Deadlock in TestCSLocker.java due to blocking GC while allocating

The following test timed out in the JDK21 CI:

gc/cslocker/TestCSLocker.java

Here's a snippet from the log file:

#section:main
----------messages:(8/332)----------
command: main -Xmx256m gc.cslocker.TestCSLocker
reason: User specified action: run main/native/othervm -Xmx256m gc.cslocker.TestCSLocker
started: Sun May 14 00:09:45 UTC 2023
Mode: othervm [/othervm specified]
Timeout information:
--- Timeout information end.
finished: Sun May 14 00:21:43 UTC 2023
elapsed time (seconds): 718.384
----------configuration:(0/0)----------
----------System.out:(2/38)----------
sleeping...
Timeout refired 480 times
----------System.err:(0/0)----------
----------rerun:(39/7096)*----------

<snip>

result: Error. Program `/opt/mach5/mesos/work_dir/jib-master/install/jdk-21+23-1940/linux-x64.jdk/jdk-21/bin/java' timed out (timeout set to 480000ms, elapsed time including timeout handling was 718378ms).

The test task's JVM args are:
-XX:+UseZGC -XX:+ZGenerational