1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 412f9775d19c..5bbf33ad49f1 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -47,6 +47,7 @@
 
 static DEFINE_SPINLOCK(tty_ldisc_lock);
 static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
+static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
 /* Line disc dispatch table */
 static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
 
@@ -83,6 +84,7 @@ static void put_ldisc(struct tty_ldisc *ld)
                 return;
         }
         local_irq_restore(flags);
+        wake_up(&tty_ldisc_idle);
 }
 
 /**
@@ -531,6 +533,23 @@ static int tty_ldisc_halt(struct tty_struct *tty)
 }
 
 /**
+ *      tty_ldisc_wait_idle     -       wait for the ldisc to become idle
+ *      @tty: tty to wait for
+ *
+ *      Wait for the line discipline to become idle. The discipline must
+ *      have been halted for this to guarantee it remains idle.
+ */
+static int tty_ldisc_wait_idle(struct tty_struct *tty)
+{
+        int ret;
+        ret = wait_event_interruptible_timeout(tty_ldisc_idle,
+                        atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
+        if (ret < 0)
+                return ret;
+        return ret > 0 ? 0 : -EBUSY;
+}
+
+/**
  *      tty_set_ldisc           -       set line discipline
  *      @tty: the terminal to set
  *      @ldisc: the line discipline
@@ -634,8 +653,17 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         flush_scheduled_work();
 
+        retval = tty_ldisc_wait_idle(tty);
+
         tty_lock();
         mutex_lock(&tty->ldisc_mutex);
+
+        /* handle wait idle failure locked */
+        if (retval) {
+                tty_ldisc_put(new_ldisc);
+                goto enable;
+        }
+
         if (test_bit(TTY_HUPPED, &tty->flags)) {
                 /* We were raced by the hangup method. It will have stomped
                    the ldisc data and closed the ldisc down */
@@ -669,6 +697,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 
         tty_ldisc_put(o_ldisc);
 
+enable:
         /*
          *      Allow ldisc referencing to occur again
          */