mm/memory-failure: fix race with compound page split/merge

get_hwpoison_page() must recheck relation between head and tail pages.

n-horiguchi said: without this recheck, the race causes kernel to pin an
irrelevant page, and finally makes kernel crash for refcount mismatch.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 78f5f2641b91..ca5acee53b7a 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -888,7 +888,15 @@ int get_hwpoison_page(struct page *page)
                 }
         }
 
-        return get_page_unless_zero(head);
+        if (get_page_unless_zero(head)) {
+                if (head == compound_head(page))
+                        return 1;
+
+                pr_info("MCE: %#lx cannot catch tail\n", page_to_pfn(page));
+                put_page(head);
+        }
+
+        return 0;
 }
 EXPORT_SYMBOL_GPL(get_hwpoison_page);