The mcp251xfd driver uses a TX FIFO for sending CAN frames and a TX Event FIFO (TEF) for completed TX-requests. The TEF event handling in the mcp251xfd_handle_tefif() function has a race condition. It first increments the tx-ring's tail counter to signal that there's room in the TX and TEF FIFO, then it increments the TEF FIFO in hardware. A running mcp251xfd_start_xmit() on a different CPU might not stop the txqueue (as the tx-ring still shows free space). The next mcp251xfd_start_xmit() will push a message into the chip and the TX complete event might overflow the TEF FIFO. This patch changes the order to fix the problem. Fixes: 68c0c1c7f966 ("can: mcp251xfd: tef-path: reduce number of SPI core requests to set UINC bit") Link: https://lore.kernel.org/r/20210105214138.3150886-2-mkl@xxxxxxxxxxxxxx Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx> --- drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c index 77129d5f410b..85a1a8b7c0e7 100644 --- a/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c +++ b/drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c @@ -1368,13 +1368,10 @@ static int mcp251xfd_handle_tefif(struct mcp251xfd_priv *priv) struct mcp251xfd_tx_ring *tx_ring = priv->tx; struct spi_transfer *last_xfer; - tx_ring->tail += len; - /* Increment the TEF FIFO tail pointer 'len' times in * a single SPI message. - */ - - /* Note: + * + * Note: * * "cs_change == 1" on the last transfer results in an * active chip select after the complete SPI @@ -1391,6 +1388,8 @@ static int mcp251xfd_handle_tefif(struct mcp251xfd_priv *priv) if (err) return err; + tx_ring->tail += len; + err = mcp251xfd_check_tef_tail(priv); if (err) return err; -- 2.29.2