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Date:   Thu, 27 May 2021 08:58:59 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc:     linux-mm@kvack.org, Mike Kravetz <mike.kravetz@oracle.com>,
        Oscar Salvador <osalvador@suse.de>,
        Muchun Song <songmuchun@bytedance.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] hugetlb: pass head page to remove_hugetlb_page()
Message-ID: <YK9DM03ymX9PG0Zk@dhcp22.suse.cz>
References: <20210526235257.2769473-1-nao.horiguchi@gmail.com>
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On Thu 27-05-21 08:52:57, Naoya Horiguchi wrote:
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> When memory_failure() or soft_offline_page() is called on a tail page of
> some hugetlb page, "BUG: unable to handle page fault" error can be
> triggered.
> 
> remove_hugetlb_page() dereferences page->lru, so it's assumed that the
> page points to a head page, but one of the caller,
> dissolve_free_huge_page(), provides remove_hugetlb_page() with 'page'
> which could be a tail page.  So pass 'head' to it, instead.
> 
> Fixes: 6eb4e88a6d27 ("hugetlb: create remove_hugetlb_page() to separate functionality")
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>

This is really nasty and easy to overlook. I have completely missed that
when reviewing and I do remember checking for head vs page as there is
quite some non trivial handling of both here.

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

Thanks!

> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git v5.13-rc3/mm/hugetlb.c v5.13-rc3_patched/mm/hugetlb.c
> index 95918f410c0f..470f7b5b437e 100644
> --- v5.13-rc3/mm/hugetlb.c
> +++ v5.13-rc3_patched/mm/hugetlb.c
> @@ -1793,7 +1793,7 @@ int dissolve_free_huge_page(struct page *page)
>  			SetPageHWPoison(page);
>  			ClearPageHWPoison(head);
>  		}
> -		remove_hugetlb_page(h, page, false);
> +		remove_hugetlb_page(h, head, false);
>  		h->max_huge_pages--;
>  		spin_unlock_irq(&hugetlb_lock);
>  		update_and_free_page(h, head);
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs