Comment 29 for bug 1875577

Validated with ZFS from focal-proposed, according to test case from description:
ubuntu@z-rotomvm34:~$ dpkg -l | grep zfsutils
ii zfsutils-linux 0.8.3-1ubuntu12.12 amd64 command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm34:~$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
rpool 2.50G 25.6G 176K /
rpool/ROOT 2.50G 25.6G 176K none
rpool/ROOT/zfsroot 2.50G 25.6G 2.50G /
ubuntu@z-rotomvm34:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm34:~$ lsblk -e 7
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 512M 0 part /boot/efi
└─vda2 252:2 0 29.5G 0 part
nvme0n1 259:0 0 9.8G 0 disk
└─nvme0n1p1 259:1 0 9.8G 0 part
  └─swap 253:0 0 9.8G 0 crypt [SWAP]

In addition to the test above, I've also tested the configurations suggested in the [Test Plan] section. Besides validating the ordering bug, I've also done basic smoke tests and verified that the ZFS pools are working as expected.

- Encrypted rootfs on LVM + separate ZFS partitions:
ubuntu@ubuntu-focal:~$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfspool 492K 4.36G 96K /mnt/zfspool
zfspool/tank 96K 4.36G 96K /mnt/zfspool/tank
ubuntu@ubuntu-focal:~$ dpkg -l | grep zfsutils
ii zfsutils-linux 0.8.3-1ubuntu12.12 amd64 command-line tools to manage OpenZFS filesystems
ubuntu@ubuntu-focal:~$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfspool 492K 4.36G 96K /mnt/zfspool
zfspool/tank 96K 4.36G 96K /mnt/zfspool/tank
ubuntu@ubuntu-focal:~$ sudo journalctl -b | grep -i ordering
ubuntu@ubuntu-focal:~$ lsblk -e7
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sr0 11:0 1 1024M 0 rom
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 512M 0 part /boot/efi
├─vda2 252:2 0 1K 0 part
├─vda5 252:5 0 731M 0 part /boot
└─vda6 252:6 0 28.8G 0 part
  └─vda6_crypt 253:0 0 28.8G 0 crypt
    ├─vgubuntu--focal-root 253:1 0 27.8G 0 lvm /
    └─vgubuntu--focal-swap_1 253:2 0 980M 0 lvm [SWAP]
vdb 252:16 0 5G 0 disk
├─vdb1 252:17 0 5G 0 part
└─vdb9 252:25 0 8M 0 part

- ZFS on LUKS
ubuntu@z-rotomvm33:~$ dpkg -l | grep zfsutils
ii zfsutils-linux 0.8.3-1ubuntu12.12 amd64 command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm33:~$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfspool 612K 9.20G 96K /mnt/zfspool
zfspool/tank 96K 9.20G 96K /mnt/zfspool/tank
ubuntu@z-rotomvm33:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm33:~$ lsblk -e7
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 512M 0 part /boot/efi
└─vda2 252:2 0 29.5G 0 part /
nvme0n1 259:0 0 9.8G 0 disk
└─nvme0n1p1 259:1 0 9.8G 0 part
  └─zfspool 253:0 0 9.8G 0 crypt
ubuntu@z-rotomvm33:~$ cat /etc/crypttab
# <target name> <source device> <key file> <options>
zfspool /dev/nvme0n1p1 /etc/keyfile luks

- ZFS on dm-raid
ubuntu@z-rotomvm33:~$ dpkg -l | grep zfsutils
ii zfsutils-linux 0.8.3-1ubuntu12.12 amd64 command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm33:~$ zfs list
NAME USED AVAIL REFER MOUNTPOINT
zfspool 612K 9.20G 96K /mnt/zfspool
zfspool/tank 96K 9.20G 96K /mnt/zfspool/tank
ubuntu@z-rotomvm33:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm33:~$ lsblk -e7
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda 252:0 0 30G 0 disk
├─vda1 252:1 0 512M 0 part /boot/efi
└─vda2 252:2 0 29.5G 0 part /
nvme0n1 259:0 0 9.8G 0 disk
└─md127 9:127 0 9.8G 0 raid0
  ├─md127p1 259:1 0 9.8G 0 part
  └─md127p9 259:2 0 8M 0 part