serial: 8250: Flush DMA Rx on RLSI

commit 1980860e0c8299316cddaf0992dd9e1258ec9d88 upstream.

Returning true from handle_rx_dma() without flushing DMA first creates
a data ordering hazard. If DMA Rx has handled any character at the
point when RLSI occurs, the non-DMA path handles any pending characters
jumping them ahead of those characters that are pending under DMA.

Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221108121952.5497-5-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 3be008a85f68680880e3a39a52ac28a40aa8c571..065bde35ab87dc529ea8ac0d2f84710bde9dd220 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1802,10 +1802,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
                if (!up->dma->rx_running)
                        break;
                /* fall-through */
+       case UART_IIR_RLSI:
        case UART_IIR_RX_TIMEOUT:
                serial8250_rx_dma_flush(up);
-               /* fall-through */
-       case UART_IIR_RLSI:
                return true;
        }
        return up->dma->rx_dma(up);