[PATCH -next 25/27] tty: Fix hung task on pty hangup

Peter Hurley
2014-10-16T21:00:56Z

When hanging up one end of a pty pair, there may be waiting
readers/writers on the other end which may not exit, preventing
tty_ldisc_lock_pair() from acquiring the other side's ldisc lock.

Only acquire this side's ldisc lock; although this will no longer
prevent the other side from writing new input, that input will not
be processing until after the ldisc hangup is complete.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
drivers/tty/tty_ldisc.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 5bdc241..1dbe278 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -326,6 +326,24 @@ static inline void __tty_ldisc_unlock(struct tty_struct *tty)
}

static int __lockfunc
+tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout)
+{
+ int ret;
+
+ ret = __tty_ldisc_lock(tty, timeout);
+ if (!ret)
+ return -EBUSY;
+ set_bit(TTY_LDISC_HALTED, &tty->flags);
+ return 0;
+}
+
+static void tty_ldisc_unlock(struct tty_struct *tty)
+{
+ clear_bit(TTY_LDISC_HALTED, &tty->flags);
+ __tty_ldisc_unlock(tty);
+}
+
+static int __lockfunc
tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2,
unsigned long timeout)
{
@@ -682,7 +700,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
*
* Avoid racing set_ldisc or tty_ldisc_release
*/
- tty_ldisc_lock_pair(tty, tty->link);
+ tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);

if (tty->ldisc) {

@@ -704,7 +722,7 @@ void tty_ldisc_hangup(struct tty_struct *tty)
WARN_ON(tty_ldisc_open(tty, tty->ldisc));
}
}
- tty_ldisc_enable_pair(tty, tty->link);
+ tty_ldisc_unlock(tty);
if (reset)
tty_reset_termios(tty);

--
2.1.1