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-rw-r--r--kernel/cgroup.c29
1 files changed, 25 insertions, 4 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7f5221..0d4ee1ea5c31 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3446,9 +3446,28 @@ 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) && !list_empty(&cgrp->cset_links)) {
- ret = -EBUSY;
- goto out_unlock;
+ 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;
}
/* save and update control masks and prepare csses */
@@ -3899,7 +3918,9 @@ void cgroup_file_notify(struct cgroup_file *cfile)
* cgroup_task_count - count the number of tasks in a cgroup.
* @cgrp: the cgroup in question
*
- * Return the number of tasks in the cgroup.
+ * Return the number of tasks in the cgroup. The returned number can be
+ * higher than the actual number of tasks due to css_set references from
+ * namespace roots and temporary usages.
*/
static int cgroup_task_count(const struct cgroup *cgrp)
{