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

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Message-ID: <Z44mDi3NqMONI6Yw@shell.armlinux.org.uk>
Date: Mon, 20 Jan 2025 10:31:42 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: Jakub Kicinski <kuba@...nel.org>, 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>,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2] net: phy: Fix suspicious rcu_dereference
 usage

On Mon, Jan 20, 2025 at 10:37:22AM +0100, Kory Maincent wrote:
> 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?

In general, fixes are still accepted into net-next if the pull request
hasn't been sent and the code that is being fixed is only in net-next.

-- 
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