netdev - Re: [PATCH net-next 01/12] net: sched: flower: don't check for rtnl on head dereference

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Message-ID: <CAM_iQpWfOoKxipJnha72e6dGv5RHEuDQvCjqU6nL1b_2tQMn9g@mail.gmail.com>
Date:   Wed, 27 Feb 2019 16:49:43 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 01/12] net: sched: flower: don't check for rtnl
 on head dereference

On Tue, Feb 26, 2019 at 6:57 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
>
> On Mon 25 Feb 2019 at 22:39, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Mon, Feb 25, 2019 at 8:11 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> >>
> >>
> >> On Fri 22 Feb 2019 at 19:32, Cong Wang <xiyou.wangcong@...il.com> wrote:
> >> >
> >> > So if it is no longer RCU any more, why do you still use
> >> > rcu_dereference_protected()? That is, why not just deref it as a raw
> >> > pointer?
> >
> >
> > Any answer for this question?
>
> I decided that since there is neither possibility of concurrent pointer
> assignment nor deallocation of object that it points to, most performant
> solution would be using rcu_dereference_protected() which is the only
> RCU dereference helper that doesn't use READ_ONCE. I now understand that
> this is confusing (and most likely doesn't provide any noticeable
> performance improvement anyway!) and will change this patch to use
> rcu_dereference_raw() as you suggest.

Yeah, please make sure sparse is happy with that. :)