Re: [RFC PATCH 7/8] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros

[Will Deacon]

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@xxxxxxxxxx> 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