Commit 1f1e030b authored Jan 06, 2006 by NeilBrown Committed by Linus Torvalds Jan 06, 2006

[PATCH] knfsd: fix hash function for IP addresses on 64bit little-endian machines.



The hash.h hash_long function, when used on a 64 bit machine, ignores many
of the middle-order bits.  (The prime chosen it too bit-sparse).

IP addresses for clients of an NFS server are very likely to differ only in
the low-order bits.  As addresses are stored in network-byte-order, these
bits become middle-order bits in a little-endian 64bit 'long', and so do
not contribute to the hash.  Thus you can have the situation where all
clients appear on one hash chain.

So, until hash_long is fixed (or maybe forever), us a hash function that
works well on IP addresses - xor the bytes together.

Thanks to "Iozone" <capps@iozone.org> for identifying this problem.

Cc: "Iozone" <capps@iozone.org>

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

parent 4b2f0260

net/sunrpc/svcauth_unix.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -101,10 +101,22 @@ static void ip_map_put(struct cache_head item, struct cache_detail cd)
		}
		}

		#if IP_HASHBITS == 8
		/* hash_long on a 64 bit machine is currently REALLY BAD for
		* IP addresses in reverse-endian (i.e. on a little-endian machine).
		* So use a trivial but reliable hash instead
		*/
		static inline int hash_ip(unsigned long ip)
		{
		int hash = ip ^ (ip>>16);
		return (hash ^ (hash>>8)) & 0xff;
		}
		#endif

		static inline int ip_map_hash(struct ip_map *item)
		{
		return hash_str(item->m_class, IP_HASHBITS) ^
		hash_long((unsigned long)item->m_addr.s_addr, IP_HASHBITS);
		hash_ip((unsigned long)item->m_addr.s_addr);
		}
		static inline int ip_map_match(struct ip_map item, struct ip_map tmp)
		{

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