On Thu, Mar 25, 2021 at 1:24 PM Paolo Abeni <pab...@redhat.com> wrote: > > When UDP packets generated locally by a socket with UDP_SEGMENT > traverse the following path: > > UDP tunnel(xmit) -> veth (segmentation) -> veth (gro) -> > UDP tunnel (rx) -> UDP socket (no UDP_GRO) > > they are segmented as part of the rx socket receive operation, and > present a CHECKSUM_NONE after segmentation.
would be good to capture how this happens, as it was not immediately obvious. > > Additionally the segmented packets UDP CB still refers to the original > GSO packet len. Overall that causes unexpected/wrong csum validation > errors later in the UDP receive path. > > We could possibly address the issue with some additional checks and > csum mangling in the UDP tunnel code. Since the issue affects only > this UDP receive slow path, let's set a suitable csum status there. > > v1 -> v2: > - restrict the csum update to the packets strictly needing them > - hopefully clarify the commit message and code comments > > Signed-off-by: Paolo Abeni <pab...@redhat.com> > + if (skb->ip_summed == CHECKSUM_NONE && !skb->csum_valid) > + skb->csum_valid = 1; Not entirely obvious is that UDP packets arriving on a device with rx checksum offload off, i.e., with CHECKSUM_NONE, are not matched by this test. I assume that such packets are not coalesced by the GRO layer in the first place. But I can't immediately spot the reason for it..
