netdev - Re: [PATCH net] net: dlink: handle dma_map

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Message-Id: <DDA4Y2GRUHD4.1DFHX01NOJYCB@gmail.com>
Date: Sun, 05 Oct 2025 14:22:43 +0900
From: "Yeounsu Moon" <yyyynoom@...il.com>
To: "Simon Horman" <horms@...nel.org>
Cc: "Andrew Lunn" <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>,
 <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: dlink: handle dma_map_single() failure
 properly

Hello Simon.

I'm currenly re-writing the code as you suggested. I think `alloc_list()` 
can easily adopt the `goto` pattern, but for others functions, it's not 
that straightforward.

My question is whether a style combining `goto`, `continue`, and `break`
would be acceptable in this context:

```c
	if (np->cur_rx - np->old_rx >= RX_RING_SIZE) {
		printk(KERN_INFO "Try to recover rx ring exhausted...\n");
		/* Re-allocate skbuffs to fill the descriptor ring */
		for (; np->cur_rx - np->old_rx > 0; np->old_rx++) {
			struct sk_buff *skb;
			dma_addr_t addr;
			entry = np->old_rx % RX_RING_SIZE;
			/* Dropped packets don't need to re-allocate */
			if (np->rx_skbuff[entry])
				goto fill_entry;

			skb = netdev_alloc_skb_ip_align(dev, np->rx_buf_sz);
			if (skb == NULL)
				goto out_clear_fraginfo;

			addr = dma_map_single(&np->pdev->dev, skb->data,
					      np->rx_buf_sz,
					      DMA_FROM_DEVICE);
			if (dma_mapping_error(&np->pdev->dev, addr))
				goto out_kfree_skb;

			np->rx_skbuff[entry] = skb;
			np->rx_ring[entry].fraginfo = cpu_to_le64(addr);
fill_entry:
			np->rx_ring[entry].fraginfo |=
			    cpu_to_le64((u64)np->rx_buf_sz << 48);
			np->rx_ring[entry].status = 0;
			continue;

out_kfree_skb:
			dev_kfree_skb_irq(skb);
out_clear_fraginfo:
			np->rx_ring[entry].fraginfo = 0;
			printk(KERN_INFO
			       "%s: Still unable to re-allocate Rx skbuff.#%d\n"
			       , dev->name, entry);
			break;
		} /* end for */
	} /* end if */
	spin_unlock_irqrestore (&np->rx_lock, flags);
	np->timer.expires = jiffies + next_tick;
	add_timer(&np->timer);
}
```

Or is there any better way to handle errors here?
I'd appreciate your guidance.