[ovs-dev] [PATCH v3 1/2] ofproto: Allow xlate_actions() to fail.

Joe Stringer joestringer at nicira.com
Wed Nov 25 23:12:02 UTC 2015


On 25 November 2015 at 15:06, Jarno Rajahalme <jarno at ovn.org> wrote:
>
>> On Nov 25, 2015, at 2:58 PM, Joe Stringer <joe at ovn.org> wrote:
>>
>> On 25 November 2015 at 11:23, Jarno Rajahalme <jarno at ovn.org <mailto:jarno at ovn.org>> wrote:
>>>
>>> On Nov 25, 2015, at 11:11 AM, Jarno Rajahalme <jarno at ovn.org> wrote:
>>>
>>>
>>> On Nov 25, 2015, at 10:52 AM, Joe Stringer <joe at ovn.org> wrote:
>>>
>>> On 25 November 2015 at 10:31, Jarno Rajahalme <jarno at ovn.org> wrote:
>>>
>>>
>>> On Nov 24, 2015, at 5:02 PM, Joe Stringer <joe at ovn.org> wrote:
>>>
>>> On 24 November 2015 at 13:41, Jarno Rajahalme <jarno at ovn.org> wrote:
>>>
>>> Sometimes xlate_actions() fails due to too deep recursion, too many
>>> MPLS labels, or missing recirculation context.  Make xlate_actions()
>>> clear out the produced odp actions in these cases to make it easy for
>>> the caller to install a drop flow (instead or installing a flow with
>>> partially translated actions).  Also, return a specific error code, so
>>> that the error can be properly propagated where meaningful.
>>>
>>> Before this patch it was possible that the revalidation installed a
>>> flow with a recirculation ID with an invalid recirc ID (== 0), due to
>>> the introduction of in-place modification in commit 43b2f131a229
>>> (ofproto: Allow in-place modifications of datapath flows).
>>>
>>> Signed-off-by: Jarno Rajahalme <jarno at ovn.org>
>>>
>>>
>>> Should this also set the error when receiving packets on a mirror port
>>> in xlate_actions()? Or when receiving tagged VLAN traffic that doesn't
>>> correspond to the port's vlan tag? Or when a group has no live bucket?
>>> Are there any other cases that should also be covered? (I just scanned
>>> across ofproto/ofproto-dpif-xlate.c looking for cases where we're
>>> already logging that we drop the packet, but maybe there's a reasoning
>>> behind not including these - if so, please enlighten me)
>>>
>>>
>>> No reasoning for missing those, I just did not notice them. Thanks for
>>> pointing them out.
>>>
>>>
>>> OK, I thought it may have been something like "expected errors" vs.
>>> "unexpected errors".
>>>
>>>
>>> Looking into these I noticed this to be the case. Must discern whether to
>>> fail just the individual action v.s. the whole pipeline.
>>>
>>>
>>> How about this incremental to cover two cases here (rest are “expected
>>> errors” IMO):
>>>
>>> diff --git a/ofproto/ofproto-dpif-xlate.c b/ofproto/ofproto-dpif-xlate.c
>>> index 36a6fbc..2908339 100644
>>> --- a/ofproto/ofproto-dpif-xlate.c
>>> +++ b/ofproto/ofproto-dpif-xlate.c
>>> @@ -336,6 +336,10 @@ const char *xlate_strerror(enum xlate_error error)
>>>         return "Recirculation conflict";
>>>     case XLATE_TOO_MANY_MPLS_LABELS:
>>>         return "Too many MPLS labels";
>>> +    case XLATE_BUCKET_CHAINING_TOO_DEEP:
>>> +        return "Bucket chaining too deep";
>>> +    case XLATE_NO_INPUT_BUNDLE:
>>> +        return "No input bundle";
>>>     }
>>>     return "Unknown error";
>>> }
>>> @@ -1444,10 +1448,9 @@ bucket_is_alive(const struct xlate_ctx *ctx,
>>>                 struct ofputil_bucket *bucket, int depth)
>>> {
>>>     if (depth >= MAX_LIVENESS_RECURSION) {
>>> -        static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
>>> -
>>> -        VLOG_WARN_RL(&rl, "bucket chaining exceeded %d links",
>>> -                     MAX_LIVENESS_RECURSION);
>>> +        XLATE_REPORT_ERROR(ctx, "bucket chaining exceeded %d links",
>>> +                           MAX_LIVENESS_RECURSION);
>>> +        ctx->error = XLATE_BUCKET_CHAINING_TOO_DEEP;
>>>         return false;
>>>     }
>>>
>>> @@ -2323,7 +2326,8 @@ xlate_normal(struct xlate_ctx *ctx)
>>>     in_xbundle = lookup_input_bundle(ctx->xbridge, flow->in_port.ofp_port,
>>>                                      ctx->xin->packet != NULL, &in_port);
>>>     if (!in_xbundle) {
>>> -        xlate_report(ctx, "no input bundle, dropping");
>>> +        XLATE_REPORT_ERROR(ctx, "no input bundle, dropping");
>>> +        ctx->error = XLATE_NO_INPUT_BUNDLE;
>>>         return;
>>>     }
>>>
>>>
>>> The last one is debatable, as setting the error fails the whole translation
>>> rather than just the normal action. But this is most likely an configuration
>>> error, so maybe failing the whole pipeline (and installing a drop flow) is
>>> the right thing to do here?
>>
>> Jarno and I discussed this offline, and I'll try to summarise here.
>> Broadly speaking, we're talking about the decision between failing an
>> individual (piece of an) action or completely failing the action
>> processing for the flow. And I think arguably the approach should be
>> that if it is a serious error such as running out of resources or an
>> internal conflict of recirc IDs, then we should fail the entire action
>> processing. In this case it will have two user-visible effects:
>> 1) ofproto/trace will tell the user which serious condition is being
>> triggered that causes dropping of the flow
>> 2) OpenFlow controllers attempting packet_out could be notified that
>> the error occurred (rather than silently failing like currently)
>>
>> However, in the two cases in the incremental patch here, the actions
>> inherently have some ambiguity as to whether they successfully execute
>> (eg output) or not. The more obvious case is in the bucket_is_alive()
>> logic, where recursion will cause a bucket to be not used. If a bucket
>> is not live in the spec, this doesn't mean that the entire flow should
>> stop processing. In the case of normal, I'd argue it's very similar in
>> that 'normal' doesn't specifically attempt to output to a particular
>> port; sending packets out to different ports may fail for different
>> reasons, but this shouldn't prevent later actions in the actions list
>> from being executed.
>>
>> I think the latter cases should be reported for ofproto/trace, though.
>>
>> Looking back across this thread, it looks not far off your reasoning
>> described earlier so I think we're converging on the same view. Does
>> this sound like a fair approach?
>>
>> --
>>
>> In the mirror case, the point is moot because do_xlate_actions() isn't
>> even called in that case, so it's purely a matter of whether we want
>> to return the error up the stack or not. Maybe that should be reported
>> for ofproto/trace as well.
>>
>> I didn't see any other cases that might need handling through this.
>
> So the only ask I see here is that more of the cases of individual actions bailing out should have xlate_report() calls on them. To me this sounds like a different patch, not directly related to erroring out the whole translation. As such I hope to get an Ack on the original patch of this now lengthy discussion…

I agree.

Acked-by: Joe Stringer <joe at ovn.org>



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