galera.galera_var_slave_threads: Test failure: mysql_socket.h:779: mysqld got signal 6

./mtr --suite galera --force --big-test --max-test-fail=0 --parallel=auto

galera.galera_var_slave_threads 'innodb' w4 [ fail ]

mysqltest: At line 114: query 'SET GLOBAL wsrep_cluster_address=''' failed: 2013: Lost connection to MySQL server during query

The result from queries just before the failure was:

< snip >

SET GLOBAL wsrep_slave_threads = 1;

connection node_1;

connection node_2;

SELECT COUNT(*) FROM t2;

COUNT(*)

64

SELECT COUNT(*) FROM INFORMATION_SCHEMA.PROCESSLIST WHERE USER = 'system user' AND STATE LIKE '%wsrep aborter%';

COUNT(*)

1

SET GLOBAL wsrep_slave_threads = 5;

SET GLOBAL wsrep_slave_threads = 1;

connection node_2;

Shutting down server ...

connection node_1;

show status like 'wsrep_cluster_size';

Variable_name	Value

wsrep_cluster_size	1

SET GLOBAL wsrep_slave_threads = 6;

SET GLOBAL wsrep_slave_threads = 1;

SET GLOBAL wsrep_cluster_address='';

mysqld: /home/stepan/galera/git/10.4/server/include/mysql/psi/mysql_socket.h:779: inline_mysql_socket_recv: Assertion `mysql_socket.fd != -1' failed.

190227 13:48:16 [ERROR] mysqld got signal 6 ;