netdev - Re: [PATCH net v2] net/sched: act_police: fix race condition on state variables

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Message-ID: <CANn89i+TVx2D+hC+m+JwFZP+2brpRyu-dpoMX4KkfN5AFkkrDA@mail.gmail.com>
Date:   Tue, 20 Nov 2018 15:29:52 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     dcaratti@...hat.com, Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, netdev <netdev@...r.kernel.org>,
        ivecera@...hat.com
Subject: Re: [PATCH net v2] net/sched: act_police: fix race condition on state variables

On Tue, Nov 20, 2018 at 3:28 PM David Miller <davem@...emloft.net> wrote:
>
> From: Davide Caratti <dcaratti@...hat.com>
> Date: Tue, 20 Nov 2018 22:18:44 +0100
>
> > after 'police' configuration parameters were converted to use RCU instead
> > of spinlock, the state variables used to compute the traffic rate (namely
> > 'tcfp_toks', 'tcfp_ptoks' and 'tcfp_t_c') are erroneously read/updated in
> > the traffic path without any protection.
> >
> > Use a dedicated spinlock to avoid race conditions on these variables, and
> > ensure proper cache-line alignment. In this way, 'police' is still faster
> > than what we observed when 'tcf_lock' was used in the traffic path _ i.e.
> > reverting commit 2d550dbad83c ("net/sched: act_police: don't use spinlock
> > in the data path"). Moreover, we preserve the throughput improvement that
> > was obtained after 'police' started using per-cpu counters, when 'avrate'
> > is used instead of 'rate'.
> >
> > Changes since v1 (thanks to Eric Dumazet):
> > - call ktime_get_ns() before acquiring the lock in the traffic path
> > - use a dedicated spinlock instead of tcf_lock
> > - improve cache-line usage
> >
> > Fixes: 2d550dbad83c ("net/sched: act_police: don't use spinlock in the data path")
> > Reported-and-suggested-by: Eric Dumazet <eric.dumazet@...il.com>
> > Signed-off-by: Davide Caratti <dcaratti@...hat.com>
>
> Applied.

We need a fix to make lockdep happy, as reported by Cong.

Cong, do you want to handle this ?

Thanks !