For some reason I don't understand, the last UDF filesystem update makes
the UDF deadlock when I write a bunch of mp3 files to a CDRW using the
packet writing patch.  Both "cp" and pdflush get stuck in __down. 

Reverting the semaphore changes makes the problem go away.  Use the
kernel lock again, until whatever recursive offender gets fixed.

(The offensive recursion seems to be: write() takes the inode semaphore,
causes memory pressure, and then trying to write back the inode or dirty
data to disk tries to get the semaphore again and deadlocks.)