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@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>

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

Francesco