From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zheng Liu Subject: Re: [PATCH 03/12] ext4: Remove bogus wait for unwritten extents in ext4_ind_direct_IO Date: Wed, 23 Jan 2013 00:00:17 +0800 Message-ID: <20130122160017.GA2072@gmail.com> References: <1358510446-19174-1-git-send-email-jack@suse.cz> <1358510446-19174-4-git-send-email-jack@suse.cz> <87k3r5qxpf.fsf@openvz.org> <20130122134400.GB28331@quack.suse.cz> <20130122142221.GA1763@gmail.com> <20130122152243.GB32366@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dmitry Monakhov , Ted Tso , linux-ext4@vger.kernel.org To: Jan Kara Return-path: Received: from mail-pb0-f42.google.com ([209.85.160.42]:57124 "EHLO mail-pb0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753101Ab3AVPqX (ORCPT ); Tue, 22 Jan 2013 10:46:23 -0500 Received: by mail-pb0-f42.google.com with SMTP id rp2so4069795pbb.29 for ; Tue, 22 Jan 2013 07:46:23 -0800 (PST) Content-Disposition: inline In-Reply-To: <20130122152243.GB32366@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Jan 22, 2013 at 04:22:43PM +0100, Jan Kara wrote: > On Tue 22-01-13 22:22:21, Zheng Liu wrote: > > On Tue, Jan 22, 2013 at 02:44:00PM +0100, Jan Kara wrote: > > > On Tue 22-01-13 15:11:24, Dmitry Monakhov wrote: > > > > On Fri, 18 Jan 2013 13:00:37 +0100, Jan Kara wrote: > > > > > When using indirect blocks there is no possibility to have any unwritten > > > > > extents. So wait for them in ext4_ind_direct_IO() is just bogus. > > > > But as soon as i remember indirect implementation may also be used by > > > > extents based inodes 3074: ext4_ext_direct_IO > > > > /* Use the old path for reads and writes beyond i_size. */ > > > > if (rw != WRITE || final_size > inode->i_size) > > > > return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs); > > > > > > > > Am I missing ? > > > Ah, that's a catch. Thanks for pointing that out! So my patch is wrong > > > and that code path needs some cleaning and commenting. In particular I'm > > > afraid using dioread_nolock for inodes with indirect map causes data > > > exposure bugs when unlocked DIO read races with DIO write because such > > > inodes don't support uninitialized extents. > > > > Sorry, but I am still confused. dioread_nolock is only for extent-based > > file. So when a file system without extent feature, dioread_nolock > > couldn't be enabled. It seems that we don't need to worry about > > exposing stale data here. > Well, you can have fs with extent feature enabled but still with inodes > using indirect map. But as Dmitry pointed out, ext4_should_dioread_nolock() > handles that correctly. So there's not a bug I was suspecting. Yep, the patch itself is fine. But that would be great if a comment is added here. Regards, - Zheng