[PATCH 4/4] tty/lockdep: Add ldisc_sem asserts

[Dmitry Safonov <dima@arista.com>]

It should nicely document that each change to line discipline should
held write semaphor. Otherwise potential reader will have a good time.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 drivers/tty/tty_ldisc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index b72266461c00..9ef0b33a4132 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -444,6 +444,7 @@ static void tty_set_termios_ldisc(struct tty_struct *tty, int disc)
 
 static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 {
+	lockdep_assert_held(&tty->ldisc_sem);
 	WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
 	if (ld->ops->open) {
 		int ret;
@@ -469,6 +470,7 @@ 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)
@@ -490,6 +492,7 @@ 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;
@@ -613,6 +616,7 @@ 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;
 	/*
@@ -660,6 +664,7 @@ 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);
@@ -823,6 +828,7 @@ 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