net: Dont use ifindices in hash fns

Eric noticed, that when there will be devices with equal indices, some
hash functions that use them will become less effective as they could.
Fix this in advance by mixing the net_device address into the hash value
instead of the device index.

This is true for arp and ndisc hash fns. The netlabel, can and llc ones
are also ifindex-based, but that three are init_net-only, thus will not
be affected.

Many thanks to David and Eric for the hash32_ptr implementation!

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index 96a3b5c03e37..980d263765cf 100644
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -49,6 +49,7 @@ enum {
 #include <linux/types.h>
 #include <linux/if_arp.h>
 #include <linux/netdevice.h>
+#include <linux/hash.h>
 
 #include <net/neighbour.h>
 
@@ -134,7 +135,7 @@ static inline u32 ndisc_hashfn(const void *pkey, const struct net_device *dev, _
 {
 	const u32 *p32 = pkey;
 
-	return (((p32[0] ^ dev->ifindex) * hash_rnd[0]) +
+	return (((p32[0] ^ hash32_ptr(dev)) * hash_rnd[0]) +
 		(p32[1] * hash_rnd[1]) +
 		(p32[2] * hash_rnd[2]) +
 		(p32[3] * hash_rnd[3]));