linux-kernel - Re: [PATCH v3 3/6] mm: hugetlb: fix a race between freeing and dissolving the page

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Date:   Mon, 11 Jan 2021 17:06:16 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Muchun Song <songmuchun@...edance.com>, akpm@...ux-foundation.org
Cc:     n-horiguchi@...jp.nec.com, ak@...ux.intel.com, mhocko@...e.cz,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3 3/6] mm: hugetlb: fix a race between freeing and
 dissolving the page

On 1/10/21 4:40 AM, Muchun Song wrote:
> There is a race condition between __free_huge_page()
> and dissolve_free_huge_page().
> 
> CPU0:                         CPU1:
> 
> // page_count(page) == 1
> put_page(page)
>   __free_huge_page(page)
>                               dissolve_free_huge_page(page)
>                                 spin_lock(&hugetlb_lock)
>                                 // PageHuge(page) && !page_count(page)
>                                 update_and_free_page(page)
>                                 // page is freed to the buddy
>                                 spin_unlock(&hugetlb_lock)
>     spin_lock(&hugetlb_lock)
>     clear_page_huge_active(page)
>     enqueue_huge_page(page)
>     // It is wrong, the page is already freed
>     spin_unlock(&hugetlb_lock)
> 
> The race windows is between put_page() and dissolve_free_huge_page().
> 
> We should make sure that the page is already on the free list
> when it is dissolved.
> 
> Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Cc: stable@...r.kernel.org
> ---
>  mm/hugetlb.c | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)

Thanks,

It is unfortunate that we have to add more huge page state information
to fix this issue.  However, I believe we have explored all other options.

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

-- 
Mike Kravetz