On Wed, Jan 03, 2024 at 10:43:40PM -0800, Dan Williams wrote: > 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. Doubtful whether that's correct. The kernel is compiled with -fno-delete-null-pointer-checks since commit a3ca86aea507 ("Add '-fno-delete-null-pointer-checks' to gcc CFLAGS"). So these NULL pointer checks are generally not optimized away. I've just responded to the discussion you've linked above: https://lore.kernel.org/all/20240104065744.GA6055@xxxxxxxxx/ Thanks, Lukas
