linux-kernel - Re: Debugging Thinkpad T430s occasional suspend failure.

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Message-ID: <alpine.LNX.2.00.1302161803430.23675@eggly.anvils>
Date:	Sat, 16 Feb 2013 18:21:01 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Airlie <airlied@...ux.ie>, Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul McKenney <paul.mckenney@...aro.org>,
	DRI <dri-devel@...ts.freedesktop.org>
Subject: Re: Debugging Thinkpad T430s occasional suspend failure.

On Sat, 16 Feb 2013, Hugh Dickins wrote:
> On Sat, 16 Feb 2013, Linus Torvalds wrote:
> > 
> > I think it's worth it to give them a heads-up already. So I've cc'd
> > the main suspects here..
> 
> Okay, thanks.
> 
> > 
> > Daniel, Dave - any comments about a NULL fb in
> > intel_choose_pipe_bpp_dither() during either suspend or resume? Some
> > googling shows this:
> > 
> >     https://bugzilla.redhat.com/show_bug.cgi?id=895123
> 
> Great, yes, I'm sure that's the same (though it says "suspend"
> and I say "resume").
> 
> > 
> > which sounds remarkably similar, and is also during a suspend attempt
> > (but apparently Satish got a full oops out).. Some timing race with a
> > worker entry?

Comparing Satish's backtrace and drivers/gpu/drm history, it's clear that
the oops comes from Daniel's 3.8-rc2 45e2b5f640b3 "drm/i915: force restore
on lid open", whose force_restore case now passes down crtc->base.fb.  But
I wouldn't have a clue why that's usually non-NULL but occasionally NULL:
your timing race with a worker entry, perhaps.

And 45e2b5f640b3 contains a fine history of going back and forth, so I
wouldn't want to play further with it out of ignorance - though tempted
to replace the "if (force_restore) {" by an interim safe-seeming
compromise of "if (force_restore && crtc->base.fb) {".

Hugh
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