Seeking advice for debugging a kernel panic problem

Hi, developers. My router has a random reboot problem caused by kernel panic within netfilter. I have found the code causing panic, but I still have to investigate why the problem is happening (the net device for a packet sometimes can be NULL.) I have submitted the details of my issue to:

https://bugs.openwrt.org/index.php?do=details&task_id=2943&pagenum=1

I hope someone can give me advice on how to dig further into this problem. Really appreciate it.

Thanks!