[PATCH 4.7 20/41] mm: memcontrol: fix memcg id ref counter on swap charge move

[Greg Kroah-Hartman]

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vladimir Davydov <vdavy...@virtuozzo.com>

commit 615d66c37c755c49ce022c9e5ac0875d27d2603d upstream.

Since commit 73f576c04b94 ("mm: memcontrol: fix cgroup creation failure
after many small jobs") swap entries do not pin memcg->css.refcnt
directly.  Instead, they pin memcg->id.ref.  So we should adjust the
reference counters accordingly when moving swap charges between cgroups.

Fixes: 73f576c04b941 ("mm: memcontrol: fix cgroup creation failure after many 
small jobs")
Link: 
http://lkml.kernel.org/r/9ce297c64954a42dc90b543bc76106c4a94f07e8.1470219853.git.vdavy...@virtuozzo.com
Signed-off-by: Vladimir Davydov <vdavy...@virtuozzo.com>
Acked-by: Michal Hocko <mho...@suse.com>
Acked-by: Johannes Weiner <han...@cmpxchg.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 mm/memcontrol.c |   24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4083,9 +4083,9 @@ static struct cftype mem_cgroup_legacy_f
 
 static DEFINE_IDR(mem_cgroup_idr);
 
-static void mem_cgroup_id_get(struct mem_cgroup *memcg)
+static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
-       atomic_inc(&memcg->id.ref);
+       atomic_add(n, &memcg->id.ref);
 }
 
 static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
@@ -4106,9 +4106,9 @@ static struct mem_cgroup *mem_cgroup_id_
        return memcg;
 }
 
-static void mem_cgroup_id_put(struct mem_cgroup *memcg)
+static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
-       if (atomic_dec_and_test(&memcg->id.ref)) {
+       if (atomic_sub_and_test(n, &memcg->id.ref)) {
                idr_remove(&mem_cgroup_idr, memcg->id.id);
                memcg->id.id = 0;
 
@@ -4117,6 +4117,16 @@ static void mem_cgroup_id_put(struct mem
        }
 }
 
+static inline void mem_cgroup_id_get(struct mem_cgroup *memcg)
+{
+       mem_cgroup_id_get_many(memcg, 1);
+}
+
+static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
+{
+       mem_cgroup_id_put_many(memcg, 1);
+}
+
 /**
  * mem_cgroup_from_id - look up a memcg from a memcg id
  * @id: the memcg id to look up
@@ -4754,6 +4764,8 @@ static void __mem_cgroup_clear_mc(void)
                if (!mem_cgroup_is_root(mc.from))
                        page_counter_uncharge(&mc.from->memsw, mc.moved_swap);
 
+               mem_cgroup_id_put_many(mc.from, mc.moved_swap);
+
                /*
                 * we charged both to->memory and to->memsw, so we
                 * should uncharge to->memory.
@@ -4761,9 +4773,9 @@ static void __mem_cgroup_clear_mc(void)
                if (!mem_cgroup_is_root(mc.to))
                        page_counter_uncharge(&mc.to->memory, mc.moved_swap);
 
-               css_put_many(&mc.from->css, mc.moved_swap);
+               mem_cgroup_id_get_many(mc.to, mc.moved_swap);
+               css_put_many(&mc.to->css, mc.moved_swap);
 
-               /* we've already done css_get(mc.to) */
                mc.moved_swap = 0;
        }
        memcg_oom_recover(from);