Hello Marc,
Thanks for your feedback.
On Tue, 2024-04-30 at 11:10 +0200, Marc Kleine-Budde wrote:
> On 11.03.2024 12:11:43, 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 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@xxxxxxxxxxxxxxx
> > Signed-off-by: Vitor Soares <vitor.soares@xxxxxxxxxxx>
> > ---
> >
> > 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.
Doing this way, I have to can_free_echo_skb() and it won't be possible
to return NETDEV_TX_BUSY.
Do you know how can we return NETDEV_TX_BUSY when spi_async() == EBUSY
to allow the network stack to retry to transmit the package?
Best regards,
Vitor Soares
>
> regards,
> Marc
>
