Re: [PATCH 1/2] arm64: hugetlb: remove the wrong pmd check in find_num_contig()

[Huang Shijie]

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
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;
        }
   ------------------------------------------------------


Thanks
Huang Shijie
> find_num_contig() actually return 0? These are more likely real bugs, so
> no point in setting the huge pte.