On Fri, Nov 04, 2016 at 10:52:17AM +0800, Huang Shijie wrote:
> On Thu, Nov 03, 2016 at 06:16:16PM -0600, Catalin Marinas wrote:
> > On Thu, Nov 03, 2016 at 10:27:38AM +0800, Huang Shijie wrote:
> > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > > index 2e49bd2..4811ef1 100644
> > > --- a/arch/arm64/mm/hugetlbpage.c
> > > +++ b/arch/arm64/mm/hugetlbpage.c
> > > @@ -61,10 +61,6 @@ static int find_num_contig(struct mm_struct *mm,
> > > unsigned long addr,
> > > return 1;
> > > }
> > > pmd = pmd_offset(pud, addr);
> > > - if (!pmd_present(*pmd)) {
> > > - VM_BUG_ON(!pmd_present(*pmd));
> > > - return 1;
> > > - }
> > > if ((pte_t *)pmd == ptep) {
> > > *pgsize = PMD_SIZE;
> > > return CONT_PMDS;
> >
> > BTW, for the !pud_present() and !pgd_present() cases, shouldn't
> > find_num_contig() actually return 0? These are more likely real bugs, so
> > no point in setting the huge pte.
>
> The kernel will not call the find_num_contig() if the PGD/PUD are empty.
> Please see the code in the hugetlb_fault().
>
> ------------------------------------------------------
> ptep = huge_pte_offset(mm, address);
> if (ptep) {
> ...............................
> } else {
> ptep = huge_pte_alloc(mm, address, huge_page_size(h));
> if (!ptep)
> return VM_FAULT_OOM;
> }
> ------------------------------------------------------
Exactly. So what is the reason for returning 1 if !pgd_present()? Would
removing the checks entirely or adding BUG() be a better option?
--
Catalin
