Overload: Reset H2 server stream only use codec level reset mechanism #18895

KBaichoo · 2021-11-04T14:00:34Z

Signed-off-by: Kevin Baichoo kbaichoo@google.com

Commit Message: Overload: Reset H2 server stream use lower level reset mechanism
Additional Description: If we saw the Envoy level stream is complete, overload action reset_high_memory_stream should only use the codec level reset mechanism to reset the H2 stream.
Risk Level: med
Testing: integration test
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A
[Optional Runtime guard:]
Fixes #18551
[Optional Fixes commit #PR or SHA]
[Optional Deprecated:]
[Optional API Considerations:]

stream finished. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

KBaichoo · 2021-11-04T14:01:05Z

/assign @alyssawilk

Mind taking a look? Thanks!

alyssawilk

Ooh, this is a nice subtle corner case - thanks for fixing and testing!

envoy/buffer/buffer.h

alyssawilk · 2021-11-04T16:02:33Z

source/common/http/http2/codec_impl.cc

@@ -537,7 +537,16 @@ void ConnectionImpl::ServerStreamImpl::resetStream(StreamResetReason reason) {
    buffer_memory_account_->clearDownstream();
  }

-  StreamImpl::resetStream(reason);
+  if (buffer_memory_account_ && buffer_memory_account_->sawEnvoyStreamComplete()) {


So the underlying problem here, is that the filter manager believes the stream to be complete, and the codec does not? I think we don't want the buffer accounting to be the entity handling this disconnect because there could be other entities with this lifetime confusion.

either entities which can down-call a reset should be explicitly made aware of a stream being complete, or the filter manager should handle reset being called after it thinks that the stream is complete. Make sense?
cc @snowp for second opinion

The Envoy level stream object (ConnectionManagerImpl::ActiveStream is complete) and so the filter manager also thinks the stream is complete, but the codec doesn't as you said as it has yet to call onStreamClose.

AFAIK, the only entities that'll try to reset the stream at this point is either the reset_high_memory_stream action or the OnPendingFlushTimer though in the latter case the codec will know the stream has ended.

there's also cases in envoy mobile where we've had a reset-after-fin (Snow has reviewed) so again I'd rather make this a bit more resistant

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk · 2021-11-04T18:21:34Z

source/common/http/http2/codec_impl.cc

+  if (buffer_memory_account_ && buffer_memory_account_->envoyStreamComplete()) {
+    // We should use a lower level reset mechanism to reset the stream.
+    resetStreamWorker(reason);
+    if (parent_.sendPendingFramesAndHandleError()) {


After some more offline discussion I'd suggested using local_end_stream_ rather than adding yet another way to communicate a stream is done. @KBaichoo thinks that's sketchy because of interplay between local_end_stream_ and the deferred reset code.
Pulling in @yanavlasov and @antoniovicente to comment.

interplay between local_end_stream and runResetCallbacks(reason) I think can be sketchy (sorry if I didn't convey that well)

This change feels brittle.

I think we need to dig deeper and make object lifetimes more clear. We need to eliminate all cases where an object remains registered after deletion.

yeah that's my thought too. @KBaichoo if we're in a hurry to get this landed I'd be OK merging with a TODO to fix if you can help resolve the real lifetime issues right after, but if we're not in a rush I think we want to sort out the lifetime issues now in a less fragile way.
/wait

Thanks for the pushback. I've dug deeper and have done the following:

Delay H1 ActiveRequest dtor until after the Envoy level stream is destroyed -- didn't have the invariant that codec stream outlived the envoy stream in local reply cases.

With the above, it's safe to in doDeferredStreamDestroy access the response encoder (codec stream) and remove the envoy level stream from callbacks, and notify the codec level stream it's done.

Removed changes to buffer account interface

KBaichoo · 2021-11-04T21:00:11Z

/retest

repokitteh-read-only · 2021-11-04T21:00:15Z

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #18895 (comment) was created by @KBaichoo.

see: more, trace.

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

stream destroyed. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

during reset. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk · 2021-11-09T19:42:32Z

envoy/http/codec.h

+  /**
+   * Fired when the Envoy level stream representation has been destroyed.
+   */
+  virtual void onEnvoyStreamComplete() PURE;


I'm still not clear why we need this.
If the HCM is going to delete an Envoy stream, it generally has either sent end_stream or resets the stream. The only case I can think of where it doesn't, is where the connection is reset, where I don't know why the codec would be doing work. Can you clue me in on what the life cycle of the stream is where those calls are insufficient for the codec to realize it shouldn't be calling back to Envoy any more?

May be easier to hash this out in real time -feel free to snag time on my calendar.

In order to maintain the invariant that the codec level stream outlives the Envoy level stream (and hence the Envoy level stream can safely unsubscribe from callbacks in doDeferredStreamDestroy in the HCM), this was added.

The above invariant wasn’t true in the case for H1 local reply, wherein we’d have a dangling pointer to the underlying codec at the Envoy level. See the diagram below starting at local reply encoded:

I tried to go down the route of leveraging local_end_stream_ instead as suggested, e.g. if the HCM has sent the codec local_end_stream treat it as an implicit detach (don’t raise reset callbacks) but it seems to break an implicit invariant (breaking lots of integration tests).

https://github.com/envoyproxy/envoy/blob/main/source/common/http/codec_helper.h#L42-L43

I wonder if this is good enough for now. @mattklein123 WDYT?

I'm with @alyssawilk that I'm not thrilled about adding more tricky lifetime logic to logic that is already too tricky and hard to understand.

Just so I understand the actual problem we are fixing, what is the crashing call stack prior to this fix? I'm not sure I understand the original problem.

I tried to go down the route of leveraging local_end_stream_ instead as suggested, e.g. if the HCM has sent the codec local_end_stream treat it as an implicit detach (don’t raise reset callbacks) but it seems to break an implicit invariant (breaking lots of integration tests).

Possibly related to my question above, but is the local reply case the case that is broken wrt to the overload manager? I'm trying to understand the sequence of events that leads to the lifetime issue. I'm wondering if there is a different fix that we could do that would allow us to make this work with local_end_stream_, etc.

KBaichoo · 2021-11-09T21:26:34Z

/retest

repokitteh-read-only · 2021-11-09T21:26:38Z

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #18895 (comment) was created by @KBaichoo.

see: more, trace.

rojkov · 2021-11-15T08:06:38Z

Looks like the main branch needs to be merged.

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

KBaichoo · 2021-11-16T02:19:15Z

/retest

repokitteh-read-only · 2021-11-16T02:19:19Z

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #18895 (comment) was created by @KBaichoo.

see: more, trace.

… tied up with Watermark callbacks. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

source/common/http/http2/codec_impl.cc

envoy/http/codec.h

source/common/http/conn_manager_impl.cc

mattklein123 · 2021-11-17T16:33:35Z

envoy/http/codec.h

+  /**
+   * Fired when the Envoy level stream representation has been destroyed.
+   */
+  virtual void onEnvoyStreamComplete() PURE;


I'm with @alyssawilk that I'm not thrilled about adding more tricky lifetime logic to logic that is already too tricky and hard to understand.

Just so I understand the actual problem we are fixing, what is the crashing call stack prior to this fix? I'm not sure I understand the original problem.

I tried to go down the route of leveraging local_end_stream_ instead as suggested, e.g. if the HCM has sent the codec local_end_stream treat it as an implicit detach (don’t raise reset callbacks) but it seems to break an implicit invariant (breaking lots of integration tests).

Possibly related to my question above, but is the local reply case the case that is broken wrt to the overload manager? I'm trying to understand the sequence of events that leads to the lifetime issue. I'm wondering if there is a different fix that we could do that would allow us to make this work with local_end_stream_, etc.

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

KBaichoo · 2021-11-20T19:51:54Z

/retest

repokitteh-read-only · 2021-11-20T19:51:58Z

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #18895 (comment) was created by @KBaichoo.

see: more, trace.

KBaichoo · 2021-11-22T14:52:57Z

I've now address the comments, implementing the fix on the top of the refactor in #19062.

alyssawilk

This is fantastic! Thanks for all your patience and refactoring reworking it - it's really going to help not just this use case but other lifetime issues!

source/common/http/conn_manager_impl.cc

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk

Awesome! Will defer to @mattklein123 for merge on Monday.

mattklein123

Awesome! Thank you.

* main: (77 commits) Fix verify_and_print_latest_release logic (envoyproxy#19111) http2: drain only once when reached max_requests_per_connection (envoyproxy#19078) Overload: Reset H2 server stream only use codec level reset mechanism (envoyproxy#18895) Update QUICHE from c2ddf95dc to 7f2d442e3 (envoyproxy#19095) tools: Fix dependency checker release dates bug (envoyproxy#19109) cve_scan: Use `envoy.dependency.cve_scan` (envoyproxy#19047) tcp: fix overenthusiastic bounds on the new pool (envoyproxy#19036) dep: update Proxy-Wasm C++ host (2021-11-18). (envoyproxy#19074) build(deps): bump frozendict from 2.0.7 to 2.1.0 in /tools/base (envoyproxy#19080) kafka: dependency upgrades (envoyproxy#18995) build(deps): bump charset-normalizer in /tools/dependency (envoyproxy#19105) build(deps): bump slack-sdk in /.github/actions/pr_notifier (envoyproxy#19093) dep: Remove dependency - six (envoyproxy#19085) Remove requested_server_name_ field from StreamInfo (envoyproxy#19102) broken link path fix for items http_filters/grpc_json_transcoder_filter (envoyproxy#19101) quic: turn off GRO (envoyproxy#19088) Listener: Add global conn limit opt out. (envoyproxy#18876) Specify type for matching Subject Alternative Name. (envoyproxy#18628) Fix a broken example in Lua filter docs (envoyproxy#19086) Fix a small typo (envoyproxy#19058) ... Signed-off-by: Michael Puncel <mpuncel@squareup.com>

Use lower level reset mechanism for reset stream if saw Envoy level

3533da7

stream finished. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

repokitteh-read-only bot assigned alyssawilk Nov 4, 2021

alyssawilk reviewed Nov 4, 2021

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s/sawEnvoyStreamComplete/envoyStreamComplete and make interface const.

22c6521

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk reviewed Nov 4, 2021

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repokitteh-read-only bot added the waiting label Nov 8, 2021

KBaichoo added 3 commits November 9, 2021 14:08

Revert Changes to Account interface, if doing OM reset don't defer.

8008823

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

onEnvoyStreamComplete to delay H1 codec destruction until Envoy level

c8f7bdc

stream destroyed. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Merge remote-tracking branch 'upstream/main' into rst-low-level

ff20da9

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

repokitteh-read-only bot removed the waiting label Nov 9, 2021

Iterator stability if for mock stream since we can remove observer

b6211fc

during reset. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk reviewed Nov 9, 2021

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KBaichoo added 2 commits November 16, 2021 00:02

merge main.

3d320f0

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Used local_end_stream_ for http1.

2dc1eff

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk added the waiting label Nov 16, 2021

Use encode_complete_ instead of local_end_stream_ since the latter is…

0b98a9c

… tied up with Watermark callbacks. Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

repokitteh-read-only bot removed the waiting label Nov 16, 2021

mattklein123 requested changes Nov 17, 2021

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mattklein123 added the waiting label Nov 17, 2021

KBaichoo mentioned this pull request Nov 19, 2021

HTTP1: Refactor HTTP1 Active Request to be defer deletable. #19062

Merged

Merge remote-tracking branch 'upstream/main' into rst-low-level

4bb2619

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

KBaichoo added 2 commits November 20, 2021 13:51

Revert onEnvoyStreamComplete.

c3fa8ab

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Update comments.

f4c4199

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

repokitteh-read-only bot removed the waiting label Nov 20, 2021

Revert unneeded mock method.

189d9b2

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk reviewed Nov 23, 2021

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source/common/http/conn_manager_impl.cc Outdated Show resolved Hide resolved

KBaichoo added 2 commits November 23, 2021 16:49

Don't null response_encoder_.

84c517d

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

Merge remote-tracking branch 'upstream/main' into rst-low-level

b75d8ac

Signed-off-by: Kevin Baichoo <kbaichoo@google.com>

alyssawilk approved these changes Nov 23, 2021

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mattklein123 approved these changes Nov 29, 2021

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mattklein123 merged commit 3b45d6c into envoyproxy:main Nov 29, 2021

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Overload: Reset H2 server stream only use codec level reset mechanism #18895

Overload: Reset H2 server stream only use codec level reset mechanism #18895

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Overload: Reset H2 server stream only use codec level reset mechanism #18895

Overload: Reset H2 server stream only use codec level reset mechanism #18895

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