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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, Jiri Slaby <jslaby@suse.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Mark Rutland <mark.rutland@arm.com>,
        Dmitry Safonov <dima@arista.com>
Subject: [PATCH 4.19 03/99] tty: Simplify tty->count math in tty_reopen()
Date:   Mon, 21 Jan 2019 14:47:55 +0100
Message-Id: <20190121134914.048479004@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Dmitry Safonov <dima@arista.com>

commit cf62a1a13749db0d32b5cdd800ea91a4087319de upstream.

As notted by Jiri, tty_ldisc_reinit() shouldn't rely on tty counter.
Simplify math by increasing the counter after reinit success.

Cc: Jiri Slaby <jslaby@suse.com>
Link: lkml.kernel.org/r/<20180829022353.23568-2-dima@arista.com>
Suggested-by: Jiri Slaby <jslaby@suse.com>
Reviewed-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/tty_io.c |   13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1271,16 +1271,13 @@ static int tty_reopen(struct tty_struct
 	if (retval)
 		return retval;
 
-	tty->count++;
-	if (tty->ldisc)
-		goto out_unlock;
+	if (!tty->ldisc)
+		retval = tty_ldisc_reinit(tty, tty->termios.c_line);
+	tty_ldisc_unlock(tty);
 
-	retval = tty_ldisc_reinit(tty, tty->termios.c_line);
-	if (retval)
-		tty->count--;
+	if (retval == 0)
+		tty->count++;
 
-out_unlock:
-	tty_ldisc_unlock(tty);
 	return retval;
 }