linux-kernel - [PATCH net v2] net: ethernet: ti: am65-cpsw: Fix NAPI registration sequence

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Message-ID: <20250311130103.68971-1-s-vadapalli@ti.com>
Date: Tue, 11 Mar 2025 18:31:03 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>, <rogerq@...nel.org>,
        <horms@...nel.org>, <alexander.sverdlin@...mens.com>,
        <dan.carpenter@...aro.org>, <c-vankar@...com>, <jpanis@...libre.com>
CC: <vigneshr@...com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <srk@...com>, <s-vadapalli@...com>
Subject: [PATCH net v2] net: ethernet: ti: am65-cpsw: Fix NAPI registration sequence

From: Vignesh Raghavendra <vigneshr@...com>

Registering the interrupts for TX or RX DMA Channels prior to registering
their respective NAPI callbacks can result in a NULL pointer dereference.
This is seen in practice as a random occurrence since it depends on the
randomness associated with the generation of traffic by Linux and the
reception of traffic from the wire.

Fixes: 681eb2beb3ef ("net: ethernet: ti: am65-cpsw: ensure proper channel cleanup in error path")
Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
Co-developed-by: Siddharth Vadapalli <s-vadapalli@...com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
---

Hello,

This patch is based on commit
4d872d51bc9d Merge tag 'x86-urgent-2025-03-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
of Mainline Linux.

v1 of this patch is at:
https://lore.kernel.org/all/20250311061214.4111634-1-s-vadapalli@ti.com/
Changes since v1:
- Based on the feedback provided by Alexander Sverdlin <alexander.sverdlin@...mens.com>
  the patch has been updated to account for the cleanup path in terms of an imbalance
  between the number of successful netif_napi_add_tx/netif_napi_add calls and the
  number of successful devm_request_irq() calls. In the event of an error, we will
  always have one extra successful netif_napi_add_tx/netif_napi_add that needs to be
  cleaned up before we clean an equal number of netif_napi_add_tx/netif_napi_add and
  devm_request_irq.

Regards,
Siddharth.

 drivers/net/ethernet/ti/am65-cpsw-nuss.c | 28 +++++++++++++-----------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
index 2806238629f8..b88edf2dd8f4 100644
--- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
+++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
@@ -2306,14 +2306,18 @@ static void am65_cpsw_nuss_remove_tx_chns(struct am65_cpsw_common *common)
 static int am65_cpsw_nuss_ndev_add_tx_napi(struct am65_cpsw_common *common)
 {
 	struct device *dev = common->dev;
+	struct am65_cpsw_tx_chn *tx_chn;
 	int i, ret = 0;
 
 	for (i = 0; i < common->tx_ch_num; i++) {
-		struct am65_cpsw_tx_chn *tx_chn = &common->tx_chns[i];
+		tx_chn = &common->tx_chns[i];
 
 		hrtimer_init(&tx_chn->tx_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
 		tx_chn->tx_hrtimer.function = &am65_cpsw_nuss_tx_timer_callback;
 
+		netif_napi_add_tx(common->dma_ndev, &tx_chn->napi_tx,
+				  am65_cpsw_nuss_tx_poll);
+
 		ret = devm_request_irq(dev, tx_chn->irq,
 				       am65_cpsw_nuss_tx_irq,
 				       IRQF_TRIGGER_HIGH,
@@ -2323,19 +2327,16 @@ static int am65_cpsw_nuss_ndev_add_tx_napi(struct am65_cpsw_common *common)
 				tx_chn->id, tx_chn->irq, ret);
 			goto err;
 		}
-
-		netif_napi_add_tx(common->dma_ndev, &tx_chn->napi_tx,
-				  am65_cpsw_nuss_tx_poll);
 	}
 
 	return 0;
 
 err:
-	for (--i ; i >= 0 ; i--) {
-		struct am65_cpsw_tx_chn *tx_chn = &common->tx_chns[i];
-
-		netif_napi_del(&tx_chn->napi_tx);
+	netif_napi_del(&tx_chn->napi_tx);
+	for (--i; i >= 0; i--) {
+		tx_chn = &common->tx_chns[i];
 		devm_free_irq(dev, tx_chn->irq, tx_chn);
+		netif_napi_del(&tx_chn->napi_tx);
 	}
 
 	return ret;
@@ -2569,6 +2570,9 @@ static int am65_cpsw_nuss_init_rx_chns(struct am65_cpsw_common *common)
 			     HRTIMER_MODE_REL_PINNED);
 		flow->rx_hrtimer.function = &am65_cpsw_nuss_rx_timer_callback;
 
+		netif_napi_add(common->dma_ndev, &flow->napi_rx,
+			       am65_cpsw_nuss_rx_poll);
+
 		ret = devm_request_irq(dev, flow->irq,
 				       am65_cpsw_nuss_rx_irq,
 				       IRQF_TRIGGER_HIGH,
@@ -2579,9 +2583,6 @@ static int am65_cpsw_nuss_init_rx_chns(struct am65_cpsw_common *common)
 			flow->irq = -EINVAL;
 			goto err_flow;
 		}
-
-		netif_napi_add(common->dma_ndev, &flow->napi_rx,
-			       am65_cpsw_nuss_rx_poll);
 	}
 
 	/* setup classifier to route priorities to flows */
@@ -2590,10 +2591,11 @@ static int am65_cpsw_nuss_init_rx_chns(struct am65_cpsw_common *common)
 	return 0;
 
 err_flow:
-	for (--i; i >= 0 ; i--) {
+	netif_napi_del(&flow->napi_rx);
+	for (--i; i >= 0; i--) {
 		flow = &rx_chn->flows[i];
-		netif_napi_del(&flow->napi_rx);
 		devm_free_irq(dev, flow->irq, flow);
+		netif_napi_del(&flow->napi_rx);
 	}
 
 err:
-- 
2.34.1