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.
