Linux Device Drivers Development

Mutex

Mutual exclusion (mutex) is the de facto, most-used locking mechanism. To understand how it works, let's see what its structure looks like in include/linux/mutex.h:

struct mutex { 
    /* 1: unlocked, 0: locked, negative: locked, possible waiters */ 
    atomic_t count; 
    spinlock_t wait_lock; 
    struct list_head wait_list; 
    [...] 
}; 

As we have seen in the wait queue section, there is also a list type field in the structure: wait_list. The principle of sleeping is the same.

Contenders are removed from the scheduler run queue and put onto the wait list (wait_list) in a sleep state. The kernel then schedules and executes other tasks. When the lock is released, a waiter in the wait queue is woken, moved off the wait_list, and scheduled back.