Comment # 54 on bug 1080485 from - -

(In reply to Martin Wilck from comment #53)
> > I consider the kernel patches as a workaround of the problem.
> 
> Not sure what you meant to say, but judging from the other testers'
> feedback, it looks as if these patches were actually the solution to the
> problem described in this bug. I wouldn't call this a workaround.

Workarounds are solutions by definition. Poor solutions.

Anyway, I can confirm that the issue has been solved in the Tumbleweed 20190115
snapshot:
kernel-default-4.20.0-1.5.x86_64
systemd-239-3.1.x86_64
dracut-044.1-22.1.x86_64

The error messages have stopped appearing.

/oldroot and /oldroot/var mounts: 
 - both ro at the pre-shutdown breakpoint;
 - not listed at the shutdown breakpoint.

The cmdline entry in /proc/<pid> for the bpfilter umh process contains
"bpfilter_umh" followed by a null byte. The dir isn't available at the shutdown
breakpoint (or - in other words - the process has been killed earlier, as
expected).

> @all, do we have a fool-proof setup procedure for a VM to reproduce this problem?

I suspect that the issue affects every system where bpfilter_umh is started,
but verbose errors appear only if the dracut's shutdown hook is enabled.