Re: net: cleanup_net is slow

[Florian Westphal]

Florian Westphal <f...@strlen.de> wrote:
> Indeed.  Setting net.netfilter.nf_conntrack_default_on=0 cuts time
> cleanup time by 2/3 ...
> 
> nf unregister is way too happy to issue synchronize_net(), I'll work on
> a fix.

I'll test this patch as a start.  Maybe we can also leverage exit_batch
more on netfilter side.

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index a87a6f8a74d8..08fe1f526265 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -126,14 +126,15 @@ int nf_register_net_hook(struct net *net, const struct 
nf_hook_ops *reg)
 }
 EXPORT_SYMBOL(nf_register_net_hook);
 
-void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
+static struct nf_hook_entry *
+__nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
 {
        struct nf_hook_entry __rcu **pp;
        struct nf_hook_entry *p;
 
        pp = nf_hook_entry_head(net, reg);
        if (WARN_ON_ONCE(!pp))
-               return;
+               return NULL;
 
        mutex_lock(&nf_hook_mutex);
        for (; (p = nf_entry_dereference(*pp)) != NULL; pp = &p->next) {
@@ -145,7 +146,7 @@ void nf_unregister_net_hook(struct net *net, const struct 
nf_hook_ops *reg)
        mutex_unlock(&nf_hook_mutex);
        if (!p) {
                WARN(1, "nf_unregister_net_hook: hook not found!\n");
-               return;
+               return NULL;
        }
 #ifdef CONFIG_NETFILTER_INGRESS
        if (reg->pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_INGRESS)
@@ -154,6 +155,17 @@ void nf_unregister_net_hook(struct net *net, const struct 
nf_hook_ops *reg)
 #ifdef HAVE_JUMP_LABEL
        static_key_slow_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);
 #endif
+
+       return p;
+}
+
+void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
+{
+       struct nf_hook_entry *p = __nf_unregister_net_hook(net, reg);
+
+       if (!p)
+               return;
+
        synchronize_net();
        nf_queue_nf_hook_drop(net, p);
        /* other cpu might still process nfqueue verdict that used reg */
@@ -183,10 +195,36 @@ int nf_register_net_hooks(struct net *net, const struct 
nf_hook_ops *reg,
 EXPORT_SYMBOL(nf_register_net_hooks);
 
 void nf_unregister_net_hooks(struct net *net, const struct nf_hook_ops *reg,
-                            unsigned int n)
+                            unsigned int hookcount)
 {
-       while (n-- > 0)
-               nf_unregister_net_hook(net, &reg[n]);
+       struct nf_hook_entry *to_free[16];
+       unsigned int i, n;
+
+       WARN_ON_ONCE(hookcount > ARRAY_SIZE(to_free));
+
+ next_round:
+       n = min_t(unsigned int, hookcount, ARRAY_SIZE(to_free));
+
+       for (i = 0; i < n; i++)
+               to_free[i] = __nf_unregister_net_hook(net, &reg[i]);
+
+       synchronize_net();
+
+       for (i = 0; i < n; i++) {
+               if (to_free[i])
+                       nf_queue_nf_hook_drop(net, to_free[i]);
+       }
+
+       synchronize_net();
+
+       for (i = 0; i < n; i++)
+               kfree(to_free[i]);
+
+       if (n < hookcount) {
+               hookcount -= n;
+               reg += n;
+               goto next_round;
+       }
 }
 EXPORT_SYMBOL(nf_unregister_net_hooks);