[SRU][Cosmic][Bionic][PATCH v1 1/1] tty: do not set TTY_IO_ERROR flag if console port

[woodrow.shen at canonical.com]

From: Chanho Park <parkch98 at gmail.com>

BugLink: https://bugs.launchpad.net/bugs/1808097

Since Commit 761ed4a94582 ('tty: serial_core: convert uart_close to use
tty_port_close') and Commit 4dda864d7307 ('tty: serial_core: Fix serial
console crash on port shutdown), a serial port which is used as
console can be stuck when logging out if there is a remained process.
After logged out, agetty will try to grab the serial port but it will
be failed because the previous process did not release the port
correctly. To fix this, TTY_IO_ERROR bit should not be enabled of
tty_port_close if the port is console port.

Reproduce step:
- Run background processes from serial console
$ while true; do sleep 10; done &

- Log out
$ logout
-> Stuck

- Read journal log by journalctl | tail
Jan 28 16:07:01 ubuntu systemd[1]: Stopped Serial Getty on ttyAMA0.
Jan 28 16:07:01 ubuntu systemd[1]: Started Serial Getty on ttyAMA0.
Jan 28 16:07:02 ubuntu agetty[1643]: /dev/ttyAMA0: not a tty

Fixes: 761ed4a94582 ("tty: serial_core: convert uart_close to use tty_port_close")
Cc: Geert Uytterhoeven <geert+renesas at glider.be>
Cc: Rob Herring <robh at kernel.org>
Cc: Jiri Slaby <jslaby at suse.com>
Signed-off-by: Chanho Park <parkch98 at gmail.com>
Cc: stable <stable at vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 2a48602615e0a2f563549c7d5c8d507f904cf96e)
Signed-off-by: Woodrow Shen <woodrow.shen at canonical.com>
---
 drivers/tty/tty_port.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 25d7368..c699d41 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -640,7 +640,8 @@ void tty_port_close(struct tty_port *port, struct tty_struct *tty,
 	if (tty_port_close_start(port, tty, filp) == 0)
 		return;
 	tty_port_shutdown(port, tty);
-	set_bit(TTY_IO_ERROR, &tty->flags);
+	if (!port->console)
+		set_bit(TTY_IO_ERROR, &tty->flags);
 	tty_port_close_end(port, tty);
 	tty_port_tty_set(port, NULL);
 }
-- 
2.7.4