Correct Document(xv6-risc) Errors

[ChenMiaoi]

Correct Document(xv6-risc) Errors

• Recently I was doing MIT6.S081 2021 Fall, and while reading the xv6-riscv documentation, in Chapter 6, Section 5, the discussion of Re-entrant locks, there is an example:

struct spinlock lock;
int data = 0; // protected by lock
f() {
    acquire(&lock);
    if(data == 0) {
        call_once();
        h();
        data = 1;
    }release(&lock);
}

g() {
    aquire(&lock);
    if(data == 0) { 
        call_once();
        data = 1;
    }
    release(&lock);
}

• In fact, I didn't find a definition for h(). From a context perspective, it should be g() because Re-entrant locks cause call_once() to be called more than twice.
• I don't know if I missed it somewhere, but I did think so. If you have any questions, please let me know. thank you.

Here is what I think the version is, along with a screenshot of the original documentation:

struct spinlock lock;
int data = 0; // protected by lock
f() {
    acquire(&lock);
    if(data == 0) {
        call_once();
        g(); // here, I guess it is g() not h()
        data = 1;
    }release(&lock);
}

g() {
    aquire(&lock);
    if(data == 0) { 
        call_once();
        data = 1;
    }
    release(&lock);
}