1 files changed, 24 insertions, 0 deletions
diff --git a/mysql-test/suite/innodb/t/foreign_key.test b/mysql-test/suite/innodb/t/foreign_key.test
index b586f3e9406..7a8a9295ee7 100644
--- a/mysql-test/suite/innodb/t/foreign_key.test
+++ b/mysql-test/suite/innodb/t/foreign_key.test
@@ -289,3 +289,27 @@ insert into t2(f1) values(1);
 drop table t2, t1;
 
 --source include/wait_until_count_sessions.inc
+
+#
+# MDEV-12669 Circular foreign keys cause a loop and OOM upon LOCK TABLE
+#
+SET FOREIGN_KEY_CHECKS=0;
+CREATE TABLE staff (
+  staff_id TINYINT UNSIGNED NOT NULL AUTO_INCREMENT,
+  store_id TINYINT UNSIGNED NOT NULL,
+  PRIMARY KEY  (staff_id),
+  KEY idx_fk_store_id (store_id),
+  CONSTRAINT fk_staff_store FOREIGN KEY (store_id) REFERENCES store (store_id) ON DELETE RESTRICT ON UPDATE CASCADE
+) ENGINE=InnoDB;
+CREATE TABLE store (
+  store_id TINYINT UNSIGNED NOT NULL AUTO_INCREMENT,
+  manager_staff_id TINYINT UNSIGNED NOT NULL,
+  PRIMARY KEY  (store_id),
+  UNIQUE KEY idx_unique_manager (manager_staff_id),
+  CONSTRAINT fk_store_staff FOREIGN KEY (manager_staff_id) REFERENCES staff (staff_id) ON DELETE RESTRICT ON UPDATE CASCADE
+) ENGINE=InnoDB;
+SET FOREIGN_KEY_CHECKS=DEFAULT;
+
+LOCK TABLE staff WRITE;
+UNLOCK TABLES;
+DROP TABLES staff, store;