census: Fix retry stats data race (v2) #8459
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ejona86
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Sep 1, 2021
| this.status = status; | ||
| boolean shouldRecordFinishedCall = false; | ||
| synchronized (lock) { | ||
| if (callEnded) { |
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It's not possible unless there's some bug like #7921.
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Then how about we log a warning if it happens? An assert would be great, but I don't think we are that confident. A warning with "this is a bug" at least would mean we'd learn if it happens. If it does trigger, it seems it'd probably be at a low rate.
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Uhh... if we think it can happen, then let's just have the notice of the bug here and return like you had.
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Do you mean to include the link to the issue in the log?
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No, I mean delete the log statement. I was suggesting the log statement only if we thought it wasn't possible but it would be worrisome to add an assert. If we think it is possible, just having a comment seems good.
dapengzhang0
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There is data race in `CensusStatsModule. CallAttemptsTracerFactory`: If client call is cancelled while an active stream on the transport is not committed, then a [noop substream](https://github.com/grpc/grpc-java/blob/v1.40.0/core/src/main/java/io/grpc/internal/RetriableStream.java#L486) will be committed and the active stream will be cancelled. Because the active stream cancellation triggers the stream listener closed() on the _transport_ thread, the closed() method can be invoked concurrently with the call listener onClose(). Therefore, one `CallAttemptsTracerFactory.attemptEnded()` can be called concurrently with `CallAttemptsTracerFactory.callEnded()`, and there could be data race on RETRY_DELAY_PER_CALL. See also the regression test added. The same data race can happen in hedging case when one of hedges is committed and completes the call, other uncommitted hedges would cancel themselves and trigger their stream listeners closed() on the transport_thread concurrently. Fixing the race by recording RETRY_DELAY_PER_CALL once both the conditions are met: - callEnded is true - number of active streams is 0.
dapengzhang0
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Sep 2, 2021
There is data race in `CensusStatsModule. CallAttemptsTracerFactory`: If client call is cancelled while an active stream on the transport is not committed, then a [noop substream](https://github.com/grpc/grpc-java/blob/v1.40.0/core/src/main/java/io/grpc/internal/RetriableStream.java#L486) will be committed and the active stream will be cancelled. Because the active stream cancellation triggers the stream listener closed() on the _transport_ thread, the closed() method can be invoked concurrently with the call listener onClose(). Therefore, one `CallAttemptsTracerFactory.attemptEnded()` can be called concurrently with `CallAttemptsTracerFactory.callEnded()`, and there could be data race on RETRY_DELAY_PER_CALL. See also the regression test added. The same data race can happen in hedging case when one of hedges is committed and completes the call, other uncommitted hedges would cancel themselves and trigger their stream listeners closed() on the transport_thread concurrently. Fixing the race by recording RETRY_DELAY_PER_CALL once both the conditions are met: - callEnded is true - number of active streams is 0.
ejona86
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TODO:backport
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(This is a modified version of #8422 using a lock for synchronization.)
There is data race in
CensusStatsModule. CallAttemptsTracerFactory:If client call is cancelled while an active stream on the transport is not committed, then a noop substream will be committed and the active stream will be cancelled. Because the active stream cancellation triggers the stream listener closed() on the transport thread, the closed() method can be invoked concurrently with the call listener onClose(). Therefore, one
CallAttemptsTracerFactory.attemptEnded()can be called concurrently withCallAttemptsTracerFactory.callEnded(), and there could be data race on RETRY_DELAY_PER_CALL. See also the regression test added.The same data race can happen in hedging case when one of hedges is committed and completes the call, other uncommitted hedges would cancel themselves and trigger their stream listeners closed() on the transport_thread concurrently.
Fixing the race by recording RETRY_DELAY_PER_CALL once both the conditions are met: