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

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Message-ID: <1453243654.1223.290.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 19 Jan 2016 14:47:34 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jesse Gross <jesse@...nel.org>
Cc:	John <john.phillips5@....com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Tom Herbert <tom@...bertland.com>, david.roth@....com,
	Pravin B Shelar <pshelar@...ira.com>
Subject: Re: Kernel memory leak in bnx2x driver with vxlan tunnel

On Tue, 2016-01-19 at 13:07 -0800, Jesse Gross wrote:
> 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.


Wow.... What is the purpose of using skb_dst_set() on skb before calling
gro_cells_receive() exactly ?

Commit 2e15ea390e6f4466655066d97e22ec66870a042c changelog is not
helpful :

    Following patch create new tunnel flag which enable
    tunnel metadata collection on given device.

This is rather strange since later the dst is thrown away with the
skb_valid_dst() test.

Note also that IP early demux is broken as well, since it does not use
skb_valid_dst() but a simple :

if (sysctl_ip_early_demux && !skb_dst(skb) && !skb->sk) {
 ...
}