linux-kernel - Re: [PATCH v2 6/6] mm: hugetlb: remove VM_BUG_ON_PAGE from page_huge

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Date:   Wed, 6 Jan 2021 18:16:32 +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 6/6] mm: hugetlb: remove VM_BUG_ON_PAGE from
 page_huge_active

On Wed 06-01-21 16:47:39, Muchun Song wrote:
> The page_huge_active() can be called from scan_movable_pages() which
> do not hold a reference count to the HugeTLB page. So when we call
> page_huge_active() from scan_movable_pages(), the HugeTLB page can
> be freed parallel. Then we will trigger a BUG_ON which is in the
> page_huge_active() when CONFIG_DEBUG_VM is enabled. Just remove the
> VM_BUG_ON_PAGE.
> 
> Fixes: 7e1f049efb86 ("mm: hugetlb: cleanup using paeg_huge_active()")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>

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

The BUG_ON looks like a wrong thing to do regardless of the memory
hotplug use. Which is admittedly ugly as well.

> ---
>  mm/hugetlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 67200dd25b1d..7a24ed28ec4f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1372,7 +1372,6 @@ struct hstate *size_to_hstate(unsigned long size)
>   */
>  bool page_huge_active(struct page *page)
>  {
> -	VM_BUG_ON_PAGE(!PageHuge(page), page);
>  	return PageHead(page) && PagePrivate(&page[1]);
>  }
>  
> -- 
> 2.11.0

-- 
Michal Hocko
SUSE Labs