Florian Westphal <fw@xxxxxxxxx> wrote:
> 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.
Yet another alternative is to place an rcu_head at the end of
struct nf_hook_entries.
This is a bit tricky because the location is not fixed due to
dynamically sized array members.
But if you do this you can use call_rcu to do the freeing which removes
need for all but the nfqueue related synchronize_net() calls.
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