在执行加法时使用pthread的分段错误？

#include <stdio.h>
#include <pthread.h>

int sum = 0;
pthread_mutex_t mutex;

void* add(void* arg) {
    pthread_mutex_lock(&mutex);  // 获取互斥锁
    sum += *(int*)arg;  // 执行加法操作
    pthread_mutex_unlock(&mutex);  // 释放互斥锁
    pthread_exit(NULL);
}

int main() {
    pthread_t thread1, thread2;
    int num1 = 10, num2 = 20;

    pthread_mutex_init(&mutex, NULL);  // 初始化互斥锁

    pthread_create(&thread1, NULL, add, (void*)&num1);
    pthread_create(&thread2, NULL, add, (void*)&num2);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    pthread_mutex_destroy(&mutex);  // 销毁互斥锁

    printf("Sum: %d\n", sum);

    return 0;
}