On Mon, Nov 9, 2020 at 11:57 AM Alexander Lobakin <aloba...@pm.me> wrote: > > While testing UDP GSO fraglists forwarding through driver that uses > Fast GRO (via napi_gro_frags()), I was observing lots of out-of-order > iperf packets: > > [ ID] Interval Transfer Bitrate Jitter > [SUM] 0.0-40.0 sec 12106 datagrams received out-of-order > > Simple switch to napi_gro_receive() any other method without frag0 > shortcut completely resolved them. > > I've found that UDP GRO uses udp_hdr(skb) in its .gro_receive() > callback. While it's probably OK for non-frag0 paths (when all > headers or even the entire frame are already in skb->data), this > inline points to junk when using Fast GRO (napi_gro_frags() or > napi_gro_receive() with only Ethernet header in skb->data and all > the rest in shinfo->frags) and breaks GRO packet compilation and > the packet flow itself. > To support both modes, skb_gro_header_fast() + skb_gro_header_slow() > are typically used. UDP even has an inline helper that makes use of > them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr() > to get rid of the out-of-order delivers. > > Present since the introduction of plain UDP GRO in 5.0-rc1. > > Since v1 [1]: > - added a NULL pointer check for "uh" as suggested by Willem. > > [1] > https://lore.kernel.org/netdev/yazu6gezbdpyzmdmwjirxdx7b4sualpdg68adzy...@cp4-web-034.plabs.ch > > Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.") > Signed-off-by: Alexander Lobakin <aloba...@pm.me>
Acked-by: Willem de Bruijn <will...@google.com> Thanks
