No, they're not, the mutex trickery seems completely pointless, and the
conditional (on _is_locked no less) locking is horrible.

Ok.

Will spend some more time on exploring solutions using rcu primitives only
(synchronize_net or something similar).

If nothing  of only-RCU is feasible then, I think, we need to resize the skb if it has
already skipped the tailroom instead of WARN_ON. This will come in to picuture
only during the race cases. But this wont get rid of race.

Thanks
Yogesh