From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932806AbdBVOfa (ORCPT ); Wed, 22 Feb 2017 09:35:30 -0500 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:53600 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932686AbdBVOfX (ORCPT ); Wed, 22 Feb 2017 09:35:23 -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: Wed, 22 Feb 2017 23:35:17 +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: <20170222143517.GA18974@bbox> References: <1487741964-17913-1-git-send-email-minchan@kernel.org> <20170222121100.GA7954@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170222121100.GA7954@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 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 > 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.