netdev - Re: Correct usage of dev_base

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Message-ID: <20201130205053.mb6ouveu3nsts3np@skbuf>
Date:   Mon, 30 Nov 2020 22:50:53 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Eric Dumazet <edumazet@...gle.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 09:43:01PM +0100, Eric Dumazet wrote:
> Understood, but really dev_base_lock can only be removed _after_ we
> convert all usages to something else (mutex based, and preferably not
> the global RTNL)

Sure.
A large part of getting rid of dev_base_lock seems to be just:
- deleting the bogus usage from mlx4 infiniband and friends
- converting procfs, sysfs and friends to netdev_lists_mutex
- renaming whatever is left into something related to the RFC 2863
  operstate.

> Focusing on dev_base_lock seems a distraction really.

Maybe.
But it's going to be awkward to explain in words what the locking rules
are, when the read side can take optionally the dev_base_lock, RCU, or
netdev_lists_lock, and the write side can take optionally the dev_base_lock,
RTNL, or netdev_lists_lock. Not to mention that anybody grepping for
dev_base_lock will see the current usage and not make a lot out of it.

I'm not really sure how to order this rework to be honest.