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 [off-list ref]
SUSE Labs, CR