Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup

Andrea Parri
2019-05-23T08:30:25Z

Hi Mark,

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)?

Thanks,
Andrea