From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755637AbcFQNcc (ORCPT ); Fri, 17 Jun 2016 09:32:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:40928 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752337AbcFQNca (ORCPT ); Fri, 17 Jun 2016 09:32:30 -0400 Subject: Re: [PATCH v3 7/9] mm/page_owner: avoid null pointer dereference To: js1304@gmail.com, Andrew Morton References: <1466150259-27727-1-git-send-email-iamjoonsoo.kim@lge.com> <1466150259-27727-8-git-send-email-iamjoonsoo.kim@lge.com> Cc: mgorman@techsingularity.net, Minchan Kim , Alexander Potapenko , Hugh Dickins , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sasha Levin , Sudip Mukherjee , Sudip Mukherjee , Joonsoo Kim From: Vlastimil Babka Message-ID: <09cfe295-87d0-16d9-36ed-458378b3bd05@suse.cz> Date: Fri, 17 Jun 2016 15:32:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 MIME-Version: 1.0 In-Reply-To: <1466150259-27727-8-git-send-email-iamjoonsoo.kim@lge.com> Content-Type: text/plain; charset=iso-8859-2; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/17/2016 09:57 AM, js1304@gmail.com wrote: > From: Sudip Mukherjee > > We have dereferenced page_ext before checking it. Lets check it first > and then used it. > > Link: http://lkml.kernel.org/r/1465249059-7883-1-git-send-email-sudipm.mukherjee@gmail.com > Signed-off-by: Sudip Mukherjee > Signed-off-by: Joonsoo Kim Hmm, this is already in mmotm as http://www.ozlabs.org/~akpm/mmotm/broken-out/mm-page_owner-use-stackdepot-to-store-stacktrace-fix.patch But imho it's fixing a problem not related to your patch, but something that the commit f86e4271978b missed. So it should separately go to 4.7 ASAP. Acked-by: Vlastimil Babka Fixes: f86e4271978b ("mm: check the return value of lookup_page_ext for all call sites") > --- > mm/page_owner.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index dc92241..ec6dc18 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -295,13 +295,15 @@ void __dump_page_owner(struct page *page) > .skip = 0 > }; > depot_stack_handle_t handle; > - gfp_t gfp_mask = page_ext->gfp_mask; > - int mt = gfpflags_to_migratetype(gfp_mask); > + gfp_t gfp_mask; > + int mt; > > if (unlikely(!page_ext)) { > pr_alert("There is not page extension available.\n"); > return; > } > + gfp_mask = page_ext->gfp_mask; > + mt = gfpflags_to_migratetype(gfp_mask); > > if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) { > pr_alert("page_owner info is not active (free page?)\n"); >