linux-kernel - Re: [ext3/4] PROBLEM: fdatasync not syncing appended data (w/test program)

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Date:	Mon, 3 Sep 2012 15:57:56 +0200
From:	Jan Kara <jack@...e.cz>
To:	Kristian Nielsen <knielsen@...elsen-hq.org>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [ext3/4] PROBLEM: fdatasync not syncing appended data (w/test
 program)

On Mon 03-09-12 10:45:15, Kristian Nielsen wrote:
> It appears that ext3 and ext4 fdatasync() does not fully sync data to
> disk. Specifically, when new data is written at the end (so that the file
> length is increased), not all of the new data is synced by fdatasync().
> 
> It looks as if the problem is when the new data fits in the last allocated
> page for the file - then ext3/4 flushes the new data page to disk, but _not_
> the new metadata with the longer file size.
  Thanks for the detailed analysis. This is indeed a genuine bug. While
fixing some fsync issues I introduced (or better didn't fix) this problem.
The culprit is that we forget to update i_datasync_tid when we change only
inode size. Thus inode is not forced to disk during fdatasync(). I will send
fixes for this in a moment.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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