From: Peter Hurley Subject: [PATCH -next 6/9] pty: Fix packet mode setting race Date: Thu, 16 Oct 2014 15:33:27 -0400 Message-ID: <1413488010-16885-7-git-send-email-peter@hurleysoftware.com> References: <1413488010-16885-1-git-send-email-peter@hurleysoftware.com> Return-path: In-Reply-To: <1413488010-16885-1-git-send-email-peter@hurleysoftware.com> Sender: linux-kernel-owner@vger.kernel.org To: Greg Kroah-Hartman Cc: Jiri Slaby , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, One Thousand Gnomes , Peter Hurley List-Id: linux-serial@vger.kernel.org Because pty_set_pktmode() does not claim the slave's ctrl_lock to clear ->ctrl_status (to avoid unnecessary lock nesting), pty_set_pktmode() may accidentally erase new ->ctrl_status updates. For example, CPU 0 | CPU 1 pty_set_pktmode() | pty_start() spin_lock(master's ctrl_lock) | tty->packet = 1 | | if (tty->link->packet) | spin_lock(slave's ctrl_lock) | tty->ctrl_status = TIOCPKT_START tty->link->ctrl_status = 0 | Ensure the clear of ->ctrl_status occurs before packet mode is set (and observable on another cpu). Signed-off-by: Peter Hurley --- drivers/tty/pty.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index e554393..bcec4c7 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -186,8 +186,9 @@ static int pty_set_pktmode(struct tty_struct *tty, int __user *arg) spin_lock_irq(&tty->ctrl_lock); if (pktmode) { if (!tty->packet) { - tty->packet = 1; tty->link->ctrl_status = 0; + smp_mb(); + tty->packet = 1; } } else tty->packet = 0; -- 2.1.1