linux-kernel - [PATCH net] net: fec: tx processing does not call XDP APIs if budget is 0

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Message-Id: <20230725074148.2936402-1-wei.fang@nxp.com>
Date:   Tue, 25 Jul 2023 15:41:48 +0800
From:   Wei Fang <wei.fang@....com>
To:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        shenwei.wang@....com, xiaoning.wang@....com, pabeni@...hat.com,
        netdev@...r.kernel.org
Cc:     linux-imx@....com, linux-kernel@...r.kernel.org
Subject: [PATCH net] net: fec: tx processing does not call XDP APIs if budget is 0

According to the clarification [1] in the latest napi.rst, the tx
processing cannot call any XDP (or page pool) APIs if the "budget"
is 0. Because NAPI is called with the budget of 0 (such as netpoll)
indicates we may be in an IRQ context, however, we cannot use the
page pool from IRQ context.

[1] https://lore.kernel.org/all/20230720161323.2025379-1-kuba@kernel.org/

Fixes: 20f797399035 ("net: fec: recycle pages for transmitted XDP frames")
Signed-off-by: Wei Fang <wei.fang@....com>
Suggested-by: Jakub Kicinski <kuba@...nel.org>
---
 drivers/net/ethernet/freescale/fec_main.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index 073d61619336..66b5cbdb43b9 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1372,7 +1372,7 @@ fec_enet_hwtstamp(struct fec_enet_private *fep, unsigned ts,
 }
 
 static void
-fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
+fec_enet_tx_queue(struct net_device *ndev, u16 queue_id, int budget)
 {
 	struct	fec_enet_private *fep;
 	struct xdp_frame *xdpf;
@@ -1416,6 +1416,14 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 			if (!skb)
 				goto tx_buf_done;
 		} else {
+			/* 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)
 				dma_unmap_single(&fep->pdev->dev,
@@ -1508,14 +1516,14 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 		writel(0, txq->bd.reg_desc_active);
 }
 
-static void fec_enet_tx(struct net_device *ndev)
+static void fec_enet_tx(struct net_device *ndev, int budget)
 {
 	struct fec_enet_private *fep = netdev_priv(ndev);
 	int i;
 
 	/* Make sure that AVB queues are processed first. */
 	for (i = fep->num_tx_queues - 1; i >= 0; i--)
-		fec_enet_tx_queue(ndev, i);
+		fec_enet_tx_queue(ndev, i, budget);
 }
 
 static void fec_enet_update_cbd(struct fec_enet_priv_rx_q *rxq,
@@ -1858,7 +1866,7 @@ static int fec_enet_rx_napi(struct napi_struct *napi, int budget)
 
 	do {
 		done += fec_enet_rx(ndev, budget - done);
-		fec_enet_tx(ndev);
+		fec_enet_tx(ndev, budget);
 	} while ((done < budget) && fec_enet_collect_events(fep));
 
 	if (done < budget) {
-- 
2.25.1