linux-kernel - Re: [PATCH] ipv6: Not to probe neighbourless routes

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Message-ID: <7788439f-6207-6da0-a6f8-db2d2fc61fe4@gmail.com>
Date:   Tue, 27 Aug 2019 17:22:34 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Yi Wang <wang.yi59@....com.cn>, davem@...emloft.net
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        xue.zhihong@....com.cn, wang.liang82@....com.cn,
        Cheng Lin <cheng.lin130@....com.cn>
Subject: Re: [PATCH] ipv6: Not to probe neighbourless routes



On 8/27/19 11:08 AM, Yi Wang wrote:
> From: Cheng Lin <cheng.lin130@....com.cn>
> 
> Originally, Router Reachability Probing require a neighbour entry
> existed. Commit 2152caea7196 ("ipv6: Do not depend on rt->n in
> rt6_probe().") removed the requirement for a neighbour entry. And
> commit f547fac624be ("ipv6: rate-limit probes for neighbourless
> routes") adds rate-limiting for neighbourless routes.
> 
> And, the Neighbor Discovery for IP version 6 (IPv6)(rfc4861) says,
> "
> 7.2.5.  Receipt of Neighbor Advertisements
> 
> When a valid Neighbor Advertisement is received (either solicited or
> unsolicited), the Neighbor Cache is searched for the target's entry.
> If no entry exists, the advertisement SHOULD be silently discarded.
> There is no need to create an entry if none exists, since the
> recipient has apparently not initiated any communication with the
> target.
> ".
> 
> In rt6_probe(), just a Neighbor Solicitation message are transmited.
> When receiving a Neighbor Advertisement, the node does nothing in a
> Neighborless condition.
> 
> Not sure it's needed to create a neighbor entry in Router
> Reachability Probing. And the Original way may be the right way.
> 
> This patch recover the requirement for a neighbour entry.
> 
> Signed-off-by: Cheng Lin <cheng.lin130@....com.cn>
> ---
>  include/net/ip6_fib.h | 5 -----
>  net/ipv6/route.c      | 5 +----
>  2 files changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
> index 4b5656c..8c2e022 100644
> --- a/include/net/ip6_fib.h
> +++ b/include/net/ip6_fib.h
> @@ -124,11 +124,6 @@ struct rt6_exception {
>  
>  struct fib6_nh {
>  	struct fib_nh_common	nh_common;
> -
> -#ifdef CONFIG_IPV6_ROUTER_PREF
> -	unsigned long		last_probe;
> -#endif
> -
>  	struct rt6_info * __percpu *rt6i_pcpu;
>  	struct rt6_exception_bucket __rcu *rt6i_exception_bucket;
>  };
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index fd059e0..c4bcffc 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -639,12 +639,12 @@ static void rt6_probe(struct fib6_nh *fib6_nh)
>  	nh_gw = &fib6_nh->fib_nh_gw6;
>  	dev = fib6_nh->fib_nh_dev;
>  	rcu_read_lock_bh();
> -	idev = __in6_dev_get(dev);
>  	neigh = __ipv6_neigh_lookup_noref(dev, nh_gw);
>  	if (neigh) {
>  		if (neigh->nud_state & NUD_VALID)
>  			goto out;
>  
> +		idev = __in6_dev_get(dev);
>  		write_lock(&neigh->lock);
>  		if (!(neigh->nud_state & NUD_VALID) &&
>  		    time_after(jiffies,
> @@ -654,9 +654,6 @@ static void rt6_probe(struct fib6_nh *fib6_nh)
>  				__neigh_set_probe_once(neigh);
>  		}
>  		write_unlock(&neigh->lock);
> -	} else if (time_after(jiffies, fib6_nh->last_probe +
> -				       idev->cnf.rtr_probe_interval)) {
> -		work = kmalloc(sizeof(*work), GFP_ATOMIC);
>  	}
>  
>  	if (work) {
> 

Have you really compiled this patch ?