Merge branch 'md-next' of git://git.kernel.org/pub/scm/linux/kernel/git/song/md into for-5.6/drivers
Pull MD changes from Song.
* 'md-next' of git://git.kernel.org/pub/scm/linux/kernel/git/song/md:
md/raid1: introduce wait_for_serialization
md/raid1: use bucket based mechanism for IO serialization
md: introduce a new struct for IO serialization
md: don't destroy serial_info_pool if serialize_policy is true
raid1: serialize the overlap write
md: reorgnize mddev_create/destroy_serial_pool
md: add serialize_policy sysfs node for raid1
md: prepare for enable raid1 io serialization
md: fix a typo s/creat/create
md: rename wb stuffs
raid5: remove worker_cnt_per_group argument from alloc_thread_groups
md/raid6: fix algorithm choice under larger PAGE_SIZE
raid6/test: fix a compilation warning
raid6/test: fix a compilation error
md-bitmap: small cleanups
