netfilter: nf_conntrack: speed up module removal path if netns in use

The patch introduces nf_conntrack_cleanup_net_list(), which cleanups
nf_conntrack for a list of netns and calls synchronize_net() only once
for them all. This should reduce netns destruction time.

I've measured cleanup time for 1k dummy net ns. Here are the results:

 <without the patch>
 # modprobe nf_conntrack
 # time modprobe -r nf_conntrack

 real	0m10.337s
 user	0m0.000s
 sys	0m0.376s

 <with the patch>
 # modprobe nf_conntrack
 # time modprobe -r nf_conntrack

 real    0m5.661s
 user    0m0.000s
 sys     0m0.216s

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 42 insertions, 20 deletions

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 1068deb97c8b..007e8c43d19a 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1365,30 +1365,48 @@ void nf_conntrack_cleanup_end(void)
  */
 void nf_conntrack_cleanup_net(struct net *net)
 {
+        LIST_HEAD(single);
+
+        list_add(&net->exit_list, &single);
+        nf_conntrack_cleanup_net_list(&single);
+}
+
+void nf_conntrack_cleanup_net_list(struct list_head *net_exit_list)
+{
+        int busy;
+        struct net *net;
+
         /*
          * This makes sure all current packets have passed through
          *  netfilter framework.  Roll on, two-stage module
          *  delete...
          */
         synchronize_net();
- i_see_dead_people:
-        nf_ct_iterate_cleanup(net, kill_all, NULL);
-        nf_ct_release_dying_list(net);
-        if (atomic_read(&net->ct.count) != 0) {
+i_see_dead_people:
+        busy = 0;
+        list_for_each_entry(net, net_exit_list, exit_list) {
+                nf_ct_iterate_cleanup(net, kill_all, NULL);
+                nf_ct_release_dying_list(net);
+                if (atomic_read(&net->ct.count) != 0)
+                        busy = 1;
+        }
+        if (busy) {
                 schedule();
                 goto i_see_dead_people;
         }
 
-        nf_ct_free_hashtable(net->ct.hash, net->ct.htable_size);
-        nf_conntrack_proto_pernet_fini(net);
-        nf_conntrack_helper_pernet_fini(net);
-        nf_conntrack_ecache_pernet_fini(net);
-        nf_conntrack_tstamp_pernet_fini(net);
-        nf_conntrack_acct_pernet_fini(net);
-        nf_conntrack_expect_pernet_fini(net);
-        kmem_cache_destroy(net->ct.nf_conntrack_cachep);
-        kfree(net->ct.slabname);
-        free_percpu(net->ct.stat);
+        list_for_each_entry(net, net_exit_list, exit_list) {
+                nf_ct_free_hashtable(net->ct.hash, net->ct.htable_size);
+                nf_conntrack_proto_pernet_fini(net);
+                nf_conntrack_helper_pernet_fini(net);
+                nf_conntrack_ecache_pernet_fini(net);
+                nf_conntrack_tstamp_pernet_fini(net);
+                nf_conntrack_acct_pernet_fini(net);
+                nf_conntrack_expect_pernet_fini(net);
+                kmem_cache_destroy(net->ct.nf_conntrack_cachep);
+                kfree(net->ct.slabname);
+                free_percpu(net->ct.stat);
+        }
 }
 
 void *nf_ct_alloc_hashtable(unsigned int *sizep, int nulls)
diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
index 6bcce401fd1c..6c69fbdb8361 100644
--- a/net/netfilter/nf_conntrack_standalone.c
+++ b/net/netfilter/nf_conntrack_standalone.c
@@ -545,16 +545,20 @@ out_init:
         return ret;
 }
 
-static void nf_conntrack_pernet_exit(struct net *net)
+static void nf_conntrack_pernet_exit(struct list_head *net_exit_list)
 {
-        nf_conntrack_standalone_fini_sysctl(net);
-        nf_conntrack_standalone_fini_proc(net);
-        nf_conntrack_cleanup_net(net);
+        struct net *net;
+
+        list_for_each_entry(net, net_exit_list, exit_list) {
+                nf_conntrack_standalone_fini_sysctl(net);
+                nf_conntrack_standalone_fini_proc(net);
+        }
+        nf_conntrack_cleanup_net_list(net_exit_list);
 }
 
 static struct pernet_operations nf_conntrack_net_ops = {
-        .init = nf_conntrack_pernet_init,
-        .exit = nf_conntrack_pernet_exit,
+        .init           = nf_conntrack_pernet_init,
+        .exit_batch     = nf_conntrack_pernet_exit,
 };
 
 static int __init nf_conntrack_standalone_init(void)