Subject: Re: [PATCH for 2.6.32 (untested)] netns: Add quota for number of NET_NS instances.

From: [email-masked] (Eric W. Biederman)
Date: Sun, 20 Nov 2011 15:13:58 -0800

Tetsuo Handa <[email-masked]> writes:

> In order to solve below problems, can we add sysctl variable for
> restricting number of NET_NS instances?

I don't have any particular problems with patch but I don't think it
will result in a working system that is easy to keep working.  Tuning
static limits can be fickle.

Simply throttling the number of processes as anything reasonable will do
should keep the problem in check.  The practical issue is that we have
a huge build of network namespaces that don't get cleaned up.

My inclination in this case the practical fix is that during network
namespace allocation someone take a look at the cleanup_list.  See
that there is ongoing cleanup activity, and wait until at least one
network namespace has cleaned up.  Perhaps by creating a work struct
and waiting for it to cycle through the netns workqueue.

That should throttle network namespace creation to the same speed as
network namespace deletion and prevent the problem of too many
dead network namespaces building up and taking resources.

Eric

> --------------------------------------------------
> [PATCH for 2.6.32 (untested)] netns: Add quota for number of NET_NS instances.
>
> CONFIG_NET_NS support in 2.6.32 has a problem that leads to OOM killer when
> clone(CLONE_NEWNET) is called instantly.
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/720095
> But disabling CONFIG_NET_NS broke lxc containers.
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/790863
>
> This patch introduces /proc/sys/net/core/netns_max interface that limits
> max number of network namespace instances.
>
> Signed-off-by: Tetsuo Handa <[email-masked]>
> ---
>  include/net/sock.h         |    4 ++++
>  net/core/net_namespace.c   |    9 +++++++++
>  net/core/sysctl_net_core.c |   10 ++++++++++
>  3 files changed, 23 insertions(+)
>
> --- linux-2.6.32.48.orig/include/net/sock.h
> +++ linux-2.6.32.48/include/net/sock.h
> @@ -1598,4 +1598,8 @@ extern int sysctl_optmem_max;
>  extern __u32 sysctl_wmem_default;
>  extern __u32 sysctl_rmem_default;
>  
> +#ifdef CONFIG_NET_NS
> +extern int max_netns_count;
> +#endif
> +
>  #endif	/* _SOCK_H */
> --- linux-2.6.32.48.orig/net/core/net_namespace.c
> +++ linux-2.6.32.48/net/core/net_namespace.c
> @@ -81,12 +81,18 @@ static struct net_generic *net_alloc_gen
>  #ifdef CONFIG_NET_NS
>  static struct kmem_cache *net_cachep;
>  static struct workqueue_struct *netns_wq;
> +static atomic_t used_netns_count = ATOMIC_INIT(0);
> +unsigned int max_netns_count;
>  
>  static struct net *net_alloc(void)
>  {
>  	struct net *net = NULL;
>  	struct net_generic *ng;
>  
> +	atomic_inc(&used_netns_count);
> +	if (atomic_read(&used_netns_count) > max_netns_count)
> +		goto out;
> +
>  	ng = net_alloc_generic();
>  	if (!ng)
>  		goto out;
> @@ -96,7 +102,9 @@ static struct net *net_alloc(void)
>  		goto out_free;
>  
>  	rcu_assign_pointer(net->gen, ng);
> +	return net;
>  out:
> +	atomic_dec(&used_netns_count);
>  	return net;
>  
>  out_free:
> @@ -115,6 +123,7 @@ static void net_free(struct net *net)
>  #endif
>  	kfree(net->gen);
>  	kmem_cache_free(net_cachep, net);
> +	atomic_dec(&used_netns_count);
>  }
>  
>  static struct net *net_create(void)
> --- linux-2.6.32.48.orig/net/core/sysctl_net_core.c
> +++ linux-2.6.32.48/net/core/sysctl_net_core.c
> @@ -89,6 +89,16 @@ static struct ctl_table net_core_table[]
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec
>  	},
> +#ifdef CONFIG_NET_NS
> +	{
> +		.ctl_name       = CTL_UNNUMBERED,
> +		.procname       = "netns_max",
> +		.data           = &max_netns_count,
> +		.maxlen         = sizeof(int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec,
> +	},
> +#endif
>  #endif /* CONFIG_NET */
>  	{
>  		.ctl_name	= NET_CORE_BUDGET,