panic: pmap_demote_section: No l2_bucket for wired mapping

[Zbigniew Bodek]

2015-03-22 20:45 GMT+01:00 Paul Mather <paul at gromit.dlib.vt.edu>:
> On Mar 22, 2015, at 7:54 AM, Michael Tuexen <tuexen at freebsd.org> wrote:
>
>> Dear all,
>>
>> running head on a Raspberry Pi became unstable. When running
>> r280329 for a while (the machine is exposed to the Internet, so
>> ssh logins are continuously tried), the machine panics:
>>
>> panic: pmap_demote_section: No l2_bucket for wired mapping
>> KDB: enter: panic
>
>
> I get this panic when booting to multi-user on my newly-updated BBB (FreeBSD 11.0-CURRENT #0 r280350).  As pointed out later in this thread, setting vm.pmap.sp_enabled=0 prevents the panic (so far) and allows booting.
>
> Cheers,
>
> Paul.
>

I was able to reproduce this on my R-Pi too.
The bug may be related to shared libraries mapping since excluding
pmap_enter_section() (the one in the pmap_enter_object() that is
responsible for doing the work for shared libraries mappings) results
in normal operation even with page promotion/demotion enabled.
I will try to find some time to look into that to ensure that this is
not just covering the problem. If it doesn't then we may consider
disabling pmap_enter_section() (by adding "return FALSE;") to have WA
(without disabling superpages) until we find the real solution.
pmap_enter_section() was being used very rarely before shared
libraries superpage mappings were enabled so it is reasonable to think
that the bug is somewhere around. Please let me know in case you find
something.

Best regards
zbb