TOMOYO: Simplify garbage collector.

When TOMOYO started using garbage collector at commit 847b173 "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 2e503bb
"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>

security/tomoyo/common.h

@@ -52,6 +52,9 @@
 
 #define TOMOYO_EXEC_TMPSIZE     4096
 
+/* Garbage collector is trying to kfree() this element. */
+#define TOMOYO_GC_IN_PROGRESS -1
+
 /* Profile number is an integer between 0 and 255. */
 #define TOMOYO_MAX_PROFILES 256
 
@@ -398,7 +401,7 @@ enum tomoyo_pref_index {
 /* Common header for holding ACL entries. */
 struct tomoyo_acl_head {
 	struct list_head list;
-	bool is_deleted;
+	s8 is_deleted; /* true or false or TOMOYO_GC_IN_PROGRESS */
 } __packed;
 
 /* Common header for shared entries. */
@@ -665,7 +668,7 @@ struct tomoyo_condition {
 struct tomoyo_acl_info {
 	struct list_head list;
 	struct tomoyo_condition *cond; /* Maybe NULL. */
-	bool is_deleted;
+	s8 is_deleted; /* true or false or TOMOYO_GC_IN_PROGRESS */
 	u8 type; /* One of values in "enum tomoyo_acl_entry_type_index". */
 } __packed;
 

security/tomoyo/condition.c

@@ -400,8 +400,9 @@ static struct tomoyo_condition *tomoyo_commit_condition
 		found = true;
 		goto out;
 	}
-	list_for_each_entry_rcu(ptr, &tomoyo_condition_list, head.list) {
-		if (!tomoyo_same_condition(ptr, entry))
+	list_for_each_entry(ptr, &tomoyo_condition_list, head.list) {
+		if (!tomoyo_same_condition(ptr, entry) ||
+		    atomic_read(&ptr->head.users) == TOMOYO_GC_IN_PROGRESS)
 			continue;
 		/* Same entry found. Share this entry. */
 		atomic_inc(&ptr->head.users);
@@ -411,8 +412,7 @@ static struct tomoyo_condition *tomoyo_commit_condition
 	if (!found) {
 		if (tomoyo_memory_ok(entry)) {
 			atomic_set(&entry->head.users, 1);
-			list_add_rcu(&entry->head.list,
-				     &tomoyo_condition_list);
+			list_add(&entry->head.list, &tomoyo_condition_list);
 		} else {
 			found = true;
 			ptr = NULL;

security/tomoyo/domain.c

@@ -39,6 +39,8 @@ int tomoyo_update_policy(struct tomoyo_acl_head *new_entry, const int size,
 	if (mutex_lock_interruptible(&tomoyo_policy_lock))
 		return -ENOMEM;
 	list_for_each_entry_rcu(entry, list, list) {
+		if (entry->is_deleted == TOMOYO_GC_IN_PROGRESS)
+			continue;
 		if (!check_duplicate(entry, new_entry))
 			continue;
 		entry->is_deleted = param->is_delete;
@@ -115,6 +117,8 @@ int tomoyo_update_domain(struct tomoyo_acl_info *new_entry, const int size,
 	if (mutex_lock_interruptible(&tomoyo_policy_lock))
 		goto out;
 	list_for_each_entry_rcu(entry, list, list) {
+		if (entry->is_deleted == TOMOYO_GC_IN_PROGRESS)
+			continue;
 		if (!tomoyo_same_acl_head(entry, new_entry) ||
 		    !check_duplicate(entry, new_entry))
 			continue;