[v1.x] [MAC] test_operator.test_index_copy causes `bus error`, possible segfault

[r3stl355]

Description

This only happens on my Mac on v1.x. The same test on v2.0 runs and passes. I can also see that the same test succeeds on centos-cpu CI. Other posts for this type error i found online suggest possible segfault as an underlying problem.

To reproduce

nosetests tests/python/unittest/test_operator.py:test_index_copy

Environment

OS: Catalina: 10.15.6

clang --version: Apple clang version 12.0.0 (clang-1200.0.31.1) Target: x86_64-apple-darwin19.6.0 Thread model: posix

What have you tried to solve it?

The bus error is thrown at this line: https://github.com/apache/incubator-mxnet/blob/8dbed966e35b979d8f770b0d5b0ec9f707b3a2f1/tests/python/unittest/test_operator.py#L5711

Commenting out https://github.com/apache/incubator-mxnet/blob/8dbed966e35b979d8f770b0d5b0ec9f707b3a2f1/tests/python/unittest/test_operator.py#L5709 prevents the error but then test fails at line 5711 when comparing gradents. The same is for line 5717 and subsequent assertions

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[szha]

@r3stl355 thanks for reporting the issue. Could you set environment variables DMLC_LOG_STACK_TRACE_DEPTH=150 MXNET_ENGINE_TYPE=NaiveEngine and run the same program again and share the stacktrace?

[r3stl355]

Thank you @szha , MXNET_ENGINE_TYPE=NaiveEngine did the trick, no more errors, I'm now going to read-up to understand what it does

[szha]

@r3stl355 it forces the execution to be synchronous, and if it resolves the issue it means there's a race condition that needs to be resolved.