[PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit

[PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit

[David Ahern]

From: David Ahern <dsahern@gmail.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@oracle.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
---
 net/core/neighbour.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index aff051e5521d..9b9da5142613 100644
--- 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_device *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);
-- 
2.11.0

Re: [PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit

[Alan Maguire]

On Wed, 1 May 2019, David Ahern wrote:

> From: David Ahern <dsahern@gmail.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@oracle.com>
> Signed-off-by: David Ahern <dsahern@gmail.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  net/core/neighbour.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index aff051e5521d..9b9da5142613 100644
> --- 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_device *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);
> -- 
> 2.11.0
> 
> 

Re: [PATCH net] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit

[David Miller]

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

> From: David Ahern <dsahern@gmail.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@oracle.com>
> Signed-off-by: David Ahern <dsahern@gmail.com>

Applied and queued up for -stable.