cgroups: make root_list contains active hierarchies only

Don't link rootnode to the root list, so root_list contains active
hierarchies only as the comment indicates.  And rename for_each_root() to
for_each_active_root().

Also remove redundant check in cgroup_kill_sb().

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 12 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f55af3daffc2..fd572d057691 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -84,7 +84,7 @@ struct cgroupfs_root {
         /* Tracks how many cgroups are currently defined in hierarchy.*/
         int number_of_cgroups;
 
-        /* A list running through the mounted hierarchies */
+        /* A list running through the active hierarchies */
         struct list_head root_list;
 
         /* Hierarchy-specific flags */
@@ -148,8 +148,8 @@ static int notify_on_release(const struct cgroup *cgrp)
 #define for_each_subsys(_root, _ss) \
 list_for_each_entry(_ss, &_root->subsys_list, sibling)
 
-/* for_each_root() allows you to iterate across the active hierarchies */
-#define for_each_root(_root) \
+/* for_each_active_root() allows you to iterate across the active hierarchies */
+#define for_each_active_root(_root) \
 list_for_each_entry(_root, &roots, root_list)
 
 /* the list of cgroups eligible for automatic release. Protected by
@@ -1111,10 +1111,9 @@ static void cgroup_kill_sb(struct super_block *sb) {
         }
         write_unlock(&css_set_lock);
 
-        if (!list_empty(&root->root_list)) {
-                list_del(&root->root_list);
-                root_count--;
-        }
+        list_del(&root->root_list);
+        root_count--;
+
         mutex_unlock(&cgroup_mutex);
 
         kfree(root);
@@ -2559,7 +2558,6 @@ int __init cgroup_init_early(void)
         INIT_HLIST_NODE(&init_css_set.hlist);
         css_set_count = 1;
         init_cgroup_root(&rootnode);
-        list_add(&rootnode.root_list, &roots);
         root_count = 1;
         init_task.cgroups = &init_css_set;
 
@@ -2666,15 +2664,12 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
 
         mutex_lock(&cgroup_mutex);
 
-        for_each_root(root) {
+        for_each_active_root(root) {
                 struct cgroup_subsys *ss;
                 struct cgroup *cgrp;
                 int subsys_id;
                 int count = 0;
 
-                /* Skip this hierarchy if it has no active subsystems */
-                if (!root->actual_subsys_bits)
-                        continue;
                 seq_printf(m, "%lu:", root->subsys_bits);
                 for_each_subsys(root, ss)
                         seq_printf(m, "%s%s", count++ ? "," : "", ss->name);