--- zzzz-none-000/linux-2.6.32.61/drivers/char/n_tty.c	2013-06-10 09:43:48.000000000 +0000
+++ ar10-7272-687/linux-2.6.32.61/drivers/char/n_tty.c	2014-06-26 08:59:44.000000000 +0000
@@ -1969,7 +1969,9 @@
 				tty->ops->flush_chars(tty);
 		} else {
 			while (nr > 0) {
+				mutex_lock(&tty->output_lock);
 				c = tty->ops->write(tty, b, nr);
+				mutex_unlock(&tty->output_lock);
 				if (c < 0) {
 					retval = c;
 					goto break_out;