netdev - Re: [PATCH 6/7] get rid of tc_u

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Date:   Fri, 7 Sep 2018 05:28:56 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH 6/7] get rid of tc_u_common ->rcu

On Thu, Sep 06, 2018 at 09:18:47PM -0700, Cong Wang wrote:
> On Wed, Sep 5, 2018 at 12:04 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > From: Al Viro <viro@...iv.linux.org.uk>
> >
> > unused
> >
> > Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> > ---
> >  net/sched/cls_u32.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> > index 8a1a573487bd..be9240ae1417 100644
> > --- a/net/sched/cls_u32.c
> > +++ b/net/sched/cls_u32.c
> > @@ -98,7 +98,6 @@ struct tc_u_common {
> >         int                     refcnt;
> >         struct idr              handle_idr;
> >         struct hlist_node       hnode;
> > -       struct rcu_head         rcu;
> >  };
> 
> Just FYI:
> 
> This was added when RCU was introduced to u32 fast path,
> it looks like on fast path we never touch tc_u_common, we
> only use tp->root, all the rest are slow paths with RTNL lock,
> so it is probably fine to just remove it rather than converting
> that kfree() to kfree_rcu().

*nod*

In any case, if u32_classify() grows that dereference, we can always
re-add ->rcu at the same time.