linux-kernel - Re: [net-next v11 4/7] net: mtip: The L2 switch driver for imx287

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Message-ID: <3e91e070-24a2-4dab-bca5-157fea921bf0@redhat.com>
Date: Tue, 6 May 2025 13:23:21 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Lukasz Majewski <lukma@...x.de>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, davem@...emloft.net,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>,
 Richard Cochran <richardcochran@...il.com>, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 Stefan Wahren <wahrenst@....net>, Simon Horman <horms@...nel.org>,
 Andrew Lunn <andrew@...n.ch>
Subject: Re: [net-next v11 4/7] net: mtip: The L2 switch driver for imx287

On 5/6/25 1:04 PM, Lukasz Majewski wrote:
>> On 5/4/25 4:55 PM, Lukasz Majewski wrote:
>>> +		/* This does 16 byte alignment, exactly what we
>>> need.
>>> +		 * The packet length includes FCS, but we don't
>>> want to
>>> +		 * include that when passing upstream as it messes
>>> up
>>> +		 * bridging applications.
>>> +		 */
>>> +		skb = netdev_alloc_skb(pndev, pkt_len +
>>> NET_IP_ALIGN);
>>> +		if (unlikely(!skb)) {
>>> +			dev_dbg(&fep->pdev->dev,
>>> +				"%s: Memory squeeze, dropping
>>> packet.\n",
>>> +				pndev->name);
>>> +			pndev->stats.rx_dropped++;
>>> +			goto err_mem;
>>> +		} else {
>>> +			skb_reserve(skb, NET_IP_ALIGN);
>>> +			skb_put(skb, pkt_len);      /* Make room */
>>> +			skb_copy_to_linear_data(skb, data,
>>> pkt_len);
>>> +			skb->protocol = eth_type_trans(skb, pndev);
>>> +			napi_gro_receive(&fep->napi, skb);
>>> +		}
>>> +
>>> +		bdp->cbd_bufaddr = dma_map_single(&fep->pdev->dev,
>>> data,
>>> +						  bdp->cbd_datlen,
>>> +						  DMA_FROM_DEVICE);
>>> +		if (unlikely(dma_mapping_error(&fep->pdev->dev,
>>> +					       bdp->cbd_bufaddr)))
>>> {
>>> +			dev_err(&fep->pdev->dev,
>>> +				"Failed to map descriptor rx
>>> buffer\n");
>>> +			pndev->stats.rx_errors++;
>>> +			pndev->stats.rx_dropped++;
>>> +			dev_kfree_skb_any(skb);
>>> +			goto err_mem;
>>> +		}  
>>
>> This is doing the mapping and ev. dropping the skb _after_ pushing the
>> skb up the stack, you must attempt the mapping first.
>>
>>> +static void mtip_free_buffers(struct net_device *dev)
>>> +{
>>> +	struct mtip_ndev_priv *priv = netdev_priv(dev);
>>> +	struct switch_enet_private *fep = priv->fep;
>>> +	struct sk_buff *skb;
>>> +	struct cbd_t *bdp;
>>> +	int i;
>>> +
>>> +	bdp = fep->rx_bd_base;
>>> +	for (i = 0; i < RX_RING_SIZE; i++) {
>>> +		skb = fep->rx_skbuff[i];
>>> +
>>> +		if (bdp->cbd_bufaddr)
>>> +			dma_unmap_single(&fep->pdev->dev,
>>> bdp->cbd_bufaddr,
>>> +					 MTIP_SWITCH_RX_FRSIZE,
>>> +					 DMA_FROM_DEVICE);
>>> +		if (skb)
>>> +			dev_kfree_skb(skb);  
>>
>> I suspect that on error paths mtip_free_buffers() can be invoked
>> multiple consecutive times with any successful allocation in between:
>> skb will be freed twice. Likely you need to clear fep->rx_skbuff[i]
>> here.
> 
> I don't know what I shall say now.... really... 

I suspect my email was not clear. AFAICS the current code contains at
least 2 serious issues, possibly more not yet discovered due to the
patch size. You need to submit (at least) a new revision coping with the
provided feedback.

Thanks,

Paolo