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

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Date:   Wed, 14 Nov 2018 11:21:04 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bart Van Assche <bvanassche@....org>,
        Jens Axboe <axboe@...nel.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Tom Lendacky <thomas.lendacky@....com>,
        Martin Hundebøll <martin@...nix.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [GIT PULL] PCI changes for v4.20


* Bjorn Helgaas <helgaas@...nel.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@...nel.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