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

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Date:   Tue, 10 Dec 2019 14:50:00 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
Cc:     Lukas Wunner <lukas@...ner.de>, Jaroslav Kysela <perex@...ex.cz>,
        Alex Deucher <alexander.deucher@....com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "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

On Tue, 10 Dec 2019 14:47:28 +0100,
Nicholas Johnson wrote:
> 
> On Tue, Dec 10, 2019 at 02:39:50PM +0100, Lukas Wunner wrote:
> > 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.
> > 
> > Fixes: 586bc4aab878 ("ALSA: hda/hdmi - fix vgaswitcheroo detection for AMD")
> > Link: https://lore.kernel.org/r/PSXP216MB0438BFEAA0617283A834E11580580@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM/
> > 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
> > 
> Extremely fast turnaround from bisect to patch.
> 
> If you want the bugzilla.kernel.org report then I can do that ASAP, but 
> I feel that it is redundant now.

We have now Link tag to track the ML archive, so it should suffice, I
suppose.

> Thank you for handling my bug report.

And thank you for your quick testing.


Takashi