On Sun, Oct 12, 2014 at 04:50:58PM +0800, Eryu Guan wrote:

Corrupted ext4_dir_entry_2 struct on disk may have wrong inode number,
when the inode number is 8 (EXT4_JOURNAL_INO) and the file is deleted,
the journal inode is gone, and unmounting such a fs could trigger the
following BUG_ON() in start_this_handle()....

I believe the bug that this patch is trying to fix has been addressed
by this commit:

http://git.kernel.org/cgit/linux/kernel/git/tytso/ext4.git/commit/?h=dev&id=bf8ad98e1bffa5ce178ef5e4ea803a86ac30f9e5

ext4: add ext4_iget_normal() which is to be used for dir tree lookups
If there is a corrupted file system which has directory entries that
point at reserved, metadata inodes, prohibit them from being used by
treating them the same way we treat Boot Loader inodes --- that is,
mark them to be bad inodes.  This prohibits them from being opened,
deleted, or modified via chmod, chown, utimes, etc.

In particular, this prevents a corrupted file system which has a
directory entry which points at the journal inode from being deleted
and its blocks released, after which point Much Hilarity Ensues.

Reported-by: Sami Liedes <redacted>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

					- Ted