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

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Message-ID: <51893B68.1010907@hurleysoftware.com>
Date:	Tue, 07 May 2013 13:35:36 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Dave Jones <davej@...hat.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 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.

Regards,
Peter Hurley

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