Gentoo > Setting MTU freezes system

I encountered the strangest issue I ever experienced so far: When I set the MTU on an interface which is down, my system freezes completely after around 10 seconds.

I can reproduce it like this:

ip link set eno1 down
ip link set eno1 mtu 1400

It works if the interface is up though.

This mimics the behavior of systemd-networkd on a fresh system boot, where I encountered the issue the first time.

I have an I226-V (rev 06) Ethernet controller on an ASUS ROG STRIX B760-F GAMING WIFI board, issue happens on 5.15.102-gentoo-dist and 6.1.19-gentoo-dist kernels.

I even did some amateur debugging and could narrow down the line where the freeze occurs:

It goes from here and freezes somewhere in this wrfl() function.

The freeze is so bad that I don't get any more kernel or journal logs and even my zsh history corrupts from time to time (lol). Sysreq won't save me either, only hardware reset worked so far :(

Is this a kernel bug or is my mainboard garbage?

My current workaround is:

systemctl edit systemd-networkd

[Service]
ExecStartPost=ip link set eno1 mtu 1400

23:00 18.03.2023