Re: [dpdk-dev] [PATCH 1/2] vhost: reference count fix for nb_started_ports

["Charles (Chas) Williams" <ciwillia@brocade.com>]

On 12/29/2016 03:51 AM, Yuanhan Liu wrote:
> On Wed, Dec 28, 2016 at 04:10:51PM -0500, Charles (Chas) Williams wrote:
>> From: Wen Chiu <wchiu@brocade.com>
>>
>> Only increment and decrement nb_started_ports on the first and last
>> device start and stop.  Otherwise, nb_started_ports can become negative
>> if a device is stopped multiple times.
>
> How could you be able to stop dev (precisely, invoke eth_dev_stop)
> multiple times, judging that eth_dev_stop() will be invoked once
> only?
>
>     void
>     rte_eth_dev_stop(uint8_t port_id)
>     {
>             struct rte_eth_dev *dev;
>
>             RTE_ETH_VALID_PORTID_OR_RET(port_id);
>             dev = &rte_eth_devices[port_id];
>
>             RTE_FUNC_PTR_OR_RET(*dev->dev_ops->dev_stop);
>
> ==>         if (dev->data->dev_started == 0) {
>                     RTE_PMD_DEBUG_TRACE("Device with port_id=%" PRIu8
>                             " already stopped\n",
>                             port_id);
>                     return;
>             }
>
> ==>         dev->data->dev_started = 0;
>             (*dev->dev_ops->dev_stop)(dev);
>     }
>
> Multiple threads?

No, we aren't using multiple threads for control.  But eth_dev_stop()
is called in rte_pmd_vhost_remove():

	static int
	rte_pmd_vhost_remove(const char *name)
	{
	...
		pthread_mutex_lock(&internal_list_lock);
		TAILQ_REMOVE(&internal_list, list, next);
		pthread_mutex_unlock(&internal_list_lock);
		rte_free(list);

		eth_dev_stop(eth_dev);
	...

So, if we .dev_stop() and deatch the virtual device, eth_dev_stop()
gets called twice.  Calling .dev_stop() when you are about to detach
the device seems completely reasonable.  It also seems reasonable to
call eth_dev_stop() inside rte_pmd_vhost_remove() in case the end
user didn't do a .dev_stop().