serial: sh-sci: Stop TX DMA workqueue during port shutdown

This change “serial: sh-sci: Stop TX DMA workqueue during port shutdown” in Linux kernel is authored by Geert Uytterhoeven <geert+renesas [at]> on Fri Jul 6 11:05:42 2018 +0200.

serial: sh-sci: Stop TX DMA workqueue during port shutdown

The transmit DMA workqueue is never stopped, hence the work function may
be called after the port has been shut down.

Fix this race condition by cancelling queued work, if any, before DMA
release.  Don't initialize the work if DMA initialization failed, as it
won't be used anyway.

Signed-off-by: Geert Uytterhoeven <>
Signed-off-by: Greg Kroah-Hartman <>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit f661131.

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/tty/serial/sh-sci.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index c5c891c..f3432cc 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1293,6 +1293,7 @@ static void sci_tx_dma_release(struct sci_port *s)
 	struct dma_chan *chan = s->chan_tx_saved;
+	cancel_work_sync(&s->work_tx);
 	s->chan_tx_saved = s->chan_tx = NULL;
 	s->cookie_tx = -EINVAL;
@@ -1548,10 +1549,9 @@ static void sci_request_dma(struct uart_port *port)
 				__func__, UART_XMIT_SIZE,
 				port->state->xmit.buf, &s->tx_dma_addr);
+			INIT_WORK(&s->work_tx, work_fn_tx);
 			s->chan_tx_saved = s->chan_tx = chan;
-		INIT_WORK(&s->work_tx, work_fn_tx);
 	chan = sci_request_dma_chan(port, DMA_DEV_TO_MEM);

The commit for this change in Linux stable tree is f661131 (patch).

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