linux-kernel - [PATCH] can: mcp251xfd: fix infinite loop when xmit fails

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Date: Thu,  7 Mar 2024 12:04:42 +0000
From: Vitor Soares <ivitro@...il.com>
To: mkl@...gutronix.de,
	manivannan.sadhasivam@...aro.org,
	thomas.kopp@...rochip.com
Cc: wg@...ndegger.com,
	linux-can@...r.kernel,
	linux-kernel@...r.kernel.org,
	vitor.soares@...adex.com,
	stable@...r.kernel.org
Subject: [PATCH] can: mcp251xfd: fix infinite loop when xmit fails

From: Vitor Soares <vitor.soares@...adex.com>

When the mcp251xfd_start_xmit() function fails, the driver stops
processing messages, and the interrupt routine does not return,
running indefinitely even after killing the running application.

Error messages:
[  441.298819] mcp251xfd spi2.0 can0: ERROR in mcp251xfd_start_xmit: -16
[  441.306498] mcp251xfd spi2.0 can0: Transmit Event FIFO buffer not empty. (seq=0x000017c7, tef_tail=0x000017cf, tef_head=0x000017d0, tx_head=0x000017d3).
.. and repeat forever.

The issue can be triggered when multiple devices share the same
SPI interface. And there is concurrent access to the bus.

The problem occurs because tx_ring->head increments even if
mcp251xfd_start_xmit() fails. Consequently, the driver skips one
TX package while still expecting a response in
mcp251xfd_handle_tefif_one().

This patch resolves the issue by decreasing tx_ring->head if
mcp251xfd_start_xmit() fails. With the fix, if we attempt to trigger
the issue again, the driver prints an error and discard the message.

Fixes: 55e5b97f003e ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN")
Cc: stable@...r.kernel.org
Signed-off-by: Vitor Soares <vitor.soares@...adex.com>
---
 drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c | 27 ++++++++++----------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
index 160528d3cc26..a8eb941c1b95 100644
--- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
+++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c
@@ -181,25 +181,26 @@ netdev_tx_t mcp251xfd_start_xmit(struct sk_buff *skb,
 	tx_obj = mcp251xfd_get_tx_obj_next(tx_ring);
 	mcp251xfd_tx_obj_from_skb(priv, tx_obj, skb, tx_ring->head);
 
-	/* Stop queue if we occupy the complete TX FIFO */
 	tx_head = mcp251xfd_get_tx_head(tx_ring);
-	tx_ring->head++;
-	if (mcp251xfd_get_tx_free(tx_ring) == 0)
-		netif_stop_queue(ndev);
-
 	frame_len = can_skb_get_frame_len(skb);
-	err = can_put_echo_skb(skb, ndev, tx_head, frame_len);
-	if (!err)
-		netdev_sent_queue(priv->ndev, frame_len);
+	can_put_echo_skb(skb, ndev, tx_head, frame_len);
+
+	tx_ring->head++;
 
 	err = mcp251xfd_tx_obj_write(priv, tx_obj);
-	if (err)
-		goto out_err;
+	if (err) {
+		can_free_echo_skb(ndev, tx_head, NULL);
 
-	return NETDEV_TX_OK;
+		tx_ring->head--;
+
+		netdev_err(priv->ndev, "ERROR in %s: %d\n", __func__, err);
+	} else {
+		/* Stop queue if we occupy the complete TX FIFO */
+		if (mcp251xfd_get_tx_free(tx_ring) == 0)
+			netif_stop_queue(ndev);
 
- out_err:
-	netdev_err(priv->ndev, "ERROR in %s: %d\n", __func__, err);
+		netdev_sent_queue(priv->ndev, frame_len);
+	}
 
 	return NETDEV_TX_OK;
 }
-- 
2.34.1