From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753067AbdKIH5N (ORCPT ); Thu, 9 Nov 2017 02:57:13 -0500 Received: from mx2.suse.de ([195.135.220.15]:49698 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753035AbdKIH5L (ORCPT ); Thu, 9 Nov 2017 02:57:11 -0500 Date: Thu, 9 Nov 2017 08:57:09 +0100 From: Michal Hocko To: akpm@linux-foundation.org Cc: Jaewon Kim , Joonsoo Kim , vbabka@suse.cz, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com Subject: Re: [PATCH] mm: page_ext: check if page_ext is not prepared Message-ID: <20171109075709.b4umhipfg3n33qs7@dhcp22.suse.cz> References: <20171107094131.14621-1-jaewon31.kim@samsung.com> <20171107094730.5732nqqltx2miszq@dhcp22.suse.cz> <20171108075956.GC18747@js1304-P5Q-DELUXE> <20171108142106.v76ictdykeqjzhhh@dhcp22.suse.cz> <20171109043552.GC24383@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171109043552.GC24383@js1304-P5Q-DELUXE> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew, On Thu 09-11-17 13:35:53, Joonsoo Kim wrote: > On Wed, Nov 08, 2017 at 03:21:06PM +0100, Michal Hocko wrote: > > On Wed 08-11-17 16:59:56, Joonsoo Kim wrote: > > > On Tue, Nov 07, 2017 at 10:47:30AM +0100, Michal Hocko wrote: [...] > > > > I suspec this goes all the way down to when page_ext has been > > > > resurrected. It is quite interesting that nobody has noticed this in 3 > > > > years but maybe the feature is not used all that much and the HW has to > > > > be quite special to trigger. Anyway the following should be added > > > > > > > > Fixes: eefa864b701d ("mm/page_ext: resurrect struct page extending code for debugging") > > > > Cc: stable > > > > > > IIRC, caller of lookup_page_ext() doesn't check 'NULL' until > > > f86e427197 ("mm: check the return value of lookup_page_ext for all > > > call sites"). So, this problem would happen old kernel even if this > > > patch is applied to old kernel. > > > > OK, then the changelog should mention dependency on that check so that > > anybody who backports this patch to pre 4.7 kernels knows to pull that > > one as well. > > > > > IMO, proper fix is to check all the pfn in the section. It is sent > > > from Jaewon in other mail. > > > > I believe that this patch is valuable on its own and the other one > > should build on top of it. > > Okay, agreed. could you add a note that stable backporters need to consider f86e427197. Something like Cc: stable # depends on f86e427197 Thanks -- Michal Hocko SUSE Labs