1. XFS_bread for buffers with no vnode calls brelse which in turn calls bdirty
   and blows up in reassignbuf. Currently the only known case which can trip on
   this is XFS log writes during recovery. Since buffer is locked recursively
   in xlog_bwrite, I work around the whole issue by simply unlocking the
   buffer if BUF_REFCNT(bp) > 1. Need a proper fix.

2. Unmount seems to blow up if some processor still has XFS directory as
   its current directory.
