It will be free of concurrency bugs including deadlocks. This is the promise of CSP. The requirement is data is shared only via blocking IPC and never directly using a lock. (and similarly one must not share a pointer to private data, as another poster has pointed out)

You can compose small systems, even with multiple parties, prove they cannot deadlock, then make them a 'black box' with defined IO, and build larger, more complex systems with equal properties.

The downside is you must guard every piece of shared data with a separate thread, but there may be ways to reduce the performance penalty.