Re: [PATCH v3 3/6] mm: hugetlb: fix a race between freeing and dissolving the page

Mike Kravetz
2021-01-12T01:06:31Z

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 <songmuchun@bytedance.com>
> 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 <mike.kravetz@oracle.com>

--
Mike Kravetz