From 918a8c2c4ea4fab8b7855b8da48bbaf0a733ebb0 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Sun, 23 Jul 2017 08:18:26 -0400 Subject: [PATCH] cgroup: remove unnecessary empty check when enabling threaded mode 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. Acked-by: Waiman Long Signed-off-by: Tejun Heo --- Documentation/cgroup-v2.txt | 5 +++-- kernel/cgroup/cgroup.c | 7 ------- 2 files changed, 3 insertions(+), 9 deletions(-) diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt index cb9ea281ab72..dec5afdaa36d 100644 --- a/Documentation/cgroup-v2.txt +++ b/Documentation/cgroup-v2.txt @@ -274,8 +274,9 @@ thread mode, the following conditions must be met. - 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:: diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index e9a377dc5bdb..e0a558c4d358 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -3146,13 +3146,6 @@ static int cgroup_enable_threaded(struct cgroup *cgrp) !cgroup_can_be_thread_root(dom_cgrp)) 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.