The information about current owners of Hotspot Mutex is often very useful for dealock investigations.

The jcmd usually doesn't work because VM can't reach or exit safepoints. So it doesn't respond to jcmd.

The SA 'jstack --mixed' provides information about stacktraces on Java and non-Java Threads. So having information about locks along with stack traces might significantly help to identify issues.

The gdb allows to provide stacktraces, but the debug symbols are required to get info about locks. These symbols are often absent during execution.
Also the debugger solution is OS specifc.