We weren't taking the reference count in the delegation recall thread until
we'd already started the new delegation thread (and possibly returned from the
break_lease callback).  That's too late.

Also document some assumptions.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>