diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index ccec722213a4b4361ebd280b4acf312e62a5dc7e..8ba6809853358edd50ae3392169495d98fc3ca46 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -207,6 +207,7 @@ struct cg_cgroup_link {
 	 * cgroup, anchored on cgroup->css_sets
 	 */
 	struct list_head cgrp_link_list;
+	struct cgroup *cgrp;
 	/*
 	 * List running through cg_cgroup_links pointing at a
 	 * single css_set object, anchored on css_set->cg_links
@@ -233,8 +234,11 @@ static int cgroup_subsys_init_idr(struct cgroup_subsys *ss);
 static DEFINE_RWLOCK(css_set_lock);
 static int css_set_count;
 
-/* hash table for cgroup groups. This improves the performance to
- * find an existing css_set */
+/*
+ * hash table for cgroup groups. This improves the performance to find
+ * an existing css_set. This hash doesn't (currently) take into
+ * account cgroups in empty hierarchies.
+ */
 #define CSS_SET_HASH_BITS	7
 #define CSS_SET_TABLE_SIZE	(1 << CSS_SET_HASH_BITS)
 static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];
@@ -343,6 +347,78 @@ static inline void put_css_set_taskexit(struct css_set *cg)
 	__put_css_set(cg, 1);
 }
 
+/*
+ * compare_css_sets - helper function for find_existing_css_set().
+ * @cg: candidate css_set being tested
+ * @old_cg: existing css_set for a task
+ * @new_cgrp: cgroup that's being entered by the task
+ * @template: desired set of css pointers in css_set (pre-calculated)
+ *
+ * Returns true if "cg" matches "old_cg" except for the hierarchy
+ * which "new_cgrp" belongs to, for which it should match "new_cgrp".
+ */
+static bool compare_css_sets(struct css_set *cg,
+			     struct css_set *old_cg,
+			     struct cgroup *new_cgrp,
+			     struct cgroup_subsys_state *template[])
+{
+	struct list_head *l1, *l2;
+
+	if (memcmp(template, cg->subsys, sizeof(cg->subsys))) {
+		/* Not all subsystems matched */
+		return false;
+	}
+
+	/*
+	 * Compare cgroup pointers in order to distinguish between
+	 * different cgroups in heirarchies with no subsystems. We
+	 * could get by with just this check alone (and skip the
+	 * memcmp above) but on most setups the memcmp check will
+	 * avoid the need for this more expensive check on almost all
+	 * candidates.
+	 */
+
+	l1 = &cg->cg_links;
+	l2 = &old_cg->cg_links;
+	while (1) {
+		struct cg_cgroup_link *cgl1, *cgl2;
+		struct cgroup *cg1, *cg2;
+
+		l1 = l1->next;
+		l2 = l2->next;
+		/* See if we reached the end - both lists are equal length. */
+		if (l1 == &cg->cg_links) {
+			BUG_ON(l2 != &old_cg->cg_links);
+			break;
+		} else {
+			BUG_ON(l2 == &old_cg->cg_links);
+		}
+		/* Locate the cgroups associated with these links. */
+		cgl1 = list_entry(l1, struct cg_cgroup_link, cg_link_list);
+		cgl2 = list_entry(l2, struct cg_cgroup_link, cg_link_list);
+		cg1 = cgl1->cgrp;
+		cg2 = cgl2->cgrp;
+		/* Hierarchies should be linked in the same order. */
+		BUG_ON(cg1->root != cg2->root);
+
+		/*
+		 * If this hierarchy is the hierarchy of the cgroup
+		 * that's changing, then we need to check that this
+		 * css_set points to the new cgroup; if it's any other
+		 * hierarchy, then this css_set should point to the
+		 * same cgroup as the old css_set.
+		 */
+		if (cg1->root == new_cgrp->root) {
+			if (cg1 != new_cgrp)
+				return false;
+		} else {
+			if (cg1 != cg2)
+				return false;
+		}
+	}
+	return true;
+}
+
 /*
  * find_existing_css_set() is a helper for
  * find_css_set(), and checks to see whether an existing
@@ -384,10 +460,11 @@ static struct css_set *find_existing_css_set(
 
 	hhead = css_set_hash(template);
 	hlist_for_each_entry(cg, node, hhead, hlist) {
-		if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
-			/* All subsystems matched */
-			return cg;
-		}
+		if (!compare_css_sets(cg, oldcg, cgrp, template))
+			continue;
+
+		/* This css_set matches what we need */
+		return cg;
 	}
 
 	/* No existing cgroup group matched */
@@ -441,8 +518,13 @@ static void link_css_set(struct list_head *tmp_cg_links,
 	link = list_first_entry(tmp_cg_links, struct cg_cgroup_link,
 				cgrp_link_list);
 	link->cg = cg;
+	link->cgrp = cgrp;
 	list_move(&link->cgrp_link_list, &cgrp->css_sets);
-	list_add(&link->cg_link_list, &cg->cg_links);
+	/*
+	 * Always add links to the tail of the list so that the list
+	 * is sorted by order of hierarchy creation
+	 */
+	list_add_tail(&link->cg_link_list, &cg->cg_links);
 }
 
 /*
@@ -462,6 +544,7 @@ static struct css_set *find_css_set(
 	struct list_head tmp_cg_links;
 
 	struct hlist_head *hhead;
+	struct cg_cgroup_link *link;
 
 	/* First see if we already have a cgroup group that matches
 	 * the desired set */
@@ -497,18 +580,14 @@ static struct css_set *find_css_set(
 	/* Add reference counts and links from the new css_set. */
 	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 		struct cgroup *cgrp = res->subsys[i]->cgroup;
-		struct cgroup_subsys *ss = subsys[i];
 		atomic_inc(&cgrp->count);
-		/*
-		 * We want to add a link once per cgroup, so we
-		 * only do it for the first subsystem in each
-		 * hierarchy
-		 */
-		if (ss->root->subsys_list.next == &ss->sibling)
-			link_css_set(&tmp_cg_links, res, cgrp);
 	}
-	if (list_empty(&rootnode.subsys_list))
-		link_css_set(&tmp_cg_links, res, dummytop);
+	list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
+		struct cgroup *c = link->cgrp;
+		if (c->root == cgrp->root)
+			c = cgrp;
+		link_css_set(&tmp_cg_links, res, c);
+	}
 
 	BUG_ON(!list_empty(&tmp_cg_links));
 
@@ -523,6 +602,41 @@ static struct css_set *find_css_set(
 	return res;
 }
 
+/*
+ * Return the cgroup for "task" from the given hierarchy. Must be
+ * called with cgroup_mutex held.
+ */
+static struct cgroup *task_cgroup_from_root(struct task_struct *task,
+					    struct cgroupfs_root *root)
+{
+	struct css_set *css;
+	struct cgroup *res = NULL;
+
+	BUG_ON(!mutex_is_locked(&cgroup_mutex));
+	read_lock(&css_set_lock);
+	/*
+	 * No need to lock the task - since we hold cgroup_mutex the
+	 * task can't change groups, so the only thing that can happen
+	 * is that it exits and its css is set back to init_css_set.
+	 */
+	css = task->cgroups;
+	if (css == &init_css_set) {
+		res = &root->top_cgroup;
+	} else {
+		struct cg_cgroup_link *link;
+		list_for_each_entry(link, &css->cg_links, cg_link_list) {
+			struct cgroup *c = link->cgrp;
+			if (c->root == root) {
+				res = c;
+				break;
+			}
+		}
+	}
+	read_unlock(&css_set_lock);
+	BUG_ON(!res);
+	return res;
+}
+
 /*
  * There is one global cgroup mutex. We also require taking
  * task_lock() when dereferencing a task's cgroup subsys pointers.
@@ -1361,27 +1475,6 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
 	return 0;
 }
 
-/*
- * Return the first subsystem attached to a cgroup's hierarchy, and
- * its subsystem id.
- */
-
-static void get_first_subsys(const struct cgroup *cgrp,
-			struct cgroup_subsys_state **css, int *subsys_id)
-{
-	const struct cgroupfs_root *root = cgrp->root;
-	const struct cgroup_subsys *test_ss;
-	BUG_ON(list_empty(&root->subsys_list));
-	test_ss = list_entry(root->subsys_list.next,
-			     struct cgroup_subsys, sibling);
-	if (css) {
-		*css = cgrp->subsys[test_ss->subsys_id];
-		BUG_ON(!*css);
-	}
-	if (subsys_id)
-		*subsys_id = test_ss->subsys_id;
-}
-
 /**
  * cgroup_attach_task - attach task 'tsk' to cgroup 'cgrp'
  * @cgrp: the cgroup the task is attaching to
@@ -1398,12 +1491,9 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 	struct css_set *cg;
 	struct css_set *newcg;
 	struct cgroupfs_root *root = cgrp->root;
-	int subsys_id;
-
-	get_first_subsys(cgrp, NULL, &subsys_id);
 
 	/* Nothing to do if the task is already in that cgroup */
-	oldcgrp = task_cgroup(tsk, subsys_id);
+	oldcgrp = task_cgroup_from_root(tsk, root);
 	if (cgrp == oldcgrp)
 		return 0;
 
@@ -1961,7 +2051,7 @@ int cgroup_task_count(const struct cgroup *cgrp)
  * the start of a css_set
  */
 static void cgroup_advance_iter(struct cgroup *cgrp,
-					  struct cgroup_iter *it)
+				struct cgroup_iter *it)
 {
 	struct list_head *l = it->cg_link;
 	struct cg_cgroup_link *link;
@@ -2964,6 +3054,7 @@ int __init cgroup_init_early(void)
 	init_task.cgroups = &init_css_set;
 
 	init_css_set_link.cg = &init_css_set;
+	init_css_set_link.cgrp = dummytop;
 	list_add(&init_css_set_link.cgrp_link_list,
 		 &rootnode.top_cgroup.css_sets);
 	list_add(&init_css_set_link.cg_link_list,
@@ -3071,7 +3162,6 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
 	for_each_active_root(root) {
 		struct cgroup_subsys *ss;
 		struct cgroup *cgrp;
-		int subsys_id;
 		int count = 0;
 
 		seq_printf(m, "%lu:", root->subsys_bits);
@@ -3081,8 +3171,7 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
 			seq_printf(m, "%sname=%s", count ? "," : "",
 				   root->name);
 		seq_putc(m, ':');
-		get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
-		cgrp = task_cgroup(tsk, subsys_id);
+		cgrp = task_cgroup_from_root(tsk, root);
 		retval = cgroup_path(cgrp, buf, PAGE_SIZE);
 		if (retval < 0)
 			goto out_unlock;
@@ -3408,13 +3497,11 @@ int cgroup_is_descendant(const struct cgroup *cgrp, struct task_struct *task)
 {
 	int ret;
 	struct cgroup *target;
-	int subsys_id;
 
 	if (cgrp == dummytop)
 		return 1;
 
-	get_first_subsys(cgrp, NULL, &subsys_id);
-	target = task_cgroup(task, subsys_id);
+	target = task_cgroup_from_root(task, cgrp->root);
 	while (cgrp != target && cgrp!= cgrp->top_cgroup)
 		cgrp = cgrp->parent;
 	ret = (cgrp == target);
@@ -3824,6 +3911,59 @@ static u64 current_css_set_refcount_read(struct cgroup *cont,
 	return count;
 }
 
+static int current_css_set_cg_links_read(struct cgroup *cont,
+					 struct cftype *cft,
+					 struct seq_file *seq)
+{
+	struct cg_cgroup_link *link;
+	struct css_set *cg;
+
+	read_lock(&css_set_lock);
+	rcu_read_lock();
+	cg = rcu_dereference(current->cgroups);
+	list_for_each_entry(link, &cg->cg_links, cg_link_list) {
+		struct cgroup *c = link->cgrp;
+		const char *name;
+
+		if (c->dentry)
+			name = c->dentry->d_name.name;
+		else
+			name = "?";
+		seq_printf(seq, "Root %lu group %s\n",
+			   c->root->subsys_bits, name);
+	}
+	rcu_read_unlock();
+	read_unlock(&css_set_lock);
+	return 0;
+}
+
+#define MAX_TASKS_SHOWN_PER_CSS 25
+static int cgroup_css_links_read(struct cgroup *cont,
+				 struct cftype *cft,
+				 struct seq_file *seq)
+{
+	struct cg_cgroup_link *link;
+
+	read_lock(&css_set_lock);
+	list_for_each_entry(link, &cont->css_sets, cgrp_link_list) {
+		struct css_set *cg = link->cg;
+		struct task_struct *task;
+		int count = 0;
+		seq_printf(seq, "css_set %p\n", cg);
+		list_for_each_entry(task, &cg->tasks, cg_list) {
+			if (count++ > MAX_TASKS_SHOWN_PER_CSS) {
+				seq_puts(seq, "  ...\n");
+				break;
+			} else {
+				seq_printf(seq, "  task %d\n",
+					   task_pid_vnr(task));
+			}
+		}
+	}
+	read_unlock(&css_set_lock);
+	return 0;
+}
+
 static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft)
 {
 	return test_bit(CGRP_RELEASABLE, &cgrp->flags);
@@ -3849,6 +3989,16 @@ static struct cftype debug_files[] =  {
 		.read_u64 = current_css_set_refcount_read,
 	},
 
+	{
+		.name = "current_css_set_cg_links",
+		.read_seq_string = current_css_set_cg_links_read,
+	},
+
+	{
+		.name = "cgroup_css_links",
+		.read_seq_string = cgroup_css_links_read,
+	},
+
 	{
 		.name = "releasable",
 		.read_u64 = releasable_read,