spin_lock_init 采用什么参数？

Question

I want to initialize at run time the spin_lock using the spin_lock_init function, but don't know what argument it takes, I saw from the docs that it takes a pointer to spinlock_t type but I don't know how to implement it. How can we init spinlock at run time using that function?

int __init(void)
{
    spinlock_t my_lock; // spin lock type
    spin_lock_init(&my_lock); // void
    
    return 64;
}

Answer 1

Your usage is correct. The spin_lock_init() function is intended to be used when you need to initialize a spinlock at run time . What is odd in your example is the fact that you are defining the spinlock inside a function: what purpose will that spinlock ever have if it's only defined there and gets discarded immediately when the function returns? You usually want to be able to lock/unlock it from different functions (or different calls of the same function).

Therefore, you usually want to have spinlocks as global variables, something like:

static spinlock_t my_lock;

int __init myinit(void)
{
    spin_lock_init(&my_lock);
    return 0;
}

For usages in which you do not need to initialize the spinlock at runtime (because you already know that you will need it initialized right away), you can use the DEFINE_SPINLOCK() macro, that will both declare and initialize it for you at compile time, saving time and code:

static DEFINE_SPINLOCK(my_lock);