I want to understand CAS logic, and write my own stack code without pop function. I doubt that my function is whether vulnerable or not.

#define MAX_STACK_ENTRY 256
int stack_entry[MAX_STACK_ENTRY];
int entry_num = 0;

void push(int inp)
{
    int last;
    __atomic_load(&entry_num, &last, __ATOMIC_RELAXED);
    do
    {
        // because we want to check stack is full, first load entry_num 
        if(last >= MAX_STACK_ENTRY)
        {
            printf("stack is full");
            return;
        }
        // check entry_num == last -> this thread success CAS. -> entry_num = last + 1 
        // check entry_num != last -> another thread success CAS. -> last = entry_num
    } while(!__atomic_compare_exchange_n(&entry_num, &last, last+1, 1, __ATOMIC_RELAXED, __ATOMIC_RELAXED));

    stack_entry[last] = inp;
}

I think this code is not vulnerable unless there is no pop function. __atomic_compare_exchange_n doesn't need to get other memory order. ot.

Preventing reordering is not needed, because operations are dependent with each other and executed sequentially.

I think it is not correct, then,

while(!__atomic_compare_exchange_n(&entry_num, &last, last+1, 1, __ATOMIC_ACQUIRE, __ATOMIC_RELEASE));

is needed.

I want to clarity my understand is wrong or not.