[SRU B] [PATCH 1/4] tty: Drop tty->count on tty_reopen() failure

[Guilherme G. Piccoli]

From: Dmitry Safonov <dima at arista.com>

BugLink: https://bugs.launchpad.net/bugs/1791758

In case of tty_ldisc_reinit() failure, tty->count should be decremented
back, otherwise we will never release_tty().
Tetsuo reported that it fixes noisy warnings on tty release like:
  pts pts4033: tty_release: tty->count(10529) != (#fd's(7) + #kopen's(0))

Fixes: commit 892d1fa7eaae ("tty: Destroy ldisc instance on hangup")

Cc: stable at vger.kernel.org # v4.6+
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Jiri Slaby <jslaby at suse.com>
Reviewed-by: Jiri Slaby <jslaby at suse.cz>
Tested-by: Jiri Slaby <jslaby at suse.com>
Tested-by: Mark Rutland <mark.rutland at arm.com>
Tested-by: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
Signed-off-by: Dmitry Safonov <dima at arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry-picked from fe32416790093b31364c08395727de17ec96ace1 upstream)
Signed-off-by: Guilherme G. Piccoli <gpiccoli at canonical.com>
---
 drivers/tty/tty_io.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 495686cd0086..67e2ea4e7f1d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1255,6 +1255,7 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *
 static int tty_reopen(struct tty_struct *tty)
 {
 	struct tty_driver *driver = tty->driver;
+	int retval;
 
 	if (driver->type == TTY_DRIVER_TYPE_PTY &&
 	    driver->subtype == PTY_TYPE_MASTER)
@@ -1268,10 +1269,14 @@ static int tty_reopen(struct tty_struct *tty)
 
 	tty->count++;
 
-	if (!tty->ldisc)
-		return tty_ldisc_reinit(tty, tty->termios.c_line);
+	if (tty->ldisc)
+		return 0;
 
-	return 0;
+	retval = tty_ldisc_reinit(tty, tty->termios.c_line);
+	if (retval)
+		tty->count--;
+
+	return retval;
 }
 
 /**
-- 
2.19.2