linux-kernel - Re: [PATCH] mm,hugetlb: take hugetlb_lock before decrementing h->resv_huge

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Message-ID: <Y04J/FxGLAhY+z6O@monkey>
Date:   Mon, 17 Oct 2022 19:05:48 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...nel.org, Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Glen McCready <gkmccready@...a.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>, kernel-team@...a.com
Subject: Re: [PATCH] mm,hugetlb: take hugetlb_lock before decrementing
 h->resv_huge_pages

On 10/17/22 20:25, Rik van Riel wrote:
> The h->*_huge_pages counters are protected by the hugetlb_lock, but
> alloc_huge_page has a corner case where it can decrement the counter
> outside of the lock.
> 
> This could lead to a corrupted value of h->resv_huge_pages, which we
> have observed on our systems.
> 
> Take the hugetlb_lock before decrementing h->resv_huge_pages to avoid
> a potential race.
> 
> Fixes: a88c76954804 ("mm: hugetlb: fix hugepage memory leak caused by wrong reserve count")
> Cc: stable@...nel.org
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Glen McCready <gkmccready@...a.com>
> Cc: Mike Kravetz <mike.kravetz@...cle.com>
> Cc: Muchun Song <songmuchun@...edance.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  mm/hugetlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks Rik!  That case did slip through the cracks.

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

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b586cdd75930..dede0337c07c 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2924,11 +2924,11 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
>  		page = alloc_buddy_huge_page_with_mpol(h, vma, addr);
>  		if (!page)
>  			goto out_uncharge_cgroup;
> +		spin_lock_irq(&hugetlb_lock);
>  		if (!avoid_reserve && vma_has_reserves(vma, gbl_chg)) {
>  			SetHPageRestoreReserve(page);
>  			h->resv_huge_pages--;
>  		}
> -		spin_lock_irq(&hugetlb_lock);
>  		list_add(&page->lru, &h->hugepage_activelist);
>  		set_page_refcounted(page);
>  		/* Fall through */
> -- 
> 2.37.2
> 
>