Comment 7 for bug 1730717

Out of the IRC discussions documenting potentially related issues:
- this bug: KVM: Host-Kernel: Xenial-GA, Qemu: Xenial-Ocata, Guest: Bionic
- bug 1722311 KVM: Host-Kernel: Xenial-GA, Qemu: Xenial, Guest: Artful - some relation to cache pressure
- bug 1713751 AWS: triggered by Xenial kernel update, supposed fixed but shown up again and again
- bug 1655842 Host-Kernel: Xenial-GA, Qemu: Xenial, Guest: Artful - some relation to cache pressure
These might after all just run into the same soft lockup symptom, but I thought it was worth to mention for thos enot reading the IRC log.

These cases seem to somewhat agree on:
- Recent guest kernel
- Xenial Host kernel
- some memory pressure

To get further I thought some sort of local reproducer for the kernel Team to work on easier than needing a full cloud.
But so far I failed at setting such a local case up (http://paste.ubuntu.com/25916781/).

Thanks Laney for the openstack based repro description.
@Laney I found it interesting that you essentially only needed to start+reboot.
I assume on the host you had other workload goes on in the background (since it is lcy01)?
If you'd have any sort of non-busy but otherwise comparable system - could you check to confirm the assumption we have so far that there all is fine?
If yes - then the memory pressure theory gets more likely, if not we can focus on simpler reproducers - so we can only win by that check.

Crossing fingers for jsalisbury's hope that 4.14 might already have a fix.