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Date:   Mon, 9 Dec 2019 15:12:39 +0200
From:   "mika.westerberg@linux.intel.com" <mika.westerberg@linux.intel.com>
To:     Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
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
Message-ID: <20191209131239.GP2665@lahna.fi.intel.com>
References: <PSXP216MB0438BFEAA0617283A834E11580580@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
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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).