d4814b5f3812ca7 is actually based on v4.15 with the packaging and SAUCE from -1.2 added on top.
There is no diff to drm/i915 in the distro kernel compared to upstream which would explain this.. So I assume you just haven't hit racy bug with mainline builds yet? Try newer versions too, 4.16 and 4.17.
note that d4814b5f3812ca7 is not the same as building off 'Ubuntu-4.15.0-1.2' -tag, which you can find here:
lp:~ubuntu-kernel/ubuntu/+source/linux/+git/unstable
d4814b5f3812ca7 is actually based on v4.15 with the packaging and SAUCE from -1.2 added on top.
There is no diff to drm/i915 in the distro kernel compared to upstream which would explain this.. So I assume you just haven't hit racy bug with mainline builds yet? Try newer versions too, 4.16 and 4.17.