mm: page_alloc: validate buddy before check its migratetype.

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")
Link: https://lore.kernel.org/all/20220330154208.71aca532@gandalf.local.home/
Reported-and-tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index bdc8f60..6c6af86 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1108,6 +1108,9 @@ continue_merging:
 
                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