On 11.03.2024 12:11:43, 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 trigger the issue and the err = -EBUSY, the driver returns NETDEV_TX_BUSY. The network stack retries to transmit the message. Otherwise, it prints an error and discards the message.
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
V2->V3:
- Add tx_dropped stats.
- netdev_sent_queue() only if can_put_echo_skb() succeed.
V1->V2:
- Return NETDEV_TX_BUSY if mcp251xfd_tx_obj_write() == -EBUSY.
- Rework the commit message to address the change above.
- Change can_put_echo_skb() to be called after mcp251xfd_tx_obj_write() succeed. Otherwise, we get Kernel NULL pointer dereference error.
drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c | 34 ++++++++++++-------- 1 file changed, 21 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..146c44e47c60 100644 --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-tx.c @@ -166,6 +166,7 @@ netdev_tx_t mcp251xfd_start_xmit(struct sk_buff *skb, struct net_device *ndev) { struct mcp251xfd_priv *priv = netdev_priv(ndev);
- struct net_device_stats *stats = &ndev->stats; struct mcp251xfd_tx_ring *tx_ring = priv->tx; struct mcp251xfd_tx_obj *tx_obj; unsigned int frame_len;
@@ -181,25 +182,32 @@ 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);
- tx_ring->head++;
err = mcp251xfd_tx_obj_write(priv, tx_obj);
- if (err)
goto out_err;
- if (err) {
tx_ring->head--;
- return NETDEV_TX_OK;
if (err == -EBUSY)return NETDEV_TX_BUSY;
- out_err:
- netdev_err(priv->ndev, "ERROR in %s: %d\n", __func__, err);
stats->tx_dropped++;if (net_ratelimit())netdev_err(priv->ndev,"ERROR in %s: %d\n", __func__, err);- } else {
err = can_put_echo_skb(skb, ndev, tx_head, frame_len);if (!err)netdev_sent_queue(priv->ndev, frame_len);/* Stop queue if we occupy the complete TX FIFO */if (mcp251xfd_get_tx_free(tx_ring) == 0)netif_stop_queue(ndev);- }
Once you have sent the TX objects to the chip, it can trigger a TX complete IRQ. This is not very likely as the SPI sends asynchronously and the xmit handler cannot sleep.
This means you have to call can_put_echo_skb() and stop the queue if needed, _before_ you call mcp251xfd_tx_obj_write(). In case of an error, you have to roll-back these.
regards, Marc