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[BUG] Race condition two threads getting expected reply error #439

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amgross opened this issue Nov 17, 2024 · 1 comment
Open
2 tasks done

[BUG] Race condition two threads getting expected reply error #439

amgross opened this issue Nov 17, 2024 · 1 comment
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@amgross
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amgross commented Nov 17, 2024

Describe the bug

In short: in case of two client threads requesting in same time from server, they may get each one the answer of the else and hence return kErpcStatus_ExpectedReply due to wrong sequence number

Deep dive to the scenario:
In case of simple client is used (not arbitrated), the function performClientRequest sends and receives without locking the mutex (but the receive itself and the send itself runs locked in the framed transport class).

That may lead to scenario of the following steps:

  1. thread A sends request
  2. context switch happens and thread B running and send request (may likely happen if B has higher priority and it tried to send request when A was in middle, and was blocked on the send lock till A will finish his send)
  3. thread B enters receive and blocks/busy waiting to response
  4. server get request A (as it was sent first) and responds to it
  5. thread B get the respond to A and return kErpcStatus_ExpectedReply due to wrong sequence number and releasing the lock
  6. Thread A get into recieve
  7. server get request B (as it was sent first) and responds to it
  8. thread A get the respond to B and return kErpcStatus_ExpectedReply due to wrong sequence number

It should be noted this is probably won't happen in arbitrated client where all client are assigning there sequence number and the arbitrator waking up the relevant thread according the sequence number.

To Reproduce

run two client threads with different priorities on long send/receive loops

Expected behavior

Each thread getting its response

Screenshots

Not applicable

Desktop (please complete the following information)

  • OS: linux
  • eRPC Version: 1.10.0

Steps you didn't forgot to do

  • I checked if there is no related issue opened/closed.
  • I checked that there doesn't exist opened PR which is solving this issue.

Additional context

@amgross amgross added the bug label Nov 17, 2024
@amgross
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amgross commented Nov 17, 2024

I think it related #374

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