Re: [PATCH 1/2] mm: avoid spurious 'bad pmd' warning messages

[Ross Zwisler]

On Wed, May 17, 2017 at 10:33:58AM -0700, Dave Hansen wrote:
> On 05/17/2017 10:16 AM, Ross Zwisler wrote:
> > @@ -3061,7 +3061,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
> >  	 * through an atomic read in C, which is what pmd_trans_unstable()
> >  	 * provides.
> >  	 */
> > -	if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> > +	if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> >  		return VM_FAULT_NOPAGE;
> 
> I'm worried we are very unlikely to get this right in the future.  It's
> totally not obvious what the ordering requirement is here.
> 
> Could we move pmd_devmap() and pmd_trans_unstable() into a helper that
> gets the ordering right and also spells out the ordering requirement?

Sure, I'll fix this for v2.

Thanks for the review.