Re: [PATCH net-next V4 1/3] net: Add GRO support for UDP encapsulating protocols

On Tue, 2014-01-14 at 23:51 +0200, Or Gerlitz wrote:

quoted

quoted

+       rcu_read_lock();
+
+       uo_priv = rcu_dereference(udp_offload_base);
+       for (; uo_priv != NULL; uo_priv = rcu_dereference(uo_priv->next)) {
+               if (uo_priv->offload->port == uh->dest &&
+                   uo_priv->offload->callbacks.gro_complete)
+                       goto found;
+       }
+
+       rcu_read_unlock();
+       return err;
+
+found:
+       atomic_inc(&uo_priv->refcount);

This is an expensive operation in the critical path.

I know, but I don't see how to get away without having the ref/unref
wrapping, ideas welcome

quoted

Can uo_priv be protected by rcu also?

uo_priv is the actual element which is rcu protected, not sure to
follow on your question.

Seems pretty easy : unlock rcu after calling gro_complete() as in :

found:
       err = uo_priv->offload->callbacks.gro_complete(skb, nhoff + sizeof(struct udphdr));
       rcu_read_unlock();
       return err;