[PATCH 01/10] cgroup: separate out cgroup_has_tasks()

[Tejun Heo]

Separate out cgroup_has_tasks() test from
cgroup_subtree_control_write().  This will be used by the following
changes.

This patch doesn't cause any behavior changes.

Signed-off-by: Tejun Heo <t...@kernel.org>
---
 kernel/cgroup/cgroup.c | 49 +++++++++++++++++++++++++++----------------------
 1 file changed, 27 insertions(+), 22 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8d4e85eae42c..dcd120af4084 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -581,6 +581,30 @@ static bool css_set_populated(struct css_set *cset)
        return !list_empty(&cset->tasks) || !list_empty(&cset->mg_tasks);
 }
 
+static bool cgroup_has_tasks(struct cgroup *cgrp)
+{
+       struct cgrp_cset_link *link;
+       bool has_tasks = false;
+
+       /*
+        * Because namespaces pin csets too, @cgrp->cset_links
+        * might not be empty even when @cgrp is empty.  Walk and
+        * verify each cset.
+        */
+       spin_lock_irq(&css_set_lock);
+
+       list_for_each_entry(link, &cgrp->cset_links, cset_link) {
+               if (css_set_populated(link->cset)) {
+                       has_tasks = true;
+                       break;
+               }
+       }
+
+       spin_unlock_irq(&css_set_lock);
+
+       return has_tasks;
+}
+
 /**
  * cgroup_update_populated - updated populated count of a cgroup
  * @cgrp: the target cgroup
@@ -2886,28 +2910,9 @@ static ssize_t cgroup_subtree_control_write(struct 
kernfs_open_file *of,
         * Except for the root, subtree_control must be zero for a cgroup
         * with tasks so that child cgroups don't compete against tasks.
         */
-       if (enable && cgroup_parent(cgrp)) {
-               struct cgrp_cset_link *link;
-
-               /*
-                * Because namespaces pin csets too, @cgrp->cset_links
-                * might not be empty even when @cgrp is empty.  Walk and
-                * verify each cset.
-                */
-               spin_lock_irq(&css_set_lock);
-
-               ret = 0;
-               list_for_each_entry(link, &cgrp->cset_links, cset_link) {
-                       if (css_set_populated(link->cset)) {
-                               ret = -EBUSY;
-                               break;
-                       }
-               }
-
-               spin_unlock_irq(&css_set_lock);
-
-               if (ret)
-                       goto out_unlock;
+       if (enable && cgroup_parent(cgrp) && cgroup_has_tasks(cgrp)) {
+               ret = -EBUSY;
+               goto out_unlock;
        }
 
        /* save and update control masks and prepare csses */
-- 
2.13.0