1 files changed, 11 insertions, 7 deletions

diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index 4d540619ac8..3b6fa7b0be8 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -423,24 +423,28 @@ static int set_ltchars(struct tty_struct * tty, struct ltchars __user * ltchars)
  *
  *      Send a high priority character to the tty even if stopped
  *
- *      Locking: none
- *
- *      FIXME: overlapping calls with start/stop tty lose state of tty
+ *      Locking: none for xchar method, write ordering for write method.
  */
 
-static void send_prio_char(struct tty_struct *tty, char ch)
+static int send_prio_char(struct tty_struct *tty, char ch)
 {
         int     was_stopped = tty->stopped;
 
         if (tty->driver->send_xchar) {
                 tty->driver->send_xchar(tty, ch);
-                return;
+                return 0;
         }
+
+        if (mutex_lock_interruptible(&tty->atomic_write_lock))
+                return -ERESTARTSYS;
+
         if (was_stopped)
                 start_tty(tty);
         tty->driver->write(tty, &ch, 1);
         if (was_stopped)
                 stop_tty(tty);
+        mutex_unlock(&tty->atomic_write_lock);
+        return 0;
 }
 
 int n_tty_ioctl(struct tty_struct * tty, struct file * file,
@@ -514,11 +518,11 @@ int n_tty_ioctl(struct tty_struct * tty, struct file * file,
                                 break;
                         case TCIOFF:
                                 if (STOP_CHAR(tty) != __DISABLED_CHAR)
-                                        send_prio_char(tty, STOP_CHAR(tty));
+                                        return send_prio_char(tty, STOP_CHAR(tty));
                                 break;
                         case TCION:
                                 if (START_CHAR(tty) != __DISABLED_CHAR)
-                                        send_prio_char(tty, START_CHAR(tty));
+                                        return send_prio_char(tty, START_CHAR(tty));
                                 break;
                         default:
                                 return -EINVAL;