From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751674AbbCURp1 (ORCPT ); Sat, 21 Mar 2015 13:45:27 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:36452 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751527AbbCURpY (ORCPT ); Sat, 21 Mar 2015 13:45:24 -0400 Message-ID: <550DAE23.7030000@oracle.com> Date: Sat, 21 Mar 2015 11:45:07 -0600 From: David Ahern User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Linus Torvalds CC: linux-mm , LKML Subject: Re: 4.0.0-rc4: panic in free_block References: <550C37C9.2060200@oracle.com> <550CA3F9.9040201@oracle.com> <550CB8D1.9030608@oracle.com> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: userv0022.oracle.com [156.151.31.74] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/20/15 6:47 PM, Linus Torvalds wrote: > >> Here's another data point: If I disable NUMA I don't see the problem. >> Performance drops, but no NULL pointer splats which would have been panics. > > So the NUMA case triggers the per-node "n->shared" logic, which > *should* be protected by "n->list_lock". Maybe there is some bug there > - but since that code seems to do ok on x86-64 (and apparently older > sparc too), I really would look at arch-specific issues first. You raise a lot of valid questions and something to look into. But if the root cause were such a fundamental issue (CPU memory ordering, compiler bug, etc) why would it only occur on this one code path -- free with SLAB and NUMA -- and so consistently? Continuing to poke around, but open to any suggestions. I have enabled every DEBUG I can find in the memory code and nothing is popping out. In terms of races wouldn't all the DEBUG checks affect timing? Yet, I am still seeing the same stack traces due to the same root cause. David