n_hdlc: simplify freeing of buffer list

n_hdlc_release contains four loops to free each buffer list. Create a
helper (n_hdlc_free_buf_list) and call it for every list instead. It
makes n_hdlc_release more readable.

We are switching from "for (;;)" to "do {} while (buf)" which avoids the
"if (buf)" completely -- kfree is a nop for NULL pointers.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200219084118.26491-7-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/n_hdlc.c

@@ -215,6 +215,16 @@ static struct tty_ldisc_ops n_hdlc_ldisc = {
 	.flush_buffer   = flush_rx_queue,
 };
 
+static void n_hdlc_free_buf_list(struct n_hdlc_buf_list *list)
+{
+	struct n_hdlc_buf *buf;
+
+	do {
+		buf = n_hdlc_buf_get(list);
+		kfree(buf);
+	} while (buf);
+}
+
 /**
  * n_hdlc_release - release an n_hdlc per device line discipline info structure
  * @n_hdlc - per device line discipline info structure
@@ -222,7 +232,6 @@ static struct tty_ldisc_ops n_hdlc_ldisc = {
 static void n_hdlc_release(struct n_hdlc *n_hdlc)
 {
 	struct tty_struct *tty = n_hdlc2tty (n_hdlc);
-	struct n_hdlc_buf *buf;
 
 	/* Ensure that the n_hdlcd process is not hanging on select()/poll() */
 	wake_up_interruptible (&tty->read_wait);
@@ -231,37 +240,11 @@ static void n_hdlc_release(struct n_hdlc *n_hdlc)
 	if (tty->disc_data == n_hdlc)
 		tty->disc_data = NULL;	/* Break the tty->n_hdlc link */
 
-	/* Release transmit and receive buffers */
-	for(;;) {
-		buf = n_hdlc_buf_get(&n_hdlc->rx_free_buf_list);
-		if (buf) {
-			kfree(buf);
-		} else
-			break;
-	}
-	for(;;) {
-		buf = n_hdlc_buf_get(&n_hdlc->tx_free_buf_list);
-		if (buf) {
-			kfree(buf);
-		} else
-			break;
-	}
-	for(;;) {
-		buf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
-		if (buf) {
-			kfree(buf);
-		} else
-			break;
-	}
-	for(;;) {
-		buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
-		if (buf) {
-			kfree(buf);
-		} else
-			break;
-	}
+	n_hdlc_free_buf_list(&n_hdlc->rx_free_buf_list);
+	n_hdlc_free_buf_list(&n_hdlc->tx_free_buf_list);
+	n_hdlc_free_buf_list(&n_hdlc->rx_buf_list);
+	n_hdlc_free_buf_list(&n_hdlc->tx_buf_list);
 	kfree(n_hdlc);
-	
 }	/* end of n_hdlc_release() */
 
 /**