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/[email protected]
Fixes: 37d5985c003d ("mm: kmem: prepare remote memcg charging infra for interrupt contexts")
Signed-off-by: Muchun Song <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Reviewed-by: Roman Gushchin <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 3 insertions, 7 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2db2aeac8a9e..845eec01ef9d 100644
--- 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;