netdev - Re: [PATCH net-next v2 1/8] ethtool: Add support for configuring frame preemption

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Message-ID: <87v9bszfzl.fsf@vcostago-mobl2.amr.corp.intel.com>
Date:   Tue, 19 Jan 2021 15:03:42 -0800
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "m-karicheri2@...com" <m-karicheri2@...com>,
        "Jose.Abreu@...opsys.com" <Jose.Abreu@...opsys.com>,
        Po Liu <po.liu@....com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        "mkubecek@...e.cz" <mkubecek@...e.cz>
Subject: Re: [PATCH net-next v2 1/8] ethtool: Add support for configuring
 frame preemption

Hi Vladimir,

Vladimir Oltean <vladimir.oltean@....com> writes:

> On Mon, Jan 18, 2021 at 04:40:21PM -0800, Vinicius Costa Gomes wrote:
>> +int ethnl_set_preempt(struct sk_buff *skb, struct genl_info *info)
>> +{
>> +	struct ethnl_req_info req_info = {};
>> +	struct nlattr **tb = info->attrs;
>> +	struct ethtool_fp preempt = {};
>> +	struct net_device *dev;
>> +	bool mod = false;
>> +	int ret;
>> +
>> +	ret = ethnl_parse_header_dev_get(&req_info,
>> +					 tb[ETHTOOL_A_PREEMPT_HEADER],
>> +					 genl_info_net(info), info->extack,
>> +					 true);
>> +	if (ret < 0)
>> +		return ret;
>> +	dev = req_info.dev;
>> +	ret = -EOPNOTSUPP;
>> +	if (!dev->ethtool_ops->get_preempt ||
>> +	    !dev->ethtool_ops->set_preempt)
>> +		goto out_dev;
>> +
>> +	rtnl_lock();
>
> I'm a bit of a noob when it comes to ethtool (netlink or otherwise).
> Why do you take the rtnl_mutex when updating some purely hardware
> values, what netdev state is there to protect? Can this get->modify->set
> sequence be serialized using other locking mechanism than rtnl_mutex?

>From what I understand, configuration changes to netdevice should be
protected by rtnl_mutex, for example, to avoid the device disappearing
while the configuration is in progress. I don't think there's any other
finer grained lock that can be used here.


Cheers,
-- 
Vinicius