linux-kernel - Re: [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks

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Message-ID: <20201114203925.GA1182595@bjorn-Precision-5520>
Date:   Sat, 14 Nov 2020 14:39:25 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        linux-pci@...r.kernel.org, kexec@...ts.infradead.org,
        x86@...nel.org, linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, andi@...stfloor.org,
        lukas@...ner.de, okaya@...nel.org, kernelfans@...il.com,
        ddstreet@...onical.com, gavin.guo@...onical.com,
        jay.vosburgh@...onical.com, kernel@...ccoli.net,
        shan.gavin@...ux.alibaba.com,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks

On Sat, Nov 14, 2020 at 12:40:10AM +0100, Thomas Gleixner wrote:
> Bjorn,
> 
> On Sat, Nov 14 2020 at 00:31, Thomas Gleixner wrote:
> > On Fri, Nov 13 2020 at 10:46, Bjorn Helgaas wrote:
> >> pci_device_shutdown() still clears the Bus Master Enable bit if we're
> >> doing a kexec and the device is in D0-D3hot, which should also disable
> >> MSI/MSI-X.  Why doesn't this solve the problem?  Is this because the
> >> device causing the storm was in PCI_UNKNOWN state?
> >
> > That's indeed a really good question.
> 
> So we do that on kexec, but is that true when starting a kdump kernel
> from a kernel crash? I doubt it.

Ah, right, I bet that's it, thanks.  The kdump path is basically this:

  crash_kexec
    machine_kexec

while the usual kexec path is:

  kernel_kexec
    kernel_restart_prepare
      device_shutdown
        while (!list_empty(&devices_kset->list))
          dev->bus->shutdown
            pci_device_shutdown            # pci_bus_type.shutdown
    machine_kexec

So maybe we need to explore doing some or all of device_shutdown() in
the crash_kexec() path as well as in the kernel_kexec() path.