Fix for CONC-154:

set stmt->state to MYSQL_STMT_FETCH_DONE if
  - result set is empty (nothing to fetch)
  - when madb_stmt_reset was called

libmariadb/my_stmt.c

@@ -1377,8 +1377,12 @@ int STDCALL mysql_stmt_store_result(MYSQL_STMT *stmt)
 
   stmt->result_cursor= stmt->result.data;
   stmt->fetch_row_func= stmt_buffered_fetch;
-  stmt->mysql->status= MYSQL_STATUS_READY; 
+  stmt->mysql->status= MYSQL_STATUS_READY;
-  stmt->state= MYSQL_STMT_USE_OR_STORE_CALLED;
+
+  if (!stmt->result.rows)
+    stmt->state= MYSQL_STMT_FETCH_DONE;
+  else
+    stmt->state= MYSQL_STMT_USE_OR_STORE_CALLED;
 
   /* set affected rows: see bug 2247 */
   stmt->upsert_status.affected_rows= stmt->result.rows;
@@ -1643,6 +1647,7 @@ static my_bool madb_reset_stmt(MYSQL_STMT *stmt, unsigned int flags)
       stmt->result.rows= 0;
       stmt->result_cursor= NULL;
       stmt->mysql->status= MYSQL_STATUS_READY;
+      stmt->state= MYSQL_STMT_FETCH_DONE;
     }
 
     /* if there is a pending result set, we will flush it */

unittest/libmariadb/ps_bugs.c

@@ -3909,7 +3909,111 @@ static int test_conc141(MYSQL *mysql)
   return OK;
 }
 
+static int test_conc154(MYSQL *mysql)
+{
+  MYSQL_STMT *stmt;
+  const char *stmtstr= "SELECT * FROM t1";
+  int rc;
+
+  /* 1st: empty result set without free_result */
+  rc= mysql_query(mysql, "DROP TABLE IF EXISTS t1");
+  check_mysql_rc(rc, mysql);
+  rc= mysql_query(mysql, "CREATE TABLE t1 (a varchar(20))");
+  check_mysql_rc(rc, mysql);
+
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, stmtstr, strlen(stmtstr));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_close(stmt);
+
+  /* 2nd: empty result set with free_result */
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, stmtstr, strlen(stmtstr));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_free_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+  rc= mysql_stmt_free_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_close(stmt);
+
+  /* 3rd: non empty result without free_result */
+  rc= mysql_query(mysql, "INSERT INTO t1 VALUES ('test_conc154')");
+  check_mysql_rc(rc, mysql);
+
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, stmtstr, strlen(stmtstr));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_close(stmt);
+
+  /* 4th non empty result set with free_result */
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, stmtstr, strlen(stmtstr));
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_free_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_execute(stmt);
+  check_stmt_rc(rc, stmt);
+
+  rc= mysql_stmt_store_result(stmt);
+  check_stmt_rc(rc, stmt);
+  rc= mysql_stmt_free_result(stmt);
+  check_stmt_rc(rc, stmt);
+
+  mysql_stmt_close(stmt);
+
+  return OK;
+}
+
 struct my_tests_st my_tests[] = {
+  {"test_conc154", test_conc154, TEST_CONNECTION_DEFAULT, 0, NULL , NULL},
   {"test_conc141", test_conc141, TEST_CONNECTION_NEW, 0, NULL , NULL},
   {"test_conc67", test_conc67, TEST_CONNECTION_DEFAULT, 0, NULL , NULL},
   {"test_conc_5", test_conc_5, TEST_CONNECTION_DEFAULT, 0, NULL , NULL},