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    Subject[PATCH 3.4 04/12] mm/memory-failure.c: recheck PageHuge() after hugetlb page migrate successfully
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jianguo Wu <wujianguo@huawei.com>

    commit a49ecbcd7b0d5a1cda7d60e03df402dd0ef76ac8 upstream.

    After a successful hugetlb page migration by soft offline, the source
    page will either be freed into hugepage_freelists or buddy(over-commit
    page). If page is in buddy, page_hstate(page) will be NULL. It will
    hit a NULL pointer dereference in dequeue_hwpoisoned_huge_page().

    BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
    IP: [<ffffffff81163761>] dequeue_hwpoisoned_huge_page+0x131/0x1d0
    PGD c23762067 PUD c24be2067 PMD 0
    Oops: 0000 [#1] SMP

    So check PageHuge(page) after call migrate_pages() successfully.

    [wujg: backport to 3.4:
    - adjust context
    - s/num_poisoned_pages/mce_bad_pages/]

    Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
    Tested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


    ---
    mm/memory-failure.c | 16 ++++++++++++----
    1 file changed, 12 insertions(+), 4 deletions(-)

    --- a/mm/memory-failure.c
    +++ b/mm/memory-failure.c
    @@ -1447,10 +1447,18 @@ static int soft_offline_huge_page(struct
    return ret;
    }
    done:
    - if (!PageHWPoison(hpage))
    - atomic_long_add(1 << compound_trans_order(hpage), &mce_bad_pages);
    - set_page_hwpoison_huge_page(hpage);
    - dequeue_hwpoisoned_huge_page(hpage);
    + /* overcommit hugetlb page will be freed to buddy */
    + if (PageHuge(hpage)) {
    + if (!PageHWPoison(hpage))
    + atomic_long_add(1 << compound_trans_order(hpage),
    + &mce_bad_pages);
    + set_page_hwpoison_huge_page(hpage);
    + dequeue_hwpoisoned_huge_page(hpage);
    + } else {
    + SetPageHWPoison(page);
    + atomic_long_inc(&mce_bad_pages);
    + }
    +
    /* keep elevated page count for bad page */
    return ret;
    }



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