SB_FLAG_RESHAPE_BACKWARDS
sb->flags |= cpu_to_le32(SB_FLAG_RESHAPE_BACKWARDS);
sb->flags &= ~(cpu_to_le32(SB_FLAG_RESHAPE_ACTIVE|SB_FLAG_RESHAPE_BACKWARDS));
(!mddev->delta_disks && (le32_to_cpu(sb->flags) & SB_FLAG_RESHAPE_BACKWARDS)))