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A concurrent update can change the encapsulation > > header between these accesses and make skb_push() underflow the skb head. > > > > Take a local snapshot of t->encap before calculating the encapsulation > > header length. > > This intorduce per-skb cost in the fast path for unlikely changelink. Assuming the common case where the tunnel doesn't use fou / gue encapsulation, the added cost is one compare and a copy of 8 bytes. > > Right approach is to convert it to RCU pointer (and remove > synchronize_net() there). > > 0ba269933f73 geneve: convert config to RCU-protected pointer > 777434f53e77 geneve: pass geneve_config pointer to helper functions It's on my TODO list since last week, but I don't have the time to work on it right now. It's a very large change (see the geneve change) that is needed across all the IP tunnels, not something that I consider suitable for net. What are you proposing for net?