On Thu, 28 Aug 2014, Naoya Horiguchi wrote:
> There is a race condition between hugepage migration and change_protection(),
> where hugetlb_change_protection() doesn't care about migration entries and
> wrongly overwrites them. That causes unexpected results like kernel crash.
>
> This patch adds is_hugetlb_entry_(migration|hwpoisoned) check in this
> function to do proper actions.
>
> ChangeLog v3:
> - handle migration entry correctly (instead of just skipping)
>
> Signed-off-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> Cc: <sta...@vger.kernel.org> # [2.6.36+]
2.6.36+? For the hwpoisoned part of it, I suppose.
Then you'd better mentioned the hwpoisoned case in the comment above.
> ---
> mm/hugetlb.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git mmotm-2014-08-25-16-52.orig/mm/hugetlb.c
> mmotm-2014-08-25-16-52/mm/hugetlb.c
> index 2aafe073cb06..1ed9df6def54 100644
> --- mmotm-2014-08-25-16-52.orig/mm/hugetlb.c
> +++ mmotm-2014-08-25-16-52/mm/hugetlb.c
> @@ -3362,7 +3362,26 @@ unsigned long hugetlb_change_protection(struct
> vm_area_struct *vma,
> spin_unlock(ptl);
> continue;
> }
> - if (!huge_pte_none(huge_ptep_get(ptep))) {
> + pte = huge_ptep_get(ptep);
> + if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
> + spin_unlock(ptl);
> + continue;
> + }
> + if (unlikely(is_hugetlb_entry_migration(pte))) {
> + swp_entry_t entry = pte_to_swp_entry(pte);
> +
> + if (is_write_migration_entry(entry)) {
> + pte_t newpte;
> +
> + make_migration_entry_read(&entry);
> + newpte = swp_entry_to_pte(entry);
> + set_pte_at(mm, address, ptep, newpte);
set_huge_pte_at.
(As usual, I can't bear to see these is_hugetlb_entry_hwpoisoned and
is_hugetlb_entry_migration examples go past without bleating about
wanting to streamline them a little; but agreed last time to leave
that to some later cleanup once all the stable backports are stable.)
> + pages++;
> + }
> + spin_unlock(ptl);
> + continue;
> + }
> + if (!huge_pte_none(pte)) {
> pte = huge_ptep_get_and_clear(mm, address, ptep);
> pte = pte_mkhuge(huge_pte_modify(pte, newprot));
> pte = arch_make_huge_pte(pte, vma, NULL, 0);
> --
> 1.9.3
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