Re: [PATCH net-next] ip6_vti: fix memleak on netns dismantle

[Breno Leitao <leitao@debian.org>]

Hello Florian,

On Mon, Apr 15, 2024 at 02:23:44PM +0200, Florian Westphal wrote:
> kmemleak reports net_device resources are no longer released, restore
> needs_free_netdev toggle.  Sample backtrace:
> 
> unreferenced object 0xffff88810874f000 (size 4096): [..]
>     [<00000000a2b8af8b>] __kmalloc_node+0x209/0x290
>     [<0000000040b0a1a9>] alloc_netdev_mqs+0x58/0x470
>     [<00000000b4be1e78>] vti6_init_net+0x94/0x230
>     [<000000008830c1ea>] ops_init+0x32/0xc0
>     [<000000006a26fa8f>] setup_net+0x134/0x2e0
> [..]
> 
> Cc: Breno Leitao <leitao@debian.org>
> Fixes: a9b2d55a8f1e ("ip6_vti: Do not use custom stat allocator")
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
>  net/ipv6/ip6_vti.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
> index 4d68a0777b0c..78344cf3867e 100644
> --- a/net/ipv6/ip6_vti.c
> +++ b/net/ipv6/ip6_vti.c
> @@ -901,6 +901,7 @@ static void vti6_dev_setup(struct net_device *dev)
>  {
>  	dev->netdev_ops = &vti6_netdev_ops;
>  	dev->header_ops = &ip_tunnel_header_ops;
> +	dev->needs_free_netdev = true;

Thanks for the fix!

Could you help me to understand how needs_free_netdev will trigger the
free()here?

I _though_ that any device that is being unregistered would have the stats
freed.

This is the flow I am reading:

1) When the device is unregistered, then it is marked as todo:

	unregister_netdevice_many_notify() {
		list_for_each_entry(dev, head, unreg_list) {
			net_set_todo(dev);
		}
	}

2) Then, "run_todo" will run later, and it does:
	netdev_run_todo() {
		list_for_each_entry_safe(dev, tmp, &list, todo_list) {
		if (unlikely(dev->reg_state != NETREG_UNREGISTERING)) {
			netdev_WARN(dev, "run_todo but not unregistering\n");
			list_del(&dev->todo_list);
			continue;
		}

		while (!list_empty(&list)) {
			netdev_do_free_pcpu_stats(dev);
		}

	}

Thank you!