netdev - Re: [Patch net] net: check dead netns for peernet2id

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Date:   Wed, 16 Nov 2016 23:17:05 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: Re: [Patch net] net: check dead netns for peernet2id_alloc()

On Wed, Nov 16, 2016 at 10:27 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
> Andrei reports we still allocate netns ID from idr after we destroy
> it in cleanup_net().
>
> cleanup_net():
>   ...
>   idr_destroy(&net->netns_ids);
>   ...
>   list_for_each_entry_reverse(ops, &pernet_list, list)
>     ops_exit_list(ops, &net_exit_list);
>       -> rollback_registered_many()
>         -> rtmsg_ifinfo_build_skb()
>          -> rtnl_fill_ifinfo()
>            -> peernet2id_alloc()
>
> After that point we should not even access net->netns_ids, we
> should check the death of the current netns as early as we can in
> peernet2id_alloc().
>
> For net-next we can consider to avoid sending rtmsg totally,
> it is a good optimization for netns teardown path.

It works for me and looks good. Thanks.

Acked-by: Andrei Vagin <avagin@...nvz.org>

>
> Fixes: 0c7aecd4bde4 ("netns: add rtnl cmd to add and get peer netns ids")
> Reported-by: Andrei Vagin <avagin@...il.com>
> Cc: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  net/core/net_namespace.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index f61c0e0..7001da9 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -219,6 +219,8 @@ int peernet2id_alloc(struct net *net, struct net *peer)
>         bool alloc;
>         int id;
>
> +       if (atomic_read(&net->count) == 0)
> +               return NETNSA_NSID_NOT_ASSIGNED;
>         spin_lock_irqsave(&net->nsid_lock, flags);
>         alloc = atomic_read(&peer->count) == 0 ? false : true;
>         id = __peernet2id_alloc(net, peer, &alloc);
> --
> 2.1.0
>