[ovs-dev] [PATCH] vxlan: Fix for the packet loop issue in vxlan

[Pravin Shelar]

On Tue, Jun 12, 2018 at 10:58 PM, Neelakantam Gaddam
<neelugaddam at gmail.com> wrote:
> Hi Pravin,
>
> I have seen the below crash.
>
> [<ffffffff80864cd4>] show_stack+0x6c/0xf8
>
> [<ffffffff80ad1628>] do_raw_spin_lock+0x168/0x170
>
> [<ffffffff80bf7b1c>] dev_queue_xmit+0x43c/0x470
>
> [<ffffffff80c32c08>] ip_finish_output+0x250/0x490
>
> [<ffffffffc0115664>] rpl_iptunnel_xmit+0x134/0x218 [openvswitch]
>
> [<ffffffffc0120f28>] rpl_vxlan_xmit+0x430/0x538 [openvswitch]
>
> [<ffffffffc00f9de0>] do_execute_actions+0x18f8/0x19e8 [openvswitch]
>
> [<ffffffffc00fa2b0>] ovs_execute_actions+0x90/0x208 [openvswitch]
>
> [<ffffffffc0101860>] ovs_dp_process_packet+0xb0/0x1a8 [openvswitch]
>
> [<ffffffffc010c5d8>] ovs_vport_receive+0x78/0x130 [openvswitch]
>
> [<ffffffffc010ce6c>] internal_dev_xmit+0x34/0x98 [openvswitch]
>
> [<ffffffff80bf74d0>] dev_hard_start_xmit+0x2e8/0x4f8
>
> [<ffffffff80c10e48>] sch_direct_xmit+0xf0/0x238
>
> [<ffffffff80bf78b8>] dev_queue_xmit+0x1d8/0x470
>
> [<ffffffff80c5ffe4>] arp_process+0x614/0x628
>
> [<ffffffff80bf0cb0>] __netif_receive_skb_core+0x2e8/0x5d8
>
> [<ffffffff80bf4770>] process_backlog+0xc0/0x1b0
>
> [<ffffffff80bf501c>] net_rx_action+0x154/0x240
>
> [<ffffffff8088d130>] __do_softirq+0x1d0/0x218
>
> [<ffffffff8088d240>] do_softirq+0x68/0x70
>
> [<ffffffff8088d3a0>] local_bh_enable+0xa8/0xb0
>
> [<ffffffff80bf5c88>] netif_rx_ni+0x20/0x30
>
>
>
>
> I have spent some time in investigation and found that crash is because of
> spinlock recursion in dev_queue_xmit function.
> The packet path traced is : netif_rx->arp->dev_queue_xmit(internal
> port)->vxlan_xmit->dev_queue_xmit(internal port).
>

Which spin-lock is it? I am surprised to see a lock taken in fast
path. Can you also share kernel version?

> The macro (XMIT_RECURSION_LIMIT) is defined as 10. This limit wont prevent
> the crash since the recursion is 2 only for my configuration.

right, The recursion limit is to avoid stack overflow.

>
>
>
> On Wed, Jun 13, 2018 at 4:11 AM, Pravin Shelar <pshelar at ovn.org> wrote:
>>
>> On Tue, Jun 12, 2018 at 10:11 AM, Neelakantam Gaddam
>> <neelugaddam at gmail.com> wrote:
>> >
>> > Hi Pravin,
>> >
>> > The below configuration is causing the spinlock recursion issue.
>> >
>> > I am able to see the issue with below configuration.
>> >
>> >
>> >
>> > ovs-vsctl add-br br0
>> >
>> > ovs-vsctl add-bond br0 bond0 p1p1 p1p2
>> >
>> > ovs-vsctl set port bond0 lacp=active bond_mode=balance-tcp
>> >
>> > ifconfig br0 100.0.0.1 up
>> >
>> > ovs-vsctl add-port br0 veth0
>> >
>> > ovs-vsctl add-port br0 vx0 -- set interface vx0 type=vxlan
>> > options:local_ip=100.0.0.1 options:remote_ip=100.0.0.2 option:key=flow
>> >
>> >
>> >
>> > ovs-ofctl add-flow br0 "table=0, priority=1, cookie=100, tun_id=100,
>> > in_port=4, action=output:3"
>> >
>> > ovs-ofctl add-flow br0 "table=0, priority=1, cookie=100, in_port=3,
>> > actions=set_field:100->tun_id output:4"
>> >
>> >
>> >
>> > The same bridge br0 is being used as the local interface for vxlan
>> > tunnel. Even though this configuration is invalid, we should not see the
>> > kernel crash.
>> >
>>
>> I agree this should not cause crash.
>> Can you post the crash or investigate why it is crashing I think such
>> configuration would hit the networking stack recursion limit
>> (XMIT_RECURSION_LIMIT) and then the packet would be dropped. I am not
>> sure which spinlock recursion issue you are referring to.
>>
>>
>> >
>> >
>> >
>> >
>> > On Tue, Jun 12, 2018 at 11:55 AM, Pravin Shelar <pshelar at ovn.org> wrote:
>> >>
>> >>
>> >>
>> >> On Tue, May 22, 2018 at 10:16 PM, Neelakantam Gaddam
>> >> <neelugaddam at gmail.com> wrote:
>> >>>
>> >>> This patch fixes the kernel soft lockup issue with vxlan configuration
>> >>> where the tunneled packet is sent on the same bridge where vxlan port
>> >>> is
>> >>> attched to. It detects the loop in vxlan xmit functionb and drops if
>> >>> loop is
>> >>> detected.
>> >>>
>> >>> Signed-off-by: Neelakantam Gaddam <neelugaddam at gmail.com>
>> >>> ---
>> >>>  datapath/linux/compat/vxlan.c | 6 ++++--
>> >>>  1 file changed, 4 insertions(+), 2 deletions(-)
>> >>>
>> >>> diff --git a/datapath/linux/compat/vxlan.c
>> >>> b/datapath/linux/compat/vxlan.c
>> >>> index 287dad2..00562fa 100644
>> >>> --- a/datapath/linux/compat/vxlan.c
>> >>> +++ b/datapath/linux/compat/vxlan.c
>> >>> @@ -1115,7 +1115,8 @@ static void vxlan_xmit_one(struct sk_buff *skb,
>> >>> struct net_device *dev,
>> >>>                         goto tx_error;
>> >>>                 }
>> >>>
>> >>> -               if (rt->dst.dev == dev) {
>> >>> +               if ((rt->dst.dev == dev) ||
>> >>> +                       (OVS_CB(skb)->input_vport->dev ==
>> >>> rt->dst.dev)) {
>> >>
>> >>
>> >> I am not sure which case the  OVS_CB(skb)->input_vport->dev is not same
>> >> as the dev when there is recursion. Can you explain how to reproduce it?
>> >>
>> >
>> >
>> >
>> > --
>> > Thanks & Regards
>> > Neelakantam Gaddam
>
>
>
>
> --
> Thanks & Regards
> Neelakantam Gaddam