netdev - Re: [PATCH net-next 12/14] net: sched: act_mirred: remove dependency on rtnl lock

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Date:   Wed, 8 Aug 2018 10:03:08 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jhs@...atatu.com,
        xiyou.wangcong@...il.com, pablo@...filter.org,
        kadlec@...ckhole.kfki.hu, fw@...len.de, ast@...nel.org,
        daniel@...earbox.net, edumazet@...gle.com, keescook@...omium.org,
        marcelo.leitner@...il.com
Subject: Re: [PATCH net-next 12/14] net: sched: act_mirred: remove dependency
 on rtnl lock

Wed, Aug 08, 2018 at 09:40:35AM CEST, vladbu@...lanox.com wrote:
>
>On Tue 07 Aug 2018 at 16:36, Jiri Pirko <jiri@...nulli.us> wrote:
>> Mon, Aug 06, 2018 at 08:54:23AM CEST, vladbu@...lanox.com wrote:
>>
>> [...]
>>
>>>diff --git a/include/net/tc_act/tc_tunnel_key.h b/include/net/tc_act/tc_tunnel_key.h
>>>index 46b8c7f1c8d5..e6e475d788c6 100644
>>>--- a/include/net/tc_act/tc_tunnel_key.h
>>>+++ b/include/net/tc_act/tc_tunnel_key.h
>>>@@ -30,26 +30,47 @@ struct tcf_tunnel_key {
>>> 
>>> static inline bool is_tcf_tunnel_set(const struct tc_action *a)
>>> {
>>>+	bool ret = false;
>>> #ifdef CONFIG_NET_CLS_ACT
>>> 	struct tcf_tunnel_key *t = to_tunnel_key(a);
>>>-	struct tcf_tunnel_key_params *params = rtnl_dereference(t->params);
>>>+	struct tcf_tunnel_key_params *params;
>>> 
>>>+	rcu_read_lock();
>>>+	params = rcu_dereference(t->params);
>>> 	if (a->ops && a->ops->type == TCA_ACT_TUNNEL_KEY)
>>>-		return params->tcft_action == TCA_TUNNEL_KEY_ACT_SET;
>>>+		ret = params->tcft_action == TCA_TUNNEL_KEY_ACT_SET;
>>>+	rcu_read_unlock();
>>> #endif
>>>-	return false;
>>>+	return ret;
>>> }
>>> 
>>> static inline bool is_tcf_tunnel_release(const struct tc_action *a)
>>
>> Why are these tunnel things in a mirred patch?
>
>Mistake during re-slit. Will move those to tunnel_key patch.

Are you sure that the changes are safe? I just quickly looked over it
and it smells:
drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:
                if (is_tcf_tunnel_set(a)) {
                        info = tcf_tunnel_info(a);

Why the "t->params" can't be nulled in the middle?