Re: [Xen-devel] irq problem with 3.3-rc3 on guest

[M A Young <m.a.young@xxxxxxxxxxxx>]

On Tue, 14 Feb 2012, M A Young wrote:

> On Tue, 14 Feb 2012, Konrad Rzeszutek Wilk wrote:
>
> > On Mon, Feb 13, 2012 at 02:12:08PM +0000, M A Young wrote:
> > > On Mon, 13 Feb 2012, Ian Campbell wrote:
> > >
> > > > On Sun, 2012-02-12 at 21:33 +0000, M A Young wrote:
> > > > > I get the backtrace below if I try to boot a PV guest running F17 Alpha
> > > > > TC2 in graphical mode. Is this a known problem?
> > > > It came up last year https://lkml.org/lkml/2011/1/6/19 which resulted in
> > > > the WARN_ON you saw instead of a kernel crash. I'm not sure if anyone
> > > > got to the bottom of the root cause though.
> > > >
> > > > That occasion was a suspend/resume thing so perhaps not really related
> > > > but it seems fishily similar.
> > > >
> > > > I've not looked at the code recently but it seems that back then I was
> > > > of the opinion that info->update_wanted == 0 must remain true until the
> > > > irq etc was all fully setup, that might be relevant now?
> > > Yes, it does sound fishily similar. I didn't mention that it does work if
> > > I do a text boot and then switch to a graphical runlevel, so it could be
> > So how does F17 do it now? Is all in the graphical mode (KMS?) and it never
> > tries to hit text mode (so plymouth is on by default?)
> I was probably wrong about that. It was a separate non-kernel bug that was 
> stopping me getting a direct graphical boot. As the backtrace happens some 
> time but not others I am not longer convinced about the graphical vs text 
> boot link. The backtrace occurs before the line
> Feb 14 20:26:31 localhost kernel: [    2.611366] Console: switching to colour 
> frame buffer device 100x37
> so it seems to be when the frame buffer first launches.
>
> > > somthing happening in the wrong order, such as the framebuffer starting
> > > before the irq is properly set up.
> > Hm, could you instrument xen-fbfront.c and see what the flow is during
> > bootup and compare that when running it under F16? That might shed some
> > light on this.
> I will have a look at what useful debugging I can put into xen-fbfront.c - it 
> might be hard for me to compare it with F16 but the comparsion between a 
> backtrace and non-backtrace boot might be useful.
My first debugging attempt gives the values
update_wanted=0 in_cons=0 in_prod=1 width=800 height=600
just before the crash occurs. I am not sure how useful this is.

        Michael Young

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