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[2620:137:e000::1:20]) by mx.google.com with ESMTP id i16-20020a0564020f1000b00461bff75d84si12857608eda.463.2022.11.23.00.33.35; Wed, 23 Nov 2022 00:33:58 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@shopee.com header.s=shopee.com header.b=VmEnvFpr; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=shopee.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236305AbiKWIXv (ORCPT + 99 others); Wed, 23 Nov 2022 03:23:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59294 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236528AbiKWIXp (ORCPT ); Wed, 23 Nov 2022 03:23:45 -0500 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D8C76FBA9F for ; Wed, 23 Nov 2022 00:23:42 -0800 (PST) Received: by mail-pl1-x631.google.com with SMTP id b21so15980545plc.9 for ; Wed, 23 Nov 2022 00:23:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shopee.com; s=shopee.com; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=yo2K84hmvJF9oKmVUE8rVWn5muORVTM6UmA/7exBFUM=; b=VmEnvFprI1mHKVy+07lphANsK+RLSjSH8ZZGVFzeZ0SQCYsAvYfb8tQwV+GaQs4jMd Fhfh4ZC4WvVGyUc3TlX3vl0ZqD5kHFvh/BahqrDF0S8wapyOl1nAVvuhgDLPI6yPojVw LuFg+XX0OxUSgPe8Zq2RVjTjeKnvONyFn0cZRTsjOuIaEo7QUKwVu9hXgIFK9LgJ14Ym u3w+77ooTwpLJsCE55lO0l2qS8XmJ7T/0uHynGwdGMPgSlRm37X1Cfy9zcnQgo28/bZd G3Tcu28J0Id40ep5xIQ7m6QU0kNdS5nxA2SEjOkuuftUUfY2jdqRM7I4BdF79Ew+iIXI HGnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=yo2K84hmvJF9oKmVUE8rVWn5muORVTM6UmA/7exBFUM=; b=sRJaOW7Unc06FRsDLJv3mrHwwdk3AQNfy0PQ/dhJPABmmdCtjhZH7ci2EczFcf/JnA 4auWpxZnYdMafgQ//P8036go3rm+raNCAHERpGf8m6v6v4tcuSoabGhpNOhSWeoZksPf DzOqfCOzFuVJ4iOXpn8nixAwQtdjSD720XGyN7F7UfcH4cDLW8NLwrBRv5dFNCPkerNL OUUzkv7weklnhnKPVENrl51yaolTm3CJyXWk5g41UtzkNAUaVsEy5wGFSEjhoRQDQ6dO 1KBLoNUNpVD4JaVdc1eRMme1JD6r20WhzwS254FhpZDRKrApBufwUot5KtFeJZSkIy53 /z/g== X-Gm-Message-State: ANoB5pkhJPTJ3Oe+dEFZ+Yyn4mUiTUmgoaoy6Ri22EcOdD4UjgRAxQgG 6UfmDHbQK8Cpix7GiBsdbKX2Fg== X-Received: by 2002:a17:90b:2688:b0:218:b9e1:ebef with SMTP id pl8-20020a17090b268800b00218b9e1ebefmr12795766pjb.65.1669191822401; Wed, 23 Nov 2022 00:23:42 -0800 (PST) Received: from ubuntu-haifeng.default.svc.cluster.local ([101.127.248.173]) by smtp.gmail.com with ESMTPSA id h17-20020aa79f51000000b0056c2e497b02sm12454017pfr.173.2022.11.23.00.23.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Nov 2022 00:23:42 -0800 (PST) From: "haifeng.xu" To: longman@redhat.com Cc: lizefan.x@bytedance.com, tj@kernel.org, hannes@cmpxchg.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, "haifeng.xu" Subject: [PATCH] cgroup/cpuset: Optimize update_tasks_nodemask() Date: Wed, 23 Nov 2022 08:21:57 +0000 Message-Id: <20221123082157.71326-1-haifeng.xu@shopee.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1750275131203508174?= X-GMAIL-MSGID: =?utf-8?q?1750275131203508174?= When change the 'cpuset.mems' under some cgroup, system will hung for a long time. From the dmesg, many processes or theads are stuck in fork/exit. The reason is show as follows. thread A: cpuset_write_resmask /* takes cpuset_rwsem */ ... update_tasks_nodemask mpol_rebind_mm /* waits mmap_lock */ thread B: worker_thread ... cpuset_migrate_mm_workfn do_migrate_pages /* takes mmap_lock */ thread C: cgroup_procs_write /* takes cgroup_mutex and cgroup_threadgroup_rwsem */ ... cpuset_can_attach percpu_down_write /* waits cpuset_rwsem */ Once update the nodemasks of cpuset, thread A wakes up thread B to migrate mm. But when thread A iterates through all tasks, including child threads and group leader, it has to wait the mmap_lock which has been take by thread B. Unfortunately, thread C wants to migrate tasks into cgroup at this moment, it must wait thread A to release cpuset_rwsem. If thread B spends much time to migrate mm, the fork/exit which acquire cgroup_threadgroup_rwsem also need to wait for a long time. There is no need to migrate the mm of child threads which is shared with group leader. Just iterate through the group leader only. Signed-off-by: haifeng.xu --- kernel/cgroup/cpuset.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 589827ccda8b..43cbd09546d0 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1968,6 +1968,9 @@ static void update_tasks_nodemask(struct cpuset *cs) cpuset_change_task_nodemask(task, &newmems); + if (!thread_group_leader(task)) + continue; + mm = get_task_mm(task); if (!mm) continue;