netdev - Re: [PATCH V2 net-next] net: fec: add XDP

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Date: Mon, 24 Jul 2023 16:51:57 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Wei Fang <wei.fang@....com>
Cc: davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 shenwei.wang@....com, xiaoning.wang@....com, ast@...nel.org,
 daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
 netdev@...r.kernel.org, linux-imx@....com, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH V2 net-next] net: fec: add XDP_TX feature support

On Fri, 21 Jul 2023 14:21:53 +0800 Wei Fang wrote:
> +			/* Tx processing cannot call any XDP (or page pool) APIs if
> +			 * the "budget" is 0. Because NAPI is called with budget of
> +			 * 0 (such as netpoll) indicates we may be in an IRQ context,
> +			 * however, we can't use the page pool from IRQ context.
> +			 */
> +			if (unlikely(!budget))
> +				break;
> +
>  			xdpf = txq->tx_buf[index].xdp;
> -			if (bdp->cbd_bufaddr)
> +			if (bdp->cbd_bufaddr &&
> +			    txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
>  				dma_unmap_single(&fep->pdev->dev,
>  						 fec32_to_cpu(bdp->cbd_bufaddr),
>  						 fec16_to_cpu(bdp->cbd_datlen),
> @@ -1474,7 +1486,10 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
>  			/* Free the sk buffer associated with this last transmit */
>  			dev_kfree_skb_any(skb);
>  		} else {
> -			xdp_return_frame(xdpf);
> +			if (txq->tx_buf[index].type == FEC_TXBUF_T_XDP_NDO)
> +				xdp_return_frame(xdpf);
> +			else
> +				xdp_return_frame_rx_napi(xdpf);

I think that you need to also break if (!budget) here,
xdp_return_frame() may call page pool APIs to return the frame 
to a page pool owned by another driver. And that needs to be fixed
in net/main already?
-- 
pw-bot: cr