Re: [dpdk-dev] [dpdk-stable] [PATCH 1/3] net/enic: restrict several handlers to primary process

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

On 10/9/2019 10:38 AM, Hyong Youb Kim (hyonkim) wrote:
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>> Sent: Wednesday, October 9, 2019 6:28 PM
>> To: Hyong Youb Kim (hyonkim) <hyonkim@cisco.com>
>> Cc: dev@dpdk.org; John Daley (johndale) <johndale@cisco.com>; Dirk-
>> Holger Lenz <dirk.lenz@ng4t.com>; stable@dpdk.org
>> Subject: Re: [dpdk-stable] [PATCH 1/3] net/enic: restrict several handlers to
>> primary process
>>
>> On 10/9/2019 9:48 AM, Hyong Youb Kim (hyonkim) wrote:
>>>> -----Original Message-----
>>>> From: Ferruh Yigit <ferruh.yigit@intel.com>
>>>> Sent: Wednesday, October 9, 2019 5:02 PM
>>>> To: Hyong Youb Kim (hyonkim) <hyonkim@cisco.com>
>>>> Cc: dev@dpdk.org; John Daley (johndale) <johndale@cisco.com>; Dirk-
>>>> Holger Lenz <dirk.lenz@ng4t.com>; stable@dpdk.org
>>>> Subject: Re: [PATCH 1/3] net/enic: restrict several handlers to primary
>>>> process
>>>>
>>>> On 9/6/2019 7:50 AM, Hyong Youb Kim wrote:
>>>>> These eth_dev_ops handlers should run only in the primary process.
>>>>> - filter_ctrl
>>>>> - reta_update
>>>>> - rss_hash_update
>>>>> - set_mc_addr_list
>>>>> - udp_tunnel_port_add
>>>>> - udp_tunnel_port_del
>>>>>
>>>>> Fixes: c2fec27b5cb0 ("net/enic: allow to change RSS settings")
>>>>> Fixes: 8d496995346c ("net/enic: support multicast filtering")
>>>>> Fixes: 8a4efd17410c ("net/enic: add handlers to add/delete vxlan port
>>>> number")
>>>>> Cc: stable@dpdk.org
>>>>>
>>>>> Reported-by: Dirk-Holger Lenz <dirk.lenz@ng4t.com>
>>>>> Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
>>>>> Tested-by: Dirk-Holger Lenz <dirk.lenz@ng4t.com>
>>>>> Reviewed-by: John Daley <johndale@cisco.com>
>>>>> ---
>>>>>  drivers/net/enic/enic_ethdev.c | 12 ++++++++++++
>>>>>  1 file changed, 12 insertions(+)
>>>>>
>>>>> diff --git a/drivers/net/enic/enic_ethdev.c
>>>> b/drivers/net/enic/enic_ethdev.c
>>>>> index 06dc67122..85d785e62 100644
>>>>> --- a/drivers/net/enic/enic_ethdev.c
>>>>> +++ b/drivers/net/enic/enic_ethdev.c
>>>>> @@ -129,6 +129,8 @@ enicpmd_dev_filter_ctrl(struct rte_eth_dev
>> *dev,
>>>>>  {
>>>>>  	int ret = 0;
>>>>>
>>>>> +	if (rte_eal_process_type() != RTE_PROC_PRIMARY)
>>>>> +		return -E_RTE_SECONDARY;
>>>>>  	ENICPMD_FUNC_TRACE();
>>>>>
>>>>>  	switch (filter_type) {
>>>>
>>>> I remember we have similar talk with John in the past about these
>> secondary
>>>> application checks in ethdev_ops.
>>>>
>>>> I would like to understand why these checks required only in enic, can you
>>>> please describe your use case?
>>>> Is there any reason secondary application can't change configuration of
>> the
>>>> device, or are you updating your driver to work with specific application?
>>>
>>> Hi,
>>>
>>> No fundamental reasons why secondary processes cannot run these
>>> handlers. These checks are to make it clear that it is not safe to do
>>> so at the moment. It is a software limitation.
>>>
>>> The firmware API (devcmd) we use to configure NIC settings assumes one
>>> user executing one command at a time. And, many of the handlers in the
>>> driver also assume primary process. The firmware itself has
>>> enough checks to prevent concurrent devcmd attempts from corrupting
>>> its internal state. But, host processes can get confused. For example,
>>> process A gets process B's results, or overwrites B's devcmd, etc.
>>>
>>> I believe these issues are all fixable in the driver. We could use
>>> locks in shared memory to serialize devcmd (though risky), fix
>>> handlers that assume primary process, and so on. It is a to-do item for
>>> this driver and would require its own patch series (e.g. allow
>>> secondary processes to run X, Y, Z safely)..
>>
>> What you have described is valid concern for all drivers, that synchronization
>> has been pushed to the application level.
>>
>> I don't see the point of just putting protection to only one driver.
>>
>> And as a alternative, what do you think about having a check in the prob for
>> the
>> secondary process and assign a subset of the ethdev_ops in that case? This
>> makes
>>  more clear what is supported in the secondary process, and it prevents
>> putting
>> secondary process checks everywhere.
> 
> Hi,
> 
> Okay, that sounds reasonable. Could you drop this one patch and apply
> the rest in the series? I may not have time to properly re-do this one
> in this cycle..

OK, will mark 1/3 as "Change Requested" and continue with others. Thanks.