1 files changed, 42 insertions, 7 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 412f9775d19..d8e96b00502 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
 	 */
@@ -714,9 +743,12 @@ static void tty_reset_termios(struct tty_struct *tty)
  *	state closed
  */
 
-static void tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
+static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
 {
-	struct tty_ldisc *ld;
+	struct tty_ldisc *ld = tty_ldisc_get(ldisc);
+
+	if (IS_ERR(ld))
+		return -1;
 
 	tty_ldisc_close(tty, tty->ldisc);
 	tty_ldisc_put(tty->ldisc);
@@ -724,10 +756,10 @@ static void tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
 	/*
 	 *	Switch the line discipline back
 	 */
-	ld = tty_ldisc_get(ldisc);
-	BUG_ON(IS_ERR(ld));
 	tty_ldisc_assign(tty, ld);
 	tty_set_termios_ldisc(tty, ldisc);
+
+	return 0;
 }
 
 /**
@@ -802,13 +834,16 @@ void tty_ldisc_hangup(struct tty_struct *tty)
 	   a FIXME */
 	if (tty->ldisc) {	/* Not yet closed */
 		if (reset == 0) {
-			tty_ldisc_reinit(tty, tty->termios->c_line);
-			err = tty_ldisc_open(tty, tty->ldisc);
+
+			if (!tty_ldisc_reinit(tty, tty->termios->c_line))
+				err = tty_ldisc_open(tty, tty->ldisc);
+			else
+				err = 1;
 		}
 		/* If the re-open fails or we reset then go to N_TTY. The
 		   N_TTY open cannot fail */
 		if (reset || err) {
-			tty_ldisc_reinit(tty, N_TTY);
+			BUG_ON(tty_ldisc_reinit(tty, N_TTY));
 			WARN_ON(tty_ldisc_open(tty, tty->ldisc));
 		}
 		tty_ldisc_enable(tty);