From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f50.google.com (mail-pa0-f50.google.com [209.85.220.50]) by kanga.kvack.org (Postfix) with ESMTP id 07A656B0069 for ; Mon, 1 Dec 2014 00:25:11 -0500 (EST) Received: by mail-pa0-f50.google.com with SMTP id bj1so10297890pad.23 for ; Sun, 30 Nov 2014 21:25:10 -0800 (PST) Received: from ozlabs.org (ozlabs.org. [103.22.144.67]) by mx.google.com with ESMTPS id wu7si4649937pbc.226.2014.11.30.21.25.08 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 30 Nov 2014 21:25:09 -0800 (PST) Date: Mon, 1 Dec 2014 16:24:48 +1100 From: Paul Mackerras Subject: Re: [PATCH v2] slab: Fix nodeid bounds check for non-contiguous node IDs Message-ID: <20141201052448.GC11234@drongo> References: <20141201042844.GB11234@drongo> <1417410134.16178.2.camel@concordia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417410134.16178.2.camel@concordia> Sender: owner-linux-mm@kvack.org List-ID: To: Michael Ellerman Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Pekka Enberg , linuxppc-dev@ozlabs.org, David Rientjes , Christoph Lameter , Joonsoo Kim On Mon, Dec 01, 2014 at 04:02:14PM +1100, Michael Ellerman wrote: > On Mon, 2014-12-01 at 15:28 +1100, Paul Mackerras wrote: > > The bounds check for nodeid in ____cache_alloc_node gives false > > positives on machines where the node IDs are not contiguous, leading > > to a panic at boot time. For example, on a POWER8 machine the node > > IDs are typically 0, 1, 16 and 17. This means that num_online_nodes() > > returns 4, so when ____cache_alloc_node is called with nodeid = 16 the > > VM_BUG_ON triggers, like this: > ... > > > > To fix this, we instead compare the nodeid with MAX_NUMNODES, and > > additionally make sure it isn't negative (since nodeid is an int). > > The check is there mainly to protect the array dereference in the > > get_node() call in the next line, and the array being dereferenced is > > of size MAX_NUMNODES. If the nodeid is in range but invalid (for > > example if the node is off-line), the BUG_ON in the next line will > > catch that. > > When did this break? How come we only just noticed? Commit 14e50c6a9bc2, which went into 3.10-rc1. You'll only notice if you have CONFIG_SLAB=y and CONFIG_DEBUG_VM=y and you're running on a machine with discontiguous node IDs. > Also needs: > > Cc: stable@vger.kernel.org It does. I remembered that a minute after I sent the patch. Paul. -- 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