Re: [PATCH 5/6] mm: hugetlb: fix a race between isolating and freeing page

Mike Kravetz
2021-01-05T01:44:24Z

On 1/3/21 10:58 PM, Muchun Song wrote:
> 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.
>
> Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/hugetlb.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)

Thanks!

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

--
Mike Kravetz