linux-kernel - Re: 3.9+ tty lockdep trace.

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Message-ID: <20130507180009.GA16771@redhat.com>
Date:	Tue, 7 May 2013 14:00:09 -0400
From:	Dave Jones <davej@...hat.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: 3.9+ tty lockdep trace.

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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