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

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Tue, Mar 29, 2016 at 02:25:03PM +0200, Vlastimil Babka wrote:
> 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@huawei.com>
> 
> Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle
> hugepage")
> Cc: stable
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks everyone for finding/fixing the bug!

Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

> >---
> >  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))
> >
> 
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