From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zheng Liu Subject: Re: [PATCH 4/7] ext4: fsync should wait for DIO writers Date: Thu, 13 Sep 2012 20:36:32 +0800 Message-ID: <20120913123632.GA13319@gmail.com> References: <1347211634-11509-1-git-send-email-dmonakhov@openvz.org> <1347211634-11509-5-git-send-email-dmonakhov@openvz.org> <20120913104621.GC11330@gmail.com> <874nn25gqi.fsf@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz, wenqing.lz@taobao.com To: Dmitry Monakhov Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:55013 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757997Ab2IMM0J (ORCPT ); Thu, 13 Sep 2012 08:26:09 -0400 Received: by pbbrr13 with SMTP id rr13so3869335pbb.19 for ; Thu, 13 Sep 2012 05:26:08 -0700 (PDT) Content-Disposition: inline In-Reply-To: <874nn25gqi.fsf@openvz.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Sep 13, 2012 at 03:01:25PM +0400, Dmitry Monakhov wrote: > On Thu, 13 Sep 2012 18:46:21 +0800, Zheng Liu wrote: > > On Sun, Sep 09, 2012 at 09:27:11PM +0400, Dmitry Monakhov wrote: > > > fsync and punch_hole are the places where we have to wait for all > > > existing writers (writeback, aio, dio), but currently we simply > > > flush pended end_io request which is not sufficient. > > > Even more i_mutex is not holded while punch_hole which obviously > > > result in dangerous data corruption due to write-after-free. > > > > Hi Dmitry, > > > > Lukas already has a patch to take i_mutex locking before punching a > > hole. Just a reminding. :-) > Yes, i've found it after patch was submitted, but this bug make me > nervous a bit because we have broken punch_hole implementation > long time ago, it allow to destroy data easily, user are able to > call it if has WR permission for a file. > So if you ask be i'll vote for hide it under CAP_SYS_RESOURCE until > proper implementation appears. > Same it true for EXT4_IO_MOVE_EXT because it allow to kernel panic > since v2.6.30-6558-g748de67, so all primary distros (RH6,Deb6) are > affected :( IMHO, it will be better when this patch is applied, and I prefer to fix the problem rather than hidding it using CAP_SYS_RESOURCE. ;-) Regards, Zheng