rpl.rpl_shutdown_wait_semisync_slaves fails: "Master server does not read semi-sync messages" error in slave log

rpl.rpl_shutdown_wait_semisync_slaves fails on 12.3 with Found warnings/errors in server log file!: the slave error log contains the ERROR line Master server does not read semi-sync messages.

Build Run Info

Failure text

rpl.rpl_shutdown_wait_semisync_slaves 'row' w21 [ fail ]  Found warnings/errors in server log file!

        Test ended at 2026-10-06 15:34:36

line

2026-10-06 15:34:29 8 [ERROR] Master server does not read semi-sync messages last_error:  (1160). Fallback to asynchronous replication

^ Found warnings in /home/buildbot/amd64-ubuntu-2204-debug/build/mysql-test/var/21/log/mysqld.2.err

ok

 - saving '/home/buildbot/amd64-ubuntu-2204-debug/build/mysql-test/var/21/log/rpl.rpl_shutdown_wait_semisync_slaves-row/' to '/home/buildbot/amd64-ubuntu-2204-debug/build/mysql-test/var/log/rpl.rpl_shutdown_wait_semisync_slaves-row/'

Retrying test rpl.rpl_shutdown_wait_semisync_slaves, attempt(2/3)...

The failure text is identical in the other two matching runs between 2026-10-02 and 2026-10-09, apart from worker id, timestamps, paths and variant: bb-10.11-pranav-MDEV-39343 on s390x-ubuntu-2204-debug (2026-10-05T11:21:58Z, variant row) and refs/pull/4817/head on amd64-ubuntu-2204-debug-ps (2026-10-06T10:08:38Z, variant stmt).

Analysis

Three distinct builders on two architectures are affected (amd64-ubuntu-2204-debug, amd64-ubuntu-2204-debug-ps and s390x-ubuntu-2204-debug), which points at the test rather than at a builder. The slave IO thread logs this message at ERROR level in sql/slave.cc when Repl_semi_sync_slave::slave_reply() fails and the thread was not killed. The test runs SHUTDOWN WAIT FOR ALL SLAVES on the master while semi-sync is enabled on the master and on server_2 and server_3, so a slave that sends its ACK after the master has closed the connection most likely takes this path; the log line reports error 1160 (ER_NET_ERROR_ON_WRITE). The test suppresses only Timeout waiting for reply of binlog on the master, while rpl_semi_sync_slave_reply_fail suppresses Master server does not read semi-sync messages*. The same message for a stopping slave was handled in MDEV-32943, and the code path is analysed in MDEV-40958.

Created via the mtr-failure-bug skill.