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From:   Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
To:     "mika.westerberg@linux.intel.com" <mika.westerberg@linux.intel.com>
CC:     Bjorn Helgaas <helgaas@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: Linux v5.5 serious PCI bug
Thread-Topic: Linux v5.5 serious PCI bug
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Date:   Mon, 9 Dec 2019 13:29:30 +0000
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On Mon, Dec 09, 2019 at 03:12:39PM +0200, mika.westerberg@linux.intel.com wrote:
> On Mon, Dec 09, 2019 at 12:34:04PM +0000, Nicholas Johnson wrote:
> > Hi,
> > 
> > I have compiled Linux v5.5-rc1 and thought all was good until I 
> > hot-removed a Gigabyte Aorus eGPU from Thunderbolt. The driver for the 
> > GPU was not loaded (blacklisted) so the crash is nothing to do with the 
> > GPU driver.
> > 
> > We had:
> > - kernel NULL pointer dereference
> > - refcount_t: underflow; use-after-free.
> > 
> > Attaching dmesg for now; will bisect and come back with results.
> 
> Looks like something related to iommu. Does it work if you disable it?
> (intel_iommu=off in the command line).
I thought it could be that, too.

The attachment "dmesg-4" from the original email is with iommu parameters.
The attachment "dmesg-5" from the original email is with no iommu parameters.
Attaching here "dmesg-6" with the iommu explicitly set off like you said.

No difference, still broken. Although, with iommu off, there are less stack traces.

Could it be sysfs-related?

Kind regards,
Nicholas