cgroups: add inactive subsystems to rootnode.subsys_list

Though for an inactive hierarchy, we have subsys->root == &rootnode, but
rootnode's subsys_list is always empty.

This conflicts with the code in find_css_set():

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
		...
		if (ss->root->subsys_list.next == &ss->sibling) {
			...
		}
	}
	if (list_empty(&rootnode.subsys_list)) {
		...
	}

The above code assumes rootnode.subsys_list links all inactive
hierarchies.

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, 3 insertions, 2 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index fd572d057691..abf7248f501a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -712,7 +712,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                         BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
                         cgrp->subsys[i] = dummytop->subsys[i];
                         cgrp->subsys[i]->cgroup = cgrp;
-                        list_add(&ss->sibling, &root->subsys_list);
+                        list_move(&ss->sibling, &root->subsys_list);
                         ss->root = root;
                         if (ss->bind)
                                 ss->bind(ss, cgrp);
@@ -726,7 +726,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
                         dummytop->subsys[i]->cgroup = dummytop;
                         cgrp->subsys[i] = NULL;
                         subsys[i]->root = &rootnode;
-                        list_del(&ss->sibling);
+                        list_move(&ss->sibling, &rootnode.subsys_list);
                 } else if (bit & final_bits) {
                         /* Subsystem state should already exist */
                         BUG_ON(!cgrp->subsys[i]);
@@ -2521,6 +2521,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
         printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
 
         /* Create the top cgroup state for this subsystem */
+        list_add(&ss->sibling, &rootnode.subsys_list);
         ss->root = &rootnode;
         css = ss->create(ss, dummytop);
         /* We don't handle early failures gracefully */