Re: "irq/matrix: Spread interrupts on allocation" breaks nouveau in mainline kernel

[Lyude Paul]

I think you are right, apologies. Glad to know this isn't a regression in the
IRQ handling code :). It looks like our nouveau problems are probably coming
from the fact that we don't just leave IRQs setup through suspend/resume which
as far as I can tell, is probably not the correct thing to do.

Going to get some patches onto the mailing list for this, thanks for the help!

On Thu, 2018-01-25 at 09:54 +0100, Thomas Gleixner wrote:
> On Wed, 24 Jan 2018, Lyude Paul wrote:
> > Sorry about that! Let me clarify a little bit: this is a problem that shows
> > up
> > on mainline. Normally when we suspend the GPU in nouveau, we free the IRQs
> > it's using before going into suspend
> > (drivers/gpu/drm/nouveau/nvkm/subdev/pci/base.c:88), then reserve IRQs again
> > on resume (drivers/gpu/drm/nouveau/nvkm/subdev/pci/base.c:134). Since this
> > patch got pushed to mainline, the IRQ we get from request_irq() ends up
> > having
> > the same MSI vector as another device on the system:
> 
> It's not the same.
> 
> >     nouveau:
> >      parent:
> >         domain:  VECTOR
> >          hwirq:   0x2f
> >          chip:    APIC
> >           flags:   0x0
> >          Vector:    35
> >          Target:     1
> 
> Vector 35 on CPU1
> 
> >     After resume and allocating the interrupt for nouveau again, we get a
> > message
> >     from the kernel saying: 
> > 
> >     [  217.150787] do_IRQ: 1.35 No irq handler for vector
> 
> That's because there is a pending irq on the old vector for unknown reasons.
> 
> >     As well, nouveau ends up getting no interrupts from the card and as a
> > result
> >     fails to come back up:
> > 
> >     [  219.153049] nouveau 0000:22:00.0: DRM: EVO timeout
> >     [  220.226254] r8169 0000:1e:00.0 enp30s0: link up
> >     [  221.153054] nouveau 0000:22:00.0: DRM: base-0: timeout
> >     [  223.153528] nouveau 0000:22:00.0: DRM: base-0: timeout
> > 
> >     If we look through all of the other IRQ allocations, we'll find that now
> > two
> >     devices have the MSI vector 35:
> > 
> >     nouveau:
> >      parent:
> >         domain:  VECTOR
> >          hwirq:   0x2f
> >          chip:    APIC
> >           flags:   0x0
> >          Vector:    35
> >          Target:     1
> 
> Vector 35 on CPU1
> 
> >     and the PCI bridge (00:01.3 PCI bridge: Advanced Micro Devices, Inc.
> > [AMD]
> >     Family 17h (Models 00h-0fh) PCIe GPP Bridge):
> > 
> >          parent:
> >             domain:  VECTOR
> >              hwirq:   0x19
> >              chip:    APIC
> >               flags:   0x0
> >              Vector:    35
> >              Target:     0
> 
> Vector 35 on CPU0. Same vector but different CPUs. So it's NOT the same
> thing.
> 
> The real issue is something completely different and the revert of this
> patch merily papers over the underlying problem. I'm pretty sure that you
> can trigger this even with the revert in place. Do the following before
> suspend:
> 
>     echo 2 >/proc/irq/$NOUVEAUIRQ/smp_affinity_list
> 
> Then do suspend/resume and you should end up with the same situation.
> 
> I can't tell from your dmesg, but I'm pretty confident that
> 
> >     [  217.150787] do_IRQ: 1.35 No irq handler for vector
> 
> happens _before_ the nouveau driver requests the irq again. Can please you
> add some printk to the code in question to verify that?
> 
> Thanks,
> 
> 	tglx