On Thu, May 23, 2019 at 10:30:13AM +0200, Andrea Parri wrote: > Hi Mark, Hi Andrea, > On Wed, May 22, 2019 at 02:22:32PM +0100, Mark Rutland wrote: > > Currently architectures return inconsistent types for atomic64 ops. Some return > > long (e..g. powerpc), some return long long (e.g. arc), and some return s64 > > (e.g. x86). > > (only partially related, but probably worth asking:) > > 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. Thanks, Mark.
