Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 31 Mar 2022 08:33:03 -0700
From:   Benson Leung <bleung@google.com>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Won Chung <wonchung@google.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Benson Leung <bleung@chromium.org>,
        Prashant Malani <pmalani@chromium.org>,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] sound/hda: Add NULL check to component match callback
 function
Message-ID: <YkXJr2KhSzHJHxRF@google.com>
References: <20220330211913.2068108-1-wonchung@google.com>
 <s5hzgl6eg48.wl-tiwai@suse.de>
 <CAOvb9yiO_n48JPZ3f0+y-fQ_YoOmuWF5c692Jt5_SKbxdA4yAw@mail.gmail.com>
 <s5hr16ieb8o.wl-tiwai@suse.de>
 <YkVzl4NEzwDAp/Zq@kuha.fi.intel.com>
 <s5hmth6eaiz.wl-tiwai@suse.de>
 <YkV1rsq1SeTNd8Ud@kuha.fi.intel.com>
 <s5hk0cae9pw.wl-tiwai@suse.de>
 <s5h7d8adzdl.wl-tiwai@suse.de>
 <s5hzgl6ciho.wl-tiwai@suse.de>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="qZ1ZF7vfmh9I4Bit"
Content-Disposition: inline
In-Reply-To: <s5hzgl6ciho.wl-tiwai@suse.de>
Precedence: bulk


--qZ1ZF7vfmh9I4Bit
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Hi Takashi,

On Thu, Mar 31, 2022 at 04:19:15PM +0200, Takashi Iwai wrote:
> On Thu, 31 Mar 2022 15:29:10 +0200,
> Takashi Iwai wrote:
> >=20
> > On Thu, 31 Mar 2022 11:45:47 +0200,
> > Takashi Iwai wrote:
> > >=20
> > > On Thu, 31 Mar 2022 11:34:38 +0200,
> > > Heikki Krogerus wrote:
> > > >=20
> > > > On Thu, Mar 31, 2022 at 11:28:20AM +0200, Takashi Iwai wrote:
> > > > > On Thu, 31 Mar 2022 11:25:43 +0200,
> > > > > Heikki Krogerus wrote:
> > > > > >=20
> > > > > > On Thu, Mar 31, 2022 at 11:12:55AM +0200, Takashi Iwai wrote:
> > > > > > > > > > -     if (!strcmp(dev->driver->name, "i915") &&
> > > > > > > > > > +     if (dev->driver && !strcmp(dev->driver->name, "i9=
15") &&
> > > > > > > > >
> > > > > > > > > Can NULL dev->driver be really seen?  I thought the compo=
nents are
> > > > > > > > > added by the drivers, hence they ought to have the driver=
 field set.
> > > > > > > > > But there can be corner cases I overlooked.
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > thanks,
> > > > > > > > >
> > > > > > > > > Takashi
> > > > > > > >=20
> > > > > > > > Hi Takashi,
> > > > > > > >=20
> > > > > > > > When I try using component_add in a different driver (usb4 =
in my
> > > > > > > > case), I think dev->driver here is NULL because the i915 dr=
ivers do
> > > > > > > > not have their component master fully bound when this new c=
omponent is
> > > > > > > > registered. When I test it, it seems to be causing a crash.
> > > > > > >=20
> > > > > > > Hm, from where component_add*() is called?  Basically dev->dr=
iver must
> > > > > > > be already set before the corresponding driver gets bound at
> > > > > > > __driver_probe_deviec().  So, if the device is added to compo=
nent from
> > > > > > > the corresponding driver's probe, dev->driver must be non-NUL=
L.
> > > > > >=20
> > > > > > The code that declares a device as component does not have to b=
e the
> > > > > > driver of that device.
> > > > > >=20
> > > > > > In our case the components are USB ports, and they are devices =
that
> > > > > > are actually never bind to any drivers: drivers/usb/core/port.c
> > > > >=20
> > > > > OK, that's what I wanted to know.  It'd be helpful if it's more
> > > > > clearly mentioned in the commit log.
> > > >=20
> > > > Agree.
> > > >=20
> > > > > BTW, the same problem must be seen in MEI drivers, too.
> > > >=20
> > > > Wasn't there a patch for those too? I lost track...
> > >=20
> > > I don't know, I just checked the latest Linus tree.
> > >=20
> > > And, looking at the HD-audio code, I still wonder how NULL dev->driver
> > > can reach there.  Is there any PCI device that is added to component
> > > without binding to a driver?  We have dev_is_pci() check at the
> > > beginning, so non-PCI devices should bail out there...
> >=20
> > Further reading on, I'm really confused.  How data=3DNULL can be passed
> > to this function?  The data argument is the value passed from the
> > component_match_add_typed() call in HD-audio driver, hence it must be
> > always the snd_hdac_bus object.
> >=20
> > And, I guess the i915 string check can be omitted completely, at
> > least, for HD-audio driver.  It already have a check of the parent of
> > the device and that should be enough.
>=20
> That said, something like below (supposing data NULL check being
> superfluous), instead.
>=20
>=20
> Takashi
>=20
> --- a/sound/hda/hdac_i915.c
> +++ b/sound/hda/hdac_i915.c
> @@ -102,18 +102,13 @@ static int i915_component_master_match(struct devic=
e *dev, int subcomponent,
>  	struct pci_dev *hdac_pci, *i915_pci;
>  	struct hdac_bus *bus =3D data;
> =20
> -	if (!dev_is_pci(dev))
> +	if (subcomponent !=3D I915_COMPONENT_AUDIO || !dev_is_pci(dev))
>  		return 0;
> =20

If I recall this bug correctly, it's not the usb port perse that is falling
through this !dev_is_pci(dev) check, it's actually the usb4-port in a new
proposed patch by Heikki and Mika to extend the usb type-c component to
encompass the usb4 specific pieces too. Is it possible usb4 ports are consi=
dered
pci devices, and that's how we got into this situation?

Also, a little more background information: This crash happens because in
our kernel configs, we config'd the usb4 driver as =3Dy (built in) instead =
of
=3Dm module, which meant that the usb4 port's driver was adding a component
likely much earlier than hdac_i915.

Thanks,
Benson

>  	hdac_pci =3D to_pci_dev(bus->dev);
>  	i915_pci =3D to_pci_dev(dev);
> =20
> -	if (!strcmp(dev->driver->name, "i915") &&
> -	    subcomponent =3D=3D I915_COMPONENT_AUDIO &&
> -	    connectivity_check(i915_pci, hdac_pci))
> -		return 1;
> -
> -	return 0;
> +	return connectivity_check(i915_pci, hdac_pci);
>  }
> =20
>  /* check whether intel graphics is present */
>=20

--=20
Benson Leung
Staff Software Engineer
Chrome OS Kernel
Google Inc.
bleung@google.com
Chromium OS Project
bleung@chromium.org

--qZ1ZF7vfmh9I4Bit
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iHUEABYKAB0WIQQCtZK6p/AktxXfkOlzbaomhzOwwgUCYkXJrwAKCRBzbaomhzOw
wpDWAP4u9qZ1yLO4Vtblx/ZmitMRfRXqpqZ1xkZTr3wjUV3NXgD8DQBQxF/RIz2w
F727wkBDJO7uAqp8N1cVAtvwIUCSSg4=
=Nqgb
-----END PGP SIGNATURE-----

--qZ1ZF7vfmh9I4Bit--