netdev - Re: [PATCH net v4] smsc911x: only update stats when interface is up

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Date:   Fri, 31 Mar 2023 11:53:46 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        Steve Glendinning <steve.glendinning@...well.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v4] smsc911x: only update stats when interface is up


> > From some light research, I can't find a trace of RCU sync. Pity, I'll
> > need to move furhter investigation to later. I'll report back if I have
> > something, but it may take a while. Thanks for the help!
> 
> If you don't want to spend too much time you can just call it yourself
> right? :) Put a synchronize_rcu() with a comment about concurrent stat
> reading after pdata->is_open = false; and that's it?

Probably. Although I trust you, I would still add code which I a) don't
fully understand myself yet and b) feels somehow wrong because something
like synchronize_rcu() should likely not be in drivers but somewhere
more generic. Given that the bug in this driver went unnoticed for years
(same with the race in other drivers), I do prefer to come back later
with the good feeling that I understood the problem and fixed it
thoroughly.


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