Eric Dumazet [off-list ref] wrote:

It seems recursion field from "struct ip_tunnel" is not anymore needed.
recursion prevention is done at the upper level (in dev_queue_xmit()),
since we use HARD_TX_LOCK protection for tunnels.

What if we get async processing in between, e.g., nf_queue?
In that case we could end up with a packet that went round and
around until it exceeded the MTU.

Cheers,
-- 
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