简单任务切换，出现stack overflow

uint32_t main(){
#if FIX_TASK_OVERFLOW==1
    rt_thread_t low_tid = rt_thread_create("task_low", task_low, RT_NULL, 1024 * 8, 6, 20);
    if(low_tid){
        rt_thread_startup(low_tid);
    }
    rt_thread_t middle_tid = rt_thread_create("task_middle", task_middle, RT_NULL, 2048, 5, 20);
    if(middle_tid){
        rt_thread_startup(middle_tid);
    }
    rt_thread_t high_tid = rt_thread_create("task_high", task_high, RT_NULL, 1024 * 8, 2, 20);
    if(high_tid){
        rt_thread_startup(high_tid);
    }
#endif
    return 0;
}

void task_high(void *param)
{
    while(1){
        rt_thread_mdelay(100);
    }
}
void task_middle(void *param)
{
    static uint32_t cnt = 0;
    while(1){
        log_d("%s: %d\r\n", __func__, cnt++);
        rt_thread_mdelay(500);
    }
}
void task_low(void *param)
{
    static uint32_t cnt=0;
    while(1){
        log_d("%s: %d\r\n", __func__, cnt++);
        rt_thread_mdelay(500);
    }
}

UART: open serial device: 0x800215cc with open flag: 0x0143
msh >[TEST]: task_low: 0
thread:task_mid stack overflow
thread   pri  status      sp     stack size max used left tick  error
-------- ---  ------- ---------- ----------  ------  ---------- ---
task_hig   2  suspend 0x00000088 0x00002000    02%   0x00000014 000
task_mid   5  ready   0x00004568 0x00000800    25%   0x00000014 -02
task_low   6  suspend 0x00000088 0x00002000    06%   0x00000014 000
tshell     6  suspend 0x00000094 0x00000400    56%   0x00000008 000
at_svr     1  suspend 0x000000c8 0x00000800    09%   0x00000005 000
tidle      7  ready   0x000000d0 0x00000200    40%   0x0000000e 000
timer      4  suspend 0x00000078 0x00000200    23%   0x00000009 000