MDEV-27006 Assertion `!lock_trx_has_sys_table_locks(trx)' failed in dberr_t row_discard_tablespace_for_mysql(dict_table_t*, trx_t*)

- InnoDB import operation fails when it tries to unlock data
dictionary lock before releasing the lock on system tables.

Author: Thirunarayanan

mysql-test/suite/innodb/r/import_bugs.result

@@ -10,3 +10,11 @@ ALTER TABLE imp_t1 IMPORT TABLESPACE;
 ERROR HY000: Schema mismatch (ROW_FORMAT mismatch)
 DROP TABLE imp_t1, t1;
 SET GLOBAL innodb_checksum_algorithm=@save_innodb_checksum_algorithm;
+#
+# MDEV-27006 Assertion `!lock_trx_has_sys_table_locks(trx)' --echo #	failed in dberr_t row_discard_tablespace_for_mysql
+#		(dict_table_t*, trx_t*)
+CREATE TABLE t1 (c INT KEY) ENGINE=INNODB;
+CREATE TABLE t2 (c INT KEY,FOREIGN KEY(c) REFERENCES t1 (c)) ENGINE=INNODB;
+ALTER TABLE t1 DISCARD TABLESPACE;
+ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails
+DROP TABLE t2, t1;

mysql-test/suite/innodb/t/import_bugs.test

@@ -18,3 +18,12 @@ DROP TABLE imp_t1, t1;
 --remove_file $datadir/test/imp_t1.ibd
 
 SET GLOBAL innodb_checksum_algorithm=@save_innodb_checksum_algorithm;
+
+--echo #
+--echo # MDEV-27006 Assertion `!lock_trx_has_sys_table_locks(trx)' --echo #	failed in dberr_t row_discard_tablespace_for_mysql
+--echo #		(dict_table_t*, trx_t*)
+CREATE TABLE t1 (c INT KEY) ENGINE=INNODB;
+CREATE TABLE t2 (c INT KEY,FOREIGN KEY(c) REFERENCES t1 (c)) ENGINE=INNODB;
+--error ER_ROW_IS_REFERENCED_2
+ALTER TABLE t1 DISCARD TABLESPACE;
+DROP TABLE t2, t1;

storage/innobase/row/row0mysql.cc

@@ -2495,6 +2495,7 @@ dberr_t row_discard_tablespace_for_mysql(dict_table_t *table, trx_t *trx)
         fts_optimize_add_table(table);
       }
       trx->rollback();
+      row_mysql_unlock_data_dictionary(trx);
       return err;
     }
   }
@@ -2508,10 +2509,7 @@ dberr_t row_discard_tablespace_for_mysql(dict_table_t *table, trx_t *trx)
 
   err= row_discard_tablespace_foreign_key_checks(trx, table);
   if (err != DB_SUCCESS)
-  {
-    row_mysql_unlock_data_dictionary(trx);
     goto rollback;
-  }
 
   /* Note: The following cannot be rolled back. Rollback would see the
   UPDATE of SYS_INDEXES.TABLE_ID as two operations: DELETE and INSERT.