netdev - Re: [PATCH 2/2] ethtool: Call begin() and complete() in __ethtool_get_link

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Date:   Mon, 13 Jan 2020 13:51:29 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>, davem@...emloft.ne,
        jeffrey.t.kirsher@...el.com,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Li RongQing <lirongqing@...du.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ethtool: Call begin() and complete() in
 __ethtool_get_link_ksettings()

On Fri, Jan 10, 2020 at 03:41:59PM +0800, Kai-Heng Feng wrote:
> Device like igb gets runtime suspended when there's no link partner. We
> can't get correct speed under that state:
> $ cat /sys/class/net/enp3s0/speed
> 1000
> 
> In addition to that, an error can also be spotted in dmesg:
> [  385.991957] igb 0000:03:00.0 enp3s0: PCIe link lost
> 
> It's because the igb device doesn't get runtime resumed before calling
> get_link_ksettings().
> 
> So let's call begin() and complete() like what dev_ethtool() does, to
> runtime resume/suspend or power up/down the device properly.
> 
> Once this fix is in place, igb can show the speed correctly without link
> partner:
> $ cat /sys/class/net/enp3s0/speed
> -1

I agree that we definitely should make sure ->begin() and ->complete()
are always called around ethtool_ops calls. But even if nesting should
be safe now (for in-tree drivers, that is), I'm not really happy about
calling them even in places where we positively know we are always
inside a begin / complete block as e.g. vxlan or net_failover do. (And
also linkinfo.c and linkmodes.c but it may be easier to call
->get_link_ksettings() directly there.)

How about having two helpers: one simple for "ethtool context" where we
know we already are between ->begin() and ->complete() and one with the
begin/complete calls for the rest? Another interesting question is if
any of the callers which do not have their own begin()/complete() wrap
does actually need anything more than speed and duplex (I didn't do
a full check).

Michal

> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  net/ethtool/ioctl.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
> index 182bffbffa78..c768dbf45fc4 100644
> --- a/net/ethtool/ioctl.c
> +++ b/net/ethtool/ioctl.c
> @@ -423,13 +423,26 @@ struct ethtool_link_usettings {
>  int __ethtool_get_link_ksettings(struct net_device *dev,
>  				 struct ethtool_link_ksettings *link_ksettings)
>  {
> +	int rc;
> +
>  	ASSERT_RTNL();
>  
>  	if (!dev->ethtool_ops->get_link_ksettings)
>  		return -EOPNOTSUPP;
>  
> +	if (dev->ethtool_ops->begin) {
> +		rc = dev->ethtool_ops->begin(dev);
> +		if (rc  < 0)
> +			return rc;
> +	}
> +
>  	memset(link_ksettings, 0, sizeof(*link_ksettings));
> -	return dev->ethtool_ops->get_link_ksettings(dev, link_ksettings);
> +	rc = dev->ethtool_ops->get_link_ksettings(dev, link_ksettings);
> +
> +	if (dev->ethtool_ops->complete)
> +		dev->ethtool_ops->complete(dev);
> +
> +	return rc;
>  }
>  EXPORT_SYMBOL(__ethtool_get_link_ksettings);
>  
> -- 
> 2.17.1
>