Re: [RFC PATCH] netfilter: call synchronize_net only once from nf_register_net_hooks

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Giuseppe Scrivano <gscrivan@xxxxxxxxxx> wrote:
> SELinux, if enabled, registers for each new network namespace 6
> netfilter hooks.  Avoid to use synchronize_net for each new hook, but do
> it once after all the hooks are added.  The net benefit on an SMP
> machine with two cores is that creating a new network namespace takes
> -40% of the original time.

but this needs more work.

> Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
> ---
>  net/netfilter/core.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/net/netfilter/core.c b/net/netfilter/core.c
> index 52cd2901a097..beeb0b36f429 100644
> --- a/net/netfilter/core.c
> +++ b/net/netfilter/core.c
> @@ -252,7 +252,7 @@ static struct nf_hook_entries __rcu **nf_hook_entry_head(struct net *net, const
>  	return NULL;
>  }
>  
> -int nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)
> +static int __nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)

Change this to return struct nf_hook_entries *

>  {
>  	struct nf_hook_entries *p, *new_hooks;
>  	struct nf_hook_entries __rcu **pp;
> @@ -291,11 +291,19 @@ int nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)
>  #ifdef HAVE_JUMP_LABEL
>  	static_key_slow_inc(&nf_hooks_needed[reg->pf][reg->hooknum]);
>  #endif
> -	synchronize_net();
>  	BUG_ON(p == new_hooks);
>  	kvfree(p);

remove kvfree()

>  	return 0;

return p;

> +int nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)
> +{
> +	int ret = __nf_register_net_hook(net, reg);
> +	if (ret < 0)
> +		return ret;
> +	synchronize_net();

then free p here.

> +	return 0;
> +}
>  EXPORT_SYMBOL(nf_register_net_hook);
>  
>  /*
> @@ -379,10 +387,11 @@ int nf_register_net_hooks(struct net *net, const struct nf_hook_ops *reg,
>  	int err = 0;
>  
>  	for (i = 0; i < n; i++) {
> -		err = nf_register_net_hook(net, &reg[i]);
> +		err = __nf_register_net_hook(net, &reg[i]);

here, store the old 'p' values and then
free them after synchronize_net().
--
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