From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754755AbdBVMLK (ORCPT ); Wed, 22 Feb 2017 07:11:10 -0500 Received: from mx2.suse.de ([195.135.220.15]:57172 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752397AbdBVMLE (ORCPT ); Wed, 22 Feb 2017 07:11:04 -0500 Date: Wed, 22 Feb 2017 13:11:00 +0100 From: Michal Hocko To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, kernel-team@lge.com, Matthew Wilcox , stable@vger.kernel.org Subject: Re: [PATCH] mm: do not access page->mapping directly on page_endio Message-ID: <20170222121100.GA7954@dhcp22.suse.cz> References: <1487741964-17913-1-git-send-email-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1487741964-17913-1-git-send-email-minchan@kernel.org> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 22-02-17 14:39:24, Minchan Kim wrote: > With rw_page, page_endio is used for completing IO on a page > and it propagates write error to the address space if the IO > fails. The problem is it accesses page->mapping directly which > might be okay for file-backed pages but it shouldn't for > anonymous page. Otherwise, it can corrupt one of field from > anon_vma under us and system goes panic randomly. I was about to say that anonymous pages shouldn't hit that path because the end_swap_bio_write doesn call page_endio. But then I've noticed that zram does call this function. On a closer look, though, it doesn't seem to call it with err != 0 so it cannot hit this path. So I am wondering whether this actually fixes anything. Why it has been marked for stable? > > Cc: Matthew Wilcox > Cc: > Signed-off-by: Minchan Kim > --- > mm/filemap.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 2ba46f410c7c..1944c631e3e6 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1008,9 +1008,12 @@ void page_endio(struct page *page, bool is_write, int err) > unlock_page(page); > } else { > if (err) { > + struct address_space *mapping; > + > SetPageError(page); > - if (page->mapping) > - mapping_set_error(page->mapping, err); > + mapping = page_mapping(page); > + if (mapping) > + mapping_set_error(mapping, err); > } > end_page_writeback(page); > } > -- > 2.7.4 -- Michal Hocko SUSE Labs