"Be careful with mutexes" is good advice, but I'm surprised it doesn't explicitly call out the various channels that tokio provides as alternatives (detailed here: https://docs.rs/tokio/latest/tokio/sync/index.html). There are a variety of options that fit different use cases, and you don't even need to enable the runtime feature to use them (e.g. if you want to do a single check for completion rather than await). I'd estimate that at least half of the bottlenecks I've seen with mutexes when using tokio could have been avoided by not even using a mutex at all and instead passing the data that's truly needed across different tasks with some type of channel.
The other trick I've used a few times that's a bit hacky but can get the job done is when reading a snapshot of the data under a mutex is enough without needing to prevent other changes; if that's the case, you can just clone the data and drop the mutex to allow other uses move forward at the cost of the data potentially being stale.
The other trick I've used a few times that's a bit hacky but can get the job done is when reading a snapshot of the data under a mutex is enough without needing to prevent other changes; if that's the case, you can just clone the data and drop the mutex to allow other uses move forward at the cost of the data potentially being stale.