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

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Message-ID: <ZVyEe0zH8Zo1NLFO@shell.armlinux.org.uk>
Date: Tue, 21 Nov 2023 10:20:43 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	thomas.petazzoni@...tlin.com, Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Herve Codina <herve.codina@...tlin.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Köry Maincent <kory.maincent@...tlin.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [RFC PATCH net-next v2 04/10] net: sfp: Add helper to return the
 SFP bus name

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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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