Comment 73 for bug 1518457

Some further debugging: On my t2.micro test case, the machine comes up with 9 memory devices, the last of which is offline at boot. Bringing that device online by hand (with the udev rules disabled) triggers the bug.

# echo online > /sys/devices/system/memory/memory8/state

So something about bringing that node online causes the problem. The udev bugfix causes udev to automatically bring it up, which is why that introduced the issue, but it doesn't seem like udev is really the root problem here.