netdev - Re: [PATCH net V3 1/3] bonding: implement xdo_dev_state

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Message-ID: <e7ee528b3db5ba94937ca6c933f9060e32f79f3d.camel@nvidia.com>
Date: Thu, 15 Aug 2024 01:23:05 +0000
From: Jianbo Liu <jianbol@...dia.com>
To: "liuhangbin@...il.com" <liuhangbin@...il.com>
CC: "davem@...emloft.net" <davem@...emloft.net>, Tariq Toukan
	<tariqt@...dia.com>, "andy@...yhouse.net" <andy@...yhouse.net>, Gal Pressman
	<gal@...dia.com>, "jv@...sburgh.net" <jv@...sburgh.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "kuba@...nel.org"
	<kuba@...nel.org>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"pabeni@...hat.com" <pabeni@...hat.com>, Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>
Subject: Re: [PATCH net V3 1/3] bonding: implement xdo_dev_state_free and call
 it after deletion

On Wed, 2024-08-14 at 11:11 +0800, Hangbin Liu wrote:
> On Wed, Aug 14, 2024 at 02:03:58AM +0000, Jianbo Liu wrote:
> > On Tue, 2024-08-13 at 07:14 -0700, Jakub Kicinski wrote:
> > > On Tue, 13 Aug 2024 02:58:12 +0000 Jianbo Liu wrote:
> > > > > > +       rcu_read_lock();
> > > > > > +       bond = netdev_priv(bond_dev);
> > > > > > +       slave = rcu_dereference(bond->curr_active_slave);
> > > > > > +       real_dev = slave ? slave->dev : NULL;
> > > > > > +       rcu_read_unlock();  
> > > > > 
> > > > > What's holding onto real_dev once you drop the rcu lock
> > > > > here?  
> > > > 
> > > > I think it should be xfrm state (and bond device).
> > > 
> > > Please explain it in the commit message in more certain terms.
> > 
> > Sorry, I don't understand. The real_dev is saved in xs-
> > >xso.real_dev,
> > and also bond's slave. It's straightforward. What else do I need to
> > explain?
> 
> I think Jakub means you need to make sure the real_dev is not freed
> during
> xfrmdev_ops. See bond_ipsec_add_sa(). You unlock it too early and
> later
> xfrmdev_ops is not protected.

This RCU lock is to protect the reading of curr_active_slave, which is
pointing to a big stuct - slave struct, so there is no error to get
real_dev from slave->dev.

Thanks!
Jianbo