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Subject[PATCH 5.1 17/70] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit
From: David Ahern <>

[ Upstream commit 4b2a2bfeb3f056461a90bd621e8bd7d03fa47f60 ]

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 <>
Signed-off-by: David Ahern <>
Tested-by: Alan Maguire <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
net/core/neighbour.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -31,6 +31,7 @@
#include <linux/times.h>
#include <net/net_namespace.h>
#include <net/neighbour.h>
+#include <net/arp.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/netevent.h>
@@ -2984,7 +2985,13 @@ int neigh_xmit(int index, struct net_dev
if (!tbl)
goto out;
- neigh = __neigh_lookup_noref(tbl, addr, dev);
+ if (index == NEIGH_ARP_TABLE) {
+ u32 key = *((u32 *)addr);
+ neigh = __ipv4_neigh_lookup_noref(dev, key);
+ } else {
+ neigh = __neigh_lookup_noref(tbl, addr, dev);
+ }
if (!neigh)
neigh = __neigh_create(tbl, addr, dev, false);
err = PTR_ERR(neigh);

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