Make sure under CONFIG_LOCKDEP that each change to line discipline is done with held write semaphor. 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. 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); WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags)); clear_bit(TTY_LDISC_OPEN, &tty->flags); if (ld->ops->close) @@ -492,6 +493,7 @@ static int tty_ldisc_failto(struct tty_struct *tty, int ld) struct tty_ldisc *disc = tty_ldisc_get(tty, ld); int r; + lockdep_assert_held(&tty->ldisc_sem); if (IS_ERR(disc)) return PTR_ERR(disc); tty->ldisc = disc; @@ -615,6 +617,7 @@ EXPORT_SYMBOL_GPL(tty_set_ldisc); */ static void tty_ldisc_kill(struct tty_struct *tty) { + lockdep_assert_held(&tty->ldisc_sem); if (!tty->ldisc) return; /* @@ -662,6 +665,7 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc) struct tty_ldisc *ld; int retval; + lockdep_assert_held(&tty->ldisc_sem); ld = tty_ldisc_get(tty, disc); if (IS_ERR(ld)) { BUG_ON(disc == N_TTY); @@ -825,6 +829,7 @@ int tty_ldisc_init(struct tty_struct *tty) */ void tty_ldisc_deinit(struct tty_struct *tty) { + /* no ldisc_sem, tty is being destroyed */ if (tty->ldisc) tty_ldisc_put(tty->ldisc); tty->ldisc = NULL; -- 2.13.6