On Tue, Sep 11, 2018 at 02:48:19AM +0100, Dmitry Safonov wrote: > Make sure under CONFIG_LOCKDEP that each change to line discipline > is done with held write semaphor.
But you don't do that. You just assert it is held, not for writing. > Otherwise potential reader will have a good time dereferencing > incomplete/uninitialized ldisc. > > Exception here is tty_ldisc_open(), as it's called without ldisc_sem > locked by tty_init_dev() for the tty->link. You fail to explain how that is not broken... > Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> > Cc: Jiri Slaby <jsl...@suse.com> > Signed-off-by: Dmitry Safonov <d...@arista.com> > --- > drivers/tty/tty_ldisc.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c > index fc4c97cae01e..202cb645582f 100644 > --- a/drivers/tty/tty_ldisc.c > +++ b/drivers/tty/tty_ldisc.c > @@ -471,6 +471,7 @@ static int tty_ldisc_open(struct tty_struct *tty, struct > tty_ldisc *ld) > > static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld) > { > + lockdep_assert_held(&tty->ldisc_sem); Did you want: lockdep_assert_held_exclusive(&tty->ldisc_sem); ? > WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags)); > clear_bit(TTY_LDISC_OPEN, &tty->flags); > if (ld->ops->close)