Re: [PATCH net-next v2] net: phy: Fix suspicious rcu_dereference usage

From: Kory Maincent
Date: Sun Jan 19 2025 - 11:28:18 EST


On Sun, 19 Jan 2025 14:27:53 +0000
"Russell King (Oracle)" <linux@xxxxxxxxxxxxxxx> 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@xxxxxxxxxx> 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