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>

2 files changed, 6 insertions, 0 deletions

diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c
index 2f4f584d796d..757a810d8f15 100644
--- a/net/ipv6/anycast.c
+++ b/net/ipv6/anycast.c
@@ -189,6 +189,9 @@ void ipv6_sock_ac_close(struct sock *sk)
         struct net *net = sock_net(sk);
         int     prev_index;
 
+        if (!np->ipv6_ac_list)
+                return;
+
         write_lock_bh(&ipv6_sk_ac_lock);
         pac = np->ipv6_ac_list;
         np->ipv6_ac_list = NULL;
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index b19ed51a45bb..28dfa5f3801f 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -284,6 +284,9 @@ void ipv6_sock_mc_close(struct sock *sk)
         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) {