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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Thomas Abraham <thomas.abraham@linaro.org>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Hyeonkook Kim <hk619.kim@samsung.com>,
        Jiri Slaby <jslaby@suse.cz>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 184/218] serial: samsung_tty: do not unlock port->lock for uart_write_wakeup()
Date:   Mon, 18 Apr 2022 14:14:10 +0200
Message-Id: <20220418121206.303533332@linuxfoundation.org>
In-Reply-To: <20220418121158.636999985@linuxfoundation.org>
References: <20220418121158.636999985@linuxfoundation.org>
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From: Jiri Slaby <jslaby@suse.cz>

[ Upstream commit 988c7c00691008ea1daaa1235680a0da49dab4e8 ]

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@linaro.org>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Hyeonkook Kim <hk619.kim@samsung.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220308115153.4225-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/samsung.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/tty/serial/samsung.c b/drivers/tty/serial/samsung.c
index 8c89697c5357..15b9bf35457b 100644
--- a/drivers/tty/serial/samsung.c
+++ b/drivers/tty/serial/samsung.c
@@ -764,11 +764,8 @@ static irqreturn_t s3c24xx_serial_tx_chars(int irq, void *id)
 		goto out;
 	}
 
-	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