This is a note to let you know that I've just added the patch titled IPv6: Set SIT tunnel hard_header_len to zero to the 5.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ipv6-set-sit-tunnel-hard_header_len-to-zero.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Mon Nov 16 07:48:29 PM CET 2020 From: Oliver Herms <oliver.peter.herms@xxxxxxxxx> Date: Tue, 3 Nov 2020 11:41:33 +0100 Subject: IPv6: Set SIT tunnel hard_header_len to zero From: Oliver Herms <oliver.peter.herms@xxxxxxxxx> [ Upstream commit 8ef9ba4d666614497a057d09b0a6eafc1e34eadf ] Due to the legacy usage of hard_header_len for SIT tunnels while already using infrastructure from net/ipv4/ip_tunnel.c the calculation of the path MTU in tnl_update_pmtu is incorrect. This leads to unnecessary creation of MTU exceptions for any flow going over a SIT tunnel. As SIT tunnels do not have a header themsevles other than their transport (L3, L2) headers we're leaving hard_header_len set to zero as tnl_update_pmtu is already taking care of the transport headers sizes. This will also help avoiding unnecessary IPv6 GC runs and spinlock contention seen when using SIT tunnels and for more than net.ipv6.route.gc_thresh flows. Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.") Signed-off-by: Oliver Herms <oliver.peter.herms@xxxxxxxxx> Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx> Link: https://lore.kernel.org/r/20201103104133.GA1573211@tws Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv6/sit.c | 2 -- 1 file changed, 2 deletions(-) --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -1128,7 +1128,6 @@ static void ipip6_tunnel_bind_dev(struct if (tdev && !netif_is_l3_master(tdev)) { int t_hlen = tunnel->hlen + sizeof(struct iphdr); - dev->hard_header_len = tdev->hard_header_len + sizeof(struct iphdr); dev->mtu = tdev->mtu - t_hlen; if (dev->mtu < IPV6_MIN_MTU) dev->mtu = IPV6_MIN_MTU; @@ -1426,7 +1425,6 @@ static void ipip6_tunnel_setup(struct ne dev->priv_destructor = ipip6_dev_free; dev->type = ARPHRD_SIT; - dev->hard_header_len = LL_MAX_HEADER + t_hlen; dev->mtu = ETH_DATA_LEN - t_hlen; dev->min_mtu = IPV6_MIN_MTU; dev->max_mtu = IP6_MAX_MTU - t_hlen; Patches currently in stable-queue which might be from oliver.peter.herms@xxxxxxxxx are queue-5.9/ipv6-set-sit-tunnel-hard_header_len-to-zero.patch