From 1e0e635be82132167a134b5a9c884e70e61f8373 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@hotmail.com>
Date: Tue, 8 Sep 2015 15:03:13 -0700
Subject: [PATCH] mm/hwpoison: fix PageHWPoison test/set race

There is a race between madvise_hwpoison path and memory_failure:

 CPU0					CPU1

madvise_hwpoison
get_user_pages_fast
PageHWPoison check (false)
					memory_failure
					TestSetPageHWPoison
soft_offline_page
PageHWPoison check (true)
return -EBUSY (without put_page)

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Suggested-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>
---
 mm/memory-failure.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 8ad923a93539..863544d84a09 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1719,6 +1719,8 @@ int soft_offline_page(struct page *page, int flags)
 
 	if (PageHWPoison(page)) {
 		pr_info("soft offline: %#lx page already poisoned\n", pfn);
+		if (flags & MF_COUNT_INCREASED)
+			put_page(page);
 		return -EBUSY;
 	}
 	if (!PageHuge(page) && PageTransHuge(hpage)) {