On 1/10/21 4:40 AM, Muchun Song wrote:

There is a race condition between __free_huge_page()
and dissolve_free_huge_page().

CPU0:                         CPU1:

// page_count(page) == 1
put_page(page)
  __free_huge_page(page)
                              dissolve_free_huge_page(page)
                                spin_lock(&hugetlb_lock)
                                // PageHuge(page) && !page_count(page)
                                update_and_free_page(page)
                                // page is freed to the buddy
                                spin_unlock(&hugetlb_lock)
    spin_lock(&hugetlb_lock)
    clear_page_huge_active(page)
    enqueue_huge_page(page)
    // It is wrong, the page is already freed
    spin_unlock(&hugetlb_lock)

The race windows is between put_page() and dissolve_free_huge_page().

We should make sure that the page is already on the free list
when it is dissolved.

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Signed-off-by: Muchun Song <redacted>
Cc: stable@vger.kernel.org
---
 mm/hugetlb.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

Thanks,

It is unfortunate that we have to add more huge page state information
to fix this issue.  However, I believe we have explored all other options.

Reviewed-by: Mike Kravetz <redacted>

-- 
Mike Kravetz