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

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Message-ID: <vbfwot12qk7.fsf@reg-r-vrt-018-180.mtr.labs.mlnx>
Date:   Wed, 08 Aug 2018 11:47:04 +0300
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Jiri Pirko <jiri@...nulli.us>
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


On Wed 08 Aug 2018 at 08:03, Jiri Pirko <jiri@...nulli.us> wrote:
> 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?

First of all, no API is actually "unlocked" with this patch. It is a
preparation, rtnl mutex is still in use.

Callers of these functions will have to be updated, for example, to use
their _rcu version while holding rcu_read_lock.