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

[Kory Maincent]

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:
> > > 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.. ?

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.
 
> If I'm wrong I think we should mention this is from suspend and
> add Claudiu's stack trace to the commit msg.

Ack.

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