Re: [dpdk-dev] [dpdk-stable] [PATCH 2/2] app/testpmd: fix invalid port detaching

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

On 2/13/2020 1:36 PM, Thomas Monjalon wrote:
> More details below about the plan for 20.02.
> 
> 13/02/2020 13:37, Thomas Monjalon:
>> Hi,
>>
>> This discussion becomes confusing so I do a summary below.
>> I think we can do several fixes in 20.02.

Thanks for checking this.

>>
>> 12/02/2020 14:49, Ferruh Yigit:
>>> On 2/3/2020 5:10 PM, Matan Azrad wrote:
>>
>> [stripping long discussion in favor of a summary below]
>>
>>>> Even if the PMD clear the device pointer, the testpmd still may release wrong rte_device.
>>>
>>> Yes it may, although that is less likely to occur, it requires a new device hot
>>> added between close() and detach of the other device.
>>>
>>> Would you be agree to say there are two problems:
>>>
>>> 1) When testpmd close a port, a new attached port can re-use it over writing
>>> some fields, relying the data structures of the closed port is not safe.
>>>
>>> 2) PMD not cleaning ethdev->device pointer in the .remove() may cause issues in
>>> double detach of a port.
>>>
>>>
>>> For (1) I suggest fixing it in the attach path, don't re-use an eth_dev port id
>>> unless it is completely freed, may need to add new state for it. Does it make sense?
>>
>> Yes we could add a CLOSED state which is set on ethdev close.
>> When the rte_device is freed, the PMD could set attached ports as UNUSED.
>> But given some ethdev ports can be open and closed dynamically,
>> I am not sure it is a good solution to keep them in CLOSED state and ask
>> PMD to remember them.
>>
>> An alternative workaround could be to allocate port_id by incrementing
>> a saved biggest id. So the race condition would be very unlikely.
>> The drawbacks are having big port_id numbers and changing the id
>> allocation algorithm (which is not documented anyway).

OK to keep increase port_id instead of re-using closed ones, that simplifies a lot.

>>
>> The proposals above for port_id allocation or states rework cannot be
>> done in 20.02. Let's discuss and work on it in a separated thread.

+1

>>
>>> For (2) PMDs want to get hotplug support needs to fix it.
>>
>> Yes PMDs should clear rte_eth_devices[port_id].device in .remove().
> 
> I am sending a patch adding
> 	memset(eth_dev, 0, sizeof(struct rte_eth_dev));
> in rte_eth_dev_release_port().
> But this patch cannot be merged after 20.02-rc1. It will wait for 20.05.

Not sure about this, close() calls the 'rte_eth_dev_release_port()', memset the
struct in close() will wipe the device pointers and prevents freeing them in hot
remove, silently.

> 
>> We must also protect from user calling detach on a closed port
>> by adding a check in cmd_operate_detach_port_parsed(),
>> before calling detach_port_device().
> 
> I am sending a patch adding RTE_ETH_VALID_PORTID_OR_RET()
> in cmd_operate_detach_port_parsed().
> It should fix the issue observed by Matan with double detach.
> It will be a double protection if keeping the check
> port_id_is_invalid() in detach_port_device().

OK

> 
>> The hotplug rmv_port_callback() must be able to call detach after close.
>> There are three possible fixes:
>> 	- revert the port_id_is_invalid() check in detach_port_device()
>> 	- call rte_dev_remove(rte_device) directly
>> 	- call a new function with rte_device (detach_port_device() can use it)
> 
> I am sending a patch implementing the third alternative
> as it is both keeping the detach behaviour and fixing the race condition
> (i.e. protect from new port re-using the port_id between close and detach).

Should work, only concern if any possible side affect occurs, can be discussed
on patch.

> 
>> About the function detach_port_device() itself, yes this function is
>> strange to say the least. It was a convenience for detaching a rte_device
>> from a port_id.
>> The cleanup of siblings with RTE_ETH_FOREACH_DEV_OF(sibling, dev),
>> should probably be removed. I've added it as a temporary solution
>> before all PMDs are properly fixed:
>> 	rte_eth_devices[sibling].device = NULL;
> 
> I propose sending such patch in 20.05 in order to merge the memset above
> first, and have time to get agreement from all PMD maintainers.

OK

> 
>> For info, there is a function detach_device() used by the command
>> 	"device detach <identifier>"
> 
> 
>