From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751568AbdBWX0c (ORCPT ); Thu, 23 Feb 2017 18:26:32 -0500 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:43067 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751387AbdBWX03 (ORCPT ); Thu, 23 Feb 2017 18:26:29 -0500 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Fri, 24 Feb 2017 08:26:09 +0900 From: Minchan Kim To: Michal Hocko 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: <20170223232609.GA5631@bbox> References: <1487741964-17913-1-git-send-email-minchan@kernel.org> <20170222121100.GA7954@dhcp22.suse.cz> <20170222143517.GA18974@bbox> <20170222145316.GL5753@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170222145316.GL5753@dhcp22.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 22, 2017 at 03:53:16PM +0100, Michal Hocko wrote: > On Wed 22-02-17 23:35:17, Minchan Kim wrote: > > On Wed, Feb 22, 2017 at 01:11:00PM +0100, Michal Hocko wrote: > > > 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 > > > > No. For driver to support rw_page, every swap_writepage calls rw_page. > > > > swap_writepage > > bdev_writepage > > ops->rw_page > > Ohh, you are right, I have missed this option. I was looking at the > normal swapout path which uses bio. > > > > 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? > > > > Look at other drivers to support rw_page, not zram, esp, brd. > > They can be used for swap device and then can hit the case. > > > > In fact, I encountered the BUG during zram development(i.e., it doesn't > > land to upstream) and it was really hard to figure it out because it made > > random crash, sometime mmap_sem lockdep, sometime other places where > > places never related to zram/zsmalloc, sometime not reproducible. > > > > When I consider how that bug is subtle and people do fast-swap test as brd, > > it's worth to add stable mark, I think. > > Sure, could you add this to the changelog. Along with Fixes tag? I > suspect it is dd6bd0d9c7db ("swap: use bdev_read_page() / > bdev_write_page()") which has introduced this but I didn't look too > close. The patch is trivially correct. Sure. Thanks for the review. Andrew, Could you change description with this? >>From 9efb87a873db67a9e6ebf44fdabf7d05fe4b4e21 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Fri, 4 Nov 2016 09:12:39 +0900 Subject: [PATCH v2] mm: do not access page->mapping directly on page_endio 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. swap_writepage bdev_writepage ops->rw_page I encountered the BUG during developing new zram feature and it was really hard to figure it out because it made random crash, somtime mmap_sem lockdep, sometime other places where places never related to zram/zsmalloc, and not reproducible with some configuration. When I consider how that bug is subtle and people do fast-swap test with brd, it's worth to add stable mark, I think. Fixes: dd6bd0d9c7db ("swap: use bdev_read_page() / bdev_write_page()") Cc: Michal Hocko Cc: Matthew Wilcox Cc: Signed-off-by: Minchan Kim --- * from v1 * add more detailed description with Fix tag - Michal 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