[PATCH 3.11 094/121] mm/memory-failure.c: move refcount only in !MF_COUNT_INCREASED

[Luis Henriques]

3.11.10.5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>

commit 8d547ff4ac5927245e0833ac18528f939da0ee0e upstream.

mce-test detected a test failure when injecting error to a thp tail
page.  This is because we take page refcount of the tail page in
madvise_hwpoison() while the fix in commit a3e0f9e47d5e
("mm/memory-failure.c: transfer page count from head page to tail page
after split thp") assumes that we always take refcount on the head page.

When a real memory error happens we take refcount on the head page where
memory_failure() is called without MF_COUNT_INCREASED set, so it seems
to me that testing memory error on thp tail page using madvise makes
little sense.

This patch cancels moving refcount in !MF_COUNT_INCREASED for valid
testing.

[akpm at linux-foundation.org: s/&&/&/]
Signed-off-by: Naoya Horiguchi <n-horiguchi at ah.jp.nec.com>
Cc: Andi Kleen <andi at firstfloor.org>
Cc: Wanpeng Li <liwanp at linux.vnet.ibm.com>
Cc: Chen Gong <gong.chen at linux.intel.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 mm/memory-failure.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index bfee485..a869081 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -943,8 +943,10 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
 			 * to it. Similarly, page lock is shifted.
 			 */
 			if (hpage != p) {
-				put_page(hpage);
-				get_page(p);
+				if (!(flags & MF_COUNT_INCREASED)) {
+					put_page(hpage);
+					get_page(p);
+				}
 				lock_page(p);
 				unlock_page(hpage);
 				*hpagep = p;
-- 
1.9.0