Comment # 52 on bug 1080485 from - -

(In reply to Martin Wilck from comment #50)
> Could you please test with 4.20.1 as requested in comment 47?

I'm sorry, but I would prefer to wait for the release in the official repo.
(Won't it appear any day now?)
I had recently even more issues with the rd.break=shutdown option, so I'll try
to give you a deatailed answer then, but I cannot guarantee it.

Maybe could you consider adding an extra test to openqa, which could show you
most reliably if the patches have had the desired effect? It would also be
useful for detecting similar issues in the future.

> > There is also a patch in systemd 240:
> > https://github.com/systemd/systemd/commit/
> > e45154c770567507cc51eb78b28a1fae1fcdf396
> 
> That one looks orthogonal with what we are discussing here. It deals with
> _not killing_ kernel threads, where we must ensure that systemd _does kill_
> this user mode helper.

It corrects kthread distinguishing to ensure killing user mode helpers.
Checking the PF_KTHREAD flag is the right solution IMO and dracut too should
implement it.
The old hacky way - checking if /proc/{PID}/cmdline is empty, isn't reliable
enough as we all have seen ;)
I consider the kernel patches as a workaround of the problem.