Re: [Intel-gfx] [PATCH] drm/i915: Remove unused IRQ chip data of HDMI LPE audio

[Ville Syrjälä]

On Mon, Jan 29, 2018 at 07:09:22PM +0200, Ville Syrjälä wrote:
> On Wed, Dec 13, 2017 at 03:06:55PM +0100, Thomas Gleixner wrote:
> > On Wed, 13 Dec 2017, Takashi Iwai wrote:
> > > On Wed, 13 Dec 2017 12:35:54 +0100,
> > > Thomas Gleixner wrote:
> > > > 
> > > > > > On Mon, 11 Dec 2017, Anand, Jerome wrote:
> > > > > > > > On Fri, 8 Dec 2017, Ville Syrjälä wrote:
> > > > > > > >
> > > > > > > > > On Fri, Dec 08, 2017 at 05:33:23PM +0800, Augustine.Chen wrote:
> > > > > > > > > > The chip data of HDMI LPE audio is set to drm_i915_private which
> > > > > > > > > > is not consistent with the expectation by x86 APIC driver.
> > > > > > > > >
> > > > > > > > > Hmm. Why is the apic code looking at data for an irq chip it
> > > > > > > > > hasn't created?
> > > > > > > > >
> > > > > > >
> > > > > > > apic code expects an irq domain to be place as generic approach.
> > > > > > 
> > > > > > APIC code does not even see that interrupt at all. It's completely disconnected.
> > > > > > 
> > > > > 
> > > > > That's the problem - APIC just converts the chip data to its internal
> > > > > format and fails.
> > > > 
> > > > How does APIC code end up to touch that interrupt at all? Call stack please.
> > > 
> > > It's found in the bugzilla referred in the patch:
> > >   https://bugs.freedesktop.org/show_bug.cgi?id=103731
> > > 
> > > [   87.353072] irq 298 idata->chip->name hdmi_lpe_audio_irqchip
> > > [   87.353072] irq 298 apic_chip_data
> > > [   87.353073] irq 298 data->domain is NULL
> > > [   87.353120] BUG: unable to handle kernel NULL pointer dereference at (null)
> > > [   87.353132] IP: setup_vector_irq+0x1ba/0x230
> > > [   87.353133] PGD 0
> > > 
> > > If my understanding is correct, it happens only with 4.14 and earlier
> > > kernels where __setup_vector_irq() loops over the all irqs:
> > > 
> > > static void __setup_vector_irq(int cpu)
> > > {
> > > 	struct apic_chip_data *data;
> > > 	struct irq_desc *desc;
> > > 	int irq, vector;
> > > 
> > > 	/* Mark the inuse vectors */
> > > 	for_each_irq_desc(irq, desc) {
> > > 		struct irq_data *idata = irq_desc_get_irq_data(desc);
> > > 
> > > 		data = apic_chip_data(idata);
> > > 		if (!data || !cpumask_test_cpu(cpu, data->domain))
> > > 			continue;
> > > 		....
> > > 
> > > And since we have assigned a non-APIC chip data in the driver, the
> > > code above refers to a wrong object, leading to Oops.
> > 
> > Bah crap. This information should have been provided earlier instead of
> > handwavy 'doesnt work with CONFIG_FOO and hotplug'.
> > 
> > > As a further note, the setup_vector_irq() code has been changed in
> > > 4.15, and such a reference won't happen any longer.  So the patch
> > > isn't necessary for now, although it's not bad to take as a cleanup.
> > > And we can eventually put Cc to stable there since it actually works
> > > around the issue above for the older kernels -- of course, with more
> > > detailed descriptions about the background.
> > 
> > No, that's just tinkering. The proper fix is to make that code robust.
> > 
> > Something like the completely untested patch below should do the trick.
> > 
> > Thanks,
> > 
> > 	tglx
> > ---
> > diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
> > index f3557a1eb562..02e6a3cc0d74 100644
> > --- a/arch/x86/kernel/apic/vector.c
> > +++ b/arch/x86/kernel/apic/vector.c
> > @@ -58,6 +58,9 @@ static struct apic_chip_data *apic_chip_data(struct irq_data *irq_data)
> >  	while (irq_data->parent_data)
> >  		irq_data = irq_data->parent_data;
> >  
> > +	if (irq_data->domain != x86_vector_domain)
> > +		return NULL;
> > +
> >  	return irq_data->chip_data;
> >  }
> >  
> > 
> 
> Did this patch resolve the issue?

Ping.

-- 
Ville Syrjälä
Intel OTC