세그먼테이션 폴트 원인을 못찾겠습니다

int *array = NULL;
 
void *div_array(void *arg);
void merge_sort(int *, unsigned int);
 
typedef struct argument{
        int *arr;
        int start,end;
}arg;
 
void *left_sort(void *size)
{
        int s = *((int *)size);
        int middle = s/2;
        arg x={array,0,middle};
        div_array((void *)&x);
}
 
void *right_sort(void *size)
{
        int s = *((int *)size);
        int middle = s/2;
        arg x={array,middle +1,s};
        div_array((void *)&x);
}
 
 
void merge(int *arr, int start, int middle, int end)
{
        int *arr_left, *arr_right;
        int left = 0, right = 0;
        int count = 0;
 
        arr_left = (int*)malloc(sizeof(int) * (middle - start + 2));
        arr_right = (int*)malloc(sizeof(int) * (end - middle + 1));
 
        for(count = 0 ; count <= middle - start ; count ++)
        {
                arr_left[count] = arr[start + count];
        }
        arr_left[count] = CHECK_END;
        for(count = 0 ; count < end - middle ; count ++)
        {
                arr_right[count] = arr[middle + count + 1];
        }
        arr_right[count] = CHECK_END;
        for(count = start ; count <= end ; count ++)
        {
                if((arr_left[left] == CHECK_END || arr_left[left] > arr_right[right])
                 && arr_right[right] != CHECK_END)
                {
                        arr[count] = arr_right[right ++];
                }
                else
                        arr[count] = arr_left[left ++];
        }
        free(arr_left);
        free(arr_right);
}
void *div_array(void *darg)
{
        pthread_t thread_x,thread_y;
        arg *p = (arg*)darg;
 
        int middle = (p->start + p->end) / 2;
        arg x[2] = {{p->arr, p->start, middle},{p->arr,middle+1,p->end}};
 
        printf("11");
        if(p->start < p->end)
        {
 
                pthread_create(&thread_x, NULL, div_array,(void *)&x[0]);
                pthread_create(&thread_y, NULL, div_array,(void *)&x[1]);
 
                pthread_join(thread_x, NULL);
                pthread_join(thread_y, NULL);
 
//              div_array((void *)&x[0]);
//              div_array((void *)&x[1]);
                merge(p->arr, p->start, middle, p->end );
        }
 
}
void sort_merge(int size)
{       pthread_t tid[2];
        size = size - 1;
 
        pthread_create(&tid[0], NULL,  &left_sort, &size);
        pthread_create(&tid[1], NULL,  &right_sort, &size);
 
        pthread_join(tid[0], NULL);
        pthread_join(tid[1], NULL);
 
        merge(array, 0, size/2, size);
}