linux-kernel - Re: Linux v5.5 serious PCI bug

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Date:   Tue, 10 Dec 2019 12:52:30 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     Lukas Wunner <lukas@...ner.de>
CC:     "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "alexander.deucher@....com" <alexander.deucher@....com>,
        "tiwai@...e.de" <tiwai@...e.de>
Subject: Re: Linux v5.5 serious PCI bug

On Tue, Dec 10, 2019 at 01:29:41PM +0100, Lukas Wunner wrote:
> [cc += Alex, Takashi]
> 
> On Tue, Dec 10, 2019 at 12:00:23PM +0000, Nicholas Johnson wrote:
> > On Tue, Dec 10, 2019 at 09:28:00AM +0200, mika.westerberg@...ux.intel.com wrote:
> > > On Mon, Dec 09, 2019 at 01:33:49PM +0000, Nicholas Johnson wrote:
> > > > On Mon, Dec 09, 2019 at 03:12:39PM +0200, mika.westerberg@...ux.intel.com wrote:
> > > > > On Mon, Dec 09, 2019 at 12:34:04PM +0000, Nicholas Johnson wrote:
> > > > > > 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.
> > 
> > The following is the culprit responsible for the issues:
> > 
> > commit 586bc4aab878efcf672536f0cdec3d04b6990c94
> > Author: Alex Deucher <alexander.deucher@....com>
> > Date:   Fri Nov 22 16:43:50 2019 -0500
> > 
> >     ALSA: hda/hdmi - fix vgaswitcheroo detection for AMD
> 
> Does the below fix the issue?
> 
> -- >8 --
> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> index 35b4526f0d28..b856b89378ac 100644
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -1419,7 +1419,6 @@ static bool atpx_present(void)
>  				return true;
>  			}
>  		}
> -		pci_dev_put(pdev);
>  	}
>  	return false;
>  }
Yes, removing the pci_dev_put() as above solves the issue.

Thanks.

Kind regards,
Nicholas.