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

[Mike Kravetz]

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@xxxxxxxxxxxxx>
> ---
>  mm/hugetlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Thanks!

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

-- 
Mike Kravetz