From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966630Ab2JZVyf (ORCPT ); Fri, 26 Oct 2012 17:54:35 -0400 Received: from www.linutronix.de ([62.245.132.108]:36311 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964839Ab2JZVyd (ORCPT ); Fri, 26 Oct 2012 17:54:33 -0400 Date: Fri, 26 Oct 2012 23:54:28 +0200 (CEST) From: Thomas Gleixner To: Peter LaDow cc: Eric Dumazet , linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, netfilter@vger.kernel.org Subject: Re: Process Hang in __read_seqcount_begin In-Reply-To: Message-ID: References: <1350925299.8609.978.camel@edumazet-glaptop> <1351053164.6537.95.camel@edumazet-glaptop> <1351270087.30380.9.camel@edumazet-glaptop> <1351285552.30380.20.camel@edumazet-glaptop> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 26 Oct 2012, Peter LaDow wrote: > On Fri, Oct 26, 2012 at 2:05 PM, Eric Dumazet wrote: > If this were safe, we wouldn't be seeing this lockup and your patch > wouldn't be needed. So it seems that your patch doesn't really > address the issue that we are not "sure a thread cannot be interrupted > by a softirq, and cannot migrate to another cpu". Well, we know it > cannot migrate to another CPU, because there isn't another CPU. So > apparently, it can be interrupted by a softirq. So local_bh_disable > isn't doing anything useful in the RT patches with regard to this. RT changes the semantics slightly. And yes it's not prepared for stuff which is relying on some of the magic mainline implicit semantics. Let me have a look at the whole scenario, once I'm more awake. Thanks, tglx