ip6_gre: update mtu properly in ip6gre_err
Now when probessing ICMPV6_PKT_TOOBIG, ip6gre_err only subtracts the offset of gre header from mtu info. The expected mtu of gre device should also subtract gre header. Otherwise, the next packets still can't be sent out. Jianlin found this issue when using the topo: client(ip6gre)<---->(nic1)route(nic2)<----->(ip6gre)server and reducing nic2's mtu, then both tcp and sctp's performance with big size data became 0. This patch is to fix it by also subtracting grehdr (tun->tun_hlen) from mtu info when updating gre device's mtu in ip6gre_err(). It also needs to subtract ETH_HLEN if gre dev'type is ARPHRD_ETHER. Reported-by: NJianlin Shi <jishi@redhat.com> Signed-off-by: NXin Long <lucien.xin@gmail.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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