Removed redundant SE lock for tmp tables

CREATE TEMPORARY TABLE locks SE plugin 6 times. 5 of these locks are
released by the end of the statement. And only 1 acquired by
init_from_binary_frm_image() / plugin_lock() remains.

The lock removed in this patch was clearly redundant.

Part of MDEV-17805 - Remove InnoDB cache for temporary tables.

mysql-test/main/plugin.result

@@ -378,3 +378,18 @@ select PLUGIN_NAME,PLUGIN_STATUS,PLUGIN_TYPE from information_schema.plugins whe
 PLUGIN_NAME	PLUGIN_STATUS	PLUGIN_TYPE
 UNINSTALL SONAME 'ha_example';
 ERROR 42000: SONAME ha_example.so does not exist
+#
+# Make sure temporary tables maintain plugin references properly
+#
+INSTALL PLUGIN example SONAME 'ha_example';
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=example;
+UNINSTALL PLUGIN example;
+Warnings:
+Warning	1620	Plugin is busy and will be uninstalled on shutdown
+INSTALL PLUGIN example SONAME 'ha_example';
+ERROR HY000: Plugin 'example' already installed
+DROP TABLE t1;
+INSTALL PLUGIN example SONAME 'ha_example';
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=example;
+DROP TABLE t1;
+UNINSTALL PLUGIN example;

mysql-test/main/plugin.test

@@ -267,3 +267,19 @@ RENAME TABLE t1 TO t2;
 DROP TABLE t1;
 
 --source include/install_plugin_if_exists.inc
+
+
+--echo #
+--echo # Make sure temporary tables maintain plugin references properly
+--echo #
+INSTALL PLUGIN example SONAME 'ha_example';
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=example;
+UNINSTALL PLUGIN example;
+--error ER_PLUGIN_INSTALLED
+INSTALL PLUGIN example SONAME 'ha_example';
+DROP TABLE t1;
+
+INSTALL PLUGIN example SONAME 'ha_example';
+CREATE TEMPORARY TABLE t1(a INT) ENGINE=example;
+DROP TABLE t1;
+UNINSTALL PLUGIN example;

sql/sql_class.h

@@ -4738,8 +4738,7 @@ class THD: public THD_count, /* this must be first */
   };
   bool has_thd_temporary_tables();
 
-  TABLE *create_and_open_tmp_table(handlerton *hton,
-                                   LEX_CUSTRING *frm,
+  TABLE *create_and_open_tmp_table(LEX_CUSTRING *frm,
                                    const char *path,
                                    const char *db,
                                    const char *table_name,
@@ -4780,7 +4779,7 @@ class THD: public THD_count, /* this must be first */
   bool has_temporary_tables();
   uint create_tmp_table_def_key(char *key, const char *db,
                                 const char *table_name);
-  TMP_TABLE_SHARE *create_temporary_table(handlerton *hton, LEX_CUSTRING *frm,
+  TMP_TABLE_SHARE *create_temporary_table(LEX_CUSTRING *frm,
                                           const char *path, const char *db,
                                           const char *table_name);
   TABLE *find_temporary_table(const char *key, uint key_length,

sql/sql_table.cc

@@ -5039,9 +5039,9 @@ int create_table_impl(THD *thd, const LEX_CSTRING &orig_db,
   create_info->table= 0;
   if (!frm_only && create_info->tmp_table())
   {
-    TABLE *table= thd->create_and_open_tmp_table(create_info->db_type, frm,
-                                                 path, db.str,
-                                                 table_name.str, true, false);
+    TABLE *table= thd->create_and_open_tmp_table(frm, path, db.str,
+                                                 table_name.str, true,
+                                                 false);
 
     if (!table)
     {
@@ -9863,7 +9863,7 @@ do_continue:;
     DBUG_ASSERT(!table->s->tmp_table);
 
     if (!(altered_table=
-          thd->create_and_open_tmp_table(new_db_type, &frm,
+          thd->create_and_open_tmp_table(&frm,
                                          alter_ctx.get_tmp_path(),
                                          alter_ctx.new_db.str,
                                          alter_ctx.new_name.str,
@@ -9990,8 +9990,8 @@ do_continue:;
   no_ha_table= false;
 
   /* Open the table since we need to copy the data. */
-  new_table=
-    thd->create_and_open_tmp_table(new_db_type, &frm, alter_ctx.get_tmp_path(),
+  new_table= thd->create_and_open_tmp_table(&frm,
+                                            alter_ctx.get_tmp_path(),
                                             alter_ctx.new_db.str,
                                             alter_ctx.new_name.str,
                                             true, true);

sql/temporary_tables.cc

@@ -49,7 +49,6 @@ bool THD::has_thd_temporary_tables()
 /**
   Create a temporary table, open it and return the TABLE handle.
 
-  @param hton [IN]                    Handlerton
   @param frm  [IN]                    Binary frm image
   @param path [IN]                    File path (without extension)
   @param db   [IN]                    Schema name
@@ -60,8 +59,7 @@ bool THD::has_thd_temporary_tables()
   @return Success                     A pointer to table object
           Failure                     NULL
 */
-TABLE *THD::create_and_open_tmp_table(handlerton *hton,
-                                      LEX_CUSTRING *frm,
+TABLE *THD::create_and_open_tmp_table(LEX_CUSTRING *frm,
                                       const char *path,
                                       const char *db,
                                       const char *table_name,
@@ -73,7 +71,7 @@ TABLE *THD::create_and_open_tmp_table(handlerton *hton,
   TMP_TABLE_SHARE *share;
   TABLE *table= NULL;
 
-  if ((share= create_temporary_table(hton, frm, path, db, table_name)))
+  if ((share= create_temporary_table(frm, path, db, table_name)))
   {
     open_options|= HA_OPEN_FOR_CREATE;
     table= open_temporary_table(share, table_name, open_in_engine);
@@ -905,7 +903,6 @@ uint THD::create_tmp_table_def_key(char *key, const char *db,
 /**
   Create a temporary table.
 
-  @param hton [IN]                    Handlerton
   @param frm  [IN]                    Binary frm image
   @param path [IN]                    File path (without extension)
   @param db   [IN]                    Schema name
@@ -914,8 +911,7 @@ uint THD::create_tmp_table_def_key(char *key, const char *db,
   @return Success                     A pointer to table share object
           Failure                     NULL
 */
-TMP_TABLE_SHARE *THD::create_temporary_table(handlerton *hton,
-                                             LEX_CUSTRING *frm,
+TMP_TABLE_SHARE *THD::create_temporary_table(LEX_CUSTRING *frm,
                                              const char *path,
                                              const char *db,
                                              const char *table_name)
@@ -953,8 +949,6 @@ TMP_TABLE_SHARE *THD::create_temporary_table(handlerton *hton,
   init_tmp_table_share(this, share, saved_key_cache, key_length,
                        strend(saved_key_cache) + 1, tmp_path);
 
-  share->db_plugin= ha_lock_engine(this, hton);
-
   /*
     Prefer using frm image over file. The image might not be available in
     ALTER TABLE, when the discovering engine took over the ownership (see