cgroup: add cgroup_subsys->css_released()

Add a new cgroup subsys callback css_released().  This is called when
the reference count of the css (cgroup_subsys_state) reaches zero
before RCU scheduling free.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>

2 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 1d5196889048..e717a39f22ea 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -612,6 +612,7 @@ struct cgroup_subsys {
         struct cgroup_subsys_state *(*css_alloc)(struct cgroup_subsys_state *parent_css);
         int (*css_online)(struct cgroup_subsys_state *css);
         void (*css_offline)(struct cgroup_subsys_state *css);
+        void (*css_released)(struct cgroup_subsys_state *css);
         void (*css_free)(struct cgroup_subsys_state *css);
         void (*css_reset)(struct cgroup_subsys_state *css);
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index dffa54041d4a..c8558693102b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4380,6 +4380,8 @@ static void css_release_work_fn(struct work_struct *work)
         if (ss) {
                 /* css release path */
                 cgroup_idr_remove(&ss->css_idr, css->id);
+                if (ss->css_released)
+                        ss->css_released(css);
         } else {
                 /* cgroup release path */
                 cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);