2 files changed, 17 insertions, 5 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 76dadd77a120..1737db0c63fe 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -77,6 +77,7 @@ struct cgroup_subsys_state {
 
 /* bits in struct cgroup_subsys_state flags field */
 enum {
+        CSS_NO_REF      = (1 << 0), /* no reference counting for this css */
         CSS_ONLINE      = (1 << 1), /* between ->css_online() and ->css_offline() */
 };
 
@@ -88,7 +89,8 @@ enum {
  */
 static inline void css_get(struct cgroup_subsys_state *css)
 {
-        percpu_ref_get(&css->refcnt);
+        if (!(css->flags & CSS_NO_REF))
+                percpu_ref_get(&css->refcnt);
 }
 
 /**
@@ -103,7 +105,9 @@ static inline void css_get(struct cgroup_subsys_state *css)
  */
 static inline bool css_tryget_online(struct cgroup_subsys_state *css)
 {
-        return percpu_ref_tryget_live(&css->refcnt);
+        if (!(css->flags & CSS_NO_REF))
+                return percpu_ref_tryget_live(&css->refcnt);
+        return true;
 }
 
 /**
@@ -114,7 +118,8 @@ static inline bool css_tryget_online(struct cgroup_subsys_state *css)
  */
 static inline void css_put(struct cgroup_subsys_state *css)
 {
-        percpu_ref_put(&css->refcnt);
+        if (!(css->flags & CSS_NO_REF))
+                percpu_ref_put(&css->refcnt);
 }
 
 /* bits in struct cgroup flags field */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c01e8e8dfad0..0343d7ee6d62 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4593,11 +4593,17 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
         /* We don't handle early failures gracefully */
         BUG_ON(IS_ERR(css));
         init_and_link_css(css, ss, &cgrp_dfl_root.cgrp);
+
+        /*
+         * Root csses are never destroyed and we can't initialize
+         * percpu_ref during early init.  Disable refcnting.
+         */
+        css->flags |= CSS_NO_REF;
+
         if (early) {
                 /* allocation can't be done safely during early init */
                 css->id = 1;
         } else {
-                BUG_ON(percpu_ref_init(&css->refcnt, css_release));
                 css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
                 BUG_ON(css->id < 0);
         }
@@ -4636,6 +4642,8 @@ int __init cgroup_init_early(void)
         int i;
 
         init_cgroup_root(&cgrp_dfl_root, &opts);
+        cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
+
         RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
 
         for_each_subsys(ss, i) {
@@ -4684,7 +4692,6 @@ int __init cgroup_init(void)
                         struct cgroup_subsys_state *css =
                                 init_css_set.subsys[ss->id];
 
-                        BUG_ON(percpu_ref_init(&css->refcnt, css_release));
                         css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2,
                                                    GFP_KERNEL);
                         BUG_ON(css->id < 0);