netdev - Re: [PATCH net-next V7 4/4] net/sched: Introduce act_tunnel

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Date:   Thu, 08 Sep 2016 07:19:12 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Hadar Hen Zion <hadarh@...lanox.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jiri Pirko <jiri@...lanox.com>, Jiri Benc <jbenc@...hat.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Shmulik Ladkani <shmulik.ladkani@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Amir Vadai <amirva@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>, Amir Vadai <amir@...ai.me>
Subject: Re: [PATCH net-next V7 4/4] net/sched: Introduce act_tunnel_key

On Thu, 2016-09-08 at 16:23 +0300, Hadar Hen Zion wrote:
> From: Amir Vadai <amir@...ai.me>
> 
> This action could be used before redirecting packets to a shared tunnel
> device, or when redirecting packets arriving from a such a device.


> +static void tunnel_key_release(struct tc_action *a, int bind)
> +{
> +	struct tcf_tunnel_key *t = to_tunnel_key(a);
> +	struct tcf_tunnel_key_params *params;
> +
> +	rcu_read_lock();
> +	params = rcu_dereference(t->params);
> +
> +	if (params->tcft_action == TCA_TUNNEL_KEY_ACT_SET)
> +		dst_release(&params->tcft_enc_metadata->dst);
> +
> +	kfree_rcu(params, rcu);
> +
> +	rcu_read_unlock();
> +}

Note that you own the action here, so technically speaking no writer
could possibly modify t->params while this function is running.

So you could use 

params = rcu_dereference_protected(t->params, 1)

(I could not find a way to express the 'I own this action and am the
last user' for LOCKDEP sake so I used 1)

instead of

rcu_read_lock();
params = rcu_dereference(t->params);
rcu_read_unlock();


But this is a very minor detail, and this patch looks fine to me, thanks
a lot for your patience Hadar .

Acked-by: Eric Dumazet <edumazet@...gle.com>