Hi Marc,

On Thu, 2024-03-07 at 13:23 +0100, Marc Kleine-Budde wrote:

Sorry, resend. I fsck up the linux-can ML's address.

Thanks for that.

On 07.03.2024 12:04:42, Vitor Soares wrote:

...

From: Vitor Soares vitor.soares@toradex.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.

What about returning NETDEV_TX_BUSY, then the networking stack will retry.

Do you mean when err == -EBUSY?

...

Fixes: 55e5b97f003e ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN") Cc: stable@vger.kernel.org Signed-off-by: Vitor Soares vitor.soares@toradex.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--;

I'm testing returning here when err = -EBUSY, but can_put_echo_skb() should be invoked after mcp251xfd_tx_obj_write(). Otherwise, I get a Kernel NULL pointer dereference error.

I'm not sure, if we want an error message for -EBUSY. We could add proper ethtool statistics.

...

+               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;  }

regards, Marc

Best regards, Vitor Soares