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Groups > linux.kernel > #1515261
| From | Catalin Marinas <catalin.marinas@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 1/2] arm64: hugetlb: remove the wrong pmd check in find_num_contig() |
| Date | 2016-11-04 16:50 +0100 |
| Message-ID | <szOUF-3Dx-1@gated-at.bofh.it> (permalink) |
| References | <szAoG-2F9-11@gated-at.bofh.it> <szAoG-2F9-13@gated-at.bofh.it> <szAoG-2F9-9@gated-at.bofh.it> <szOUF-3Dx-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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
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Re: [PATCH 1/2] arm64: hugetlb: remove the wrong pmd check in find_num_contig() Catalin Marinas <catalin.marinas@arm.com> - 2016-11-04 01:20 +0100 Re: [PATCH 1/2] arm64: hugetlb: remove the wrong pmd check in find_num_contig() Catalin Marinas <catalin.marinas@arm.com> - 2016-11-04 16:50 +0100
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