pmap fault during buildworld on rpi2

[bob prohaska]

On Sat, Oct 07, 2017 at 01:13:19AM +0200, Svatopluk Kraus wrote:
> I have already suggested the following:
> https://lists.freebsd.org/pipermail/freebsd-arm/2017-September/016697.html
> 
I read your message and didn't understand it well enough to follow the 
advice.

> Nevertheless, I'm not sure that I understand the way how it happens.
> Does it crash on rebooting or during buildworld? 
During buildworld.

> Are you saying that
> all kernels after r322520 crash during buildworld with pmap panic?
> 

Correct, to a good approximation.  

The approximation is that on one occasion, very shortly after r322520,
a kernel managed to complete a buildworld without a panic. That makes
one success out of about five tries.

Mark Millard reported what seemed like a similar panic about a year
ago, but it went away by itself. When the successful build following
r322520 happened I expected the same thing to happen. It didn't.

bob prohaska

> 
> On Fri, Oct 6, 2017 at 5:58 PM, bob prohaska <fbsd at www.zefox.net> wrote:
> > For about one  month now, buildworld has been crashing with
> > a pmap error. Rebooting an older kernel always seems to solve
> > the problem, but on rebooting the newly-compiled system the
> > pmap fault happens again on the next buildworld.
> >
> > There seems to be no such problem during other compilations.
> >
> > A top window freezes with cc and ld as the dominant processes.
> >
> > The last kernel I have which works is r322520.
> >
> > Since nobody else seems to be reporting this behavior
> > it's tempting to think the problem is local. Can anyone
> > suggest where I might look? Console, top and log are at:
> > http://www.zefox.net/~fbsd/rpi2/crashes/crash_10_6_17/
> >
> > Thanks for reading,
> >
> > bob prohaska
> >
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