[Bug 1912331] Re: Many interfaces lead to "kernel receive buffer overrun"

[transeunte]

I have 4 servers with Ubuntu 20.04.2 with more than 5 physical ethernets
interfaces each (one of then has 18 ethernets) and I had the problem
with 2 of them.

I can give you access to one of the servers with bug if needed. It's not
in production yet and I can cleanup everything after debug.

I tried to emulate the problem using KVM. I saw errors too (apparently
non directly related with this issue) when use a lot of interfaces with
bridges and vlans.

Maybe this script can help to debug:

wget https://releases.ubuntu.com/20.04/ubuntu-20.04.2-live-server-
amd64.iso

qemu-img create -f qcow2 disk1.qcow2 20G

sudo -E kvm -m 4096 -netdev user,id=user.0 -device e1000,netdev=user.0
-device e1000,id=n1,mac=00:e0:4c:f6:02:3d -net tap,script=no,id=n1
-device e1000,id=n2,mac=00:e0:4c:f6:03:3d -net tap,id=n2 -device
e1000,id=n3,mac=00:e0:4c:f6:04:3d -net tap,id=n3 -device
e1000,id=n4,mac=00:e0:4c:f6:05:3d -net tap,id=n4 -device
e1000,id=n5,mac=00:e0:4c:f6:06:3d -net tap,id=n5 -device
e1000,id=n6,mac=00:e0:4c:f6:07:3d -net tap,id=n6 -device
e1000,id=n7,mac=00:e0:4c:f6:08:3d -net tap,id=n7 -device
e1000,id=n8,mac=00:e0:4c:f6:09:3d -net tap,id=n8 -device
e1000,id=n9,mac=00:e0:4c:f6:10:3d -net tap,id=n9 -device
e1000,id=n10,mac=00:e0:4c:f6:11:3d -net tap,id=n10 -device
e1000,id=n11,mac=00:e0:4c:f6:12:3d -net tap,id=n11 -device
e1000,id=n12,mac=00:e0:4c:f6:13:3d -net tap,id=n12 -device
e1000,id=n13,mac=00:e0:4c:f6:14:3d -net tap,id=n13 -device
e1000,id=n14,mac=00:e0:4c:f6:15:3d -net tap,id=n14 -device
e1000,id=n15,mac=00:e0:4c:f6:16:3d -net tap,id=n15 -device
e1000,id=n16,mac=00:e0:4c:f6:17:3d -net tap,id=n16 -vga virtio -display
gtk -hda disk1.qcow2 -cdrom ubuntu-20.04.2-live-server-amd64.iso -boot c
-smp 8

# Proceed with installation

# Poweroff the machine

# Power on with
sudo -E kvm -m 4096 -netdev user,id=user.0 -device e1000,netdev=user.0 -device e1000,id=n1,mac=00:e0:4c:f6:02:3d -net tap,script=no,id=n1 -device e1000,id=n2,mac=00:e0:4c:f6:03:3d -net tap,id=n2 -device e1000,id=n3,mac=00:e0:4c:f6:04:3d -net tap,id=n3 -device e1000,id=n4,mac=00:e0:4c:f6:05:3d -net tap,id=n4 -device e1000,id=n5,mac=00:e0:4c:f6:06:3d -net tap,id=n5 -device e1000,id=n6,mac=00:e0:4c:f6:07:3d -net tap,id=n6 -device e1000,id=n7,mac=00:e0:4c:f6:08:3d -net tap,id=n7 -device e1000,id=n8,mac=00:e0:4c:f6:09:3d -net tap,id=n8 -device e1000,id=n9,mac=00:e0:4c:f6:10:3d -net tap,id=n9 -device e1000,id=n10,mac=00:e0:4c:f6:11:3d -net tap,id=n10 -device e1000,id=n11,mac=00:e0:4c:f6:12:3d -net tap,id=n11 -device e1000,id=n12,mac=00:e0:4c:f6:13:3d -net tap,id=n12 -device e1000,id=n13,mac=00:e0:4c:f6:14:3d -net tap,id=n13 -device e1000,id=n14,mac=00:e0:4c:f6:15:3d -net tap,id=n14 -device e1000,id=n15,mac=00:e0:4c:f6:16:3d -net tap,id=n15 -device e1000,id=n16,mac=00:e0:4c:f6:17:3d -net tap,id=n16 -vga virtio -display gtk -hda disk1.qcow2 -smp 8

# Login and…

sudo apt-get update
sudo apt-get install ansible magic-wormhole sshpass
ansible-galaxy install mrlesmithjr.netplan

#Copy the unzipped attached files debug-systemd.yml and hosts to vm

#at host
wormhole send debug-systemd.yml 
wormhole send hosts

#receive files at vm
wormhole receive ...
wormhole receive ...


# Configure the hosts file properly with ssh credentials (an example is
attached)

ansible-playbook -i hosts debug-systemd.yml
reboot

#login and...
networkctl -a
# you will see a lot of failing/degraded/pending interfaces
ip -br a
# You will see a log of interfaces without ip



** Attachment added: "debug-systemd.yml.zip"
   https://bugs.launchpad.net/ubuntu/focal/+source/systemd/+bug/1912331/+attachment/5483521/+files/debug-systemd.yml.zip

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https://bugs.launchpad.net/bugs/1912331

Title:
  Many interfaces lead to "kernel receive buffer overrun"

Status in systemd:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Confirmed
Status in systemd source package in Groovy:
  Fix Released

Bug description:
  This is about a systemd-networkd bug, described here:

  https://github.com/systemd/systemd/issues/14417

  There's a patch available:

  https://github.com/systemd/systemd/pull/16982

  Can this be backported to Focal?

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