netdev - Re: [PATCH RFC V1 net-next 1/4] net: ethtool: Refactor identical get_ts

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Date:   Fri, 21 Jan 2022 11:56:37 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Richard Cochran <richardcochran@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH RFC V1 net-next 1/4] net: ethtool: Refactor identical
 get_ts_info implementations.

On Thu, Jan 20, 2022 at 04:13:29PM +0000, Vladimir Oltean wrote:
> > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> > index b60e22f6394a..f28b88b67b9e 100644
> > --- a/drivers/net/bonding/bond_main.c
> > +++ b/drivers/net/bonding/bond_main.c
> > @@ -5353,23 +5353,13 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
> >  				    struct ethtool_ts_info *info)
> >  {
> >  	struct bonding *bond = netdev_priv(bond_dev);
> > -	const struct ethtool_ops *ops;
> >  	struct net_device *real_dev;
> > -	struct phy_device *phydev;
> >  
> >  	rcu_read_lock();
> >  	real_dev = bond_option_active_slave_get_rcu(bond);
> >  	rcu_read_unlock();
> 
> Side note: I'm a bit confused about this rcu_read_lock() ->
> rcu_dereference_protected() -> rcu_read_unlock() pattern, and use of the
> real_dev outside the RCU critical section. Isn't ->get_ts_info()
> protected by the rtnl_mutex? Shouldn't there be a
> bond_option_active_slave_get() which uses rtnl_dereference()?
> I see the code has been recently added by Hangbin Liu.

Hi Vladimir,

Yes, it should be enough to use rtnl_dereference() since ->get_ts_info is
protected by the rtnl_lock. I just thought there is an existing get active
slave function and rcu read should be OK to be used here. So I just used the
existing one.

Hi Jay,

Do you think if there is a need to add a rtnl version of
bond_option_active_slave_get()?

Thanks
Hangbin