From: BlaisorBlade <blaisorblade_spam@yahoo.it>, Chris Wright <chrisw@osdl.org>

Avoid deadlocking onto the request lock in the UBD driver, i.e.  don't lock
the queue spinlock when called from the request function.

In detail:

Rename ubd_finish() to __ubd_finish() and remove ubd_io_lock from it.  Add
wrapper, ubd_finish(), which grabs lock before calling __ubd_finish().  Update
do_ubd_request to use the lock free __ubd_finish() to avoid deadlock.  Also,
apparently prepare_request is called with ubd_io_lock held, so remove locks
there.
Signed-off-by: Chris Wright <chrisw@osdl.org>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>