netdev - Re: [PATCH v2] net: openvswitch: Avoid needlessly taking the RTNL on vport destroy

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Message-ID: <961802A0-4E7F-4D11-8944-46B35EDF83D0@redhat.com>
Date: Mon, 22 Dec 2025 12:44:07 +0100
From: Eelco Chaudron <echaudro@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Toke Høiland-Jørgensen <toke@...hat.com>,
 Adrian Moreno <amorenoz@...hat.com>, Aaron Conole <aconole@...hat.com>,
 Ilya Maximets <i.maximets@....org>, Alexei Starovoitov <ast@...nel.org>,
 Jesse Gross <jesse@...ira.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, netdev@...r.kernel.org, dev@...nvswitch.org
Subject: Re: [PATCH v2] net: openvswitch: Avoid needlessly taking the RTNL on
 vport destroy



On 22 Dec 2025, at 12:29, Paolo Abeni wrote:

> On 12/15/25 1:31 PM, Eelco Chaudron wrote:
>> On 15 Dec 2025, at 12:58, Toke Høiland-Jørgensen wrote:
>>> Eelco Chaudron <echaudro@...hat.com> writes:
>>>> On 11 Dec 2025, at 12:50, Toke Høiland-Jørgensen wrote:
>>>>> The openvswitch teardown code will immediately call
>>>>> ovs_netdev_detach_dev() in response to a NETDEV_UNREGISTER notification.
>>>>> It will then start the dp_notify_work workqueue, which will later end up
>>>>> calling the vport destroy() callback. This callback takes the RTNL to do
>>>>> another ovs_netdev_detach_port(), which in this case is unnecessary.
>>>>> This causes extra pressure on the RTNL, in some cases leading to
>>>>> "unregister_netdevice: waiting for XX to become free" warnings on
>>>>> teardown.
>>>>>
>>>>> We can straight-forwardly avoid the extra RTNL lock acquisition by
>>>>> checking the device flags before taking the lock, and skip the locking
>>>>> altogether if the IFF_OVS_DATAPATH flag has already been unset.
>>>>>
>>>>> Fixes: b07c26511e94 ("openvswitch: fix vport-netdev unregister")
>>>>> Tested-by: Adrian Moreno <amorenoz@...hat.com>
>>>>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>>>>
>>>> Guess the change looks good, but I’m waiting for some feedback from
>>>> Adrian to see if this change makes sense.
>>>
>>> OK.
>>>
>>>> Any luck reproducing the issue it’s supposed to fix?
>>>
>>> We got a report from the customer that originally reported it (who had
>>> their own reproducer) that this patch fixes their issue to the point
>>> where they can now delete ~2000 pods/node without triggering the
>>> unregister_netdevice warning at all (where before it triggered at around
>>> ~500 pod deletions). So that's encouraging :)
>>
>> That’s good news; just wanted to make sure we are not chasing a red herring :)
>>
>> Acked-by: Eelco Chaudron echaudro@...hat.com
>
> @Eelco: your SoB above is lacking the required <> around the email
> address. I'm fixing that while applying the patch, but please take care
> of it in the next reviews.

Thanks Paolo, no idea what happened here :(
>
> Thanks,
>
> Paolo