tty: Don't hold tty_lock for ldisc release

The tty->ldisc_sem write lock is sufficient for serializing changes
to tty->ldisc; holding the tty lock is not required.

Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 4 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 2d822aa259b2..332a622b7203 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -764,6 +764,8 @@ static void tty_ldisc_kill(struct tty_struct *tty)
  *      Called during the final close of a tty/pty pair in order to shut down
  *      the line discpline layer. On exit the ldisc assigned is N_TTY and the
  *      ldisc has not been opened.
+ *
+ *      Holding ldisc_sem write lock serializes tty->ldisc changes.
  */
 
 void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
@@ -776,13 +778,9 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
         tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc);
 
         tty_ldisc_lock_pair(tty, o_tty);
-        tty_lock_pair(tty, o_tty);
-
         tty_ldisc_kill(tty);
         if (o_tty)
                 tty_ldisc_kill(o_tty);
-
-        tty_unlock_pair(tty, o_tty);
         tty_ldisc_unlock_pair(tty, o_tty);
 
         /* And the memory resources remaining (buffers, termios) will be