OK, if we're going to discuss what this comment should be here, let's keep this constructive and on topic (the content of what the documentation should be). I propose this wording:

> * C code should carefully consider whether it could intentionally block the thread in some syscall (not all rust tasks are prepared for arbitrarily blocking).

In my opinion, libstd has nothing to do with this wording. Additionally, this is factually true of all calls to C code, so I don't understand where you concern is about this wording. Perhaps it needs more explanation below?

Are you opposed to this wording or would you want to revise it?