pps: Use pps_lookup_dev to reduce ldisc coupling

Now that N_TTY uses tty->disc_data for its private data,
'subclass' ldiscs cannot use ->disc_data for their own private data.
(This is a regression is v3.8-rc1)

Use pps_lookup_dev to associate the tty with the pps source instead.

This fixes a crashing regression in 3.8-rc1.

Signed-off-by: George Spelvin <linux@horizon.com>
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 6 deletions

diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
index 79451f2dea6a..60cee9e0ecb3 100644
--- a/drivers/pps/clients/pps-ldisc.c
+++ b/drivers/pps/clients/pps-ldisc.c
@@ -31,7 +31,7 @@
 static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status,
                                 struct pps_event_time *ts)
 {
-        struct pps_device *pps = (struct pps_device *)tty->disc_data;
+        struct pps_device *pps = pps_lookup_dev(tty);
 
         BUG_ON(pps == NULL);
 
@@ -67,9 +67,9 @@ static int pps_tty_open(struct tty_struct *tty)
                 pr_err("cannot register PPS source \"%s\"\n", info.path);
                 return -ENOMEM;
         }
-        tty->disc_data = pps;
+        pps->lookup_cookie = tty;
 
-        /* Should open N_TTY ldisc too */
+        /* Now open the base class N_TTY ldisc */
         ret = alias_n_tty_open(tty);
         if (ret < 0) {
                 pr_err("cannot open tty ldisc \"%s\"\n", info.path);
@@ -81,7 +81,6 @@ static int pps_tty_open(struct tty_struct *tty)
         return 0;
 
 err_unregister:
-        tty->disc_data = NULL;
         pps_unregister_source(pps);
         return ret;
 }
@@ -90,11 +89,10 @@ static void (*alias_n_tty_close)(struct tty_struct *tty);
 
 static void pps_tty_close(struct tty_struct *tty)
 {
-        struct pps_device *pps = (struct pps_device *)tty->disc_data;
+        struct pps_device *pps = pps_lookup_dev(tty);
 
         alias_n_tty_close(tty);
 
-        tty->disc_data = NULL;
         dev_info(pps->dev, "removed\n");
         pps_unregister_source(pps);
 }