Re: 8.3: kernel panic in bpf.c catchpacket()



On Oct 10, 2012, at 1:37 PM, Alexander V. Chernikov <melifaro@freebsd.org> =
wrote:

> On 10.10.2012 00:36, Guy Helmer wrote:
>> =

>> On Oct 8, 2012, at 8:09 AM, Guy Helmer <guy.helmer@gmail.com> wrote:
>> =

>>> I'm seeing a consistent new kernel panic in FreeBSD 8.3:
>>> I'm not seeing how bd_sbuf would be NULL here. Any ideas?
>> =

>> Since I've not had any replies, I hope nobody minds if I reply with more=
 information.
>> =

>> This panic seems to be occasionally triggered now that my user land code=
 is changing the packet filter a while after the bpd device has been opened=
 and an initial packet filter was set (previously, my code did not change t=
he filter after it was initially set).
>> =

>> I'm focusing on bpf_setf() since that seems to be the place that could b=
e tickling a problem, and I see that bpf_setf() calls reset_d(d) to clear t=
he hold buffer. I have manually verified that the BPFD lock is held during =
the call to reset_d(), and the lock is held every other place that the buff=
ers are manipulated, so I haven't been able to find any place that seems vu=
lnerable to losing one of the bpf buffers. Still searching, but any help wo=
uld be appreciated.
> =

> Can you please check this code on -current?
> Locking has changed quite significantly some time ago, so there is good c=
hance that you can get rid of this panic (or discover different one which i=
s really "new") :).

I'm not ready to run this app on current, so I have merged revs 229898, 233=
937, 233938, 233946, 235744, 235745, 235746, 235747, 236231, 236251, 236261=
, 236262, 236559, and 236806 to my 8.3 checkout to get code that should be =
virtually identical to current without the timestamp changes.

Unfortunately, I have only been able to trigger the panic in my test lab on=
ce -- so I'm not sure whether a lack of problems with the updated code will=
 be indicative of likely success in the field where this has been trigged r=
egularly at some sites=85

Thanks,
Guy

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