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From: Oliver Herms <>
Subject: [PATCH] IPv6: Set SIT tunnel hard_header_len to zero
Date: Tue, 3 Nov 2020 11:41:33 +0100
Message-ID: <20201103104133.GA1573211@tws> (raw)

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

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 <>
 net/ipv6/sit.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index 5e2c34c0ac97..5e7983cb6154 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -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;

             reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-03 10:41 Oliver Herms [this message]
2020-11-03 18:42 ` Willem de Bruijn
2020-11-04 19:30   ` Oliver Herms
2020-11-04 19:52     ` Willem de Bruijn
2020-11-09  9:05       ` Oliver Herms
2020-11-09 15:10         ` Willem de Bruijn
2020-11-09 23:16 ` Jakub Kicinski

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