Commit 63c6f81c authored Jun 12, 2014 by Eric Dumazet Committed by David S. Miller Jun 13, 2014

udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup



Its too easy to add thousand of UDP sockets on a particular bucket,
and slow down an innocent multicast receiver.

Early demux is supposed to be an optimization, we should avoid spending
too much time in it.

It is interesting to note __udp4_lib_demux_lookup() only tries to
match first socket in the chain.

10 is the threshold we already have in __udp4_lib_lookup() to switch
to secondary hash.

Fixes: 421b3885 ("udp: ipv4: Add udp early demux")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: David Held <drheld@google.com>
Cc: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 2853af6a

net/ipv4/udp.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -1861,6 +1861,10 @@ static struct sock __udp4_lib_mcast_demux_lookup(struct net net,
		unsigned int count, slot = udp_hashfn(net, hnum, udp_table.mask);
		struct udp_hslot *hslot = &udp_table.hash[slot];

		/* Do not bother scanning a too big list */
		if (hslot->count > 10)
		return NULL;

		rcu_read_lock();
		begin:
		count = 0;

Admin message