diff options
| author | Eric Dumazet <edumazet@google.com> | 2026-03-27 04:06:46 +0000 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-03-29 11:45:48 -0700 |
| commit | 02d0e59e36e06fb728eb4dea8479f502c67b9fbc (patch) | |
| tree | f0b79435b9274910a7231c398499a751dbf4b1bd /net/ipv6 | |
| parent | 30fcf28d83ee30494454b3f62f89a86e9e67bc25 (diff) | |
| download | lwn-02d0e59e36e06fb728eb4dea8479f502c67b9fbc.tar.gz lwn-02d0e59e36e06fb728eb4dea8479f502c67b9fbc.zip | |
tcp: use __jhash_final() in inet6_ehashfn()
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 <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260327040646.3849503-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv6')
| -rw-r--r-- | net/ipv6/inet6_hashtables.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c index 109fbf620ad7..b111b51d69fc 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 |