Messages in this thread Patch in this message | | | Date | Thu, 25 Nov 2010 17:44:48 +0100 | From | Jiri Slaby <> | Subject | Re: mmotm 2010-11-23 - WARNING: at drivers/tty/tty_io.c:1331 |
| |
On 11/25/2010 04:14 PM, Kyle McMartin wrote: > On Tue, Nov 23, 2010 at 11:55:39PM -0500, Valdis.Kletnieks@vt.edu wrote: >> On Tue, 23 Nov 2010 16:13:06 PST, akpm@linux-foundation.org said: >>> The mm-of-the-moment snapshot 2010-11-23-16-12 has been uploaded to >>> >>> http://userweb.kernel.org/~akpm/mmotm/ >> >> Seen during boot: >> >> [ 23.015448] Modules linked in: >> [ 23.015453] Pid: 1207, comm: plymouthd Not tainted 2.6.37-rc3-mmotm1123 #3 >> [ 23.015455] Call Trace: > > I've been trying to figure this one out for a while, without much luck. > (Users are seeing it in 2.6.36 as well.) > > I *think* (I added a rawhide debugging patch to print the tty->name) > that plymouth is always opening tty7 to cause this. My guess is the BKL > removal has exposed some kind of race, but it's not obvious to me (and > there's many other bugs to sort through too. :( > > CC-ing Jiri since he seems to be the poor guy who's been poking this > recently (there's a good few threads about this (though the others look > like an ldisc attach race...)) I wouldn't think that's the case here > since N_TTY is the default...
Ok, tty_reopen is called without TTY_LDISC set. For further considerations, note tty_lock is held in tty_open. TTY_LDISC is cleared in:
1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this section tty_lock is held.
2) tty_release via tty_ldisc_release till the end of tty existence. If tty->count <= 1, tty_lock is taken, TTY_CLOSING bit set and then tty_ldisc_release called. tty_reopen checks TTY_CLOSING before checking TTY_LDISC.
3) tty_set_ldisc from tty_ldisc_halt to tty_ldisc_enable. We take tty_lock, set TTY_LDISC_CHANGING, put tty_lock, do some other work, take tty_lock, call tty_ldisc_enable, put tty_lock.
So the only option I see is 3) and we should do: --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1310,7 +1310,8 @@ static int tty_reopen(struct tty_struct *tty) { struct tty_driver *driver = tty->driver;
- if (test_bit(TTY_CLOSING, &tty->flags)) + if (test_bit(TTY_CLOSING, &tty->flags) || + test_bit(TTY_LDISC_CHANGING, &tty->flags)) return -EIO;
if (driver->type == TTY_DRIVER_TYPE_PTY && Alan, Greg?
thanks, -- js suse labs
| |