netdev - Re: Correct usage of dev_base

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Message-ID: <20201130194617.kzfltaqccbbfq6jr@skbuf>
Date:   Mon, 30 Nov 2020 21:46:17 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netdev <netdev@...r.kernel.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Jiri Benc <jbenc@...hat.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: Correct usage of dev_base_lock in 2020

On Mon, Nov 30, 2020 at 08:22:01PM +0100, Eric Dumazet wrote:
> And ?
>
> A bonding device can absolutely maintain a private list, ready for
> bonding ndo_get_stats() use, regardless
> of register/unregister logic.
>
> bond_for_each_slave() is simply a macro, you can replace it by something else.

Also, coming to take the comment at face value.
Can it really? How? Freeing a net_device at unregister time happens
after an RCU grace period. So whatever the bonding driver does to keep a
private list of slave devices, those pointers need to be under RCU
protection. And that doesn't help with the sleepable context that we're
looking for.