Re: [PATCH net v2] net: consume xmit errors of GSO frames

[Ben Hutchings <ben@decadent.org.uk>]

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On Mon, 2026-02-23 at 15:51 -0800, Jakub Kicinski wrote:
[...]
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4822,6 +4822,8 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
>  		 * to -1 or to their cpu id, but not to our id.
>  		 */
>  		if (READ_ONCE(txq->xmit_lock_owner) != cpu) {
> +			bool is_list = false;
> +
>  			if (dev_xmit_recursion())
>  				goto recursion_alert;
>  
> @@ -4832,17 +4834,28 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
>  			HARD_TX_LOCK(dev, txq, cpu);
>  
>  			if (!netif_xmit_stopped(txq)) {
> +				is_list = !!skb->next;
> +
>  				dev_xmit_recursion_inc();
>  				skb = dev_hard_start_xmit(skb, dev, txq, &rc);
>  				dev_xmit_recursion_dec();
> -				if (dev_xmit_complete(rc)) {
> -					HARD_TX_UNLOCK(dev, txq);
> -					goto out;
> -				}
> +
> +				/* GSO segments a single SKB into
> +				 * a list of frames. TCP expects error
> +				 * to mean none of the data was sent.
> +				 */
> +				if (is_list)
> +					rc = NETDEV_TX_OK;
>  			}
>  			HARD_TX_UNLOCK(dev, txq);
> +			if (!skb) /* xmit completed */
> +				goto out;
> +
>  			net_crit_ratelimited("Virtual device %s asks to queue packet!\n",
>  					     dev->name);
> +			/* NETDEV_TX_BUSY or queue was stopped */
> +			if (!is_list)
> +				rc = -ENETDOWN;
>  		} else {
>  			/* Recursion is detected! It is possible,
>  			 * unfortunately
> @@ -4850,10 +4863,10 @@ int __dev_queue_xmit(struct sk_buff *skb, struct net_device *sb_dev)
>  recursion_alert:
>  			net_crit_ratelimited("Dead loop on virtual device %s, fix it urgently!\n",
>  					     dev->name);
> +			rc = -ENETDOWN;
>  		}
>  	}
>  
> -	rc = -ENETDOWN;

After removing this assignment, rc is not set properly in case the
device is down or TX is stopped.

Perhaps this assignment should be restored before the check for
(dev->flags & IFF_UP)?

Ben.

>  	rcu_read_unlock_bh();
>  
>  	dev_core_stats_tx_dropped_inc(dev);

-- 
Ben Hutchings
Theory and practice are closer in theory than in practice - John Levine

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