Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752042AbdFUU4W (ORCPT ); Wed, 21 Jun 2017 16:56:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37978 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751108AbdFUU4V (ORCPT ); Wed, 21 Jun 2017 16:56:21 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com A47137EBD6 Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx03.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=oleg@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com A47137EBD6 Date: Wed, 21 Jun 2017 22:56:17 +0200 From: Oleg Nesterov To: Linus Torvalds Cc: Hugh Dickins , kernel test robot , Michal Hocko , LKML , LKP Subject: Re: [lkp-robot] [mm] 1be7107fbe: kernel_BUG_at_mm/mmap.c Message-ID: <20170621205617.GA29841@redhat.com> References: <20170621023552.GB32082@yexl-desktop> <20170621193338.GA29222@redhat.com> <20170621202751.GA29638@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 21 Jun 2017 20:56:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1047 Lines: 29 On 06/21, Linus Torvalds wrote: > > On Wed, Jun 21, 2017 at 1:27 PM, Oleg Nesterov wrote: > > > > Now __do_page_fault() tries to expand the stack itself, and this check > > fails. > > But we want that check to trigger and cause the access to fail. > Accessing the stack below the stack pointer is wrong. I understand. My point is that this check was invalidated by stack-guard-page a long ago, and this means that we add the user-visible change now. > Do you have a pointer to the report for this regression? I must have missed it. See http://marc.info/?t=149794523000001&r=1&w=2 this thread is a bit confusing, the most relevant emails are http://marc.info/?l=linux-kernel&m=149806256621440&w=2 (with test case) http://marc.info/?l=linux-kernel&m=149806452322233&w=2 Actually, I got another (redhat internal) bug report after this discussion, and at first glance this is the same thing. Just in case, I agree that mmap(MAP_GROWSDOWN) is mostly useless, perhaps we do not even care. But still this is regression. Oleg.