Re: [PATCH] usb: ohci: remove unreachable platform_driver_unregister() call

[Alan Stern <stern@rowland.harvard.edu>]

On Mon, Mar 22, 2021 at 07:58:50AM +0300, Dan Carpenter wrote:
> On Fri, Mar 19, 2021 at 10:24:43PM -0400, Alan Stern wrote:
> > On Sat, Mar 20, 2021 at 09:31:51AM +0800, Jay Fang wrote:
> > > From: Zihao Tang <tangzihao1@hisilicon.com>
> > > 
> > > Fix the following smatch warnings:
> > > 
> > > drivers/usb/host/ohci-hcd.c:1318 ohci_hcd_mod_init() warn:
> > > ignoring unreachable code.
> > > 
> > > platform_driver_register(&TMIO_OHCI_DRIVER) is the last
> > > platform_driver_register() call in ohci_hcd_mod_init(), so if it
> > > failed, there's no need to unregister it, but just goto error_tmio.
> > > 
> > > So remove the unreachable platform_driver_unregister(&TMIO_OHCI_DRIVER).
> > > No functionality change.
> > 
> > Doesn't the compiler realize that the call is unreachable, and 
> > therefore avoid generating any object for it?
> >
> 
> This is a static checker warning.  For example, Heart Bleed bug was an
> ignored unreachable code static checker warning.
> 
> > It's true that the function call is, strictly speaking, unnecessary.  
> > However, it provides a pleasing symmetry and it acts as a guide in the 
> > unlikely event that anyone wants to add another platform-specific 
> > driver in the future.
> 
> Hopefully future programmers can figure out basic stuff like that.
> 
> This code doesn't trigger a Smatch warning on my .config because the
> Smatch check doesn't warn if the previous line was an #endif.  On the
> other hand, the ifdefs are also why I forwarded the email when I saw the
> warning from kbuild.  Normally kbuild is better at picking the person
> to blame but because this is a .config thing that confused it.  Anyway,
> I glanced at the warning and thought it looked suspicious enough to
> warrant a further look.
> 
> When I first wrote the Smatch unreachable code warning there were a
> handful of places which used that style of code:
> 
> 	return 0;
> 
> 	unreachable_release();
> err_release:
> 	release_something();
> 
> I just left those as-is because it was obvious to me that it was done
> intentionally.  However, it seems that other people have removed all of
> those behind my back so I can't find an example of this now except for
> in ohci_hcd_mod_init().
> 
> Anyway, I would have put a special case to silence these false positives
> but it wasn't common practice in 2014 and no one does it these days.

Well, I guess it would be okay to convert the code to a comment.  Just 
so long as it isn't removed entirely.

Alan Stern