[PATCH v2 2/5] mm/hwpoison: fix PageHWPoison test/set race

[Wanpeng Li <wanpeng.li@hotmail.com>]

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)

Suggested-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 mm/memory-failure.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 56b8a71..e0eb7ab 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1704,6 +1704,8 @@ 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)) {
-- 
1.7.1

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