Re: [PATCH v2] sound/hda: Add NULL check to component match callback function

Takashi Iwai
2022-03-31T09:29:16Z

On Thu, 31 Mar 2022 11:25:43 +0200,
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

OK, that's what I wanted to know. It'd be helpful if it's more
clearly mentioned in the commit log.

BTW, the same problem must be seen in MEI drivers, too.

Takashi