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

On Sun, 19 Jan 2025 14:27:53 +0000
"Russell King (Oracle)" [off-list ref] wrote:

On Sun, Jan 19, 2025 at 01:45:18PM +0100, Kory Maincent wrote:

quoted

On Fri, 17 Jan 2025 19:07:20 -0800
Jakub Kicinski [off-list ref] wrote:
  

quoted

On Fri, 17 Jan 2025 23:16:59 +0100 Kory Maincent wrote:  

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quoted

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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