net: Allow xfrm_user_net_exit to batch efficiently.

xfrm.nlsk is provided by the xfrm_user module and is access via rcu from
other parts of the xfrm code.  Add xfrm.nlsk_stash a copy of xfrm.nlsk that
will never be set to NULL.  This allows the synchronize_net and
netlink_kernel_release to be deferred until a whole batch of xfrm.nlsk sockets
have been set to NULL.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 11 insertions, 8 deletions

diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index 1ba912749caa..56f8e5585df7 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -43,6 +43,7 @@ struct netns_xfrm {
         struct work_struct      policy_hash_work;
 
         struct sock             *nlsk;
+        struct sock             *nlsk_stash;
 
         u32                     sysctl_aevent_etime;
         u32                     sysctl_aevent_rseqth;
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index fb42d778d278..1ada6186933c 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2721,22 +2721,24 @@ static int __net_init xfrm_user_net_init(struct net *net)
                                      xfrm_netlink_rcv, NULL, THIS_MODULE);
         if (nlsk == NULL)
                 return -ENOMEM;
+        net->xfrm.nlsk_stash = nlsk; /* Don't set to NULL */
         rcu_assign_pointer(net->xfrm.nlsk, nlsk);
         return 0;
 }
 
-static void __net_exit xfrm_user_net_exit(struct net *net)
+static void __net_exit xfrm_user_net_exit(struct list_head *net_exit_list)
 {
-        struct sock *nlsk = net->xfrm.nlsk;
-
-        rcu_assign_pointer(net->xfrm.nlsk, NULL);
-        synchronize_rcu();
-        netlink_kernel_release(nlsk);
+        struct net *net;
+        list_for_each_entry(net, net_exit_list, exit_list)
+                rcu_assign_pointer(net->xfrm.nlsk, NULL);
+        synchronize_net();
+        list_for_each_entry(net, net_exit_list, exit_list)
+                netlink_kernel_release(net->xfrm.nlsk_stash);
 }
 
 static struct pernet_operations xfrm_user_net_ops = {
-        .init = xfrm_user_net_init,
-        .exit = xfrm_user_net_exit,
+        .init       = xfrm_user_net_init,
+        .exit_batch = xfrm_user_net_exit,
 };
 
 static int __init xfrm_user_init(void)