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751934AbYHLBXC (ORCPT ); Mon, 11 Aug 2008 21:23:02 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:34562 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751659AbYHLBXA (ORCPT ); Mon, 11 Aug 2008 21:23:00 -0400 Date: Mon, 11 Aug 2008 21:22:58 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: David Miller cc: a.p.zijlstra@chello.nl, jkacur@gmail.com, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de Subject: Re: [PATCH] BUG: using smp_processor_id() in preemptible [00000000] code: caller is __qdisc_run In-Reply-To: <20080811.142359.145735170.davem@davemloft.net> Message-ID: References: <520f0cf10808110611y62f6a4e2v94a0d0cde1d5d79d@mail.gmail.com> <20080811.140014.94581847.davem@davemloft.net> <1218488979.15798.39.camel@lappy.programming.kicks-ass.net> <20080811.142359.145735170.davem@davemloft.net> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 Aug 2008, David Miller wrote: > From: Peter Zijlstra > Date: Mon, 11 Aug 2008 23:09:38 +0200 > > > On Mon, 2008-08-11 at 14:00 -0700, David Miller wrote: > > > From: "John Kacur" > > > Date: Mon, 11 Aug 2008 15:11:46 +0200 > > > > > > > __qdisc_run() calls qdisc_restart() which calls > > > > handle_dev_cpu_collision(skb, dev, q); and then the problem shows up > > > > here: > > > > __get_cpu_var(netdev_rx_stat).cpu_collision++; > > > > > > > > The solution is to disable interrupts around the above increment. Here > > > > is an attached patch to do so. (Thank's to Peter Zijlstra for help in > > > > the analysis and dropping the answer in my lap, so if I got it right > > > > it is due to his help, but if I messed it up, then I did that part all > > > > by myself.) > > > > > > __qdisc_run() always runs in software interrupt context, > > > so I guess this is some problem with the -rt stuff running > > > software interrupts in threads? > > > > Hmm, good point - and those threads should be cpu affine on -rt if I'm > > not mistaken. Steven, do you happen to remember details? > > The key issue is whether those threads run software interrupts > in a compatible environment. And such a proper environment allows > plain smp_processor_id() without any special preparations. > Yes, we have a softirq thread per CPU. We should have a test in the smp_processor_id for rt to not bug if it is called by known "per_cpu" threads. -- Steve