pty: Don't claim slave's ctrl_lock for master's packet mode

The slave's ctrl_lock serializes updates to the ctrl_status field
only, whereas the master's ctrl_lock serializes updates to the
packet mode enable (ie., the master does not have ctrl_status and
the slave does not have packet mode). Thus, claiming the slave's
ctrl_lock to access ->packet is useless.

Unlocked reads of ->packet are already smp-safe.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_tty.c

@@ -351,13 +351,13 @@ static void n_tty_packet_mode_flush(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&tty->ctrl_lock, flags);
 	if (tty->link->packet) {
+		spin_lock_irqsave(&tty->ctrl_lock, flags);
 		tty->ctrl_status |= TIOCPKT_FLUSHREAD;
+		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 		if (waitqueue_active(&tty->link->read_wait))
 			wake_up_interruptible(&tty->link->read_wait);
 	}
-	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 }
 
 /**

drivers/tty/pty.c

@@ -339,26 +339,26 @@ static void pty_start(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&tty->ctrl_lock, flags);
 	if (tty->link && tty->link->packet) {
+		spin_lock_irqsave(&tty->ctrl_lock, flags);
 		tty->ctrl_status &= ~TIOCPKT_STOP;
 		tty->ctrl_status |= TIOCPKT_START;
+		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
 	}
-	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 }
 
 static void pty_stop(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	spin_lock_irqsave(&tty->ctrl_lock, flags);
 	if (tty->link && tty->link->packet) {
+		spin_lock_irqsave(&tty->ctrl_lock, flags);
 		tty->ctrl_status &= ~TIOCPKT_START;
 		tty->ctrl_status |= TIOCPKT_STOP;
+		spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 		wake_up_interruptible_poll(&tty->link->read_wait, POLLIN);
 	}
-	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
 }
 
 /**