[PATCH] mm: page_alloc: validate buddy before check its migratetype.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

Whenever a buddy page is found, page_is_buddy() should be called to
check its validity. Add the missing check during pageblock merge check.

Fixes: 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable pageblocks with others")

Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 mm/page_alloc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bdc8f60ae462..6c6af8658775 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1108,6 +1108,9 @@ static inline void __free_one_page(struct page *page,
 
 		buddy_pfn = __find_buddy_pfn(pfn, order);
 		buddy = page + (buddy_pfn - pfn);
+
+		if (!page_is_buddy(page, buddy, order))
+			goto done_merging;
 		buddy_mt = get_pageblock_migratetype(buddy);
 
 		if (migratetype != buddy_mt
-- 
2.35.1