netdev - Re: [PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in neigh

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Message-Id: <20190504.004111.284554825798498883.davem@davemloft.net>
Date:   Sat, 04 May 2019 00:41:11 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, alan.maguire@...cle.com,
        jwestfall@...realistic.net, dsahern@...il.com
Subject: Re: [PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in
 neigh_xmit

From: David Ahern <dsahern@...nel.org>
Date: Wed,  1 May 2019 18:18:42 -0700

> From: David Ahern <dsahern@...il.com>
> 
> Commit cd9ff4de0107 changed the key for IFF_POINTOPOINT devices to
> INADDR_ANY but neigh_xmit which is used for MPLS encapsulations was not
> updated to use the altered key. The result is that every packet Tx does
> a lookup on the gateway address which does not find an entry, a new one
> is created only to find the existing one in the table right before the
> insert since arp_constructor was updated to reset the primary key. This
> is seen in the allocs and destroys counters:
>     ip -s -4 ntable show | head -10 | grep alloc
> 
> which increase for each packet showing the unnecessary overhread.
> 
> Fix by having neigh_xmit use __ipv4_neigh_lookup_noref for NEIGH_ARP_TABLE.
> 
> Fixes: cd9ff4de0107 ("ipv4: Make neigh lookup keys for loopback/point-to-point devices be INADDR_ANY")
> Reported-by: Alan Maguire <alan.maguire@...cle.com>
> Signed-off-by: David Ahern <dsahern@...il.com>

Applied and queued up for -stable.