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?