netdev - Re: [PATCH net-next V3 4/4] net/sched: Introduce act_tunnel

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Date:   Tue, 30 Aug 2016 08:05:03 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Amir Vadai <amir@...ai.me>, Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Hadar Hen Zion <hadarh@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>, Jiri Benc <jbenc@...hat.com>,
        Shmulik Ladkani <shmulik.ladkani@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Amir Vadai <amirva@...lanox.com>
Subject: Re: [PATCH net-next V3 4/4] net/sched: Introduce act_tunnel_key

On 16-08-30 07:03 AM, Amir Vadai wrote:
> On Sun, Aug 28, 2016 at 10:04:21PM -0700, Cong Wang wrote:
>> On Fri, Aug 26, 2016 at 12:16 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>> On Fri, 2016-08-26 at 11:26 -0700, Cong Wang wrote:


> Regarding the specific action in this patchset, correct me if I'm wrong,
> but I think that the lock could be removed safely.
>

 From what Eric suggested (refer to my posting on skbmod),
this becomes:

+struct tcf_tunnel_key_p {
+	int			tcft_action;
+	struct metadata_dst     *tcft_enc_metadata;
+};

/* rcu protected */
+struct tcf_tunnel_key {
+	struct tc_action	common;
+       struct tcf_tunnel_key_p *p;
+};

At init() - always alloc struct tcf_tunnel_key_p, new

old = rtnl_dereference(mykey->p);
if (ovr)
     spin_lock_bh(&mykey->tcf_lock);
... update all params here ..
rcu_assign_pointer(mykey->p, new);
if (ovr) {
      spin_unlock_bh(&mykey->tcf_lock);
      synchronize_rcu();
}

kfree(old);

at act():

rcu_read_lock();
struct tcf_tunnel_key_p *p = rcu_dereference(mykey->p);
... use p here ...
rcu_read_unlock();

Cong was looking to do something more generic for all actions.

cheers,
jamal