[X/Z SRU + Artful] kernel panic -not syncing: Fatal exception: panic_on_oops

[Stefan Bader]

https://bugs.launchpad.net/bugs/1708399

Impact: A race in context flushing is causing a kernel panic on the s390x
architecture.

Fix:
 - For Xenial 3 patches are required. All have been backported by
   the IBM maintainers and the backport was tested.
   - Patch #1 is already upstream in the linux main tree
   - Patch #2 and Patch #3 are in linux-next
 - For Zesty, the 2 new patches can be cherry-picked from linux-next.
   - Test build ok, but no verification on that kernel from IBM
 - For Artful the same 2 patches as for Zesty should apply and are
   expected to be part of a stable update. So we could either apply
   the same or wait.

-Stefan