linux-kernel - Re: [net-next v18 5/7] net: mtip: Add mtip_switch_{rx|tx} functions to the L2 switch driver

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Message-ID: <20250815183359.352a0ecb@kernel.org>
Date: Fri, 15 Aug 2025 18:33:59 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Lukasz Majewski <lukasz.majewski@...lbox.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, davem@...emloft.net, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 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>
Subject: Re: [net-next v18 5/7] net: mtip: Add mtip_switch_{rx|tx} functions
 to the L2 switch driver

On Wed, 13 Aug 2025 09:07:53 +0200 Lukasz Majewski wrote:
> +		page = fep->page[bdp - fep->rx_bd_base];
> +		/* Process the incoming frame */
> +		pkt_len = bdp->cbd_datlen;
> +
> +		dma_sync_single_for_cpu(&fep->pdev->dev, bdp->cbd_bufaddr,
> +					pkt_len, DMA_FROM_DEVICE);
> +		net_prefetch(page_address(page));
> +		data = page_address(page);
> +
> +		if (fep->quirks & FEC_QUIRK_SWAP_FRAME)
> +			swap_buffer(data, pkt_len);
> +
> +		eth_hdr = (struct ethhdr *)data;
> +		mtip_atable_get_entry_port_number(fep, eth_hdr->h_source,
> +						  &rx_port);
> +		if (rx_port == MTIP_PORT_FORWARDING_INIT)
> +			mtip_atable_dynamicms_learn_migration(fep,
> +							      mtip_get_time(),
> +							      eth_hdr->h_source,
> +							      &rx_port);
> +
> +		if ((rx_port == 1 || rx_port == 2) && fep->ndev[rx_port - 1])
> +			pndev = fep->ndev[rx_port - 1];
> +		else
> +			pndev = dev;
> +
> +		*port = rx_port;
> +
> +		/* 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);
> +			page_pool_recycle_direct(fep->page_pool, page);
> +			pndev->stats.rx_dropped++;
> +			return -ENOMEM;
> +		}
> +
> +		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);
> +		skb->offload_fwd_mark = fep->br_offload;
> +		napi_gro_receive(&fep->napi, skb);

The rx buffer circulation is very odd. You seem to pre-allocate buffers
for the full ring from a page_pool. And then copy the data out of those
pages. The normal process is that after packet is received a new page is
allocated to give to HW, and old is attached to an skb, and sent up the
stack.

Also you are releasing the page to be recycled without clearing it from
the ring. I think you'd free it again on shutdown, so it's a
double-free.
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