[Devel] [PATCH rh7 2/2] mm: Warn on zero uncharge in memcg_uncharge_kmem()

[Kirill Tkhai]

page_counter_uncharge() must return 0 only on the final uncharge of kmem,
but memcg_uncharge_kmem(0) may bring to use-after-free after it.
WARN to find callers, who charge for 0.

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 mm/memcontrol.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c3586e8e27ca..010d580f39cc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3508,6 +3508,9 @@ void memcg_uncharge_kmem(struct mem_cgroup *memcg,
 {
 	u64 kmem;
 
+	if (WARN_ON_ONCE(!nr_pages))
+		return;
+
 	kmem = page_counter_uncharge(&memcg->kmem, nr_pages);
 
 	page_counter_uncharge(&memcg->memory, nr_pages);