[PATCH 5.15 133/177] bonding: do not discard lowest hash bit for non layer3+4 hashing

Greg Kroah-Hartman
2022-05-04T17:42:21Z

From: suresh kumar <suresh2514@gmail.com>

[ Upstream commit 49aefd131739df552f83c566d0665744c30b1d70 ]

Commit b5f862180d70 was introduced to discard lowest hash bit for layer3+4 hashing
but it also removes last bit from non layer3+4 hashing

Below script shows layer2+3 hashing will result in same slave to be used with above commit.
$ cat hash.py
#/usr/bin/python3.6

h_dests=[0xa0, 0xa1]
h_source=0xe3
hproto=0x8
saddr=0x1e7aa8c0
daddr=0x17aa8c0

for h_dest in h_dests:
hash = (h_dest ^ h_source ^ hproto ^ saddr ^ daddr)
hash ^= hash >> 16
hash ^= hash >> 8
print(hash)

print("with last bit removed")
for h_dest in h_dests:
hash = (h_dest ^ h_source ^ hproto ^ saddr ^ daddr)
hash ^= hash >> 16
hash ^= hash >> 8
hash = hash >> 1
print(hash)

Output:
$ python3.6 hash.py
522133332
522133333 <-------------- will result in both slaves being used

with last bit removed
261066666
261066666 <-------------- only single slave used

Signed-off-by: suresh kumar <suresh2514@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/bonding/bond_main.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 46c3301a5e07..2e75b7e8f70b 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3817,14 +3817,19 @@ static bool bond_flow_dissect(struct bonding *bond, struct sk_buff *skb, const v
return true;
}

-static u32 bond_ip_hash(u32 hash, struct flow_keys *flow)
+static u32 bond_ip_hash(u32 hash, struct flow_keys *flow, int xmit_policy)
{
hash ^= (__force u32)flow_get_u32_dst(flow) ^
(__force u32)flow_get_u32_src(flow);
hash ^= (hash >> 16);
hash ^= (hash >> 8);
+
/* discard lowest hash bit to deal with the common even ports pattern */
- return hash >> 1;
+ if (xmit_policy == BOND_XMIT_POLICY_LAYER34 ||
+ xmit_policy == BOND_XMIT_POLICY_ENCAP34)
+ return hash >> 1;
+
+ return hash;
}

/* Generate hash based on xmit policy. If @skb is given it is used to linearize
@@ -3854,7 +3859,7 @@ static u32 __bond_xmit_hash(struct bonding *bond, struct sk_buff *skb, const voi
memcpy(&hash, &flow.ports.ports, sizeof(hash));
}

- return bond_ip_hash(hash, &flow);
+ return bond_ip_hash(hash, &flow, bond->params.xmit_policy);
}

/**
@@ -5012,7 +5017,7 @@ static u32 bond_sk_hash_l34(struct sock *sk)
/* L4 */
memcpy(&hash, &flow.ports.ports, sizeof(hash));
/* L3 */
- return bond_ip_hash(hash, &flow);
+ return bond_ip_hash(hash, &flow, BOND_XMIT_POLICY_LAYER34);
}

static struct net_device *__bond_sk_get_lower_dev(struct bonding *bond,
--
2.35.1