tty: the vhangup syscall is racy

We now have the infrastructure to sort this out but rather than teaching
the syscall tty lock rules we move the hard work into a tty helper

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_io.c

@@ -729,6 +729,25 @@ void tty_vhangup(struct tty_struct *tty)
 
 EXPORT_SYMBOL(tty_vhangup);
 
+/**
+ *	tty_vhangup_self	-	process vhangup for own ctty
+ *
+ *	Perform a vhangup on the current controlling tty
+ */
+
+void tty_vhangup_self(void)
+{
+	struct tty_struct *tty;
+
+	mutex_lock(&tty_mutex);
+	tty = get_current_tty();
+	if (tty) {
+		tty_vhangup(tty);
+		tty_kref_put(tty);
+	}
+	mutex_unlock(&tty_mutex);
+}
+
 /**
  *	tty_hung_up_p		-	was tty hung up
  *	@filp: file pointer of tty