From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753628AbdKJSmx (ORCPT ); Fri, 10 Nov 2017 13:42:53 -0500 Received: from mail-io0-f174.google.com ([209.85.223.174]:47131 "EHLO mail-io0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753490AbdKJSmv (ORCPT ); Fri, 10 Nov 2017 13:42:51 -0500 X-Google-Smtp-Source: AGs4zMYVmdBapzhvTCtlWhfZRGs+vX0xrR3izzqD+JT9ARp2fI1nm0T+V5l3Zk/4Bz4c7RT7vK8AuufcpMrPRd0HKN0= MIME-Version: 1.0 In-Reply-To: <23f7da04-95f7-24e7-ee70-ce40c5b8fee3@gentoo.org> References: <20171109193715.GB21978@ZenIV.linux.org.uk> <40ad7c6e-f0d7-959a-bf29-d3e3843f5d31@gentoo.org> <23f7da04-95f7-24e7-ee70-ce40c5b8fee3@gentoo.org> From: Linus Torvalds Date: Fri, 10 Nov 2017 10:42:49 -0800 X-Google-Sender-Auth: FWPapppnz9Wjuk3uf1WWad2VEHc Message-ID: Subject: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and 4.13.11 To: Patrick McLean Cc: Al Viro , Bruce Fields , "Darrick J. Wong" , Linux Kernel Mailing List , Linux NFS Mailing List , stable , Thorsten Leemhuis Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 9, 2017 at 5:58 PM, Patrick McLean wrote: > > Something must have changed since 4.13.8 to trigger this though. Well, yes and no. Obviously something changed, but it doesn't necessarily have to be anything particular. Almost every time we've seen compiler bugs, it's been an innocuous change that just happened to trigger a latent issue. Pretty much by definition compiler bugs tend to be about rare situations, so it's some odd special case that triggers. Since it's apparently fairly repeatable for you, a bisection between 4.13.8 and 4.13.11 would be very interesting, and shouldn't take all that long. There's only 142 commits in that range, so even just a partial bisection of say four of five rounds should narrow it down to just a couple of commits. And even a full bisection should only take something like 8 build/test cycles. Arnd pointed to some commits that might be relevant for the cp210x module, but those are all already in 4.13.8, so if 4.13.8 really is rock solid for you, I don't think that's it. I really don't see anything that looks even half-way suspicious in that 4.13.8..11 range. But as mentioned, compiler interactions can be _really_ subtle. And hey, it can be a real kernel bug too, that just happens to be exposed by RANDSTRUCT, so a bisect really would be very nice. Because in the end, compiler bugs are very rare. They are particularly annoying when they do happen, though, so they loom big in the mind of people who have had to chase them down. Linus