| Message ID | 20180622232747.145594-1-edumazet@google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | [net-next] netns: get more entropy from net_hash_mix() | expand |
From: Eric Dumazet <edumazet@google.com> Date: Fri, 22 Jun 2018 16:27:47 -0700 > struct net are effectively allocated from order-1 pages on x86, > with one object per slab, meaning that the 13 low order bits > of their addresses are zero. > > Once shifted by L1_CACHE_SHIFT, this leaves 7 zero-bits, > meaning that net_hash_mix() does not help spreading > objects on various hash tables. > > For example, TCP listen table has 32 buckets, meaning that > all netns use the same bucket for port 80 or port 443. > > Signed-off-by: Eric Dumazet <edumazet@google.com> > Reported-by: Maciej Żenczykowski <maze@google.com> Good catch, applied, thanks Eric.
diff --git a/include/net/netns/hash.h b/include/net/netns/hash.h index 24c78183a4c262e086c29cde1e61b7f397d8bab0..16a842456189f2fc1a3363685b5dd4310a32b2b8 100644 --- a/include/net/netns/hash.h +++ b/include/net/netns/hash.h @@ -9,12 +9,7 @@ struct net; static inline u32 net_hash_mix(const struct net *net) { #ifdef CONFIG_NET_NS - /* - * shift this right to eliminate bits, that are - * always zeroed - */ - - return (u32)(((unsigned long)net) >> L1_CACHE_SHIFT); + return (u32)(((unsigned long)net) >> ilog2(sizeof(*net))); #else return 0; #endif
struct net are effectively allocated from order-1 pages on x86, with one object per slab, meaning that the 13 low order bits of their addresses are zero. Once shifted by L1_CACHE_SHIFT, this leaves 7 zero-bits, meaning that net_hash_mix() does not help spreading objects on various hash tables. For example, TCP listen table has 32 buckets, meaning that all netns use the same bucket for port 80 or port 443. Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Maciej Żenczykowski <maze@google.com> --- include/net/netns/hash.h | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)