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

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Date:   Wed, 18 May 2022 11:54:27 -0400
From:   Jonathan Toppins <jtoppins@...hat.com>
To:     Hangbin Liu <liuhangbin@...il.com>
Cc:     andy@...yhouse.net, davem@...emloft.net, dsahern@...il.com,
        eric.dumazet@...il.com, j.vosburgh@...il.com, kuba@...nel.org,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzbot+92beb3d46aab498710fa@...kaller.appspotmail.com,
        vfalico@...il.com, vladimir.oltean@....com,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 net] bonding: fix missed rcu protection

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@...hat.com>
>> ---
>> 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
>