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

[Jonathan Toppins]

On 5/17/22 22:18, Hangbin Liu wrote:
> On Tue, May 17, 2022 at 01:32:58PM -0400, Jonathan Toppins wrote:
> > Signed-off-by: Jonathan Toppins <jtoppins@xxxxxxxxxx>
> > ---
> > RESEND, list still didn't receive my last version
> >
> > The diffstat is slightly larger but IMO a slightly more readable version.
> > When I was reading v2 I found myself jumping around.
>
> Hi Jon,
>
> Thanks for the commit. But..
>
> > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> > index 38e152548126..f9d27b63c454 100644
> > --- a/drivers/net/bonding/bond_main.c
> > +++ b/drivers/net/bonding/bond_main.c
> > @@ -5591,23 +5591,32 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
> >   	const struct ethtool_ops *ops;
> >   	struct net_device *real_dev;
> >   	struct phy_device *phydev;
> > +	int ret = 0;
> >   
> > +	rcu_read_lock();
> >   	real_dev = bond_option_active_slave_get_rcu(bond);
> > -	if (real_dev) {
> > -		ops = real_dev->ethtool_ops;
> > -		phydev = real_dev->phydev;
> > -
> > -		if (phy_has_tsinfo(phydev)) {
> > -			return phy_ts_info(phydev, info);
> > -		} else if (ops->get_ts_info) {
> > -			return ops->get_ts_info(real_dev, info);
> > -		}
> > -	}
> > +	if (real_dev)
> > +		dev_hold(real_dev);
> > +	rcu_read_unlock();
> > +
> > +	if (!real_dev)
> > +		goto software;
> >   
> > +	ops = real_dev->ethtool_ops;
> > +	phydev = real_dev->phydev;
> > +
> > +	if (phy_has_tsinfo(phydev))
> > +		ret = phy_ts_info(phydev, info);
> > +	else if (ops->get_ts_info)
> > +		ret = ops->get_ts_info(real_dev, info);
> 	else {
> 		dev_put(real_dev);
> 		goto software;
> 	}
>
> Here we need another check and goto software if !phy_has_tsinfo() and
> no ops->get_ts_info. With this change we also have 2 goto and dev_put().

Ah yes. I cannot think of a way to make this simpler. The patch below 
looks good.

> > +
> > +	dev_put(real_dev);
> > +	return ret;
> > +
> > +software:
> >   	info->so_timestamping = SOF_TIMESTAMPING_RX_SOFTWARE |
> >   				SOF_TIMESTAMPING_SOFTWARE;
> >   	info->phc_index = -1;
> > -
> >   	return 0;
> >   }
>
> As Jakub remind, dev_hold() and dev_put() can take NULL now. So how about
> this new patch:
>
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 38e152548126..b5c5196e03ee 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -5591,16 +5591,23 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
>   	const struct ethtool_ops *ops;
>   	struct net_device *real_dev;
>   	struct phy_device *phydev;
> +	int ret = 0;
>   
> +	rcu_read_lock();
>   	real_dev = bond_option_active_slave_get_rcu(bond);
> +	dev_hold(real_dev);
> +	rcu_read_unlock();
> +
>   	if (real_dev) {
>   		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;
>   		}
>   	}
>   
> @@ -5608,7 +5615,9 @@ static int bond_ethtool_get_ts_info(struct net_device *bond_dev,
>   				SOF_TIMESTAMPING_SOFTWARE;
>   	info->phc_index = -1;
>   
> -	return 0;
> +out:
> +	dev_put(real_dev);
> +	return ret;
>   }
>
> Thanks
> Hangbin