linux-kernel - Re: [PATCH NET] net/hns:bugfix of ethtool -t phy self

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Date:   Thu, 22 Jun 2017 11:49:46 +0800
From:   l00371289 <linyunsheng@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Florian Fainelli <f.fainelli@...il.com>, <davem@...emloft.net>,
        <huangdaode@...ilicon.com>, <xuwei5@...ilicon.com>,
        <liguozhu@...ilicon.com>, <Yisen.Zhuang@...wei.com>,
        <gabriele.paoloni@...wei.com>, <john.garry@...wei.com>,
        <linuxarm@...wei.com>, <salil.mehta@...wei.com>,
        <lipeng321@...wei.com>, <yankejian@...wei.com>,
        <tremyfr@...il.com>, <xieqianqian@...wei.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH NET] net/hns:bugfix of ethtool -t phy self_test

Hi, Andrew

On 2017/6/22 11:35, Andrew Lunn wrote:
>> I don't think returning to user space is an option, because it mean
>> ethtool phy self test would fail because if availability of some software
>> resoure, which is not some application would expect. here is what I can
>> think of:
>>
>> driver/net/ethernet/hisilicon/hns/hns_ethtool.c
>> int phy_loopback_selftest(struct phy_device *dev)
>> {
>> 	int err;
>>
>> 	mutex_lock(dev->mutex);
>>
>> 	if (dev->drv->loopback)
>> 		err = dev->drv->loopback(dev, 1);
>>
>> 	if (err)
>> 		goto out;
>> 	
>> 	/* mac driver do the test*/
>> 	.................
>>
>>
>> 	if (dev->drv->loopback)
>> 		err = dev->drv->loopback(dev, 0);
>>
>> 	if (err)
>> 		goto out;
>>
>> out:
>> 	mutex_unlock(dev->mutex);
>> 	return err;
>> }
> 
> I don't think you need a mutex here. dev_ioctl.c:
> 
>        case SIOCETHTOOL:
>                 dev_load(net, ifr.ifr_name);
>                 rtnl_lock();
>                 ret = dev_ethtool(net, &ifr);
>                 rtnl_unlock();
>  
> So all ethtool operations are protected by the rtnl. You cannot have
> two tests running at once.
> 
>> One question I can think of is that, how do we ensure mac driver enable and
>> disable phy loopback in pair, enable loopback after dev->mutex is taken,
>> disable loopback  before dev->mutex is released?
>> I hope I am not missing something obvious, any suggestion and idea?
> 
> You cannot ensure this. But it would be a pretty obvious bug.
> 
Thanks for your reply, I will send a new patch based on the discussion above.
Please let me know if there is anything else need changing.

Best Regards
Yunsheng Lin