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

[Kirill A. Shutemov]

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@xxxxxxxxxxxxx>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

> ---
>  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