mm: memcontrol: fix get_active_memcg return value

We use a global percpu int_active_memcg variable to store the remote memcg
when we are in the interrupt context.  But get_active_memcg always return
the current->active_memcg or root_mem_cgroup.  The remote memcg (set in
the interrupt context) is ignored.  This is not what we want.  So fix it.

Link: https://lkml.kernel.org/r/20210223091101.42150-1-songmuchun@bytedance.com
Fixes: 37d5985c003d ("mm: kmem: prepare remote memcg charging infra for interrupt contexts")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2db2aeac8a9e26a6723518372b402695825ec9ea..845eec01ef9d0dbe1392ee71ad0ec1e758fe85eb 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1061,13 +1061,9 @@ static __always_inline struct mem_cgroup *get_active_memcg(void)
 
        rcu_read_lock();
        memcg = active_memcg();
-       if (memcg) {
-               /* current->active_memcg must hold a ref. */
-               if (WARN_ON_ONCE(!css_tryget(&memcg->css)))
-                       memcg = root_mem_cgroup;
-               else
-                       memcg = current->active_memcg;
-       }
+       /* remote memcg must hold a ref. */
+       if (memcg && WARN_ON_ONCE(!css_tryget(&memcg->css)))
+               memcg = root_mem_cgroup;
        rcu_read_unlock();
 
        return memcg;