netdev - Re: [PATCH net] net: xdp: don't call notifiers during driver init

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Date:   Thu, 16 Mar 2023 14:54:18 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     Tariq Toukan <ttoukan.linux@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, tariqt@...dia.com, bpf@...r.kernel.org
Subject: Re: [PATCH net] net: xdp: don't call notifiers during driver init

On Thu, 16 Mar 2023 12:03:57 +0100 Lorenzo Bianconi wrote:
> > I maybe need to dig deeper, but, it looks strange to still
> > call_netdevice_notifiers in cases > NETREG_REGISTERED.
> > 
> > Isn't it problematic to call it with NETREG_UNREGISTERED ?
> > 
> > For comparison, netif_set_real_num_tx_queues has this ASSERT_RTNL() only
> > under dev->reg_state == NETREG_REGISTERED || dev->reg_state ==
> > NETREG_UNREGISTERING.  
> 
> does it make sense to run call_netdevice_notifiers() in xdp_set_features_flag()
> just if dev->reg_state is NETREG_REGISTERED?

I was thinking - we'll adjust it if someone complains, but indeed
the detection is somewhat weak, a call on a dead device but under
rtnl_lock won't warn. Let me just copy what the queue helpers do,
exactly, then.

> Moreover, looking at the code it seems netdev code can run with dev->reg_state
> set to NETREG_UNREGISTERED and without holding RTNL lock, right?

You mean - part of unregistration is done without rtnl lock held?