program stack in function BOOL ICACHE_FLASH_ATTR MQTT_InitClient

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I use this code to test my esp8266,it stack in BOOL ICACHE_FLASH_ATTR MQTT_InitClient(),and I add some print mark,like this:
system_os_task(MQTT_Task, MQTT_TASK_PRIO, mqtt_procTaskQueue, MQTT_TASK_QUEUE_SIZE); system_os_post(MQTT_TASK_PRIO, 0, (os_param_t)mqttClient); MQTT_INFO("done!\r\n"); return false;
in file mqtt.c,the end of function BOOL ICACHE_FLASH_ATTR MQTT_InitClient(MQTT_Client mqttClient, uint8_t client_id, uint8_t* client_user, uint8_t* client_pass, uint32_t keepAliveTime, uint8_t cleanSession)
and user_main.c like this:
`static void ICACHE_FLASH_ATTR app_init(void)
{
uart_init(BIT_RATE_115200, BIT_RATE_115200);
print_info();
INFO("1\n");
MQTT_InitConnection(&mqttClient, MQTT_HOST, MQTT_PORT, DEFAULT_SECURITY);
//MQTT_InitConnection(&mqttClient, "192.168.11.122", 1880, 0);
INFO("2\n");
if ( !MQTT_InitClient(&mqttClient, MQTT_CLIENT_ID, MQTT_USER, MQTT_PASS, MQTT_KEEPALIVE, MQTT_CLEAN_SESSION) )
{
INFO("Failed to initialize properly. Check MQTT version.\r\n");
return;
}
// MQTT_InitClient(&mqttClient, MQTT_CLIENT_ID, MQTT_USER, MQTT_PASS, MQTT_KEEPALIVE, MQTT_CLEAN_SESSION);
INFO("3\n");
//MQTT_InitClient(&mqttClient, "client_id", "user", "pass", 120, 1);
MQTT_InitLWT(&mqttClient, "/lwt", "offline", 0, 0);
INFO("4\n");
MQTT_OnConnected(&mqttClient, mqttConnectedCb);
INFO("5\n");
MQTT_OnDisconnected(&mqttClient, mqttDisconnectedCb);
INFO("6\n");
MQTT_OnPublished(&mqttClient, mqttPublishedCb);
INFO("7\n");
MQTT_OnData(&mqttClient, mqttDataCb);
INFO("8\n");

WIFI_Connect(STA_SSID, STA_PASS, wifiConnectCb);
INFO("9\n");
}`

when program running ,I got this:
[INFO] BOOTUP...
[INFO] SDK: 2.1.0(ce90efd)
[INFO] Chip ID: 00152E6F
[INFO] Memory info:
data : 0x3ffe8000 ~ 0x3ffe87f0, len: 2032
rodata: 0x3ffe87f0 ~ 0x3ffe9724, len: 3892
bss : 0x3ffe9728 ~ 0x3ffefd70, len: 26184
heap : 0x3ffefd70 ~ 0x3fffc000, len: 49808
[INFO] -------------------------------------------
[INFO] Build time: 2017-9月-21_16:04:29_CST
[INFO] -------------------------------------------
1
MQTT:InitConnection
2
MQTT:InitClient
done!

and secs latter,esp8266 reboot,agin and agin.
I'm really confused,how can I resolve this problem,thanks!

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The same problem with SDK v2.0.0