Kernel Synchronization – Part 1

With the previous chapter and the one preceding it (Chapters 11 and 10, respectively), you learned a good deal about CPU (or task) scheduling on the Linux OS. In this chapter and the following one, we shall dive into the – at times necessarily complex – topic of kernel synchronization.

As any developer familiar with programming in a multithreaded environment is well aware, there is a need for synchronization whenever two or more threads (code paths in general) may work upon a shared writable data item. Without synchronization (or mutual exclusion) in accessing the shared data, they can race; that is, the outcome cannot be predicted. This is called a data race. (In fact, data races can even occur when multiple single-threaded processes work on any kind of shared memory object, or where interrupts are a possibility.) Pure code itself is never an issue as its permissions are read+execute (r-x); reading and executing code simultaneously...