On Wed, Feb 6, 2019 at 8:51 PM Mahesh Bandewar (महेश बंडेवार) <mahe...@google.com> wrote: > > On Tue, Feb 5, 2019 at 11:36 AM Michael Chan <michael.c...@broadcom.com> > wrote: > > > > 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? > Yes, so I added those two flags and ended up writing a test-module for > the device (which I will include while posting the patch-series). > However, adding those flags is also not sufficient since the qdisc is > initialized to noop_qdisc so qdisc enqueue will drop packets before > hitting the ndo_start_xmit().
I have another version of the fix (with help from Eric) and this should hit the .ndo_start_xmit() of the blackhole_dev. I'm adding these flags during the setup and then calling dev_activate() to change noop qdisc to null qdisc. Please give this patch set a try and let me know if the blackhole_dev xmit path gets exercised in your test scenario.
0001-loopback-create-blackhole-net-device-similar-to-loop.patch
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0002-blackhole_netdev-use-blackhole_netdev-to-invalidate-.patch
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0003-blackhole_dev-add-a-selftest.patch
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