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[PATCH 4.10 54/81] tty/serial: atmel: fix race condition (TX+DMA)

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  [PATCH 4.10 54/81] tty/serial: atmel: fix race condition (TX+DMA) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-04-06 11:00 +0200

#1617657 — [PATCH 4.10 54/81] tty/serial: atmel: fix race condition (TX+DMA)

4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Genoud <richard.genoud@gmail.com>

commit 31ca2c63fdc0aee725cbd4f207c1256f5deaabde upstream.

If uart_flush_buffer() is called between atmel_tx_dma() and
atmel_complete_tx_dma(), the circular buffer has been cleared, but not
atmel_port->tx_len.
That leads to a circular buffer overflow (dumping (UART_XMIT_SIZE -
atmel_port->tx_len) bytes).

Tested-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/serial/atmel_serial.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1938,6 +1938,11 @@ static void atmel_flush_buffer(struct ua
 		atmel_uart_writel(port, ATMEL_PDC_TCR, 0);
 		atmel_port->pdc_tx.ofs = 0;
 	}
+	/*
+	 * in uart_flush_buffer(), the xmit circular buffer has just
+	 * been cleared, so we have to reset tx_len accordingly.
+	 */
+	atmel_port->tx_len = 0;
 }
 
 /*

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