Re: [RFC PATCH net-next] veth: apply qdisc backpressure on full ptr_ring to reduce TX drops

[kernel test robot <lkp@intel.com>]

Hi Jesper,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build errors:

[auto build test ERROR on net-next/main]

url:    https://github.com/intel-lab-lkp/linux/commits/Jesper-Dangaard-Brouer/veth-apply-qdisc-backpressure-on-full-ptr_ring-to-reduce-TX-drops/20250404-225209
base:   net-next/main
patch link:    https://lore.kernel.org/r/174377814192.3376479.16481605648460889310.stgit%40firesoul
patch subject: [RFC PATCH net-next] veth: apply qdisc backpressure on full ptr_ring to reduce TX drops
config: arm64-randconfig-002-20250405 (https://download.01.org/0day-ci/archive/20250405/202504052142.TGI9fCwf-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250405/202504052142.TGI9fCwf-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202504052142.TGI9fCwf-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/net/veth.c: In function 'veth_xmit':
>> drivers/net/veth.c:399:3: error: a label can only be part of a statement and a declaration is not a statement
      struct netdev_queue *txq = netdev_get_tx_queue(dev, rxq);
      ^~~~~~


vim +399 drivers/net/veth.c

   355	
   356	static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
   357	{
   358		struct veth_priv *rcv_priv, *priv = netdev_priv(dev);
   359		struct veth_rq *rq = NULL;
   360		struct net_device *rcv;
   361		int length = skb->len;
   362		bool use_napi = false;
   363		int ret, rxq;
   364	
   365		rcu_read_lock();
   366		rcv = rcu_dereference(priv->peer);
   367		if (unlikely(!rcv) || !pskb_may_pull(skb, ETH_HLEN)) {
   368			kfree_skb(skb);
   369			goto drop;
   370		}
   371	
   372		rcv_priv = netdev_priv(rcv);
   373		rxq = skb_get_queue_mapping(skb);
   374		if (rxq < rcv->real_num_rx_queues) {
   375			rq = &rcv_priv->rq[rxq];
   376	
   377			/* The napi pointer is available when an XDP program is
   378			 * attached or when GRO is enabled
   379			 * Don't bother with napi/GRO if the skb can't be aggregated
   380			 */
   381			use_napi = rcu_access_pointer(rq->napi) &&
   382				   veth_skb_is_eligible_for_gro(dev, rcv, skb);
   383		}
   384	
   385		skb_tx_timestamp(skb);
   386	
   387		ret = veth_forward_skb(rcv, skb, rq, use_napi);
   388		switch(ret) {
   389		case NET_RX_SUCCESS: /* same as NETDEV_TX_OK */
   390			if (!use_napi)
   391				dev_sw_netstats_tx_add(dev, 1, length);
   392			else
   393				__veth_xdp_flush(rq);
   394			break;
   395		case NETDEV_TX_BUSY:
   396			/* If a qdisc is attached to our virtual device, returning
   397			 * NETDEV_TX_BUSY is allowed.
   398			 */
 > 399			struct netdev_queue *txq = netdev_get_tx_queue(dev, rxq);
   400	
   401			if (!txq_has_qdisc(txq)) {
   402				dev_kfree_skb_any(skb);
   403				goto drop;
   404			}
   405			netif_tx_stop_queue(txq); /* Unconditional netif_txq_try_stop */
   406			if (use_napi)
   407				__veth_xdp_flush(rq);
   408	
   409			break;
   410		case NET_RX_DROP: /* same as NET_XMIT_DROP */
   411	drop:
   412			atomic64_inc(&priv->dropped);
   413			ret = NET_XMIT_DROP;
   414			break;
   415		default:
   416			net_crit_ratelimited("veth_xmit(%s): Invalid return code(%d)",
   417					     dev->name, ret);
   418		}
   419		rcu_read_unlock();
   420	
   421		return ret;
   422	}
   423	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki