From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Whitehouse <swhiteho@redhat.com>
Subject: Re: [PATCH v3] vfs: fix a bug when we do some dio reads with
 append dio writes
Date: Mon, 16 Dec 2013 09:37:34 +0000
Message-ID: <1387186654.2736.6.camel@menhir>
References: <1386413726-4610-1-git-send-email-wenqing.lz@taobao.com>
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Cc: linux-fsdevel@vger.kernel.org, Jan Kara <jack@suse.cz>,
	Christoph Hellwig <hch@infradead.org>,
	Dmitry Monakhov <dmonakhov@openvz.org>,
	Dave Chinner <david@fromorbit.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Zheng Liu <wenqing.lz@taobao.com>
To: Zheng Liu <gnehzuil.liu@gmail.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
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Hi,

On Sat, 2013-12-07 at 18:55 +0800, Zheng Liu wrote:
> From: Zheng Liu <wenqing.lz@taobao.com>
> 
> Currently we check i_size in buffered read path after we know the page
> is update.  But it could return some zero-filled pages to the userspace
> when we do some append dio writes.  We could use the following code
> snippet to reproduce this problem in a ext2/3/4 filesystem.
> 
If the page is not uptodate, then neither (potentially) is i_size, since
the underlying fs has not had a chance to get its own locks and update
the inode size.

I suspect that the correct fix would be to implement ->launder_page to
avoid the race that you've identified here, if I've understood it
correctly,

Steve.