tty: Add diagnostic for halted line discipline

Flip buffer work must not be scheduled by the line discipline
after the line discipline has been halted; issue warning.

Note: drivers can still schedule flip buffer work.

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

1 files changed, 6 insertions, 1 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index d794087c327e..c641321b9404 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -375,6 +375,7 @@ static inline void tty_ldisc_put(struct tty_ldisc *ld)
 
 void tty_ldisc_enable(struct tty_struct *tty)
 {
+        clear_bit(TTY_LDISC_HALTED, &tty->flags);
         set_bit(TTY_LDISC, &tty->flags);
         clear_bit(TTY_LDISC_CHANGING, &tty->flags);
         wake_up(&tty_ldisc_wait);
@@ -513,8 +514,11 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
 
 static int tty_ldisc_halt(struct tty_struct *tty)
 {
+        int scheduled;
         clear_bit(TTY_LDISC, &tty->flags);
-        return cancel_work_sync(&tty->port->buf.work);
+        scheduled = cancel_work_sync(&tty->port->buf.work);
+        set_bit(TTY_LDISC_HALTED, &tty->flags);
+        return scheduled;
 }
 
 /**
@@ -820,6 +824,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
         clear_bit(TTY_LDISC, &tty->flags);
         tty_unlock(tty);
         cancel_work_sync(&tty->port->buf.work);
+        set_bit(TTY_LDISC_HALTED, &tty->flags);
         mutex_unlock(&tty->ldisc_mutex);
 retry:
         tty_lock(tty);