--- zzzz-none-000/linux-2.6.39.4/drivers/tty/n_tty.c	2011-08-03 19:43:28.000000000 +0000
+++ puma6-arm-6490-729/linux-2.6.39.4/drivers/tty/n_tty.c	2021-11-10 13:23:10.000000000 +0000
@@ -1728,7 +1728,8 @@
 
 do_it_again:
 
-	BUG_ON(!tty->read_buf);
+	if (WARN_ON(!tty->read_buf))
+		return -EAGAIN;
 
 	c = job_control(tty, file);
 	if (c < 0)
@@ -1815,6 +1816,7 @@
 			/* FIXME: does n_tty_set_room need locking ? */
 			n_tty_set_room(tty);
 			timeout = schedule_timeout(timeout);
+			BUG_ON(!tty->read_buf);
 			continue;
 		}
 		__set_current_state(TASK_RUNNING);
@@ -1831,13 +1833,13 @@
 
 		if (tty->icanon && !L_EXTPROC(tty)) {
 			/* N.B. avoid overrun if nr == 0 */
+			spin_lock_irqsave(&tty->read_lock, flags);
 			while (nr && tty->read_cnt) {
 				int eol;
 
 				eol = test_and_clear_bit(tty->read_tail,
 						tty->read_flags);
 				c = tty->read_buf[tty->read_tail];
-				spin_lock_irqsave(&tty->read_lock, flags);
 				tty->read_tail = ((tty->read_tail+1) &
 						  (N_TTY_BUF_SIZE-1));
 				tty->read_cnt--;
@@ -1855,15 +1857,19 @@
 					if (tty_put_user(tty, c, b++)) {
 						retval = -EFAULT;
 						b--;
+						spin_lock_irqsave(&tty->read_lock, flags);
 						break;
 					}
 					nr--;
 				}
 				if (eol) {
 					tty_audit_push(tty);
+					spin_lock_irqsave(&tty->read_lock, flags);
 					break;
 				}
+				spin_lock_irqsave(&tty->read_lock, flags);
 			}
+			spin_unlock_irqrestore(&tty->read_lock, flags);
 			if (retval)
 				break;
 		} else {