From 91486f61f486662c27ef86dd910f875832e3a5de Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 15 Oct 2015 16:41:51 -0400 Subject: [PATCH] cgroup: make cgroup_destroy_locked() test cgroup_is_populated() cgroup_destroy_locked() currently tests whether any css_sets are associated to reject removal if the cgroup contains tasks. This works because a css_set's refcnt converges with the number of tasks linked to it and thus there's no css_set linked to a cgroup if it doesn't have any live tasks. To help tracking resource usage of zombie tasks, putting the ref of css_set will be separated from disassociating the task from the css_set which means that a cgroup may have css_sets linked to it even when it doesn't have any live tasks. This patch updates cgroup_destroy_locked() so that it tests cgroup_is_populated(), which counts the number of populated css_sets, instead of whether cgrp->cset_links is empty to determine whether the cgroup is populated or not. This ensures that rmdirs won't be incorrectly rejected for cgroups which only contain zombie tasks. Signed-off-by: Tejun Heo --- kernel/cgroup.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ea87340af871..61ee85ded6ae 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4998,16 +4998,15 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) __releases(&cgroup_mutex) __acquires(&cgroup_mutex) { struct cgroup_subsys_state *css; - bool empty; int ssid; lockdep_assert_held(&cgroup_mutex); - /* css_set_rwsem synchronizes access to ->cset_links */ - down_read(&css_set_rwsem); - empty = list_empty(&cgrp->cset_links); - up_read(&css_set_rwsem); - if (!empty) + /* + * Only migration can raise populated from zero and we're already + * holding cgroup_mutex. + */ + if (cgroup_is_populated(cgrp)) return -EBUSY; /*