linux에서 mutex Unlock시에 segmentation fault 가 발생되는 현

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>

int shm_id;

pthread_mutex_t *mutex = (pthread_mutex_t *)-1;

pthread_mutexattr_t attr;

void * thr_aaa(void * parg)
{
	int temp = (int)parg;
	pthread_mutex_t *thr_mutex = mutex;
	
	while (1)
	{
		printf("lock start 1 : [%d] [%d]\n", thr_mutex, temp);
		fflush(stdout);

		pthread_mutex_lock(thr_mutex);
		
		printf("lock start 2 : [%d] [%d]\n", thr_mutex, temp);
		fflush(stdout);

		sleep(1);
		
		printf("lock end 1 : [%d] [%d]\n", thr_mutex, temp);
		fflush(stdout);
	
		pthread_mutex_unlock(thr_mutex);
		
	
		printf("lock end 2 : [%d] [%d]\n", thr_mutex, temp);
		fflush(stdout);

		sleep(3);
	}

	return 0;
}

int main()
{
	pthread_t thr_a[20];
	int i;

	shm_id = shmget(0x9000, sizeof(pthread_mutex_t), IPC_CREAT|0666);
	
	if (shm_id == -1)
	{
		printf("sharem memory error \n");
		exit(1);
	}
	
	mutex = (pthread_mutex_t *)shmat(shm_id, NULL, 0);
	
	pthread_mutexattr_init(&attr);
	pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);

	pthread_mutex_init(mutex, &attr);
	
	for (i = 0; i < 2; i++)
	{
		if (fork() == 0)
		{
			if (pthread_create(&thr_a[i], 0, thr_aaa, (void *)i) == 0)
			{
				printf("Thread Create : [%d] [%d]\n", i, thr_a[i]);
				pthread_join(thr_a[i], NULL);
		
			}
			else
			{
				printf("Thread Create Error : [%d]\n", i);
			}
			break;
		}
	}
	
	pause();		
}

위와 같은 프로그램을 실핸시키면 실행 결과가

Thread Create : [0] [1026]
Thread Create : [1] [1026]
lock start 1 : [1073819648] [0]
lock start 2 : [1073819648] [0]
lock start 1 : [1073819648] [1]
lock end 1 : [1073819648] [0]

이렇게 되어 있고 아무동작을 안하네요
어디를 어떻게 고쳐야 할지 고수님들의 의견을 듣고 싶네요