pmap fault during buildworld on rpi2

[bob prohaska]

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