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

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Message-ID: <Z-Q-QYvFvQG2usfv@mini-arch>
Date: Wed, 26 Mar 2025 10:49:53 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Cosmin Ratiu <cratiu@...dia.com>
Cc: "pabeni@...hat.com" <pabeni@...hat.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"sdf@...ichev.me" <sdf@...ichev.me>,
	"kuba@...nel.org" <kuba@...nel.org>
Subject: Re: [PATCH net-next 2/9] net: hold instance lock during
 NETDEV_REGISTER/UP/UNREGISTER

On 03/26, Cosmin Ratiu wrote:
> On Wed, 2025-03-26 at 08:23 -0700, Stanislav Fomichev wrote:
> > @@ -2028,7 +2028,7 @@ int unregister_netdevice_notifier(struct
> > notifier_block *nb)
> >  
> >  	for_each_net(net) {
> >  		__rtnl_net_lock(net);
> > -		call_netdevice_unregister_net_notifiers(nb, net,
> > true);
> > +		call_netdevice_unregister_net_notifiers(nb, net,
> > NULL);
> >  		__rtnl_net_unlock(net);
> >  	}
> 
> I tested. The deadlock is back now, because dev != NULL and if the lock
> is held (like in the below stack), the mutex_lock will be attempted
> again:

I think I'm missing something. In this case I'm not sure why the original
"fix" worked.

You, presumably, use mlx5? And you just move this single device into
a new netns? Or there is a couple of other mlx5 devices still hanging in
the root netns?

I'll try to take a look more at register_netdevice_notifier_net under
mlx5..