On Mon, Jan 04, 2016 at 02:54:20PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 04, 2016 at 02:36:58PM +0100, Peter Zijlstra wrote:
> > On Sun, Jan 03, 2016 at 11:12:44AM +0200, Michael S. Tsirkin wrote:
> > > On Sat, Jan 02, 2016 at 11:24:38AM +0000, Russell King - ARM Linux wrote:
> >
> > > > My only concern is that it gives people an additional handle onto a
> > > > "new" set of barriers - just because they're prefixed with __*
> > > > unfortunately doesn't stop anyone from using it (been there with
> > > > other arch stuff before.)
> > > >
> > > > I wonder whether we should consider making the smp memory barriers
> > > > inline functions, so these __smp_xxx() variants can be undef'd
> > > > afterwards, thereby preventing drivers getting their hands on these
> > > > new macros?
> > >
> > > That'd be tricky to do cleanly since asm-generic depends on
> > > ifndef to add generic variants where needed.
> > >
> > > But it would be possible to add a checkpatch test for this.
> >
> > Wasn't the whole purpose of these things for 'drivers' (namely
> > virtio/xen hypervisor interaction) to use these?
>
> Ah, I see, you add virt_*mb() stuff later on for that use case.
>
> So, assuming everybody does include asm-generic/barrier.h, you could
> simply #undef the __smp version at the end of that, once we've generated
> all the regular primitives from it, no?
Not so simple - that's why I mentioned using inline functions.
The new smp_* _macros_ are:
+#define smp_mb() __smp_mb()
which means if we simply #undef __smp_mb(), smp_mb() then points at
something which is no longer available, and we'll end up with errors
saying that __smp_mb() doesn't exist.
My suggestion was to change:
#ifndef smp_mb
#define smp_mb() __smp_mb()
#endif
to:
#ifndef smp_mb
static inline void smp_mb(void)
{
__smp_mb();
}
#endif
which then means __smp_mb() and friends can be #undef'd afterwards.
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