How does linux( or any OS) file system "exactly" handle concurrent file I/O (kernel's scheduling)?

Question

I've learned about three solutions to Reader's Writer's Problem.

Considering the time efficiency, I think three of them are all usable in modern OS file system.

I'd like to get some clarification on how linux handles this problem. (NO ONE made a question about this before!)

For example, if the accesses are like, R R W R R, how does linux order these access?

1. (R R ) W (R R) / no starvation (sol 3)
2. (R R R R ) W / reader preference
3. (R) (R) (W) (R) (R) / once at a time

Thank you!