netdev - Re: [PATCH v4 net 2/3] net: Fix dev_net(dev) race in unregister_netdevice_notifier_dev

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Message-ID: <20250214002557.27185-1-kuniyu@amazon.com>
Date: Fri, 14 Feb 2025 09:25:57 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuba@...nel.org>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <horms@...nel.org>,
	<kuni1840@...il.com>, <kuniyu@...zon.com>, <netdev@...r.kernel.org>,
	<pabeni@...hat.com>, <ychemla@...dia.com>
Subject: Re: [PATCH v4 net 2/3] net: Fix dev_net(dev) race in unregister_netdevice_notifier_dev_net().

From: Jakub Kicinski <kuba@...nel.org>
Date: Thu, 13 Feb 2025 08:32:17 -0800
> On Wed, 12 Feb 2025 15:42:05 +0900 Kuniyuki Iwashima wrote:
> > +static void rtnl_net_dev_lock(struct net_device *dev)
> > +{
> > +	struct net *net;
> > +
> > +#ifdef CONFIG_NET_NS
> > +again:
> > +#endif
> > +	/* netns might be being dismantled. */
> > +	rcu_read_lock();
> > +	net = dev_net_rcu(dev);
> > +	net_passive_inc(net);
> > +	rcu_read_unlock();
> > +
> > +	rtnl_net_lock(net);
> > +
> > +#ifdef CONFIG_NET_NS
> > +	/* dev might have been moved to another netns. */
> > +	if (!net_eq(net, rcu_access_pointer(dev->nd_net.net))) {
> > +		rtnl_net_unlock(net);
> > +		net_passive_dec(net);
> > +		goto again;
> > +	}
> > +#endif
> 
> Is there a plan to clean this up in net-next? Or perhaps after Eric's
> dev_net() work? Otherwise I'm tempted to suggest to use a loop, maybe:

For sure, I will post a followup patch to net-next.

Thanks!


> 
> 	bool again;
> 
> 	do {
> 		again = false;
> 
> 		/* netns might be being dismantled. */
> 		rcu_read_lock();
> 		net = dev_net_rcu(dev);
> 		net_passive_inc(net);
> 		rcu_read_unlock();
> 
> 		rtnl_net_lock(net);
> 
> #ifdef CONFIG_NET_NS
> 		/* dev might have been moved to another netns. */
> 		if (!net_eq(net, rcu_access_pointer(dev->nd_net.net))) {
> 			rtnl_net_unlock(net);
> 			net_passive_dec(net);
> 			again = true;
> 		}
> #endif
> 	} while (again);