MDEV-19384 Deadlock in FTWRL

The deadlock happened between FTWRL under open HANDLER, LOCK TABLE and
DROP DATABASE

Fixed by reverting the previous fix for handler open in
lock_global_read_lock()

Fixed the original (wrong) test case in flush_read_lock.test to be
repeatable.

mysql-test/main/flush_read_lock.result

@@ -1677,6 +1677,8 @@ set global sql_mode=default;
 # Deadlock between FTWRL under open handler and DDL/LOCK TABLES
 #
 CREATE TABLE t1(a INT);
+#
+connect  con3,localhost,root,,;
 HANDLER t1 OPEN;
 #
 connect  con1,localhost,root,,;
@@ -1692,7 +1694,10 @@ disconnect con2;
 connection default;
 FLUSH TABLES WITH READ LOCK;
 UNLOCK TABLES;
+#
+connection con3;
 HANDLER t1 CLOSE;
+disconnect con3;
 #
 connection con1;
 UNLOCK TABLES;
@@ -1727,3 +1732,31 @@ disconnect con1;
 connection default;
 DROP TABLE t1;
 SET DEBUG_SYNC= 'RESET';
+#
+# MDEV-19384 Deadlock between FTWRL under open HANDLER, LOCK TABLE
+# and DROP DATABASE
+#
+CREATE DATABASE mysqltest;
+CREATE TABLE mysqltest.t1(a INT);
+HANDLER mysqltest.t1 OPEN as t1;
+connect  con1,localhost,root,,;
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+LOCK TABLE mysqltest.t1 WRITE;
+connect  con2,localhost,root,,;
+SET DEBUG_SYNC= 'now WAIT_FOR ready';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+DROP DATABASE mysqltest;
+connect  con3,localhost,root,,;
+SET DEBUG_SYNC= 'now WAIT_FOR ready';
+disconnect con3;
+connection default;
+FLUSH TABLES WITH READ LOCK;
+UNLOCK TABLES;
+HANDLER t1 CLOSE;
+connection con1;
+UNLOCK TABLES;
+disconnect con1;
+connection con2;
+disconnect con2;
+connection default;
+SET DEBUG_SYNC= 'RESET';

mysql-test/main/flush_read_lock.test

@@ -2023,6 +2023,9 @@ set global sql_mode=default;
 --echo # Deadlock between FTWRL under open handler and DDL/LOCK TABLES
 --echo #
 CREATE TABLE t1(a INT);
+
+--echo #
+connect (con3,localhost,root,,);
 HANDLER t1 OPEN;
 
 --echo #
@@ -2041,7 +2044,11 @@ disconnect con2;
 connection default;
 FLUSH TABLES WITH READ LOCK;
 UNLOCK TABLES;
+
+--echo #
+connection con3;
 HANDLER t1 CLOSE;
+disconnect con3;
 
 --echo #
 connection con1;
@@ -2087,3 +2094,40 @@ disconnect con1;
 connection default;
 DROP TABLE t1;
 SET DEBUG_SYNC= 'RESET';
+
+--echo #
+--echo # MDEV-19384 Deadlock between FTWRL under open HANDLER, LOCK TABLE
+--echo # and DROP DATABASE
+--echo #
+
+CREATE DATABASE mysqltest;
+CREATE TABLE mysqltest.t1(a INT);
+HANDLER mysqltest.t1 OPEN as t1;
+
+connect (con1,localhost,root,,);
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+--send LOCK TABLE mysqltest.t1 WRITE
+connect (con2,localhost,root,,);
+SET DEBUG_SYNC= 'now WAIT_FOR ready';
+SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL ready';
+--send DROP DATABASE mysqltest
+
+connect (con3,localhost,root,,);
+SET DEBUG_SYNC= 'now WAIT_FOR ready';
+disconnect con3;
+
+connection default;
+FLUSH TABLES WITH READ LOCK;
+UNLOCK TABLES;
+HANDLER t1 CLOSE;
+connection con1;
+
+--error 0,ER_NO_SUCH_TABLE
+reap;
+UNLOCK TABLES;
+disconnect con1;
+connection con2;
+reap;
+disconnect con2;
+connection default;
+SET DEBUG_SYNC= 'RESET';

sql/lock.cc

@@ -1029,6 +1029,12 @@ bool Global_read_lock::lock_global_read_lock(THD *thd)
       DBUG_RETURN(1);
     }
 
+    /*
+      Release HANDLER OPEN by the current THD as they may cause deadlocks
+      if another thread is trying to simultaneous drop the table
+    */
+    mysql_ha_cleanup_no_free(thd);
+
     DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::BACKUP, "", "",
                                                  MDL_BACKUP_FTWRL1));
     DBUG_ASSERT(! thd->mdl_context.is_lock_owner(MDL_key::BACKUP, "", "",
@@ -1050,9 +1056,6 @@ bool Global_read_lock::lock_global_read_lock(THD *thd)
 
     m_mdl_global_read_lock= mdl_request.ticket;
     m_state= GRL_ACQUIRED;
-
-    /* Release HANDLER OPEN after we have got our MDL lock */
-    mysql_ha_cleanup_no_free(thd);
   }
   /*
     We DON'T set global_read_lock_blocks_commit now, it will be set after