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

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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