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

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Message-ID: <87qzswklc7.fsf@toke.dk>
Date: Mon, 15 Dec 2025 12:58:48 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Eelco Chaudron <echaudro@...hat.com>, Adrian Moreno <amorenoz@...hat.com>
Cc: 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>, Paolo Abeni
 <pabeni@...hat.com>, 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

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 :)

-Toke