linux-kernel - [PATCH 4/4] serial: 8250: Flush DMA Rx on RLSI

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Message-Id: <20221107110708.58223-5-ilpo.jarvinen@linux.intel.com>
Date:   Mon,  7 Nov 2022 13:07:08 +0200
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        stable@...r.kernel.org, Gilles BULOZ <gilles.buloz@...tron.com>
Subject: [PATCH 4/4] serial: 8250: Flush DMA Rx on RLSI

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@...r.kernel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
---
Cc: Gilles BULOZ <gilles.buloz@...tron.com>

 drivers/tty/serial/8250/8250_port.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 92dd18716169..388172289627 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1901,10 +1901,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 		if (!up->dma->rx_running)
 			break;
 		fallthrough;
+	case UART_IIR_RLSI:
 	case UART_IIR_RX_TIMEOUT:
 		serial8250_rx_dma_flush(up);
-		fallthrough;
-	case UART_IIR_RLSI:
 		return true;
 	}
 	return up->dma->rx_dma(up);
-- 
2.30.2