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.