I got this stack trace when shutting down dockerd:

https://gist.github.com/aaronlehmann/5b80c6b9d7beca9f2835aa96e14dd4a7

It looks like GracefulStop is hanging, probably because it's waiting for the handler for a streaming events Watch RPC to finish. This RPC handler needs to terminate when the server is shut down.

cc @LK4D4 @dongluochen