netdev - Re: [PATCHv2 net] bonding: fix missed rcu protection

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Date:   Tue, 17 May 2022 10:54:45 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     netdev@...r.kernel.org, Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Jonathan Toppins <jtoppins@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Paolo Abeni <pabeni@...hat.com>,
        syzbot+92beb3d46aab498710fa@...kaller.appspotmail.com,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCHv2 net] bonding: fix missed rcu protection

On Tue, 17 May 2022 16:23:12 +0800 Hangbin Liu wrote:
> +	rcu_read_lock();
>  	real_dev = bond_option_active_slave_get_rcu(bond);
>  	if (real_dev) {
> +		dev_hold(real_dev);
> +		rcu_read_unlock();
>  		ops = real_dev->ethtool_ops;
>  		phydev = real_dev->phydev;
>  
>  		if (phy_has_tsinfo(phydev)) {
> -			return phy_ts_info(phydev, info);
> +			ret = phy_ts_info(phydev, info);
> +			goto out;
>  		} else if (ops->get_ts_info) {
> -			return ops->get_ts_info(real_dev, info);
> +			ret = ops->get_ts_info(real_dev, info);
> +			goto out;
>  		}
> +	} else {
> +		rcu_read_unlock();
>  	}
>  
>  	info->so_timestamping = SOF_TIMESTAMPING_RX_SOFTWARE |
>  				SOF_TIMESTAMPING_SOFTWARE;
>  	info->phc_index = -1;
>  
> -	return 0;
> +out:
> +	if (real_dev)
> +		dev_put(real_dev);

dev_hold() and dev_put() can take NULL these days, for better or worse.
I think the code simplification is worth making use of that, even tho
it will make the backport slightly more tricky (perhaps make a not of
this in the commit message).