linux-kernel - RE: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci

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Date:   Tue, 10 Dec 2019 15:34:27 +0000
From:   "Deucher, Alexander" <Alexander.Deucher@....com>
To:     Lukas Wunner <lukas@...ner.de>, Takashi Iwai <tiwai@...e.de>
CC:     Jaroslav Kysela <perex@...ex.cz>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: RE: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci_dev

> -----Original Message-----
> From: Lukas Wunner <lukas@...ner.de>
> Sent: Tuesday, December 10, 2019 8:40 AM
> To: Takashi Iwai <tiwai@...e.de>
> Cc: Jaroslav Kysela <perex@...ex.cz>; Deucher, Alexander
> <Alexander.Deucher@....com>; Mika Westerberg
> <mika.westerberg@...ux.intel.com>; Bjorn Helgaas <helgaas@...nel.org>;
> Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>; alsa-
> devel@...a-project.org; linux-kernel@...r.kernel.org; linux-
> pci@...r.kernel.org
> Subject: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci_dev
> 
> Nicholas Johnson reports a null pointer deref as well as a refcount underflow
> upon hot-removal of a Thunderbolt-attached AMD eGPU.
> He's bisected the issue down to commit 586bc4aab878 ("ALSA: hda/hdmi - fix
> vgaswitcheroo detection for AMD").
> 
> The commit iterates over PCI devices using pci_get_class() and unreferences
> each device found, even though pci_get_class() subsequently unreferences
> the device as well.  Fix it.

The pci_dev_put() a few lines above should probably be dropped as well.

Alex

> 
> Fixes: 586bc4aab878 ("ALSA: hda/hdmi - fix vgaswitcheroo detection for
> AMD")
> Link:
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.
> kernel.org%2Fr%2FPSXP216MB0438BFEAA0617283A834E11580580%40PSXP2
> 16MB0438.KORP216.PROD.OUTLOOK.COM%2F&amp;data=02%7C01%7Calex
> ander.deucher%40amd.com%7C254649b79a6240f3a8aa08d77d76715f%7C3d
> d8961fe4884e608e11a82d994e183d%7C0%7C0%7C637115819998031934&amp
> ;sdata=qI%2B%2FJv3Z6pvwN7gQFSnZiP31YUAvd%2BKjo0ZqMERFbYU%3D&a
> mp;reserved=0
> Reported-and-tested-by: Nicholas Johnson <nicholas.johnson-
> opensource@...look.com.au>
> Signed-off-by: Lukas Wunner <lukas@...ner.de>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Cc: Alexander Deucher <alexander.deucher@....com>
> Cc: Bjorn Helgaas <helgaas@...nel.org>
> ---
>  sound/pci/hda/hda_intel.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> 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;
>  }
> --
> 2.24.0