linux-kernel - [PATCH 4.18 34/44] tty: Drop tty->count on tty

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Message-Id: <20181011152453.935481410@linuxfoundation.org>
Date:   Thu, 11 Oct 2018 17:40:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jiri Slaby <jslaby@...e.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Mark Rutland <mark.rutland@....com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Dmitry Safonov <dima@...sta.com>
Subject: [PATCH 4.18 34/44] tty: Drop tty->count on tty_reopen() failure

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dmitry Safonov <dima@...sta.com>

commit fe32416790093b31364c08395727de17ec96ace1 upstream.

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@...r.kernel.org # v4.6+
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jslaby@...e.com>
Reviewed-by: Jiri Slaby <jslaby@...e.cz>
Tested-by: Jiri Slaby <jslaby@...e.com>
Tested-by: Mark Rutland <mark.rutland@....com>
Tested-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/tty/tty_io.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1264,6 +1264,7 @@ static void tty_driver_remove_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)
@@ -1277,10 +1278,14 @@ static int tty_reopen(struct tty_struct
 
 	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;
 }
 
 /**