netdev - Re: Correct usage of dev_base

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Message-ID: <CANn89i+njuoeg7uAwWd08NKONXa4d2f47XpN4Kt83192mCZLwg@mail.gmail.com>
Date:   Mon, 30 Nov 2020 19:30:38 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        Vladimir Oltean <olteanv@...il.com>,
        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 7:14 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Mon, 30 Nov 2020 11:41:10 +0100 Eric Dumazet wrote:
> > > So dev_base_lock dates back to the Big Kernel Lock breakup back in Linux 2.4
> > > (ie before my time). The time has come to get rid of it.
> > >
> > > The use is sysfs is because could be changed to RCU. There have been issues
> > > in the past with sysfs causing lock inversions with the rtnl mutex, that
> > > is why you will see some trylock code there.
> > >
> > > My guess is that dev_base_lock readers exist only because no one bothered to do
> > > the RCU conversion.
> >
> > I think we did, a long time ago.
> >
> > We took care of all ' fast paths' already.
> >
> > Not sure what is needed, current situation does not bother me at all ;)
>
> Perhaps Vladimir has a plan to post separately about it (in that case
> sorry for jumping ahead) but the initial problem was procfs which is
> (hopefully mostly irrelevant by now, and) taking the RCU lock only
> therefore forcing drivers to have re-entrant, non-sleeping
> .ndo_get_stats64 implementations.

I think bonding also calls  ndo_get_stats64() while in non-sleeping context.