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Fri, 19 Mar 2021 09:38:42 -0700 (PDT) Received: from localhost.bytedance.net ([139.177.225.231]) by smtp.gmail.com with ESMTPSA id z25sm5860239pfn.37.2021.03.19.09.38.38 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 19 Mar 2021 09:38:42 -0700 (PDT) From: Muchun Song To: guro@fb.com, hannes@cmpxchg.org, mhocko@kernel.org, akpm@linux-foundation.org, shakeelb@google.com, vdavydov.dev@gmail.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, Muchun Song Subject: [PATCH v5 1/7] mm: memcontrol: slab: fix obtain a reference to a freeing memcg Date: Sat, 20 Mar 2021 00:38:14 +0800 Message-Id: <20210319163821.20704-2-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) In-Reply-To: <20210319163821.20704-1-songmuchun@bytedance.com> References: <20210319163821.20704-1-songmuchun@bytedance.com> MIME-Version: 1.0 X-Stat-Signature: d3oegy9wo3jsuaahmex6haazpcruox5i X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: AB5BBA0009CA Received-SPF: none (bytedance.com>: No applicable sender policy available) receiver=imf23; identity=mailfrom; envelope-from=""; helo=mail-pg1-f175.google.com; client-ip=209.85.215.175 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616171923-424152 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The rcu_read_lock/unlock only can guarantee that the memcg will not be freed, but it cannot guarantee the success of css_get (which is in the refill_stock when cached memcg changed) to memcg. rcu_read_lock() memcg =3D obj_cgroup_memcg(old) __memcg_kmem_uncharge(memcg) refill_stock(memcg) if (stock->cached !=3D memcg) // css_get can change the ref counter from 0 back to 1. css_get(&memcg->css) rcu_read_unlock() This fix is very like the commit: eefbfa7fd678 ("mm: memcg/slab: fix use after free in obj_cgroup_charge"= ) Fix this by holding a reference to the memcg which is passed to the __memcg_kmem_uncharge() before calling __memcg_kmem_uncharge(). Fixes: 3de7d4f25a74 ("mm: memcg/slab: optimize objcg stock draining") Signed-off-by: Muchun Song --- mm/memcontrol.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 845eec01ef9d..2cda76ff0629 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3181,9 +3181,17 @@ static void drain_obj_stock(struct memcg_stock_pcp= *stock) unsigned int nr_bytes =3D stock->nr_bytes & (PAGE_SIZE - 1); =20 if (nr_pages) { + struct mem_cgroup *memcg; + rcu_read_lock(); - __memcg_kmem_uncharge(obj_cgroup_memcg(old), nr_pages); +retry: + memcg =3D obj_cgroup_memcg(old); + if (unlikely(!css_tryget(&memcg->css))) + goto retry; rcu_read_unlock(); + + __memcg_kmem_uncharge(memcg, nr_pages); + css_put(&memcg->css); } =20 /* --=20 2.11.0