Service event handler: IRQ callback or FreeRTOS task?

I want to fully understand the use of RTOS in conjunction with the stack.

As an example, I took an example ble_app_hrs_freertos (SDK v15.0).

Add a service, for example, BAS.

Event handler for this service:

void ble_bas_on_ble_evt(ble_evt_t const * p_ble_evt, void * p_context)
{ 
    ... 
}

When start the project, a task is created to handle the SD events:

void SD_EVT_IRQHandler(void)
{
     BaseType_t xYieldRequired;

     xYieldRequired = xTaskResumeFromISR( m_softdevice_task );

     if( xYieldRequired == pdTRUE )
     {
         portYIELD_FROM_ISR(xYieldRequired);
     }
}


/* This function gets events from the SoftDevice and processes them. */
static void softdevice_task(void * pvParameter)
{
    NRF_LOG_DEBUG("Enter softdevice_task.");

    if (m_task_hook != NULL)
    {
        m_task_hook(pvParameter);
    }

    while (true)
    {
        nrf_sdh_evts_poll(); // Let the handlers run first, in case the EVENT occured before creating this task.
        vTaskSuspend(NULL);
    }
}


void nrf_sdh_freertos_init(nrf_sdh_freertos_task_hook_t hook_fn, void * p_context)
{
    NRF_LOG_DEBUG("Creating a SoftDevice task.");

    m_task_hook = hook_fn;

    BaseType_t xReturned = xTaskCreate(softdevice_task,
                                       "BLE",
                                       NRF_BLE_FREERTOS_SDH_TASK_STACK,
                                       p_context,
                                       2,
                                       &m_softdevice_task);
    if (xReturned != pdPASS)
    {
        NRF_LOG_ERROR("SoftDevice task not created.");
        APP_ERROR_HANDLER(NRF_ERROR_NO_MEM);
    }
}

So, question:


1. Handlers for services are called from this task or earlier, from an interrupt?

2. Event handler for service it's IRQ callback or RTOS callback (callback from softdevice_task)?

Thanks,