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Tue, 20 Apr 2021 23:27:06 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.255]) by smtp.gmail.com with ESMTPSA id w10sm815408pfq.184.2021.04.20.23.27.02 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Apr 2021 23:27:06 -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, fam.zheng@bytedance.com, Muchun Song Subject: [PATCH] mm: memcontrol: fix root_mem_cgroup charging Date: Wed, 21 Apr 2021 14:26:44 +0800 Message-Id: <20210421062644.68331-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 X-Rspamd-Queue-Id: 2B26240002C3 X-Stat-Signature: 3enhhnj19jkpd9y9ac9cwisjhqwbweuf X-Rspamd-Server: rspam02 Received-SPF: none (bytedance.com>: No applicable sender policy available) receiver=imf10; identity=mailfrom; envelope-from=""; helo=mail-pg1-f170.google.com; client-ip=209.85.215.170 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1618986420-440505 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 below scenario can cause the page counters of the root_mem_cgroup to be out of balance. CPU0: CPU1: objcg = get_obj_cgroup_from_current() obj_cgroup_charge_pages(objcg) memcg_reparent_objcgs() // reparent to root_mem_cgroup WRITE_ONCE(iter->memcg, parent) // memcg == root_mem_cgroup memcg = get_mem_cgroup_from_objcg(objcg) // do not charge to the root_mem_cgroup try_charge(memcg) obj_cgroup_uncharge_pages(objcg) memcg = get_mem_cgroup_from_objcg(objcg) // uncharge from the root_mem_cgroup page_counter_uncharge(&memcg->memory) This can cause the page counter to be less than the actual value, Although we do not display the value (mem_cgroup_usage) so there shouldn't be any actual problem, but there is a WARN_ON_ONCE in the page_counter_cancel(). Who knows if it will trigger? So it is better to fix it. Signed-off-by: Muchun Song --- mm/memcontrol.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 1e68a9992b01..81b54bd9b9e0 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2686,8 +2686,8 @@ void mem_cgroup_handle_over_high(void) css_put(&memcg->css); } -static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, - unsigned int nr_pages) +static int __try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, + unsigned int nr_pages) { unsigned int batch = max(MEMCG_CHARGE_BATCH, nr_pages); int nr_retries = MAX_RECLAIM_RETRIES; @@ -2699,8 +2699,6 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, bool drained = false; unsigned long pflags; - if (mem_cgroup_is_root(memcg)) - return 0; retry: if (consume_stock(memcg, nr_pages)) return 0; @@ -2880,6 +2878,15 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, return 0; } +static inline int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, + unsigned int nr_pages) +{ + if (mem_cgroup_is_root(memcg)) + return 0; + + return __try_charge(memcg, gfp_mask, nr_pages); +} + #if defined(CONFIG_MEMCG_KMEM) || defined(CONFIG_MMU) static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) { @@ -3125,7 +3132,7 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp, memcg = get_mem_cgroup_from_objcg(objcg); - ret = try_charge(memcg, gfp, nr_pages); + ret = __try_charge(memcg, gfp, nr_pages); if (ret) goto out;