tty_ldisc: Fix BUG() on hangup

A kernel BUG when bluetooth rfcomm connection drop while the associated
serial port is open is sometime triggered.

It seems that the line discipline can disappear between the
tty_ldisc_put and tty_ldisc_get. This patch fall back to the N_TTY line
discipline if the previous discipline is not available anymore.

Signed-off-by: Philippe Retornaz <philippe.retornaz@epfl.ch>
Acked-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 13 insertions, 7 deletions

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 5bbf33ad49f1..d8e96b005023 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -743,9 +743,12 @@ static void tty_reset_termios(struct tty_struct *tty)
  *      state closed
  */
 
-static void tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
+static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
 {
-        struct tty_ldisc *ld;
+        struct tty_ldisc *ld = tty_ldisc_get(ldisc);
+
+        if (IS_ERR(ld))
+                return -1;
 
         tty_ldisc_close(tty, tty->ldisc);
         tty_ldisc_put(tty->ldisc);
@@ -753,10 +756,10 @@ static void tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
         /*
          *      Switch the line discipline back
          */
-        ld = tty_ldisc_get(ldisc);
-        BUG_ON(IS_ERR(ld));
         tty_ldisc_assign(tty, ld);
         tty_set_termios_ldisc(tty, ldisc);
+
+        return 0;
 }
 
 /**
@@ -831,13 +834,16 @@ void tty_ldisc_hangup(struct tty_struct *tty)
            a FIXME */
         if (tty->ldisc) {       /* Not yet closed */
                 if (reset == 0) {
-                        tty_ldisc_reinit(tty, tty->termios->c_line);
-                        err = tty_ldisc_open(tty, tty->ldisc);
+
+                        if (!tty_ldisc_reinit(tty, tty->termios->c_line))
+                                err = tty_ldisc_open(tty, tty->ldisc);
+                        else
+                                err = 1;
                 }
                 /* If the re-open fails or we reset then go to N_TTY. The
                    N_TTY open cannot fail */
                 if (reset || err) {
-                        tty_ldisc_reinit(tty, N_TTY);
+                        BUG_ON(tty_ldisc_reinit(tty, N_TTY));
                         WARN_ON(tty_ldisc_open(tty, tty->ldisc));
                 }
                 tty_ldisc_enable(tty);