prevent linux thread from being interrupted by scheduler

How do you tell the thread scheduler in linux to not interrupt your thread for any reason?

Can't really be done, you need a real time system for that. The closes thing you'll get with linux is to set the scheduling policy to a realtime scheduler, e.g. SCHED_FIFO, and also set the PTHREAD_EXPLICIT_SCHED attribute. See e.g. here , even now though, e.g. irq handlers and other other stuff will interrupt your thread and run.

However, if you only care about the threads in your own process not being able to do anything, then yes, having them block on a mutex your running thread holds is sufficient.

The hard part is to coordinate all the other threads to grab that mutex whenever your thread needs to do its thing.

You should architect your sw so you're not dependent on the scheduler doing the "right" thing from your app's point of view. The scheduler is complicated. It will do what it thinks is best.

Context switches are cheap. You say

I would be wasting cpu cycles with context switches.

but you should not look at it that way. Use the multi-threaded machinery of mutexes and blocked / waiting processes. The machinery is there for you to use...

You can't. If you could what would prevent your thread from never releasing the request and starving other threads.

The best you can do is set your threads priority so that the scheduler will prefer it over lower priority threads.