c语言数据结构约瑟夫单循环链表出现异常

以下是代码#include stdio.h#include stdlib.htypedef struct Node /*结点类型定义*/{ int password,num; /*password为密码，num为序号*/ struct Node* next;}Node, *LinkList; /*Node为结构体类型，*LinkList为结构指针类型*///创建循环单链表（尾插法）void Creat_Josephring(){ LinkList L; L=(LinkList)malloc(sizeof(Node)); /*初始化链表*/ L-next = NULL; Node *rear,*s; rear = L; /*rear指针动态指向表尾，其初值指向头结点*/ int a = 1,c; printf("请输入密码："); scanf("%d",&c); while ( c != -1 ) { s = (Node*)malloc(sizeof(Node)); s-num = a; a++; s-password = c; rear-next = s; rear = s; scanf("%d",&c); } rear-next = L;}//约瑟夫环void Josephring( LinkList L, int m ) { int i; Node *p=L,*pre; p = p-next; //这个地方出现段错误 while( p-next != p ) { for( i=1; im+1; i++ ) { pre = p; p = p-next; } printf("%d",p-num); pre-next = p-next; free(p); p = pre-next; m = p-password; } printf("%d",p-num); free(p);}int main(){ LinkList L; Creat_Josephring(); Josephring(L,20); return 0;}运行之后，出现segmentation fault，求大佬们帮帮忙