Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   "Deucher, Alexander" <Alexander.Deucher@amd.com>
To:     Lukas Wunner <lukas@wunner.de>
CC:     Takashi Iwai <tiwai@suse.de>, Jaroslav Kysela <perex@perex.cz>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>,
        "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: RE: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci_dev
Thread-Topic: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci_dev
Thread-Index: AQHVr19R5YQIlg2NqEC5WtHx1mfv7qezf2rggAAD6ICAAADTMA==
Date:   Tue, 10 Dec 2019 15:53:20 +0000
Message-ID: <MWHPR12MB1358449C677259C848AAB11EF75B0@MWHPR12MB1358.namprd12.prod.outlook.com>
References: <PSXP216MB0438BFEAA0617283A834E11580580@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
 <77aa6c01aefe1ebc4004e87b0bc714f2759f15c4.1575985006.git.lukas@wunner.de>
 <MWHPR12MB1358AEEBD730A4EDA78894E6F75B0@MWHPR12MB1358.namprd12.prod.outlook.com>
 <20191210154649.o3vsqzrtofhvcjrl@wunner.de>
In-Reply-To: <20191210154649.o3vsqzrtofhvcjrl@wunner.de>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: amd.com does not designate
 permitted sender hosts)
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 17cb588d-a833-4fd9-2376-08d77d8914e4
X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Dec 2019 15:53:20.9482
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: qR1RGfD024+kNEbAM00XfTdSQRxl1r791b0wEJLRc6gUCohs/jEcUy9hYZvQyqdrpQYhEgbS6/Cf6BUVDeSg2A==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR12MB1456
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> -----Original Message-----
> From: Lukas Wunner <lukas@wunner.de>
> Sent: Tuesday, December 10, 2019 10:47 AM
> To: Deucher, Alexander <Alexander.Deucher@amd.com>
> Cc: Takashi Iwai <tiwai@suse.de>; Jaroslav Kysela <perex@perex.cz>; Mika
> Westerberg <mika.westerberg@linux.intel.com>; Bjorn Helgaas
> <helgaas@kernel.org>; Nicholas Johnson <nicholas.johnson-
> opensource@outlook.com.au>; alsa-devel@alsa-project.org; linux-
> kernel@vger.kernel.org; linux-pci@vger.kernel.org
> Subject: Re: [PATCH] ALSA: hda/hdmi - Fix duplicate unref of pci_dev
>=20
> On Tue, Dec 10, 2019 at 03:34:27PM +0000, Deucher, Alexander 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.
> >
> > The pci_dev_put() a few lines above should probably be dropped as well.
>=20
> That one looks fine to me.  The refcount is already increased in the call=
er
> get_bound_vga() via pci_get_domain_bus_and_slot() and it's increased
> again in atpx_present() via pci_get_class().  It needs to be decremented =
in
> atpx_present() to avoid leaking a ref.

I'm not following.  This is part of the same loop as the one you removed.  =
All we are doing is checking whether the ATPX method exists or not om the p=
latform.  The pdev may not be the same one as the one in pci_get_domain_bus=
_and_slot().  The APTX method in the APU's ACPI namespace, not the dGPUs.

Alex

>=20
> Thanks,
>=20
> Lukas
>=20
> > > 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