diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 07275d0e30a2..9d1e247ee330 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -516,8 +516,11 @@ static void __proc_set_tty(struct tty_struct *tty)
 {
 	unsigned long flags;
 
-	/* We should not have a session or pgrp to put here but.... */
 	spin_lock_irqsave(&tty->ctrl_lock, flags);
+	/*
+	 * The session and fg pgrp references will be non-NULL if
+	 * tiocsctty() is stealing the controlling tty
+	 */
 	put_pid(tty->session);
 	put_pid(tty->pgrp);
 	tty->pgrp = get_pid(task_pgrp(current));