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

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Message-ID: <ebe10b79-34c2-4e85-2cf7-b7491266748e@gmail.com>
Date:   Thu, 16 Mar 2023 08:49:38 +0200
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, lorenzo@...nel.org, tariqt@...dia.com,
        bpf@...r.kernel.org, Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net] net: xdp: don't call notifiers during driver init



On 16/03/2023 2:29, Jakub Kicinski wrote:
> Drivers will commonly perform feature setting during init, if they use
> the xdp_set_features_flag() helper they'll likely run into an ASSERT_RTNL()
> inside call_netdevice_notifiers_info().
> 
> Don't call the notifier until the device is actually registered.
> Nothing should be tracking the device until its registered.
> 
> Fixes: 4d5ab0ad964d ("net/mlx5e: take into account device reconfiguration for xdp_features flag")
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> CC: ast@...nel.org
> CC: daniel@...earbox.net
> CC: hawk@...nel.org
> CC: john.fastabend@...il.com
> CC: lorenzo@...nel.org
> CC: tariqt@...dia.com
> CC: bpf@...r.kernel.org
> ---
>   net/core/xdp.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 87e654b7d06c..5722a1fc6e9e 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -781,6 +781,9 @@ void xdp_set_features_flag(struct net_device *dev, xdp_features_t val)
>   		return;
>   
>   	dev->xdp_features = val;
> +
> +	if (dev->reg_state < NETREG_REGISTERED)
> +		return;

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.

>   	call_netdevice_notifiers(NETDEV_XDP_FEAT_CHANGE, dev);
>   }
>   EXPORT_SYMBOL_GPL(xdp_set_features_flag);