From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f179.google.com (mail-pd0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id BA8436B0038 for ; Sat, 21 Mar 2015 13:45:24 -0400 (EDT) Received: by pdbcz9 with SMTP id cz9so140329463pdb.3 for ; Sat, 21 Mar 2015 10:45:24 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id ug8si12999126pac.7.2015.03.21.10.45.22 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 21 Mar 2015 10:45:23 -0700 (PDT) Message-ID: <550DAE23.7030000@oracle.com> Date: Sat, 21 Mar 2015 11:45:07 -0600 From: David Ahern MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds Cc: linux-mm , LKML 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org