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

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Message-ID: <20231123143502.3a9a9047@device.home>
Date:   Thu, 23 Nov 2023 14:35:02 +0100
From:   Maxime Chevallier <maxime.chevallier@...tlin.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>, 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

Hi Andrew, Russell,

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