On Wed 13-01-21 13:22:06, 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.

Please describe the effect of the bug.
"
As a result __free_huge_page would corrupt page(s) already in the buddy
allocator.
"

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Mike Kravetz <redacted>
Cc: stable@vger.kernel.org

[...]

I believe we have agreed to retry for this temporary state.

+
 		/*
 		 * Move PageHWPoison flag from head page to the raw error page,
 		 * which makes any subpages rather than the error page reusable.
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs