cgroup: build list of all cgroups under a given cgroupfs_root

Build a list of all cgroups anchored at cgroupfs_root->allcg_list and
going through cgroup->allcg_node.  The list is protected by
cgroup_mutex and will be used to improve cgroup file handling.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>

2 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 5a85b3415c1b..ad2a14680b7f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -191,6 +191,8 @@ struct cgroup {
          */
         struct list_head css_sets;
 
+        struct list_head allcg_node;    /* cgroupfs_root->allcg_list */
+
         /*
          * Linked list running through all cgroups that can
          * potentially be reaped by the release agent. Protected by
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8f72853131d3..db4319c030d0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -127,6 +127,9 @@ struct cgroupfs_root {
         /* A list running through the active hierarchies */
         struct list_head root_list;
 
+        /* All cgroups on this root, cgroup_mutex protected */
+        struct list_head allcg_list;
+
         /* Hierarchy-specific flags */
         unsigned long flags;
 
@@ -1350,11 +1353,14 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
 static void init_cgroup_root(struct cgroupfs_root *root)
 {
         struct cgroup *cgrp = &root->top_cgroup;
+
         INIT_LIST_HEAD(&root->subsys_list);
         INIT_LIST_HEAD(&root->root_list);
+        INIT_LIST_HEAD(&root->allcg_list);
         root->number_of_cgroups = 1;
         cgrp->root = root;
         cgrp->top_cgroup = cgrp;
+        list_add_tail(&cgrp->allcg_node, &root->allcg_list);
         init_cgroup_housekeeping(cgrp);
 }
 
@@ -3790,6 +3796,8 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         /* The cgroup directory was pre-locked for us */
         BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
 
+        list_add_tail(&cgrp->allcg_node, &root->allcg_list);
+
         err = cgroup_populate_dir(cgrp);
         /* If err < 0, we have a half-filled directory - oh well ;) */
 
@@ -3998,6 +4006,8 @@ again:
         list_del_init(&cgrp->sibling);
         cgroup_unlock_hierarchy(cgrp->root);
 
+        list_del_init(&cgrp->allcg_node);
+
         d = dget(cgrp->dentry);
 
         cgroup_d_remove_dir(d);