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

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Message-ID: <20250117190720.1bb02d71@kernel.org>
Date: Fri, 17 Jan 2025 19:07:20 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Kory Maincent <kory.maincent@...tlin.com>
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 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.
-- 
pw-bot: cr