On Thu, 2017-06-01 at 08:58 -0700, Eric Dumazet wrote:

On Thu, 2017-06-01 at 12:39 +0200, Paolo Abeni wrote:

quoted

On Wed, 2017-05-31 at 10:00 -0700, Eric Dumazet wrote:

quoted

On Mon, 2017-05-29 at 17:27 +0200, Paolo Abeni wrote:

quoted

Since UDP no more uses sk->destructor, we can clear completely
the skb head state before enqueuing.

...

quoted

@@ -1739,6 +1740,9 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		sk_mark_napi_id_once(sk, skb);
 	}
 
+	/* drop all pending head states; dst, nf and sk are dropped by caller */
+	secpath_reset(skb);
+

I wonder if using skb_release_head_state() would be more appropriate ?

Surely more descriptive and probably not more expensive since all
cache lines should be already hot at this point.

Thank you for reviewing this.

I would prefer not adding more code to the core, but I think we would
need something new, like:

skb_reset_head_state()
{
	skb_dst_drop(skb);
        secpath_reset(skb);
        nf_reset(skb);
	skb_orphan(skb);
}

because elsewhere the skb could be in inconsistent state: skb->sp !=
NULL but with its refcount is already decremented. WDYT?

I do not believe skb->sk is set anymore in UDP receive path.

If early demux sets skb->sk for a moment, skb_steal_sock() would set
skb->sk back to NULL

I'm sorry, I do not follow. I'm concerned about the secpath field (skb-

sp), which is the only one that can be not NULL in

__udp_queue_rcv_skb().

If the secpath is not NULL, calling there secpath_reset() (or the to-
be-introduced skb_reset_head_state()), we will properly release it and
we will clear the field, too.

Calling skb_release_head_state() in the same scenario, we release the
secpath, but we don't clear it. So if the packet is later dropped we
will get a double free, unless we add and use a specialized a
free_stateless_skb(), too.

Paolo