On boot, I was getting:

BUG: scheduling while atomic: swapon/x
BUG: scheduling while atomic: swapper/x
bad: scheduling from the idle thread!
BUG: scheduling while atomic: swapper/x

The above is due to some bug/conflict with the VirtualBox Kernel Modules and the Realtime Linux Kernel. To prevent them loading on boot, run the following command:

sudo touch /etc/modules-load.d/virtualbox-host-dkms.conf

Then when you want to use VirtualBox, load the kernel modules as follows:

sudo modprobe vboxdrv