r194546 amd64: kernel panic in tcp_sack.c

[Lawrence Stewart]

Kamigishi Rei wrote:
> Lawrence Stewart wrote:
>> I'm not intimately familiar with our SACK implementation, and these 
>> things are often extremely painful to track down. First step: is the 
>> panic reproducible?
> So far I couldn't reproduce it, but I think the fact that I couldn't 
> reproduce it has something to do with frequent reboots due to 
> buildworld/buildkernel lately because of other problems.

Ok. I'm working on a patch to address a different TCP/SACK issue, but it 
may in fact be partially relevant to the cause of your panic... can't 
promise when I'll be able to take a close look at this but I'm aware of 
it now so that's a start. If you run into it again or find the trigger 
for the panic, please let me know.

>> How did you try to get it to save the core? A dump would be very 
>> useful to have around.
> Since I'm not much of an expert in the kernel debugger, I tried to let 
> it continue with the panic, i.e. typed 'continue' which produced a fatal 
> trap 12 right after "Dumping XXXX MB: (~3 values were here)".

Next time from the ddb prompt, try typing "call doadump" instead of 
"continue". That will hopefully get you a usable core dump which would 
be handy. After it finishes dumping the core type "reset" to reboot the 
machine.

Cheers,
Lawrence