> > While reading the series, I realized that the following expression: > > > > atomic64_t v; > > ... > > typeof(v.counter) my_val = atomic64_set(&v, VAL); > > > > is a valid expression on some architectures (in part., on architectures > > which #define atomic64_set() to WRITE_ONCE()) but is invalid on others. > > (This is due to the fact that WRITE_ONCE() can be used as an rvalue in > > the above assignment; TBH, I ignore the reasons for having such rvalue?) > > > > IIUC, similar considerations hold for atomic_set(). > > > > The question is whether this is a known/"expected" inconsistency in the > > implementation of atomic64_set() or if this would also need to be fixed > > /addressed (say in a different patchset)? > > In either case, I don't think the intent is that they should be used that way, > and from a quick scan, I can only fine a single relevant instance today: > > [mark@lakrids:~/src/linux]% git grep '\(return\|=\)\s\+atomic\(64\)\?_set' > include/linux/vmw_vmci_defs.h: return atomic_set((atomic_t *)var, (u32)new_val); > include/linux/vmw_vmci_defs.h: return atomic64_set(var, new_val); > > > [mark@lakrids:~/src/linux]% git grep '=\s+atomic_set' | wc -l > 0 > [mark@lakrids:~/src/linux]% git grep '=\s+atomic64_set' | wc -l > 0 > > Any architectures implementing arch_atomic_* will have both of these functions > returning void. Currently that's x86 and arm64, but (time permitting) I intend > to migrate other architectures, so I guess we'll have to fix the above up as > required. > > I think it's best to avoid the construct above. Thank you for the clarification, Mark. I agree with you that it'd be better to avoid such constructs. (FWIW, it is not currently possible to use them in litmus tests for the LKMM...) Thanks, Andrea
