MDEV-29002 Spider: remove SPIDER_CONN::loop_check_meraged_last

The field is assigned but unused, and it causes heap-use-after-free.

storage/spider/mysql-test/spider/bugfix/r/mdev_29002.result

+for master_1
+for child2
+for child3
+SET spider_same_server_link= on;
+CREATE SERVER s FOREIGN DATA WRAPPER mysql
+OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+CREATE TABLE t (a INT);
+CREATE TABLE t1_spider (a INT) ENGINE=SPIDER COMMENT = "wrapper 'mysql', srv 's', table 't'";
+CREATE TABLE t2_spider (a INT) ENGINE=SPIDER COMMENT = "wrapper 'mysql', srv 's', table 't'";
+SELECT * FROM t1_spider, t2_spider;
+a	a
+SELECT table_name, index_name, cardinality FROM INFORMATION_SCHEMA.STATISTICS WHERE table_name IN ('t1_spider','t2_spider');
+table_name	index_name	cardinality
+RENAME TABLE t1_spider TO t3_spider;
+SELECT * FROM t3_spider;
+a
+DROP TABLE t3_spider, t2_spider, t;
+drop server s;
+CREATE TABLE t1 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+CREATE TABLE t2 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+CREATE TABLE t3 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+SHOW TABLE STATUS;
+Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment	Max_index_length	Temporary
+t1	SPIDER	10		NULL	0	0	0	0	0	NULL	NULL	NULL	NULL	latin1_swedish_ci	NULL		Unable to connect to foreign data source: srv	0	
+t2	SPIDER	10		NULL	0	0	0	0	0	NULL	NULL	NULL	NULL	latin1_swedish_ci	NULL		Unable to connect to foreign data source: srv	0	
+t3	SPIDER	10		NULL	0	0	0	0	0	NULL	NULL	NULL	NULL	latin1_swedish_ci	NULL		Unable to connect to foreign data source: srv	0	
+Warnings:
+Warning	1429	Unable to connect to foreign data source: srv
+Warning	1429	Unable to connect to foreign data source: srv
+Warning	1429	Unable to connect to foreign data source: srv
+drop table t1, t2, t3;
+for master_1
+for child2
+for child3

storage/spider/mysql-test/spider/bugfix/t/mdev_29002.test

+--disable_query_log
+--disable_result_log
+--source ../../t/test_init.inc
+--enable_result_log
+--enable_query_log
+SET spider_same_server_link= on;
+evalp CREATE SERVER s FOREIGN DATA WRAPPER mysql
+OPTIONS (SOCKET "$MASTER_1_MYSOCK", DATABASE 'test',user 'root');
+
+CREATE TABLE t (a INT);
+CREATE TABLE t1_spider (a INT) ENGINE=SPIDER COMMENT = "wrapper 'mysql', srv 's', table 't'";
+CREATE TABLE t2_spider (a INT) ENGINE=SPIDER COMMENT = "wrapper 'mysql', srv 's', table 't'";
+SELECT * FROM t1_spider, t2_spider;
+SELECT table_name, index_name, cardinality FROM INFORMATION_SCHEMA.STATISTICS WHERE table_name IN ('t1_spider','t2_spider');
+RENAME TABLE t1_spider TO t3_spider;
+SELECT * FROM t3_spider;
+
+DROP TABLE t3_spider, t2_spider, t;
+drop server s;
+
+# case by roel
+CREATE TABLE t1 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+CREATE TABLE t2 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+CREATE TABLE t3 (c INT) ENGINE=Spider COMMENT='WRAPPER "mysql",HOST "srv",TABLE "t"';
+SHOW TABLE STATUS;
+drop table t1, t2, t3;
+
+--disable_query_log
+--disable_result_log
+--source ../../t/test_deinit.inc
+--enable_result_log
+--enable_query_log

storage/spider/spd_conn.cc

@@ -1783,13 +1783,7 @@ int spider_conn_queue_and_merge_loop_check(
     lcptr->flag = SPIDER_LOP_CHK_MERAGED;
     lcptr->next = NULL;
     if (!conn->loop_check_meraged_first)
-    {
       conn->loop_check_meraged_first = lcptr;
-      conn->loop_check_meraged_last = lcptr;
-    } else {
-      conn->loop_check_meraged_last->next = lcptr;
-      conn->loop_check_meraged_last = lcptr;
-    }
   }
   DBUG_RETURN(0);
 

storage/spider/spd_include.h

@@ -940,7 +940,6 @@ typedef struct st_spider_conn
   SPIDER_CONN_LOOP_CHECK *loop_check_ignored_first;
   SPIDER_CONN_LOOP_CHECK *loop_check_ignored_last;
   SPIDER_CONN_LOOP_CHECK *loop_check_meraged_first;
-  SPIDER_CONN_LOOP_CHECK *loop_check_meraged_last;
 } SPIDER_CONN;
 
 typedef struct st_spider_lgtm_tblhnd_share