在STM32F407上移植RTThread后，创建一个线程成功，但是通过打印发现该线程只执行一次？

th_uart2 = rt_thread_create("uart2_rec" , Serial2Th_entry , RT_NULL , 512 ,10 , 100);
    if(RT_NULL != th_uart2)
    {
        rt_thread_startup(th_uart2);
    }
void Serial2Th_entry(void * parameter)
{
 static char uart2rx_buffer;
    while(1)
    {
        LOG_D("jion Serial2Th_entry\r\n");
        while(rt_device_read(serial_u2 , 0 , &uart2rx_buffer , 1) != 1)
        {
            rt_sem_take(&uart2rx_sem , RT_WAITING_FOREVER);
            LOG_D("%c\r\n" , uart2rx_buffer);
        }
        rt_device_write(serial_u2,0,&uart2rx_buffer,sizeof(uart2rx_buffer));
    }
}