[patch] mm: memcontrol: use page lists for uncharge batching fix - hugetlb page->lru

[patch] mm: memcontrol: use page lists for uncharge batching fix - hugetlb page->lru

[Johannes Weiner]

Naoya-san reports that page->lru of hugetlb pages gets corrupted when
they hit the uncharge path from put_page().

Add a preliminary check for whether the page is even a valid memcg
page before messing with it's ->lru list.

Reported-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b2f924359e79..0eb1eaa2f1ff 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6606,9 +6606,16 @@ static void uncharge_list(struct list_head *page_list)
  */
 void mem_cgroup_uncharge(struct page *page)
 {
+	struct page_cgroup *pc;
+
 	if (mem_cgroup_disabled())
 		return;
 
+	/* Don't touch page->lru of any random page, pre-check: */
+	pc = lookup_page_cgroup(page);
+	if (!PageCgroupUsed(pc))
+		return;
+
 	INIT_LIST_HEAD(&page->lru);
 	uncharge_list(&page->lru);
 }
-- 
2.0.0

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