Re: [PATCH/RFC] IPoIB: Free ipoib neigh on path record failure so path rec queries are retried

[Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 25/02/2013 19:46, Roland Dreier wrote:
> If IPoIB fails to look up a path record (eg if it tries during an SM
> failover when one SM is dead but the new one hasn't taken over yet), the
> driver ends up with a neighbour structure but no address handle (AH).
> There's no mechanism to recover from this: any further packets sent to
> this destination will be silently dumped in ipoib_start_xmit().

Looking on the flow of sending ARP probes, I see that in 
unicast_arp_send, if there's no AH for the path, a path query is initiated,

   if (path->ah) {
                 ipoib_dbg(priv, "Send unicast ARP to %04x\n",
be16_to_cpu(path->pathrec.dlid));

                 spin_unlock_irqrestore(&priv->lock, flags);
                 ipoib_send(dev, skb, path->ah, IPOIB_QPN(cb->hwaddr));
                 return;
         } else if ((path->query || !path_rec_start(dev, path)) &&
                    skb_queue_len(&path->queue) < 
IPOIB_MAX_PATH_REC_QUEUE) {
                 __skb_queue_tail(&path->queue, skb);
         } else {
                 ++dev->stats.tx_dropped;
                 dev_kfree_skb_any(skb);
         }


so eventually the traffic should resume once the ND state machine sends 
a probe, agree? did you only wanted to make that faster?

Or.

> Fix this by freeing the neighbour structures when a path rec query fails, so that the next packet queued to be sent will trigger a new path record query.

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