TOMOYO: Simplify garbage collector.

When TOMOYO started using garbage collector at commit 847b173e "TOMOYO: Add
garbage collector.", we waited for close() before kfree(). Thus, elements to be
kfree()d were queued up using tomoyo_gc_list list.

But it turned out that tomoyo_element_linked_by_gc() tends to choke garbage
collector when certain pattern of entries are queued.

Since garbage collector is no longer waiting for close() since commit 2e503bbb
"TOMOYO: Fix lockdep warning.", we can remove tomoyo_gc_list list and
tomoyo_element_linked_by_gc() by doing sequential processing.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 169 insertions, 311 deletions

diff --git a/security/tomoyo/gc.c b/security/tomoyo/gc.c
index 7747ceb9a22..f2295c65f1e 100644
--- a/security/tomoyo/gc.c
+++ b/security/tomoyo/gc.c
@@ -13,35 +13,6 @@ static LIST_HEAD(tomoyo_io_buffer_list);
 /* Lock for protecting tomoyo_io_buffer_list. */
 static DEFINE_SPINLOCK(tomoyo_io_buffer_list_lock);
 
-/* Size of an element. */
-static const u8 tomoyo_element_size[TOMOYO_MAX_POLICY] = {
-        [TOMOYO_ID_GROUP] = sizeof(struct tomoyo_group),
-        [TOMOYO_ID_ADDRESS_GROUP] = sizeof(struct tomoyo_address_group),
-        [TOMOYO_ID_PATH_GROUP] = sizeof(struct tomoyo_path_group),
-        [TOMOYO_ID_NUMBER_GROUP] = sizeof(struct tomoyo_number_group),
-        [TOMOYO_ID_AGGREGATOR] = sizeof(struct tomoyo_aggregator),
-        [TOMOYO_ID_TRANSITION_CONTROL] =
-        sizeof(struct tomoyo_transition_control),
-        [TOMOYO_ID_MANAGER] = sizeof(struct tomoyo_manager),
-        /* [TOMOYO_ID_CONDITION] = "struct tomoyo_condition"->size, */
-        /* [TOMOYO_ID_NAME] = "struct tomoyo_name"->size, */
-        /* [TOMOYO_ID_ACL] =
-           tomoyo_acl_size["struct tomoyo_acl_info"->type], */
-        [TOMOYO_ID_DOMAIN] = sizeof(struct tomoyo_domain_info),
-};
-
-/* Size of a domain ACL element. */
-static const u8 tomoyo_acl_size[] = {
-        [TOMOYO_TYPE_PATH_ACL] = sizeof(struct tomoyo_path_acl),
-        [TOMOYO_TYPE_PATH2_ACL] = sizeof(struct tomoyo_path2_acl),
-        [TOMOYO_TYPE_PATH_NUMBER_ACL] = sizeof(struct tomoyo_path_number_acl),
-        [TOMOYO_TYPE_MKDEV_ACL] = sizeof(struct tomoyo_mkdev_acl),
-        [TOMOYO_TYPE_MOUNT_ACL] = sizeof(struct tomoyo_mount_acl),
-        [TOMOYO_TYPE_INET_ACL] = sizeof(struct tomoyo_inet_acl),
-        [TOMOYO_TYPE_UNIX_ACL] = sizeof(struct tomoyo_unix_acl),
-        [TOMOYO_TYPE_ENV_ACL] = sizeof(struct tomoyo_env_acl),
-};
-
 /**
  * tomoyo_struct_used_by_io_buffer - Check whether the list element is used by /sys/kernel/security/tomoyo/ users or not.
  *
@@ -59,15 +30,11 @@ static bool tomoyo_struct_used_by_io_buffer(const struct list_head *element)
         list_for_each_entry(head, &tomoyo_io_buffer_list, list) {
                 head->users++;
                 spin_unlock(&tomoyo_io_buffer_list_lock);
-                if (mutex_lock_interruptible(&head->io_sem)) {
-                        in_use = true;
-                        goto out;
-                }
+                mutex_lock(&head->io_sem);
                 if (head->r.domain == element || head->r.group == element ||
                     head->r.acl == element || &head->w.domain->list == element)
                         in_use = true;
                 mutex_unlock(&head->io_sem);
-out:
                 spin_lock(&tomoyo_io_buffer_list_lock);
                 head->users--;
                 if (in_use)
@@ -81,15 +48,14 @@ out:
  * tomoyo_name_used_by_io_buffer - Check whether the string is used by /sys/kernel/security/tomoyo/ users or not.
  *
  * @string: String to check.
- * @size:   Memory allocated for @string .
  *
  * Returns true if @string is used by /sys/kernel/security/tomoyo/ users,
  * false otherwise.
  */
-static bool tomoyo_name_used_by_io_buffer(const char *string,
-                                          const size_t size)
+static bool tomoyo_name_used_by_io_buffer(const char *string)
 {
         struct tomoyo_io_buffer *head;
+        const size_t size = strlen(string) + 1;
         bool in_use = false;
 
         spin_lock(&tomoyo_io_buffer_list_lock);
@@ -97,10 +63,7 @@ static bool tomoyo_name_used_by_io_buffer(const char *string,
                 int i;
                 head->users++;
                 spin_unlock(&tomoyo_io_buffer_list_lock);
-                if (mutex_lock_interruptible(&head->io_sem)) {
-                        in_use = true;
-                        goto out;
-                }
+                mutex_lock(&head->io_sem);
                 for (i = 0; i < TOMOYO_MAX_IO_READ_QUEUE; i++) {
                         const char *w = head->r.w[i];
                         if (w < string || w > string + size)
@@ -109,7 +72,6 @@ static bool tomoyo_name_used_by_io_buffer(const char *string,
                         break;
                 }
                 mutex_unlock(&head->io_sem);
-out:
                 spin_lock(&tomoyo_io_buffer_list_lock);
                 head->users--;
                 if (in_use)
@@ -119,84 +81,6 @@ out:
         return in_use;
 }
 
-/* Structure for garbage collection. */
-struct tomoyo_gc {
-        struct list_head list;
-        enum tomoyo_policy_id type;
-        size_t size;
-        struct list_head *element;
-};
-/* List of entries to be deleted. */
-static LIST_HEAD(tomoyo_gc_list);
-/* Length of tomoyo_gc_list. */
-static int tomoyo_gc_list_len;
-
-/**
- * tomoyo_add_to_gc - Add an entry to to be deleted list.
- *
- * @type:    One of values in "enum tomoyo_policy_id".
- * @element: Pointer to "struct list_head".
- *
- * Returns true on success, false otherwise.
- *
- * Caller holds tomoyo_policy_lock mutex.
- *
- * Adding an entry needs kmalloc(). Thus, if we try to add thousands of
- * entries at once, it will take too long time. Thus, do not add more than 128
- * entries per a scan. But to be able to handle worst case where all entries
- * are in-use, we accept one more entry per a scan.
- *
- * If we use singly linked list using "struct list_head"->prev (which is
- * LIST_POISON2), we can avoid kmalloc().
- */
-static bool tomoyo_add_to_gc(const int type, struct list_head *element)
-{
-        struct tomoyo_gc *entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
-        if (!entry)
-                return false;
-        entry->type = type;
-        if (type == TOMOYO_ID_ACL)
-                entry->size = tomoyo_acl_size[
-                              container_of(element,
-                                           typeof(struct tomoyo_acl_info),
-                                           list)->type];
-        else if (type == TOMOYO_ID_NAME)
-                entry->size = strlen(container_of(element,
-                                                  typeof(struct tomoyo_name),
-                                                  head.list)->entry.name) + 1;
-        else if (type == TOMOYO_ID_CONDITION)
-                entry->size =
-                        container_of(element, typeof(struct tomoyo_condition),
-                                     head.list)->size;
-        else
-                entry->size = tomoyo_element_size[type];
-        entry->element = element;
-        list_add(&entry->list, &tomoyo_gc_list);
-        list_del_rcu(element);
-        return tomoyo_gc_list_len++ < 128;
-}
-
-/**
- * tomoyo_element_linked_by_gc - Validate next element of an entry.
- *
- * @element: Pointer to an element.
- * @size:    Size of @element in byte.
- *
- * Returns true if @element is linked by other elements in the garbage
- * collector's queue, false otherwise.
- */
-static bool tomoyo_element_linked_by_gc(const u8 *element, const size_t size)
-{
-        struct tomoyo_gc *p;
-        list_for_each_entry(p, &tomoyo_gc_list, list) {
-                const u8 *ptr = (const u8 *) p->element->next;
-                if (ptr < element || element + size < ptr)
-                        continue;
-                return true;
-        }
-        return false;
-}
-
 /**
  * tomoyo_del_transition_control - Delete members in "struct tomoyo_transition_control".
  *
@@ -204,7 +88,7 @@ static bool tomoyo_element_linked_by_gc(const u8 *element, const size_t size)
  *
  * Returns nothing.
  */
-static void tomoyo_del_transition_control(struct list_head *element)
+static inline void tomoyo_del_transition_control(struct list_head *element)
 {
         struct tomoyo_transition_control *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -219,7 +103,7 @@ static void tomoyo_del_transition_control(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_aggregator(struct list_head *element)
+static inline void tomoyo_del_aggregator(struct list_head *element)
 {
         struct tomoyo_aggregator *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -234,7 +118,7 @@ static void tomoyo_del_aggregator(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_manager(struct list_head *element)
+static inline void tomoyo_del_manager(struct list_head *element)
 {
         struct tomoyo_manager *ptr =
                 container_of(element, typeof(*ptr), head.list);
@@ -330,44 +214,24 @@ static void tomoyo_del_acl(struct list_head *element)
  *
  * @element: Pointer to "struct list_head".
  *
- * Returns true if deleted, false otherwise.
+ * Returns nothing.
  */
-static bool tomoyo_del_domain(struct list_head *element)
+static inline void tomoyo_del_domain(struct list_head *element)
 {
         struct tomoyo_domain_info *domain =
                 container_of(element, typeof(*domain), list);
         struct tomoyo_acl_info *acl;
         struct tomoyo_acl_info *tmp;
         /*
-         * Since we don't protect whole execve() operation using SRCU,
-         * we need to recheck domain->users at this point.
-         *
-         * (1) Reader starts SRCU section upon execve().
-         * (2) Reader traverses tomoyo_domain_list and finds this domain.
-         * (3) Writer marks this domain as deleted.
-         * (4) Garbage collector removes this domain from tomoyo_domain_list
-         *     because this domain is marked as deleted and used by nobody.
-         * (5) Reader saves reference to this domain into
-         *     "struct linux_binprm"->cred->security .
-         * (6) Reader finishes SRCU section, although execve() operation has
-         *     not finished yet.
-         * (7) Garbage collector waits for SRCU synchronization.
-         * (8) Garbage collector kfree() this domain because this domain is
-         *     used by nobody.
-         * (9) Reader finishes execve() operation and restores this domain from
-         *     "struct linux_binprm"->cred->security.
-         *
-         * By updating domain->users at (5), we can solve this race problem
-         * by rechecking domain->users at (8).
+         * Since this domain is referenced from neither
+         * "struct tomoyo_io_buffer" nor "struct cred"->security, we can delete
+         * elements without checking for is_deleted flag.
          */
-        if (atomic_read(&domain->users))
-                return false;
         list_for_each_entry_safe(acl, tmp, &domain->acl_info_list, list) {
                 tomoyo_del_acl(&acl->list);
                 tomoyo_memory_free(acl);
         }
         tomoyo_put_name(domain->domainname);
-        return true;
 }
 
 /**
@@ -416,10 +280,9 @@ void tomoyo_del_condition(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_name(struct list_head *element)
+static inline void tomoyo_del_name(struct list_head *element)
 {
-        const struct tomoyo_name *ptr =
-                container_of(element, typeof(*ptr), head.list);
+        /* Nothing to do. */
 }
 
 /**
@@ -429,7 +292,7 @@ static void tomoyo_del_name(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_path_group(struct list_head *element)
+static inline void tomoyo_del_path_group(struct list_head *element)
 {
         struct tomoyo_path_group *member =
                 container_of(element, typeof(*member), head.list);
@@ -443,7 +306,7 @@ static void tomoyo_del_path_group(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_group(struct list_head *element)
+static inline void tomoyo_del_group(struct list_head *element)
 {
         struct tomoyo_group *group =
                 container_of(element, typeof(*group), head.list);
@@ -469,10 +332,109 @@ static inline void tomoyo_del_address_group(struct list_head *element)
  *
  * Returns nothing.
  */
-static void tomoyo_del_number_group(struct list_head *element)
+static inline void tomoyo_del_number_group(struct list_head *element)
 {
-        struct tomoyo_number_group *member =
-                container_of(element, typeof(*member), head.list);
+        /* Nothing to do. */
+}
+
+/**
+ * tomoyo_try_to_gc - Try to kfree() an entry.
+ *
+ * @type:    One of values in "enum tomoyo_policy_id".
+ * @element: Pointer to "struct list_head".
+ *
+ * Returns nothing.
+ *
+ * Caller holds tomoyo_policy_lock mutex.
+ */
+static void tomoyo_try_to_gc(const enum tomoyo_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.
+         * tomoyo_domain_list). Also, synchronize_srcu() guarantees that the
+         * list element became no longer referenced by syscall users.
+         */
+        __list_del_entry(element);
+        mutex_unlock(&tomoyo_policy_lock);
+        synchronize_srcu(&tomoyo_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 tomoyo_io_buffer"->r.{domain,group,acl}
+         * and "struct tomoyo_io_buffer"->w.domain forget this element.
+         */
+        if (tomoyo_struct_used_by_io_buffer(element))
+                goto reinject;
+        switch (type) {
+        case TOMOYO_ID_TRANSITION_CONTROL:
+                tomoyo_del_transition_control(element);
+                break;
+        case TOMOYO_ID_MANAGER:
+                tomoyo_del_manager(element);
+                break;
+        case TOMOYO_ID_AGGREGATOR:
+                tomoyo_del_aggregator(element);
+                break;
+        case TOMOYO_ID_GROUP:
+                tomoyo_del_group(element);
+                break;
+        case TOMOYO_ID_PATH_GROUP:
+                tomoyo_del_path_group(element);
+                break;
+        case TOMOYO_ID_ADDRESS_GROUP:
+                tomoyo_del_address_group(element);
+                break;
+        case TOMOYO_ID_NUMBER_GROUP:
+                tomoyo_del_number_group(element);
+                break;
+        case TOMOYO_ID_CONDITION:
+                tomoyo_del_condition(element);
+                break;
+        case TOMOYO_ID_NAME:
+                /*
+                 * Don't kfree() until all "struct tomoyo_io_buffer"->r.w[]
+                 * forget this element.
+                 */
+                if (tomoyo_name_used_by_io_buffer
+                    (container_of(element, typeof(struct tomoyo_name),
+                                  head.list)->entry.name))
+                        goto reinject;
+                tomoyo_del_name(element);
+                break;
+        case TOMOYO_ID_ACL:
+                tomoyo_del_acl(element);
+                break;
+        case TOMOYO_ID_DOMAIN:
+                /*
+                 * Don't kfree() until all "struct cred"->security forget this
+                 * element.
+                 */
+                if (atomic_read(&container_of
+                                (element, typeof(struct tomoyo_domain_info),
+                                 list)->users))
+                        goto reinject;
+                tomoyo_del_domain(element);
+                break;
+        case TOMOYO_MAX_POLICY:
+                break;
+        }
+        mutex_lock(&tomoyo_policy_lock);
+        tomoyo_memory_free(element);
+        return;
+reinject:
+        /*
+         * We can safely reinject this element here bacause
+         * (1) Appending list elements and removing list elements are protected
+         *     by tomoyo_policy_lock mutex.
+         * (2) Only this function removes list elements and this function is
+         *     exclusively executed by tomoyo_gc_mutex mutex.
+         * are true.
+         */
+        mutex_lock(&tomoyo_policy_lock);
+        list_add_rcu(element, element->prev);
 }
 
 /**
@@ -481,19 +443,19 @@ static void tomoyo_del_number_group(struct list_head *element)
  * @id:          One of values in "enum tomoyo_policy_id".
  * @member_list: Pointer to "struct list_head".
  *
- * Returns true if some elements are deleted, false otherwise.
+ * Returns nothing.
  */
-static bool tomoyo_collect_member(const enum tomoyo_policy_id id,
+static void tomoyo_collect_member(const enum tomoyo_policy_id id,
                                   struct list_head *member_list)
 {
         struct tomoyo_acl_head *member;
-        list_for_each_entry(member, member_list, list) {
+        struct tomoyo_acl_head *tmp;
+        list_for_each_entry_safe(member, tmp, member_list, list) {
                 if (!member->is_deleted)
                         continue;
-                if (!tomoyo_add_to_gc(id, &member->list))
-                        return false;
+                member->is_deleted = TOMOYO_GC_IN_PROGRESS;
+                tomoyo_try_to_gc(id, &member->list);
         }
-        return true;
 }
 
 /**
@@ -501,22 +463,22 @@ static bool tomoyo_collect_member(const enum tomoyo_policy_id id,
  *
  * @list: Pointer to "struct list_head".
  *
- * Returns true if some elements are deleted, false otherwise.
+ * Returns nothing.
  */
-static bool tomoyo_collect_acl(struct list_head *list)
+static void tomoyo_collect_acl(struct list_head *list)
 {
         struct tomoyo_acl_info *acl;
-        list_for_each_entry(acl, list, list) {
+        struct tomoyo_acl_info *tmp;
+        list_for_each_entry_safe(acl, tmp, list, list) {
                 if (!acl->is_deleted)
                         continue;
-                if (!tomoyo_add_to_gc(TOMOYO_ID_ACL, &acl->list))
-                        return false;
+                acl->is_deleted = TOMOYO_GC_IN_PROGRESS;
+                tomoyo_try_to_gc(TOMOYO_ID_ACL, &acl->list);
         }
-        return true;
 }
 
 /**
- * tomoyo_collect_entry - Scan lists for deleted elements.
+ * tomoyo_collect_entry - Try to kfree() deleted elements.
  *
  * Returns nothing.
  */
@@ -525,36 +487,40 @@ static void tomoyo_collect_entry(void)
         int i;
         enum tomoyo_policy_id id;
         struct tomoyo_policy_namespace *ns;
-        int idx;
-        if (mutex_lock_interruptible(&tomoyo_policy_lock))
-                return;
-        idx = tomoyo_read_lock();
+        mutex_lock(&tomoyo_policy_lock);
         {
                 struct tomoyo_domain_info *domain;
-                list_for_each_entry_rcu(domain, &tomoyo_domain_list, list) {
-                        if (!tomoyo_collect_acl(&domain->acl_info_list))
-                                goto unlock;
+                struct tomoyo_domain_info *tmp;
+                list_for_each_entry_safe(domain, tmp, &tomoyo_domain_list,
+                                         list) {
+                        tomoyo_collect_acl(&domain->acl_info_list);
                         if (!domain->is_deleted || atomic_read(&domain->users))
                                 continue;
-                        /*
-                         * Nobody is referring this domain. But somebody may
-                         * refer this domain after successful execve().
-                         * We recheck domain->users after SRCU synchronization.
-                         */
-                        if (!tomoyo_add_to_gc(TOMOYO_ID_DOMAIN, &domain->list))
-                                goto unlock;
+                        tomoyo_try_to_gc(TOMOYO_ID_DOMAIN, &domain->list);
                 }
         }
-        list_for_each_entry_rcu(ns, &tomoyo_namespace_list, namespace_list) {
+        list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
                 for (id = 0; id < TOMOYO_MAX_POLICY; id++)
-                        if (!tomoyo_collect_member(id, &ns->policy_list[id]))
-                                goto unlock;
+                        tomoyo_collect_member(id, &ns->policy_list[id]);
                 for (i = 0; i < TOMOYO_MAX_ACL_GROUPS; i++)
-                        if (!tomoyo_collect_acl(&ns->acl_group[i]))
-                                goto unlock;
+                        tomoyo_collect_acl(&ns->acl_group[i]);
+        }
+        {
+                struct tomoyo_shared_acl_head *ptr;
+                struct tomoyo_shared_acl_head *tmp;
+                list_for_each_entry_safe(ptr, tmp, &tomoyo_condition_list,
+                                         list) {
+                        if (atomic_read(&ptr->users) > 0)
+                                continue;
+                        atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
+                        tomoyo_try_to_gc(TOMOYO_ID_CONDITION, &ptr->list);
+                }
+        }
+        list_for_each_entry(ns, &tomoyo_namespace_list, namespace_list) {
                 for (i = 0; i < TOMOYO_MAX_GROUP; i++) {
                         struct list_head *list = &ns->group_list[i];
                         struct tomoyo_group *group;
+                        struct tomoyo_group *tmp;
                         switch (i) {
                         case 0:
                                 id = TOMOYO_ID_PATH_GROUP;
@@ -566,139 +532,37 @@ static void tomoyo_collect_entry(void)
                                 id = TOMOYO_ID_ADDRESS_GROUP;
                                 break;
                         }
-                        list_for_each_entry(group, list, head.list) {
-                                if (!tomoyo_collect_member
-                                    (id, &group->member_list))
-                                        goto unlock;
+                        list_for_each_entry_safe(group, tmp, list, head.list) {
+                                tomoyo_collect_member(id, &group->member_list);
                                 if (!list_empty(&group->member_list) ||
-                                    atomic_read(&group->head.users))
+                                    atomic_read(&group->head.users) > 0)
                                         continue;
-                                if (!tomoyo_add_to_gc(TOMOYO_ID_GROUP,
-                                                      &group->head.list))
-                                        goto unlock;
+                                atomic_set(&group->head.users,
+                                           TOMOYO_GC_IN_PROGRESS);
+                                tomoyo_try_to_gc(TOMOYO_ID_GROUP,
+                                                 &group->head.list);
                         }
                 }
         }
-        id = TOMOYO_ID_CONDITION;
-        for (i = 0; i < TOMOYO_MAX_HASH + 1; i++) {
-                struct list_head *list = !i ?
-                        &tomoyo_condition_list : &tomoyo_name_list[i - 1];
+        for (i = 0; i < TOMOYO_MAX_HASH; i++) {
+                struct list_head *list = &tomoyo_name_list[i];
                 struct tomoyo_shared_acl_head *ptr;
-                list_for_each_entry(ptr, list, list) {
-                        if (atomic_read(&ptr->users))
+                struct tomoyo_shared_acl_head *tmp;
+                list_for_each_entry_safe(ptr, tmp, list, list) {
+                        if (atomic_read(&ptr->users) > 0)
                                 continue;
-                        if (!tomoyo_add_to_gc(id, &ptr->list))
-                                goto unlock;
+                        atomic_set(&ptr->users, TOMOYO_GC_IN_PROGRESS);
+                        tomoyo_try_to_gc(TOMOYO_ID_NAME, &ptr->list);
                 }
-                id = TOMOYO_ID_NAME;
         }
-unlock:
-        tomoyo_read_unlock(idx);
         mutex_unlock(&tomoyo_policy_lock);
 }
 
 /**
- * tomoyo_kfree_entry - Delete entries in tomoyo_gc_list.
- *
- * Returns true if some entries were kfree()d, false otherwise.
- */
-static bool tomoyo_kfree_entry(void)
-{
-        struct tomoyo_gc *p;
-        struct tomoyo_gc *tmp;
-        bool result = false;
-
-        list_for_each_entry_safe(p, tmp, &tomoyo_gc_list, list) {
-                struct list_head *element = p->element;
-
-                /*
-                 * list_del_rcu() in tomoyo_add_to_gc() guarantees that the
-                 * list element became no longer reachable from the list which
-                 * the element was originally on (e.g. tomoyo_domain_list).
-                 * Also, synchronize_srcu() in tomoyo_gc_thread() guarantees
-                 * that the list element became no longer referenced by syscall
-                 * users.
-                 *
-                 * However, there are three users which may still be using the
-                 * list element. We need to defer until all of these users
-                 * forget the list element.
-                 *
-                 * Firstly, defer until "struct tomoyo_io_buffer"->r.{domain,
-                 * group,acl} and "struct tomoyo_io_buffer"->w.domain forget
-                 * the list element.
-                 */
-                if (tomoyo_struct_used_by_io_buffer(element))
-                        continue;
-                /*
-                 * Secondly, defer until all other elements in the
-                 * tomoyo_gc_list list forget the list element.
-                 */
-                if (tomoyo_element_linked_by_gc((const u8 *) element, p->size))
-                        continue;
-                switch (p->type) {
-                case TOMOYO_ID_TRANSITION_CONTROL:
-                        tomoyo_del_transition_control(element);
-                        break;
-                case TOMOYO_ID_AGGREGATOR:
-                        tomoyo_del_aggregator(element);
-                        break;
-                case TOMOYO_ID_MANAGER:
-                        tomoyo_del_manager(element);
-                        break;
-                case TOMOYO_ID_CONDITION:
-                        tomoyo_del_condition(element);
-                        break;
-                case TOMOYO_ID_NAME:
-                        /*
-                         * Thirdly, defer until all "struct tomoyo_io_buffer"
-                         * ->r.w[] forget the list element.
-                         */
-                        if (tomoyo_name_used_by_io_buffer(
-                            container_of(element, typeof(struct tomoyo_name),
-                                         head.list)->entry.name, p->size))
-                                continue;
-                        tomoyo_del_name(element);
-                        break;
-                case TOMOYO_ID_ACL:
-                        tomoyo_del_acl(element);
-                        break;
-                case TOMOYO_ID_DOMAIN:
-                        if (!tomoyo_del_domain(element))
-                                continue;
-                        break;
-                case TOMOYO_ID_PATH_GROUP:
-                        tomoyo_del_path_group(element);
-                        break;
-                case TOMOYO_ID_ADDRESS_GROUP:
-                        tomoyo_del_address_group(element);
-                        break;
-                case TOMOYO_ID_GROUP:
-                        tomoyo_del_group(element);
-                        break;
-                case TOMOYO_ID_NUMBER_GROUP:
-                        tomoyo_del_number_group(element);
-                        break;
-                case TOMOYO_MAX_POLICY:
-                        break;
-                }
-                tomoyo_memory_free(element);
-                list_del(&p->list);
-                kfree(p);
-                tomoyo_gc_list_len--;
-                result = true;
-        }
-        return result;
-}
-
-/**
  * tomoyo_gc_thread - Garbage collector thread function.
  *
  * @unused: Unused.
  *
- * In case OOM-killer choose this thread for termination, we create this thread
- * as a short live thread whenever /sys/kernel/security/tomoyo/ interface was
- * close()d.
- *
  * Returns 0.
  */
 static int tomoyo_gc_thread(void *unused)
@@ -707,13 +571,7 @@ static int tomoyo_gc_thread(void *unused)
         static DEFINE_MUTEX(tomoyo_gc_mutex);
         if (!mutex_trylock(&tomoyo_gc_mutex))
                 goto out;
-
-        do {
-                tomoyo_collect_entry();
-                if (list_empty(&tomoyo_gc_list))
-                        break;
-                synchronize_srcu(&tomoyo_ss);
-        } while (tomoyo_kfree_entry());
+        tomoyo_collect_entry();
         {
                 struct tomoyo_io_buffer *head;
                 struct tomoyo_io_buffer *tmp;