From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753574AbXC3U1L (ORCPT ); Fri, 30 Mar 2007 16:27:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753594AbXC3U1L (ORCPT ); Fri, 30 Mar 2007 16:27:11 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:50617 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753575AbXC3U1J (ORCPT ); Fri, 30 Mar 2007 16:27:09 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Greg KH Cc: Andrew Morton , Mitch Williams , linux-pci@atrey.karlin.mff.cuni.cz, linux-kernel@vger.kernel.org, auke-jan.h.kok@intel.com Subject: Re: [PATCH 2.6.21-rc5] Flush MSI-X table writes (rev 3) References: <1175280848.17652.5.camel@strongmad> <20070330124747.f20c9eb0.akpm@linux-foundation.org> <20070330194956.GA8028@suse.de> Date: Fri, 30 Mar 2007 14:26:03 -0600 In-Reply-To: <20070330194956.GA8028@suse.de> (Greg KH's message of "Fri, 30 Mar 2007 12:49:56 -0700") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Greg KH writes: > On Fri, Mar 30, 2007 at 12:47:47PM -0700, Andrew Morton wrote: >> Did we end up deciding whether this is (needed*safe) enough for 2.6.21? > > I say no for now, I have seen no bug reports for any hardware that is > not in a lab for this. The bug report would be phrased as someone seeing "No irq for vector" on x86_64. Unless they are a skilled developer they are unlikely to trace it down to not flushing posted writes to a MSI bar during irq migration. It part it is a subtle hardware/software race. I have seen some unresolved bug reports described this way on machines that have MSI-X capable hardware. The are against fedora core and I can't haven't been able to get the reporters to try 2.6.21-rcX and the other irq back ports don't work so well. I currently count 7 drivers in 2.6.21 that are susceptible to the race this bug closes. This version of the patch seems to meet all of the criteria for being obviously correct, and all it does is insert a stupid readl. Not very dangerous. This fix removes a race between hardware and software that you likely need to migrate MSI-X irqs a lot to trigger. Which can be the kind of thing that bytes you after you have a month of uptime. This is a very nasty condition to track down from bug reports. I'd rather not have a known culprit out there. Eric