Panic in the udp_input() under heavy load

[Maxim Sobolev]

On 12/30/2011 3:31 PM, Robert N. M. Watson wrote:
> Looking back at a recent post from you, it appears that you are on 8.x and not 9.x, as I had assumed form your original e-mail. The patch I was referring to in 9-CURRENT has long since been merged for 9.0 and will appear in that release. However, it does not apply to 8.x, as the bug it fixed was introduced during the 9.x cycle. We'll need to do a from-scratch diagnosis here rather than assume it's the same problem. Could I ask you to follow up to this post with version information, stack traces from relevant threads, etc? I am not aware of any other reports of UDP-related crashes along the lines of what you've described in 8.x, so it may be being triggered by some unusual aspect of your workload (or just bad luck). Sorry that there's no instant "merge a patch" fix for this one.

I see. Would you guys mind if I put that NULL pointer check into the 
code for the time being and turn it into some kind of big nasty warning 
in 8-stable branch only? As far as I can tell, the most harm it can do 
is some memory being leaked. And this condition happens just few times a 
day, so it's not a biggie.

By the way it would be interesting project to put libexecinfo interface 
into the FreeBSD kernel. It would provide interesting new aspect of 
debugging such rare non-critical conditions by dumping stack traces and 
possibly doing some damage control instead of plainly crashing.

-Maxim