Re: [PATCH 3/3 v5] USB: Fix device driver race

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Jul 25, 2020 at 03:57:07PM -0400, Alan Stern wrote:
> On Sat, Jul 25, 2020 at 05:24:20PM +0200, Bastien Nocera wrote:
> > On Sat, 2020-07-25 at 10:59 -0400, Alan Stern wrote:
> > <snip>
> > > > +	udev = to_usb_device(dev);
> > > > +	if (usb_device_match_id(udev, new_udriver->id_table) == NULL &&
> > > > +	    (!new_udriver->match || new_udriver->match(udev) != 0))
> > > > +		return 0;
> > > > +
> > > > +	(void)!device_reprobe(dev);
> > > 
> > > What's that '!' doing hiding in there?  It doesn't affect the final 
> > > outcome, but it sure looks weird -- if people notice it at all.
> > 
> > It's how we stop gcc from complaining about the warn_unused_result
> > attribute on device_reprobe()... (void) is enough with clang, but not
> > with gcc.
> 
> Hmmm.  Maybe this is an indication that device_reprobe() doesn't really 
> need to be __must_check.
> 
> Greg, do you know why it's annotated this way?

Because you really should pass up the return value if an error happens
here.  Why do we think it is safe to ignore?

And that "(void)!" is not ok, if the annotation is safe to ignore, then
we need to remove the annotation, don't work around stuff like this
without at the very least, a comment saying why it is ok.

thanks,

greg k-h