netdev - Re: [PATCH] net_namespace: fixed net

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Date:   Thu, 8 Sep 2016 16:33:38 -0700
From:   Jojy Varghese <jojy.varghese@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] net_namespace: fixed net_device reference leak

Sorry last patch was just the delta over my original patch. Here is
the complete patch:

---
 net/core/dst.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index a1656e3..f63027e 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -433,8 +433,11 @@ static void dst_ifdown(struct dst_entry *dst,
struct net_device *dev,
                dst->input = dst_discard;
                dst->output = dst_discard_out;
        } else {
-               dst->dev = dev_net(dst->dev)->loopback_dev;
-               dev_hold(dst->dev);
+               if (dst->dev != dev_net(dst->dev)->loopback_dev) {
+                       dst->dev = dev_net(dst->dev)->loopback_dev;
+                       dev_hold(dst->dev);
+               }
+
                dev_put(dev);
        }
 }
--
1.8.3.1

On Thu, Sep 8, 2016 at 4:16 PM, Jojy Varghese <jojy.varghese@...il.com> wrote:
> The dst's do disappear but the net device does not. A better solution
> is to only hold reference to dst's net device ONLY if it is not a
> loopback device. In the case of the loopback device, we want to do
> only a "put" on it and skip the "hold".
>
> Updating the patch below:
>
> ---
>  net/core/dst.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/dst.c b/net/core/dst.c
> index 7e45593..f63027e 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -433,12 +433,11 @@ static void dst_ifdown(struct dst_entry *dst,
> struct net_device *dev,
>                 dst->input = dst_discard;
>                 dst->output = dst_discard_out;
>         } else {
> -               if (dst->dev == dev_net(dst->dev)->loopback_dev)
> -                       dst->dev = init_net.loopback_dev;
> -               else
> +               if (dst->dev != dev_net(dst->dev)->loopback_dev) {
>                         dst->dev = dev_net(dst->dev)->loopback_dev;
> +                       dev_hold(dst->dev);
> +               }
>
> -               dev_hold(dst->dev);
>                 dev_put(dev);
>         }
>  }
> --
> 1.8.3.1
>
>
>
> On Thu, Sep 8, 2016 at 3:16 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Thu, 2016-09-08 at 15:12 -0700, Jojy Varghese wrote:
>>> Hi Eric/Lance
>>>
>>>  Thanks for taking time to look at the patch. The problem in dst.c's
>>> "dst_ifdown" is that it will never do an actual "dev_put" on the
>>> loopback net device. This results in the loopback net device to be
>>> alive even when the dst goes away.
>>
>> Sure, but the dst themselves should disappear, and thus release their
>> dst->dev reference.
>>
>> Something is missing.
>>
>> loopback device is only used when we remove one device from the system,
>> but namespace (and loopback device) is still around.
>>
>>
>>
>
>
>
> --
> Jojy G Varghese



-- 
Jojy G Varghese