From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Cree Subject: Re: Regression bisected to f2f84b05e02b (bug: consolidate warn_slowpath_fmt() usage) Date: Fri, 12 Jun 2020 16:47:57 +1200 Message-ID: <20200612044757.GA10703@tower> References: <20200602024804.GA3776630@p50-ethernet.mattst88.com> <202006021052.E52618F@keescook> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-alpha-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Matt Turner Cc: Kees Cook , Linux-Arch , LKML , linux-alpha , Richard Henderson , Ivan Kokshaysky 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.