ESP32 Forum

Posted: **Tue Apr 06, 2021 9:39 am**

ESP-IDF V4.2

Two threads call esp_netif_new(), that calls esp_netif_get_handle_from_ifkey(), that calls esp_netif_list_lock()
The first thread creates and takes the semaphore; the second waits for xSemaphoreTake() returning.
The first threads gives the semaphore then delete it, beeing s_esp_netif_counter still zero.
When the second thread calls esp_netif_unlock() assert(s_list_lock) fails beeing the semaphore handle NULL.
The semaphore cannot protect itself.

Code from esp_netif_objects.c

Code: [Select all] [Expand/Collapse]

 
 static size_t s_esp_netif_counter = 0;
 
 
esp_netif_t *esp_netif_new(const esp_netif_config_t *esp_netif_config)
{
    // mandatory configuration must be provided when creating esp_netif object
    if (esp_netif_config == NULL ||
        esp_netif_config->base->if_key == NULL ||
        NULL != esp_netif_get_handle_from_ifkey(esp_netif_config->base->if_key)) {
        ESP_LOGE(TAG, "%s: Failed to configure netif with config=%p (config or if_key is NULL or duplicate key)",
        __func__,  esp_netif_config);
        return NULL;
    }
 
   …
 
}
 
 
esp_netif_t *esp_netif_get_handle_from_ifkey(const char *if_key)
{
    esp_err_t ret;
    if ((ret = esp_netif_list_lock()) != ESP_OK) {
        ESP_LOGE(TAG, "Failed to lock esp-netif list with %d", ret);
        return NULL;
    }
 
    esp_netif_t *esp_netif = esp_netif_next_unsafe(NULL);
    do {
        if (esp_netif && strcmp(if_key, esp_netif_get_ifkey(esp_netif))==0) {
            esp_netif_list_unlock();
            return esp_netif;
        }
    } while (NULL != (esp_netif = esp_netif_next_unsafe(esp_netif)));
    esp_netif_list_unlock();
    return NULL;
}
 
void esp_netif_list_unlock(void)
{
    assert(s_list_lock);
    xSemaphoreGive(s_list_lock);
    if(s_esp_netif_counter == 0) {
      vQueueDelete(s_list_lock);
      s_list_lock = NULL;
    }
}
 
esp_err_t esp_netif_list_lock(void)
{
    if (s_list_lock == NULL) {
        s_list_lock = xSemaphoreCreateMutex();
        if (s_list_lock == NULL) {
            return ESP_ERR_NO_MEM;
        }
    }
    xSemaphoreTake(s_list_lock, portMAX_DELAY);
    return ESP_OK;
}

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