Re: [PATCH 01/18] mm, hugetlb: protect reserved pages whensoftofflining requests the pages

[Hillf Danton]

On Mon, Jul 29, 2013 at 1:31 PM, Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> wrote:
> alloc_huge_page_node() use dequeue_huge_page_node() without
> any validation check, so it can steal reserved page unconditionally.

Well, why is it illegal to use reserved page here?

> To fix it, check the number of free_huge_page in alloc_huge_page_node().
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6782b41..d971233 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -935,10 +935,11 @@ static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
>   */
>  struct page *alloc_huge_page_node(struct hstate *h, int nid)
>  {
> -       struct page *page;
> +       struct page *page = NULL;
>
>         spin_lock(&hugetlb_lock);
> -       page = dequeue_huge_page_node(h, nid);
> +       if (h->free_huge_pages - h->resv_huge_pages > 0)
> +               page = dequeue_huge_page_node(h, nid);
>         spin_unlock(&hugetlb_lock);
>
>         if (!page)
> --
> 1.7.9.5
>
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