Code review comment for lp:~alan-griffiths/mir/fix-1526248

There's a lock order inversion report (with a TSan build)

but It looks benign since the only time the locks in question are acquired in different order is during surface creation.

During creation:

Callback MirSurface::created is invoked
-locks MirSurface::mutex
-calls buffer_stream_factory->make_producer_stream
--calls MirConnection::on_stream_created
---calls ConnectionSurfaceMap::insert
----write locks ConnectionSurfaceMap::guard

During normal operation:

MirProtobufRpcChannel::process_event_sequence
-calls ConnectionSurfaceMap::with_surface_do
--Read locks ConnectionSurfaceMap::guard
---Invokes callback which does MirSurface::handle_event
----locks MirSurface::mutex

http://paste.ubuntu.com/14054652/

I don't think the buffer stream creation needs to be done with a locked MirSurface::mutex; We should take a closer look at the uses of MirSurface::mutex, some don't seem necessary -but that's a separate issue outside the scope of this MP.