netdev - Re: [PATCH v3 01/11] net: sched: use rcu for action cookie update

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Date:   Mon, 28 May 2018 18:37:41 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     jiri@...nulli.us, netdev@...r.kernel.org, jhs@...atatu.com,
        xiyou.wangcong@...il.com, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net, kliteyn@...lanox.com,
        Jiri Pirko <jiri@...lanox.com>
Subject: Re: [PATCH v3 01/11] net: sched: use rcu for action cookie update

On Mon, May 28, 2018 at 12:17:19AM +0300, Vlad Buslov wrote:
> Implement functions to atomically update and free action cookie
> using rcu mechanism.
> 
> Signed-off-by: Vlad Buslov <vladbu@...lanox.com>
> Signed-off-by: Jiri Pirko <jiri@...lanox.com>

Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>

> ---
>  include/net/act_api.h |  2 +-
>  include/net/pkt_cls.h |  1 +
>  net/sched/act_api.c   | 44 ++++++++++++++++++++++++++++++--------------
>  3 files changed, 32 insertions(+), 15 deletions(-)
> 
> diff --git a/include/net/act_api.h b/include/net/act_api.h
> index 9e59ebfded62..f7b59ef7303d 100644
> --- a/include/net/act_api.h
> +++ b/include/net/act_api.h
> @@ -37,7 +37,7 @@ struct tc_action {
>  	spinlock_t			tcfa_lock;
>  	struct gnet_stats_basic_cpu __percpu *cpu_bstats;
>  	struct gnet_stats_queue __percpu *cpu_qstats;
> -	struct tc_cookie	*act_cookie;
> +	struct tc_cookie	__rcu *act_cookie;
>  	struct tcf_chain	*goto_chain;
>  };
>  #define tcf_index	common.tcfa_index
> diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
> index e828d31be5da..3068cc8aa0f1 100644
> --- a/include/net/pkt_cls.h
> +++ b/include/net/pkt_cls.h
> @@ -769,6 +769,7 @@ struct tc_mqprio_qopt_offload {
>  struct tc_cookie {
>  	u8  *data;
>  	u32 len;
> +	struct rcu_head rcu;
>  };
>  
>  struct tc_qopt_offload_stats {
> diff --git a/net/sched/act_api.c b/net/sched/act_api.c
> index 3f4cf930f809..02670c7489e3 100644
> --- a/net/sched/act_api.c
> +++ b/net/sched/act_api.c
> @@ -55,6 +55,24 @@ static void tcf_action_goto_chain_exec(const struct tc_action *a,
>  	res->goto_tp = rcu_dereference_bh(chain->filter_chain);
>  }
>  
> +static void tcf_free_cookie_rcu(struct rcu_head *p)
> +{
> +	struct tc_cookie *cookie = container_of(p, struct tc_cookie, rcu);
> +
> +	kfree(cookie->data);
> +	kfree(cookie);
> +}
> +
> +static void tcf_set_action_cookie(struct tc_cookie __rcu **old_cookie,
> +				  struct tc_cookie *new_cookie)
> +{
> +	struct tc_cookie *old;
> +
> +	old = xchg(old_cookie, new_cookie);
> +	if (old)
> +		call_rcu(&old->rcu, tcf_free_cookie_rcu);
> +}
> +
>  /* XXX: For standalone actions, we don't need a RCU grace period either, because
>   * actions are always connected to filters and filters are already destroyed in
>   * RCU callbacks, so after a RCU grace period actions are already disconnected
> @@ -65,10 +83,7 @@ static void free_tcf(struct tc_action *p)
>  	free_percpu(p->cpu_bstats);
>  	free_percpu(p->cpu_qstats);
>  
> -	if (p->act_cookie) {
> -		kfree(p->act_cookie->data);
> -		kfree(p->act_cookie);
> -	}
> +	tcf_set_action_cookie(&p->act_cookie, NULL);
>  	if (p->goto_chain)
>  		tcf_action_goto_chain_fini(p);
>  
> @@ -567,16 +582,22 @@ tcf_action_dump_1(struct sk_buff *skb, struct tc_action *a, int bind, int ref)
>  	int err = -EINVAL;
>  	unsigned char *b = skb_tail_pointer(skb);
>  	struct nlattr *nest;
> +	struct tc_cookie *cookie;
>  
>  	if (nla_put_string(skb, TCA_KIND, a->ops->kind))
>  		goto nla_put_failure;
>  	if (tcf_action_copy_stats(skb, a, 0))
>  		goto nla_put_failure;
> -	if (a->act_cookie) {
> -		if (nla_put(skb, TCA_ACT_COOKIE, a->act_cookie->len,
> -			    a->act_cookie->data))
> +
> +	rcu_read_lock();
> +	cookie = rcu_dereference(a->act_cookie);
> +	if (cookie) {
> +		if (nla_put(skb, TCA_ACT_COOKIE, cookie->len, cookie->data)) {
> +			rcu_read_unlock();
>  			goto nla_put_failure;
> +		}
>  	}
> +	rcu_read_unlock();
>  
>  	nest = nla_nest_start(skb, TCA_OPTIONS);
>  	if (nest == NULL)
> @@ -719,13 +740,8 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
>  	if (err < 0)
>  		goto err_mod;
>  
> -	if (name == NULL && tb[TCA_ACT_COOKIE]) {
> -		if (a->act_cookie) {
> -			kfree(a->act_cookie->data);
> -			kfree(a->act_cookie);
> -		}
> -		a->act_cookie = cookie;
> -	}
> +	if (!name && tb[TCA_ACT_COOKIE])
> +		tcf_set_action_cookie(&a->act_cookie, cookie);
>  
>  	/* module count goes up only when brand new policy is created
>  	 * if it exists and is only bound to in a_o->init() then
> -- 
> 2.7.5
>