On Mon, Dec 16, 2013 at 04:40:04PM +0000, Will Deacon wrote:
> > --- a/arch/ia64/include/asm/barrier.h
> > +++ b/arch/ia64/include/asm/barrier.h
> > @@ -45,14 +45,37 @@
> > # define smp_rmb() rmb()
> > # define smp_wmb() wmb()
> > # define smp_read_barrier_depends() read_barrier_depends()
> > +
> > #else
> > +
> > # define smp_mb() barrier()
> > # define smp_rmb() barrier()
> > # define smp_wmb() barrier()
> > # define smp_read_barrier_depends() do { } while(0)
> > +
> > #endif
> >
> > /*
> > + * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no
> > + * need for asm trickery!
> > + */
> > +
> > +#define smp_store_release(p, v) \
> > +do { \
> > + compiletime_assert_atomic_type(*p); \
> > + barrier(); \
> > + ACCESS_ONCE(*p) = (v); \
> > +} while (0)
> > +
> > +#define smp_load_acquire(p) \
> > +({ \
> > + typeof(*p) ___p1 = ACCESS_ONCE(*p); \
> > + compiletime_assert_atomic_type(*p); \
> > + barrier(); \
> > + ___p1; \
> > +})
> > +
> > +/*
> > * XXX check on this ---I suspect what Linus really wants here is
> > * acquire vs release semantics but we can't discuss this stuff with
> > * Linus just yet. Grrr...
>
> I guess you can remove this comment now?
I suppose so, but I'll leave that up to the ia64 people.. The comment
relates to set_mb() and that hasn't actually changed.
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -298,6 +298,11 @@ void ftrace_likely_update(struct ftrace_
> > # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
> > #endif
> >
> > +/* Is this type a native word size -- useful for atomic operations */
> > +#ifndef __native_word
> > +# define __native_word(t) (sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long))
> > +#endif
> > +
> > /* Compile time object size, -1 for unknown */
> > #ifndef __compiletime_object_size
> > # define __compiletime_object_size(obj) -1
> > @@ -337,6 +342,10 @@ void ftrace_likely_update(struct ftrace_
> > #define compiletime_assert(condition, msg) \
> > _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> >
> > +#define compiletime_assert_atomic_type(t) \
> > + compiletime_assert(__native_word(t), \
> > + "Need native word sized stores/loads for atomicity.")
> > +
>
> At least for ARM, it's not so much the type that cause issues with
> atomicity, but whether or not its naturally aligned, which we don't check
> here...
Yeah I know, but you actually need to do weird things to get unaligned
pointers. Also, I'm fairly sure ARM will fail a 20 byte store-release so
the size check isn't entirely pointless.
I suppose if anybody really cares you can have some DEBUG symbol
dependent alignment check in there, but it will generate extra code.
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