linux-kernel - [PATCH] serial: samsung_tty: do not unlock port->lock for uart_write

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Message-Id: <20220308115153.4225-1-jslaby@suse.cz>
Date:   Tue,  8 Mar 2022 12:51:53 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>,
        Thomas Abraham <thomas.abraham@...aro.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Hyeonkook Kim <hk619.kim@...sung.com>
Subject: [PATCH] serial: samsung_tty: do not unlock port->lock for uart_write_wakeup()

The commit c15c3747ee32 (serial: samsung: fix potential soft lockup
during uart write) added an unlock of port->lock before
uart_write_wakeup() and a lock after it. It was always problematic to
write data from tty_ldisc_ops::write_wakeup and it was even documented
that way. We fixed the line disciplines to conform to this recently.
So if there is still a missed one, we should fix them instead of this
workaround.

On the top of that, s3c24xx_serial_tx_dma_complete() in this driver
still holds the port->lock while calling uart_write_wakeup().

So revert the wrap added by the commit above.

Cc: Thomas Abraham <thomas.abraham@...aro.org>
Cc: Kyungmin Park <kyungmin.park@...sung.com>
Cc: Hyeonkook Kim <hk619.kim@...sung.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/serial/samsung_tty.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
index 95018a847023..ab26520c9c21 100644
--- a/drivers/tty/serial/samsung_tty.c
+++ b/drivers/tty/serial/samsung_tty.c
@@ -921,11 +921,8 @@ static void s3c24xx_serial_tx_chars(struct s3c24xx_uart_port *ourport)
 		return;
 	}

-	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) {
-		spin_unlock(&port->lock);
+	if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
 		uart_write_wakeup(port);
-		spin_lock(&port->lock);
-	}

 	if (uart_circ_empty(xmit))
 		s3c24xx_serial_stop_tx(port);
-- 
2.35.1