Commit 8ef9ba4d authored Nov 03, 2020 by Oliver Herms Committed by Jakub Kicinski Nov 09, 2020

IPv6: Set SIT tunnel hard_header_len to zero



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: c5441932 ("GRE: Refactor GRE tunneling code.")
Signed-off-by: Oliver Herms <oliver.peter.herms@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20201103104133.GA1573211@tws


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 4e0396c5

net/ipv6/sit.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -1128,7 +1128,6 @@ static void ipip6_tunnel_bind_dev(struct net_device *dev)
		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 net_device *dev)
		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;

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