linux-kernel - Re: [PATCH v2 5/6] mm: hugetlb: fix a race between isolating and freeing page

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Date:   Wed, 6 Jan 2021 18:10:48 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        n-horiguchi@...jp.nec.com, ak@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] mm: hugetlb: fix a race between isolating and
 freeing page

On Wed 06-01-21 16:47:38, 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@...edance.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!
> ---
>  mm/hugetlb.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bf02e81e3953..67200dd25b1d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5587,9 +5587,9 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
>  {
>  	bool ret = true;
>  
> -	VM_BUG_ON_PAGE(!PageHead(page), page);
>  	spin_lock(&hugetlb_lock);
> -	if (!page_huge_active(page) || !get_page_unless_zero(page)) {
> +	if (!PageHeadHuge(page) || !page_huge_active(page) ||
> +	    !get_page_unless_zero(page)) {
>  		ret = false;
>  		goto unlock;
>  	}
> -- 
> 2.11.0

-- 
Michal Hocko
SUSE Labs