[ovs-dev] dpif-netdev bug regarding packet matches or ufids?

Ben Pfaff blp at ovn.org
Tue Oct 9 17:27:58 UTC 2018


Thank you very much!  I think you found the exact problem.  I applied
this to master and backported as far as branch-2.7.

On Tue, Oct 09, 2018 at 07:21:24PM +0300, Ilya Maximets wrote:
> Hi Ben.
> Thanks for your report and the really useful script.
> I spent a few hours debugging the issue and came up with the following patch:
> 	https://patchwork.ozlabs.org/patch/981408/
> Please, take a look.
> Additionally we may add ufid lookup support in flow_put_on_pmd()
> as a separate fix. This, probably, will speed up the operation.
> 
> Will wait for your opinion.
> 
> Best regards, Ilya Maximets.
> 
> > Hi Ian (or others), do you have any thoughts about this?
> > 
> > On Fri, Sep 28, 2018 at 04:24:33PM -0700, Ben Pfaff wrote:
> >> I have been playing with the OFTest framework off and on over the last
> >> few months and I believe it's caught an actual bug with its
> >> DirectVlanPackets test.  I'm appending a script that demonstrates it.
> >> To see it, run "make sandbox" then execute the script inside it.
> >> 
> >> At some level at least, the problem is in dpif-netdev, which during the
> >> test logs messages like this indicating that a datapath flow can't be
> >> found and therefore can't be modified:
> >> 
> >>     WARN|dummy at ovs-dummy: failed to put[modify] (No such file or
> >>     directory) ufid:b2fe59af-26bd-4aa0-960e-fd559dc10c54
> >>     skb_priority(0/0),skb_mark(0/0),ct_state(0/0),ct_zone(0/0),ct_mark(0/0),ct_label(0/0),recirc_id(0),dp_hash(0/0),in_port(1),packet_type(ns=0,id=0),eth(src=00:06:07:08:09:0a,dst=00:01:02:03:04:05),eth_type(0x8100),vlan(vid=1000/0x0,pcp=5/0x0),encap(eth_type(0x0800),ipv4(src=127.0.0.1/0.0.0.0,dst=127.0.0.1/0.0.0.0,proto=0/0,tos=0/0,ttl=64/0,frag=no)),
> >>     actions:userspace(pid=0,controller(reason=7,dont_send=0,continuation=0,recirc_id=1,rule_cookie=0,controller_id=0,max_len=65535))
> >> 
> >> It's possible that the caller is screwing up by providing a flow match
> >> different from one in the datapath flow table.  I have not looked at
> >> that question.  But the really strange thing here is that the caller is
> >> providing a ufid and dpif-netdev is ignoring it.  When I make it honor
> >> the ufid, like the following, then the test suddenly starts working.
> >> This seems like a bug to me.
> >> 
> >> (The following patch is not actually the real fix because the code
> >> should still look at the key if no ufid was provided.)
> >> 
> >> Any thoughts?
> >> 
> >> Thanks,
> >> 
> >> Ben.
> >> 
> >> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> >> index e322f5553fa8..4855cc08f7b7 100644
> >> --- a/lib/dpif-netdev.c
> >> +++ b/lib/dpif-netdev.c
> >> @@ -3273,7 +3273,7 @@ dp_netdev_flow_add(struct dp_netdev_pmd_thread *pmd,
> >>  
> >>  static int
> >>  flow_put_on_pmd(struct dp_netdev_pmd_thread *pmd,
> >> -                struct netdev_flow_key *key,
> >> +                struct netdev_flow_key *key OVS_UNUSED,
> >>                  struct match *match,
> >>                  ovs_u128 *ufid,
> >>                  const struct dpif_flow_put *put,
> >> @@ -3287,7 +3287,7 @@ flow_put_on_pmd(struct dp_netdev_pmd_thread *pmd,
> >>      }
> >>  
> >>      ovs_mutex_lock(&pmd->flow_mutex);
> >> -    netdev_flow = dp_netdev_pmd_lookup_flow(pmd, key, NULL);
> >> +    netdev_flow = dp_netdev_pmd_find_flow(pmd, ufid, NULL, 0);
> >>      if (!netdev_flow) {
> >>          if (put->flags & DPIF_FP_CREATE) {
> >>              if (cmap_count(&pmd->flow_table) < MAX_FLOWS) {
> >> 
> >> 
> >> 
> >> --8<--------------------------cut here-------------------------->8--
> >> 
> >> #! /bin/sh -ex
> >> 
> >> # Create a bridge and add port p1 on port 1, p2 on port 2
> >> ovs-appctl vlog/set netdev_dummy dpif
> >> ovs-vsctl --if-exists del-br br0 \
> >>        -- add-br br0 \
> >>        -- add-port br0 p1 -- set interface p1 ofport_request=1 options:tx_pcap=p1-tx.pcap options:rxq_pcap=p1-rx.pcap \
> >>        -- add-port br0 p2 -- set interface p2 ofport_request=2 options:tx_pcap=p2-tx.pcap options:rxq_pcap=p2-rx.pcap
> >> 
> >> # Add a flow that directs some packets received on p1 to p2 and the
> >> # rest back out p1.
> >> #
> >> # Then inject a packet of the form that should go to p2.  Dump the
> >> # datapath flow to see that it goes to p2 ("actions:2").  Trace the
> >> # same packet for good measure, to also see that it should go to p2.
> >> packet=00010203040500060708090a8100a3e80800450000140001000040007ce77f0000017f000001
> >> ovs-ofctl add-flow br0 priority=1,ip,in_port=1,dl_src=00:06:07:08:09:0a,dl_dst=00:01:02:03:04:05,actions=output:2
> >> ovs-ofctl add-flow br0 priority=0,in_port=1,actions=IN_PORT
> >> ovs-appctl netdev-dummy/receive p1 $packet
> >> ovs-appctl ofproto/trace br0 in_port=p1 $packet
> >> ovs-appctl dpif/dump-flows br0
> >> 
> >> # Delete the flows, then add new flows that would not match the same
> >> # packet as before.
> >> ovs-ofctl del-flows br0
> >> ovs-ofctl add-flow br0 priority=1,in_port=1,dl_src=00:06:07:08:09:0a,dl_dst=00:01:02:03:04:05,dl_type=0x0801,actions=output:2
> >> ovs-ofctl add-flow br0 priority=0,in_port=1,actions=IN_PORT
> >> 
> >> # Give the datapath a few seconds to revalidate.
> >> sleep 2
> >> 
> >> # Now inject the same packet again.  It should go to p1 because it
> >> # only matches the priority-0 flow, as shown by the trace.  However, instead,
> >> # the original datapath flow is still there and its counters get incremented.
> >> ovs-appctl netdev-dummy/receive p1 $packet
> >> ovs-appctl ofproto/trace br0 in_port=p1 $packet
> >> ovs-appctl dpif/dump-flows br0
> >> 
> >> # Give the datapath some time to expire the flow.
> >> sleep 12
> >> 
> >> # Try again.
> >> ovs-appctl netdev-dummy/receive p1 $packet
> >> ovs-appctl ofproto/trace br0 in_port=p1 $packet
> >> ovs-appctl dpif/dump-flows br0
> 


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