From 0e1efe9d5e10921f1e2152b108e013605fca3c9f Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 5 Dec 2012 09:18:10 +0000
Subject: [PATCH] ipv6: avoid taking locks at socket dismantle

ipv6_sock_mc_close() is called for ipv6 sockets at close time, and most
of them don't use multicast.

Add a test to avoid contention on a shared spinlock.

Same heuristic applies for ipv6_sock_ac_close(), to avoid contention
on a shared rwlock.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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