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From:   Muchun Song <songmuchun@bytedance.com>
To:     hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com,
        akpm@linux-foundation.org, guro@fb.com, shakeelb@google.com
Cc:     cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Muchun Song <songmuchun@bytedance.com>
Subject: [PATCH] mm: memcontrol: fix get_active_memcg return value
Date:   Tue, 23 Feb 2021 17:11:01 +0800
Message-Id: <20210223091101.42150-1-songmuchun@bytedance.com>
MIME-Version: 1.0
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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.

Fixes: 37d5985c003d ("mm: kmem: prepare remote memcg charging infra for interrupt contexts")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/memcontrol.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index be6bc5044150..bbe25655f7eb 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;
-- 
2.11.0