From 706b7c83f1b558b628f2a2cd6a34f31b874df12d Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 22 Jun 2018 16:27:47 -0700 Subject: [PATCH] netns: get more entropy from net_hash_mix() MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Reported-by: Maciej Żenczykowski Signed-off-by: David S. Miller --- include/net/netns/hash.h | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/include/net/netns/hash.h b/include/net/netns/hash.h index 24c78183a4c26..16a842456189f 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 -- 2.39.5