Subject: Re: [PATCH net-next 4/5] veth: introduce more xdp counters

From: Lorenzo Bianconi <[email-masked]>
Date: Fri, 20 Mar 2020 14:37:37 +0100

> On 2020/03/20 1:41, Lorenzo Bianconi wrote:
> > Introduce xdp_xmit counter in order to distinguish between XDP_TX and
> > ndo_xdp_xmit stats. Introduce the following ethtool counters:
> > - rx_xdp_tx
> > - rx_xdp_tx_errors
> > - tx_xdp_xmit
> > - tx_xdp_xmit_errors
> > - rx_xdp_redirect
> 
> Thank you for working on this!
> 
> > Signed-off-by: Lorenzo Bianconi <[email-masked]>
> > ---
> ...
> > @@ -395,7 +404,8 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
> >   	}
> >   	rcv_priv = netdev_priv(rcv);
> > -	rq = &rcv_priv->rq[veth_select_rxq(rcv)];
> > +	qidx = veth_select_rxq(rcv);
> > +	rq = &rcv_priv->rq[qidx];
> >   	/* Non-NULL xdp_prog ensures that xdp_ring is initialized on receive
> >   	 * side. This means an XDP program is loaded on the peer and the peer
> >   	 * device is up.
> > @@ -424,6 +434,17 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
> >   	if (flags & XDP_XMIT_FLUSH)
> >   		__veth_xdp_flush(rq);
> > +	rq = &priv->rq[qidx];
> 
> I think there is no guarantee that this rq exists. Qidx is less than
> rcv->real_num_rx_queues, but not necessarily less than
> dev->real_num_rx_queues.
> 
> > +	u64_stats_update_begin(&rq->stats.syncp);
> 
> So this can cuase NULL pointer dereference.

oh right, thanks for spotting this.
I think we can recompute qidx for tx netdevice in this case, doing something
like:

qidx = veth_select_rxq(dev);
rq = &priv->rq[qidx];

what do you think?

Regards,
Lorenzo

> 
> Toshiaki Makita
> 
> > +	if (ndo_xmit) {
> > +		rq->stats.vs.xdp_xmit += n - drops;
> > +		rq->stats.vs.xdp_xmit_err += drops;
> > +	} else {
> > +		rq->stats.vs.xdp_tx += n - drops;
> > +		rq->stats.vs.xdp_tx_err += drops;
> > +	}
> > +	u64_stats_update_end(&rq->stats.syncp);
> > +
> >   	if (likely(!drops)) {
> >   		rcu_read_unlock();
> >   		return n;
> > @@ -437,11 +458,17 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
> >   	return ret;
> >   }
> > +static int veth_ndo_xdp_xmit(struct net_device *dev, int n,
> > +			     struct xdp_frame **frames, u32 flags)
> > +{
> > +	return veth_xdp_xmit(dev, n, frames, flags, true);
> > +}
> > +
> >   static void veth_xdp_flush_bq(struct net_device *dev, struct veth_xdp_tx_bq *bq)
> >   {
> >   	int sent, i, err = 0;
> > -	sent = veth_xdp_xmit(dev, bq->count, bq->q, 0);
> > +	sent = veth_xdp_xmit(dev, bq->count, bq->q, 0, false);
> >   	if (sent < 0) {
> >   		err = sent;
> >   		sent = 0;
> > @@ -753,6 +780,7 @@ static int veth_xdp_rcv(struct veth_rq *rq, int budget,
> >   	}
> >   	u64_stats_update_begin(&rq->stats.syncp);
> > +	rq->stats.vs.xdp_redirect += stats->xdp_redirect;
> >   	rq->stats.vs.xdp_bytes += stats->xdp_bytes;
> >   	rq->stats.vs.xdp_drops += stats->xdp_drops;
> >   	rq->stats.vs.rx_drops += stats->rx_drops;
> > @@ -1172,7 +1200,7 @@ static const struct net_device_ops veth_netdev_ops = {
> >   	.ndo_features_check	= passthru_features_check,
> >   	.ndo_set_rx_headroom	= veth_set_rx_headroom,
> >   	.ndo_bpf		= veth_xdp,
> > -	.ndo_xdp_xmit		= veth_xdp_xmit,
> > +	.ndo_xdp_xmit		= veth_ndo_xdp_xmit,
> >   };
> >   #define VETH_FEATURES (NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_HW_CSUM | \
> >