Comment 5 for bug 1826385

I think this patch can get this issue fixed on Cosmic:
https://github.com/torvalds/linux/commit/43a1b0cb4cd6dbfd3cd9c10da663368394d299d8
(found in this thread https://lkml.org/lkml/2018/12/3/1219)

Test kernel:
http://people.canonical.com/~phlin/kernel/lp-1826385-ftrace-hang/

Cosmic KVM and bare-metal passed the ftrace test with this test kernel.

The commit that fixed by this patch has already landed in Cosmic for a while, for now I can't tell why this was only gets triggered recently and why this is not failing in the last cycle. (The gcc version in the last cycle is already 8, 4:8.3.0-1ubuntu1.1 from -proposed.)