Re: [dpdk-dev] [dpdk-stable] [PATCH v1 2/3] net/ring: fix eth_dev device pointer on allocation

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 5/6/2020 1:33 PM, Gaëtan Rivet wrote:
> On 06/05/20 12:48 +0100, Ferruh Yigit wrote:
>> On 5/5/2020 8:10 PM, Gaetan Rivet wrote:
>>> When a net_ring device is allocated, its device pointer is not set
>>> before calling rte_eth_dev_probing_finish, which is incorrect.
>>>
>>> The following:
>>>   commit: 96cb19521147 ("net/ring: use EAL APIs in PMD specific API")
>>>   commit: a6992e961050 ("net/ring: set ethernet device field")
>>>
>>> already attempted to fix this issue in 17.08, which was fine at the
>>> time. Adding the hook rte_eth_dev_probing_finish() however created this
>>> bug, as the eth_dev exposed when this hook is executed is expected to be
>>> complete.
>>>
>>> Remove the prior attempts to fix the issue in rte_pmd_ring_probe() and
>>> write the pointer properly in do_eth_dev_ring_create().
>>>
>>> Cc: stable@dpdk.org
>>> Fixes: fbe90cdd776c ("ethdev: add probing finish function")
>>> Cc: ferruh.yigit@intel.com
>>> Cc: thomas@monjalon.net
>>> Signed-off-by: Gaetan Rivet <grive@u256.net>
>>
>> <...>
>>
>>> @@ -325,10 +346,17 @@ do_eth_dev_ring_create(const char *name,
>>>  	data->kdrv = RTE_KDRV_NONE;
>>>  	data->numa_node = numa_node;
>>>  
>>> -	/* finally assign rx and tx ops */
>>> +	/* assign rx and tx ops */
>>>  	eth_dev->rx_pkt_burst = eth_ring_rx;
>>>  	eth_dev->tx_pkt_burst = eth_ring_tx;
>>>  
>>> +	/* finally set the rte_device pointer in eth_dev. */
>>> +	eth_dev->device = ring_device_from_name(name);
>>> +	if (eth_dev->device == NULL) {
>>> +		rte_errno = ENODEV;
>>> +		goto error;
>>> +	}
>>> +
>>>  	rte_eth_dev_probing_finish(eth_dev);
>>>  	*eth_dev_p = eth_dev;
>>
>> Why not move the 'rte_eth_dev_probing_finish()' to the 'rte_pmd_ring_probe()',
>> below where 'eth_dev->device' set?
> 
> Hi Ferruh,
> 
> Sure it would work. The reason I did it this way is two-fold:
> 
>   * I disliked having two places where eth_dev->device was conditionally
>     set. It makes it harder to read rte_pmd_ring_probe.

Agree, what about using a 'goto' to have the assignment and
'rte_eth_dev_probing_finish()' in a single place?
But check seems needed since creation may failed at that stage, if you think
better check can be done on 'ret' instead of 'eth_dev'...

> 
>   * I was actually thinking, doing this patch, that we should modify
>     rte_eth_dev_allocate() to take an rte_device as parameter, as all
>     eth_dev are meant to be backed by an rte_device. Keeping this in
>     mind, I meant to move writing the pointer closer to the
>     rte_eth_dev_allocate() call.

That is a bigger change, may affect many (if not all) PMDs, so I think this can
be considered when that change is available.

And although that change may fix the issues that 'eth_dev->device' is not set,
which we had a few times before, not sure it worth to change all PMDs and ethdev
API directly couple with rte_device, instead of PMD being the glue. Can be
discussed more on its own patch.

> 
> But you are right that it is needlessly verbose, using
> vdev_bus->find_device() to do this stuff. I'm ok with changing it as you
> described if you prefer.
> 

That was the concern, that is too much code to take a value which is already
available a few level up the stack.