Re: [RFC net-next v3 1/4] net: protect queue -> napi linking with netdev_lock()

[Joe Damato]

On Mon, Jan 27, 2025 at 01:37:56PM -0800, Jakub Kicinski wrote:
> On Tue, 21 Jan 2025 19:10:41 +0000 Joe Damato wrote:
> > From: Jakub Kicinski <kuba@xxxxxxxxxx>
> > 
> > netdev netlink is the only reader of netdev_{,rx_}queue->napi,
> > and it already holds netdev->lock. Switch protection of the
> > writes to netdev->lock as well.
> > 
> > Add netif_queue_set_napi_locked() for API completeness,
> > but the expectation is that most current drivers won't have
> > to worry about locking any more. Today they jump thru hoops
> > to take rtnl_lock.
> 
> I started having second thoughts about this patch, sorry to say.
> NAPI objects were easy to protect with the lock because there's
> a clear registration and unregistration API. Queues OTOH are made
> visible by the netif_set_real_num_queues() call, which is tricky 
> to protect with the instance lock. Queues are made visible, then
> we configure them.
> 
> My thinking changed a bit, I think we should aim to protect all
> ndos and ethtool ops with the instance lock. Stanislav and Saeed
> seem to be working on that:
> https://lore.kernel.org/all/Z5LhKdNMO5CvAvZf@mini-arch/
> so hopefully that doesn't cause too much of a delay.
> But you may need to rework this series further :(

OK, I'll wait for something to emerge from that work before
re-spinning this.