On Wed, Jan 30, 2019 at 5:00 PM Mahesh Bandewar (महेश बंडेवार) <mahe...@google.com> wrote: > > On Wed, Jan 30, 2019 at 1:07 AM Michael Chan <michael.c...@broadcom.com> > wrote: > > > > On Tue, Jan 22, 2019 at 10:29 AM Mahesh Bandewar (महेश बंडेवार) > > <mahe...@google.com> wrote: > > > > > > > > The idea behind the fix is very simple and it is to create a dst-only > > > (unregistered) device with a very low MTU and use it instead of 'lo' > > > while invalidating the dst. This would make it *not* forward packets > > > to driver which might need fragmentation. > > > > > > > We tested the 2 patches many times and including an overnight test. I > > can confirm that the oversize UDP packets are no longer seen with the > > patches applied. However, I don't see the blackhole xmit function > > getting called to free the SKBs though. > > > Thanks for the confirmation Michael. The blackhole device mtu is > really small, so I would assume the fragmentation code dropped those > packets before calling the xmit function (in ip_fragment), you could > verify that with icmp counters. >
I've looked at this a little more. The blackhole_dev is not IFF_UP | IFF_RUNNING, right? May be that's why the packets are never getting to the xmit function?
