linux-kernel - [PATCH v2] ipv6: Not to probe neighbourless routes

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Date:   Wed, 28 Aug 2019 10:19:25 +0800
From:   Yi Wang <wang.yi59@....com.cn>
To:     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.yi59@....com.cn,
        wang.liang82@....com.cn, Cheng Lin <cheng.lin130@....com.cn>
Subject: [PATCH v2] ipv6: Not to probe neighbourless routes

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      | 6 +-----
 2 files changed, 1 insertion(+), 10 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..1839dd7 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,
@@ -654,13 +654,9 @@ 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) {
-		fib6_nh->last_probe = jiffies;
 		INIT_WORK(&work->work, rt6_probe_deferred);
 		work->target = *nh_gw;
 		dev_hold(dev);
-- 
1.8.3.1