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

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Message-ID: <20250924161151.7d6054c2@kernel.org>
Date: Wed, 24 Sep 2025 16:11:51 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Yeounsu Moon" <yyyynoom@...il.com>
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, 25 Sep 2025 01:36:57 +0900 Yeounsu Moon wrote:
> > 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.

I don't understand.