Yes, me too.  generic_shutdown_super() takes lock_super().  And udf uses
lock_super for protecting its block allocation data strutures.  Trivial
deadlock on unmount.

Below is a fix to switch udf to it's own private locking.  It's safe
because it doesn't intefere with VFS lock_super usage anywhere.

udf_free_inode has some more updates than simply switching the used
lock:

 - clear_inode() call moved outside locked section to avoid another
   deadlock
 - unused variable ino killed
 - is_directory moved into the conditional it's actually used in
Signed-off-by: Christoph Hellwig <hch@lst.de>

(note that I see memory corruption in UDF_I_DATA(inode), but I've
reproduced that with a kernel without all recent udf changes.  I'll
debug that one further)
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>