tty: Handle NULL tty->ldisc

In preparation of destroying line discipline on hangup, fix
ldisc core operations to properly handle when the tty's ldisc is
NULL.

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

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index d6805e1aee599ce68c496a1bb1c6b5e5f798d5e4..982af70c95ce48d0a531e297ecf1610466697fe3 100644 (file)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -269,7 +269,8 @@ const struct file_operations tty_ldiscs_proc_fops = {
 struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 {
        ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
-       WARN_ON(!tty->ldisc);
+       if (!tty->ldisc)
+               ldsem_up_read(&tty->ldisc_sem);
        return tty->ldisc;
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
@@ -460,7 +461,7 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
                if (ret)
                        clear_bit(TTY_LDISC_OPEN, &tty->flags);
 
-               tty_ldisc_debug(tty, "%p: opened\n", tty->ldisc);
+               tty_ldisc_debug(tty, "%p: opened\n", ld);
                return ret;
        }
        return 0;
@@ -481,7 +482,7 @@ static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
        clear_bit(TTY_LDISC_OPEN, &tty->flags);
        if (ld->ops->close)
                ld->ops->close(tty);
-       tty_ldisc_debug(tty, "%p: closed\n", tty->ldisc);
+       tty_ldisc_debug(tty, "%p: closed\n", ld);
 }
 
 /**
@@ -544,6 +545,11 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
        if (retval)
                goto err;
 
+       if (!tty->ldisc) {
+               retval = -EIO;
+               goto out;
+       }
+
        /* Check the no-op case */
        if (tty->ldisc->ops->num == ldisc)
                goto out;
@@ -659,7 +665,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
        int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
        int err = 0;
 
-       tty_ldisc_debug(tty, "%p: closing\n", tty->ldisc);
+       tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
 
        ld = tty_ldisc_ref(tty);
        if (ld != NULL) {
@@ -743,6 +749,8 @@ int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 
 static void tty_ldisc_kill(struct tty_struct *tty)
 {
+       if (!tty->ldisc)
+               return;
        /*
         * Now kill off the ldisc
         */