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net: small bug on rxhash calculation 

In the current rxhash calculation function, while the
sorting of the ports/addrs is coherent (you get the
same rxhash for packets sharing the same 4-tuple, in
both directions), ports and addrs are sorted
independently. This implies packets from a connection
between the same addresses but crossed ports hash to
the same rxhash.

For example, traffic between A=S:l and B=L:s is hashed
(in both directions) from {L, S, {s, l}}. The same
rxhash is obtained for packets between C=S:s and D=L:l.

This patch ensures that you either swap both addrs and ports,
or you swap none. Traffic between A and B, and traffic
between C and D, get their rxhash from different sources
({L, S, {l, s}} for A<->B, and {L, S, {s, l}} for C<->D)

The patch is co-written with Eric Dumazet <edumazet@google.com>

Signed-off-by: Chema Gonzalez <chema@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Chema Gonzalez 2012-09-07 13:40:50 +00:00 committed by David S. Miller
parent 777bf135b7
commit 6862234238
1 changed files with 6 additions and 5 deletions
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11
net/core/dev.c
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@ -2647,15 +2647,16 @@ void __skb_get_rxhash(struct sk_buff *skb)
if (!skb_flow_dissect(skb, &keys))
return;
if (keys.ports) {
if ((__force u16)keys.port16[1] < (__force u16)keys.port16[0])
swap(keys.port16[0], keys.port16[1]);
if (keys.ports)
skb->l4_rxhash = 1;
}
/* get a consistent hash (same value on both flow directions) */
if ((__force u32)keys.dst < (__force u32)keys.src)
if (((__force u32)keys.dst < (__force u32)keys.src) ||
(((__force u32)keys.dst == (__force u32)keys.src) &&
((__force u16)keys.port16[1] < (__force u16)keys.port16[0]))) {
swap(keys.dst, keys.src);
swap(keys.port16[0], keys.port16[1]);
}
hash = jhash_3words((__force u32)keys.dst,
(__force u32)keys.src,