Re: [RFC PATCH net-next v2 04/10] net: sfp: Add helper to return the SFP bus name

From: Maxime Chevallier <maxime.chevallier@bootlin.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: "Andrew Lunn" <andrew@lunn.ch>,
	davem@davemloft.net, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, thomas.petazzoni@bootlin.com,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Eric Dumazet" <edumazet@google.com>,
	"Paolo Abeni" <pabeni@redhat.com>,
	linux-arm-kernel@lists.infradead.org,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	"Herve Codina" <herve.codina@bootlin.com>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Vladimir Oltean" <vladimir.oltean@nxp.com>,
	"Köry Maincent" <kory.maincent@bootlin.com>,
	"Jesse Brandeburg" <jesse.brandeburg@intel.com>
Subject: Re: [RFC PATCH net-next v2 04/10] net: sfp: Add helper to return the SFP bus name
Date: Thu, 23 Nov 2023 14:35:02 +0100	[thread overview]
Message-ID: <20231123143502.3a9a9047@device.home> (raw)
In-Reply-To: <ZVyEe0zH8Zo1NLFO@shell.armlinux.org.uk>

Hi Andrew, Russell,

On Tue, 21 Nov 2023 10:20:43 +0000
"Russell King (Oracle)" <linux@armlinux.org.uk> wrote:

> On Tue, Nov 21, 2023 at 02:00:58AM +0100, Andrew Lunn wrote:
> > > +const char *sfp_get_name(struct sfp_bus *bus)
> > > +{
> > > +	if (bus->sfp_dev)
> > > +		return dev_name(bus->sfp_dev);
> > > +
> > > +	return NULL;
> > > +}  
> > 
> > Locking? Do you assume rtnl? Does this function need to take rtnl?  
> 
> Yes, rtnl needs to be held to safely access bus->sfp_dev, and that
> either needs to happen in this function, or be documented as being
> requried (and ASSERT_RTNL() added here.)
> 
> The reason is that sfp_dev is the SFP socket device which can be
> unbound via sfp_unregister_socket(), which will set bus->sfp_dev to
> NULL. This could race with the above.
> 

That's right, I'll add an assert and document it, thanks for spotting
this.

Maxime

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