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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Torin Cooper-Bennun <torin@maxiluxsystems.com>,
        Marc Kleine-Budde <mkl@pengutronix.de>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 087/141] can: m_can: m_can_tx_work_queue(): fix tx_skb race condition
Date:   Mon, 17 May 2021 16:02:19 +0200
Message-Id: <20210517140245.715713873@linuxfoundation.org>
In-Reply-To: <20210517140242.729269392@linuxfoundation.org>
References: <20210517140242.729269392@linuxfoundation.org>
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From: Marc Kleine-Budde <mkl@pengutronix.de>

[ Upstream commit e04b2cfe61072c7966e1a5fb73dd1feb30c206ed ]

The m_can_start_xmit() function checks if the cdev->tx_skb is NULL and
returns with NETDEV_TX_BUSY in case tx_sbk is not NULL.

There is a race condition in the m_can_tx_work_queue(), where first
the skb is send to the driver and then the case tx_sbk is set to NULL.
A TX complete IRQ might come in between and wake the queue, which
results in tx_skb not being cleared yet.

Fixes: f524f829b75a ("can: m_can: Create a m_can platform framework")
Tested-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/can/m_can/m_can.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index b2224113987c..de275ccb4fd0 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -1418,6 +1418,8 @@ static netdev_tx_t m_can_tx_handler(struct m_can_classdev *cdev)
 	int i;
 	int putidx;
 
+	cdev->tx_skb = NULL;
+
 	/* Generate ID field for TX buffer Element */
 	/* Common to all supported M_CAN versions */
 	if (cf->can_id & CAN_EFF_FLAG) {
@@ -1534,7 +1536,6 @@ static void m_can_tx_work_queue(struct work_struct *ws)
 						tx_work);
 
 	m_can_tx_handler(cdev);
-	cdev->tx_skb = NULL;
 }
 
 static netdev_tx_t m_can_start_xmit(struct sk_buff *skb,
-- 
2.30.2