netdev - Re: [PATCH net-next 2/9] net: hold instance lock during NETDEV

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Message-ID: <86b753c439badc25968a01d03ed59b734886ad9b.camel@nvidia.com>
Date: Wed, 26 Mar 2025 15:03:07 +0000
From: Cosmin Ratiu <cratiu@...dia.com>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "sdf@...ichev.me"
	<sdf@...ichev.me>
CC: "edumazet@...gle.com" <edumazet@...gle.com>, "davem@...emloft.net"
	<davem@...emloft.net>, "kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>
Subject: Re: [PATCH net-next 2/9] net: hold instance lock during
 NETDEV_REGISTER/UP/UNREGISTER

On Tue, 2025-03-25 at 14:30 -0700, Stanislav Fomichev wrote:
> @@ -2072,8 +2087,8 @@ static void
> __move_netdevice_notifier_net(struct net *src_net,
>  					  struct net *dst_net,
>  					  struct notifier_block *nb)
>  {
> -	__unregister_netdevice_notifier_net(src_net, nb);
> -	__register_netdevice_notifier_net(dst_net, nb, true);
> +	__unregister_netdevice_notifier_net(src_net, nb, false);
> +	__register_netdevice_notifier_net(dst_net, nb, true, false);
>  }

I tested with your (and the rest of Jakub's) patches.
The problem with this approach is that when a netdev's net is changed,
its lock will be acquired, but the notifiers for ALL netdevs in the old
and the new namespace will be called, which will result in correct
behavior for that device and lockdep_assert_held failure for all
others.

Cosmin.