Re: [PATCH] mm/hugetlb: fix gigantic page initialization/allocation

Kirill A. Shutemov
2016-02-02T22:51:03Z

On Tue, Feb 02, 2016 at 02:33:40PM -0800, Mike Kravetz wrote:
> Attempting to preallocate 1G gigantic huge pages at boot time with
> "hugepagesz=1G hugepages=1" on the kernel command line will prevent
> booting with the following:
>
> kernel BUG at mm/hugetlb.c:1218!
>
> When mapcount accounting was reworked, the setting of compound_mapcount_ptr
> in prep_compound_gigantic_page was overlooked. As a result, the validation
> of mapcount in free_huge_page fails.

Oops. Soory for that.

>
> The "BUG_ON" checks in free_huge_page were also changed to "VM_BUG_ON_PAGE"
> to assist with debugging.
>
> Fixes: af5642a8af ("mm: rework mapcount accounting to enable 4k mapping of THPs")
> Suggested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

> ---
> mm/hugetlb.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 12908dc..d7a8024 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1214,8 +1214,8 @@ void free_huge_page(struct page *page)
>
> set_page_private(page, 0);
> page->mapping = NULL;
> - BUG_ON(page_count(page));
> - BUG_ON(page_mapcount(page));
> + VM_BUG_ON_PAGE(page_count(page), page);
> + VM_BUG_ON_PAGE(page_mapcount(page), page);
> restore_reserve = PagePrivate(page);
> ClearPagePrivate(page);
>
> @@ -1286,6 +1286,7 @@ static void prep_compound_gigantic_page(struct page *page, unsigned int order)
> set_page_count(p, 0);
> set_compound_head(p, page);
> }
> + atomic_set(compound_mapcount_ptr(page), -1);
> }
>
> /*
> --
> 2.4.3
>
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--
Kirill A. Shutemov