[PATCH] mm/memcg: avoid page count check for zone device

[jglisse@redhat.com]

From: JA(C)rA'me Glisse <jglisse@redhat.com>

Fix for 4.14, zone device page always have an elevated refcount
of one and thus page count sanity check in uncharge_page() is
inappropriate for them.

Signed-off-by: JA(C)rA'me Glisse <jglisse@redhat.com>
Reported-by: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
---
 mm/memcontrol.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 15af3da5af02..d51d3e1f49c9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5648,7 +5648,8 @@ static void uncharge_batch(const struct uncharge_gather *ug)
 static void uncharge_page(struct page *page, struct uncharge_gather *ug)
 {
 	VM_BUG_ON_PAGE(PageLRU(page), page);
-	VM_BUG_ON_PAGE(!PageHWPoison(page) && page_count(page), page);
+	VM_BUG_ON_PAGE(!PageHWPoison(page) && !is_zone_device_page(page) &&
+			page_count(page), page);
 
 	if (!page->mem_cgroup)
 		return;
-- 
2.13.5

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