Merge tag 'md/3.13-fixes' of git://neil.brown.name/md

Pull md fixes from Neil Brown:
 "Three bug fixes for md in 3.13-rc

  All recent regressions, one in 3.12 so marked for -stable"

* tag 'md/3.13-fixes' of git://neil.brown.name/md:
  md/raid5: fix newly-broken locking in get_active_stripe.
  md: test mddev->flags more safely in md_check_recovery.
  md/raid5: fix new memory-reference bug in alloc_thread_groups.