netdev - Re: Kernel memory leak in bnx2x driver with vxlan tunnel

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Date:	Tue, 19 Jan 2016 13:07:43 -0800
From:	Jesse Gross <jesse@...nel.org>
To:	John <john.phillips5@....com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Tom Herbert <tom@...bertland.com>, david.roth@....com
Subject: Re: Kernel memory leak in bnx2x driver with vxlan tunnel

On Thu, Jan 14, 2016 at 9:17 AM, John <john.phillips5@....com> wrote:
> I'm getting what seems to be a kernel memory leak while doing a TCP
> throughput test between two VMs on identical systems, in order to test a
> broadcom NIC's performance with a kernel 4.4.0-rc8 and OpenVSwitch version
> 2.4.90. The host system of the receiving (server) VM leaks memory during the
> throughput test. The memory leaks fast enough to make the system completely
> unusable within five minutes. Once I stop the throughput test, the memory
> stops
> leaking. A couple of times, the kernel on the host system has actually
> killed
> the qemu process for me, but this doesn't happen reliably. The leaked memory
> doesn't become available again even after the VM is killed.

It looks like the problem is in napi_skb_finish(). If we when do
GRO_MERGED_FREE we have NAPI_GRO_CB(skb)->free ==
NAPI_GRO_FREE_STOLEN_HEAD then we will just free the skb memory itself
but not any of the associated elements. Historically, this would have
been OK but these days we will have allocated a dst entry already for
tunnel metadata, which will get leaked.

If we don't have NAPI_GRO_FREE_STOLEN_HEAD then we'll do a
__kfree_skb(), which will release the dst entry. That would explain
why some drivers have the problem but not others since the memory is
laid out differently.