cgroup: remove for_each_root_subsys()

After the previous patch which introduced for_each_css(),
for_each_root_subsys() only has two users left.  This patch replaces
it with for_each_subsys() + explicit subsys_mask testing and remove
for_each_root_subsys() along with cgroupfs_root->subsys_list handling.

This patch doesn't introduce any behavior changes.

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

2 files changed, 16 insertions, 30 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 8b9a594f0c92..cfaf416492dd 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -319,9 +319,6 @@ struct cgroupfs_root {
         /* Unique id for this hierarchy. */
         int hierarchy_id;
 
-        /* A list running through the attached subsystems */
-        struct list_head subsys_list;
-
         /* The root cgroup for this hierarchy */
         struct cgroup top_cgroup;
 
@@ -617,12 +614,8 @@ struct cgroup_subsys {
 #define MAX_CGROUP_TYPE_NAMELEN 32
         const char *name;
 
-        /*
-         * Link to parent, and list entry in parent's children.
-         * Protected by cgroup_lock()
-         */
+        /* link to parent, protected by cgroup_lock() */
         struct cgroupfs_root *root;
-        struct list_head sibling;
 
         /* list of cftype_sets */
         struct list_head cftsets;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 329fde82ef7c..fb1193bec4af 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -283,10 +283,6 @@ static int notify_on_release(const struct cgroup *cgrp)
         for ((i) = 0; (i) < CGROUP_BUILTIN_SUBSYS_COUNT &&              \
              (((ss) = cgroup_subsys[i]) || true); (i)++)
 
-/* iterate each subsystem attached to a hierarchy */
-#define for_each_root_subsys(root, ss)                                  \
-        list_for_each_entry((ss), &(root)->subsys_list, sibling)
-
 /* iterate across the active hierarchies */
 #define for_each_active_root(root)                                      \
         list_for_each_entry((root), &cgroup_roots, root_list)
@@ -1033,7 +1029,6 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                                            cgroup_css(cgroup_dummy_top, ss));
                         cgroup_css(cgrp, ss)->cgroup = cgrp;
 
-                        list_move(&ss->sibling, &root->subsys_list);
                         ss->root = root;
                         if (ss->bind)
                                 ss->bind(cgroup_css(cgrp, ss));
@@ -1052,7 +1047,6 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                         RCU_INIT_POINTER(cgrp->subsys[i], NULL);
 
                         cgroup_subsys[i]->root = &cgroup_dummy_root;
-                        list_move(&ss->sibling, &cgroup_dummy_root.subsys_list);
 
                         /* subsystem is now free - drop reference on module */
                         module_put(ss->module);
@@ -1079,10 +1073,12 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
 {
         struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
         struct cgroup_subsys *ss;
+        int ssid;
 
         mutex_lock(&cgroup_root_mutex);
-        for_each_root_subsys(root, ss)
-                seq_printf(seq, ",%s", ss->name);
+        for_each_subsys(ss, ssid)
+                if (root->subsys_mask & (1 << ssid))
+                        seq_printf(seq, ",%s", ss->name);
         if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
                 seq_puts(seq, ",sane_behavior");
         if (root->flags & CGRP_ROOT_NOPREFIX)
@@ -1352,7 +1348,6 @@ 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);
         root->number_of_cgroups = 1;
         cgrp->root = root;
@@ -4151,7 +4146,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
         struct cgroup *cgrp;
         struct cgroup_name *name;
         struct cgroupfs_root *root = parent->root;
-        int err = 0;
+        int ssid, err = 0;
         struct cgroup_subsys *ss;
         struct super_block *sb = root->sb;
 
@@ -4237,10 +4232,12 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                 goto err_destroy;
 
         /* let's create and online css's */
-        for_each_root_subsys(root, ss) {
-                err = create_css(cgrp, ss);
-                if (err)
-                        goto err_destroy;
+        for_each_subsys(ss, ssid) {
+                if (root->subsys_mask & (1 << ssid)) {
+                        err = create_css(cgrp, ss);
+                        if (err)
+                                goto err_destroy;
+                }
         }
 
         mutex_unlock(&cgroup_mutex);
@@ -4536,7 +4533,6 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
         cgroup_init_cftsets(ss);
 
         /* Create the top cgroup state for this subsystem */
-        list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);
         ss->root = &cgroup_dummy_root;
         css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss));
         /* We don't handle early failures gracefully */
@@ -4626,7 +4622,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
                 return PTR_ERR(css);
         }
 
-        list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);
         ss->root = &cgroup_dummy_root;
 
         /* our new subsystem will be attached to the dummy hierarchy. */
@@ -4702,9 +4697,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
         /* deassign the subsys_id */
         cgroup_subsys[ss->subsys_id] = NULL;
 
-        /* remove subsystem from the dummy root's list of subsystems */
-        list_del_init(&ss->sibling);
-
         /*
          * disentangle the css from all css_sets attached to the dummy
          * top. as in loading, we need to pay our respects to the hashtable
@@ -4901,11 +4893,12 @@ int proc_cgroup_show(struct seq_file *m, void *v)
         for_each_active_root(root) {
                 struct cgroup_subsys *ss;
                 struct cgroup *cgrp;
-                int count = 0;
+                int ssid, count = 0;
 
                 seq_printf(m, "%d:", root->hierarchy_id);
-                for_each_root_subsys(root, ss)
-                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+                for_each_subsys(ss, ssid)
+                        if (root->subsys_mask & (1 << ssid))
+                                seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
                 if (strlen(root->name))
                         seq_printf(m, "%sname=%s", count ? "," : "",
                                    root->name);