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

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Message-ID: <20250119172755.4fb94a86@kmaincent-XPS-13-7390>
Date: Sun, 19 Jan 2025 17:27:55 +0100
From: Kory Maincent <kory.maincent@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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 Sun, 19 Jan 2025 14:27:53 +0000
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> On Sun, Jan 19, 2025 at 01:45:18PM +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:  
>  [...]  
>  [...]  
> > > 
> > > 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.. ?  
> > 
> > Should we add an ASSERT_RTNL call in the phy_detach function? (Maybe
> > also in phy_attach to be consistent)
> > Even thought, I think it may raise lots of warning from other NIT drivers.  
> 
> How many drivers use phy_detach() ?
> 
> The answer is... phylink, bcm genet and xgbe.

phy_detach() is also called by phy_disconnect() which is much more used by the
net drivers.

> Of the phylink ones:
> 
> 1. phylink_connect_phy() - for use by drivers. This had better be
>    called _before_ the netdev is registered (without rtnl) or
>    from .ndo_open that holds the RTNL.
> 
> 2. phylink_fwnode_phy_connect() - same as above.
> 
> 3. phylink_sfp_config_phy(), called from the SFP code, and its state
>    machines. It will be holding RTNL, because it is only safe to
>    attach and detach PHYs from a registered netdev while holding RTNL.
> 
> I haven't looked any further.
> 

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