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    Subject[PATCH 4.4 32/38] mm: hugetlb: fix a race between isolating and freeing page
    Date
    From: Muchun Song <songmuchun@bytedance.com>

    commit 0eb2df2b5629794020f75e94655e1994af63f0d4 upstream.

    There is a race between isolate_huge_page() and __free_huge_page().

    CPU0: CPU1:

    if (PageHuge(page))
    put_page(page)
    __free_huge_page(page)
    spin_lock(&hugetlb_lock)
    update_and_free_page(page)
    set_compound_page_dtor(page,
    NULL_COMPOUND_DTOR)
    spin_unlock(&hugetlb_lock)
    isolate_huge_page(page)
    // trigger BUG_ON
    VM_BUG_ON_PAGE(!PageHead(page), page)
    spin_lock(&hugetlb_lock)
    page_huge_active(page)
    // trigger BUG_ON
    VM_BUG_ON_PAGE(!PageHuge(page), page)
    spin_unlock(&hugetlb_lock)

    When we isolate a HugeTLB page on CPU0. Meanwhile, we free it to the
    buddy allocator on CPU1. Then, we can trigger a BUG_ON on CPU0, because
    it is already freed to the buddy allocator.

    Link: https://lkml.kernel.org/r/20210115124942.46403-5-songmuchun@bytedance.com
    Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
    Acked-by: Michal Hocko <mhocko@suse.com>
    Reviewed-by: Oscar Salvador <osalvador@suse.de>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: Yang Shi <shy828301@gmail.com>
    Cc: <stable@vger.kernel.org>
    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/hugetlb.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/mm/hugetlb.c
    +++ b/mm/hugetlb.c
    @@ -4544,9 +4544,9 @@ bool isolate_huge_page(struct page *page
    {
    bool ret = true;

    - VM_BUG_ON_PAGE(!PageHead(page), page);
    spin_lock(&hugetlb_lock);
    - if (!page_huge_active(page) || !get_page_unless_zero(page)) {
    + if (!PageHeadHuge(page) || !page_huge_active(page) ||
    + !get_page_unless_zero(page)) {
    ret = false;
    goto unlock;
    }

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