The previous email misses the v3 on the subject, added on this one.

On Mon, 2024-03-11 at 12:11 +0000, 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); +       }           return NETDEV_TX_OK;  }

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