On Thu, 31 Oct 2024, Yazen Ghannam wrote: > On Thu, Oct 31, 2024 at 12:08:20PM +0200, Ilpo Järvinen wrote: > > On Thu, 31 Oct 2024, Zhuo, Qiuxu wrote: > > > > > > From: Yazen Ghannam <yazen.ghannam@xxxxxxx> > > > > [...] > > > > +struct pci_dev *amd_node_get_root(u16 node) { > > > > + struct pci_dev *df_f0 __free(pci_dev_put) = NULL; > > > > > > NULL pointer initialization is not necessary. > > > > It is, because __free() is used... > > > > > > + struct pci_dev *root; > > > > + u16 cntl_off; > > > > + u8 bus; > > > > + > > > > + if (!boot_cpu_has(X86_FEATURE_ZEN)) > > > > + return NULL; > > > > ...This would try to free() whatever garbage df_f0 holds... > > > > > > + /* > > > > + * D18F0xXXX [Config Address Control] (DF::CfgAddressCntl) > > > > + * Bits [7:0] (SecBusNum) holds the bus number of the root device for > > > > + * this Data Fabric instance. The segment, device, and function will be > > > > 0. > > > > + */ > > > > + df_f0 = amd_node_get_func(node, 0); > > > > ...However, the recommended practice when using __free() is this (as > > documented in include/linux/cleanup.h): > > > > * Given that the "__free(...) = NULL" pattern for variables defined at > > * the top of the function poses this potential interdependency problem > > * the recommendation is to always define and assign variables in one > > * statement and not group variable definitions at the top of the > > * function when __free() is used. > > > > I know the outcome will look undesirable to some, me included, but > > there's little that can be done to that because there's no other way for > > the compiler to infer the order. > > > > That being said, strictly speaking it isn't causing issue in this function > > as is but it's still a bad pattern to initialize to = NULL because in > > other instances it will cause problems. So better to steer away from the > > pattern entirely rather than depend on reviewers noticing the a cleaup > > ordering problem gets introduced by some later change to the function. > > > > I originally read that in the context of using a guard(). But really we > should do like this in any case, correct? > > struct pci_dev *df_f0 __free(pci_dev_put) = amd_node_get_func(node, 0); Yes, that is the recommendation. It says "always" so not only the cases where guard() or other __free()s are used. Of course this only applies to use of __free(), other variables should still be declared in the usual place and not spread around. -- i.