Re: [PATCH] mm: fix invalid node in alloc_migrate_target()

[Vlastimil Babka]

On 03/25/2016 07:56 AM, Xishi Qiu wrote:
> It is incorrect to use next_node to find a target node, it will
> return MAX_NUMNODES or invalid node. This will lead to crash in
> buddy system allocation.

One possible place of crash is:
alloc_huge_page_node()
    dequeue_huge_page_node()
        [accesses h->hugepage_freelists[nid] with size MAX_NUMANODES]

> Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx>

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to 
handle hugepage")
Cc: stable
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>   mm/page_isolation.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 92c4c36..31555b6 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -289,11 +289,11 @@ struct page *alloc_migrate_target(struct page *page, unsigned long private,
>   	 * now as a simple work-around, we use the next node for destination.
>   	 */
>   	if (PageHuge(page)) {
> -		nodemask_t src = nodemask_of_node(page_to_nid(page));
> -		nodemask_t dst;
> -		nodes_complement(dst, src);
> +		int node = next_online_node(page_to_nid(page));
> +		if (node == MAX_NUMNODES)
> +			node = first_online_node;
>   		return alloc_huge_page_node(page_hstate(compound_head(page)),
> -					    next_node(page_to_nid(page), dst));
> +					    node);
>   	}
>
>   	if (PageHighMem(page))