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Subject[PATCH] tty_ldisc: Fix BUG() on hangup
Date
Hello

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.

This seem to fix the BUG(), but I don't know if it's correct.

Regards,

Philippe

---
--- linux-2.6.34.x86_64/drivers/char/tty_ldisc.c.orig 2010-05-16
23:17:36.000000000 +0200
+++ linux-2.6.34.x86_64/drivers/char/tty_ldisc.c 2010-10-15 10:48:01.871721197
+0200
@@ -712,9 +712,12 @@ static void tty_reset_termios(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);
@@ -722,10 +725,10 @@ static void tty_ldisc_reinit(struct tty_
/*
* 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;
}

/**
@@ -787,13 +790,16 @@ void tty_ldisc_hangup(struct tty_struct
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);

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