Re: [PATCH v4] USB: Fix device driver race

[Bastien Nocera <hadess@hadess.net>]

On Fri, 2020-07-24 at 13:32 +0300, Andy Shevchenko wrote:
> On Fri, Jul 24, 2020 at 12:03 PM Bastien Nocera <hadess@hadess.net>
> wrote:
> > When a new device with a specialised device driver is plugged in,
> > the
> > new driver will be modprobe()'d but the driver core will attach the
> > "generic" driver to the device.
> > 
> > After that, nothing will trigger a reprobe when the modprobe()'d
> > device
> > driver has finished initialising, as the device has the "generic"
> > driver attached to it.
> > 
> > Trigger a reprobe ourselves when new specialised drivers get
> > registered.
> 
> ...
> 
> > +static int __usb_bus_reprobe_drivers(struct device *dev, void
> > *data)
> > +{
> > +       struct usb_device_driver *new_udriver = data;
> > +       struct usb_device_driver *udriver;
> > +       struct usb_device *udev;
> > +
> > +       if (!dev->driver)
> > +               return 0;
> > +
> > +       udriver = to_usb_device_driver(dev->driver);
> > +       if (udriver != &usb_generic_driver)
> > +               return 0;
> 
> What about
> 
> static bool is_dev_usb_generic_driver(dev)
> {
>       struct usb_device_driver *udd = dev->driver ?
> to_usb_device_driver(dev->driver) : NULL;
> 
>       return udd == &usb_generic_driver;
> }
> 
>   if (!is_dev_usb_generic_driver)
>     return 0;
> 
> ?

Great, done locally.

> > +       udev = to_usb_device(dev);
> > +       if (usb_device_match_id(udev, new_udriver->id_table) !=
> > NULL ||
> > +           (new_udriver->match && new_udriver->match(udev) == 0))
> > +               device_reprobe(dev);
> > +
> > +       return 0;
> 
> What about
> 
>      udev = to_usb_device(dev);
>      if (usb_device_match_id(udev, new_udriver->id_table) == NULL)
>        return 0;
> ?
> 
>   if (new_udriver->match && new_udriver->match(udev) == 0))
>                device_reprobe(dev);
>     return 0;

That's not the same conditionals. If there's ->match but no matching
->id_table, you're not going to reprobe, when we'd want to.

> > +}
> 
> ...
> 
> > +               /* Check whether any device could be better served
> > with
> > +                * this new driver
> > +                */
> 
> Comment style?

Fixed locally.

> ...
> 
> > +               if (new_udriver->match || new_udriver->id_table)
> 
> But match check is incorporated in the loop function.

It's ->match || ->id_table, not simply ->match. Drivers can have
either, and we need to reprobe if either of those are present (and
we're also checking in the function to avoid calling a NULL pointer ;)

> > +                       bus_for_each_dev(&usb_bus_type, NULL,
> > new_udriver,
> > +                                        __usb_bus_reprobe_drivers)
> > ;