netdev - Re: netns refcnt leak for kernel accept sock

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Message-ID: <20150727181946.GJ16447@oracle.com>
Date:	Mon, 27 Jul 2015 20:19:46 +0200
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	Cong Wang <cwang@...pensource.com>
Cc:	netdev <netdev@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>
Subject: Re: netns refcnt leak for kernel accept sock

On (07/27/15 11:13), Cong Wang wrote:
> 
> That refcnt should be released in sock destructor too, when the tcp
> connection is terminated.

yes, but in my case, the listen socket is opened as part of
the ->init indirection in pernet_operations (thus it is a kernel socket)
and the expectation is that this listen socket, and any accept sockets
derived from it, will be closed in ->exit.

But if the accept socket is treated as a uspace socket (thus holds a get_net())
then it will block cleanup_net() and the associated ->exit cleanup operations.

This is probably not a problem for other systems like vxlan/gue/geneve etc
because they all use udp sockets, thus dont have the "accept" equivalent.

But fundamentally, its wrong for a kspace listen socket to result in a
"uspace" accept socket.

> Given the fact that sk_destruct() checks for sk_net_refcnt, your
> patch makes sense to me. But I am not sure how a TCP kernel
> socket is supposed to use.

Thanks for the confirmation - I think RDS is a bit of a maverick here in
that it uses tcp sockets unlike vxlan etc.
For those curious about RDS-TCP, I've actually updated the documentation at
https://oss.oracle.com/projects/rds/dist/documentation/rds-3.1-spec.html
recently. I hope that helps.

--Sowmini
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