Re: 3.9+ tty lockdep trace.

From: Dave Jones
Date: Tue May 07 2013 - 14:37:05 EST


On Tue, May 07, 2013 at 01:35:36PM -0400, Peter Hurley wrote:
> On 05/07/2013 11:04 AM, Dave Jones wrote:
> > On Tue, May 07, 2013 at 10:14:09AM -0400, Peter Hurley wrote:
> >
> > > >> Just hit this again, by switching tty's during bootup.
> > > >> The previous time was switching from X to console iirc, so that seems to be
> > > >> the key to triggering this.
> > > >
> > > > Sorry for not getting back to this sooner, merge window fun...
> > > >
> > > > Anyway, Peter, could this be something that your ldisc patches are
> > > > triggering?
> > >
> > > Yes, although early analysis also suggests the lockdep splat is possible
> > > regardless, just much less likely.
> > >
> > > I looked at this over the weekend, but I wasn't able to determine (in
> > > the limited time I had available) if the splat was valid; ie., if the
> > > cpu states could actually be concurrent and result in deadlock.
> > >
> > > I need to study the VT_DISALLOCATE ioctl in more detail which I plan
> > > to do this week.
> >
> > I don't know if it proves/disproves anything, but shortly before the dump
> > gets printed, everything is kind of locked up. I can switch tty's, but
> > the gettys on them are dead to the world until after the dump.
> >
> > ISTR a pause for a while when I hit this switching from X too.
>
> It would help to know the steps to reproduce. For example, you mention
> unresponsive gettys but the VT_DISALLOCATE ioctl doesn't work (and isn't
> designed to) on open ttys.

Hmm, dunno. I booted up, and tried to log in on tty1 (no X on that box), and after
I entered my password everything just hung for a while. I flipped to tty2
to try and log in as root, but after changing tty, I just got a blinking cursor.
10 seconds or so later, lockdep spew.

Dave

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