From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A51D2C282DD for ; Thu, 9 Jan 2020 15:06:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8276B2067D for ; Thu, 9 Jan 2020 15:06:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732057AbgAIPGI (ORCPT ); Thu, 9 Jan 2020 10:06:08 -0500 Received: from mx2.suse.de ([195.135.220.15]:53916 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728346AbgAIPGI (ORCPT ); Thu, 9 Jan 2020 10:06:08 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 7E64DAE34; Thu, 9 Jan 2020 15:06:06 +0000 (UTC) From: =?UTF-8?q?Michal=20Koutn=C3=BD?= To: cgroups@vger.kernel.org Cc: Tejun Heo , Li Zefan , Johannes Weiner , linux-kernel@vger.kernel.org, Christian Brauner Subject: [PATCH] cgroup: Prevent double killing of css when enabling threaded cgroup Date: Thu, 9 Jan 2020 16:05:59 +0100 Message-Id: <20200109150559.14457-1-mkoutny@suse.com> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20191219022716.o7vxxia6o67tyfmf@wittgenstein> References: <20191219022716.o7vxxia6o67tyfmf@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The test_cgcore_no_internal_process_constraint_on_threads selftest when running with subsystem controlling noise triggers two warnings: > [ 597.443115] WARNING: CPU: 1 PID: 28167 at kernel/cgroup/cgroup.c:3131 cgroup_apply_control_enable+0xe0/0x3f0 > [ 597.443413] WARNING: CPU: 1 PID: 28167 at kernel/cgroup/cgroup.c:3177 cgroup_apply_control_disable+0xa6/0x160 Both stem from a call to cgroup_type_write. The first warning was also triggered by syzkaller. When we're switching cgroup to threaded mode shortly after a subsystem was disabled on it, we can see the respective subsystem css dying there. The warning in cgroup_apply_control_enable is harmless in this case since we're not adding new subsys anyway. The warning in cgroup_apply_control_disable indicates an attempt to kill css of recently disabled subsystem repeatedly. The commit prevents these situations by making cgroup_type_write wait for all dying csses to go away before re-applying subtree controls. When at it, the locations of WARN_ON_ONCE calls are moved so that warning is triggered only when we are about to misuse the dying css. Reported-by: syzbot+5493b2a54d31d6aea629@syzkaller.appspotmail.com Reported-by: Christian Brauner Signed-off-by: Michal Koutný --- kernel/cgroup/cgroup.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 53098c1d45e2..97cc713079df 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3054,8 +3054,6 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp) for_each_subsys(ss, ssid) { struct cgroup_subsys_state *css = cgroup_css(dsct, ss); - WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt)); - if (!(cgroup_ss_mask(dsct) & (1 << ss->id))) continue; @@ -3065,6 +3063,8 @@ static int cgroup_apply_control_enable(struct cgroup *cgrp) return PTR_ERR(css); } + WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); + if (css_visible(css)) { ret = css_populate_dir(css); if (ret) @@ -3100,11 +3100,11 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp) for_each_subsys(ss, ssid) { struct cgroup_subsys_state *css = cgroup_css(dsct, ss); - WARN_ON_ONCE(css && percpu_ref_is_dying(&css->refcnt)); - if (!css) continue; + WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); + if (css->parent && !(cgroup_ss_mask(dsct) & (1 << ss->id))) { kill_css(css); @@ -3391,7 +3391,8 @@ static ssize_t cgroup_type_write(struct kernfs_open_file *of, char *buf, if (strcmp(strstrip(buf), "threaded")) return -EINVAL; - cgrp = cgroup_kn_lock_live(of->kn, false); + /* drain dying csses before we re-apply (threaded) subtree control */ + cgrp = cgroup_kn_lock_live(of->kn, true); if (!cgrp) return -ENOENT; -- 2.24.1