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    Subject[PATCH 4.4 230/241] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit
    Date
    From: David Ahern <dsahern@gmail.com>

    [ 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 <alan.maguire@oracle.com>
    Signed-off-by: David Ahern <dsahern@gmail.com>
    Tested-by: Alan Maguire <alan.maguire@oracle.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/core/neighbour.c | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    --- a/net/core/neighbour.c
    +++ b/net/core/neighbour.c
    @@ -30,6 +30,7 @@
    #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>
    @@ -2490,7 +2491,13 @@ int neigh_xmit(int index, struct net_dev
    if (!tbl)
    goto out;
    rcu_read_lock_bh();
    - 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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