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Date: Thu, 7 May 2026 09:01:27 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Bobby Eshleman <bobbyeshleman@gmail.com>
Cc: Paolo Abeni <pabeni@redhat.com>, Alexander Duyck
 <alexanderduyck@fb.com>, kernel-team@meta.com, Andrew Lunn
 <andrew+netdev@lunn.ch>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Russell King <linux@armlinux.org.uk>,
 netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Bobby Eshleman
 <bobbyeshleman@meta.com>
Subject: Re: [PATCH net v2] eth: fbnic: fix double-free of PCS on phylink
 creation failure
Message-ID: <20260507090127.285a5087@kernel.org>
In-Reply-To: <afyxOaFhFzEKDK//@devvm29614.prn0.facebook.com>
References: <20260504-fbnic-pcs-fix-v2-1-de45192821d9@meta.com>
	<6cec0c03-5bdc-4131-9899-bc5c77fba198@redhat.com>
	<20260507072453.5eec7051@kernel.org>
	<20260507072954.263ae8dd@kernel.org>
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On Thu, 7 May 2026 08:35:21 -0700 Bobby Eshleman wrote:
> > > fbd is a devlink priv, not netdev priv, touching it after free_netdev()
> > > is perfectly fine. I wish Gemini tried a *little* harder instead of
> > > guessing :| Sorry for not commenting earlier.  
> > 
> > Ugh, not enough coffee. It's complaining about MDIO reads, I think
> > that's valid.  
> 
> It is, but I think the race pre-exists.
> 
> static int
> fbnic_mdio_read_pmd(struct fbnic_dev *fbd, int addr, int regnum)
> [...]
> 	if (fbd->netdev) {
> 		fbn = netdev_priv(fbd->netdev);
> 		if (fbn->aui < FBNIC_AUI_UNKNOWN)
> 			aui = fbn->aui;
> 	}
> 
> 
> Definitely possible that ->netdev gets freed concurrently with
> fbd->netdev evaluating to true... but fbnic_netdev_free() faces the same
> race.
> 
> I'm open to fixing this all at once, if preferred. Probably need to look
> at some of the other fbnic_net ptr guards too.

I agree with Paolo, seems separate.

FWIW I think the fix may be to move the single aui field that mdio
cares about to fbd instead of fbn ? Feels like the problem is due
to a layering violation, mdio should not be touching fbn fields.