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

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Message-ID: <20191210122941.zzybs4z5jphpjsu2@wunner.de>
Date:   Tue, 10 Dec 2019 13:29:41 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
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, tiwai@...e.de
Subject: Re: Linux v5.5 serious PCI bug

[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;
 }