Merge branch 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md...

Pull MD changes from Song.

* 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md:
  md: no longer compare spare disk superblock events in super_load
  md: improve handling of bio with REQ_PREFLUSH in md_flush_request()
  md/bitmap: avoid race window between md_bitmap_resize and bitmap_file_clear_bit
  md/raid0: Fix an error message in raid0_make_request()