netdev - Re: [PATCH net-next v2] net: phy: Fix suspicious rcu

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Message-ID: <20250120103722.706b5bc8@kmaincent-XPS-13-7390>
Date: Mon, 20 Jan 2025 10:37:22 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Claudiu Beznea
 <claudiu.beznea.uj@...renesas.com>, thomas.petazzoni@...tlin.com, Andrew
 Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, Russell King
 <linux@...linux.org.uk>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2] net: phy: Fix suspicious rcu_dereference
 usage

On Fri, 17 Jan 2025 19:07:20 -0800
Jakub Kicinski <kuba@...nel.org> wrote:

> On Fri, 17 Jan 2025 23:16:59 +0100 Kory Maincent wrote:
> > > If not protected by RTNL, what prevents two threads from calling this
> > > function at the same time,
> > > thus attempting to kfree_rcu() the same pointer twice ?    
> > 
> > I don't think this function can be called simultaneously from two threads,
> > if this were the case we would have already seen several issues with the
> > phydev pointer. But maybe I am wrong.
> > 
> > The rcu_lock here is to prevent concurrent dev->hwprov pointer modification
> > done under rtnl_lock in net/ethtool/tsconfig.c.  
> 
> I could also be wrong, but I don't recall being told that suspend path
> can't race with anything else. So I think ravb should probably take
> rtnl_lock or some such when its shutting itself down.. ?
> 
> If I'm wrong I think we should mention this is from suspend and
> add Claudiu's stack trace to the commit msg.

Is it ok if I send the v3 fix in net-next even if it is closed?

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com