Linux使用clone（）做异步

我试图用克隆来计算一个数字，但我发现我是这样使用的。我会让它只工作在第一个孩子，然后得到分割错误。我怎样才能异步执行add_计数器

下面是我的代码：

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#define STACK 8192

int counter;
void * stack;
int add_counter(){
    while(1) {
        printf("This is son, the pid is:%d, the a is: %d\n", getpid(), ++counter);
        free(stack);
        if (counter == 1000)
            exit(1);
    }
}
int main() {
    void * stack;
    counter = 0;
    stack = malloc(STACK);
    if(!stack) {
            printf("The stack failed\n");
            exit(0);
    }

    int i;
    for (i = 0; i < 10; i++) {
        clone(&add_counter, (char *)stack + STACK, CLONE_VM|CLONE_VFORK, 0);   
    }

    printf("This is father, my pid is: %d, the a is: %d\n", getpid(), counter);
    // exit(1);
}

提前谢谢

......
This is son, the pid is:3865, the a is: 985
This is son, the pid is:3865, the a is: 986
This is son, the pid is:3865, the a is: 987
This is son, the pid is:3865, the a is: 988
This is son, the pid is:3865, the a is: 989
This is son, the pid is:3865, the a is: 990
This is son, the pid is:3865, the a is: 991
This is son, the pid is:3865, the a is: 992
This is son, the pid is:3865, the a is: 993
This is son, the pid is:3865, the a is: 994
This is son, the pid is:3865, the a is: 995
This is son, the pid is:3865, the a is: 996
This is son, the pid is:3865, the a is: 997
This is son, the pid is:3865, the a is: 998
This is son, the pid is:3865, the a is: 999
This is son, the pid is:3865, the a is: 1000
Segmentation fault