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udp: ipv4: do not waste time in __udp4_lib_mcast_demux_lookup

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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: 421b3885bf ("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>
This commit is contained in:
Eric Dumazet 2014-06-12 16:13:06 -07:00 committed by David S. Miller
parent 2853af6a2e
commit 63c6f81cdd
1 changed files with 4 additions and 0 deletions
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4
net/ipv4/udp.c
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@ -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;