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

[Ingo Molnar <mingo@kernel.org>]

* Bjorn Helgaas <helgaas@kernel.org> wrote:

> [+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@kernel.org> 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.

Thanks!

Took me about a day to bisect this, on this hard to bisect machine. :-/

> 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.

Yeah.

Thanks,

	Ingo