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

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

On Sun, Jul 26, 2020 at 10:17:08AM -0400, Alan Stern wrote:
> On Sun, Jul 26, 2020 at 10:36:55AM +0200, Greg Kroah-Hartman wrote:
> > 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.
> 
> I suppose Bastien could log an error message at that point.  There isn't 
> much else to do.

It looks like no one does anything with the return value of that
function, so we should just change it to void and stop checking it
entirely :(

greg k-h