Performing verification for Focal.

I started two VMs, both running Focal. One will be the server, the other the client.

On the server:

ubuntu@focal-server:~$ sudo apt update
ubuntu@focal-server:~$ sudo apt install nfs-kernel-server
...
Do you want to continue? [Y/n] y
Get:1 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libtirpc-common all 1.2.5-1ubuntu0.1 [7712 B]
Get:2 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libtirpc3 amd64 1.2.5-1ubuntu0.1 [77.9 kB]
Get:3 http://archive.ubuntu.com/ubuntu focal/main amd64 rpcbind amd64 1.2.5-8 [42.8 kB]
Get:4 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 keyutils amd64 1.6-6ubuntu1.1 [44.8 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal/main amd64 libnfsidmap2 amd64 0.25-5.1ubuntu1 [27.9 kB]
Get:6 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 nfs-common amd64 1:1.3.4-2.5ubuntu3.4 [204 kB]
Get:7 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 nfs-kernel-server amd64 1:1.3.4-2.5ubuntu3.4 [98.9 kB]
...
ubuntu@focal-server:~$ sudo mkdir -p /mnt/nfs_share
ubuntu@focal-server:~$ sudo chown -R nobody:nogroup /mnt/nfs_share/
ubuntu@focal-server:~$ sudo chmod 777 /mnt/nfs_share/
ubuntu@focal-server:~$ echo "/mnt/nfs_share 192.168.122.0/24(rw,sync,no_subtree_check)" | sudo tee /etc/exports
/mnt/nfs_share 192.168.122.0/24(rw,sync,no_subtree_check)
ubuntu@focal-server:~$ sudo exportfs -a
ubuntu@focal-server:~$ sudo systemctl restart nfs-kernel-server
ubuntu@focal-server:~$ echo "Testfile" | tee /mnt/nfs_share/testfile
Testfile
ubuntu@focal-server:~$ ip addr
2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:fa:b4:bc brd ff:ff:ff:ff:ff:ff
    inet 192.168.122.142/24 brd 192.168.122.255 scope global dynamic enp1s0

On the client, using nfs-common 1.3.4-2.5ubuntu3.4 from -updates:

ubuntu@focal-client:~$ sudo apt update
ubuntu@focal-client:~$ sudo apt install nfs-common
...
Get:1 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libtirpc-common all 1.2.5-1ubuntu0.1 [7712 B]
Get:2 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 libtirpc3 amd64 1.2.5-1ubuntu0.1 [77.9 kB]
Get:3 http://archive.ubuntu.com/ubuntu focal/main amd64 rpcbind amd64 1.2.5-8 [42.8 kB]
Get:4 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 keyutils amd64 1.6-6ubuntu1.1 [44.8 kB]
Get:5 http://archive.ubuntu.com/ubuntu focal/main amd64 libnfsidmap2 amd64 0.25-5.1ubuntu1 [27.9 kB]
Get:6 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 nfs-common amd64 1:1.3.4-2.5ubuntu3.4 [204 kB]
...
ubuntu@focal-client:~$ sudo mkdir -p /mnt/nfs_clientshare

On the 5.4 kernel:

ubuntu@focal-client:~$ uname -rv
5.4.0-152-generic #169-Ubuntu SMP Tue Jun 6 22:23:09 UTC 2023
ubuntu@focal-client:~$ sudo mount -t nfs 192.168.122.142:/mnt/nfs_share /mnt/nfs_clientshare -s -o invalid,intr
ubuntu@focal-client:~$ cd /mnt/nfs_clientshare/
ubuntu@focal-client:/mnt/nfs_clientshare$ ll
total 12
drwxrwxrwx 2 nobody nogroup 4096 Aug 20 08:26 ./
drwxr-xr-x 3 root   root    4096 Aug 20 08:27 ../
-rw-rw-r-- 1 ubuntu ubuntu     9 Aug 20 08:26 testfile
ubuntu@focal-client:/mnt/nfs_clientshare$ cat testfile
Testfile

Mounting the share with 1.3.4-2.5ubuntu3.4 in -updates succeeds.

On the 5.15 HWE kernel:

ubuntu@focal-client:~$ uname -rv
5.15.0-79-generic #86~20.04.2-Ubuntu SMP Mon Jul 17 23:27:17 UTC 2023
ubuntu@focal-client:~$ sudo mount -t nfs 192.168.122.142:/mnt/nfs_share /mnt/nfs_clientshare -s -o invalid,intr
mount.nfs: an incorrect mount option was specified

Mounting the share with 1.3.4-2.5ubuntu3.4 in -updates fails, due to the kernel changing how the sloppy mount option is applied, and doesn't like the "invalid" option included on the mount command.

I then enabled -proposed, and installed nfs-common 1.3.4-2.5ubuntu3.5 on the client.

With the 5.4 kernel and 1.3.4-2.5ubuntu3.5 from -proposed:

ubuntu@focal-client:~$ uname -rv
5.4.0-152-generic #169-Ubuntu SMP Tue Jun 6 22:23:09 UTC 2023
ubuntu@focal-client:~$ sudo apt-cache policy nfs-common | grep Installed
  Installed: 1:1.3.4-2.5ubuntu3.5
ubuntu@focal-client:~$ sudo mount -t nfs 192.168.122.142:/mnt/nfs_share /mnt/nfs_clientshare -s -o invalid,intr
ubuntu@focal-client:~$ cd /mnt/nfs_clientshare/
ubuntu@focal-client:/mnt/nfs_clientshare$ ll
total 12
drwxrwxrwx 2 nobody nogroup 4096 Aug 20 08:26 ./
drwxr-xr-x 3 root   root    4096 Aug 20 08:27 ../
-rw-rw-r-- 1 ubuntu ubuntu     9 Aug 20 08:26 testfile
ubuntu@focal-client:/mnt/nfs_clientshare$ cat testfile
Testfile

Mounting the share with 1.3.4-2.5ubuntu3.5 from -proposed continues to succeed, and the new package does not introduce any regressions with the 5.4 kernel.

With the 5.15 kernel and 1.3.4-2.5ubuntu3.5 from -proposed:

ubuntu@focal-client:~$ sudo apt-cache policy nfs-common | grep Installed
  Installed: 1:1.3.4-2.5ubuntu3.5
ubuntu@focal-client:~$ uname -rv
5.15.0-79-generic #86~20.04.2-Ubuntu SMP Mon Jul 17 23:27:17 UTC 2023
ubuntu@focal-client:~$ sudo mount -t nfs 192.168.122.142:/mnt/nfs_share /mnt/nfs_clientshare -s -o invalid,intr
ubuntu@focal-client:~$ cd /mnt/nfs_clientshare/
ubuntu@focal-client:/mnt/nfs_clientshare$ ll
total 12
drwxrwxrwx 2 nobody nogroup 4096 Aug 20 08:26 ./
drwxr-xr-x 3 root   root    4096 Aug 20 08:27 ../
-rw-rw-r-- 1 ubuntu ubuntu     9 Aug 20 08:26 testfile
ubuntu@focal-client:/mnt/nfs_clientshare$ cat testfile
Testfile

Mounting the share with 1.3.4-2.5ubuntu3.5 in -proposed succeeds, and fixes the issue.

1.3.4-2.5ubuntu3.5 fixes the issue with the 5.15 HWE kernel, and does not introduce any regressions when used with the 5.4 kernel. Happy to mark as verified for focal.