systemd-networkd fails to renew DHCP v4 lease when renew attempt times out

[mark]

I'm seeing exactly what this gist describes:
https://gist.github.com/raggi/1f8d0b9f45c5b62e7131b03e6e2ffe68

Summary:
1. Configure a machine with a DHCPv4 lease on a network with a DHCPv4 server.
2. Place machine under unusual load sufficient to cause a timeout on netlink requests.
3. Observe the interface failing with the following logs:

systemd-networkd[139370]: eth0: Could not set DHCPv4 address: Connection timed out
systemd-networkd[139370]: eth0: Failed

The error seems to come from here: https://github.com/systemd/systemd/blob/v245.4/src/network/networkd-dhcp4.c#L781

Expected behavior
The DHCPv4 client should retry the lease refresh when the issue is a timeout, eventually succeeding in these scenarios.

Actual behavior
Permanent loss of connectivity on the affected interface.

Additional info:
$ lsb_release -rd
Description: Ubuntu 20.04.6 LTS
Release: 20.04

$ apt-cache policy systemd
systemd:
  Installed: 245.4-4ubuntu3.23
  Candidate: 245.4-4ubuntu3.23
  Version table:
 *** 245.4-4ubuntu3.23 500
        500 http://ap-southeast-2.ec2.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        500 mirror+file:/etc/apt/source-mirrors.txt focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     245.4-4ubuntu3.20 500
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
        500 mirror+file:/etc/apt/source-mirrors.txt focal-security/main amd64 Packages
     245.4-4ubuntu3 500
        500 http://ap-southeast-2.ec2.archive.ubuntu.com/ubuntu focal/main amd64 Packages
        500 mirror+file:/etc/apt/source-mirrors.txt focal/main amd64 Packages

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Nick Rosbrook (enr0n)]

I think this would be better suited as an upstream issue, because AFAICT this case is still not handled in the latest version. If you do open an upstream bug (https://github.com/systemd/systemd/issues), they will want to see this reproduced on at least systemd v254.

Please comment back here if you open a bug upstream.