Ryzen issues on FreeBSD ? (with sort of workaround)

[Don Lewis]

On 30 Jan, Mike Tancsa wrote:
> On 1/30/2018 5:23 PM, Nimrod Levy wrote:
>> That's really strange. I never saw those kinds of deadlocks, but I did
>> notice that if I kept the cpu busy using distributed.net
>> <http://distributed.net> I could keep the full system lockups away for
>> at least a week if not longer.
>> 
>> Not to keep harping on it, but what worked for me was lowering the
>> memory speed. I'm at 11 days of uptime so far without anything running
>> the cpu. Before the change it would lock up anywhere from an hour to a day.
>> 
> Spoke too soon. After a dozen loops, the process has hung again.  Note,
> this is not the box locking up, just the compile.  I do have memory at a
> lower speed too. -- 2133 instead of the default 2400

I suspect the problem is a race condition that causes a wakeup to be
lost.  Adding load changes the timing enough to avoid the problem most
of the time.

> I also just tried upgrading to the latest HEAD with a generic kernel and
> same / similar lockups although procstat -kk gives some odd results
> 
> 
> root at amdtestr12:/home/mdtancsa # procstat -kk 6067
>   PID    TID COMM                TDNAME              KSTACK
> 
>  6067 100865 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100900 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100901 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100902 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100903 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100904 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100905 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100906 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100907 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100908 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100909 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100910 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0
>  6067 100911 python2.7           -                   ??+0 ??+0 ??+0 ??+0
> ??+0 ??+0 ??+0 ??+0 ??+0 ??+0

Strange ... kernel vs. world mismatch?  Some other new regression in
HEAD?