On Tue, 12 May 2015 09:20:35 +0000 Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote:
> Currently the initial value of order in dissolve_free_huge_page is 64 or 32,
> which leads to the following warning in static checker:
>
> mm/hugetlb.c:1203 dissolve_free_huge_pages()
> warn: potential right shift more than type allows '9,18,64'
>
> This is a potential risk of infinite loop, because 1 << order (== 0) is used
> in for-loop like this:
>
> for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order)
> ...
>
> So this patch simply avoids the risk by initializing with UINT_MAX.
>
> ..
>
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1188,7 +1188,7 @@ static void dissolve_free_huge_page(struct page *page)
> */
> void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
> {
> - unsigned int order = 8 * sizeof(void *);
> + unsigned int order = UINT_MAX;
> unsigned long pfn;
> struct hstate *h;
>
> @@ -1200,6 +1200,7 @@ void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
> if (order > huge_page_order(h))
> order = huge_page_order(h);
> VM_BUG_ON(!IS_ALIGNED(start_pfn, 1 << order));
> + VM_BUG_ON(order == UINT_MAX);
> for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order)
> dissolve_free_huge_page(pfn_to_page(pfn));
Do we need to calculate this each time? Can it be done in
hugetlb_init_hstates(), save the result in a global?
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