Re: [PATCH] mm,hugetlb: take hugetlb_lock before decrementing h->resv_huge_pages

[Mike Kravetz <mike.kravetz@oracle.com>]

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@kernel.org
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Glen McCready <gkmccready@meta.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Muchun Song <songmuchun@bytedance.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Rik van Riel <riel@surriel.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@oracle.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
> 
>