Re: [PATCH v3 3/3] hugetlbfs: add swap entry check in follow_hugetlb_page()

[Rik van Riel <riel@redhat.com>]

On 04/03/2013 02:35 PM, Naoya Horiguchi wrote:
> With applying the previous patch "hugetlbfs: stop setting VM_DONTDUMP in
> initializing vma(VM_HUGETLB)" to reenable hugepage coredump, if a memory
> error happens on a hugepage and the affected processes try to access
> the error hugepage, we hit VM_BUG_ON(atomic_read(&page->_count) <= 0)
> in get_page().
>
> The reason for this bug is that coredump-related code doesn't recognise
> "hugepage hwpoison entry" with which a pmd entry is replaced when a memory
> error occurs on a hugepage.
> In other words, physical address information is stored in different bit layout
> between hugepage hwpoison entry and pmd entry, so follow_hugetlb_page()
> which is called in get_dump_page() returns a wrong page from a given address.
>
> We need to filter out only hwpoison hugepages to have data on healthy
> hugepages in coredump. So this patch makes follow_hugetlb_page() avoid
> trying to get page when a pmd is in swap entry like format.
>
> ChangeLog v3:
>   - add comment about using is_swap_pte()
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Reviewed-by: Michal Hocko <mhocko@suse.cz>
> Acked-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> Cc: stable@vger.kernel.org

Reviewed-by: Rik van Riel <riel@redhat.com>

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