Re: [PATCH v5 8/9] PCI: Define scoped based management functions

[Dan Williams]

Lukas Wunner wrote:
> On Wed, Dec 20, 2023 at 04:17:35PM -0800, Ira Weiny wrote:
> > --- a/include/linux/pci.h
> > +++ b/include/linux/pci.h
> > @@ -1170,6 +1170,7 @@ int pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge);
> >  u8 pci_common_swizzle(struct pci_dev *dev, u8 *pinp);
> >  struct pci_dev *pci_dev_get(struct pci_dev *dev);
> >  void pci_dev_put(struct pci_dev *dev);
> > +DEFINE_FREE(pci_dev_put, struct pci_dev *, if (_T) pci_dev_put(_T))
> 
> pci_dev_put() already performs a NULL pointer check internally.
> Why duplicate it here?

Greg asked the same for the introduction of __free(kvfree), and Peter
clarified:

http://lore.kernel.org/r/20230814161731.GN776869@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Essentially, that check is more for build-time than runtime because when
the macro is expanded the compiler can notice scenarios where @pdev is
set to NULL (likely by no_free_ptr()) and skip the call to pci_dev_put()
altogether. pci_dev_put() also happens to be out-of-line, so saving a
call when @pdev is NULL a small win in that respect as well.