From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cn.fujitsu.com ([222.73.24.84]:47894 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1754465Ab2F2CTw (ORCPT ); Thu, 28 Jun 2012 22:19:52 -0400 Message-ID: <4FED107B.9020308@cn.fujitsu.com> Date: Fri, 29 Jun 2012 10:18:35 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com MIME-Version: 1.0 To: Josef Bacik CC: "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH] Btrfs: fix dio write vs buffered read race V2 References: <1340718176-4999-1-git-send-email-jbacik@fusionio.com> <4FEBD0EC.6070802@cn.fujitsu.com> <20120628123422.GB1729@localhost.localdomain> In-Reply-To: <20120628123422.GB1729@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Thu, 28 Jun 2012 08:34:23 -0400, Josef Bacik wrote: > On Wed, Jun 27, 2012 at 09:35:08PM -0600, Miao Xie wrote: >> On Tue, 26 Jun 2012 09:42:56 -0400, Josef Bacik wrote: >>> From: Josef Bacik >>> >>> Miao pointed out there's a problem with mixing dio writes and buffered >>> reads. If the read happens between us invalidating the page range and >>> actually locking the extent we can bring in pages into page cache. Then >>> once the write finishes if somebody tries to read again it will just find >>> uptodate pages and we'll read stale data. So we need to lock the extent and >>> check for uptodate bits in the range. If there are uptodate bits we need to >>> unlock and invalidate again. This will keep this race from happening since >>> we will hold the extent locked until we create the ordered extent, and then >>> teh read side always waits for ordered extents. Thanks, >> >> This patch still can not work well. It is because we don't update i_size in time. >> Writer Worker Reader >> lock_extent >> do direct io >> end io >> finish io >> unlock_extent >> lock_extent >> check the pos is beyond EOF or not >> beyond EOF, zero the page and set it uptodate >> unlock_extent >> update i_size >> >> So I think we must update the i_size in time, and I wrote a small patch to do it: >> > > We should probably be updating i_size when we create an extent past EOF in the > write stuff, not during endio, I will work this out and fold it into my patch. > Good catch. It is better that update i_size in endio, I think. because during endio, we are sure that the data is flushed into the disk successfully, and can update i_size at ease. and if the error happens when flushing the data into the disk, we also needn't reset i_size. Thanks Miao