diff --git a/security/caitsith/gc.c b/security/caitsith/gc.c
new file mode 100644
index 0000000..d55f02d
--- /dev/null
+++ b/security/caitsith/gc.c
@@ -0,0 +1,373 @@
+/*
+ * security/caitsith/gc.c
+ *
+ * Copyright (C) 2005-2012  NTT DATA CORPORATION
+ */
+
+#include "caitsith.h"
+
+/* The list for "struct cs_io_buffer". */
+static LIST_HEAD(cs_io_buffer_list);
+/* Lock for protecting cs_io_buffer_list. */
+static DEFINE_SPINLOCK(cs_io_buffer_list_lock);
+
+static bool cs_name_used_by_io_buffer(const char *string, const size_t size);
+static bool cs_struct_used_by_io_buffer(const struct list_head *element);
+static int cs_gc_thread(void *unused);
+static void cs_collect_acl(struct list_head *list);
+static void cs_collect_entry(void);
+static void cs_try_to_gc(const enum cs_policy_id type,
+			 struct list_head *element);
+
+/*
+ * Lock for syscall users.
+ *
+ * This lock is held for only protecting single SRCU section.
+ */
+struct srcu_struct cs_ss;
+
+/**
+ * cs_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/caitsith/ users or not.
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns true if @element is used by /sys/kernel/security/caitsith/ users,
+ * false otherwise.
+ */
+static bool cs_struct_used_by_io_buffer(const struct list_head *element)
+{
+	struct cs_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&cs_io_buffer_list_lock);
+	list_for_each_entry(head, &cs_io_buffer_list, list) {
+		head->users++;
+		spin_unlock(&cs_io_buffer_list_lock);
+		mutex_lock(&head->io_sem);
+		if (head->r.acl == element || head->r.subacl == element ||
+		    &head->w.acl->list == element)
+			in_use = true;
+		mutex_unlock(&head->io_sem);
+		spin_lock(&cs_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&cs_io_buffer_list_lock);
+	return in_use;
+}
+
+/**
+ * cs_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/caitsith/ users or not.
+ *
+ * @string: String to check.
+ * @size:   Memory allocated for @string .
+ *
+ * Returns true if @string is used by /sys/kernel/security/caitsith/ users,
+ * false otherwise.
+ */
+static bool cs_name_used_by_io_buffer(const char *string, const size_t size)
+{
+	struct cs_io_buffer *head;
+	bool in_use = false;
+
+	spin_lock(&cs_io_buffer_list_lock);
+	list_for_each_entry(head, &cs_io_buffer_list, list) {
+		int i;
+
+		head->users++;
+		spin_unlock(&cs_io_buffer_list_lock);
+		mutex_lock(&head->io_sem);
+		for (i = 0; i < CS_MAX_IO_READ_QUEUE; i++) {
+			const char *w = head->r.w[i];
+
+			if (w < string || w > string + size)
+				continue;
+			in_use = true;
+			break;
+		}
+		mutex_unlock(&head->io_sem);
+		spin_lock(&cs_io_buffer_list_lock);
+		head->users--;
+		if (in_use)
+			break;
+	}
+	spin_unlock(&cs_io_buffer_list_lock);
+	return in_use;
+}
+
+/**
+ * cs_acl_info_has_sub_acl - Clear "struct cs_acl_info"->acl_info.
+ *
+ * @list: Pointer to "struct list_head".
+ *
+ * Returns true if @list is not empty, false otherwise.
+ */
+static bool cs_acl_info_has_sub_acl(struct list_head *list)
+{
+	struct cs_acl_info *acl;
+	struct cs_acl_info *tmp;
+
+	if (list_empty(list))
+		return false;
+	mutex_lock(&cs_policy_lock);
+	list_for_each_entry_safe(acl, tmp, list, list) {
+		cs_try_to_gc(CS_ID_ACL, &acl->list);
+	}
+	mutex_unlock(&cs_policy_lock);
+	return !list_empty(list);
+}
+
+/**
+ * cs_del_acl - Delete members in "struct cs_acl_info".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
+static inline void cs_del_acl(struct list_head *element)
+{
+	struct cs_acl_info *acl = container_of(element, typeof(*acl), list);
+
+	cs_put_condition(acl->cond);
+}
+
+/**
+ * cs_del_condition - Delete members in "struct cs_condition".
+ *
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ */
+void cs_del_condition(struct list_head *element)
+{
+	struct cs_condition *cond = container_of(element, typeof(*cond),
+						 head.list);
+	const union cs_condition_element *condp = (typeof(condp)) (cond + 1);
+
+	while ((void *) condp < (void *) ((u8 *) cond) + cond->size) {
+		const enum cs_conditions_index right = condp->right;
+
+		condp++;
+		if (right == CS_IMM_NAME_ENTRY) {
+			if (condp->path != &cs_null_name)
+				cs_put_name(condp->path);
+			condp++;
+		}
+	}
+}
+
+/**
+ * cs_try_to_gc - Try to kfree() an entry.
+ *
+ * @type:    One of values in "enum cs_policy_id".
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ *
+ * Caller holds cs_policy_lock mutex.
+ */
+static void cs_try_to_gc(const enum cs_policy_id type,
+			 struct list_head *element)
+{
+	/*
+	 * __list_del_entry() guarantees that the list element became no longer
+	 * reachable from the list which the element was originally on (e.g.
+	 * cs_domain_list). Also, synchronize_srcu() guarantees that the list
+	 * element became no longer referenced by syscall users.
+	 */
+	__list_del_entry(element);
+	mutex_unlock(&cs_policy_lock);
+	synchronize_srcu(&cs_ss);
+	/*
+	 * However, there are two users which may still be using the list
+	 * element. We need to defer until both users forget this element.
+	 *
+	 * Don't kfree() until "struct cs_io_buffer"->r.{acl,subacl} and
+	 * "struct cs_io_buffer"->w.acl forget this element.
+	 */
+	if (cs_struct_used_by_io_buffer(element))
+		goto reinject;
+	switch (type) {
+	case CS_ID_CONDITION:
+		cs_del_condition(element);
+		break;
+	case CS_ID_NAME:
+		/*
+		 * Don't kfree() until all "struct cs_io_buffer"->r.w[] forget
+		 * this element.
+		 */
+		if (cs_name_used_by_io_buffer
+		    (container_of(element, typeof(struct cs_name),
+				  head.list)->entry.name,
+		     container_of(element, typeof(struct cs_name),
+				  head.list)->size))
+			goto reinject;
+		break;
+	case CS_ID_ACL:
+		/*
+		 * Don't kfree() until "struct cs_acl_info"->acl_info_list
+		 * becomes empty.
+		 */
+		if (cs_acl_info_has_sub_acl
+		    (&container_of(element, typeof(struct cs_acl_info),
+				   list)->acl_info_list))
+			goto reinject;
+		cs_del_acl(element);
+		break;
+	default:
+		break;
+	}
+	mutex_lock(&cs_policy_lock);
+	cs_memory_used[CS_MEMORY_POLICY] -= ksize(element);
+	kfree(element);
+	return;
+reinject:
+	/*
+	 * We can safely reinject this element here bacause
+	 * (1) Appending list elements and removing list elements are protected
+	 *     by cs_policy_lock mutex.
+	 * (2) Only this function removes list elements and this function is
+	 *     exclusively executed by cs_gc_mutex mutex.
+	 * are true.
+	 */
+	mutex_lock(&cs_policy_lock);
+	list_add_rcu(element, element->prev);
+}
+
+/**
+ * cs_collect_acl - Delete elements in "struct cs_acl_info".
+ *
+ * @list: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ *
+ * Caller holds cs_policy_lock mutex.
+ */
+static void cs_collect_acl(struct list_head *list)
+{
+	struct cs_acl_info *acl;
+	struct cs_acl_info *tmp;
+
+	list_for_each_entry_safe(acl, tmp, list, list) {
+		if (!acl->is_deleted)
+			continue;
+		cs_try_to_gc(CS_ID_ACL, &acl->list);
+	}
+}
+
+/**
+ * cs_collect_entry - Try to kfree() deleted elements.
+ *
+ * Returns nothing.
+ */
+static void cs_collect_entry(void)
+{
+	int i;
+
+	mutex_lock(&cs_policy_lock);
+	for (i = 0; i < CS_MAX_MAC_INDEX; i++) {
+		struct cs_acl_info *ptr;
+		struct cs_acl_info *tmp;
+		struct list_head * const list = &cs_acl_list[i];
+
+		list_for_each_entry_safe(ptr, tmp, list, list) {
+			cs_collect_acl(&ptr->acl_info_list);
+			if (!ptr->is_deleted)
+				continue;
+			ptr->is_deleted = CS_GC_IN_PROGRESS;
+			cs_try_to_gc(CS_ID_ACL, &ptr->list);
+		}
+	}
+	{
+		struct cs_shared_acl_head *ptr;
+		struct cs_shared_acl_head *tmp;
+
+		list_for_each_entry_safe(ptr, tmp, &cs_condition_list, list) {
+			if (atomic_read(&ptr->users) > 0)
+				continue;
+			atomic_set(&ptr->users, CS_GC_IN_PROGRESS);
+			cs_try_to_gc(CS_ID_CONDITION, &ptr->list);
+		}
+	}
+	for (i = 0; i < CS_MAX_HASH; i++) {
+		struct list_head *list = &cs_name_list[i];
+		struct cs_shared_acl_head *ptr;
+		struct cs_shared_acl_head *tmp;
+
+		list_for_each_entry_safe(ptr, tmp, list, list) {
+			if (atomic_read(&ptr->users) > 0)
+				continue;
+			atomic_set(&ptr->users, CS_GC_IN_PROGRESS);
+			cs_try_to_gc(CS_ID_NAME, &ptr->list);
+		}
+	}
+	mutex_unlock(&cs_policy_lock);
+}
+
+/**
+ * cs_gc_thread - Garbage collector thread function.
+ *
+ * @unused: Unused.
+ *
+ * Returns 0.
+ */
+static int cs_gc_thread(void *unused)
+{
+	/* Garbage collector thread is exclusive. */
+	static DEFINE_MUTEX(cs_gc_mutex);
+
+	if (!mutex_trylock(&cs_gc_mutex))
+		goto out;
+	cs_collect_entry();
+	{
+		struct cs_io_buffer *head;
+		struct cs_io_buffer *tmp;
+
+		spin_lock(&cs_io_buffer_list_lock);
+		list_for_each_entry_safe(head, tmp, &cs_io_buffer_list,
+					 list) {
+			if (head->users)
+				continue;
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
+		}
+		spin_unlock(&cs_io_buffer_list_lock);
+	}
+	mutex_unlock(&cs_gc_mutex);
+out:
+	/* This acts as do_exit(0). */
+	return 0;
+}
+
+/**
+ * cs_notify_gc - Register/unregister /sys/kernel/security/caitsith/ users.
+ *
+ * @head:        Pointer to "struct cs_io_buffer".
+ * @is_register: True if register, false if unregister.
+ *
+ * Returns nothing.
+ */
+void cs_notify_gc(struct cs_io_buffer *head, const bool is_register)
+{
+	bool is_write = false;
+
+	spin_lock(&cs_io_buffer_list_lock);
+	if (is_register) {
+		head->users = 1;
+		list_add(&head->list, &cs_io_buffer_list);
+	} else {
+		is_write = head->write_buf != NULL;
+		if (!--head->users) {
+			list_del(&head->list);
+			kfree(head->read_buf);
+			kfree(head->write_buf);
+			kfree(head);
+		}
+	}
+	spin_unlock(&cs_io_buffer_list_lock);
+	if (is_write)
+		kthread_run(cs_gc_thread, NULL, "CaitSith's GC");
+}
