Re: [PATCH 3/14][TUN]: Introduce the tun_net structure.

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Apr 10, 2008 at 07:06:24PM +0400, Pavel Emelyanov wrote:
> This is the first step in making tuntap devices work in net 
> namespaces. The structure mentioned is pointed by generic
> net pointer with tun_net_id id, and tun driver fills one on 
> its load. It will contain only the tun devices list.
> 
> So declare this structure and introduce net init and exit hooks.

OK, I have to ask...  What prevents someone else from invoking
net_generic() concurrently with a call to tun_exit_net(), potentially
obtaining a pointer to the structure that tun_exit_net() is about
to kfree()?

						Thanx, Paul

> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
> 
> ---
>  drivers/net/tun.c |   53 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 52 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 7b816a0..9bfba02 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -63,6 +63,7 @@
>  #include <linux/if_tun.h>
>  #include <linux/crc32.h>
>  #include <net/net_namespace.h>
> +#include <net/netns/generic.h>
> 
>  #include <asm/system.h>
>  #include <asm/uaccess.h>
> @@ -73,6 +74,11 @@ static int debug;
> 
>  /* Network device part of the driver */
> 
> +static unsigned int tun_net_id;
> +struct tun_net {
> +	struct list_head dev_list;
> +};
> +
>  static LIST_HEAD(tun_dev_list);
>  static const struct ethtool_ops tun_ethtool_ops;
> 
> @@ -873,6 +879,37 @@ static const struct ethtool_ops tun_ethtool_ops = {
>  	.set_rx_csum	= tun_set_rx_csum
>  };
> 
> +static int tun_init_net(struct net *net)
> +{
> +	struct tun_net *tn;
> +
> +	tn = kmalloc(sizeof(*tn), GFP_KERNEL);
> +	if (tn == NULL)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&tn->dev_list);
> +
> +	if (net_assign_generic(net, tun_net_id, tn)) {
> +		kfree(tn);
> +		return -ENOMEM;
> +	}
> +
> +	return 0;
> +}
> +
> +static void tun_exit_net(struct net *net)
> +{
> +	struct tun_net *tn;
> +
> +	tn = net_generic(net, tun_net_id);
> +	kfree(tn);
> +}
> +
> +static struct pernet_operations tun_net_ops = {
> +	.init = tun_init_net,
> +	.exit = tun_exit_net,
> +};
> +
>  static int __init tun_init(void)
>  {
>  	int ret = 0;
> @@ -880,9 +917,22 @@ static int __init tun_init(void)
>  	printk(KERN_INFO "tun: %s, %s\n", DRV_DESCRIPTION, DRV_VERSION);
>  	printk(KERN_INFO "tun: %s\n", DRV_COPYRIGHT);
> 
> +	ret = register_pernet_gen_device(&tun_net_id, &tun_net_ops);
> +	if (ret) {
> +		printk(KERN_ERR "tun: Can't register pernet ops\n");
> +		goto err_pernet;
> +	}
> +
>  	ret = misc_register(&tun_miscdev);
> -	if (ret)
> +	if (ret) {
>  		printk(KERN_ERR "tun: Can't register misc device %d\n", TUN_MINOR);
> +		goto err_misc;
> +	}
> +	return 0;
> +
> +err_misc:
> +	unregister_pernet_gen_device(tun_net_id, &tun_net_ops);
> +err_pernet:
>  	return ret;
>  }
> 
> @@ -899,6 +949,7 @@ static void tun_cleanup(void)
>  	}
>  	rtnl_unlock();
> 
> +	unregister_pernet_gen_device(tun_net_id, &tun_net_ops);
>  }
> 
>  module_init(tun_init);
> -- 
> 1.5.3.4
> 
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