[PATCH v2 7/8] mm: memory-failure: fetch compound head after extra page refcnt is held

[Miaohe Lin]

Page might become thp, huge page or being splited after compound head
is fetched but before page refcnt is bumped. So hpage might be a tail
page leading to VM_BUG_ON_PAGE(PageTail(page)) in PageTransHuge().

Fixes: 415c64c1453a ("mm/memory-failure: split thp earlier in memory error handling")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
---
 mm/memory-failure.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index db4c530944d6..af34fd4669d3 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2186,8 +2186,6 @@ int memory_failure(unsigned long pfn, int flags)
 		goto unlock_mutex;
 	}
 
-	hpage = compound_head(p);
-
 	/*
 	 * We need/can do nothing about count=0 pages.
 	 * 1) it's a free page, and therefore in safe hand:
@@ -2226,6 +2224,7 @@ int memory_failure(unsigned long pfn, int flags)
 		}
 	}
 
+	hpage = compound_head(p);
 	if (PageTransHuge(hpage)) {
 		/*
 		 * The flag must be set after the refcount is bumped
-- 
2.33.0