kernel panic with netgraph and mpd3.8

[Donald Baud]

> On 2016-07-10 10:49, Donald Baud via freebsd-net wrote:
>> Hi I'm running an l2tp lns through mpd3.8 and it's been crashing 
>> twice in 24h.
>> This is a new project replacing a cisco 7206, 700-sessions 800mbit/s
>>
>>
>> I am not familiar with troubleshooting kernel panic's,
>>
>> I am suspecting that the crash is happening inside the netgraph 
>> module because the crash is happening at the
>>
>> instruction pointer = 0x20:0xffffffff81c38283
>> I included the 2 two crash logs.  I need some help to to figure out 
>> what to do next.
>>
>> -Dbaud
>>
>>
> On 7/10/16 5:14 PM, Hooman Fazaeli wrote:
> - Upgrade to mpd 5 (/usr/ports/net/mpd5)
> - Try below workarounds:
> https://lists.freebsd.org/pipermail/freebsd-bugs/2014-June/056548.html
> https://lists.freebsd.org/pipermail/freebsd-bugs/2014-June/056549.html
> https://lists.freebsd.org/pipermail/freebsd-net/2014-June/038954.html
>
>
- I'm already using the latest mpd5:
 > mpd5 --version
Version 5.8 (root at 101amd64-quarterly-job-15 12:36  5-Jun-2016)

- I had already reviewed those links you mentioned.
Here is a summary of the main suggestions in them.
* Add a "sleep 1" to up-down interface events.
* Revert to RELENG8 or 9
* boost net.graph sysctl/loader.conf
   net.graph.maxdata=262140 # /boot/loader.conf
   net.graph.maxalloc=262140 # /boot.loader.conf

I was using the following tunings
net.graph.maxdgram=524288  (via sysctl.conf default=20480)
net.graph.recvspace=524288 (via sysctl.conf default=20480)
net.graph.maxdata=65536   (via loader.conf default=4096 )
net.graph.maxalloc=65536  (via loader.conf default=4096 )

I am suspecting that the panic might be caused by a too high maxdata and maxalloc values:
I reduced the value to 20480, I'll report back if that will reduce the occurence of kernel panics.

> vmstat -z | head -1 ; vmstat -z | grep -i graph
ITEM                   SIZE  LIMIT     USED     FREE      REQ FAIL SLEEP
NetGraph items:          72,  20491,       2,    1672,467166841,   0,   0
NetGraph data items:     72,  20491,       0,    1643,1240166475,   0,   0