linux-kernel - [PATCH V2] tty: serial: fsl_lpuart: add timeout for wait_event

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Date:   Fri,  3 Dec 2021 11:04:41 +0800
From:   Sherry Sun <sherry.sun@....com>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-imx@....com
Subject: [PATCH V2] tty: serial: fsl_lpuart: add timeout for wait_event_interruptible in .shutdown()

Use wait_event_interruptible in lpuart_dma_shutdown isn't a reasonable
behavior, since it may cause the system hang here if the condition
!sport->dma_tx_in_progress never to be true in some corner case, such as
when enable the flow control, the dma tx request may never be completed
due to the peer's CTS setting when run .shutdown().

So here change to use wait_event_interruptible_timeout instead of
wait_event_interruptible, the tx dma will be forcibly terminated if the
tx dma request cannot be completed within 300ms.
Considering the worst tx dma case is to have a 4K bytes tx buffer, which
would require about 300ms to complete when the baudrate is 115200.

Signed-off-by: Sherry Sun <sherry.sun@....com>
---
changes in V2
1. Increase the timeout to 300ms, need to consider the worst tx dma case.
---
 drivers/tty/serial/fsl_lpuart.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index ac5112def40d..3affe52a364d 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1793,8 +1793,8 @@ static void lpuart_dma_shutdown(struct lpuart_port *sport)
 	}

 	if (sport->lpuart_dma_tx_use) {
-		if (wait_event_interruptible(sport->dma_wait,
-			!sport->dma_tx_in_progress) != false) {
+		if (wait_event_interruptible_timeout(sport->dma_wait,
+			!sport->dma_tx_in_progress, msecs_to_jiffies(300)) <= 0) {
 			sport->dma_tx_in_progress = false;
 			dmaengine_terminate_all(sport->dma_tx_chan);
 		}
-- 
2.17.1