decnet3.service fails on boot - debian 12.12.0 i386

[majenkotech]

The decnet3.service unit is failing to start on bootup on a clean Debian 12.12.0 i386 installation.

The problem is related to loading the module, which fails with a "Device or resource busy" error.

Starting the service manually after boot works, just not during boot.

Oct 25 15:02:32 debian systemd[1]: Starting decnet3.service - Load DECnet module and start...
Oct 25 15:02:32 debian dnetLoadModule[424]: modprobe: ERROR: could not insert 'decnet3': Device or resource busy
Oct 25 15:02:32 debian dnetd[426]: /proc/sys/net/decnet/node_address missing, is DECnet module loaded?
Oct 25 15:02:32 debian systemd[1]: decnet3.service: Main process exited, code=exited, status=255/EXCEPTION
Oct 25 15:02:32 debian systemd[1]: decnet3.service: Failed with result 'exit-code'.
Oct 25 15:02:32 debian systemd[1]: Failed to start decnet3.service - Load DECnet module and start.

[majenkotech]

As an experiment I tried adding a sleep 1 to the module loading script and that seems to have improved it. So it's probably some race condition or concurrency issue.

[JohnForecast]

Certainly looks like a timing issue. There should be a message in syslog indicating why the DECnet module is failing to load. The strange thing is that the code never returns EBUSY (which is the "Device or resource busy" error).

If your network interface takes a long time to start up, systemd may reach network.target without the interface being up and try to start DECnet early. This certainly the case if you are using bridging and there is a note in README.Bridging detailing how to work around this issue. Can you try that workaround - just replace "br0" with your interface name.

[majenkotech]

It's currently in a libvirt VM. I'm in the process of setting up some real hardware that it's intended to run on.

[majenkotech]

Seems to work normally on real (old, vintage, slow) hardware. Same OS version.

[JohnForecast]

Possibly the host taking longer to initialize the NIC relative to the performance of the VM instruction execution. Is the host heavily loaded? I do most of my debugging on a Raspberry Pi or a Proxmox VM which is essentially a libvirt VM.

[majenkotech]

I wouldn't say "heavily loaded" during bootup, no. But it is slow. It's a dual CPU 2.4GHz Xeon (HT) from around 2002.

[majenkotech]

Oh sorry, you meant the VM's host. No, no load at all. 10th gen i7 with nothing else much running on it.

[JohnForecast]

Looks like I might want to change:

After=network.target

to:

BindsTo=sys-devices-virtual-net-xxx.device
After=sys-devices-virtual-net-xxx.device

where xxx is the network interface name. That will delay loading DECnet until the xxx interface becomes active. Let me think about it some more.

[JohnForecast]

BindsTo= and After= works fine on a Raspberry Pi with a bridge device. Can you try that on your failing system? If it works, I can easily change the installation procedure.