tty_ldisc: Fix BUG() on hangup

commit 1c95ba1e1de7edffc0c4e275e147f1a9eb1f81ae upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index df5e7db40d1386ade286766720d50833d4ac8b44..7af1a1563e8fd04645542c313bc34a0889d898db 100644 (file)
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -741,9 +741,12 @@ 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);
@@ -751,10 +754,10 @@ 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;
 }
 
 /**
@@ -816,13 +819,16 @@ 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);