Re: [PATCH] can: mcp251xfd: fix infinite loop when xmit fails

[Marc Kleine-Budde]

On 07.03.2024 12:04:42, Vitor Soares wrote:
> From: Vitor Soares <vitor.soares@xxxxxxxxxxx>
> 
> 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.

> Fixes: 55e5b97f003e ("can: mcp25xxfd: add driver for Microchip MCP25xxFD SPI CAN")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Vitor Soares <vitor.soares@xxxxxxxxxxx>
> ---
>  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 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

-- 
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