Killed connection threads might get their sockets closed twice on shutdown

[Laurynas Biveinis]

This shows up as a Valgrind warning

==18197== Warning: invalid file descriptor -1 in syscall close()
==18197== at 0x5F6E5BD: ??? (syscall-template.S:84)
==18197== by 0xF95F34: inline_mysql_socket_close (mysql_socket.h:1090)
==18197== by 0xF96AF3: vio_shutdown (viosocket.c:490)
==18197== by 0x7C6BE0: THD::disconnect() (sql_class.cc:2057)
==18197== by 0x637486: close_connection(THD*, unsigned int) (mysqld.cc:2886)
==18197== by 0x7D63E3: do_handle_one_connection(THD*) (sql_connect.cc:1547)
==18197== by 0x7D5E57: handle_one_connection (sql_connect.cc:1444)
==18197== by 0xB98416: pfs_spawn_thread (pfs.cc:1860)
==18197== by 0x5F656F9: start_thread (pthread_create.c:333)
==18197== by 0x6B22B5C: clone (clone.S:109)

on e.g.

rpl.rpl_semi_sync_shutdown_hang 'mix' [ fail ] Found warnings/errors in server log file!
rpl.rpl_gtid_mts_relay_log_recovery_auto_pos_on_off 'mix' w3 [ fail ] Found warnings/errors in server log file!
rpl.rpl_report_port 'mix' w1 [ fail ] Found warnings/errors in server log file!
rpl.rpl_recovery_replicate_same_server_id 'mix' w4 [ fail ] Found warnings/errors in server log file!
rpl.rpl_change_master_crash_safe 'mix' w2 [ fail ] Found warnings/errors in server log file!
rpl.rpl_change_master 'mix' w1 [ fail ] Found warnings/errors in server log file!
rpl.rpl_alter_repository 'mix' w3 [ fail ] Found warnings/errors in server log file!
rpl.rpl_gtid_deployment_step 'mix' w1 [ fail ] Found warnings/errors in server log file!
rpl.rpl_recovery_replicate_same_server_id 'row' w4 [ fail ] Found warnings/errors in server log file!
main.mysql_client_test w4 [ fail ] Found warnings/errors in server log file!
auth_sec.mysql_native_plugin w3 [ fail ] Found warnings/errors in server log file!

The reason is that THD::disconnect is getting called twice, once from server thread-killing thread:
kill_server_threads -> kill_server -> close_connections -> close_connection -> THD::disconnect;
and the second time from the query thread itself, as in the above stacktrace.

[Laurynas Biveinis (laurynas-biveinis)]

https://github.com/percona/percona-server/pull/500, https://github.com/percona/percona-server/pull/501

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-3429