netdev - Re: [PATCH net-next v4 07/17] net: sched: protect filter_chain list with filter_chain

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Date:   Mon, 18 Feb 2019 10:31:29 -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>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net-next v4 07/17] net: sched: protect filter_chain list
 with filter_chain_lock mutex

On Mon, Feb 18, 2019 at 3:06 AM Vlad Buslov <vladbu@...lanox.com> wrote:
>
> On Fri 15 Feb 2019 at 22:35, Cong Wang <xiyou.wangcong@...il.com> wrote:
> > On Mon, Feb 11, 2019 at 12:56 AM Vlad Buslov <vladbu@...lanox.com> wrote:
> >> +#ifdef CONFIG_PROVE_LOCKING
> >> +static inline bool lockdep_tcf_chain_is_locked(struct tcf_chain *chain)
> >> +{
> >> +       return lockdep_is_held(&chain->filter_chain_lock);
> >> +}
> >> +#else
> >> +static inline bool lockdep_tcf_chain_is_locked(struct tcf_block *chain)
> >> +{
> >> +       return true;
> >> +}
> >> +#endif /* #ifdef CONFIG_PROVE_LOCKING */
> >> +
> >> +#define tcf_chain_dereference(p, chain)                                        \
> >> +       rcu_dereference_protected(p, lockdep_tcf_chain_is_locked(chain))
> >
> >
> > Are you sure you need this #ifdef CONFIG_PROVE_LOCKING?
> > rcu_dereference_protected() should already test CONFIG_PROVE_RCU.
> >
> > Ditto for tcf_proto_dereference().
>
> I implemented these macro same way as rtnl_dereference() is implemented,
> which they are intended to substitute.
>
> After removing them I get following compilation error with
> CONFIG_PROVE_LOCKING disabled:


This is pretty odd, because net/core/neighbour.c uses it without
any #ifdef CONFIG_PROVE_LOCKING, for instance:

 192                 neigh = rcu_dereference_protected(n->next,
 193
lockdep_is_held(&tbl->lock));
 194                 rcu_assign_pointer(*np, neigh);
 195                 neigh_mark_dead(n);
 196                 retval = true;

So how does this compile when CONFIG_PROVE_LOCKING
is disabled? :-/