From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.0 required=3.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C83DDC433E0 for ; Fri, 12 Jun 2020 05:08:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8D3A220801 for ; Fri, 12 Jun 2020 05:08:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726473AbgFLFIc (ORCPT ); Fri, 12 Jun 2020 01:08:32 -0400 Received: from smtp-1.orcon.net.nz ([60.234.4.34]:34317 "EHLO smtp-1.orcon.net.nz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725858AbgFLFIb (ORCPT ); Fri, 12 Jun 2020 01:08:31 -0400 X-Greylist: delayed 1223 seconds by postgrey-1.27 at vger.kernel.org; Fri, 12 Jun 2020 01:08:30 EDT Received: from [121.99.228.40] (port=19283 helo=tower) by smtp-1.orcon.net.nz with esmtpa (Exim 4.90_1) (envelope-from ) id 1jjbbm-0007KJ-5z; Fri, 12 Jun 2020 16:48:02 +1200 Date: Fri, 12 Jun 2020 16:47:57 +1200 From: Michael Cree To: Matt Turner Cc: Kees Cook , Linux-Arch , LKML , linux-alpha , Richard Henderson , Ivan Kokshaysky Subject: Re: Regression bisected to f2f84b05e02b (bug: consolidate warn_slowpath_fmt() usage) Message-ID: <20200612044757.GA10703@tower> Mail-Followup-To: Michael Cree , Matt Turner , Kees Cook , Linux-Arch , LKML , linux-alpha , Richard Henderson , Ivan Kokshaysky References: <20200602024804.GA3776630@p50-ethernet.mattst88.com> <202006021052.E52618F@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-GeoIP: NZ X-Spam_score: -2.9 X-Spam_score_int: -28 X-Spam_bar: -- Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 11, 2020 at 09:23:52PM -0700, Matt Turner wrote: > Since I noticed earlier that using maxcpus=1 on a 2-CPU system > prevented the system from hanging, I tried disabling CONFIG_SMP on my > 1-CPU system as well. In doing so, I discovered that the RCU torture > module (RCU_TORTURE_TEST) triggers some null pointer dereferences on > Alpha when CONFIG_SMP is set, but works successfully when CONFIG_SMP > is unset. > > That seems likely to be a symptom of the same underlying problem that > started this thread, don't you think? If so, I'll focus my attention > on that. I wonder if that is related to user space segfaults we are now seeing on SMP systems but not UP systems while building Alpha debian-ports. It's happening in the test-suites of builds of certain software (such as autogen and guile) but they always build successfully with the test suite passing on a UP system. When investigating I seem to recall it was a NULL (or near NULL) pointer dereference but couldn't make any sense of how it might have got into such an obviously wrong state. Cheers, Michael.