Re: [GIT PULL] PCI changes for v4.20

[Bjorn Helgaas]

[+cc Martin, Rafael, Len, linux-acpi]

On Tue, Nov 13, 2018 at 11:20:04AM +0100, Borislav Petkov wrote:
> On Tue, Nov 13, 2018 at 08:17:12AM +0100, Ingo Molnar wrote:
> > 
> > * Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> > 
> > > PCI changes:
> > > 
> > >   - Pay attention to device-specific _PXM node values (Jonathan Cameron)
> > 
> > There's a new boot regression, my AMD ThreadRipper system (MSI X399 SLI 
> > PLUS (MS-7B09)) hangs during early bootup, and I have bisected it down to 
> > this commit:
> > 
> >   bad7dcd94f39: ACPI/PCI: Pay attention to device-specific _PXM node values
> > 
> > Reverting it solves the hang.
> > 
> > Unfortunately there's no console output when it hangs, even with 
> > earlyprintk. It just hangs after the "loading initrd" line.
> > 
> > Config is an Ubuntu-ish config with PROVE_LOCKING=y and a few other debug 
> > options.
> > 
> > All my other testsystems boot fine with similar configs, so it's probably 
> > something specific to this system.

Martin reported the same thing [1] (unfortunately the archive didn't
capture Martin's original emails, I think because they were multi-part
messages with attachments).

Looks like Martin might have a similar system:

  DMI: To Be Filled By O.E.M. To Be Filled By O.E.M./X399 Taichi, BIOS P3.30 08/14/2018
  smpboot: CPU0: AMD Ryzen Threadripper 2950X 16-Core Processor (family: 0x17, model: 0x8, stepping: 0x2)

Given how painful this is to debug, I queued up a revert on my
for-linus branch until we figure out what sanity checks are needed to
make the original patch safe.

I would expect proximity information to be basically just a hint for
optimization, not a functional requirement, so it would be really
interesting to figure out why this causes such a catastrophic failure.
Maybe there's a way to improve that path as well so it would be more
robust or at least more debuggable.

Bjorn

[1] https://lore.kernel.org/linux-pci/20180912152140.3676-2-Jonathan.Cameron@xxxxxxxxxx