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>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f55af3d..fd572d0 100644 (file)
--- 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);