[PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[Vitor Soares]

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;
 }
-- 
2.34.1

Re: [PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[vitor]

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;
>  }

Re: [PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[Francesco Dolcini]

Hello Mark,

On Mon, Mar 11, 2024 at 12:11:43PM +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>

Any other feedback on this? Just reaching out to be that this does not
fall through the cracks.

Francesco

Re: [PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[Marc Kleine-Budde]

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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

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

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Re: [PATCH v3] can: mcp251xfd: fix infinite loop when xmit fails

[Vitor Soares]

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@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.

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
>