linux-kernel - Re: [PATCH net v3 2/2] net: dlink: handle copy

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Message-Id: <DD16EAXYP4SM.1JYDYPDJ4I7VV@gmail.com>
Date: Thu, 25 Sep 2025 01:36:57 +0900
From: "Yeounsu Moon" <yyyynoom@...il.com>
To: "Jakub Kicinski" <kuba@...nel.org>
Cc: "Andrew Lunn" <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>, "Paolo Abeni"
 <pabeni@...hat.com>, <netdev@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v3 2/2] net: dlink: handle copy_thresh allocation
 failure

On Thu Sep 18, 2025 at 8:09 AM KST, Jakub Kicinski wrote:

Thank you for reviewing! and sorry for the delayed reply.
There have been quite a lot of things on my end recently.

> On Wed, 17 Sep 2025 03:33:05 +0900 Yeounsu Moon wrote:
>> @@ -965,14 +965,11 @@ receive_packet (struct net_device *dev)
>>  			struct sk_buff *skb;
>>  
>>  			/* Small skbuffs for short packets */
>> -			if (pkt_len > copy_thresh) {
>> -				dma_unmap_single(&np->pdev->dev,
>> -						 desc_to_dma(desc),
>> -						 np->rx_buf_sz,
>> -						 DMA_FROM_DEVICE);
>> -				skb_put(skb = np->rx_skbuff[entry], pkt_len);
>> -				np->rx_skbuff[entry] = NULL;
>> -			} else if ((skb = netdev_alloc_skb_ip_align(dev, pkt_len))) {
>> +			if (pkt_len <= copy_thresh) {
>> +				skb = netdev_alloc_skb_ip_align(dev, pkt_len);
>> +				if (!skb)
>> +					goto fallback_to_normal_path;
>
> The goto looks pretty awkward.
>
> 	skb = NULL;
> 	if (pkt_len <= copy_thresh)
> 		skb = netdev_alloc_skb_ip_align(dev, pkt_len);
> 	if (!skb) {
> 		// existing non-copy path
> 	} else {
> 		// existing copybreak path
> 	}

I totally agree with your point. However, the two cases handle `skb` and
`rx_skbuff` differently depending on the `copy_thresh` condition,
regardless of whether `skb` is NULL or not.

This patch is only intended to gracefully handle the failure case when `skb`
allocation fails.

	Yeounsu Moon