On Thu, 28 Aug 2014, Naoya Horiguchi wrote:
> If __unmap_hugepage_range() tries to unmap the address range over which
> hugepage migration is on the way, we get the wrong page because pte_page()
> doesn't work for migration entries. This patch calls pte_to_swp_entry() and
> migration_entry_to_page() to get the right page for migration entries.
>
> Signed-off-by: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
> Cc: <sta...@vger.kernel.org> # [2.6.36+]
2.6.36+? But this one doesn't affect hwpoisoned.
I admit I've lost track of how far back hugetlb migration goes:
oh, to 2.6.37+, that fits with what you marked on some commits earlier.
But then 2/6 says 3.12+. Help! Please remind me of the sequence of events.
> ---
> mm/hugetlb.c | 9 ++++++++-
> 1 file changed, 8 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 1ed9df6def54..0a4511115ee0 100644
> --- mmotm-2014-08-25-16-52.orig/mm/hugetlb.c
> +++ mmotm-2014-08-25-16-52/mm/hugetlb.c
> @@ -2652,6 +2652,13 @@ void __unmap_hugepage_range(struct mmu_gather *tlb,
> struct vm_area_struct *vma,
> if (huge_pte_none(pte))
> goto unlock;
>
> + if (unlikely(is_hugetlb_entry_migration(pte))) {
> + swp_entry_t entry = pte_to_swp_entry(pte);
> +
> + page = migration_entry_to_page(entry);
> + goto clear;
> + }
> +
This surprises me: are you sure? Obviously you know hugetlb migration
much better than I do: is it done in a significantly different way from
order:0 page migration? In the order:0 case, there is no reference to
the page corresponding to the migration entry placed in a page table,
just the remaining reference held by the task doing the migration. But
here you are jumping to the code which unmaps and frees a present page.
I can see that a fix is necessary, but I would have expected it to
consist of merely changing the "HWPoisoned" comment below to include
migration entries, and changing its test from
if (unlikely(is_hugetlb_entry_hwpoisoned(pte))) {
to
if (unlikely(!pte_present(pte))) {
> /*
> * HWPoisoned hugepage is already unmapped and dropped reference
> */
> @@ -2677,7 +2684,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb,
> struct vm_area_struct *vma,
> */
> set_vma_resv_flags(vma, HPAGE_RESV_UNMAPPED);
> }
> -
> +clear:
> pte = huge_ptep_get_and_clear(mm, address, ptep);
> tlb_remove_tlb_entry(tlb, ptep, address);
> if (huge_pte_dirty(pte))
> --
> 1.9.3
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