I misread jhash2() implementation. Last round should use __jhash_final() instead of __jhash_mix(). Using __jhash_mix() here leaves entropy distributed across a, b, and c, which might lead to incomplete diffusion of the faddr and fport bits into the bucket index. Replacing this last __jhash_mix() with __jhash_final() provides the correct avalanche properties for the returned value in c. $ scripts/bloat-o-meter -t vmlinux.0 vmlinux add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-4 (-4) Function old new delta inet6_ehashfn 306 302 -4 Total: Before=25155089, After=25155085, chg -0.00% Fixes: 854587e69ef3 ("tcp: improve inet6_ehashfn() entropy") Signed-off-by: Eric Dumazet Reviewed-by: Kuniyuki Iwashima --- v2: also update the comment (Jakub) net/ipv6/inet6_hashtables.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c index 109fbf620ad7cde54300b937db58ada0d5c80664..b111b51d69fc9b77ac6ea2576c1b553c74bb139d 100644 --- a/net/ipv6/inet6_hashtables.c +++ b/net/ipv6/inet6_hashtables.c @@ -42,7 +42,7 @@ u32 inet6_ehashfn(const struct net *net, * Hash laddr + faddr + lport/fport + net_hash_mix. * Notes: * We combine laddr[0] (high order 32 bits of local address) - * with net_hash_mix() to avoid using __jhash_final(a, b, c). + * with net_hash_mix() to hash a multiple of 3 words. * * We do not include JHASH_INITVAL + 36 contribution * to initial values of a, b, c. @@ -63,7 +63,7 @@ u32 inet6_ehashfn(const struct net *net, a += (__force u32)faddr->s6_addr32[2]; b += (__force u32)faddr->s6_addr32[3]; c += (__force u32)fport; - __jhash_mix(a, b, c); + __jhash_final(a, b, c); /* Note: We need to add @lport instead of fully hashing it. * See commits 9544d60a2605 ("inet: change lport contribution -- 2.53.0.1018.g2bb0e51243-goog