netdev - Re: [PATCH net-next 08/11] net_sched: act_nat: use RCU in tcf_nat

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Message-ID: <20250708125411.GG452973@horms.kernel.org>
Date: Tue, 8 Jul 2025 13:54:11 +0100
From: Simon Horman <horms@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org,
	eric.dumazet@...il.com
Subject: Re: [PATCH net-next 08/11] net_sched: act_nat: use RCU in
 tcf_nat_dump()

On Mon, Jul 07, 2025 at 01:01:07PM +0000, Eric Dumazet wrote:
> Also storing tcf_action into struct tcf_nat_params
> makes sure there is no discrepancy in tcf_nat_act().
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

...

> @@ -268,21 +268,20 @@ static int tcf_nat_dump(struct sk_buff *skb, struct tc_action *a,
>  			int bind, int ref)
>  {
>  	unsigned char *b = skb_tail_pointer(skb);
> -	struct tcf_nat *p = to_tcf_nat(a);
> +	const struct tcf_nat *p = to_tcf_nat(a);
> +	const struct tcf_nat_parms *parms;
>  	struct tc_nat opt = {
>  		.index    = p->tcf_index,
>  		.refcnt   = refcount_read(&p->tcf_refcnt) - ref,
>  		.bindcnt  = atomic_read(&p->tcf_bindcnt) - bind,
>  	};
> -	struct tcf_nat_parms *parms;
>  	struct tcf_t t;
>  
> -	spin_lock_bh(&p->tcf_lock);
> -
> -	opt.action = p->tcf_action;
> +	rcu_read_lock();
>  
> -	parms = rcu_dereference_protected(p->parms, lockdep_is_held(&p->tcf_lock));
> +	parms = rcu_dereference(p->parms);
>  
> +	opt.action = parms->action;
>  	opt.old_addr = parms->old_addr;
>  	opt.new_addr = parms->new_addr;
>  	opt.mask = parms->mask;
> @@ -294,12 +293,12 @@ static int tcf_nat_dump(struct sk_buff *skb, struct tc_action *a,
>  	tcf_tm_dump(&t, &p->tcf_tm);
>  	if (nla_put_64bit(skb, TCA_NAT_TM, sizeof(t), &t, TCA_NAT_PAD))
>  		goto nla_put_failure;
> -	spin_unlock_bh(&p->tcf_lock);
> +	rcu_read_lock();

Hi Eric,

Should this be rcu_read_unlock()?
                        ^^

Flagged by Smatch.


>  
>  	return skb->len;
>  
>  nla_put_failure:
> -	spin_unlock_bh(&p->tcf_lock);
> +	rcu_read_unlock();
>  	nlmsg_trim(skb, b);
>  	return -1;
>  }
> -- 
> 2.50.0.727.gbf7dc18ff4-goog
>