netdev - Re: Correct usage of dev_base

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Message-ID: <CANn89i+H9dVgVE0NbucHizZX2une+bjscjcCT+ZvVNj5YFHYpg@mail.gmail.com>
Date:   Mon, 30 Nov 2020 21:29:15 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Jakub Kicinski <kuba@...nel.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 9:26 PM Vladimir Oltean <olteanv@...il.com> wrote:
>
> On Mon, Nov 30, 2020 at 12:21:29PM -0800, Stephen Hemminger wrote:
> > if device is in a private list (in bond device), the way to handle
> > this is to use dev_hold() to keep a ref count.
>
> Correct, dev_hold is a tool that can also be used. But it is a tool that
> does not solve the general problem - only particular ones. See the other
> interesting callers of dev_get_stats in parisc, appldata, net_failover.
> We can't ignore that RTNL is used for write-side locking forever.

dev_base_lock is used to protect the list of devices (eg for /proc/net/devices),
so this will need to be replaced by something. dev_hold() won't
protect the 'list' from changing under us.