[Bug 227404] UP FreeBSD VM always hangs on reboot since 20180329-r331740

[Bruce Evans]

On Tue, 10 Apr 2018 a bug that doesn't want replies at freebsd.org wrote:

> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=227404
> ...
> --- Comment #1 from Dexuan Cui <decui at microsoft.com> ---
> When the issue happens, the cpu utilization of the UP VM is 100%.
>
> While we're trying to find the first bad revision, it would be great if
> somebody can report if the issue also happens to bare metal or other
> hypervisors.

This has been happening for at least several months on real hardware too.
SMP kernels hang on a 1-CPU system and on an 8-CPU systems with all except
1 CPU turned off in the BIOS.  They don't hang on the 8-CPU system with at
least 2 CPUs turned on.  UP kernels don't hang.  I use SCHED_4BSD.
SCHED_ULE is apparently not much different for this.

Bruce