7 files changed, 187 insertions, 142 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 20ab84b2cf4e..2bf3951ca88f 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -250,7 +250,7 @@ bool cgroup_enable_per_threadgroup_rwsem __read_mostly;
 
 /* cgroup namespace for init task */
 struct cgroup_namespace init_cgroup_ns = {
-	.ns		= NS_COMMON_INIT(init_cgroup_ns, 2),
+	.ns		= NS_COMMON_INIT(init_cgroup_ns),
 	.user_ns	= &init_user_ns,
 	.root_cset	= &init_css_set,
 };
diff --git a/kernel/nscommon.c b/kernel/nscommon.c
index c910b979e433..bdc3c86231d3 100644
--- a/kernel/nscommon.c
+++ b/kernel/nscommon.c
@@ -2,6 +2,7 @@
 /* Copyright (c) 2025 Christian Brauner <brauner@kernel.org> */
 
 #include <linux/ns_common.h>
+#include <linux/nstree.h>
 #include <linux/proc_ns.h>
 #include <linux/user_namespace.h>
 #include <linux/vfsdebug.h>
@@ -61,14 +62,10 @@ int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_ope
 	ns->ops = ops;
 	ns->ns_id = 0;
 	ns->ns_type = ns_type;
-	RB_CLEAR_NODE(&ns->ns_tree_node);
-	RB_CLEAR_NODE(&ns->ns_unified_tree_node);
-	RB_CLEAR_NODE(&ns->ns_owner_tree_node);
-	INIT_LIST_HEAD(&ns->ns_list_node);
-	INIT_LIST_HEAD(&ns->ns_unified_list_node);
-	ns->ns_owner_tree = RB_ROOT;
-	INIT_LIST_HEAD(&ns->ns_owner);
-	INIT_LIST_HEAD(&ns->ns_owner_entry);
+	ns_tree_node_init(&ns->ns_tree_node);
+	ns_tree_node_init(&ns->ns_unified_node);
+	ns_tree_node_init(&ns->ns_owner_node);
+	ns_tree_root_init(&ns->ns_owner_root);
 
 #ifdef CONFIG_DEBUG_VFS
 	ns_debug(ns, ops);
@@ -85,7 +82,7 @@ int __ns_common_init(struct ns_common *ns, u32 ns_type, const struct proc_ns_ope
 	 * active use (installed in nsproxy) and decremented when all
 	 * active uses are gone. Initial namespaces are always active.
 	 */
-	if (is_initial_namespace(ns))
+	if (is_ns_init_inum(ns))
 		atomic_set(&ns->__ns_ref_active, 1);
 	else
 		atomic_set(&ns->__ns_ref_active, 0);
diff --git a/kernel/nstree.c b/kernel/nstree.c
index 97404fb90749..5270e0fa67a2 100644
--- a/kernel/nstree.c
+++ b/kernel/nstree.c
@@ -9,89 +9,165 @@
 #include <linux/user_namespace.h>
 
 static __cacheline_aligned_in_smp DEFINE_SEQLOCK(ns_tree_lock);
-static struct rb_root ns_unified_tree = RB_ROOT; /* protected by ns_tree_lock */
-static LIST_HEAD(ns_unified_list); /* protected by ns_tree_lock */
 
-/**
- * struct ns_tree - Namespace tree
- * @ns_tree: Rbtree of namespaces of a particular type
- * @ns_list: Sequentially walkable list of all namespaces of this type
- * @type: type of namespaces in this tree
- */
-struct ns_tree {
-	struct rb_root ns_tree;
-	struct list_head ns_list;
-	int type;
+DEFINE_LOCK_GUARD_0(ns_tree_writer,
+		    write_seqlock(&ns_tree_lock),
+		    write_sequnlock(&ns_tree_lock))
+
+DEFINE_LOCK_GUARD_0(ns_tree_locked_reader,
+		    read_seqlock_excl(&ns_tree_lock),
+		    read_sequnlock_excl(&ns_tree_lock))
+
+static struct ns_tree_root ns_unified_root = { /* protected by ns_tree_lock */
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(ns_unified_root.ns_list_head),
 };
 
-struct ns_tree mnt_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(mnt_ns_tree.ns_list),
-	.type = CLONE_NEWNS,
+struct ns_tree_root mnt_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(mnt_ns_tree.ns_list_head),
 };
 
-struct ns_tree net_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(net_ns_tree.ns_list),
-	.type = CLONE_NEWNET,
+struct ns_tree_root net_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(net_ns_tree.ns_list_head),
 };
 EXPORT_SYMBOL_GPL(net_ns_tree);
 
-struct ns_tree uts_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(uts_ns_tree.ns_list),
-	.type = CLONE_NEWUTS,
+struct ns_tree_root uts_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(uts_ns_tree.ns_list_head),
 };
 
-struct ns_tree user_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(user_ns_tree.ns_list),
-	.type = CLONE_NEWUSER,
+struct ns_tree_root user_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(user_ns_tree.ns_list_head),
 };
 
-struct ns_tree ipc_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(ipc_ns_tree.ns_list),
-	.type = CLONE_NEWIPC,
+struct ns_tree_root ipc_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(ipc_ns_tree.ns_list_head),
 };
 
-struct ns_tree pid_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(pid_ns_tree.ns_list),
-	.type = CLONE_NEWPID,
+struct ns_tree_root pid_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(pid_ns_tree.ns_list_head),
 };
 
-struct ns_tree cgroup_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(cgroup_ns_tree.ns_list),
-	.type = CLONE_NEWCGROUP,
+struct ns_tree_root cgroup_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(cgroup_ns_tree.ns_list_head),
 };
 
-struct ns_tree time_ns_tree = {
-	.ns_tree = RB_ROOT,
-	.ns_list = LIST_HEAD_INIT(time_ns_tree.ns_list),
-	.type = CLONE_NEWTIME,
+struct ns_tree_root time_ns_tree = {
+	.ns_rb = RB_ROOT,
+	.ns_list_head = LIST_HEAD_INIT(time_ns_tree.ns_list_head),
 };
 
+/**
+ * ns_tree_node_init - Initialize a namespace tree node
+ * @node: The node to initialize
+ *
+ * Initializes both the rbtree node and list entry.
+ */
+void ns_tree_node_init(struct ns_tree_node *node)
+{
+	RB_CLEAR_NODE(&node->ns_node);
+	INIT_LIST_HEAD(&node->ns_list_entry);
+}
+
+/**
+ * ns_tree_root_init - Initialize a namespace tree root
+ * @root: The root to initialize
+ *
+ * Initializes both the rbtree root and list head.
+ */
+void ns_tree_root_init(struct ns_tree_root *root)
+{
+	root->ns_rb = RB_ROOT;
+	INIT_LIST_HEAD(&root->ns_list_head);
+}
+
+/**
+ * ns_tree_node_empty - Check if a namespace tree node is empty
+ * @node: The node to check
+ *
+ * Returns true if the node is not in any tree.
+ */
+bool ns_tree_node_empty(const struct ns_tree_node *node)
+{
+	return RB_EMPTY_NODE(&node->ns_node);
+}
+
+/**
+ * ns_tree_node_add - Add a node to a namespace tree
+ * @node: The node to add
+ * @root: The tree root to add to
+ * @cmp: Comparison function for rbtree insertion
+ *
+ * Adds the node to both the rbtree and the list, maintaining sorted order.
+ * The list is maintained in the same order as the rbtree to enable efficient
+ * iteration.
+ *
+ * Returns: NULL if insertion succeeded, existing node if duplicate found
+ */
+struct rb_node *ns_tree_node_add(struct ns_tree_node *node,
+				  struct ns_tree_root *root,
+				  int (*cmp)(struct rb_node *, const struct rb_node *))
+{
+	struct rb_node *ret, *prev;
+
+	/* Add to rbtree */
+	ret = rb_find_add_rcu(&node->ns_node, &root->ns_rb, cmp);
+
+	/* Add to list in sorted order */
+	prev = rb_prev(&node->ns_node);
+	if (!prev) {
+		/* No previous node, add at head */
+		list_add_rcu(&node->ns_list_entry, &root->ns_list_head);
+	} else {
+		/* Add after previous node */
+		struct ns_tree_node *prev_node;
+		prev_node = rb_entry(prev, struct ns_tree_node, ns_node);
+		list_add_rcu(&node->ns_list_entry, &prev_node->ns_list_entry);
+	}
+
+	return ret;
+}
+
+/**
+ * ns_tree_node_del - Remove a node from a namespace tree
+ * @node: The node to remove
+ * @root: The tree root to remove from
+ *
+ * Removes the node from both the rbtree and the list atomically.
+ */
+void ns_tree_node_del(struct ns_tree_node *node, struct ns_tree_root *root)
+{
+	rb_erase(&node->ns_node, &root->ns_rb);
+	RB_CLEAR_NODE(&node->ns_node);
+	list_bidir_del_rcu(&node->ns_list_entry);
+}
+
 static inline struct ns_common *node_to_ns(const struct rb_node *node)
 {
 	if (!node)
 		return NULL;
-	return rb_entry(node, struct ns_common, ns_tree_node);
+	return rb_entry(node, struct ns_common, ns_tree_node.ns_node);
 }
 
 static inline struct ns_common *node_to_ns_unified(const struct rb_node *node)
 {
 	if (!node)
 		return NULL;
-	return rb_entry(node, struct ns_common, ns_unified_tree_node);
+	return rb_entry(node, struct ns_common, ns_unified_node.ns_node);
 }
 
 static inline struct ns_common *node_to_ns_owner(const struct rb_node *node)
 {
 	if (!node)
 		return NULL;
-	return rb_entry(node, struct ns_common, ns_owner_tree_node);
+	return rb_entry(node, struct ns_common, ns_owner_node.ns_node);
 }
 
 static int ns_id_cmp(u64 id_a, u64 id_b)
@@ -118,35 +194,22 @@ static int ns_cmp_owner(struct rb_node *a, const struct rb_node *b)
 	return ns_id_cmp(node_to_ns_owner(a)->ns_id, node_to_ns_owner(b)->ns_id);
 }
 
-void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree *ns_tree)
+void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree_root *ns_tree)
 {
-	struct rb_node *node, *prev;
+	struct rb_node *node;
 	const struct proc_ns_operations *ops = ns->ops;
 
 	VFS_WARN_ON_ONCE(!ns->ns_id);
-	VFS_WARN_ON_ONCE(ns->ns_type != ns_tree->type);
 
-	write_seqlock(&ns_tree_lock);
+	guard(ns_tree_writer)();
 
-	node = rb_find_add_rcu(&ns->ns_tree_node, &ns_tree->ns_tree, ns_cmp);
-	/*
-	 * If there's no previous entry simply add it after the
-	 * head and if there is add it after the previous entry.
-	 */
-	prev = rb_prev(&ns->ns_tree_node);
-	if (!prev)
-		list_add_rcu(&ns->ns_list_node, &ns_tree->ns_list);
-	else
-		list_add_rcu(&ns->ns_list_node, &node_to_ns(prev)->ns_list_node);
+	/* Add to per-type tree and list */
+	node = ns_tree_node_add(&ns->ns_tree_node, ns_tree, ns_cmp);
 
 	/* Add to unified tree and list */
-	rb_find_add_rcu(&ns->ns_unified_tree_node, &ns_unified_tree, ns_cmp_unified);
-	prev = rb_prev(&ns->ns_unified_tree_node);
-	if (!prev)
-		list_add_rcu(&ns->ns_unified_list_node, &ns_unified_list);
-	else
-		list_add_rcu(&ns->ns_unified_list_node, &node_to_ns_unified(prev)->ns_unified_list_node);
+	ns_tree_node_add(&ns->ns_unified_node, &ns_unified_root, ns_cmp_unified);
 
+	/* Add to owner's tree if applicable */
 	if (ops) {
 		struct user_namespace *user_ns;
 
@@ -156,55 +219,40 @@ void __ns_tree_add_raw(struct ns_common *ns, struct ns_tree *ns_tree)
 			struct ns_common *owner = &user_ns->ns;
 			VFS_WARN_ON_ONCE(owner->ns_type != CLONE_NEWUSER);
 
-			/* Insert into owner's rbtree */
-			rb_find_add_rcu(&ns->ns_owner_tree_node, &owner->ns_owner_tree, ns_cmp_owner);
-
-			/* Insert into owner's list in sorted order */
-			prev = rb_prev(&ns->ns_owner_tree_node);
-			if (!prev)
-				list_add_rcu(&ns->ns_owner_entry, &owner->ns_owner);
-			else
-				list_add_rcu(&ns->ns_owner_entry, &node_to_ns_owner(prev)->ns_owner_entry);
+			/* Insert into owner's tree and list */
+			ns_tree_node_add(&ns->ns_owner_node, &owner->ns_owner_root, ns_cmp_owner);
 		} else {
 			/* Only the initial user namespace doesn't have an owner. */
 			VFS_WARN_ON_ONCE(ns != to_ns_common(&init_user_ns));
 		}
 	}
-	write_sequnlock(&ns_tree_lock);
 
 	VFS_WARN_ON_ONCE(node);
 }
 
-void __ns_tree_remove(struct ns_common *ns, struct ns_tree *ns_tree)
+void __ns_tree_remove(struct ns_common *ns, struct ns_tree_root *ns_tree)
 {
 	const struct proc_ns_operations *ops = ns->ops;
 	struct user_namespace *user_ns;
 
-	VFS_WARN_ON_ONCE(RB_EMPTY_NODE(&ns->ns_tree_node));
-	VFS_WARN_ON_ONCE(list_empty(&ns->ns_list_node));
-	VFS_WARN_ON_ONCE(ns->ns_type != ns_tree->type);
+	VFS_WARN_ON_ONCE(ns_tree_node_empty(&ns->ns_tree_node));
+	VFS_WARN_ON_ONCE(list_empty(&ns->ns_tree_node.ns_list_entry));
 
 	write_seqlock(&ns_tree_lock);
-	rb_erase(&ns->ns_tree_node, &ns_tree->ns_tree);
-	RB_CLEAR_NODE(&ns->ns_tree_node);
-
-	list_bidir_del_rcu(&ns->ns_list_node);
 
-	rb_erase(&ns->ns_unified_tree_node, &ns_unified_tree);
-	RB_CLEAR_NODE(&ns->ns_unified_tree_node);
+	/* Remove from per-type tree and list */
+	ns_tree_node_del(&ns->ns_tree_node, ns_tree);
 
-	list_bidir_del_rcu(&ns->ns_unified_list_node);
+	/* Remove from unified tree and list */
+	ns_tree_node_del(&ns->ns_unified_node, &ns_unified_root);
 
-	/* Remove from owner's rbtree if this namespace has an owner */
+	/* Remove from owner's tree if applicable */
 	if (ops) {
 		user_ns = ops->owner(ns);
 		if (user_ns) {
 			struct ns_common *owner = &user_ns->ns;
-			rb_erase(&ns->ns_owner_tree_node, &owner->ns_owner_tree);
-			RB_CLEAR_NODE(&ns->ns_owner_tree_node);
+			ns_tree_node_del(&ns->ns_owner_node, &owner->ns_owner_root);
 		}
-
-		list_bidir_del_rcu(&ns->ns_owner_entry);
 	}
 
 	write_sequnlock(&ns_tree_lock);
@@ -235,7 +283,7 @@ static int ns_find_unified(const void *key, const struct rb_node *node)
 	return 0;
 }
 
-static struct ns_tree *ns_tree_from_type(int ns_type)
+static struct ns_tree_root *ns_tree_from_type(int ns_type)
 {
 	switch (ns_type) {
 	case CLONE_NEWCGROUP:
@@ -266,7 +314,7 @@ static struct ns_common *__ns_unified_tree_lookup_rcu(u64 ns_id)
 
 	do {
 		seq = read_seqbegin(&ns_tree_lock);
-		node = rb_find_rcu(&ns_id, &ns_unified_tree, ns_find_unified);
+		node = rb_find_rcu(&ns_id, &ns_unified_root.ns_rb, ns_find_unified);
 		if (node)
 			break;
 	} while (read_seqretry(&ns_tree_lock, seq));
@@ -276,7 +324,7 @@ static struct ns_common *__ns_unified_tree_lookup_rcu(u64 ns_id)
 
 static struct ns_common *__ns_tree_lookup_rcu(u64 ns_id, int ns_type)
 {
-	struct ns_tree *ns_tree;
+	struct ns_tree_root *ns_tree;
 	struct rb_node *node;
 	unsigned int seq;
 
@@ -286,7 +334,7 @@ static struct ns_common *__ns_tree_lookup_rcu(u64 ns_id, int ns_type)
 
 	do {
 		seq = read_seqbegin(&ns_tree_lock);
-		node = rb_find_rcu(&ns_id, &ns_tree->ns_tree, ns_find);
+		node = rb_find_rcu(&ns_id, &ns_tree->ns_rb, ns_find);
 		if (node)
 			break;
 	} while (read_seqretry(&ns_tree_lock, seq));
@@ -314,22 +362,20 @@ struct ns_common *ns_tree_lookup_rcu(u64 ns_id, int ns_type)
  * there is no next/previous namespace, -ENOENT is returned.
  */
 struct ns_common *__ns_tree_adjoined_rcu(struct ns_common *ns,
-					 struct ns_tree *ns_tree, bool previous)
+					 struct ns_tree_root *ns_tree, bool previous)
 {
 	struct list_head *list;
 
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "suspicious ns_tree_adjoined_rcu() usage");
 
 	if (previous)
-		list = rcu_dereference(list_bidir_prev_rcu(&ns->ns_list_node));
+		list = rcu_dereference(list_bidir_prev_rcu(&ns->ns_tree_node.ns_list_entry));
 	else
-		list = rcu_dereference(list_next_rcu(&ns->ns_list_node));
-	if (list_is_head(list, &ns_tree->ns_list))
+		list = rcu_dereference(list_next_rcu(&ns->ns_tree_node.ns_list_entry));
+	if (list_is_head(list, &ns_tree->ns_list_head))
 		return ERR_PTR(-ENOENT);
 
-	VFS_WARN_ON_ONCE(list_entry_rcu(list, struct ns_common, ns_list_node)->ns_type != ns_tree->type);
-
-	return list_entry_rcu(list, struct ns_common, ns_list_node);
+	return list_entry_rcu(list, struct ns_common, ns_tree_node.ns_list_entry);
 }
 
 /**
@@ -422,9 +468,9 @@ static struct ns_common *lookup_ns_owner_at(u64 ns_id, struct ns_common *owner)
 
 	VFS_WARN_ON_ONCE(owner->ns_type != CLONE_NEWUSER);
 
-	read_seqlock_excl(&ns_tree_lock);
-	node = owner->ns_owner_tree.rb_node;
+	guard(ns_tree_locked_reader)();
 
+	node = owner->ns_owner_root.ns_rb.rb_node;
 	while (node) {
 		struct ns_common *ns;
 
@@ -441,7 +487,6 @@ static struct ns_common *lookup_ns_owner_at(u64 ns_id, struct ns_common *owner)
 
 	if (ret)
 		ret = ns_get_unless_inactive(ret);
-	read_sequnlock_excl(&ns_tree_lock);
 	return ret;
 }
 
@@ -553,18 +598,21 @@ static ssize_t do_listns_userns(struct klistns *kls)
 	}
 
 	ret = 0;
-	head = &to_ns_common(kls->user_ns)->ns_owner;
+	head = &to_ns_common(kls->user_ns)->ns_owner_root.ns_list_head;
 	kls->userns_capable = ns_capable_noaudit(kls->user_ns, CAP_SYS_ADMIN);
 
 	rcu_read_lock();
 
 	if (!first_ns)
-		first_ns = list_entry_rcu(head->next, typeof(*ns), ns_owner_entry);
+		first_ns = list_entry_rcu(head->next, typeof(*first_ns), ns_owner_node.ns_list_entry);
 
-	for (ns = first_ns; &ns->ns_owner_entry != head && nr_ns_ids;
-	     ns = list_entry_rcu(ns->ns_owner_entry.next, typeof(*ns), ns_owner_entry)) {
+	ns = first_ns;
+	list_for_each_entry_from_rcu(ns, head, ns_owner_node.ns_list_entry) {
 		struct ns_common *valid;
 
+		if (!nr_ns_ids)
+			break;
+
 		valid = legitimize_ns(kls, ns);
 		if (!valid)
 			continue;
@@ -597,7 +645,7 @@ static ssize_t do_listns_userns(struct klistns *kls)
 static struct ns_common *lookup_ns_id_at(u64 ns_id, int ns_type)
 {
 	struct ns_common *ret = NULL;
-	struct ns_tree *ns_tree = NULL;
+	struct ns_tree_root *ns_tree = NULL;
 	struct rb_node *node;
 
 	if (ns_type) {
@@ -606,11 +654,12 @@ static struct ns_common *lookup_ns_id_at(u64 ns_id, int ns_type)
 			return NULL;
 	}
 
-	read_seqlock_excl(&ns_tree_lock);
+	guard(ns_tree_locked_reader)();
+
 	if (ns_tree)
-		node = ns_tree->ns_tree.rb_node;
+		node = ns_tree->ns_rb.rb_node;
 	else
-		node = ns_unified_tree.rb_node;
+		node = ns_unified_root.ns_rb.rb_node;
 
 	while (node) {
 		struct ns_common *ns;
@@ -635,33 +684,32 @@ static struct ns_common *lookup_ns_id_at(u64 ns_id, int ns_type)
 
 	if (ret)
 		ret = ns_get_unless_inactive(ret);
-	read_sequnlock_excl(&ns_tree_lock);
 	return ret;
 }
 
 static inline struct ns_common *first_ns_common(const struct list_head *head,
-						struct ns_tree *ns_tree)
+						struct ns_tree_root *ns_tree)
 {
 	if (ns_tree)
-		return list_entry_rcu(head->next, struct ns_common, ns_list_node);
-	return list_entry_rcu(head->next, struct ns_common, ns_unified_list_node);
+		return list_entry_rcu(head->next, struct ns_common, ns_tree_node.ns_list_entry);
+	return list_entry_rcu(head->next, struct ns_common, ns_unified_node.ns_list_entry);
 }
 
 static inline struct ns_common *next_ns_common(struct ns_common *ns,
-					       struct ns_tree *ns_tree)
+					       struct ns_tree_root *ns_tree)
 {
 	if (ns_tree)
-		return list_entry_rcu(ns->ns_list_node.next, struct ns_common, ns_list_node);
-	return list_entry_rcu(ns->ns_unified_list_node.next, struct ns_common, ns_unified_list_node);
+		return list_entry_rcu(ns->ns_tree_node.ns_list_entry.next, struct ns_common, ns_tree_node.ns_list_entry);
+	return list_entry_rcu(ns->ns_unified_node.ns_list_entry.next, struct ns_common, ns_unified_node.ns_list_entry);
 }
 
 static inline bool ns_common_is_head(struct ns_common *ns,
 				     const struct list_head *head,
-				     struct ns_tree *ns_tree)
+				     struct ns_tree_root *ns_tree)
 {
 	if (ns_tree)
-		return &ns->ns_list_node == head;
-	return &ns->ns_unified_list_node == head;
+		return &ns->ns_tree_node.ns_list_entry == head;
+	return &ns->ns_unified_node.ns_list_entry == head;
 }
 
 static ssize_t do_listns(struct klistns *kls)
@@ -669,7 +717,7 @@ static ssize_t do_listns(struct klistns *kls)
 	u64 __user *ns_ids = kls->uns_ids;
 	size_t nr_ns_ids = kls->nr_ns_ids;
 	struct ns_common *ns, *first_ns = NULL, *prev = NULL;
-	struct ns_tree *ns_tree = NULL;
+	struct ns_tree_root *ns_tree = NULL;
 	const struct list_head *head;
 	u32 ns_type;
 	ssize_t ret;
@@ -694,9 +742,9 @@ static ssize_t do_listns(struct klistns *kls)
 
 	ret = 0;
 	if (ns_tree)
-		head = &ns_tree->ns_list;
+		head = &ns_tree->ns_list_head;
 	else
-		head = &ns_unified_list;
+		head = &ns_unified_root.ns_list_head;
 
 	rcu_read_lock();
 
diff --git a/kernel/pid.c b/kernel/pid.c
index a5a63dc0a491..a31771bc89c1 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -71,7 +71,7 @@ static int pid_max_max = PID_MAX_LIMIT;
  * the scheme scales to up to 4 million PIDs, runtime.
  */
 struct pid_namespace init_pid_ns = {
-	.ns = NS_COMMON_INIT(init_pid_ns, 2),
+	.ns = NS_COMMON_INIT(init_pid_ns),
 	.idr = IDR_INIT(init_pid_ns.idr),
 	.pid_allocated = PIDNS_ADDING,
 	.level = 0,
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index 650be58d8d18..e48f5de41361 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -184,7 +184,7 @@ struct pid_namespace *copy_pid_ns(u64 flags,
 
 void put_pid_ns(struct pid_namespace *ns)
 {
-	if (ns && ns != &init_pid_ns && ns_ref_put(ns))
+	if (ns && ns_ref_put(ns))
 		schedule_work(&ns->work);
 }
 EXPORT_SYMBOL_GPL(put_pid_ns);
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 19911f88e2b8..e76be24b132c 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -478,7 +478,7 @@ const struct proc_ns_operations timens_for_children_operations = {
 };
 
 struct time_namespace init_time_ns = {
-	.ns		= NS_COMMON_INIT(init_time_ns, 3),
+	.ns		= NS_COMMON_INIT(init_time_ns),
 	.user_ns	= &init_user_ns,
 	.frozen_offsets	= true,
 };
diff --git a/kernel/user.c b/kernel/user.c
index 4b3132e786d9..7aef4e679a6a 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -35,7 +35,7 @@ EXPORT_SYMBOL_GPL(init_binfmt_misc);
  * and 1 for... ?
  */
 struct user_namespace init_user_ns = {
-	.ns = NS_COMMON_INIT(init_user_ns, 3),
+	.ns = NS_COMMON_INIT(init_user_ns),
 	.uid_map = {
 		{
 			.extent[0] = {