Patch "serial: samsung_tty: do not unlock port->lock for uart_write_wakeup()" has been added to the 5.16-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    serial: samsung_tty: do not unlock port->lock for uart_write_wakeup()

to the 5.16-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     serial-samsung_tty-do-not-unlock-port-lock-for-uart_.patch
and it can be found in the queue-5.16 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c78a1aa532afbfcce1326b2dcb469a22b2ecd0b8
Author: Jiri Slaby <jslaby@xxxxxxx>
Date:   Tue Mar 8 12:51:53 2022 +0100

    serial: samsung_tty: do not unlock port->lock for uart_write_wakeup()
    
    [ 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@xxxxxxxxxx>
    Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
    Cc: Hyeonkook Kim <hk619.kim@xxxxxxxxxxx>
    Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
    Link: https://lore.kernel.org/r/20220308115153.4225-1-jslaby@xxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
index ca084c10d0bb..78f01ddab1c6 100644
--- a/drivers/tty/serial/samsung_tty.c
+++ b/drivers/tty/serial/samsung_tty.c
@@ -922,11 +922,8 @@ 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);