Re: [PATCH] x86/PAE: Fix pte_clear for the >4GB RAM case

[Andi Kleen]

On Friday 28 April 2006 07:23, Chris Wright wrote:
> * Andi Kleen (ak@xxxxxxx) wrote:
> > > +static inline void pmd_clear(pmd_t *pmd)
> > > +{
> > > +	u32 *tmp = (u32 *)pmd;
> > > +	*tmp = 0;
> > > +	smp_wmb();
> > > +	*(tmp + 1) = 0;
> > > +}
> > 
> > I think that's still wrong - it should be wmb() not smp_wmb because this
> > problem can happen on a UP kernel already.
> 
> I thought the barrier is to keep compiler from reordering not processor.

Yes, but with smp_wmb() it will go away on UP. And even on UP the
CPU is free to speculate.

-Andi
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