tty: Only guarantee termios read safety for throttle/unthrottle

No tty driver modifies termios during throttle() or unthrottle().
Therefore, only read safety is required.

However, tty_throttle_safe and tty_unthrottle_safe must still be
mutually exclusive; introduce throttle_mutex for that purpose.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 0 insertions, 4 deletions

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index d0c8805d8131..b78ee464bd09 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1518,9 +1518,7 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
                 tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
                 if (receive_room(tty) >= TTY_THRESHOLD_THROTTLE)
                         break;
-                up_read(&tty->termios_rwsem);
                 throttled = tty_throttle_safe(tty);
-                down_read(&tty->termios_rwsem);
                 if (!throttled)
                         break;
         }
@@ -2086,9 +2084,7 @@ do_it_again:
                         if (!tty->count)
                                 break;
                         n_tty_set_room(tty);
-                        up_read(&tty->termios_rwsem);
                         unthrottled = tty_unthrottle_safe(tty);
-                        down_read(&tty->termios_rwsem);
                         if (!unthrottled)
                                 break;
                 }