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

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Message-ID: <edd72057-61b3-4bb3-b2ee-446d71e6f427@redhat.com>
Date: Mon, 22 Dec 2025 12:29:41 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Eelco Chaudron <echaudro@...hat.com>,
 Toke Høiland-Jørgensen <toke@...hat.com>
Cc: 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 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