[PATCH net-next 2/3] ipv4: rate limit updating of next hop exceptions with same pmtu

["Timo Teräs" <timo.teras@iki.fi>]

The tunnel devices call update_pmtu for each packet sent, this causes
contention on the fnhe_lock. Ignore the pmtu update if pmtu is not
actually changed, and there is still plenty of time before the entry
expires.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
---
 net/ipv4/route.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 561a378..a4082be 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -947,6 +947,10 @@ static void __ip_rt_update_pmtu(struct rtable *rt, struct flowi4 *fl4, u32 mtu)
 	if (mtu < ip_rt_min_pmtu)
 		mtu = ip_rt_min_pmtu;
 
+	if (rt->rt_pmtu == mtu &&
+	    time_before(jiffies, dst->expires - ip_rt_mtu_expires / 2))
+		return;
+
 	rcu_read_lock();
 	if (fib_lookup(dev_net(dst->dev), fl4, &res) == 0) {
 		struct fib_nh *nh = &FIB_RES_NH(res);
-- 
1.8.2.3