linux-kernel - Re: [net-next,v20,3/7] net: mtip: Add buffers management functions to the L2 switch driver

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Message-ID: <20260128224852.62b16788@wsk>
Date: Wed, 28 Jan 2026 22:48:52 +0100
From: Łukasz Majewski <lukasz.majewski@...lbox.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: festevam@...il.com, linux-arm-kernel@...ts.infradead.org,
 s.hauer@...gutronix.de, kernel@...gutronix.de, horms@...nel.org,
 shawnguo@...nel.org, imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
 conor+dt@...nel.org, devicetree@...r.kernel.org, wahrenst@....net,
 pabeni@...hat.com, davem@...emloft.net, netdev@...r.kernel.org,
 richardcochran@...il.com, edumazet@...gle.com, andrew+netdev@...n.ch,
 robh@...nel.org, krzk+dt@...nel.org, andrew@...n.ch
Subject: Re: [net-next,v20,3/7] net: mtip: Add buffers management functions
 to the L2 switch driver

Hi Jakub,

> This is an AI-generated review of your patch. The human sending this
> email has considered the AI review valid, or at least plausible.
> 
> For local reproduction steps see
> https://netdev-ai.bots.linux.dev/ai-local.html ---
> net: mtip: Add buffers management functions to the L2 switch driver
> 
> This patch adds buffer management functions for the MTIP L2 switch
> driver, implementing mtip_free_buffers(), mtip_create_page_pool(), and
> mtip_alloc_buffers() for RX page pool and TX bounce buffer handling.
> 
> > diff --git a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c
> > b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c index
> > 03c5163d6508..9c21a3d29c1c 100644 ---
> > a/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c +++
> > b/drivers/net/ethernet/freescale/mtipsw/mtipl2sw.c @@ -888,11
> > +888,96 @@ static void mtip_get_drvinfo(struct net_device *dev,
> >
> >  static void mtip_free_buffers(struct net_device *dev)
> >  {
> > +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> > +	struct switch_enet_private *fep = priv->fep;
> > +	int i;
> > +
> > +	for (i = 0; i < RX_RING_SIZE; i++) {
> > +		page_pool_put_full_page(fep->page_pool,
> > +					fep->page[i], false);  
> 
> Can fep->page[i] be NULL here?  When mtip_alloc_buffers() fails
> partway through the RX allocation loop, it calls mtip_free_buffers()
> via the error path.  At that point, only some fep->page[] entries
> have been allocated - the rest remain NULL from the kzalloc
> initialization.
> 
> The call chain page_pool_put_full_page()->page_pool_put_netmem()->
> page_pool_unref_and_test()->page_pool_unref_netmem()->
> netmem_get_pp_ref_count_ref() will attempt to access
> &NULL->pp_ref_count when passed a NULL page, causing a NULL pointer
> dereference.
> 
> Should there be a NULL check before calling page_pool_put_full_page()?
> 

Yes, such check shall be added.

> > +		fep->page[i] = NULL;
> > +	}
> > +
> > +	page_pool_destroy(fep->page_pool);
> > +	fep->page_pool = NULL;
> > +
> > +	for (i = 0; i < TX_RING_SIZE; i++)
> > +		kfree(fep->tx_bounce[i]);
> >  }  
> 
> [ ... ]
> 
> > +static int mtip_alloc_buffers(struct net_device *dev)
> > +{
> > +	struct mtip_ndev_priv *priv = netdev_priv(dev);
> > +	struct switch_enet_private *fep = priv->fep;
> > +	struct cbd_t *bdp;
> > +	struct page *page;
> > +	int i, ret;
> > +
> > +	ret = mtip_create_page_pool(fep, RX_RING_SIZE);
> > +	if (ret < 0) {
> > +		dev_err(&fep->pdev->dev, "Failed to create page
> > pool\n");
> > +		return ret;
> > +	}
> > +
> > +	bdp = fep->rx_bd_base;
> > +	for (i = 0; i < RX_RING_SIZE; i++) {
> > +		page = page_pool_dev_alloc_pages(fep->page_pool);
> > +		if (!page) {
> > +			dev_err(&fep->pdev->dev,
> > +				"Failed to allocate page for rx
> > buffer\n");
> > +			goto err;
> > +		}  
> 
> [ ... ]
> 
> > + err:
> > +	mtip_free_buffers(dev);  
> 
> When this error path is taken, fep->page[] may contain NULL entries
> for pages that were never allocated.
> 
> > +	return -ENOMEM;
> >  }  

I will add proper fix for v21.

-- 
Best regards,

Łukasz Majewski