[PATCH] mm: soft-offline: fix num_poisoned_pages counting on concurrent events

[Naoya Horiguchi]

If multiple soft offline events hit one free page/hugepage concurrently,
soft_offline_page() can handle the free page/hugepage multiple times,
which makes num_poisoned_pages counter increased more than once.
This patch fixes this wrong counting by checking TestSetPageHWPoison for
normal papes and by checking the return value of dequeue_hwpoisoned_huge_page()
for hugepages.

Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx  # v3.14+
---
# This problem might happen before 3.14, but it's rare and non-critical,
# so I want this patch to be backported to stable trees only if the patch
# cleanly applies (i.e. v3.14+).
---
 mm/memory-failure.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git v4.0.orig/mm/memory-failure.c v4.0/mm/memory-failure.c
index 2cc1d578144b..72a5224c8084 100644
--- v4.0.orig/mm/memory-failure.c
+++ v4.0/mm/memory-failure.c
@@ -1721,12 +1721,12 @@ int soft_offline_page(struct page *page, int flags)
 	} else if (ret == 0) { /* for free pages */
 		if (PageHuge(page)) {
 			set_page_hwpoison_huge_page(hpage);
-			dequeue_hwpoisoned_huge_page(hpage);
-			atomic_long_add(1 << compound_order(hpage),
+			if (!dequeue_hwpoisoned_huge_page(hpage))
+				atomic_long_add(1 << compound_order(hpage),
 					&num_poisoned_pages);
 		} else {
-			SetPageHWPoison(page);
-			atomic_long_inc(&num_poisoned_pages);
+			if (!TestSetPageHWPoison(page))
+				atomic_long_inc(&num_poisoned_pages);
 		}
 	}
 	unset_migratetype_isolate(page, MIGRATE_MOVABLE);
-- 
2.1.0
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