cgroup: implement cgroup_has_tasks() and unexport cgroup_task_count()

cgroup_task_count() read-locks css_set_lock and walks all tasks to
count them and then returns the result.  The only thing all the users
want is determining whether the cgroup is empty or not.  This patch
implements cgroup_has_tasks() which tests whether cgroup->cset_links
is empty, replaces all cgroup_task_count() usages and unexports it.

Note that the test isn't synchronized.  This is the same as before.
The test has always been racy.

This will help planned css_set locking update.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index e97a6e88d036..ae190b0a196a 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -467,7 +467,7 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial)
          * be changed to have empty cpus_allowed or mems_allowed.
          */
         ret = -ENOSPC;
-        if ((cgroup_task_count(cur->css.cgroup) || cur->attach_in_progress)) {
+        if ((cgroup_has_tasks(cur->css.cgroup) || cur->attach_in_progress)) {
                 if (!cpumask_empty(cur->cpus_allowed) &&
                     cpumask_empty(trial->cpus_allowed))
                         goto out;