From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755281AbdGWMSc (ORCPT ); Sun, 23 Jul 2017 08:18:32 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:37094 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751346AbdGWMSa (ORCPT ); Sun, 23 Jul 2017 08:18:30 -0400 Date: Sun, 23 Jul 2017 08:18:26 -0400 From: Tejun Heo To: Waiman Long Cc: Li Zefan , Johannes Weiner , Peter Zijlstra , Ingo Molnar , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, pjt@google.com, luto@amacapital.net, efault@gmx.de, torvalds@linux-foundation.org, guro@fb.com Subject: [PATCH] cgroup: remove unnecessary empty check when enabling threaded mode Message-ID: <20170723121826.GC1498614@devbig577.frc2.facebook.com> References: <1500669293-21792-1-git-send-email-longman@redhat.com> <1500669293-21792-2-git-send-email-longman@redhat.com> <20170722134358.GB3329631@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170722134358.GB3329631@devbig577.frc2.facebook.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org cgroup_enable_threaded() checks that the cgroup doesn't have any tasks or children and fails the operation if so. This test is unnecessary because the first part is already checked by cgroup_can_be_thread_root() and the latter is unnecessary. The latter actually cause a behavioral oddity. Please consider the following hierarchy. All cgroups are domains. A / \ B C \ D If B is made threaded, C and D becomes invalid domains. Due to the no children restriction, threaded mode can't be enabled on C. For C and D, the only thing the user can do is removal. There is no reason for this restriction. Remove it. Signed-off-by: Tejun Heo Cc: Waiman Long --- Hello, So, the only thing inconsistent there was the extra restriction when enabling threaded mode when all the necessary conditions are already checked by when verifying the parent's domain. Thanks. Documentation/cgroup-v2.txt | 5 +++-- kernel/cgroup/cgroup.c | 7 ------- 2 files changed, 3 insertions(+), 9 deletions(-) --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt @@ -274,8 +274,9 @@ thread mode, the following conditions mu - As the cgroup will join the parent's resource domain. The parent must either be a valid (threaded) domain or a threaded cgroup. -- The cgroup must be empty. No enabled controllers, child cgroups or - processes. +- When the parent is an unthreaded domain, it must not have any domain + controllers enabled or populated domain children. The root is + exempt from this requirement. Topology-wise, a cgroup can be in an invalid state. Please consider the following toplogy:: --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3147,13 +3147,6 @@ static int cgroup_enable_threaded(struct return -EOPNOTSUPP; /* - * Allow enabling thread mode only on empty cgroups to avoid - * implicit migrations and recursive operations. - */ - if (cgroup_has_tasks(cgrp) || css_has_online_children(&cgrp->self)) - return -EBUSY; - - /* * The following shouldn't cause actual migrations and should * always succeed. */