[Regression] kdump fails to get DHCP address unless booting with pci=nomsi or without nr_cpus=1

[Coiby Xu]

On Mon, Aug 11, 2025 at 03:52:04PM +0100, Marc Zyngier wrote:
>On Mon, 11 Aug 2025 14:03:21 +0100,
>Thomas Gleixner <tglx at linutronix.de> wrote:
>>
>> On Mon, Aug 11 2025 at 15:02, Thomas Gleixner wrote:
>>
>> CC+ Marc
>>
>> > On Mon, Aug 11 2025 at 11:23, Coiby Xu wrote:
>> >> Recently I met an issue that on certain virtual machines, the kdump
>> >> kernel fails to get DHCP IP address most of times starting from
>> >> 6.11-rc2. git bisection shows commit b5712bf89b4b ("irqchip/gic-v3-its:
>> >> Provide MSI parent for PCI/MSI[-X]") is the 1st bad commit,
>> >>
>> >>      # good: [7d189c77106ed6df09829f7a419e35ada67b2bd0] PCI/MSI: Provide
>> >>      # MSI_FLAG_PCI_MSI_MASK_PARENT
>> >>      git bisect good 7d189c77106ed6df09829f7a419e35ada67b2bd0
>> >>      # good: [48f71d56e2b87839052d2a2ec32fc97a79c3e264] irqchip/gic-v3-its:
>> >>      # Provide MSI parent infrastructure
>> >>      git bisect good 48f71d56e2b87839052d2a2ec32fc97a79c3e264
>> >>      # good: [8c41ccec839c622b2d1be769a95405e4e9a4cb20] irqchip/irq-msi-lib:
>> >>      # Prepare for PCI MSI/MSIX
>> >>      git bisect good 8c41ccec839c622b2d1be769a95405e4e9a4cb20
>> >>      # first bad commit: [b5712bf89b4bbc5bcc9ebde8753ad222f1f68296]
>> >>      # irqchip/gic-v3-its: Provide MSI parent for PCI/MSI[-X]
>> >
>> > There were follow up fixes on this, so isolating this one is not really
>> > conclusive.
>> >
>> > Is the problem still there on v6.16 and v6.17-rc1?
>
>Yeah, there are way too many things that have been addressed since.
>kdump is also a particularly nasty case, as it tends to rely on the
>redistributor tables programmed by the previous kernel.

Thanks for providing a clue. This may also explain explain why I fails
to reproduce this issue against 1st kernel even with the same cmdline of
the kdump kernel.

>
>Also, this says "virtual machines". What's the hypervisor? 

I'll contact the lab administrator. What kinds of info I should collect
to help you narrow down the issue?

> How hard is it to reproduce?

It can be reproduced reliably on certain machines. But as of writing I
haven't reproduced it on other KVM virtual machines on three different
host machines.

>
>Thanks,
>
>	M.
>
>-- 
>Without deviation from the norm, progress is not possible.
>

-- 
Best regards,
Coiby