Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760915AbXJDQyd (ORCPT ); Thu, 4 Oct 2007 12:54:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757209AbXJDQyZ (ORCPT ); Thu, 4 Oct 2007 12:54:25 -0400 Received: from extu-mxob-2.symantec.com ([216.10.194.135]:49182 "EHLO extu-mxob-2.symantec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755796AbXJDQyY (ORCPT ); Thu, 4 Oct 2007 12:54:24 -0400 Date: Thu, 4 Oct 2007 17:53:46 +0100 (BST) From: Hugh Dickins X-X-Sender: hugh@blonde.wat.veritas.com To: Linus Torvalds cc: gurudas pai , Nick Piggin , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [BUG] kernel BUG at arch/i386/mm/highmem.c:15! on 2.6.23-rc8/rc9 In-Reply-To: Message-ID: References: <47048A0C.4020608@oracle.com> <200710040053.19570.nickpiggin@yahoo.com.au> <200710040139.04201.nickpiggin@yahoo.com.au> <4704BA1F.4070408@oracle.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1373 Lines: 40 On Thu, 4 Oct 2007, Linus Torvalds wrote: > > Ouch. Very much so. > > The patch looks obviously correct, to the point that I don't understand > how this bug happened in the first place. It seems to have been > introduced by Nick in d0217ac04ca6591841e5665f518e38064f4e65bd ("mm: fault > feedback #1") if I read it right. Yes, I think you are reading that right. > > So "do_nonlinear_fault()" would effectively end up unmapping the PTE > twice, right? And if I understand the problem right, this wasn't noticed > immediately, because it probably only matters on: > > - CONFIG_HIGHPTE > *and* > - a filesystem that allows VM_NONLINEAR, which became very rare with > dirty accounting. > > Correct? Correct. And though I eventually realized the nonlinear dirty accounting issue (which I did highlight in the patch comment), I'd forgotten all about needing CONFIG_HIGHPTE in addition to CONFIG_HIGHMEM - yes, that increased the probability of overlooking it too. No excuses that we did miss it in all these months those patches have been around; but it's an object lesson in the trouble rare paths give. Hugh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/