almost always, the recommendation is to not embed your mutex; give it a name.
foo.mu.Lock()
This way you don't expose your primitives, preventing poor usage from causing a deadlock. Generally you don't want the user of your struct to have to know when or when to not lock.
Alas, locks don't compose, ie often your users will have to know about the internals when you are using locks.
But it's good advice when it works.