stable inclusion
from linux-4.19.170
commit f9f5547bf02a8ec1a9240b8ab6fece5b28d74d1b

--------------------------------

commit 9b594826 upstream.

With external metadata device, flush requests are not passed down to the
data device.

Fix this by submitting the flush request in dm_integrity_flush_buffers. In
order to not degrade performance, we overlap the data device flush with
the metadata device flush.
Reported-by: NLukas Straub <lukasstraub2@web.de>
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: NMike Snitzer <snitzer@redhat.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>