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SubjectRe: [PATCH v2] sound/hda: Add NULL check to component match callback function
On Thu, Mar 31, 2022 at 12:25:43PM +0300, Heikki Krogerus wrote:
> 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, "i915") &&
> > > >
> > > > Can NULL dev->driver be really seen? I thought the components are
> > > > added by the drivers, hence they ought to have the driver field set.
> > > > But there can be corner cases I overlooked.
> > > >
> > > >
> > > > thanks,
> > > >
> > > > Takashi
> > >
> > > Hi Takashi,
> > >
> > > When I try using component_add in a different driver (usb4 in my
> > > case), I think dev->driver here is NULL because the i915 drivers do
> > > not have their component master fully bound when this new component is
> > > registered. When I test it, it seems to be causing a crash.
> >
> > Hm, from where component_add*() is called? Basically dev->driver must
> > be already set before the corresponding driver gets bound at
> > __driver_probe_deviec(). So, if the device is added to component from
> > the corresponding driver's probe, dev->driver must be non-NULL.
>
> The code that declares a device as component does not have to be the
> driver of that device.
>
> 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

Why is a USB device being passed to this code that assumes it is looking
for a PCI device with a specific driver name? As I mentioned on the
mei patch, triggering off of a name is really a bad idea, as is assuming
the device type without any assurance it is such a device (there's a
reason we didn't provide device type identification in the driver core,
don't abuse that please...)

thanks,

greg k-h

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