Netgraph Crash with vtnet Workaround

Netgraph Crash with vtnet Workaround

Goal

Prevent a FreeBSD host from crashing when restarting Netgraph VNET jails, which are bridged to a vtnet network interface.

Background

A few weeks ago I experimented with VNET jails and Netgraph, and noticed that one of my FreeBSD 14.3 VMs kept kernel panicking, everytime I stopped or restarted the VNET jails. These crashes only occurred on this one FreeBSD VM, which uses the vtnet VirtIO Ethernet driver for the virtual NICs it gets from Proxmox VE.

Workaround

After not being able to find a solution for the kernel panics myself, I searched on the Internet™️ and found this FreeBSD bug report: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238326#c41

Some of the commenters recommended removing the VNET interface from the jails, before shutting them down, to prevend the Host from crashing. Here are the changes I made to my VNET jail’s jail.conf to stop my FreeBSD VM from crashing:

...
  vnet;
  vnet.interface += ng0_nsd04;
  exec.prestart += "jng bridge nsd04 vtnet1";
  exec.prestart += "ifconfig ng0_nsd04 ether 58:9c:fc:2a:1c:9b";
+ exec.prestop += "/usr/sbin/jexec ${name} /bin/sh /etc/rc.shutdown";
+ exec.prestop += "jng shutdown nsd04";
- exec.poststop += "jng shutdown nsd04";
}

The lines with a + represend the added lines, the line with the - represents the remved line.

Now that the services inside the jail are stopped and the Netgraph VNET interface is detached before the jail is stopped, kernel panics on the FreeBSD host have ceased for now.