diff options
authorLinus Torvalds <>2009-10-03 21:44:21 -0700
committerLinus Torvalds <>2009-10-03 21:44:21 -0700
commit0b5759c654e74c8dc317ea2c6b3a7476160f688a (patch)
parentf0a221ef47df3cdde2123fe75ce3b61bb7df656d (diff)
tty: Avoid dropping ldisc_mutex over hangup tty re-initialization
A couple of people have hit the WARN_ON() in drivers/char/tty_io.c, tty_open() that is unhappy about seeing the tty line discipline go away during the tty hangup. See for example and the reason is that we do the tty_ldisc_halt() outside the ldisc_mutex in order to be able to flush the scheduled work without a deadlock with vhangup_work. However, it turns out that we can solve this particular case by - using "cancel_delayed_work_sync()" in tty_ldisc_halt(), which waits for just the particular work, rather than synchronizing with any random outstanding pending work. This won't deadlock, since the we synchronize with doesn't care about the ldisc_mutex, it just flushes the tty ldisc buffers. - realize that for this particular case, we don't need to wait for any hangup work, because we are inside the hangup codepaths ourselves. so as a result we can just drop the flush_scheduled_work() entirely, and then move the tty_ldisc_halt() call to inside the mutex. That way we never expose the partially torn down ldisc state to tty_open(), and hold the ldisc_mutex over the whole sequence. Reported-by: Ingo Molnar <> Reported-by: Heinz Diehl <> Cc: Signed-off-by: Linus Torvalds <>
1 files changed, 2 insertions, 5 deletions
diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index aafdbaebc16..feb55075819 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -518,7 +518,7 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
static int tty_ldisc_halt(struct tty_struct *tty)
clear_bit(TTY_LDISC, &tty->flags);
- return cancel_delayed_work(&tty->;
+ return cancel_delayed_work_sync(&tty->;
@@ -756,12 +756,9 @@ void tty_ldisc_hangup(struct tty_struct *tty)
* N_TTY.
if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
- /* Make sure the old ldisc is quiescent */
- tty_ldisc_halt(tty);
- flush_scheduled_work();
/* Avoid racing set_ldisc or tty_ldisc_release */
+ tty_ldisc_halt(tty);
if (tty->ldisc) { /* Not yet closed */
/* Switch back to N_TTY */