interesting way to break ext3 using loop devices

[Andi Kleen <ak@suse.de>]

By mistake i found a sick way to break ext3:

Create a sparse (only consisting of a large hole) loop file on a ext3 file system.
losetup a loop device over it
Create a ext3 file system in the loop device
Mount it.
Copy the "parent" file system into the mounted loop fs with cp -rv
Eventually it will work on the copy of the loop file.

When you Ctrl-C it the system becomes quite confused: 
- Syslog is flooded with IO errors
- The loop fs cannot be unmounted anymore
- sync gets stuck

Of course this was clearly an operator error and
copying a file system into itself is clearly a sick thing 
to do, but still it shouldn't cause symptoms like this. Perhaps
it points to a deeper issue.

-Andi