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>
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index b19ed51a..28dfa5f 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -284,6 +284,9 @@
struct ipv6_mc_socklist *mc_lst;
struct net *net = sock_net(sk);
+ if (!rcu_access_pointer(np->ipv6_mc_list))
+ return;
+
spin_lock(&ipv6_sk_mc_lock);
while ((mc_lst = rcu_dereference_protected(np->ipv6_mc_list,
lockdep_is_held(&ipv6_sk_mc_lock))) != NULL) {