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SubjectRe: [RFC PATCH 7/8] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros
On Fri, Jan 10, 2020 at 08:42:37PM +0100, Arnd Bergmann wrote:
> On Fri, Jan 10, 2020 at 5:57 PM Will Deacon <will@kernel.org> wrote:
>
> > @@ -128,10 +128,10 @@ do { \
> > #ifndef __smp_load_acquire
> > #define __smp_load_acquire(p) \
> > ({ \
> > - typeof(*p) ___p1 = READ_ONCE(*p); \
> > + __unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p); \
> > compiletime_assert_atomic_type(*p); \
> > __smp_mb(); \
> > - ___p1; \
> > + (typeof(*p))___p1; \
> > })
>
> Doesn't that last (typeof(*p))___p1 mean you put the potential
> 'volatile' back on the assignment after you went through the
> effort of taking it out?

Yes, but that's ok wrt codegen since the local variable isn't volatile,
and I definitely ran into issues with 'const' if I returned the unqualified
type here.

Will

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